GEOLOGIAN TUTKIMUSKESKUS
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GEOLOGICAL SURVEY OF FINLAND
Nuclear Waste Disposal Research
Tiedonanto YST-106
Report YST-106
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Prof. Dr. Petr Vaganov1,
with two appendices by Dr. Karl-Heinz Hellmuth2
1
Geological Faculty, University of St. Petersburg, Russia
2
STUK, Helsinki, Finland
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Petr Vaganov, 2002. ,$($&RRUGLQDWHG5HVHDUFK3URMHFW&537KHXVHRIVHOHFWHGVDIHW\LQGLFDWRUV
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Geological Survey of Finland, Nuclear Waste Disposal Research, Report YST-106, ISBN 951-690-819-5, ISSN
0783-3555.
The purpose of this reportis to compile basic scientific knowledge on natural geochemical cycles leading to
dispersion and concentration of chemical elements in various environments as a basis for better understanding
the influences of geochemical processes to be expected in the context of deep geological disposal of nuclear
waste. In a strictly systematic approach the different processes and mechanisms of migration of elements in the
upper part of the geosphere are classified. Quantitative estimates of geochemical fluxes in different climatic and
geological environments are given.
The analytical aspects of the measurement of the geochemical background and the definition and identification
of geochemical anomalies are discussed. Special focus is laid on methods to identify mobile and weakly bonded
forms of elements. By these methods even migration halos around deeply buried geochemical anomalies could
be sensitively detected which is illustrated by typical case studies.
The central question which is addressed in the report is how geochemical anomalies find expression on the
earth’s surface in the form of dispersion halos. Dispersion halos of ore bodies are classified according to the type
of ore deposit, the geological environment and the type of dispersion mechanism. Numerous case studies with
special focus on uranium deposits are used to illustrate different types of halo formation. The development of
uranium hydrochemical halos requires access of surface waters to U ore bodies.
In Appendix 1 natural average geochemical fluxes of radioactive and chemotoxic elements relevant to waste
disposal are evaluated. The types of fluxes to be considered are (1) groundwater transport, (2) glacial erosion, (3)
non-glacial weathering and (4) river transport. All chemical elements are characterized by the same order of
relative magnitude of fluxes: glacial erosion > total non-glacial weathering > chemical decomposition > groundwater transport. Effective equivalent doses induced by natural fluxes of radionuclides are estimated. For
groundwater transport the largest contribution comes from 238U.
The objective of Appendix 2 is to elucidate, if and how geochemical cycles can cause concentrations of harmful
elements in the biosphere that exceed limits set to protect human health. It seems that heavy metal soils are
common, but generally very local phenomena which are connected to near-surface sources such as e.g. outcropping ore bodies. Secondary enrichments of heavy metals transported by deep groundwater to the surface are
rare and difficult to recognize as such.
Finally, in Appendix 3 a short overview is given over geochemical halos associated with large ore bodies in
Finland. Although most of the ore bodies reached near to the ground surface, secondary geochemical halos were
usually limited and heavy metal dispersion by groundwater was negligible compared with mechanical glacial
dispersion mechanisms.
3
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The IAEA launched a Coordinated Research Project (CRP) "The use of selected safety indicators (concentrations; fluxes) in the assessment of radioactive waste disposal" for the period 1999-2003. The CRP’s objective is
to contribute, through the development of international consensus, to the assessment of the long-term safety of
radioactive waste disposal by means of additional safety indicators based on the observation of natural systems.
The participation of Finland in theCRP resulted in a large amount of data and knowledge which must be adequately published, in order to ensure practical benefit for the purpose of application in a future safety case. Intergration into a safety case can happen in different ways, most of which require the availability of the whole background material which has been compiled and treated within the project.
The Finnish contribution to the CRP consists to a large part of results of compilation of natural elemental concentration and flux data from existing data bases, but also from experimental work and from simulations and
calculations.
In addition, a number of supporting generic studies on natural geochemical cycles and geochemical anomalies on
a global, regional and local scale has been conducted which are indispensable for putting the results of the CRP
into the context.
A publication of the material and the conclusions from the various parts in one report series seemed to be the
most appropiate way to ensure a certain uniformity and a maximum accessability. The individual reports are
closely related and are complementing each other.
Most of the work published in the report series is a result of close cooperation between GTK (Geological Survey
of Finland), VTT (State Research Center of Finland) and STUK (Radiation and Nuclear Safety Authority of
Finland). The supporting studies are to a great part contributions by foreign experts.
The first report is intended to serve as background and supporting investigation within the CRP.
The whole work was financed by the Finnish Radiation and Nuclear Safety Authority (STUK), Helsinki, Finland
and planned and coordinated by Dr. Karl-Heinz Hellmuth.
4
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1.1.1. Geochemical processes leading to the formation of ore bodies and halos around them
1.1.2. Specific features of surficial geochemistry and trace element geochemistry
1.1.3. Forms of transportation and accumulations of element
1.1.4. Extensive and intensive parameters of migration. Equation of migration intensity
1.1.5. Dispersion patterns
1.1.6. Geochemical barriers
1.1.7. Paragenetic association of elements
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1.2.1. Basic features of mechanogenesis
1.2.2. Mechanical differentiation
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1.3.1. Thermodynamic characteristics of physico-chemical migration
1.3.2. Mechanisms of mass transportation (diffusion, convection)
1.3.3. Metamorphic and metasomatic alterations of rocks
1.3.4. Oxidation zones
1.3.5. General features of aqueous migration
1.3.5.1. Colloidal migration and sorption
1.3.5.2. Ion exchange
1.3.5.3. Redox and acidic-alkaline conditions
1.3.5.4. Intensity of aqueous migration and concentration of elements
1.3.6. Physico-chemical barriers
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1.4.1. General features of magmatic migration
1.4.2.
Series of "mantle" elements, of basic rocks elements, and of granitoids elements
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1.5.1. Magmatic-hydrothermal evolution in granitoid intrusions
1.5.2. Geochemical barriers of hydrothermal systems
1.5.3. Zoning of hydrothermal ores and generic series of elements
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1.6.1. Hypergene migration of elements as a basis for their specific geochemical classification
1.6.2. Geochemical classification of natural waters
1.6.3. Chemical composition of underground waters in different climate areas of the zone
of hypergenesis
1.6.4. Coefficients of aqueous migration and precipitation
1.6.5. Types of element concentrations on geochemical barriers in the zone of hypergenesis
1.6.6. Element associations in different crusts of weathering
1.6.7. Basic features of landscape geochemistry
1.6.7.1. Elementary landscape types
1.6.7.2. Element geochemical abundances and migration rates in landscapes
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1.7.1.
Geochemical classification of soils
1.7.2.
Driving forces of element migration in soils
1.7.3.
Heavy metals in soils (see also Appendix 2)
1.7.4. Bioaccumulation of elements in plants
1.7.5.
Geobotany in the study of heavy metal accumulation
1.7.6. Biogeochemical cycles of elements
1.7.7.
Series of biophilic elements
1.7.8.
Health risk assessment due to metal contamination of soils and plants
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2.1.1.
Clark values for the abundance and distribution of elements in rocks and soils
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2.1.2.
Definition of an anomaly (analytical context)
2.1.3.
Detection of weak anomalies
2.1.4.
Multi-element anomalies
2.1.5.
Detection limits
2.1.6. Precision and accuracy of analyses
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2.2.1. Specific features of analysis for rare and trace elements
2.2.2. Factors influencing on quality of geochemical measurements
2.2.3. Metrological parameters of modern multi-element analytical methods
2.2.4. Methods to identify mobile and weakly bonded forms of elements (MWBE)
2.2.5. Case studies
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3.1.1. Geochemical fields, their characteristics and anomalies
3.1.2. Quantitative characteristics of geochemical anomalies
3.1.3. Interrelationship of geochemical anomalies in the geosphere
3.1.4. Specific features of revealing weak anomalies
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3.2.1.
Morphostructure and dimensions of halos
3.2.2.
Conditions of the formation of halos
3.2.3.
Common features of composition zoning of primary halos
3.2.4. Primary halos around ore deposits
3.2.4.1. Zonal structure of primary halos
3.2.4.2. Indicator elements in primary halos
3.2.4.3. Coefficients of zoning of primary halos
3.2.4.4. Generalized series of indicator elements in primary haloes
3.2.4.5. Sub-background haloes of hydrothermal deposits of uranium
3.2.5.
Secondary lithochemical halos of dispersion
3.2.5.1. Classification of secondary lithochemical halos
3.2.5.2. Mechanical dispersion halos
3.2.5.3. Salt dispersion halos
3.2.5.4. Mathematical model of a secondary halo
3.2.5.5. Lithochemical fluxes of dispersion; equation of an ideal dispersion flux
3.2.5.6. Displacement of secondary halos
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3.3.1.
Forms and dimensions of primary halos
3.3.2.
Zoning of primary halos in different types of uranium deposits
3.3.3.
Major indicator elements in primary halos of uranium ores.
3.3.4.
Superficial manifestation of primary and secondary lithochemical halos of blind
endogeneous uranium deposits
3.3.5.
Hydrochemical halos of blind uranium deposits
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3.4.1. Primary buried lithochemical halos
3.4.2.
Secondary residual buried lithogeochemical halos of dispersion
3.4.3.
Secondary superimposed opened and buried lithogeochemical halos of dispersion
3.4.4. Buried lithogeochemical fluxes of dispersion
3.4.5. Hydrochemical halos and fluxes of dispersion
3.4.6. Case studies
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3.5.1.
Groups of easily discovered deposits
3.5.2.
Opened halos of uranium in the zones of taiga with continuous permafrost
3.5.3.
Opened halos of uranium in the zones of taiga with "insular" permafrost
3.5.4.
Opened halos of uranium in the zones of taiga without permafrost
3.5.5.
Opened halos of uranium in forest-steppe zones
3.5.6.
Opened halos of uranium in tundra zones
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3.6.1. Phytogeochemical associations of elements.
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3.6.2.
Contrast indices of phytogeochemical anomalies.
3.6.3.
High-contrast phytogeochemical anomalies.
3.6.4. Biogeochemical expression of deeply buried uranium mineralization
3.6.5.
False phytogeochemical anomalies
3.6.6.
Uranium-radium disequilibrium in biogeochemical cycling and its consequences
3.6.7.
On dietary intakes for natural radionuclides in normal background areas
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3.7.1. Exogeneous syngenetic deep-seated uranium deposit
3.7.2. Exogeneous epigenetic deep-seated uranium deposit
3.7.3. Endogeneous deep-seated uranium deposit
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7.
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Selection of elements
Selection of natural pathways of elemental fluxes
Groundwater transport
Glacial erosion
Non-glacial weathering
River transport
Summary of relevant natural elemental fluxes
Assessment of radiotoxicity due to average natural fluxes of radioactive elements
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1DWXUDOKHDY\PHWDOVRLOV(K-H. Hellmuth)
1. Heavy metal background in rocks and soils
2. Heavy metal soils
3. Biogeochemical aspects
4. Fractional releases from ores: Morro do Ferro case study
5. Case studies
6. Geochemical mapping
7. Natural metal-poisoned soils in Scandinavia
8. Other halos
9. Uranium halos
10. Deeply buried uranium ores
11. Soil anomalies related to U-rich groundwater
12. Uranium in peat
13. Uranium in peat in Finland
14. Halo formation in peneplain setting in Finland
15. Summary and conclusions
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Many years ago V.M.Goldschmidt put forward a concept of the geochemical cycle. This concept
provides a general link between all geosciences and environment, and it can readily place any
environment change problem into a global perspective. Diagram showing Goldschmidt’s geochemical
cycle is given in Figure 1.1 There are major and minor cycles, the latter includes three basic stages:
liberation, transport, and incorporation of elements. Crystalline rocks, generated deep in the Earth
during the major geochemical cycle, are exposed to weathering and enter the minor geochemical
cycle. In theory, during the minor geochemical cycle, products of weathering are transported through
the environment prior to being deposited in ocean sediments. In practice, as Mason pointed out, the
cycle may be “infinitely halted or short-circuited, or have its direction reversed” (Mason, 1966).
Figure 1.1. Diagram showing Goldschmidt’s geochemical cycle (from Fortescue, J.A.C., 1980)
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Geochemical processes leading to the formation of ore bodies and halos around them are governed by
the following four principal propositions of geochemistry put forward by Safronov (Safronov, 1971):
1. Universal occurrence of chemical elements in all geospheres (Vernadsky Law);
2. Continuous migration of elements in time and space;
3. Diversity of kinds and forms of the occurrence of chemical elements in nature;
4. Predominance of the state of dispersion over the state of concentration, especially for ore-forming
elements.
8
Universal occurrence of elements is confirmed by the results of analyses of chemical composition
of all rocks, minerals, natural waters, organic substances, etc. It is reflected by the values of Clarkes,
i.e. average abundances of chemical elements in the geospheres. V.I.Vernadsky claimed in 1909: “In
every drop or speck dust on the Earth surface, the more is the capability of our investigation methods,
the more is the number of elements observed. … Both in a dust spec and in a drop, as in microcosmos,
general composition of cosmos is reflected” (Vernadsky, V.I., 1954).
Migration of chemical elements is reflected in both gigantic tectono-magmatic processes
transforming the Earth crust and delicate biochemical reactions in living organisms. Migration of
elements is determined by numerous external factors including the energy of solar radiation, internal
energy of the Earth, the action of gravity, and by internal factors depending on the properties of
elements. Distinctions in migration ability (mobility) of chemical elements lead to their differentiation
and the formation of natural bodies with different quantitative interelement relationships. The
processes of concentration and dispersion of chemical elements characterize two intercorrelated and
interopposed sides of a single process of element migration.
Diversity of kinds and forms of the occurrence of chemical elements in nature is revealed by a
great number of natural chemical compounds, mechanical mixtures, and solutions presented in solid,
liquid, or gaseous states, and by a variety of physical-chemical bindings between elements as well.
Side by side with a mineral form of element existence, different non-mineral forms are displayed, for
most elements they dominate in the hydrosphere, atmosphere and biosphere. The presence of elements
in observable minerals of the lithosphere is supplemented by submicroscopic inclusions, different
indiscerned isomorphous and non-isomorphous solid solutions, intrarock water molecular-pellicular
solutions or intracrystalline gaseous-liquid inclusions, in the state of sorption and occlusion as well.
Predominance of the state of dispersion over the state of concentration means that in the process of
migration, taking into account the diversity of kinds and forms of element occurrence, the formation of
natural bodies with any (from very low to very high) concentrations is possible. However, it is
impossible to establish any objective border between low amounts of a given element, corresponding
to its dispersion, and high amounts of the same element which are associated with its concentration
state. In a series of continuous concentration of element, such border would be arbitrary, because it
would be necessary to attribute different qualitative states for two very close values disposed at
opposite sides of this border. That is why it is appropriate to introduce only two extreme levels,
implying element abundances close to its Clarkes as its dispersion state characteristic, and abundances
close to its amounts in deposits of economic importance as its concentration state characteristic. The
ratio of the average element concentration in ores to the corresponding Clarke value is named “Clarke
concentration”.
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Superficial geochemical processes occur in the zone of hypergenesis. All products of hypogene
geological processes, after their coming out above ground, begin to be adapted to a new physicalchemical environment. This adaptation is often connected with destruction and decomposition of
primary rocks. Depending on the agent taking the leading role in the transformation of rocks in the
zone of hypergenesis, three types of weathering are distinguished: physical, chemical and biological.
All three types are usually coupled, however in the conditions of humid climate, decisive role can be
played by chemical weathering on conjunction with biological one. Nevertheless, the outcome of
physical weathering can be quite dramatic, it stipulates the role of mechanical migration (see 1.2).
Chemical weathering of the earth’s crust involves relatively simple chemical reactions. However,
because the materials are complex, e.g. silicate rocks, mixtures of minerals, and water of variable
mineral composition and pH, the chemistry can be rather complicated. The key types of chemical
reactions are hydrolysis, oxidation, reduction, carbonation, hydration, cation exchange, and dialysis.
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Hydrolysis is a reaction between water ions (H+, OH−) and ions (elements) of minerals and rocks.
The most typical reaction of hydrolysis affect silicate minerals (in particular, feldspars). This reaction
can be expressed as follows:
0HSiAlOQH+OH− → 0H OH− + [Si(OH)0−4]Q + [Al(OH)6]Q3−
or Al(OH)3 + (0HH)AlRSiAlWOQ,
9
where 0Hstands for any metal cation; Q means indeterminate atomic ratios; R and Wrefer to octahedral
and tetrahedral coordination, respectively; Al is isomorphic with Si, it is placed between Si and O in
the formula. The complex [Si(OH)0−4] refers to more ore less polymerized groups of silica where the
coordination of Si relatively hydrogen ions varies between 0 and 4 depending on the degree of
polymerization. The last member of the right part of reaction (0HH)AlRSiAlWOQ can be represented by
a clay mineral, zeolite, or a fragment of primary silicate.
Under the hydrolythic action of water which is often accompanied by the influence of carbon
dioxide, silicates begin to be dissolved. Hydrolysis of feldspars leads to the formation of kaolinite, for
example:
2KalSi3O8 + 3H2O → 2 KOH + H2Al2Si2O8⋅H2O +4SiO2.
In this reaction, the decisive role is played by hydrogen ion H+, it forces a metal (K, Na, Ca) to go out
from alumosilicates and destroys their crystalline structure. The process of kaolinitization proceeds on
a large scale, it is often accompanied by the action of plant roots having a negative electrical charge,
so being surrounded by hydrogen ions. Released during weathering, potassium ions are absorbed by
plant roots. In order to promote the process of hydrolysis, intensive circulation of water is necessary,
so dissolved products of weathering would be evacuated.
As a very important result of hydrolysis, OH− ions together with metal cations are transported by
rivers into the ocean, so its alkalinity increases. As to H+ ions, they combine with alumosilicate anions
and form clay minerals which can be considered as hardly soluble and weak acids. Thus, one can say
that the land surface finally becomes acidic part of the reactions of hydrolysis, whereas the ocean
becomes alkaline part of these reactions.
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Oxidation occurs mainly in the water environment where free oxygen is available. In natural
conditions, oxidation is an exotermic reaction which is accompanied by heat released, for example:
4FeSi3O3 + O2 → 2Fe2O3 +4SiO2 + 2144 kJ.
Because the energy of iron oxidation is rather high, this element is very sensible to the process of
oxidation. When iron, which bonds silica-oxygen tetrahedrons in silicate structures, forms its oxide
after the interaction with oxygen, silicate minerals decay. This explains the fact that primary
ferriferrous silicates of igneous rocks begin to be weathered before other minerals.
Sulfides are minerals which easily become oxidized, this process yields the formation of sulfates.
In this case oxidation is associated with hydration and hydrolysis. Organic substances are also become
rather easily oxidized, their carbon turns into CO2. Oxidation of organic matter in rocks provides their
light coloration.
Not only primary hypogenic minerals are subjects of oxidation, but first products of their
decomposition as well. So, under real conditions, oxidation of pyrite is a complicated process:
2FeS2 + 2H2O +7O2 → 2FeSO4 + 2H2SO4,
12FeSO4 + 3O2 + 6H2O → 4Fe2(SO4)3 + 4Fe(OH)3.
Iron sulfate as a salt of a weak base rapidly undergoes the action of hydrolysis:
Fe2(SO4)3 + 6H2O → 2Fe(OH)3 + 3H2SO4.
Oxidation of natural compounds of iron develops easier in alkaline environments; in acidic
environments oxidation is slow, but it becomes accelerated in weakly acidic and alkaline solutions.
Limonite is a final steady product of the decay of numerous iron-bearing minerals. In sulfide and
carbon-bearing formations, oxidation of C and S is also accompanied by a termic effect:
C + O2 → CO2 + 395 kJ,
S + O2 → SO2 +293 kJ.
Dissolution of CO2 in water yields the formation of carbonic acid:
3CO2+ 3H2O → H2C3O + 3H+ + CO32− +HCO3−.
Dissolution of SO2 yields the formation of sulphurous acid and then sulphuric acid:
SO2 + H2O → H2SO3,
2H2SO3 + O2 → 2H2SO4.
Sulfuric acid is an important geochemical factor, it often causes essential changes of hosting rocks. Its
interaction with limestone leads to the formation of gypsum:
CaCO3 + H2SO4 → CaSO4⋅2H2O + H2CO3.
10
If sulfate solutions interact with clays and/or iron-bearing minerals, a chain of reactions occurs leading
to the formation of alunite KAl3(OH)6(SO4)2 and its iron-bearing analog – jarosite KFe3(OH)6(SO4)2.
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Reduction proceeds usually in water reservoirs and in some sections of soil horizons in
weathering crusts where oxygen is absent. It is governed by two basic factors: organic matter and the
activity of microorganisms (bacteria). Under natural conditions, the most spread process of reduction
is transformation of ferric iron into ferrous iron. As a result, iron can pass into solutions containing
carbonic acid. By this way iron carbonates, such as FeH2(CO3)2, are formed. If CO2 is consumed by
plants and bacteria, carbonate precipitates as insoluble siderite FeCO3. If a solution contains a lot of
oxygen, oxidation of FeH2(CO3)2 yields iron hydroxide which later turns into limonite. Reduction of
iron compounds changes rock coloration.
Reduction of iron compounds by organic matter can be expressed as follows:
2Fe2O3⋅3H2O + C → 4FeO + CO2 +3H2O,
FeO + CO2 → FeCO3.
The same reactions can be written to describe reductive action of bacteria. In this case C will mean
carbon presenting in living bacteria where it joins oxygen in biological processes.
Reduction of natural sulfates is also connected with organic matter and bacterial activity. The
most illustrative is the formation of lime and native sulfur from gypsum in the following reactions:
CaSO4 + 2C → CaS + 2CO2,
2CaS + 2H2O → Ca(OH)2 + Ca(SH)2,
Ca(OH)2 +Ca(SH)2 +2CO2 → CaCO3 + 2H2S,
H2S + O → H2O + S.
Iron sulfides presenting in coal layers and bitumenous shales are products of reduction of sulphate
solutions by coaly (carbonaceous) matter:
FeSO4 + 2C → FeS + 2CO2.
Monosulphide FeS turns, not long after, into FeS2. This process occurs also in sea muds, where FeSO4
formed by organic decomposition, is reduced.
In the processes of reduction, fixation (retention) of other metals, in their lower valence states,
takes place as well.
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The process of carbonation is an interaction of carbonate [CO32−] and bicarbonate [HCO3−] ions
with rocks and minerals. The action of these ions is one of basic factors of chemical weathering.
Under the influence of carbonation, minerals dissolves completely or partly, and their metals acquire
the form of carbonates. Carbon dioxide dissolves carbonates of two-valence metals (Ca2+, Mg2+, Fe2+,
etc.), so calcium, magnesium, iron and others pass into solution as bicarbonates Ca(HCO3)2,
Mg(HCO3)2, Fe(HCO3)2, etc. Dissolution of limestone induced by the action of carbonic acid proceeds
as follows:
CaCO3 + H2CO3 → Ca(HCO3)2.
Acidic carbonate of calcium appears, it passes easily into solution. Limestone can be dissolved as well
by the action of organic acids with the formation of soluble compounds. For example, acetic acid
provokes the following decomposition:
2CaCO3 + 2C2H4O2 → Ca(C2H3O2)2 + Ca(HCO3)2.
Decomposition of silicate rocks by hydrolysis is often accompanied by the interference of
carbonic acid. As a result of these two agents' action, silicates lose their alkaline and earth-alkaline
metals which pass into solution in the form of carbonates. Hydrated alkaline and silica also pass into
solution, whereas insoluble hydroxides of Al, Fe, Mn, and most of silica remains inaffected. The
action of H2O and CO2 on silicates can be described as follows:
0H + CO2 + H2O → 0HCO3 + SiO2 + H2O,
where 0H= K, Na, Ca, Mg, Sr, Cs, etc.
Depending on the composition and structure of silicates, the equation of reaction can be very
complicated. One of the most important natural processes is weathering of feldspars which are main
minerals of the lithosphere. Decomposition of orthoclase with the participation of carbon dioxide
proceeds as follows:
K2Al2Si6O16 + 2H2O + CO2 → H2Al2Si2O8⋅H2O + K2CO3 + 4SiO2.
11
Here kaolinite (H2Al2Si2O8⋅H2O) appears which remains at the site of weathering, and carbonate of
potassium (K2CO3) passes into solution completely, whereas silica - partly. By the similar way the
reaction of decomposition of sodium feldspar - albite - takes place. According to the final product of
weathering this process is named kaolinitization.
In general, the process of carbonation leads to the formation of soluble carbonates which remain
in a solution and, in their turn, destroy silicates. So alkaline carbonates cause dissolution and removal
of silica.
+\GUDWLRQ
Hydration, as it was mentioned above, accompanies the processes of hydrolysis, oxidation and
carbonation. For example, hydration of hematite, braunite and anhydrite is expressed by the following
reactions:
2Fe2O3 + 3H2O → 2Fe2O3⋅H2O,
Mn2O3 + H2O → Mn2O3⋅H2O,
CaSO4 + 2H2O → CaSO4⋅H2O.
Hydration of some compounds can proceed with the participation of bacteria:
4FeCO3 + 6H2O → 4Fe(OH)3 + 4CO2.
Hydration induces an increase of the volume of substances (the transformation of anhydrite into
gypsum increases the volume by 30%). The action of water on some silicates results in the formation
of zeolites - hydrated silicates of Na and Ca, developing mainly from feldspars.
&DWLRQH[FKDQJH
Cation exchange proceeds without any change in the structure of minerals. Ions which are capable
for exchange are usually weakly retained in crystalline structures. Clay minerals are better than others
adapted to cation exchange, especially those which belong to the group of montmorillonite. Their
cations are placed between two structure layers having rather low energy of exchange bonding, that is
why they are easy subjects of exchange.
Exchange ability of cations in clay minerals can be represented by the following series:
Li < Na < K < Rb < Cs,
Mg < Ca < Sr < Ba.
The reason of these sequences seems to be connected with polarization of ions. Ions with larger
dimensions become polarized easier, so the effect of polarization increases from Li+ to Cs+ and from
Mg2+ to Ba2+.
As a particular case of cation exchange, on can indicate decomposition of feldspars, their cations
are continuously replaced by H+ ions coming from water.
'LDO\VLV
Dialysis is a process of cleaning of colloidal solutions and solutions of high-molecular substances
from truly low-molecular substances which are truly dissolved in them. Dialysis between a colloidal
solution and a pure solvent is accomplished, usually under water, across a porous screen "membrane", impermeable for the particles of colloid dimensions. Clay minerals containing ions of
metals at the concentrations which are lower than the concentrations of these ions in water, are
subjects of dialysis in weakly mineralized or fresh water. Thus, because of dialysis, colloidal clay
minerals lose their metal ions in the process of establishing equilibrium in water. The most favorable
environment for dialysis is created in lakes and bogs (freshwater reservoirs), where colloidal clays are
presented in the form of water gels or suspensions. Atmospheric precipitation promotes dialysis in
shallow freshwater reservoirs.
)RUPVRIWUDQVSRUWDWLRQDQGDFFXPXODWLRQRIHOHPHQWV
Behavior of chemical elements in different thermodynamic conditions of the earth crust
essentially depend on their occurrence forms. Alexeenko proposed in 1989 to consider nine most
important occurrence forms: magmatic melts, independent mineral species, isomorphic mixtures,
dispersion, water solutions, colloids with a liquid medium, gaseous mixtures, biogenic form, and
technogenic form (Alekseenko, V.A., 1989).
0DJPDWLFPHOWV are complicated, changeable (due to the changes of thermodynamic conditions)
systems. States of elements in them remains undetermined. It is supposed that magma contains
complexes conforming to future minerals. Two major kinds of such complexes are supposed to
12
include octahedral groups (where [MgO6] and [CaO6] dominate) and tetrahedral ones (mainly [SiO4]
and [AlO4]). In addition, it is assumed the presence of free mobile cations, atoms of dissolved metals,
such compounds as FeS and FeSO4 (which behave like “electronic liquids”), and separate molecules
(first of all, molecules of gases).
,QGHSHQGHQWPLQHUDOVSHFLHV are very important in the lithosphere. Being in this form, elements
migrate in common, remaining in constant relationships. Migration of individual elements is possible
only after decomposition of minerals. A mineral form includes also specific colloidal systems with
solid dispersion media, such as crystallo-gels and crystallo-sols. Elements of these systems migrate
keeping a mineral form and always in common. By this feature, colloidal minerals are close
isomorphic mixtures.
,VRPRUSKLFPL[WXUHVrepresent numerous processes in which analogous elements substitute each
other in crystalline lattices. Practically all elements can be in this form, and for such elements as Rb,
Te, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Re, it is predominant in the lithosphere. Elements that
are isomorphic mixtures, migrate only together with host elements. This is a general property of
isomorphic and mineral forms of occurrence.
'LVSHUVLRQis a consequence of the four principal propositions of geochemistry (see above), the
state of element dispersion dominates over the state of their concentration in the earth crust.
Apparently, dispersion includes, first of all, the process of arrangement of atoms in “empty” sites of
crystalline lattices. Dispersion is an usual state of occurrence of such elements as I, Xe, Rn. The
concentrations of elements in the state of dispersion can be as low as 10−15 % (this value depends on
sensitivity of the method of measurement).
:DWHUVROXWLRQconstitute the Earth hydrosphere, they encompass hydrothermal solutions as well.
Dissociation into ions takes place in the process of dissolution of compounds with ionic, metallic, or
covalent bonding, in water. Many elements are transported in natural waters as complex compounds
formed by the association of ions with neutral molecules or ions of opposite sign.
&ROORLGVZLWKOLTXLGPHGLD are widely spread in nature. In a liquid dispersion medium, a phase of
dispersion can be in solid, liquid, or gaseous state. The phase of dispersion can be presented by metals,
oxides, sulphides, clay minerals (montmorillonite, kaolinite, halloysite, etc.). The formation of colloids
in nature proceeds by two major ways: the way of dispersion (when crystalline substances decay) and
the way of concentration (when molecular particles unite reaching colloidal dimensions). Colloidal
systems, having a high degree of dispersion and large total surface of the dispersion phase, are
characterised by a high value of free surface energy. Its spontaneous decrease leads to sorption
(concentration of a substance on the surface of phase partition).
*DVHRXV PL[WXUHV form the atmosphere above ground, but a significant amount of gases are in
sorbed state, in cavities hollows and pores within igneous and sedimentary rocks, and in the form of
inclusion as well.
%LRJHQLFIRUP means the occurrence of elements in living organisms (plants, animals, bacteria).
7HFKQRJHQLF IRUP includes compounds without natural analogues (different artificial polymers,
metal alloys, pesticides, etc.).
Perel'man proposed to consider mobile and inert occurrence forms of elements in the lithosphere
(Perel’man, A.I. 1979). Basic forms of these forms in the zone of hypergenesis, according to their
mobility, are presented in Table 1-1. Of course, in real cases, these forms can be altered, so a given
element can pass from a rather inert form to a more mobile one. The most complicated combinations
of different forms of occurrence are observed just in the zone of hypergenesis which as a whole
belongs to the biosphere of the Earth.
A major form of the occurrence of elements in the earth crust is connected with points of
crystalline lattices, which can be occupied by both host elements of a given mineral and isomorphic
admixtures, including numerous trace elements. There are two basic modes of isomorphism –
isovalent and heterovalent. Isovalent substitutions proceed between ions with the same valence (Cs+ →
Rb+, Sr2+ → Ca2+, U4+ → Zr4+), heterovalent ones – between ions having different valence (TR3+ →
Na+, U4+ → Ca2+). Equalization of the balance of electrical changes in the process of heterovalent
isomorphism can be performed by three following ways: (1) additional isomorphic substitution of two
other elements (Sr2+ + Al3+ → Na+ + Si4+, TR3+ + Ca2+→ K+ + Si4+); (2) substitution of an unequal
number of ions: (U6+ → 2Al3+); (3) participation of additional ions (U6+ → Si4+ + Ca2+).
13
7DEOH2FFXUUHQFHIRUPVRIHOHPHQWVDFFRUGLQJWRWKHLUPRELOLW\IURP3HUHO¶PDQ
Examples
Occurrence forms
Gaseous
Elements and their compounds
O2, N2, CO2, H2S,
CH4, Rn, He, Ar
Environment
Overground and underground atmospheres, natural
waters, living organisms, to lesser extent – minerals
(radiogenic gases)
Easily soluble salts and NaCl, Na2SO4, Na2CO3,
Soils, weathering crusts, continental sediments and
their ions in solutions ZnSO4, CuSO4, Na+, Cu2+, Cs+
lakes of arid steppes and deserts, zones of oxidation
of sulphide deposits. Groundwaters of regions of arid
climate, deep horizons of groundwaters (salt brines),
salt deposits
Hardly soluble salts and CaCO3, CaSO4⋅2H2O,
Soils, weathering crusts and continental sediments of
their ions in solutions CuCO3⋅Cu(OH)2, PbSO4
steppes and deserts, partly zones of oxidation of
sulphide deposits, groundwaters
Elements in living Proteins, lipids, carbo-hydrates, Continental landscapes, especially regions with warm
organisms (plants, ani- and other organic compounds, and humid climate, in a lesser extent taiga, steppes,
mals, microorganisms) consisting mainly of C, H, O, N tundra, deserts. Seas and oceans, mainly superficial
and to a lesser extent of S, P, K, horizons and coastal (riverain) sections. To an
insignificant degree – deep horizons of groundwaters
Ca, Mg, Cu, Zn
(only micro-organisms)
Colloidal sediments
Humic
substances,
colloidal Soils, muds in water reservoirs, weathering crusts,
and solutions
precipitates of hydroxides of Fe clay sedimentary rocks, ores of Fe and Mn,
and Mn, Si, Al, partly clay carboniferous-siliceous shales, peat
minerals
Adsorbed ions (mainly Ca2+, Mg2+, Na+, Cu2+, H+, Ni2+, Soils, , weathering crusts, muds in water reservoirs
cations)
Al3+, and others in colloidal
minerals
Intergrainal form in
U
Rocks
dislocations of crystals
Elements in points of Si, Al, Fe, Ca, Na, K, Mg and Minerals of rocks
many trace elements
crystalline lattices of
minerals
([WHQVLYHDQGLQWHQVLYHSDUDPHWHUVRIPLJUDWLRQ(TXDWLRQRIPLJUDWLRQLQWHQVLW\
According to A.I.Perel’man, migration of chemical elements, as any work, can be expressed by a
product of extensive and intensive parameters (Perel'man, 1979). Extensive parameters are parameters
with additive properties depending on the dimensions of a system and many other characteristics
(mass, volume, entropy, etc.). Intensive parameters do not possess additive properties, they do not
depend on the dimensions of a system, they encompass such characteristics as forces, pressure,
temperature, chemical potential, etc.).
,QWHQVLW\RIPLJUDWLRQ 3[ can be expressed by means of a special equation proposed by Perel’man.
Suppose that in a given system the amount of some element ; is determined by the value E[, and a
small portion of this amount dE[ migrates during a time interval dW. The migration rate will be dE[/dW,
however, this value does not characterize the intensity of migration, because a total mass of the
element E[ is not taken into account. The intensity migration 3[ will be produced after dividing the rate
dE[/dW by E[:
3[ = (1/E[)(dE[/dW).
In the process of efflux of an element (evacuation or emigration) the value 3[ represents the element ;
amount which became mobile in a time unit, calculated for a mass unit of the element presenting in a
system (rock). In other words, the intensity migration 3[ is the rate of leaching of 1 gram of the
element considered. The value dE[/E[ can be considered as an independent infinitely small value and
can be lettered as d8. Then there will be a simple formula for intensity migration:
3[= d8/dW
From this formula: d8= 3[⋅dW. Perel’man calls d8 an elementary impulse of migration, and 8– total
impulse of migration. Total impulse of migration can be expressed as follows:
14
W2
8=
∫ 3 GW .
[
W1
In order to determine 8, one should know the dependence of migration intensity on time,
however this dependence is often unknown. Supposing that in the process studied migration intensity
is constant, it is possible to integrate the last equation:
8= 3[(W− W),
3[ = 8/(W− W).
Taking W = 0:
3[ = 8/W.
E2
Because of d8 = dE/Eand 8=
∫ GE / E , one has
E1
8 = ln (E2/E1).
From this:
E2 = E1⋅e8 = E1⋅e3[(W− W),
where E1 – an amount of an element ; in a system before the start of process studied at the time W1, E2 –
an amount of the element ; by the time moment W2.
Thus, the dependence of the change of an amount of the element in a system on time is exponential.
'LVSHUVLRQSDWWHUQV
The formation of OLWKRJHRFKHPLFDOIOX[HV of dispersion of mineral deposits proceeds on the land
surface owing to mechanical force and dissolution ability of water, as a result of displacement of the
products of weathering by gravitation in the direction of relief lowering, into the zone of
sedimentation. The activity of contemporaneous glaciers has much less significance, however in
climatic epochs of the past, in northern regions of European countries, Canada and Alaska, the role of
glacial processes was extremely important. In mountainous areas, an essential contribution to the
formation of the field of dispersion is given by hillside wastes, stonefalls and stone fluxes, in
circumpolar regions such process as solifluction is of specific importance. The transporting force of
wind, as a rule, is not capable to form lithochemical fluxes of dispersion.
Lithochemical modes of dispersion of ore elements prevail over K\GURFKHPLFDOSURFHVVHV, this is
clearly manifested in the formation of dispersion fluxes of the majority of deposits. The distribution of
chemical elements between soluble and solid phases in the run-off is characterized by their
coefficients of water migration .[ (see 1.3.5.4) and the so-called thalassophility τ[. The coefficient of
thalassophility τ[ is a ratio of the Clarke value of an element in the hydrosphere to its Clarke value in
the lithosphere. Besides oxygen and hydrogen, only three elements – Cl, Br and S – have their Clarke
values of ocean water exceeding their Clarkes in the lithosphere. All other elements have the value of
τ[ < 1 or τ[ << 1, they do not reveal any ability to be accumulated in the hydrosphere, their basic
amounts are concentrated in the products of solid run-off.
*HRFKHPLFDOEDUULHUV
A JHRFKHPLFDOEDUULHU is a site of the earth crust where, along a short distance, a sharp drop of
migration ability of chemical elements occurs and, as a consequence, their concentration takes place.
The FRQWUDVWLQGH[ 6of a geochemical barrier is determined by a ratio of geochemical quantities
brfore and after a barrier in the direction of migration. For element concentrations, the contrast index
is as follows
6 &[2/&[1,
where &[1 and &[2 - element concentrations before and after the barrier, respectively.
The JUDGLHQW * RI D EDUULHU in the direction of migration is a measure of the change of
geochemical indicators (Eh, pH, pressure 3, concentration&[, etc). For example,
* d&[/dOor * (&[2 − &[1)/O,
15
where &[1 and &[2 - element concentrations before and after the barrier, respectively, and O LV the
barrier width. The intensity of accumulation of elements increases with the growth of the contrast
index of a barrier and the gradient of a barrier.
Detailed description of physical-chemical barriers acting in the earth crust is given below (see
1.3.6).
3DUDJHQHWLFDVVRFLDWLRQVRIHOHPHQWV
Formation of paragenetic element associations is governed, to a great degree, by phenomena of
isomorphism which implies the properties of atoms and ions to be substituted in crystalline structure.
Vernadsky in 1909 worked out a system of 18 series of isomorphously combined elements, it takes
into account, among other factors, ionic dimensions, and keeps its significance today. Table 1-2
presents 9HUQDGVN\¶VLVRPRUSKLFVHULHV with more accurate definitions made by Makarov in 1973 (he
proposed also to unite some series and to divide one of them) (Makarov, E.S. 1973).
7DEOH9HUQDGVN\¶VLVRPRUSKLFVHULHVZLWKFRUUHFWLRQVRI0DNDURY
Series
1
2 and 13
3 and 14
4 and 5
6
7
8
9 and 15
10a
10b
11
12
16
17
18
Elements
Al, Ga, Si, Fe, Cr, V, Mn, Mg, Ti
Ca, Na, Y, TR, Sc, Mn, Sr, Ba, Pb, Fe, Mg, Zn, U(IV), Th, Zr, Hf
F, OH−, Cl, Br, I, O?
P, As, V, Sb, Bi, Si, Al
Na, Ca, TR, Y, K, Rb, Cs, Tl, Li, Ag, NH4+, U(VI)?
W, Mo, Re, Nb, Ta, Sc, In
Ge, Sn
Fe(II), Mg, Mn, Zn, Be?, Cd, Cu, Ni, Co, Ca, Li, Al, Fe(III), U(IV)?
Au, Ag, Cu, Pd, Rh, Pt, Ir, Fe, Bi?, Hg?
Pb, Tl, Hg, Bi, In, Ba, Cd, Ag, Th, U, Ca, Sr, Zn?
Pt, Fe, Pd, Ir, Rh, Cu, Ni
Os, Ir, Rh, Ru, Pt, Au, Cu, Fe
Si, Ge, Al, P, Be, B?, Fe(III)?, S?
Nb, Ta, Ti, Zr, Hf, U, Th, Mo, V, W, Sn, Fe, V?, TR?, Sc?
S, Se, Te, P, As
Common accumulation of elements can be influenced by their common conditions of migration.
Of practical importance are associations of elements forming ore minerals and characteristic groups of
trace elements in these minerals. Major associations of elements observed in different types of
deposits have been settled by Alekseenko (Alekseenko, V.A., 1989), they are presented in Table 1-3.
16
7DEOH$VVRFLDWLRQVRIHOHPHQWVRFFXUULQJDWHOHYDWHGFRQFHQWUDWLRQVLQRULJLQDOURFNVRIPLQHUDO
GHSRVLWVDIWHU$OHNVHHQNR
Major components
Associations of elements
,0DJPDWLFGHSRVLWV
Chromite……………………………………………Cr, Fe, Mg, (Pt, Al)
Platinum……………………………………………Cr, Fe, Pt, (Os, Ir), Mg
Titanomagnetite…………………………………….Fe, Ti, V
Apatite-magnetite…………………………………...Fe, F, P, Ca, (Zr)
Rare-earth metals……………………………………Ti, Nb, Zr, Ta, Ge, P, Al, F, (TR), Na
Copper-nickel (sulphide)……………………………Ni, Cu, (Pt, Pd, Co)
Diamond (kimberlite)……………………………….C, Cr
Apatite………………………………………………..P, Ti, Li, Zr, Th, Be, F, Cl, Sr, Nb, Ta, TR,
,,&DUERQDWLWHGHSRVLWV
Rare-earth metals……………………………………Na, Ga, Ge, Nb, Ti, Ta, TR, Mg, Zr, F, Ca
Apatite………………………………………………P, Ca, Mg, F, Sr, Ba, TR, Ti, Zr, Nb, Ta, Cu, Mo
,,,3HJPDWLWHGHSRVLWV
Tungsten-lithium……………………………………W, Li, Sn
Monazite…………………………………………….TR (Ce-group), Th
Beryl-topaz…………………………………………..F, B, Cl, Li, Pb, Cs, Ti, Nb, Ta, TR
,96NDUQGHSRVLWV
Iron…………………………………………………..Fe, Ca, Al, Si
Copper………………………………………………..Cu, Fe, Ca, Al, Si, (Mo, Co), (Pb, Zn)
Molybdenum-tungsten………………………………..Mo, W, Fe, Ca, Al, Si
Tin…………………………………………………….Sn, Fe, Cu, (Mo, As, Zn, Pb, Bi, Ag, W), Si
Berillium………………………………………………Be, Fe, Mn, Si, Al, (Sc), W
Boron………………………………………………….B, Mg, Fe
9$OELWLWHJUHLVHQGHSRVLWV
Rare-earth metals (albitite)……………………………Be, Li, Rb, Ta, Nb, Zr, TR, Na, K, Al, Si
Greisen:
Non-sulphide……………………………………….Sn, W, Li, Be, Si, Al; Sn, W, Mo;
……………………………………….Mo, Be, Li; W, Mo, Be, F, Si
Sulphide…………………………………………….Al, (Fe, Cu, As, Bi, Zn, Pb)
9,+\GURWKHUPDOGHSRVLWV
Quartz paragenesis…………………………………….Au, As, Fe, Bi, Mo, W, U, Si, Cu
Sulphide paragenesis:
Zinc and lead………………………………………Pb, Ba, Zn, Cu, Fe, U, Mo
“Five-element” formation……………………...….Co, Bi, Ni, Ag, Ca, Ba, U, F, As, Fe, (Pb, Zn, Cu)
Cassiterite………………………………………….Sn, Pb, Zn, Fe, W
Carbonate paragenesis:
Iron………………………………………………… Fe, Mg, Ca, (Cu, Pb)
Manganese…………………………………………. Mn, Mg, Ca, (Fe, Ba)
Magnesium………………………………………….Mg, Ca
Pyrite……………………………………………………Fe, Cu, S, Zn, Pb, (Au, Ba)
Graphite-bearing………………………………………..C, Mg, Fe, Ti, Y, (Cu, Zn)
9,,6WUDWLILFDWHGGHSRVLWV
Copper………………………………………………….Cu, Fe, (Pb, Zn, Ag)
Zinc-lead………………………………………………..Pb, Zn, Ag, Fe, Mg, (Ba, F)
9,,,6HGLPHQWDU\GHSRVLWV
Boron……………………………………………………B, Mg, K
Iron………………………………………………………Fe, Mn
Manganese………………………………………………Mn, Fe
Aluminium………………………………………………Al, Fe
,;0HWDPRUSKRJHQRXVGHSRVLWV
Manganese………………………………………………Mn
Ferruginous quartzite……………………………………Fe
Titanium…………………………………………………Ti, Fe
;'HSRVLWVRIZHDWKHULQJ
Residual:
Silicate-nickel…………………………………………Ni, Mg, Al, (Co, Mn)
Ferriferrous ………………………………………….Fe, Mg, Mn, Co, Ni, Cr
Aluminium…………………………………………….Al, Fe, Mn
Uranium, formed by infiltration…………………………..U, Re, V, Cu
17
There are associations of elements typical for underground waters leaking through ore deposits.
Table 1-4 presents the associations of this kind in different types of deposits (summarized by
Alekseenko).
7DEOH$VVRFLDWLRQVRIHOHPHQWVHQULFKHGLQXQGHUJURXQGZDWHUVZLWKLQPLQHUDOGHSRVLWVRIGLIIHUHQW
W\SHVDIWHU$OHNVHHQNR
Types of deposits
Magmatic copper-nickel
Magmatic chromite
Magmatic titanomagnetite
Magmatic apatite
Rare-metal apogranite
Rare-metal pegmatite
Pegmatite tin-tunsgten
Pegmatite berillium
Pegmatite beryl- and topaz-bearing
Skarn iron
Skarn copper
Skarn molybdenium-tunsten
Skarn zinc-lead
Skarn boron
Greisen sulphide
Greisen quartz-wolframite
Hydrothermal copper-molybdenium
Hydrothermal copper-cobalt
Hydrothermal antimony
Hydrothermal mercury
Hydrothermal zinc-lead
Hydrothermal tin
Hydrothermal gold
Hydrothermal uranium
Copper pyrite
Residual silicate-nickel
Zircon-ilmenite placers
Diamond-bearing kimberlite
Hydrochemical associations of elements
Cu, Ni, Co, Fe, Ag, Cr, Zn, Pb, Sb, Sn, Ti, V
Cr, Ni, Cu
Ti, Fe, Ni, Co
Cu, Zn, Ba
F, Li, Be, Nb
Li, Be, Nb
W, Sn, Bi, Ni, Zr, Sb, (Cu, Zn, Pb, Cr)
Be, Mo, Sn, W, Zn, Bi, Zr, (Cu, Pb, Ni)
F, B
Fe, Mn
Cu, Mo, (Zn, Pb, Co)
Mo, Zn, W, Fe, (Pb, Sn)
Zn. Pb, Cu, Mo, (As, Ag, Mn, Ni, Ba, Co, Sr, Sn)
B, F, Li; As, Cu, Zn, Hg, Pb
Mo, Cu, Mn, Ti, Sr, Ni, V, Zr, W, As, Co
Mo, Mn, (Ti, Ni, V, Zr, Bi, Zn, Ag, Cu, Sr)
Mo, Cu, Mn, Ti, Ni, V, Pb, Zn, Ag, Co
Cu, Co, As, Fe, Ni, Zn, Ag
Sb, As, Pb, Zn, Ag, Bi, Cu, Ni, Co
Hg, Sb, As, Zn, Pb, Cu
Zn, Pb, Cu, Mo, Ag, (Cr, Cd, V, Bi, Sb)
Zn, Sn, Pb, Cu
As, Au, Bi, Pb, Cu, Zn, (Mo, Ag, Sb)
As, U, Cu, Zn, Pb, Ni, Mo
Cu, Zn, Pb, Mo, Fe, (As, Ag)
Ni, Co, Ti, Cu
Ti, Zr, Cr, V, (Sn, Ag, Ni, Co)
Zn, Ni, Co, Cr, V, Ga, Cu
This table shows that several metals – Cu, Zn, and Mo – are present in underground waters very often,
regardless the type of a deposit, so their indicator role is very important.
0HFKDQLFDOPLJUDWLRQ
%DVLFIHDWXUHVRIPHFKDQRJHQHVLV
Mechanogenesis includes such processes as erosion, denudation, deflation (wind erosion),
formation of clastic (detrital) deposits and other mechanical phenomena on the earth crust. Breaking
up and disintegration of rocks lead to their mechanical dispersion and provide the development of
surface phenomena (sorption, occlusion, etc.). Mechanical dispersion is accompanied by the
decomposition of many minerals: the abrasion of carbonates induces their decomposition with the
emission of oxygen, , hydrated minerals release their water, etc. The role of mechanical-chemical
phenomena in the earth crust is still insufficiently investigated.
Mechanical denudation depends on geological structure of the region to be studied, climate and
topography (relief). To quantify it, it is recommended to use an annual discharge of suspended rock
particles in a river range 30, measured in tons per 1 km2 of the river area. The values of 30 for several
rivers of the European part of Russia are as follows (in t/ km2): the Volga – 19; the Severnaya Dvina –
14; the Luga (Leningrad Region) – 4; the Neva – 3.9 (Perel’man, A.I., 1979).
In the contemporary geological epoch, on the territory of both Russia and the Earth as a whole,
mechanical denudation prevails over chemical one. If one quantifies the denudation process by an
18
annual lowering of the day surface, the average value for the territory of the former Soviet Union is 27
micrometers, where chemical denudation is responsible for only 7 micrometers (Perel’man,
A.I.,1979). Mineral density is an important factor of mechanical migration: heavy minerals behave
like larger particles. Mechanical displacement depends also on mineral hardness and their resistance to
weathering. Hard minerals, which are resistant to water abrasion, are well preserved in sediments.
0HFKDQLFDOGLIIHUHQWLDWLRQ
One of the most important characteristics and consequences of mechanogenesis is mechanical
differentiation. It is revealed by the fact that clay fractions of rocks and soils contain, as a rule, much
more metals than sand fractions. In the course of weathering, different compounds of Fe and Al form
numerous colloids, including clay minerals which contain Mg and K. Such metals as V, Cr, Ni, Co, Cu
are easily absorbed by colloids. To quantify the ability of clays relatively sands to absorb metals, the
coefficients of concentration in clays are used. The values of these coefficients .FL are determined by
the ratios:
.FL= &FL/&VL,
where &FL and &VL are Clarke values of Lth element in clays and sands, respectively.
In Table1-5 the values of .FL for some metals are presented.
7DEOH&RHIILFLHQWVRIFRQFHQWUDWLRQRIPHWDOVLQFOD\VUHODWLYHO\VDQGV.FLDIWHU3HUHO¶PDQFDOFXODWHG
XVLQJWKHGDWDRI.7XUHNLDQDQG.:HGHSRKO
Element
Co
Ni
Sr
Mo
U
V
.FL
63
34
15
13
8.2
6.5
Element
La
Al
Ti
Zr
Th
Ce-Lu
.FL
3.6
3.2
3.0
0.72
0.7
0.66 – 0.58
A rather high value of .F for uranium is explained by its both sorption and association with organic
matter, which is usually occurs in clays
*HQHUDOIHDWXUHVRISK\VLFDOFKHPLFDOPLJUDWLRQ
7KHUPRG\QDPLFFKDUDFWHULVWLFVRISK\VLFDOFKHPLFDOPLJUDWLRQ
The study of physical-chemical migration is often connected with the problem concerning a
possibility of certain chemical reactions under the given values of temperature, pressure, and
concentration. This problem can be solved either experimentally or by performing thermodynamic
calculations. In chemistry, this problem comes to the determination of chemical affinity, i.e. the ability
of elements (ions, molecules) enter in the combination. The measure of chemical affinity is the amount
of work. According to the first law of thermodynamics:
∆8= 4 − $
where ∆8 is the change of in internal energy of a system4 - the heat supplied, and $ – the work done
by the system.
If the pressure 3 is held constant (e.g. atmospheric pressure), which is a usual situation in the
zone of hypergenesis, the work is:
$ = 3d9,
where d9is the change of volume. Therefore, the heat at constant pressure (43) is:
43 = ∆83d9.
This defines ∆+, WKHHQWKDOS\FKDQJH, the common way of expressing chemical energy. Enthalpy is
connected with temperature by the expression:
∆+ = F3∆7,
19
where F3 is the heat capacity of the system at constant pressure. When ∆+ is negative the process is
exothermic, and when positive, endothermic.
According to the second law of thermodynamics, WKH HQWURS\ of the universe increases in a
spontaneous process, and does not change in a reversible process:
∆6XQLYHUVH = ∆6V\VWHP+ ∆6VXUURXQGLQJ ≥ 0.
Enthalpy and entropy are linked in the expression for WKH*LEEVIUHHHQHUJ\ *:
*= +− 76.
For a change in the free energy of the system:
∆*V\VWHP = ∆+V\VWHP − 7∆6V\VWHP.
The spontaneity of a reaction is given by the sign of ∆*:
∆* < 0, feasible (spontaneous) reaction,
∆*!0unfeasible (non-spontaneous) reaction,
∆*=0, equilibrium.
The free energy is connected with the equilibrium constant by the equation:
∆*= − 57ln.
At 7 = 25oC:
∆*= − 5.71⋅103 log10..
If ∆*0 then log10.>1 and the equilibrium lies on the side of the products which, in thermodynamic
terms, is a feasible reaction. On the other hand, if ∆*> 0 then log10.1 and the equilibrium favours
the reactants. This arises because
.= [products]/[reactants].
As ∆* becomes more negative, . becomes larger and the concentration of the products increase,
while the reverse holds when ∆* becomes more positive. When ∆* is close to zero, that is . ≈ 1,
the reactants and products may be at comparable concentrations.
0HFKDQLVPVRIPDVVWUDQVSRUWDWLRQGLIIXVLRQFRQYHFWLRQ
Physical-chemical migration occurs by the processes of diffusion, convection, or their
combination (convective diffusion). 'LIIXVLRQ arises under the influence of the gradient of
concentration which provokes the equalization of concentrations. This process leads to decreasing of
diversity and differentiation, it does not requires any external energy waste, the entropy of a system
increases. However, diffusion is possible under the influence of external factors forming gradients of
temperature, pressure, electrical potential. Correspondingly, thermodiffusion, barodiffusion, and
electrodiffusion can take place.
The law governing diffusion is similar to the law of thermoconductivity: diffusion flux is
proportional to the value of concentration gradient d&/d[:
,[ = −'(d&/d[),
where 'is the coefficient of diffusion, & – concentration, [ – distance.
&RQYHFWLRQ is a migration of the mass fluxes of a gas or a liquid. In contrast to diffusion, when
convection occurs, not only dissolved particles (atoms, ions, molecules, colloidal particles), but the
solvent itself participates in the process as well. If convection proceeds in a porous medium, it is
called filtration. Convection is possible under the influence of geothermical field or of the gradient of
concentration.
Filtration proceeds significantly faster than diffusion, that is why diffusion often plays a
subordinate role. The processes of filtration are especially important in the upper part of the earth crust
(the zone of aeration, the zone of active water exchange, etc). But they develop also in he earth depth,
in the zone of deep faults. While being in the process of filtration, the waters interact with host rocks,
where such phenomena as sorption, ion exchange, precipitation of elements on geochemical barriers
occur.
0HWDPRUSKLFDQGPHWDVRPDWLFDOWHUDWLRQVRIURFNV
A totality of processes occurring at certain depths under the influence of the changes of
temperature, pressure, and concentrations of chemically active substances, leading to mineral
20
structural transformations is called PHWDPRUSKLVP. Metamorphism resulting in the substitution of one
set of minerals by another set is called PHWDVRPDWLVP.
Metamorphism of rocks happens under the influence of the three most important factors:
temperature of the surrounding, pressure and concentrations of certain substances in rocks (including
the composition of intergranular solutions). Depending on the leading role of a concrete factor, the
following types of metamorphism are marked out.
(1) &RQWDFW PHWDPRUSKLVP proceeds in host rocks when magmatic melts intrude into them. A
sharp rising of temperature of host rocks leads to the disturbance of their mineral equilibrium, this is a
reason of recrystallization. Contact haloes around massifs of igneous rocks are sometimes very
extensive. Easily volatile substances play an important role in the course of contact metamorphism.
During the separation of a gaseous phase from a magmatic melt, mobile volatiles carry away nonvolatile components and, being saturated by them, penetrate into host rocks, where dissolved
substances are precipitated.
(2) '\QDPRPHWDPRUSKLVP – metamorphism induced by pressure. It is very significant in
structural geology and petrology, however its role in geochemistry is negligible.
(3) 5HJLRQDOPHWDPRUSKLVP – metamorphism which can be widely manifested in the geological
media, it occurs in deeply bedding rocks under the influence of interior heat of the Earth.
There are two modes of migration of chemical elements in the processes of metamorphism and
metasomatism – migration in a liquid state and migration in a solid state. According to
D.S.Korzhinsky, an intergranular liquid is a basic medium where migration of substances occurs in
metasomatic processes. Depending on the dynamics of a medium, two types of metasomatism are
possible: GLIIXVLRQ PHWDVRPDWLVP and LQILOWUDWLRQ PHWDVRPDWLVP. In the course of diffusion
metasomatism, pore solutions remaim motionless, this happens when there is not any overfail of
pressure. The leading role of this process belongs to the concentration of a dissolved substance and its
gradient. Infiltration metasomatism provides the migration of elements by means of their
transportation by a pore solution. This type of metasomatism does not occur if there is no more or less
significant overfail of pressure which causes a flow of liquids. That is why filtration metasomatism
proceeds usually in the zones of crushing, during the schist-forming processes, along microfissures, in
the zones of tectonic breaks.
Korzhinsky put forward a notion of differential mobility of components in metasomatism and
established the following series of their mobility (it decreases from left to right):
H2O – CO2 – S – SO3 – K2O – Na2O – F – CaO – O2 – FeO – P2O5 – BaO – MgO – SiO2 – Al2O3
– Fe2O3 – TiO2.
Migration in a solid state can be induced by high temperatures, without participation of liquid
pore solutions, directly by means of diffusion through crystalline lattices of minerals. This is an
extremely slow process, it does not produce any significant geochemical effect in normal conditions.
2[LGDWLRQ]RQHV
Oxidation zones are important in the formation of elemental fluxes and dispersion haloes,
especially at sulphide deposits of many metals and their non-metal satellites (Cu, Zn, Pb, Ag, Au, As,
Bi, Sb, Mo, Sn, Ni, Co, etc). Development of oxidation zones at sulphide deposits is characterised by
the following common regularities (Smirnov, S.S. 1955).
Underground waters overlaying first water-resisting horizon are in free water exchange with the
surface. Underground waters are continually replenished at the expense of infiltration of atmospheric
precipitation and condensation of vapors, and they discharge by outflow into an open drainage system
and by evaporation. As a result of dynamic equilibrium between inflow and discharge of water, a
certain level of underground waters is established, its surface follows, in a smoothed manner, the relief
of the day surface. A ground water table is a subject of seasonal and secular fluctuations, depending on
the amount of atmospheric precipitation. The ground water table lowers gradually, following
denudation lowering of the earth surface level and hypsometrical marks of the points of discharge.
Atmospheric precipitation is saturated by oxygen and carbon dioxide, so usual rain waters have
oxidizing properties, their pH value is 6.0 (technogenic «acid» rains are not discussed here). As a
result of their interaction with rocks, they get a neutral or weakly alkaline reaction. In the zone of
percolation (infiltration), atmospheric gases are present in abundant quantities, owing to pellicle and
21
capillary states of waters, this determines an oxidizing setting. Below the ground water table, a free
exchange of gases with the atmosphere becomes weak.
The process of oxidation of pyrite which is the most abundant sulphide mineral proceeds as
follows:
2FeS2 + 7O2 + 2H2O = 2FeSO4 + 2H2SO4.
In the presence of free oxygen, ferrous oxide sulphate is unstable, its oxidation yields ferric oxide
sulphate:
4FeSO4 + 2H2SO4 + O2 = 2Fe2(SO4)3 + 2H2O.
In weakly acidic waters, Fe2(SO4)3 is a subject of hydrolysis, and sulphuric acid becomes free:
Fe2(SO4)3 + 6H2O = 2Fe(OH)3↓ + 3H2SO4.
Iron hydroxide precipitates from a solution and transforms later on into stable limonite Fe2O3⋅QH2O.
The formation of sulphuric acid occurs also in the course of oxidation of other sulphides. The presence
of sulphuric acid determines an acid reaction of a setting and a sharp lowering of the pH in the vicinity
of a ground water table near an ore body.
Under the action of sulphuric acid formed by the oxidation of pyrite, further intensive dissolution
and oxidation of sulphide ores occur. Ferric oxide sulphate Fe2(SO4)3 is a very strong oxidant as well.
Oxidized ores of sulphide deposits, in the process of weathering and denudation, form mechanical
haloes of dispersion. This is supplemented by salt dispersion.
*HQHUDOIHDWXUHVRIDTXHRXVPLJUDWLRQ
&ROORLGDOPLJUDWLRQDQGVRUSWLRQ
Colloidal migration is typical for many systems of the earth crust, especially – for the zone of
hypergenesis. In the areas of damp climate, the most part of Al, Ti, Fe, Mn, Zr, Mo, Cr, V, As, Th, and
other elements migrate in colloidal forms. Such elements as Cu, Zn, Co, Sn, and Pb partially migrate
as colloids as well. From colloidal solutions (sols), these elements are precipitated, entering in the
composition of jellified sediments – gels. Gels can be also formed by deposition of elements from
usual (true) solutions. Compounds of Si, Fe, Al, Ti and Mn (about 84% of the lithosphere) easily form
gels that lose part of their water in time, acquiring crystalline structure. If crystalline structure of these
former gels can be observed with the naked eye, or by using a microscope, they are called
«metacolloids».
In soils and continental sediments of the areas of dry climate, there are a lot of calcite, their
waters have a weak alkaline reaction, they do not contain (or almost do not contain) organic acids. All
these circumstances do not favour colloidal migration. Nevertheless, even within these areas colloidal
migration is possible. Colloidal solutions containing silica, compounds of Al and other elements can
be formed in soda waters. In bogs of arid regions, humus and other colloids migrate well.
Thus, colloidal and metacolloidal states of matter are very typical for the products of weathering.
If the processes of weathering are intensive, almost all solid phase of soils and crust occurs in a
colloidal state or passes through it. Such are numerous clay minerals, hydroxides of Si, Al, Fe, and
Mn, humic substances, etc. There are also colloidal and metacolloidal carbonates (the varieties of
calcite, magnesite, siderite, etc), sulphates (barite and others), phosphates.
In the zone of hypergenesis, colloidal minerals are capable to substitute metasomatically feldspars
and other clastic minerals. Hypergenous meatasomatosis is especially characteristic for humid regions,
where colloidal hydroxides of Fe and Mn replace clay minerals, clastic silicates and alumosilicates ,
and sometimes quartz. In the process of hypergenous metasomatosis, one part of some replaced
substances are absorbed by colloids forming different admixtures (SiO2, Al2O3, etc), whereas another
part passes into underground and superficial waters.
The smashing of substances and formation of colloids requires energy which transforms partially
into geochemical energy of sorption performing a large work within the earth crust. The surface of a
single colloidal particle is very small, so the corresponding value of its superficial energy responsible
22
for sorption is also insignificant. However, the total surface of colloidal particles, calculated, for
example, for 1 gram of colloidal fraction, is thousands or millions times more than the surface of a
particle observed by the unaided eye. So superficial energy of natural colloids is indeed significant, it
is revealed by the sorption of molecules, ions, gases and vapors. Specific geochemical significance
belongs to exchange sorption of ions, when from a solution are absorbed not whole molecules, but
cations or anions. Sorption may be reversible or irreversible. Sorption is irreversible when ions are
absorbed by the surface of colloids forming resistant chemical compounds (chemosorption). As a
result of subsequent crystallization, such minerals as phosphates of iron, fervanite, ferrimolybdite are
formed. Non-polar sorption occurs when whole molecules are absorbed from a solution (for example,
molecules of gases, vapors, or organic substances). In the zone of hypergenesis, many clay minerals
contain organic molecules absorbed from solutions.
,RQH[FKDQJH
Cations of a solid phase that are capable to exchange for cations of a solution are called H[FKDQJH
FDWLRQV They are connected mainly with a colloidal fraction of soils and rocks. Multivalent cations are
absorbed with enhanced intensity, it means that the energy of absorption increases in the following
series: R3+ > R2+ > R+. Among ions with the same valence, the absorption energy increases with the
rise of atomic mass and ionic radius (Li < Na < K < Rb < Cs). A large cation of uranyl (UO22−) can be
easily absorbed by hydroxides of iron, brown coal, phosphorites, montmorillonite, and kaolinite. A
non-mineral occurrence form of U in many clays and coals is explained by its sorption from natural
waters.
Exchange absorption is governed by the law of acting masses: the more is the concentration of
cations in waters, the more intense is exchange sorption. Exchange cations appear during the processes
of weathering, as a result of the transition of cations from a non-exchange state into an exchange form,
or due to the absorption of cations from waters migrating through rocks (this is accompanied by
exchange reactions, and a portion of exchange cations presented in rocks pass into waters).
The possibility of ion exchange is connected with structural properties of minerals, sometimes –
with different energetic states of ions on the surface of a particle and in the depth of a crystalline
lattice. In contrast to interior zones of a colloidal particle, electrical charges on its surface are not
completely neutralised by neighboring ions. That is why the particle surface gets an electrical charge –
negative or positive.
In the earth crust negatively charged colloidal particles prevail over positively charged ones. They
include clay minerals, organic substances of the humic series, the gel of silicic acid, hydroxides of Mn,
etc. They are capable to adsorb from a solution cations that become rather weakly bound to the surface
and can be exchanged for other cations. Besides Ca2+, Mg2+, K+, Na+, Rb+, Cs+, Li+, Sr2+, Ba2+, Ra2+,
ions of such heavy metals as Cu2+, Pb2+, Ag2+, Hg2+ and others can be adsorbed.
Positively charged colloids that are capable to exchange anions are less disseminated in the earth
crust. They include Al, Fe, Ti, Zr, and others. Among exchange anions, Cl−, SO42−, PO43− and others
are observed.
The ability to ion exchange is typical not only for colloids. Macrocrystalline silicates are also
capable to this process. In a crystalline lattice of such minerals as analcime, chabasite, natrolite and
others, a portion of Si4+ ions is replaced by Al3+, and a missing positive charge is compensated by
cations of alkaline and alkaline-earth metals which are not tied to strictly defined states in a lattice, so
they are capable to exchange.
In hydrothermal settings, feldspars, micas, sulphides, some titano- and zirconosilicates can
acquire the ability to ion exchange. Ion exchange often reveals its isomorphous character, this mode is
called LRQH[FKDQJHLVRPRUSKLVP. It develops epigenetically, as a result of the action of thermal pore
solutions on minerals. Ion-exchange isomorphism is clearly manifested in the case of carcass
alumosilicates where a portion of Si4+ ions is substituted by Al3+ ions. Large low-valence cations (Na+,
K+, Ca2+, etc) are capable for ion exchange, whereas high-valence elements with small ionic radii (Si4+,
Al3+, P5+, Ti4+, Zr4+, Nb5+, Ta5+, etc) practically do not participate in this process.
23
5HGR[DQGDFLGLFDONDOLQHFRQGLWLRQV
Data on UHGR[UHDFWLRQV and pH dependent reactions can be summarized by plotting the potential
of a redox reactions (Eh) against the pH of the solution. The reduction potential of the reaction
2[LGL]HGVWDWH+ Qe → 5HGXFHGVWDWH,
is given by the Nernst equation:
Eh = E0 − (57/Q)) ln (5HGXFHGVWDWH/2[LGL]HG state)
This formula relates Eh and pH, as often the [H+] in the ln(UHGXFHGVWDWH/R[LGL]HGVWDWH) expression.
The approximate Eh – pH values for some environmental waters are presented in Figure 1.2 (from
Fergusson, J.L., 1982, p.58).
Fig. 1.2 The approximate Eh- pH values for some environmental waters
BBBBBB soil water subsurface waters; ««« oxidised mine waters (after Fergusson, 1982).
As to acid-alkaline settings in waters, it is necessary to note the following. Many cationogenic
elements form most soluble compounds in acid media and less soluble ones – in neutral and alkaline
media. In acid and weakly acid waters intensively migrate Ca, Sr, Ba, Ra, Cu, Zn, Cd, Fe2+, Mn, Ni
and others. In alkaline waters these elements are weakly mobile. Anionogenic elements (Cr6+, Se6+,
Mo6+, V5+, As5+, etc) migrate better in alkaline waters.
For the characterization of water migration, the pH values corresponding to the start of
precipitation of metal hydroxides from diluted solutions of their salts and the solubility products are
important. Some examples of these data are given in Table 1-6 for W = 25oC.
7DEOH7KHS+YDOXHVRIWKHVWDUWRISUHFLSLWDWLRQIURPGLOXWHGVROXWLRQVDQGWKHVROXELOLW\
SURGXFWVRIK\GUR[LGHVDWW R&DIWHU3HUHO
PDQ
Hydroxides
pH
Sn(OH)4
Zr(OH)4
Th(OH)4
Fe(OH)3
Cr(OH)3
Sn(OH)2
Hg(OH)2
2
2
3.5
2.5
5.3
3.0
7.0
Solubility
products
1⋅10−57
8⋅10−52
1⋅10−50
4⋅10−38
7⋅10−31
1⋅10−27
3⋅10−26
24
Hydroxides
pH
La(OH)3
Cu(OH)2
Zn(OH)2
Fe(OH)2
Pb(OH)2
Cd(OH)2
UO2(OH)2
8
5.4
5.2
5.5
6.0
6.7
4
Solubility
products
1⋅10−20
1.6⋅10−19
4.5⋅10−17
4.8⋅10−16
7⋅10−16
2.3⋅10−14
-
Precipitation of hydroxides usually ends at the pH that are of 0.5-1.5 higher than the pH of the
start of the process. That is why it is better to indicate the pH interval of precipitation.
Such ions as Co3+, Cr3+, Bi3+, Sn2+, Th4+, Zr4+, Ti4+, Sc3+, and others exist only in very acidic
waters which are scarcely abundant in the earth crust, so these cations easily precipitate from natural
waters, their migration ability is low. On the contrary, Ni, Co, Zn, Mn, Ag, Cd, Pd, even at the pH = 8,
can occur in significant amounts in waters. The precipitation of these metals is connected with the
formation of insoluble sulphides, phosphates, arsenates, etc. The influence of the pH can be indirect
only.
Such metals as K, Na, Rb, Cs, Ca, Sr do not form hydroxides in the earth crust, so the pH of
waters have for them only indirect significance – as a factor influencing sorption, solubility of salts,
etc.
The formation of complex anions changes strongly the conditions of precipitation of many
metals. Thus, the pH of precipitation of uranyl hydroxide UO2(OH)2 is between 4 and 6 (depending on
the concentration of U in a solution). These data would exclude the possibility of migration of U in
waters with the pH > 6. However, uranium migrates easily in these waters, because it forms soluble
carbonate complexes.
,QWHQVLW\RIDTXHRXVPLJUDWLRQDQGFRQFHQWUDWLRQRIHOHPHQWV
Absolute concentrations of chemical elements in waters can not characterize their ability to be
dissolved because the elemental abundances in the lithosphere are different. In order to quantify this
ability, Perel’man introduced a FRHIILFLHQWRIDTXHRXVPLJUDWLRQ .[ determined as follows:
.[ = P[⋅ 100/D⋅Q[,
where P[ – the concentration of an element in water (g/l); D – total mineralization of this water; Q[ –
the abundance of the element in rocks contacting with this water.
Shvartsev, using thousands of analyses, has calculated abundances of elements in underground
waters in the zone of hypergenesis, i.e. in the upper part of the earth’s crust. His values can be
considered as elemental Clarkes in these waters. The value of average total mineralization (average
mineral residue) of underground waters, according to Shvartsev, D= 0.43 g/l (Shvartsev, S.L. 1978).
As to the values of Q[, Perel’man notes that it is reasonably to use Clarkes of elements in the
lithosphere. In the Table 1-7, the values of .[ for some both abundant and rare elements are presented.
7DEOH&KDUDFWHULVWLFVRIWKHPLJUDWLRQRIHOHPHQWVLQXQGHUJURXQGZDWHUVDIWHU3HUHO¶PDQ
Abundance in
Abundance in
Abundance in
Abundance in
the litosphere, Coefficient of
the litosphere, Coefficient of
underground
underground
%
aqueous
%
aqueous
Elewaters of the
Elewaters of the
(from L.
migration
(from L.
migration
ment
zone of
ment
zone of
Ovchinnikov)
.[
Ovchinnikov)
.[
hypergenesis,
hypergenesis,
0[JO
P[JO
(after
(after
Shvartsev)
Shvartsev)
4.1⋅10−7
4.7⋅10−2
Sn
Cl
1.8⋅10−2
2.3⋅10−4
607
0.41
−4
−4
−6
Pb
Br
1.83⋅10
2.4⋅10
2.21⋅10
1.3⋅10−3
177
0.39
Cu
I
1.61⋅10−5
4.7⋅10−5
5.58⋅10−6
5.3⋅10−3
80
0.24
Mn
Mg
1.91
0.13
1.86⋅10−2
2.26
4.94⋅10−5
9⋅10−2
Ni
Sb
11.9
0.11
3.⋅10−5
1.53⋅10−6
2.31⋅10−6
7.0⋅10−3
Th
Ag
9.2
0.098
2.9⋅10−7
7.3⋅10−6
4.2⋅10−7
1⋅10−3
Ba
Na
4.4
0.097
4.55⋅10−2
2.38
1.96⋅10−5
4.7⋅10−2
−6
−4
−7
Ga
Mo
3.9
0.093
1.2⋅10
2.01⋅10
6.8⋅10
1.7⋅10−3
Co
U
3.1
0.084
3.4⋅10−6
2.6⋅10−4
8.3⋅10−7
2.3⋅10−3
Cr
Ca
2.68
0.073
4.39⋅10−2
3.81
2.9⋅10−6
9.3⋅10−3
Rb
As
2.67
0.047
1.8⋅10−4
2.07⋅10−6
2.22⋅10−6
1.1⋅10−2
V
Zn
1.16
0.03
3.4⋅10−5
6.8⋅10−3
1.55⋅10−6
1.2⋅10−2
Fe
Sr
1.16
0.024
1.85⋅10−4
3.7⋅10−2
5.47⋅10−4
3.7⋅10−2
Zr
Cs
0.54
0.019
5.2⋅10−7
4.3⋅10−4
1.3⋅10−6
1.6⋅10−2
−3
−5
Ti
K
0.50
0.005
4.59⋅10
2.13
1.07⋅10
0.53
* In the original Perel’man’s table, the values of abundances in the lithosphere given by A.P.Vinogradov in 1962
have been used. The author of this report has recalculated coefficients .[, using the lithosphere Clarke values
proposed by Ovchinnikov in 1990 (Ovchinnikov L.N., 1990); the new .[, values do not differ significantly from
the old ones.
25
The coefficients of aqueous migration provide the possibility to compare the intensity of
migration of elements with different abundance. For example, Table1-7 shows that chlorine, bromine,
and iodine, in spite of sharp distinctions in their abundance in lithosphere, migrate with more or less
similar intensity. The similar intensity of migration can be revealed by several abundant elements (Mg,
Ca, Na) and, on the other hand, by such rare elements as Zn, Sr, Mo. Uranium reveals similar mobility
with Sr, Zn and Ca. Caesium, by its .[ value, is close to K. Barium and strontium have quite different
values of .[ , though their abundances in lithosphere are close. The values of .[ of U and Th are
different in about 30 times.
The values of .[ successfully reflect the role of aqueous migration in the formation of hypergenic
anomalies. Table 1-8 gives characteristics of migration ability of some elements using their
coefficients of aqueous migration. This table was put forward by Solovov who used the Perel’man
data concerning the values of coefficients of aqueous migration of elements. Original data of
Perel’man are given below (see 1.6.4).
7DEOH0LJUDWLRQDELOLW\RIVRPHHOHPHQWVDFFRUGLQJWRWKHLUFRHIILFLHQWVRIDTXHRXVPLJUDWLRQ
IURP6RORYRY
Active aqueous migrants
.[ = Q⋅10 - Q⋅100
Cl, S, Br,B, I
.[ = Q
F, Sr
Poorly mobile and
inert elements
.[ = 0.0Q⋅- 0Qand
less
Ba, Rb, Li, Sn, Sb,
As, Al, Ti, Zr, Cr,
TR, Nb, Ta, W, Bi,
Au, Pt, Th
Elements with a contrast migration ability
.>1 or <1
Mobile and poorly Mobile and poorly
mobile in oxidizing mobile in reducing
environment
and environment (without
inert in reducing H2S) and inert in
environment
oxidizing
environment
Migrate only in
Fe, Mn, Co
acidic waters:
Zn, Cu, Ni, Pb, Cd,
Ag
Migrate
in
both
acidic and alkaline
waters:
V, U, Mo, Se
According to their migration intensity, there is a group of active aqueous migrants (.[ = Q⋅10 Q⋅100) and a group of inert elements (.[ =< 0.0Q), the behavior of inert elements practically does not
depend on acidic-alkaline and redox conditions. There is also a specific group of elements with a
contrast migration ability in a water setting, their .[ values are determined by geochemical
characteristics of the setting, first of all – by the values of pH and Eh. This group is represented by the
elements with a variable valence – for example, U and Mo which are capable for an active aqueous
migration in the oxidizing environment having a hexavalent form, but they are inert in the reducing
environment having a tetravalent form.
3K\VLFDOFKHPLFDOEDUULHUV
Geological environments of the formation of geochemical barriers are very diverse, but their
effects in different parts of the earth crust may be similar rather often. There are four basic types of
geochemical barriers: mechanical, physical-chemical, biogeochemical, and technogenic. The most
studied among them are mechanical and physical-chemical. Physical-chemical barriers are divided
into several classes and presented in Table 1-9; concentrations of the zone of hypergenesis are lettered
by Arabic figures, concentrations in hydrothermal systems – by Roman figures.
26
7DEOH&ODVVHVRIJHRFKHPLFDOEDUULHUV3HUHO¶PDQ
Oxidation-reduction characteristics
of waters
Acid-alkaline characteristics of
waters
Classes of
waters
Classes of
barriers
In hypergeneous
systems
In hydrothermal
systems
Oxidative
(oxygenic, etc) $
Sulphide
(hydrosulphuric,
etc) %
Reductive
(without H2S,
gley) &
Alkaline
D
Acidic
Composition of waters approaching a geochemical barrier
Waters with oxidizing
Waters with reducing environments
environments (oxygenic, etc)
Waters without H2S (in the zone
Hydrosulphuric and sulfide
of hypergenesis – gley)
waters
Neut- StronAciNeut- Stron- StronAciNeut- Stron- StronAciStrongly
ral
dic
gly
gly
ral
dic
gly
gly
ral
dic
gly
alkaand
and
alka- acidic
and
and
alka- acidic
and
and
acidic
line
weak- weakline
weak- weakline
weak- weakly
ly
ly
ly
ly
ly
alkaacidic
acidic alkaacidic alkaline
line
line
1
2
3
4
5
6
7
8
9
10
11
12
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
$1,
$I
$2,
$II
$3,
$III
$4,
$IV
$5,
$V
$6,
$VI
$7,
$VII
$8,
$VIII
$9,
$IX
$10,
$X
$11,
$XI
$12,
$XII
%1,
%I
%2,
%II
%3,
%III
%4,
%IV
%5,
%V
%6,
%VI
%7,
%VII
%8,
%VIII
–
–
–
–
&1,
&I
&2,
&II
&3,
&III
&4,
&IV
&5,
&V
&6,
&VI
&7,
&VII
&8,
&VIII
&9,
&IX
&10,
&X
&11,
&XI
&12,
&XII
'1,
'I
'2,
'II
'3,
'III
–
'5,
'V
'6,
'VI
'7,
'VII
–
'9,
'IX
'10,
'X
'11,
'XI
–
–
(2,
(II
(3,
(III
(4,
(IV
–
(6,
(VI
(7,
(VII
(8,
(VIII
–
(10,
(X
(11,
(XI
(12,
(XII
)1
)2
)3
)4
)5
)6
)7
)8
)9
)10
)11
)12
+1,
+I
+2,
+II
+3,
+III
+4,
+IV
+5,
+V
+6,
+VI
+7,
+VII
+8,
+VIII
+9,
+IX
+10,
+X
+11,
+XI
+12,
+XII
E
Evaporitive
F
Thermodynamic
+
27
Where a reductive environment (gley or hydrosulphric) is replaced by an oxidizing one, an
oxygenic barrier (class A) is formed, and the change of an oxidizing environment into reductive leads
to the formation of a hydrosulphuric (class B) or gley (class C) barrier. A sharp increase of the pH
value (for example, when acidic waters meet limestones or other carbonate rocks), an alkaline barrier
(class D) appears. If the pH value decreases, acidic barriers (class E) arise. Thus, barriers are
classified according to an agent leading to the concentration of elements (oxidation, reduction, etc).
From this point of view, other barriers – evaporative (class F), sorptive (class G), thermodynamic
(class H) were identified.
The concentration of elements on physical-chemical barriers depends on, firstly, from the class of
a barrier, and, second, the composition of waters approaching to the barrier. Systematization of
geochemical barriers is based just on the combination of these two factors. Every barrier is designated
by an index including the barrier class and the class of acting waters. This systematization was
constructed, using the matrix principle, which allows to forecast possible revealing of new classes of
barriers, not-observed so far in the nature. In Table 1-9, such classes as C4, B6, B7 have not been
identified for the present.
Accumulation of elements on R[\JHQLF EDUULHUV occurs at the contact of gley and or
hydrosulphuric waters with waters characterized by their oxygenic environment. The barrier A6 is
especially widespread, it can be observed almost everywhere in landscapes of damp climate. In the
geological past such barriers have been typical for the epoch of the formation of palaeo-weathering
crust. Acid gley waters of soils, grounds, and silts of damp climate landscapes are enriched in Fe2+,
Mn2+, and organic acids. Near deposits, the waters are enriched in Cu, Zn, Co, and other metals. If
such waters exit on the day surface (for example, at the base of a slope), an oxygenic barrier arises,
and hydroxides of Fe and Mn are precipitated. Gley groundwaters are often discharged at the bottom
of rivers and lakes where an oxygenic barrier with Fe and Mn accumulation appears as well. Deeporiginated uprising gley waters, going along a fault, meet an oxygenic barrier at the contact with
oxygenic waters, thus Fe and Mn are also precipitated.
Near by ore deposits, the clusters of hydroxides of Fe and Mn may be enriched in ore elements.
This is induced by the fact that hydroxides of Fe and Mn are colloid minerals, they sorb easily many
metals from waters.
Neutral and alkaline gley waters are typical for the areas of spreading of rocks and soils
containing CaCO3. Iron is less mobile than Mn, that is why hydroxides of Mn are mainly concentrated
on an oxygenic barrier within this environment (barrier A7). Barriers A8 are typical for bogs with
strong alkaline (soda) waters. Barriers A9-A12 arise at the sites of discharge of deep hydrosulphuric
waters, at the contact with oxygenic underground waters or with free oxygen of the atmosphere.
Bacteria oxidize hydrosulphur with the formation of native sulphur.
6XOSKLGH EDUULHUV appear at the sites where oxygenic or gley waters meet a hydrosulphuric
environment or sulphides. The formation of hydrosulphur is induced mainly by the activity of bacteria,
however sometimes it may be a consequence of direct chemical reactions. Sulphide barriers are of
great practical importance, because or bodies of such metals as Cu, Zn, U and others are formed on
them. More often arise geochemical anomalies of elements forming insoluble sulphides: Fe, Cu, Zn,
Pb, Co, Ni, etc. Barriers B1 appear also in the zone of hypergenesis of sulphide deposits where a
subzone of secondary sulphide enrichment may be developed.
On JOH\EDUULHUV, secondary accumulations of elements are developed, at the sites of meeting of
oxygenic, hydrosulphuric and, partially, gley waters with a gley environment. They are typical for
taiga, tundra, steppes, and tropical bogs and for deep water-bearing horizons. On a gley barrier,
uranium anomalies are formed, in sands and peats (C3, C4).
On DONDOLQH EDUULHUV, secondary accumulation of ore elements arise, at the sites of raised pH
values (for example, by the change of a strong-acid environment for a weak-acid one, or by the change
of a weak-alkaline environment for a strong-alkaline one). The most contrast barriers are typical for
the sites of transition from an acid environment to alkaline one.
$FLGLF EDUULHUV are manifested by the action of alkaline waters, in these waters such anion
elements as Si, Se, Mo, and Ge migrate very well. At the sites of lowering of the pH value, especially
if there is also a sharp decrease of alkalinity, those elements are precipitated from waters, this leads to
silicification of rocks accompanied by the concentration of Mo, Se and Ge.
29
Secondary accumulations of elements on HYDSRUDWLYHEDUULHUVarise in arid landscapes, at the sites
of evaporation of superficial, ground, or underground waters. The amplification of ore anomalies of
Cu, Zn, Ni and Co may be observed (barrier F1). Sometimes, ore-free anomalies of Mo, U and Sr may
be developed (barrier F3).
On VRUSWLYHEDUULHUVat the contacts with waters of clayey horizons of soils, clays, peats and other
rocks rich in sorbents and having a negative charge, the accumulation of Cu, Zn, and Pb is possible.
The formation of such barriers is especially typical for the sites of oxidation of sulphide deposits.
Aggregates of bauxites and limonites (bog iron ores) have a positive charge, they are capable to sorb
anions. This explains increased concentrations of V, P, As in limonites. On sorptive barriers, both
amplification of ore anomalies (barriers G1 and G5) and formation of ore-free anomalies (barriers G2
and G6) may occur.
The performance of WKHUPRG\QDPLFEDUULHUV depends on both temperature and pressure changes.
In hydrothermal systems, the decrease of pressure leads to the destruction of dissolved complexes and
precipitation of metals. This process appears to be responsible for the formation of low-temperature
(100-200° C) uranium ores. The study of gaseous-liquid inclusions in these ores demonstrated high
CO2 enrichment of solutions. The CO2 concentrations decreased along the direction of solution
movement from the system bottom upwards. In these waters uranium was presented in the form of
dissolved uranyl-carbonate complexes. Rapid lowering of pressure induced by the approaching to the
day surface, fracture opening, etc, led to the carbonate disequilibrium, so the CO2 concentration in a
solution dropped, uranyl-carbonate complexes were destroyed, and uraniferous pitchblend and calcite
were precipitated on the thermodynamic barrier.
Sometimes several barriers may be combined, in both time and space. As a consequence, complex
(combined) barriers occur. For example, the precipitation of hydroxides of Fe and Mn on oxygenic
barrier yields their active sorption of other elements, so a complex oxygenic-sorptive (A-G) barrier
appears. Another example concerns a thermodynamic-reductive (H-B) combined barrier. In the abovementioned example of the formation of low-temperature uranium ores, an important role in the process
considered is played by reductive phenomena, so this barrier has a combined character,
thermodynamic-reductive (H-B).
As a specific kind of geochemical barriers, two-way (double-sided) barriers are marked out, they
are formed when waters of different geochemical composition move towards a barrier from opposite
sides. On these barriers, the precipitation of a heterogeneous association of chemical elements takes
place; an example of these barriers is a double-sided acidic and alkaline (E3-D2) barrier. There are
also lateral and radial (vertical) barriers, the former is formed as a result of water movement in
subhorizontal direction, the latter is created by vertical (upward or downward migration of solution
within of a soil profile or rock mass.
Table 1-9 can be used for systematization of different kinds of processes of the concentration of
elements in hypergenous and hydrothermal systems. Concentrations of the zone of hypergenesis are
designated by Arabic numerals, concentrations in hydrothermal systems – by Roman numerals.
0DJPDWLFPLJUDWLRQ
*HQHUDOIHDWXUHVRIPDJPDWLFPLJUDWLRQ
Two basic mechanisms of mass transport are typical for the magma: diffusion and convection, the
latter appears to be more universal. The first thermodynamic parameter governing magmatic migration
is temperature. Many magmatic phenomena and, in particular, the processes of crystallization of
igneous rocks, are connected with the fall of temperature. Another important thermodynamic
parameter is pressure. Its values cover several orders of magnitude, from 105 Pa at the earth surface to
109 Pa in abyssal environments.
Dimensions of ions play significant role in magmatic migration, they determine the structure of
minerals crystallized. Major cations in magmatic melts are Na+, K+, Ca2+, Mg2+, Fe2+; major anions are
represented by complex silicate and alumosilicate anions such as SiO44−, AlO45−, AlSi2O6−, etc.
Indicators of oxidation-reduction and acid-alkaline conditions of the magma are mainly the
occurrence forms of chemical elements in rocks (especially, the ratio Fe3+/Fe2+) and the composition of
gaseous-liquid inclusions in minerals (H2, CO, CH4, CO/CO2, H2/H2O, etc). Fluids coming to the
30
magma from the upper mantle are of a reducing character, such reducing agents as CH4, CO, and H2
are typical for them. Reducing agents in the magma are also Fe2+, H2S, and other compounds and ions.
In contrast to the zone of hypergenesis, H2O and CO2 can act as oxidants in magmatic melts. Reactions
leading to the emanation of free oxygen may proceed in the magma, however this gas can not exist
there for a long time, because it oxidizes ferrous iron. This is confirmed by the study of gases
conserved in magmatic minerals, where free oxygen is absent. Fugacity of oxygen, calculated with the
use of thermodynamic methods for different equiponderous reactions, can serve as an indicator of
oxidizing-reducing conditions in the magma. In the magma, oxygen fugacity depends on such ratios as
Fe2+/Fe3+, H2/H2O, and other so-called buffered equilibria.
In general, by their oxidation-reduction conditions, magmas take a middle position among
different systems of the Earth. Neither reducing situations that are distinctive for the earth core,
hydrothermal systems, or bogs at the surface, nor oxidizing environments observed in rivers, seas,
oceans, lakes, and many soils are not typical for magmas. In magmas, there are no such acid or
alkaline media as at the earth surface, where the pH value varies from 0 to 12. The predominance of
strong cations (Na+, K+, Ca2+, Mg2+, Fe2+) over strong anions (Cl−, F−, O22−, CO32−, OH−, and others)
determines the prevailing of a weakly alkaline environment in magmas.
6HULHVRI³PDQWOH´HOHPHQWVRIEDVLFURFNVHOHPHQWVDQGRIJUDQLWRLGHOHPHQWV
Ultrabasic rocks (dunites, pyroxenites, etc) are supposed to have subcrustal origin, i.e. their
genesis appears to be connected with upper mantle. Ultrabasic melts are characterized by low potential
of oxygen, they contain hydrocarbonic fluids. In these rocks, free hydrogen, suboxide forms of
titanium (Ti3+), and carbon are observed, the predominance of ferrous iron is established. All these
features indicate a reductive environment of ultrabasic magma.
Comparison of ultrabasic rocks with the composition of the earth crust allows to identify, using
the Clarke concentration values, the following series of “mantle” elements:
Ni>Cr>Mg>Co>Fe>Mn>Au>(O, Si, Ge, Se, Ag, Te)>(C, Sc, V)>Cd>Cu>(N, Cl, As)>
>(Na, S, Ca, Br)>(P, Zr, Mo, Sn, Sb)>F>Hg>Bi>(Ti, Ga)>(B, W)>(Be, Al, Nb, In)>Sr>Cs>I>Li>
>(K, Rb)>Tl>Ta>Pb>(Ba, U)>Th.
Thus, the most “mantle” elements are Ni, Cr, Mg, Co, Fe, and Mn. Elements of the group of platinum
may be regarded as mantle trace elements, they are not included in the series due to uncertainties of
their Clark values. Such elements as Ta, Pb, Ba, U, and Th may be called “antimantle” (Perel’man,
1979).
The origin of basic rocks (basalts, gabbro, etc) appears to be induced by the processes of melting
of the mantle. Comparison of the Clark values of basic rocks and the earth crust gives a series of their
characteristic values, which is as follows:
Ni>(Sc, Cr, Co)>Mg>(Ca, V, Cu)>(Ti, Mn, Sb)>Fe>(P, Zn, Cd)>(Br, Mo, Pd, Ag)>Sr>I>As>
>(Al, Ge, Hg)>(Se, Te, Hf, Re)>(N, O, Ga, La, Au)>In>Si>(Na, W, Bi)>Y>S>Sn>Zr>F>
>(C, Pb)>Li>Ba>B>K>Rb>Cl>Cs>Th>(Tl, U)>Ta>Be.
Ni, Cr, Co, Mg, and Mn are among the most typical elements, this sequence is similar to one in the
case of ultrabasic rocks. Specific for basic rocks are also Sc, Ca, V, Cu, Ti, Sb, Fe, P, Zn, Cd. Such
elements as K, Rb, Cl, Cs, Th, Tl, U, Ta, and Be are not characteristic for basic magmas.
The origin of granitic magma is not identified. Granitoids are considered as as polygenic rocks,
three major groups of them can be revealed: typical intrusive granitoids (orthogranites), granitoids of
gabbroic formation, and autochthonous granitoids (paragranites). Comparison of the Clark values
yields the following series of elements according to their accumulation tendency in all granitoids:
La>Ti>Be>Cl>U>Th>(K, Cs)>Rb>Ba>C>(Pb, Li, B)>(Sn, F)>Zr>Y>W>(Na, Bi)>Si>
>(Ga, N, Au)>In>O>(Ge, Se, Nb, Mo, Te, I, Hf)>(Hg, Al)>
>(As, Sr)>S>Br>P>Zn>Ag>Mn>Fe>Ca>Sb>Ti>V>Cu>(Sc, Mg, Cr)>Co>Ni.
31
0LJUDWLRQLQK\GURWKHUPDOV\VWHPV
0DJPDWLFK\GURWKHUPDOHYROXWLRQRIJUDQLWRLGLQWUXVLRQV
According to Emmons, as granite batholites cooled down, ore elements were precipitated from
postmagmatic solutions in a certain succession affected by the dependence between a type of
paragenetic association of elements in ores and temperature of its formation. Hydrothermal solutions
connected with intrusions appear at depths less than 12 km, this corresponds to the pressure value of
3⋅108 Pa. As solutions moved to upper horizons, their pressure and temperature dropped. In essence,
hydrothermal process develops within a temperature interval 400-500C. Hence, hydrothermal deposits
(or ore bodies) can be divided into hypothermal (high-temperature), mesothermal (mid-temperature),
and epithermal (low-temperature). Many years ago, Emmons has proposed the following empirical
series going from high temperatures to low ones:
Sn-W-As-Bi-Au-Cu-Zn-Pb-Ag-Au-Sb-Hg.
A.E.Fersman has grounded a “peribatholite concept” of Emmons from the positions of
geoenergetic theory. By his approach, ore-bearing solutions in the beginning were acid, but later they
became alkaline. The interaction of a solution with host rocks was considered as a main reason of the
pH value growth. At the same time, the Eh values became decreased because practically all oxygen
had been spent at the first stages of the process. The succession of crystallization of elements,
especially of chalcophile ones, is characterized by the valence reducing and the increase of ionic radii.
That is why the sequence of crystallization should be regarded as a result of the lowering of lattice
energy of minerals formed.
Modern science doesn’t support all genetic notions of Emmons and Fersman. According to
current views, hydrothermal solutions connected with granitoids have been weakly alkaline at the time
of their origin. Near the surface, sulphide-bearing solutions , when being oxidized, can acquire an acid
reaction of the environment induced by the appearance of a strong anion SO42−. However, most of
reactions of hydrothermal process of mineralization proceed in the weak alkaline or neutral
environment. Nevertheless, the element succession established by Emmons remains valid in its basic
features, this reflects general and deep geochemical regularities. Effectiveness of his series was proved
by the study of primary haloes of numerous hydrothermal deposits (see 1.5.3).
*HRFKHPLFDOEDUULHUVRIK\GURWKHUPDOV\VWHPV
For hydrothermal systems, the following geochemical barriers are most typical: thermodynamic,
hydrosulphuric (sulphide), acid and alkaline. Hydrothermal analogues of gley barriers (without H2S)
are also possible.
Hydrothermal processes develop in a wide interval of temperature and pressure, so
thermodynamic barriers should play a significant role in the evolution of hydrothermal systems. In
several concepts of hydrothermal ore formation, a leading significance is given to the fall of
temperature. However, some authors dispute this notion, arguing that many minerals are formed under
conditions which are close to isothermic. As to pressure, its role is indisputable: the pressure lowering
leads to destruction of soluble complexes and precipitation of metals. According to Naumov and
Tugarinov, low-temperature (100-200oC) uranium ores are formed just in that way. The study of
gaseous-liquid inclusions in these ores show that solutions contained a lot of CO2, its amount
decreased in the direction of solution movement, from below to upwards. In such waters, uranium was
presented as soluble uranyl-carbonate complexes. Due to the rapid drop of pressure induced by
approaching to the surface, carbonate equilibrium became violated, the content of CO2 diminished,
uranium complexes were destroyed, uranium was precipitated on a thermodynamic barrier. It is
possible that reducing phenomena also proceeded, so the barrier was combine – thermodynamicreducing (+-%). Gelogical data show that such deposits were formed at the depth from 0.5 to 3 km,
under the maximum pressure values up to 1.2⋅108 - 7⋅107 Pa. Rapid fall of pressure (and, possibly, the
action of H2S) might evoke the precipitation of such uranium satellite as Pb, Mo, and others. These
concentrations belong to the classes of +VII, %VII, +XI (see Table 1-9). Sometimes, precipitation of
32
U takes place not only as a result of the pressure lowering (+-barrier) but under the influence of the
pH value decrease ((-barrier). In this case, thermodynamic and acid barriers are coupled, this
concentration belongs to the class of +VII-(VII.
The role of a hydrosulphuric barrier is demonstrated by contemporaneous processes in the Red
Sea basins where hot metalliferrous solutions get unloaded on a hydrosulphuric barrier with the
formation of sulphide sediments. Hydrosulphuric barriers exist also in the regions of contemporaneous
volcanism (for example, at fumarole fields of the Kuril Islands iron sulphides are formed by the
mixing of acid waters enriched in Fe2+ and alkaline springs containing H2S, this concentration refers to
%V-%VI classes). It is likely that hydrosulphuric barriers were important for the formation of many
sulphide ores in the geological past. Metals were transported by carbonic acid waters (especially in
low-temperature deposits) and local concentrations of hydrogen sulphides (partially, of biogenic
origin) served as precipitation factors.
Organic substances presenting in host rocks and waters appear to be important agents of reduction
in hydrothermal systems. At some deposits, hydrothermal ore bodies are controlled by the signs of
grafitization of rocks, development of bitumens or other carbonaceous organic matter.
Many facts indicate the existence, in hydrothermal systems, of reducing barriers without H2S,
they are analogous of gley barriers (class &) in the zone of hypergenesis. In these cases, ore do not
contain sulphides, or their amount is small. Free hydrogen, hydrocarbons, and other organic
compounds might be the agents of reduction.
As to acid (() and alkaline (') barriers in hydrothermal systems, D.S.Korzhinsky has outlined
three major types of ore deposition induced by the changes of acid-alkaline conditions, they are as
follows.
(1) Ore deposition under the lowering of the pH values of alkaline solutions and their
neutralization, i.e. on an acid (() barrier. Magnetite and some sulphide and cabonate ores were formed
by this manner. With sodium metasomatosis is connected the formation of uranium-bearing albitites
with increased amounts of P, Zr, TR, and Th. They are observed at the faults of Pre-Cambrian
basement. Precipitation of ore elements appears to be caused by the decrease of the pH value changing
solutions from strong-alkaline into weak-alkaline. It means that this precipitation proceeded on an acid
barrier. The absence or weak appearance of sulphides shows that this ore formation belongs to the
classes (VIII-&VIII.
(2) Ore deposition under the increasing of the pH values of acid solutions and their neutralization,
i.e. on an alkaline barrier (class '). These phenomena are connected, for example, with injection of
acid solutions into rocks having a more basic composition (skarns with polymetal and rare-metal
mineralization, etc).
(3) Ore deposition under the neutralization of acid solutions and their transition into the stage of
precipitation as a result of the effect of filtration (many veined hydrothermal deposits of Cu, Mo, and
other metals).
=RQLQJRIK\GURWKHUPDORUHVDQGJHQHULFVHULHVRIHOHPHQWV
According to Ovchinnikov and Grigoryan (Ovchinnikov, L.N., 1990), sulphide deposits that are
very different in their composition, origin, and geological environment, are accompanied by the same
type of haloes of major indicator elements. Zoning, following the direction of the movement of
hydrothermal solutions, was fixed. This zoning, in its major features, coincides with ore body zoning
established by Emmons. A generalized series of vertical zoning, looking from below upwards, was set
as follows:
Be-Ni-Co-Sn-Mo-W-Bi-Cu-Zn-Pb-Ag-Ba-As-Sb.
This series turned out stable, any deviations from it were small. This indicates a certain similarity in
physico-chemical conditions of endogenous ore-forming and universal character the mechanism of
element depostion.
In 1984, Solovov and Grigoryan, using additional data on haloes around very deep-seated (one
km and more) ore bodies and, taking into account the behaviour of some new indicator elements
(including such easily volatile elements as Hg, I, etc), expanded and specified the above-cited series.
33
Proposed by them an universal succession of element deposition reflecting primary zoning of
hydrothermal deposits and corresponding endogenous haloes, is as follows:
W1-Be-As1-Sn1-V-Mo-Co-Ni-Bi-W2-Cu1-Au1-Sn2-Zn-Pb-Ag-Cd-Cu2-Au2-Hg-As2-Sb-Ba-I.
Instead of 14 elements, nineteen elements are supposed to participate in this series, some of them
reveal two mineral forms (element indices refer to different mineral forms of deposition) (Solovov and
Grigoryan S.V. 1984).
0LJUDWLRQLQK\SHUJHQLFV\VWHPV
+\SHUJHQHPLJUDWLRQRIHOHPHQWVDVDEDVLVIRUWKHLUVSHFLILFJHRFKHPLFDOFODVVLILFDWLRQ
Perel’man has proposed to use main features of hypergene migration of elements as a basis for
their specific geochemical classification (Table 1-10). The first step of the classification is the division
of elements into aerial and aqueous migrants. Aerial elements migrate mainly in a gaseous state, as
volatile compounds. But they migrate also in water solutions (oxygen and hydrogen in water and
dissolved salts, carbon in Ca(HCO3)3, nitrogen in nitrates and salts of ammonia). Aqueous elements, as
a rule, do not migrate or weakly migrate in a gaseous state. They include elements migrating in
solutions mainly as ions, not-dissolved molecules, and colloidal particles.
7DEOH*HRFKHPLFDOFODVVLILFDWLRQRIHOHPHQWVEDVHGRQWKHLUDELOLW\WRK\SHUJHQHRXVPLJUDWLRQ
3HUHO¶PDQ
AERIAL MIGRANTS
Active (form chemical compounds)
Passive (do not form chemical compounds)
O, H, C, N, I
Ar, He, Ne, Kr, Xe, Rn
AQUEOUS MIGRANTS
Cationic elements
Anionic elements
9HU\PRELOH (.[= 10Q−100Q)
With constant valence: &O%U
With variable valence: 6
0RELOHZLWKFRQVWDQWYDOHQFH (.[= Q−10Q)
&D1D0J6U5D
)%
:HDNO\PRELOH (.[= 0.Q−Q)
With constant valence:
.%D5E/L%H&V
63
With variable valence:
7O
*H6Q6E$V
0RELOHDQGZHDNO\PRELOHLQR[LGL]LQJDQGJOH\HQYLURQPHQWV (.[= 0.Q−Q) DQGLQHUWLQD
UHGXFLQJ K\GURVXOSKXULFHQYLURQPHQW (.[< 0.Q), DUHSUHFLSLWDWHGRQDK\GURVXOSKXULFEDUULHU
Mobile in acid waters of oxidizing and gley
Environments and are precipitated on an alkaline
Barrier:=Q&XNi, Pb, Cd
Mobile in acid and alkaline waters of an
Oxidizing environment: Hg, Ag, Bi
0RELOHDQGZHDNO\PRELOHLQDQR[LGL]LQJHQYLURQPHQW (.[= 0.Q−Q) DQGLQHUWLQUHGXFLQJJOH\
DQG K\GURVXOSKXULFHQYLURQPHQWVDUHSUHFLSLWDWHGRQK\GURVXOSKXULFDQGJOH\EDUULHUV
90R6HU, Re
0RELOHDQGZHDNO\PRELOHLQDUHGXFLQJJOH\HQYLURQPHQWV (.[= 0.Q−Q) DQGLQHUWLQR[LGL]LQJ
DQGK\GURVXOSKXULFHQYLURQPHQWVDUHSUHFLSLWDWHGRQR[\JHQRXVDQGK\GURVXOSKXULFEDUULHUV
)H0Q&R
:HDNO\PRELOHLQPRVWHQYLURQPHQWV (.[= 0.Q−0.0Qand less)
Weak migration with organic complexes,
Weak migration with organic complexes,
Partly mobile in a strong acidic environment:
partly mobile in an alkaline environment:
Al, Ti, Cr, Y, TR, Ga, Th, Se, In
Zr, Nb, Ta, W, Hf, Te
'RQRWIRUPRUDOPRVWGRQRWIRUPFKHPLFDOFRPSRXQGVPDLQO\FKDUDFWHUL]HGE\DQDWLYHVWDWH
Os, Pd, Ru, Pt, $XRh, Ir
,QEROGIRQWDUHSUHVHQWHGFKHPLFDOHOHPHQWVZKRVHELRJHQLFDFFXPXODWLRQSOD\VDVLJQLILFDQWUROHLQ
WKHLUEHKDYLRUDQGIDWH
34
Each group detached in the classification presents an association of elements precipitated on
geochemical barriers. Within an every group, elements are displayed following their Clarke values,
because under the same conditions, the higher is the Clarke value of an element, the more important is
the role of the element in the earth crust.
The classification reflects only the most characteristic features of migration, in some systems
essential deviations are possible. Sometimes, the so-called “double nature” of certain elements may be
manifested: for example, Co is included in the same group where Fe and Mn are displayed, however
some peculiarities of its behaviour allow to unite Co with Ni, Cu and Zn. Chromium is included in a
group of weakly mobile elements, but in the desert environment its behaviour becomes similar to the
migration of V, U, Mo and Se.
It is worth noting that Perel’man classification takes into account the most widely-spread
migration in the zone of hypergenesis. In specific, comparatively rare situations (strong-acidic, strongalkaline environment, etc), more intense migration may be observed. On the other hand, it is necesary
to underline that at the surface of continents, mechanical run-off exceeds significantly salt discharge,
this essentially lowers the dependence of the mobility of chemical elements on their ability to water
migration.
Sometimes, Perel’man’s classification of aqueous migrants is called “15 Perel’man diagrams”
showing the relative abundance of particylar elements and their migration in specific geological
settings (Fortescue, J. 1996).
*HRFKHPLFDOFODVVLILFDWLRQRIQDWXUDOZDWHUV
There are several hydrogeochemical classifications of waters. Ovchinnikov A.M. has divided all
natural waters into three classes: (1) waters with gases of oxidizing environments (N2, O2, CO2, and
others); (2) waters gases of reductive environments (CH4, H2S, CO2, N2 and others); (3) waters with
gases of methamorphic environments (CO2 and others). In this classification, further division is based
on the relation between cations (Na, K, Ca, Mg) and anions ((SO42−, HCO3−, Cl−).
Alekin O.A. has proposed to distinguish the following classes of waters: hydrocarbonate and
carbonate (HCO3− + CO32−), sulphate (SO42−), and chloride (Cl−). Each class is subdivided into three
groups, according to its cation predominated – a group of calcium, a group of magnesium, a group of
sodium.
&KHPLFDOFRPSRVLWLRQRIXQGHUJURXQGZDWHUVLQGLIIHUHQWFOLPDWHDUHDVRIWKH]RQHRI
K\SHUJHQHVLV
Shvartsev has assessed chemical characteristics of underground waters in the zone of
hypergenesis, after studying very large data bases (Shvartsev, 1998). Table 1-11 presents major
characteristics of underground waters in different climate areas of the zone of hypergenesis.
Underground waters of permafrost areas are distinguished by the highest degree of freshness
(their Σ is minimum). It is natural, because infiltration of atmospheric precipitates into deep horizons
in frozen rocks is hampered. Hence, the flow ways of these waters are short, so the process of water
exchange is active. Low temperatures of permafrost areas do not favor the interaction of water with
rocks. On the other hand, underground waters of these areas have moderate acidity, but heightened
concentrations of organic matter, where fulvic acids predominate.
Rather fresh waters are formed within tropical and subtropical areas. These waters have the most
acidic composition, the highest average annual temperatures, and the prevalence of underground flux
of superficial one. A very important feature of the composition of underground waters of tropical
regions is their high concentration of silica. This is a consequence of both strong acidity and raised
temperatures of these waters. High average annual temperatures cause a high degree of mineralization
of organic matter, this is reflected by very high concentrations of carbon dioxide and its partial
pressure accompanied by lowered amounts of Corg.
35
7DEOH0DMRUFKDUDFWHULVWLFVRIXQGHUJURXQGZDWHUVLQGLIIHUHQWFOLPDWHDUHDVRIWKH]RQHRI
K\SHUJHQHVLVIURP6KYDUWVHY
Component Units
Groundwaters $YHUDJHIRU
of continental WKH]RQHRI
salinization K\SHUJHQHVLV
Leaching groundwaters
Tropical Mountain
and subtroareas
pical areas
7.25
−
pH
6.40
169
mg/l
HCO3−
109
20.3
≈
7.10
SO42−
12.7
≈
7.35
Cl−
2.26
≈
1.52
NO3−
0.25
≈
0.22
F−
0.20
≈
0.07
NO2−
13.8
≈
10.9
Na+
37.8
≈
16.6
Ca2+
14.5
≈
8.07
Mg2+
1.55
≈
2.25
K+
0.37
≈
0.09
NH4+
15.2
≈
20.9
SiO2
≈
Σ
8.11
≈
63.1
CO2, free
3.72
≈
6.62
Corg
429
µg/l
251
Fe
236
≈
147
Al
102
≈
47.5
Sr
58.1
≈
10.9
Br
27.9
≈
37.7
B
34.9
≈
71.8
P
22.7
≈
42.4
Mn
18.4
≈
37.6
Zn
14.1
≈
9.11
Ba
11.6
≈
3.35
Ti
4.25
≈
12.0
I
4.06
≈
4.63
Cu
2.22
≈
4.92
Ni
3.71
≈
2.25
Cr
2.04
≈
2.05
Pb
1.06
≈
2.22
Rb
1.34
≈
1.55
Mo
1.51
≈
<2
As
0.91
≈
1.23
V
0.57
≈
0.90
U
0.85
≈
Zr
0.57
≈
0.13
Se
0.45
≈
Sb
0.24
≈
La
0.33
≈
0.41
Co
0.20
≈
<0.5
Sn
0.32
≈
0.19
Ag
0.48
≈
Cs
0.14
≈
<0.3
Cd
0.25
≈
Th
38.3
10−9g/l
Hg
3.4
2.1
Au
≈
<0.5
0.29
Ra
10−12g/l
Areas of
moderate
climate
6.82
222
18.2
15.9
2.13
0.26
0.10
23.8
38.3
16.5
2.74
0.52
13.3
20.7
9.86
689
165
185
85.6
55.9
98.2
59.2
42.8
25.3
8.82
5.59
4.85
3.45
2.83
3.10
2.55
0.89
1.64
1.28
0.51
1.51
0.64
0.55
0.34
0.24
0.44
0.11
0.15
44.0
6.0
0.20
36
Areas of Average
permafrost
6.53
82.8
4.05
4.67
0.31
0.19
0.03
6.64
16.8
5.56
0.83
1.09
8.63
12.4
12.3
328
216
20.8
8.46
20.2
22.6
12.7
22.4
9.09
4.09
2.19
2.44
1.84
2.34
1.52
1.42
0.78
0.86
0.64
0.25
1.13
0.91
1.11
0.29
0.24
0.29
0.07
2.2
-
6.75
146
12.4
10.1
1.56
0.23
0.10
13.8
27.4
11.2
1.84
0.52
14.5
26.1
8.12
424
190
88.7
40.8
35.4
56.9
34.3
30.3
14.4
6.96
6.00
4.00
3.11
2.78
2.18
1.81
1.16
1.34
1.01
0.56
1.16
0.45
0.64
0.67
0.33
0.22
0.35
0.18
0.10
0.20
41.1
3.4
0.25
7.50
349
304
258
5.78
1.47
0.53
260
86.4
46.2
18.4
0.85
31.3
1360
28.8
8.95
710
370
560
263
248
62.6
135
85.6
33.6
59.1
9.95
11.9
5.47
4.03
6.12
2.05
4.12
1.93
2.65
4.32
1.37
1.78
0.86
0.62
0.54
0.44
0.60
0.42
0.80
13.0
1.28
The next in a rank of increasing mineralization of underground waters (Σ values) are mountain
areas, where also an active water exchange takes place and fresh waters are formed. A distinctive
attribute of the waters of these areas is their relatively high alkalinity induced by an insufficient
neutralizing influence of organic substances. In contrast to all other regions, underground waters of
mountain areas contain minimum amounts of dissolved Corg and mineralized organic matter (CO2 free).
The growth of total mineralization of waters under conditions considered is due to more active
accumulation hydrocarbonates and calcium sulphates in solutions.
The most mineralized among leaching waters are underground waters of the regions of moderate
climate, displayed on platforms, shields and sometimes on very old folding structures. Relatively
limited water exchange leads to the formation of waters close neutral ones with the total
mineralization value Σ = 354 mg/l. The increase of the total content of salts, in comparison with other
regions, is caused in the areas of moderate climate mainly by hydrocarbonates of all cations, i.e. it is a
sum of the products of mineralization of organic matter (CO2) and the products of decomposition of
rocks. At the same time, there is no essential accumulation of silica in these waters.
Concerning trace element composition, it is worth noting that underground waters of the regions
of moderate climate contain maximum quantities of radioactive elements (Th, U, Ra) and several toxic
elements (As, Sn, Hg).
In Table 1-12 major characteristics of the chemical composition of natural waters (underground
waters of the zone of hypergenesis, river and sea waters) are presented. The table shows that
underground waters are almost four times more mineralized than river waters. Underground waters
have both higher concentrations of macrocomponents and of the majority of microcomponents as well.
Many chemical elements are concentrated in underground waters more actively not only relatively
river waters, but also relatively sea waters, though the total quantity of salts in the latter is 80 times
higher than in the former.
37
7DEOH0DMRUFKDUDFWHULVWLFVRIWKHFKHPLFDOFRPSRVLWLRQRIQDWXUDOZDWHUV
Components
Units
pH
HCO3−
SO42−
Cl−
NO3−
F−
NO2−
Na+
Ca2+
Mg2+
K+
NH4+
SiO2
−
mg/l
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
µg/l
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
≈
10−9g/l
≈
10−12g/l
Σ
CO2, free
Corg
Norg
Fe
Al
Sr
Br
B
P
Mn
Zn
Ba
Ti
I
Cu
Ni
Cr
Pb
Rb
Mo
As
V
U
Zr
Se
Sb
La
Co
Sn
Cs
Ag
Th
Cd
Hg
Au
Ra
Underground
waters of the
zone of
hypergenesis
(Shvartsev,
1998)
6.90
187
76.7
59.7
2.40
0.48
0.19
67.6
39.2
18.2
5.15
0.59
17.9
26.6
8.29
0.98
481
226
183
85.2
77.9
58.0
54.5
41.4
18.3
17.4
8.02
5.58
3.58
3.03
2.97
1.86
1.75
1.46
1.34
1.31
1.20
0.72
0.68
0.67
0.39
0.39
0.26
0.26
0.24
0.24
41.1
5.32
0.46
Leaching
waters
6.75
146
12.4
10.1
1.56
0.23
0.10
13.8
27.4
11.2
1.84
0.52
14.5
26.1
8.12
424
190
88.7
40.8
35.4
56.9
34.3
30.3
14.4
6.96
6.00
4.00
3.11
2.78
2.18
1.81
1.16
1.34
1.01
0.56
1.16
0.45
0.64
0.67
0.33
0.35
0.18
0.22
0.10
0.20
41.1
3.40
0.25
Coefficients of
River waters River waters
(Living-ston, (Martin et al., Sea water concentration in
sea water
(Turekian,
1979;
1963;
relatively
1969)
Meybeck,
Turekian,
underground
1979, 1982)
1969)
waters
−
8.2
52.0
2.6
58.4
488
8.25
35.3
11.2
2712
5.75
325
7.8
19 400
0.44
−
1.0
0.10
2.7
0.10
1.3
0.03
5.15
160
6.3
10 800
13.4
10.5
15
411
3.35
70.9
4.1
1290
1.3
76.1
2.3
392
0.02
−
10.4
0.35
13.1
6.2
−
0.06
6.9
0.5
0.51
0.7
0.5
40
0.007
670
3.4
50
0.004
400
1.0
60
44.3
50
8 100
790
20
67 300
57.1
10
4 450
10
1.52
20
88
8.2
0.007
7.0
0.4
0.12
20
5.0
1.15
10
21
10.0
0.06
3.0
1.0
7.98
7.0
64
0.16
7.0
0.9
1.84
0.3
6.6
0.07
1.0
0.2
0.01
3.0
0.
64.1
1.0
120
5.71
1.0
10
1.78
2.0
2.6
1.42
0.9
1.9
2.52
0.04
3.3
0.02
0.026
0.12
0.2
0.09
0.48
1.0
0.33
0.005
0.2
0.0034
1.00
0.2
0.39
2.08
0.5
0.81
1.15
0.02
0.3
1.08
0.3
0.28
0.002
0.1
0.0004
0.46
0.11
3.65
70
150
2.07
2.0
11.0
0.22
0.35
0.1
38
&RHIILFLHQWVRIDTXHRXVPLJUDWLRQDQGSUHFLSLWDWLRQ
As it was said above (see 1.3.5.4), absolute concentrations of chemical elements in waters can not
characterize their ability to be dissolved because the elemental abundances in the lithosphere are
different. That is why Perel’man introduced a coefficient of aqueous migration .[ determined as
follows:
.[ = P[⋅ 100/D⋅Q[,
where P[ – the concentration of an element in water (g/l); D – total mineralization of this water; Q[ –
the abundance of the element in rocks contacting with this water.
Table 1-13 presents associations of elements according to their migration intensity in oxidizing
and reductive (hydrosulphuric) environments of the zone of hypergenesis (after Perel’man, 1979).
Shvartsev developed Perel’man approach , by introducing a FRHIILFLHQW RI JHRFKHPLFDO PRELOLW\
.R, its expression is:
.R = P[⋅ 100/D⋅QR,
where P[ and D are the same quantities as in the formula for .[(see above), and QR – an abundance (%)
of an element considered in rocks formed in the process of weathering, soils, hydrous ferric oxides,
carbonates, etc.
Coefficients .R, as well as coefficients .[, are relative quantities, they characterize relative rates
of the withdrawal of elements (precipitation) from a solution: the more is an element amount in a
precipitate, the less is its .R value, i.e. the more is the precipitation rate, and, correspondingly, the less
is the migration ability. Thus, in contrast to .[, which characterizes relative efflux of elements from
rocks, .R determines a relative degree of bonding of elements in secondary rocks.
39
7DEOH$VVRFLDWLRQVRIHOHPHQWVDFFRUGLQJWRWKHLUPLJUDWLRQLQWHQVLW\LQR[LGL]LQJDQGUHGXFWLYHK\GURVXOSKXULFHQYLURQPHQWVRIWKH]RQHRIK\SHUJHQHVLV
3HUHO¶PDQ
Migration
intenity
Very
strong
Strong
Intermediate
Weak
and
very
weak
1000
Oxidizing environment
Coefficient of aquaous migration
100
10
1
0.1
0.01
0.001
1000
Cl, I,
Br,S
Strong-reductive environment
Coefficient of aquaous migration
100
10
1
0.1
0.01
0.001
Cl, Br,
I
Ca, Mg, Na, F,
Sr, Zn, U
Ca, Mg’
Na, F, Sr
Co, Si, P,
Cu, Ni, Mn,
K
Si, P, K
Al, Ti, Sc,
O, Cu, Ni,
Co, Mo, TR,
Zr, Hf, Nb, Ta,
Ru, Rh, Pd, Os,
Zn, U, Pt
Fe, Al, Ti,
O, Th, Zr’
Hf, Nb, Ta,
Ru, Rh, Pd,
Os, Pt, Sn
40
7\SHVRIHOHPHQWFRQFHQWUDWLRQVRQJHRFKHPLFDOEDUULHUVLQWKH]RQHRIK\SHUJHQHVLV
Paragenic associations of elements precipitated on geochemical barriers of the zone of hypergenesis
have been established by Perel’man, they are presented in Table 1-14. These associations are classified
according to the intervals of pH values: strongly acidic (pH<3); acidic and weakly acidic (pH = 3 6.5); neutral and weakly alkaline (pH = 6.5 – 8.5), and strongly alkaline (pH>8.5). As it was said
before, the action of some barriers (B9-B12, D4, D8, D12, E1, etc) has not been identified in natural
environments. Several barriers (A4, E2, E5, E6 and others, see Table 1-14) are not typical for the zone
of hypergenesis.
41
7DEOH3DUDJHQLFDVVRFLDWLRQVRIHOHPHQWVFRQFHQWUDWHGRQJHRFKHPLFDOEDUULHUVLQWKH]RQHRIK\SHUJHQHVLV3HUHO¶PDQ
Alkalineacidic
Strongly
acidic
pH values
in the
zone of
hypergenesis
Elements
mobile in
waters of
any composition
Oxygenic
A
<3
Sulphide
B
Gley
C
Alkaline
D
Oxygenic waters
Neutral
Acidic and
and
weakly
weakly
acidic
alkaline
3 – 6.5
6.5 – 8.5
Strongly
alkaline
Composition of waters moving towards a barrier o
Gley waters
Strongly
Neutral
Strongly
Acidic and
alkaline
and
acidic
weakly
weakly
acidic
alkaline
Strongly
acidic
Hydrosulphuric waters
Neutral
Acidic and
and
weakly
weakly
acidic
alkaline
Strongly
alkaline
>8.5
Na, K, Rb, Cs, N, Cl, Br, I
A1
Fe
B1
Tl, Cu,
Hg, Pb,
Cd, Bi,
Sn, As,
Sb, Mo,
W, U
C1
Cu, U,
Mo
A2
Fe, Mn,
Co
B2
Tl, Mn,
Co, Ni,
Cu, Zn,
Pb, Cd,
Hg, Sn,
Sr, Mo, U
C2
Cu, U,
Mo
D1
Mg, Ca,
Sr, Ba, Ra,
Mn, Fe,
Co, Ni,
D2
Mg, Ca,
Sr, Ba, Ra,
Co, Ni,
Cu, Zn,
A3
Mn
A4
−
A5
Fe
B3
Tl, Cr,
Mo, U,
Se, Re,
V
B4
Cu, Ag,
Zn, Cr,
Mo, U,
V, As
B5
Tl, Pb,
Cd, Bi,
Sn
C3
Cu, Cr,
U, Mo,
Re, Se, V
D3
−
C4
Cu, Ag,
Cr, Mo, U,
Re, Se, V,
As
D4
−
A6
Fe, Mn,
Co
B6
Tl, Fe,
Co, Ni,
Pb, Cu,
Zn, Cd,
Hg, U
A8
(Mn)
A9
S, Se, (Fe)
A10
S, Se
A11
S, Se
A12
S, Se
B9
−
B10
−
B11
−
B12
−
(Mo), (U)
B8
Tl, Cu,
Zn, Cd,
Hg, Mn,
(Fe, Co,
Ni, U)
A7
(Fe), Mn,
Co
B7
Tl, Fe,
Co, Ni,
Cu, Zn,
Cd, Hg,
C5
Cu, U,
Mo
C6
Cu, U,
Mo
C7
Mo, U
C8
Mo, U
C9
−
C10
−
C11
−
C12
−
D5
Mg, Ca,
Sr, Ba, Ra,
Mn, Fe,
Co, Ni,
D6
Mg, Ca,
Sr, Ba, Ra,
Mn, Fe,
Co, Ni,
D7
Mg, Ca,
Sr, Ba,
Zn, Cd,
Mn, Co,
D8
−
D9
Mg, Ca,
Sr, Ba, Ra,
Mn, Fe,
Co, Ni,
D10
Mg, Ca,
Sr, Ba
D11
−
D12
−
42
Acidic
E
Evaporative F
Sorptive
G
Thermody
-namic H
Cu, Zn,
Pb, Cd,
Hg, Be,
Al, Ga, Y,
TR, Cr, P,
As, U
E1
−
Pb, Cd,
Hg, Be,
(U)
E2
−
E3
Si, Mo
F1
Na, K, Rb,
Tl, Cl,
Mg, Ca,
Sr, S, Mn,
Fe, Co,
Ni, Cu,
Zn, Pb,
Cd, Al,
Mo, U
G1
Al, Sc,
Ga, Si,
Ge, P, V,
As
F2
−
F3
Li, Na, K,
Rb, Tl,
N, B, F,
Cl, Br, I,
Mg, Ca,
Sr, S, Zn,
Mo, U,
V, Se
G2
Si, Ba, Zn,
Cd, Ni,
Co, Pb,
Cu, U,
Cl, Br, I,
F, S, P, V,
Mo, As
H2
Mg, Ca,
Sr, Ba,
Mn, Zn,
Pb, Co, Ni
G3
Li, Na, K,
Rb, Cs, Tl,
Zn, (Cl,
Br, I, F, B,
S, P, V,
Mo, As)
G4
Li, Na, K,
Rb, Cs, Tl,
(Cl, Br, I,
F, B, S, P,
V, Mo,
As)
H3
(Li), Mg,
Co, Sr,
Ba, Zn, Pb
H4
Zn, (Cu),
(U)
H1
−
E4
(Cu), (Zn),
Ag, Be,
Al, Ga,
Sc, Y, TR,
Si, (Ge),
Zr, (Ti),
Mo, Cr, V
F4
Li, Na, K,
Rb, Tl,
N, B, F,
Cl, Br, I,
Cu, Zn,
Mo, U,
Se, V
Cu, Zn,
Pb, Cd,
Hg, Be,
Al, Ga, Y,
TR, Cr, P,
As, (U)
E5
−
Cu, Zn,
Pb, Cd,
Hg, Be,
Al, Ga, Y,
TR, Cr, P,
As, (U)
E6
−
F5
Na, K, Rb,
Tl, Cl,
Mg, Ca,
Sr, S, Mn,
Fe, Co,
Ni, Cu,
Zn, Pb,
Cd, Al,
Mo, U
G5
Al, Sc,
Ga, Si,
Ge, P, V,
As
H5
−
Ni
Zn, Pb,
Cd, Be,
Al, Ga, Y,
TR, Cr, P,
As
E7
Si, Mo
E8
(Cu), (Zn),
Be, Al,
Ga, Sc, Y,
TR, Si, Zr,
(Ti), Mo
E9
−
E10
−
E11
Si, Ge
E12
Be, Al,
Ga, Se,
Y, TR, Si,
Ge, Zr,
(Ti)
F6
−
F7
Li, Na, K,
Rb, Tl,
N, B,
Cl, Br, I,
Mg, Ca,
Sr, S, Zn
F8
Li, Na, K,
Rb, Tl,
N, B, F
Cl, Br, I,
Zn
F9
Li, Na,
K, Rb,
F, Cl,
Br, I,
Mg, Ca,
Sr, S
F10
−
F11
Li, Na,
K, Rb,
F, Cl,
Br, I,
Mg, Ca,
Sr, S,
F12
Li, Na,
K, Rb,
N, B,
F, Cl,
Br, I
G6
Si, Ba,
Zn, Cd,
Ni, Co,
Pb, Cu, U,
Cl, Br, I,
F, S, P,
Fe, Mn
H6
Mg, Ca,
Sr, Ba,
Mn, Zn,
Pb, Co,
Ni, Fe
G7
Li, Na, K,
G8
Li, Na, K,
Rb, Cs, Tl,
(Cl, Br, I,
B, F, S, P)
G9
Al, Sc,
Ga, Si,
Ge, P, V,
As
G10
Sr, Ba,
(Cl, Br, I,
F, B, S, P)
G11
Li, Na, K,
Rb, Cs,
(Cl, Br, I,
F, B, S, P)
G12
Li, Na, K,
Rb, Cs,
(Cl, Br, I,
F, B, P)
H8
Zn, (Cu),
(U)
H9
−
H10
Mg, Ca,
Sr, Ba
H11
Mg, Ca,
Sr, Ba
H12
−
43
Rb, Cs,
Tl, Zn,
(Cl, Br, I,
F,
B, S, P)
H7
(Li), Mg,
Co, Sr,
Ba, Zn,
Pb, Mn
(OHPHQWDVVRFLDWLRQVLQGLIIHUHQWFUXVWVRIZHDWKHULQJ
Shvartsev has calculated geochemical mobility of elements (the coefficients .R, see 1.6.4) in
basic stages of rock weathering: laterization, kaolinitization, hydromicatization, montnorillonitization,
and carbonatization. These data determine the formation of element associations in different crusts of
weathering, they are presented in Table 1-15.
7DEOH*HRFKHPLFDOPRELOLW\RIVRPHHOHPHQWVDWGLIIHUHQWVWDJHVRIURFNZHDWKHULQJLQWKHR[LGDWLRQ
HQYLURQPHQW6KYDUWVHY
Laterization
Kaolinitization
0.015
5.62
0.029
0.020
0.12
0.12
18.9
30.4
56.7
40.1
0.08
-
0.006
0.45
0.69
0.014
0.007
1.27
13.6
22.3
29.2
26.2
0.12
0.011
Elements
Al
Si
V
Mn
Fe
Cu
Zn
Mg
Ca
K
Na
Ni
Cr
Weathering processes
HydroMontmicatization
morillonization
0.004
0.14
0.005
0.006
0.003
0.06
0.09
4.10
9.69
0.20
10.2
0.004
0.007
0.002
0.09
0.01
0.008
0.009
0.012
0.25
3.36
8.36
0.38
6.06
0.015
0.008
Carbonatization
0.003
0.02
0.018
0.008
0.21
3.13
2.39
0.23
14.6
-
This table shows that migration ability of the overwhelming majority continually decreases as the
processes of interaction of water with rocks develop. It is well illustrated by the behaviour of silica
whose mobility is high only for a laterite type of weathering, Shvartsev argues that this fact confirms
that an approach stating that mobility of silica should increase with the pH rise is not valid.
%DVLFIHDWXUHVRIODQGVFDSHJHRFKHPLVWU\
(OHPHQWDU\ODQGVFDSHW\SHV
B.B.Polynov, the originator of the discipline of landscape geochemistry, stressed the importance of
geochemical and biological weathering during landscape evolution in the course of pedological,
ecological and, especially, geological time. He also emphasized the importance of interactions
between the daylight surface and the water table in landscape evolution. He defined three "elementary
landscape types” which may occur together in humid landscapes, as illustrated by prism diagrams in
Figure 1.3. Where the water table is always below the daylight surface, an eluvial landscape with welldrained soil is formed. If the water table and the daylight surface are coincident a super-aqual (bog or
marsh) landscape appears, and a lake or river environment, where the water table is above the land
surface, is called an aqual landscape.
44
Figure 1.3. Landscape prism diagrams of each Polynov’s three elementary landscape types
(from Fortescue, J.A.C. 1980).
(OHPHQWJHRFKHPLFDODEXQGDQFHVDQGPLJUDWLRQUDWHVLQODQGVFDSHV
A convenient way of summarizing the abundance of elements in components of landscapes was
developed by Perel’man who provided "15 Perel’man diagrams” to show the relative abundance of
particular elements and their migration paths in specific geological settings. For example, the minor
element (Cl) has a relative high Clarke (180 ppm) and may accumulate significantly (as NaCl) in arid
landscapes to dominate their geochemistry (e.g. in saline oils and ponds). A trace element (Br) with a
similar geochemical behaviour in the landscape will also accumulate in arid landscapes, but never,
because of low Clarke (2.4 ppm), dominates the geochemistry of a landscape.
In landscape geochemistry, comparisons are often documented of temporal variations in
migration rates of elements (or other chemical entities) within particular landscape components. For
example, Perel’man viewed surface waters and ground waters as “aqueous migrants”, further
classified according to their mobility ranging from “very mobile elements” (e.g. Cl) to “poorly mobile
elements (e.g. Al in most environments). Similarly, gases flowing through the landscape (including
soil air) are recognised as “aerial migrants”, which may be active geochemically (e.g. CO2) or inactive
(e.g. Ar).
8QGHUJURXQGFKHPLFDOIOX[HV are of importance in landscape geochemistry. Special investigations
covering the territory of the former Soviet Union showed that underground chemical flux dominates
over superficial flux. Shvartsev has assessed both total chemical flux and its major constituents –
lithogenic, biogenic and atmospheric (Shvartsev, 1998). In his approach, the data on the average
chemical composition of underground waters in different landscape zones have been considered. The
chemical fluxes forming only within the zone of hypergenesis or in the zone of active water exchange
were taken into account. Any influence of surface waters and saline waters infiltrating into waterbearing horizons was excluded. Biogenic constituent was presented by the sum of the concentrations
of organic matter, carbonic acid H2CO3, and carbonate anion HCO3−. Atmospheric constituent of
chemical flux was determined mainly by the amounts of atmospheric precipitates and the intensity of
45
their evaporation. In Table1-16 the characteristics of underground chemical fluxes in major landscape
zones of the moderate climate are given.
7DEOH8QGHUJURXQGFKHPLFDOIOX[HVLQPDMRUODQGVFDSH]RQHVIURP6KYDUWVHY
Flux
constituents
Landscape zones
Lithogenic
g/s⋅km2 (%)
Biogenic
g/s⋅km2 (%)
Total
flux,
t/km2⋅y
Average
mineralization,
g/l
Average
pH
Undergro
und flux
rate,
l/s⋅km2
1.9
8.3
18.8
6.3
37.0
46.3
31.2
18.6
21.0
0.08
0.10
0.21
0.09
0.23
0.46
0.64
1.86
0.46
6.2
6.5
6.6
5.7
6.9
7.1
7.5
7.6
6.8
0.1–0.5
0.5-2.5
1.0-3.0
0.3-0.7
3.5-5.0
1.5-3.5
0.8-1.6
0.1-0.5
-
190.6
113.9
53.5
31.8
14.9
81.0
0.06
0.17
0.20
0.32
0.91
0.33
5.2
6.1
6.9
7.2
7.4
6.6
16-20
8-10
6-8
1-3
0.2-0.8
-
30.4
37.9
31.7
33.3
0.10
0.25
0.48
0.28
7.0
7.1
7.6
7.2
4-10
3-5
0.6-1.6
-
Atmogenic
g/s⋅km2 (%)
0RGHUDWHUHJLRQV
Northern bogs
Tundra
Northern taiga
Bogs of forest zones
Mixed forests
Southern taiga
Forest-steppes
Steppes
Average
0.006…
0.041
0.105
0.013
0.278
0.319
0.200
0.053
0.127
9.6
15.5
17.0
6.4
22.9
21.0
19.5
8.7
18.4
0.039
0.170
0.400
0.138
0.708
0.977
0.528
0.144
0.388
Humid savannah
Tropical forests
Subtropical forests
Dry savannah
Steppes
Average
0.434
0.498
0.468
0.197
0.061
0.332
6.9
13.3
26.7
18.8
12.5
12.5
5.311
2.852
0.892
0.459
0.151
1.933
Tundra-meadow
Mountain forest
Mountain steppe
Average
0.248
0.283
0.152
0.228
24.9
22.8
14.7
20.8
0.567
0.761
0.567
0.631
61.9
64.4
64.7
67.3
58.4
64.3
51.6
23.6
56.3
0.018
0.053
0.113
0.054
0.226
0.223
0.296
0.412
0.174
28.5
20.1
18.3
26.3
18.7
14.7
28.9
67.7
25.3
7URSLFDODQGHTXDWRULDOUHJLRQV
85.0
76.4
50.8
44.0
31.0
72.8
0.506
0.385
0.395
0.387
0.275
0.390
8.1
10.3
22.5
37.1
56.5
14.7
0RXQWDLQUHJLRQV
56.8
61.2
54.6
57.5
0.182
0.199
0.319
0.233
18.3
16.0
30.7
21.7
It can be seen that the role of ELRJHQLF FRQVWLWXHQW is very important, it prevails over other
components in the zones of tundra, northern taiga and mixed forests. In tundra this constituent
provides 62.5 % of the total flux, in the zone of mixed forests – 50.6%, whereas in the zone of steppes
– only 16.2%. It means that in landscapes with rich vegetation, soils are responsible for the formation
of chemical composition of both surface and subsurface waters. Just from soils chemical elements pass
into groundwaters. Underground waters of the zones of tundra, northern taiga and mixed forests
contain high amounts of H2CO3 and organic acids, so they are acidic. The less is the pH value of
waters, the higher is the relative portion of biogenic constituent in a total flux (see Table 1-16). Table
1-16 shows that atmospheric constituent is also significant. In the case of moderate climate, the
fraction of this component is rather high, it becomes predominate in the zone of steppes (75.4%) due
to its very strong evaporation there.
Table 1-17 allows to collate absolute values of biogenic flux (B) with the values of biological
productivity (P) of different landscape zones. One can see that only several per cent of all organic
substances produced in the landscape take part in the formation of underground chemical flux. Hence,
under the conditions of the zone of hypergenesis, biogenic flux is not limited by the shortage of
organic matter, it can depends only on the rate and trend of its decomposition.
46
7DEOH%LRJHQLFFRQVWLWXHQWVRIXQGHUJURXQGFKHPLFDOIOX[HV%DQGWRWDOELRORJLFDOSURGXFWLYLW\3
RIPDMRUODQGVFDSH]RQHVIURP6KYDUWVHY
B, t/y.km2
5.2
12.2
21.6
29.8
16.1
4.4
162
87.0
27.2
14.0
4.6
Landscape zones
Tundra
Northern taiga
Mixed forests
Southern taiga
Forest-steppes
Steppes in moderate areas
Humid savannah
Tropical forests
Subtropical forests
Dry savannah
Tropical steppes
P, t/y.km2
238
560
800
1100
700
500
1800
3420
2450
730
500
B/P, %
2.2
2.2
2.7
2.7
2.3
0.9
9.0
2.5
1.1
1.9
0.9
Summarized data on the correlation between flux and accumulation of chemical elements in the
products of weathering for major landscape zones of the Earth have been assessed by Shvarsev, they
are presented in Table 1-18.
7DEOH9ROXPHVDQGUDWHVRIGHVWUXFWLRQRIURFNVE\XQGHUJURXQGZDWHUVIURP6KYDUWVHY
Lithogenic
component of
flux,
t/year⋅km2
Ratio of flux
to
accumulation
of elements
Tundra
Northern taiga
Mixed forests
Southern taiga
Forest-steppes
Steppes
Average
1.2
3.2
8.5
9.7
6.1
1.6
5.1
1:2.8
1:3.0
1:3.5
1:3.8
1:6.0
1:9.0
1:4.7
Humid savannah
Tropical forests
Subtropical forests
Dry savannah
Steppes
Average
13.2
15.2
14.2
6.0
1.9
10.1
1:1.1
1:2.0
1:3.0
1:5.6
1:7.0
1:3.7
Tundra-meadow
Mountain forest
Mountain steppe
Average
7.8
8.6
4.6
6.9
1:2.8
1:3.5
1:6.0
1:4.1
Landscape zones
Volume of
weathered
rocks,
t/year⋅km2
Rate of
underground
chemical
weathering
cm/1000years
Rate of
underground
chemical
denudation,
cm/1000years
Total chemical
denudation
(after
Maksimovich),
cm/1000years
0.18
0.51
1.53
1.86
1.71
0.64
1.08
0.06
0.13
0.34
0.39
0.24
0.06
0.20
0.4
1.3
1.6
-
1.11
1.82
2.27
1.58
0.61
1.48
0.53
o.61
0.57
0.24
0.08
0.41
**
1.2
-
1.16
1.55
1.29
1.33
0.30
0.34
0.18
0.27
1.0
0RGHUDWHUHJLRQV
4.6
12.8
38.2
46.6
42.7
16.0
26.8
*
7URSLFDODQGHTXDWRULDOUHJLRQV
27.7
45.6
56.8
39.6
15.2
37.0
0RXQWDLQUHJLRQV
28.9
38.7
32.2
33.2
* Forests and forest-steppes
** Tropics and subtropics.
It can be seen that in the conditions of moderately humid climate, if one goes from north to south,
the ratio flux to accumulation of elements decreases gradually. This means that the portion of elements
accumulated in a solution gradually descends, relatively to the fraction which is bound in the products
of weathering. This occurs when total mineralization of underground waters increases in the same
direction (see Table 1-16). The similar dependence is revealed for tropical and mountain regions.
Therefore, the ratio considered changes with a specific zonal character, it is connected strictly with
total salinity of a solution: the higher is total mineralization of water, the larger is a portion of
chemical elements bound in secondary products. Correspondingly, there is a great difference between
47
the value of a lithogenic component of flux and the volumes of dissolved rocks, it reaches an order of
magnitude. Total volumes of rocks dissolved by underground waters correspond to the scales of
chemical weathering that change significantly depending upon landscape-climatic conditions.
From the scales of dissolution of rocks and the portion of chemical elements evacuated by this
process, it is easy to calculate the rates of chemical weathering to chemical denudation. The latter is a
portion of elements evacuated by underground waters from a weathering profile. As Table 1-18 shows,
the rate of chemical weathering is 2-10 times more than the rate of chemical denudation. This means
that a very significant portion of weathered material remains at its original site, creating necessary
prerequisitions for the formation of weathering crusts which are more preferable in temperate
(moderate) zones.
In addition, Table 1-18 gives the rate of total chemical denudation calculated by Maksimovich in
1955 (later, similar values of this parameter have been assessed by Zverev et al in 1974). His data are
very close to Shvartsev’s values of the rates of chemical weathering of rocks, but there are significant
disrepancies with Shvartsev’s calculations concerning chemical denudation of the land. The reason is ,
firstly, that Shvartsev used for assessing chemical denudation, the data on a lithogenic component
only. Second, only underground flux has been taken into account, whereas Maksimovich used both
superficial and underground fluxes.
Shvartsev argues against the approach stating that the higher is the concentration of an element in
water, the less are its amounts in weathering products. Detailed arguments are given in his book
published in 1998.
%LRJHRFKHPLFDOPLJUDWLRQ
*HRFKHPLFDOFODVVLILFDWLRQRIVRLOV
According to their geochemical properties, soils have been classified by Perel’man, he identified
20 basic classes, they are given in Table 1-19 (Perel'man, 1979).
7DEOH%DVLFJHRFKHPLFDOFODVVHVRIVRLOVDFFRUGLQJWR3HUHO¶PDQ
LQEUDFNHWV±OHDGLQJLRQVDQGJDVHV
Alkaline-acidic aqueous
environment
Strongly acidic, pH<3
Acidic and weakly acidic,
pH = 3 – 6.5
Neutral and alkaline,
weakly mineralized,
pH = 3 – 6.5
Neutral and alkaline,
Saline and subsaline,
pH = 7 – 8.5
Strongly alkaline, pH>8.5
Oxygenic waters
Strongly acidic
(CH+, Fe2+, Al3+, etc.)
Acidic
(H+)
Calcium-bearing
(Ca2+)
Redox aqueous environment
Gley waters
Hydrosulphuric waters
Strongly acid gley
Sulphatic sulphide
(H+, Fe2+)
(H+, H2S)
Acid gley
Acid sulphide
+
2+
(H , Fe )
(H+, H2S)
Carbonate-gley
Neutral carbonate sulphide
2+
2+
(Ca , Fe ),
(Ca2+, H2S)
Salt-bearing
(Na+, Cl−, SO4− −)
Salt-bearing gley
(Na+, Fe2+, Cl−, SO4− −)
Salt-bearing sulphide
(Na+, H2S)
With soda
(Na+, OH−)
Soda-gley
(Na+, Fe2+, OH−)
Soda hydrosulphide
(Na+, OH−, H2S)
'ULYLQJIRUFHVRIHOHPHQWPLJUDWLRQLQVRLOV
Kabata-Pendias indicates the following possible reactions in natural heterogenous soil systems :
(1) dissolution; (2) sorption; (3) complexation; (4) migration; (5) precipitation; (6) occlusion; (7)
diffusion; (8) binding by organic substances; (9) absorption and sorption by microbiota; (10)
volatilization (Kabata-Pentias, A., 1992).
48
+HDY\PHWDOVLQVRLOVsee also Appendix 2)
Kabata-Pentias proposes to consider three types of metals with different origins and specific
behavioural properties: lithogenic, pedogenic, and anthropogenic (Kabata-Pentias, A., 1992)
/LWKRJHQLFPHWDOVare those which are directly inherited from lithosphere (parent material). The
mobility of these elements during weathering is determined first by the stability of the host materials,
and second by their electrochemical properties. In most soils quartz is the predominant (up to 70%)
constituent of the sand and silt fractions (20-200 µ). Feldspars comprise about 20%, and the heavy
minerals −less than 5%. Thus, the behaviour of trace metals associated with quartz and feldspars is
likely to have a significant influence on their mobility behaviour in most soils.
It is still open question as to what is a major occurrence mode of trace metals in soils. It appears
that these metals are mainly bound in soil minerals by isomorphic substitution or by fixation on free
structural sites. The adsorption capacity of some soil components for trace metals is high, and
therefore a considerable amount of metals can be bound before the formation of definite metal
compounds takes place, e.g. phosphates, carbonates, sulphates, etc. All lithogenic trace metals form a
pool of relatively immobile elements. However, they are likely to be transformed into mobile species
under a change of soil conditions, and by the activity of root exudate.
3HGRJHQLFPHWDOVare of lithogenic or anthropogenic origins but their distribution in soil horizons
and soil particles are changed due to mineral transformation and other pedogenic processes. Soils
consist of an heterogeneous mixture of different organic and organic-mineral substances, clay
minerals, (hydrous) oxides of Al, Fe, and Mn, and other solid components, as well as of a variety of
soluble substances. The binding mechanisms for trace metals are therefore complex and vary with the
composition of the soil, soil acidity and redox conditions. Numerous processes reflecting various soil
processes are possible, they are listed above (see 1.7.2).
All these processes are governed by several soil properties of which pH and redox potential are
known to be the most important parameters. The sorption of most metals greatly increases with
increasing pH of the solution. Both the distribution and phytoavailability of pedogenic trace metals are
influenced by the specific adsorption of metals on various soil constituents, in particular hydrous
oxides of Fe and Mn. Metals fixed by Fe and Mn are slightly mobile, and may be unavailable to plant
roots. Amounts of clay minerals in most soils range from 10 to 30% of their mineral composition.
Their influence on trace metal behaviour is significant, specially due to the high sorption capacity for
metals.
The solubility of metals fixed by various minerals may considerably differ, but in most cases it
increases from kaolinite and biotite, to montmorillonite and freshly precipitated Fe-Al oxides. As to
the speciation of trace metals in soils, it can be said that, depending upon the variability in physicochemical characteristics of metals, their affinity to soil components governs their speciation. Easily
mobile metals (Zn and Cd) exist mainly as organically bound, exchangeable, and water soluble
species, while slightly mobile metals (Cr, Ni and Pb) are mainly bound in silicates (residual fraction;
Cu and Mo predominate in organically bound and exchangeable species. Their stability is, however,
strongly influenced by changing soil environmental conditions.
$QWKURSRJHQLFPHWDOV enter the soils by a variety of pathways: aerial deposition; pesticide and
fertilizer application; waste utilization; dredged sediment disposal; river and irrigation waters, etc. The
speciation and distribution of these metals in soils are related to their chemical forms at the time of
impact. Aerial particles transporting trace metals are most commonly in the form of oxides, silicates,
carbonates, sulphides and sulphates. In dredged sediments, metals are likely to be fixed by organic
substances, clay minerals, and Fe-Mn-Al oxides. Metals entering soils with plant residues are
organically bound or chelated, and those entering with sewage sludges differ with the sources and
treatment of the wastes.
Thus, anthropogenic metals may form different species and soils, depending on reactant surface
and external binding sites with different bonding energy. The concentration of trace metals in soil
solutions is a good index of the mobile pool of metals in soils. Any chemical stress is reflected in the
trace metal content of the soil solutions. The importance of an anthropogenic origin of trace metals in
terms of their mobility and bioavailability is particularly important for Cu, Zn, Zn, and Ni. Other
metals such as Cr, Mn and Pb seem to be influenced less by their origin but their behaviour depends
strongly on the conditions of the environment (Kabata-Pentias, A., 1992).
49
%LRDFFXPXODWLRQRIHOHPHQWVLQSODQWV
Identification of major factors governing the intake of elements by plants is a complicated problem,
because most of these factors are closely interrelated, and in many cases the action of an individual
factor depends on the whole of their combination. Nevertheless, it is possible to distinguish the
following external factors and soil properties (Tkalich, S.M., 1970).
•
6XQOLJKW KHDW DQG VRLO WHPSHUDWXUH. The concentrations of different elements in plants
(specifically those which form a plant ash) change under the influence of sunlight and heat in different
manner. The influence of soil temperature is especially strong on the supply of plants by water. Under
low temperatures, water supply sharply decreases. Correspondingly, the plant intake of elements
becomes reduced. However, some plants are capable to assimilate chemical elements directly from
soils and rocks.
•
$WPRVSKHULF SUHVVXUH. Even small changes of atmospheric pressure influence the content of
oxygen, carbon dioxide and other gases in soils and soil solutions. Accordingly, the values of Eh and
pH (see below) change, this reflects in the supply of root systems by ash elements.
•
0HFKDQLFDOFRPSRVLWLRQ Sorption ability of soils intensifies with an increase of the degree of
dispersion of soil particles: fine-grained fractions are capable of stronger sorption compared with
coarse-grained ones. This is caused by, firstly, their larger specific surface of clay and silt particles
and, secondly, the differences in particle properties. The less are sizes of soil particles, the more is
their content of humus and exchange cations, and the more is the capacity of cation exchange. In
addition, the distinctions in properties of different fractions are explained by their mineralogical
composition. The fraction of fine sand and coarse dust consists mainly of quartz and feldspars,
whereas micas and hydromicas dominate in the fractions of medium and fine dust. In slit fractions,
micas, hydromicas and minerals of the group of montmorillonite are major components. The presence
of soil colloids is of special importance. The more a soil is enriched by mineral, organic-mineral and
organic colloids, the higher is its sorption ability. The particles of soil colloids have both positive and
negative charges, so they can adsorb ions of both signs. However, the majority of mineral and organic
colloids of soils carry a negative charge, so they can adsorb different cations and pass them to plants.
•
0LQHUDO FRPSRQHQWV This component makes from 55 up to 97% of a soil mass. There are
primary minerals presented by skeletal and coarse-sand particles, and secondary minerals that prevail
in clay and colloidal soil particles. The group of primary minerals consists of quartz, feldspars, apatite,
micas (muscovite, biotite), etc.; secondary minerals include the groups of kaolinite, montmorollonite,
vermiculite, secondary hydromicas (illites), etc. Secondary minerals are distinguished by their high
sorption ability. The very specific role is played by the content of carbonates. The influence of a
carbonate content on the element availability for plants is connected with the changes of soil acidity,
the relationship between different species of organic matter and the composition of exchange cations –
in particular, the concentration of exhangeable calcium. The more is the content of carbonates, the less
is the accumulation of 90Sr by plants, but under the same conditions, the transfer of 137Cs into plants
increases. The reason is that 90Sr becomes fixed in soils, whereas 137Cs remains mobile in these soils
due to an increased number of organic compounds that are soluble in water and induce desorption of
cesium (Pavlotskaya, 1976). Indeed, the augmentation of the content of carbonates in soils changes the
relationship betwen organic acids, the concentration of fulvic acid decreases.
•
+XPLGLW\Information concerning the influence of soil water on the migration of elements in a
system “soil – plant” is rather contradictory. Some observations reveal the increase of element transfer
into plants with the rise of soil water content. Another measurements show no humidity impact.
Uncertainty of data regarding the role of humidity is connected with the fact that different elements are
extracted from soils by plants in a different manner, depending on a regime of moistening. Besides,
the influence of soil humidity on the element mobility depends on the properties of soils and biological
features of plants. Under different conditions of soil moistening, coefficients of element accumulation
by plants can remain without significant changes, however a total efflux of elements can augment due
to the growth of a plant biomass.
•
$FLGLW\ The value of pH is one of the most important factor governing the plant intake of
chemical elements from soils. As a rule, when the pH values are increased, plants absorb less cations
and more anions. But for many elements, the dependence of their behaviour in a system “soil-plant”
on soil acidity is complicated, sometimes it appears as rather contradictory. Increasing soil acidity
leads to a more intense transfer of such elements as Fe, Co, Zn, Sr, Cs into plants. When the pH values
are raised, such elements as Fe, Co, Ni and others pass from an ion form into different hydrolysated
and complex compounds, this lowers their availability for plants. Humic and other organic acids
50
reduce the pH values of soils to 3-4 At the same time, these organic acids combine with metals
forming complex compounds which are capable for a long-distant migration.
•
5HGR[ FRQGLWLRQV. Plant roots are in a media containing oxygen and other oxidants. Redox
conditions exert strong influence upon the migration of elements in the zone of hypergenesis,
including the zone of plants feeding. However, in different sections of the same landscape, redox
conditions in a media feeding plant roots, can be different. Over an oxygen surface they are
preferentially oxidative (Eh = −0.1 −0.5 V with pH = 6-8), and under this surface – reductive (Eh = 0.4
– 0.5 V). That is why different plants assimilate not only different elements, but their intake of the
same element can differ significantly.
•
2UJDQLFPDWWHU This is also a very important factor governing the migration of elements in
soils and their intake by plants. For the majority of elements (and radionuclides), the more is the
content of humus in a soil, the less is their transfer (Vodovozova, 1981). The behaviour of elements is
determined by their reactions with organic acids – humic and fulvic. The ability of these acids to sorb
ions and to form stable complex compounds with elements influences both sorption in soils and plant
intake. It was shown that the intake of Sr in ion form is stronger than the intake of this element from
organo-mineral complexes. In addition, the transfer of Sr from a fulvate is more intense compared
with a humate. Organic complexes of Cs are also available for plants; the intake of cesium fulvate is
higher than the intake of cesium humate.
•
&RQFHQWUDWLRQ RI HOHPHQWV LQ D IHHGLQJ PHGLD DQG WKHLU GLVWULEXWLRQ LQ D VRLO SURILOH The
major mass of plants consists of chemical elements which form easy mobile compounds under the
biosphere conditions; all other elements are present in plants in amounts which are often proportional
to the concentrations of their ions occurring in a feeding media. The distribution of elements (and
radionuclides) within root systems of plants affects their transfer into plants. Uniform distribution of
chemical elements in a soil profile reduces their intake by plants. On the contrary, when elements are
in upper layers of soils, their transfer into plants becomes easier. It appears that the most intense
transfer proceeds from a meadow sod.
Coefficients of biological accumulation by plants and mean concentrations in the ash of plants
have been assessed by Tkalich, they are presented in Table 1-20.
7DEOH&RHIILFLHQWVRIELRORJLFDODFFXPXODWLRQE\SODQWV.EJDQGPHDQFRQFHQWUDWLRQVLQWKHDVKRI
SODQWV&DDIWHU7NDOLFK
Elements
Au
I
Br
Cl
S
P
Ge
B
Mo
Ag
Zn
Mn
Bi
Ca
Te
K
Cu
Mg
Cr
TR
Ga
Ra
Sn
Cs
Sr
Ni
Co
Na
Ba
V
.EJ
233
125
71
59
53
38
36
33
18
14
11
7.5
5.6
5.1
5.0
4.8
4.3
3.7
3.0
2.8
2.6
2.2
2.0
1.4
0.88
0.86
0.83
0.80
0.77
0.67
&D, %
1⋅10−4
5⋅10−3
1.5⋅10−2
1.0
2.50
3.50
Q⋅10−3
4⋅10−2
2⋅10−3
1⋅10−4
9⋅10−2
7.5⋅10−1
Q⋅10−6
15.0
Q⋅10−7
12.0
2⋅10−2
7.0
2.5⋅10−2
Q⋅10−2
Q⋅10−3
2⋅10−11
5⋅10−4
Q⋅10−4
3⋅10−2
5⋅10−3
1.5⋅10−3
2.0
Q⋅10−2
6⋅10−3
Elements
Rb
Pb
Be
Si
Se
Cd
Li
Zr
Ti
Fe
U
In
As
Al
Y
Sb
W
Th
Pd
Nb
Os
F
Hg
Sc
Pt
Ir
Hf
Re
Tl
Ta
51
.EJ
0.67
0.62
0.53
0.51
0.50
0.38
0.34
0.29
0.22
0.21
0.20
0.20
0.18
0.17
0.17
0.10
0.04
0.04
0.04
0.025
0.025
0.015
0.012
0.01
0.01
0.008
0.005
0.007
0.005
0.002
&D, %
1⋅10−2
1⋅10−3
2⋅10−4
15.0
Q⋅10−6 - Q⋅10−5
1⋅10−5 - 1⋅10−6
1.1⋅10−3
Q⋅10−4
1⋅10−1
1.0
5⋅10−5
Q⋅10−6
3⋅10−5
1.4
Q⋅10−4
Q⋅10−6
Q⋅10−6
Q⋅10−5
Q⋅10−8
Q⋅10−5
Q⋅10−9
1⋅10−3
1⋅10−7
Q⋅10−6 - Q⋅10−5
Q⋅10−10
Q⋅10−10
Q⋅10−7
Q⋅10−10
Q⋅10−7
Q⋅10−7
Kovalevsky summarized the data concerning the relations between the PSC (plant-soil
coefficient) values for nonbarrier plants (which concentrate chemical elements in linear proportion to
their contents in soil) and corresponding mineral forms of some metals. A degree of mineral dispersion
has been taken into account. His results are presented in Table 1-21. Practically all investigated metals
show distinct changes of their PSC values depending on mineral forms. These changes can cover 3-5
orders of magnitude. The data like those are presented in Table 1-21 are available for a very limited
set of metals, most of elements are not studied.
7DEOH$SSUR[LPDWH36&YDOXHVIRUGLIIHUHQWPLQHUDOIRUPVRQO\QRQEDUULHUSODQWVZHUH
FRQVLGHUHGIURP.RYDOHYVN\
Elements
Zn
Cu
Hg
Approximate PSC values
1000
100
10
1
0.1
Salts dissol- Sphalerite, Sphalerite,
Fe-forms
ved in water sulphates
smithsonite,
NM-forms
Salts dissol- Compounds Chalcopyrite,
NM- and FeFe-forms,
ved in water soluble in tetrahedrite,
forms under
coarsewater
covellite, NM- soil pH>6,
grained
forms under soil mediummalachite
pH<5,
fine- grained
grained
malachite
malachite
Vaporous
mercury
Dispersed
native
mercury
-
Ra
-
Pb
-
-
Sn
-
-
Native mercury, NM-forms
calomel
Uranium blacks,
sorbed forms in
clays,
NMforms
Dispersed
cinnabar
Dispersed
Fe-forms,
pitchblendes
pitchblende
and micas, NMforms
Anglesite,
Wulfenite, NMcerussite, NM- and Fe-forms
forms
Stannite,
Quartzdispersed
sulphidecassitertie
in cassiterite
sulphides, NM- mineralization,
forms
NM-forms,
0.01
-
0.001
-
-
-
Fine-grained Coarsecinnabar
grained
cinnabar
Uraninite,
monazite,
Uranium
titanates
Fine-grained Mediumgalena
grained
galena
MediumCoarsegrained
crystalline
cassiterite
cassiterite
Coarsegrained
galena
Coarsecrystalline
cassiterite
in quartz
Data for 24 indicator elements obtained by Kovalevsky for numerous plant species (plant
shoots and their residues) show that non-barrier accumulation is observed for only 5% of bio-objects
investigated (Table 1-22). It means that a close to quantitative relation between contents in soil and
plants is an exception (radium is an important example of this exception). Nonbarrier overground parts
of plants were not identified for 9 elements (B, Mn, Fe, Co, Cu, Zn, Cs, Ba, U). For 6 elements (Li, F,
As, Rb, Sr, Ag), the relative number of nonbarrier overground bio-objects varies from 1 to 3%. Only 4
elements (Mo, W, Au, Ra) this number is equal to or exceeds 18%, reaching 36% for Mo and 100%
for Ra. Non-barrier and semi-non-barrier plants should be preferred for practice, but if these are
absent, weakly concentrating bio-ojects may be used. The use of background-barrier plants should be
avoided.
52
7DEOH6WDWLVWLVWLFDOGDWDRQWKHUHODWLYHQXPEHUVRILQYHVWLJDWHGSODQWVSHFLHVZLWKLQHDFKJURXSRI
EDUULHUFKDUDFWHULVWLFVQLVWKHQXPEHURISODQWVSHFLHVVWXGLHGIURP.RYDOHYVN\
Elements
1
Non-barrier
124
Li
226
Be
116
B
235
F
54
Mn
212
Fe
151
Co
238
Cu
162
Zn
91
As
152
Rb
157
Sr
437
Mo
227
Ag
116
Cd
212
Sn
65
Cs
303
Ba
115
W
178
Au
280
Pb
76
Bi
139
Ra
65
U
Average without Ra
1
5
0
1
0
0
0
0
0
1
1
3
36
3
7
5
0
0
18
29
4
6
100
0
5
Relative number of plant species in groups, %
Semi-barrier
Barrier, weak
Barrier, no
accumulation
accumulation
63
33
3
55
30
10
39
51
10
93
3
3
94
6
0
88
6
6
43
50
7
57
41
2
22
60
18
17
52
30
11
57
31
2
32
63
11
28
25
37
53
7
18
45
30
18
63
14
40
48
12
32
54
14
38
27
17
13
26
32
46
38
12
19
35
40
0
0
0
80
17
3
17
37
41
In order to evaluate quantitatively the intensity of plant sorption of chemical elements from different
phases the following coefficients are used (Kovalevsky, 1991):
plant-soil coefficient PSC,
plant-water coefficient PWC,
plant-gas coefficient PGC.
These values are recommended to use for non-barrier plants, each of them is the ratio of the
concentration of a given element to the concentration in a corresponding environment. It is preferable
to discern two kind of the PGC: plant root-gas coefficient PGCr anf plant nonroot-gas coefficient
PGCnr. The values of sorption coefficients for non-barrier plant species (or plant parts) evaluated by
Kovalevsky are presented in Table 1-23.
7DEOH6RUSWLRQFRHIILFLHQWVIRUQRQEDUULHUSODQWVSHFLHVRUSODQWSDUWV
Coefficients
PSC
Dry matter
Limits of
Average
variation
< 0.00003–
0.0003
- 0.005
Ash
Limits of
variation
< 0.001 –
0.2
Average
0.01
0.005–0.02
0.02-0.05
0.05-0.2
0.2-0.5
0.5-20
Elements and their
compounds
Be, B, Al, Si, Fe, Sn, W,
Au, Hg, Pb in stable
minerals
Be, Fe, Ce, Th
Most of elements
Mg, Cu, Mo, Ag, Tl
B, K, Ca, Zn, Sr, Cd, Ba
B, N, P, Zn, Hg
PWC
10-1000
100
102 - 105
3·103
Most of elements
PGCnr
3·102-3·105
1·104
104 – 107
3·105
C(CO2), N(NH3, N2O,
NO), S(SO2), Se(SeO2),
F(F2, HF), Cl, Br, I, Hg
PGCr
3·102-3·105
1·104
105 – 106
3·105
N(NH3)
53
*HRERWDQ\LQWKHVWXG\RIKHDY\PHWDODFFXPXODWLRQ
The behaviour of metals in different organs of plants was studied by Elpat’evsky (Elpat’evsky,
P.V., 1993). It was shown that tree bark is a major depositor of technogenic elements, the percentage
of a total metal stock can reach 80-90% there. The main reason of it is the binding of metals in
unsoluble organic-mineral compounds. The bark of trunks contains usually more metals than the bark
of thick roots of perennial trees. The study of bushes confirms indicator properties of the bark of
perennial plants and a possibility to use it for spatial and temporal monitoring of the environmental
pollution by heavy metals. No contrast differences between species in the ability of metal-bearing of
the bark under neither background nor anomalous conditions have been revealed. Small variations
between species are connected with the age of plants, and with the distance from a source of
contamination (when anomalous zones were considered).
The study of trees and bushes confirms barrier functions of a root system which, to a certain
extent, hinders the absorption of surplus amounts of metals. The major role in this process belongs to
the tissues of root bark. Special investigations of roots with different cross-sections showed that the
thinner are the roots, the more important is the relative contribution of their bark into the bulk mass of
roots, and the higher are the concentrations of metals. The binding of metals by plant roots takes them
out from active biogeochemical migration. At the same time, this is one of the factors of the
accumulation of metals by a humic horizon of a soil where the bulk mass of thin roots is concentrated.
Thus, the order of the increasing of the amounts of heavy metals (obtained by the studies of trees and
bushes) is the following: trunk wood < thick root wood < wood of annual sprouts < reproductive
organs < leaves < root bark < trunk bark < thin roots (with a diameter less than 1 mm). The
distribution of the elements studied (Mn, Fe, Cu, Zn, Cd, Pb) among different organs of plants appears
to be independent on neither the kind of a metal nor the species of plants.
Metal tolerance of plants was investigated by Elpat’evsky (1993). It was established that the
vegetation within natural geochemical anomalies, as a rule, is the same as at adjacent background lots.
This indicates the existence of the mechanism of tolerance of plants as regards metals. For example,
metal tolerance in the population of steppe plants at the ore manifestations of the Urals have been
described (Alexeeva-Popova N.V., 1990).
Metal tolerance with respect to Zn, Cu, Cd and Pb was established, it was fixed for species of the
family of cereals, compositae, labitae, leguminous plants, etc. The formation of metal tolerance is
considered as a result of ecological intraspecific differentiation (based on physiological heterogeneity
of a population) leading to the adaptation of the population to ecologo-geochemical factors of the
environment. It means that specific races and clones have been formed within a species, and they are
capable to be developed successfully in the presence of heightened amounts of metals in a soil.
%LRJHRFKHPLFDOF\FOHVRIHOHPHQWV
Figure 1.4 shows that the essence of the biogeocenose concept concerns interactions among five
landscape components, three of them dealing only with biota.
54
Figure 1.4. Diagram of interactions of landscape components involved in a biogeocenose
(after Sukachev and Dylis, from Fortescue, 1980).
6HULHVRIELRSKLOHHOHPHQWV
The coefficient of biological (absorption) uptake of an element is defined as
.biol = &ash/&EC,
where &as - the concentration of the element in the ash of plant or animal tissues, &EC – the mean
abundance (Clarke) of this element in the earth crust.
Calculations of the .biol values was carried by B.B.Polynov, he used them as a basis of biogenic
classification of chemical elements. Taking into account the contribution of elements into chemical
compounds of organisms, Polynov distinguished two groups of elements: organogenous and
admixtures. The first group includes (1) vitally indispensable elements, without them physiological
development of organisms is impossible: O, H, C, N, Mg, K, P; and (2) specific elements which are
necessary for many organisms, but not obligatory for all species: Si, Ca, Na, Fe, Cl, F, S, Mn, Sr, B,
Zn, Cu, Br, I. The second group (admixtures) was divided by Polynov into two subgroups as well:
absolute and ecological. Absolute subgroup embraces Na, Cl, Si, Rb, rare gases (He, Ar, Ne, Kr, Xe)
and all dispersed elements that are constantly present in all rocks and soils. According to Polynov,
these elements are not detained, as a rule, in living or dead organic matter, they depart with soil
solutions, river waters and groundwaters and pass into seas and oceans. Ecological, or local,
admixtures are connected with certain areas of dissemination of elements. Their concentrations in
solutions can exceed significantly the amounts necessary for nutrition of organisms.
There are other biogenic classifications of elements. E.Underwood considered four major groups:
(1) indispensable (Fe, I, Mn, Co, Cu, Zn); (2) probably indispensable (Sr, Ba, Mo, Se F, Br, and
others; (3) toxic – this group includes most of microelements when their concentrations in food exceed
the quantities necessary for normal development of an organism (F, Se, Mo, As, Pb, Zn, Cu); (4)
physiologically inactive (Rb, Cs, TR, Zr, Nb, Ta, and others, the role of many of them is not
understood yet).
According to V.V.Koval’sky, all elements can be divided into three basic groups: (1) elements
that are constantly present in organisms, they are involved in metabolism and are included into
55
chemical compounds, often biologically active (O, C, H, N, Ca, P, K, S, Cl, Na, Mg, Zn, Fe, Cu, I,
Mn, Mo, V, Co, Se); (2) elements which are also constantly present in organisms, however their
physiological and biogeochemical roles are not clear (Sr, Cd, Br, Si, Cr, Ni, Be and others); (3)
elements which are observed in organisms, but their both concentrations and biological role are
unknown (TR, Au, Zr, Nb, In, and others).
Polynov’s concept was developed by Perel’man. Performing further analysis of the .biol values,
he proposed the series of biological sorption of elements, they are as follows:
• Elements of very strong sorption: P, S, Cl, Br, I (.biol = Q10 – Q100);
• Elements of strong sorption: Ca, Na, K, Mg, Sr, Zn, B, Se (.biol = Q – Q10);
• Elements of intermediate sorption: Mn, F, Ba, Ni, Cu, Ga, Co, Pb, Sn, As, Mo, Hg, Ag, Ra (.biol =
0.1– 1);
• Elements of weak and very weak sorption:Si, Al, Fe, Ti, Zr, Rb, V, Cr, Li, Y, Nb, Th, Sc, Be, Cs,
Ta, U, W, Sb, Cd (.biol = 0.001 – 1).
The two first series are presented by so-called biophile elements, their .biol values are always > 1.
+HDOWKULVNDVVHVVPHQWGXHWRPHWDOFRQWDPLQDWLRQRIVRLOVDQGSODQWV
In human health risk assessment, the consequences or effects are classified into cancer risk and a
catch-all noncancer risk category. Cancer risk generally drives regulatory decisions because cancer is
an unambiguous endpoint and deeply dreaded by the public; cancer risk assessment methodology is
also well established.
The two principal indices of toxicity, i.e., quantitative expressions of dose-response information,
are known as FDQFHU SRWHQF\ IDFWRU (CSF) and UHIHUHQFH GRVH (RfD). For cancer effects of
carcinogenes, regulatory agencies assume zero threshold: i.e., there is some risk no matter how small
the dose. No distinction is made between different types of cancer. The FDQFHUVORSHIDFWRU(SF), also
called the SRWHQF\ IDFWRU, is defined as a plausible upper-bound estimate of the probability of a
response per unit intake of a chemical over a lifetime. In general, substances with relatively high slope
factors and low reference doses tend to be associated with higher toxicity.
&DQFHUXQLWULVN – risk per unit concentration of contaminant in environmental medium. There are
air unit risk ad water unit risk:
$LUXQLWULVN = risk per µg/m3 (incremental risk of cancer from inhaling 1 µg of substance per
cubic meter of air over a lifetime)
:DWHUXQLWULVN = risk per µg/L (incremental risk of cancer from ingesting 1 µg of substance per liter of
water over a lifetime.
Unit risks can be converted to VORSHIDFWRUV and vice versa by using an air inhalation rate of 20
m3/day or water consumption rate of 2L/day, human body weight of 70 kg, and accounting for any
differences in absorption rates (see Table 1-24 below):
6ORSHIDFWRU = risk per unit dose = risk per mg/(kg⋅day)
(Incremental risk of a cancer from a dose of 1 mg of substance per kilogram of body weight per day
over a lifetime).
Unit risk per µg/m3 (inhalation exposure) = (slope factor × 20 m3/day × 10 −3 mg/µg)/70 kg body
weight
Unit risk per µg/L of water (oral exposure) = (slope factor × 2 L/day × 10 −3 mg/µg)/70 kg.
7KHWKUHVKROGUHVSRQVHHIIHFWV, represented by the reference dose (RfD), allow for the existence
of safe thresholds; i.e., a certain quantity of a substance or dose is needed below which there is no
observable toxic effect by virtue of the body’s natural repair and detoxifying capacity. An RfD for a
substance is the intake or dose of the substance per unit body weight per day that is likely to be
without appreciable risk to human population, including sensitive groups (children, elderly). The U.S.
Environmental Protection Agency (EPA) defines RfD as “an estimate (with uncertainty spanning
perhaps an order of magnitude or greater) of a daily exposure level for the human population,
including sensitive subpopulations, that is likely to be without an appreciable risk of deleterious
effects during a lifetime”. Reference doses and reference concentrations (virtually safe concentration
of a substances in the air) have been developed for several hundred chemicals, both noncarcinogens
and carcinogens (noncarcinogenic effects of carcinogens), but not for all.
56
Examples of cancer slope factors/unit risks and noncancer reference doses/concentations are as
follows (taken from EPA ,5,6 (,QWHJUDWHG 5LVN $VVHVVPHQW 6\VWHP+($67 +HDOWK (IIHFWV
$VVHVVPHQW6XPPDU\7DEOHV), 1994):
• $UVHQLF (carcinogen) oral slope factor SF and unit risk are 1.75 [mg/(kg⋅day)−1] and 5⋅10−5
(µg/L)−1; oral RfD is 3⋅10−4 mg/(kg.day). An inhalation unit risk is 4.3⋅10−3 µg/m3.
• &KURPLXP 9, (carcinogen) slope factor SF by inhalation is 42 [mg/(kg⋅day)−1] and RfD by
ingestion is 5⋅10−3 mg/(kg.day); &KURPLXP ,,, oral RfD is 1 mg/(kg.day) – two or three times
orders of magnitude higher than CrVI.
• (OHPHQWDOPHUFXU\DQGPHWK\OPHUFXU\ (noncarcinogens) chronic and subchronic RfDs by the oral
route are the same, 3⋅10−4 mg/(kg.day), although methyl mercury is a more toxic form. Mercury
and methyl mercury RfC by the inhalation route is 3⋅10−4 mg/m3 air.
Using the value of slope factor SF, it is possible to calculateFDQFHUULVN. Cancer riskis the probability
of an individual developing of any type of cancer from lifetime exposure to carcinogenic hazards. For
low doses typical of environmental exposures, cancer risk can be estimated with a linear equation
(constant slope) as follows:
,QFUHPHQWDOFDQFHUULVN = average daily dose [mg/(kg⋅day)] × slope factor [mg/(kg⋅day)−1].
Cancer risk estimates higher than 10−6 to 10−4 range are generally considered to be of regulatory
concern.
1RQFDQFHUULVN is expressed in terms of KD]DUGTXRWLHQW (HQ) for a single substance or hazard
index (HI) for multiple and/or exposure pathways. These are ratios of chemical exposures to reference
doses as shown below. The ratio of exposure level, intake, or dose to RfD for the same route of
exposure (inhalation, oral) and the same exposure period (chronic, subchronic) is called a KD]DUG
TXRWLHQW:
+D]DUGTXRWLHQW (HQ) = exposure or intake [mg/(kg⋅day)]/RfD [mg/(kg⋅day)].
If the exposure or intake is less than the corresponding RfD (i.e., HQ<1), the hazards are not
considered to pose a threat to public health, including sensitive subgroups. If HQ>1, there may be
concern for potential noncancer effects. In general, the greater the value of the hazard quotient above
1, the greater is the level of concern. However, hazard quotient does not represent a statistical
probability of an effect occurring.
In the absence of information on synergistic and antagonistic mechanisms, the overall potential
for noncarcinogenic effects from simultaneous exposure to multiple chemicals and multiple routes can
be estimated by summing up hazard quotients for the same individual or subgroups. The resulting sum
is referred to as KD]DUGLQGH[. This approach assumes that multiple subthreshold exposures to several
chemicals could cumulatively result in an adverse health effect. The HI is calculated as follows:
+D]DUGLQGH[ (HI) = (1/RfD1 + (2/RfD2 + ….. + (Q/RfDQ= ΣL (L/RfDL,
where (L– exposure (average intake or dose) for the Lth toxicant [mg/(kg⋅day)], RfDL – reference dose
for the Lth toxicant [mg/(kg⋅day)].
The process of exposure assessment requires the quantification of the magnitude, frequency, and
duration of exposure for all the pathways that are considered complete and significant. For exposure
rates and receptor biological data, site-specific data values should be used to the extent feasible;
otherwise, conservative default values suggested by the US EPA can be used, they are presented in the
Table 1-24.
Exposures can be chronic (e.g., residential) or subchronic (e.g., maintenance workers). The
definitions of subchronic and chronic exposures vary, but subchronic generally indicates a few weeks
to a few years or about 10% of a lifetime, unlike chronic, which involves exposures over a substantial
period of an organism’s lifetime. It is important to make this distinction for noncarcinogenic effects
because subchronic reference doses tend to be higher than chronic, often by an order of magnitude,
due to shorter exposure periods. This distinction is not made for carcinogenic effects.
57
7DEOH(3$'HIDXOW([SRVXUH)DFWRUV(3$
Land use
Residential
Industrial and
Commercial
Agricultural
Recreational
Exposure
pathway
Daily intake
Ingestion of
potable water
2 L (adult)
1 L (child)
Ingestion of soil
and dust
200 mg (child)
100 mg (adult)
Inhalation of
contaminants
Exposure
frequency,
Days/year
350
Exposure
duration,
Years
Body weight,
Kg
30
70 (adult)
15 (child)
350
6
24
15 (child)
70 (adult)
20 m3 (adult)
12 m3 (child)
350
30
70 (adult)
15 (child)
Ingestion of
potable water
1L
250
25
70
Ingestion of soil
and dust
50 mg
250
25
70
Inhalation of
contaminants
20 m3
(workday)
250
25
70
Consumption of
homegrown
produce
42 g (fruit)
80 g (veget.)
350
30
70
54 g
350
30
70
Consumption of
locally caught
fish
Quantitative health risk assessments require the data on a diet structure of the population
considered. The studies of this kind are at the very beginning. In 1998 B. Howard et al. published the
detailed data on the food consumption in different EU countries (Howard B. J., et al., 1998).
Considerable differences in the average diets of European nations were found. It is demonstrated by
the comparison of data for three neighboring countries: Denmark, Sweden and Finland (Table 1-25).
7DEOH$QQXDOGLHWVWUXFWXUHNJSHUFDSLWD\HDULQ'HQPDUN6ZHGHQDQG)LQODQG
DIWHU+RZDUGHWDO
)RRGSURGXFW
Wheat
Rice
Barley
Corn
Rye
Oat
Edible roots
Sugar
Honey
Legumes
Olives
Vegetable oil
Tomatoes
Onion
Oranges
Other citrus fruit
Apples
Grapes
Meat
Milk
Eggs
Freshwater fish
Sea fish
Sea food
'HQPDUN
71,1
3,0
0.1
11,9
15,6
5,0
69,0
47,2
0,5
0,9
0,1
0,4
13,9
10,7
11,5
1,3
23,3
7,5
100,2
169,6
16,3
2,2
14,9
2,6
58
6ZHGHQ
57,7
10,3
0,6
2,0
11,9
4,0
72,1
43,1
0,7
1,6
0,2
2,1
20,7
4,8
31,4
1,3
19,5
6,1
64,9
359,4
12,4
2,2
18,2
6,7
)LQODQG
56,3
7,5
3,1
0,0
17,2
4,9
78,1
41,4
0,5
0,4
0,1
1,1
16,3
3,8
18,5
0,8
19,2
6,2
59,8
319,5
10,0
6,8
24,1
1,9
%LEOLRJUDSK\
Alekseenko, V.A. 1989. *HRFKHPLFDO 0HWKRGV RI ([SORUDWLRQ. Moscow: Vysshaya Shkola (in
Russian.
Alexeeva-Popova N.V., 1990 Intraspecific Differentiation of Wild Speciae under the Influence of
Heavy Metals Surplus in the Environment 1DWXUDODQG$QWKURSRJHQLFDOO\$OWHUHG%LRJHRFKHPLFDO
&\FOHV7UXG\%LRJHRFKHPLFDO/DE. V. 21. Moscow: Nauka, pp.62-71 (in Russian).
Fergusson, J.L., 1982. ,QRUJDQLF&KHPLVWU\DQGWKH(DUWK. Oxford – New York: Pergamon Press.
Elpat’evsky, P.V., 1993. *HRFKHPLVWU\RI0LJUDWLRQ)OX[HVLQ1DWXUDODQG1DWXUDO7HFKQRJHQLF
6\VWHPV. Moscow: Nauka (in Russian).
EPA 1990. ([SRVXUH)DFWRUV+DQGERRN. EPA 600/8-89/043.
EPA. 1994. ,5,6 ,QWHJUDWHG 5LVN $VVHVVPHQW 6\VWHP+($67 +HDOWK (IIHFWV $VVHVVPHQW
6XPPDU\7DEOHV).
Fortescue, J.A.C. 1980. (QYLURQPHQWDO*HRFKHPLVWU\$+ROLVWLF$SSURDFK. Berlin: Springer
Verlag.
Fortescue, J.A.C. 1996. Guidelines for a “Systematic Landscape Geoscience”. In: Berger, A.R.
and W.J.Iams (Eds.) *HRLQGLFDWRUV $VVHVVLQJ 5DSLG (QYLURQPHQWDO &KDQJHV LQ (DUWK
6\VWHPVRotterdam: A.A.Balkema, pp.351-363.
Howard B. J., Wright S. M., Barnett C. L. (Editors).1998. 6SDWLDO $QDO\VLV RI 9XOQHUDEOH
(FRV\VWHPV LQ (XURSH 6SDWLDO DQG G\QDPLF SUHGLFWLRQ RI UDGLRFDHVLXP IOX[HV LQWR (XURSHDQ IRRGV
6$9(0LGWHUP5HSRUW-DQXDU\±'HFHPEHU. Institute of Terrestrial Ecology, Centre for
Ecology and Hydrology, UK.
Kabata-Pentias, A. 1992. Behavioural Properties of Trace Elements in Soils // $SSOLHG
*HRFKHPLVWU\, Suppl. Issue N 2, pp.3-9.
Kovalevsky, A.L. 1984. %LRJHRFKHPLFDO3URVSHFWLQJRI2UH'HSRVLWV. 2nd ed., Moscow:Nedra (in
Russian).
Kovalevsky, A.L. 1991. %LRJHRNKLPL\DUDVWHQLL%LRJHRFKHPLVWU\RI3ODQWV, Moscow:Nedra (in
Russian).
Makarov, E.S. 1973. ,VRPRUSKLVPRI$WRPVLQ&U\VWDOV Moscow: Atomizdat (in Russian).
Mason, B. 1966. 3ULQFLSOHVRI*HRFKHPLVWU\. 2nd Ed. New York: John Wiley.
Ovchinnikov, L.N., 1990. 3ULNODGQD\D*HRNKLPL\D$SSOLHG*HRFKHPLVWU\ Moscow: Nedra (in
Russian).
Perel’man, A.I. 1979. *HRFKHPLVWU\. Moscow: Vysshaya Shkola (in Russian).
Perel’man A.I. 1982. *HRFKHPLVWU\RI1DWXUDO:DWHUV Moscow: Nauka (in Russian).
Safronov, N.I. 1971. 7KH )RXQGDWLRQV RI *HRFKHPLFDO 0HWKRGV RI 2UH 'HSRVLWV ([SORUDWLRQ/
Leningrad: Nedra (in Russian).
Shvartsev, S.L. 1978. +\GURJHRFKHPLVWU\RIWKH=RQHRI+\SHUJHQHVLV Moscow (in Russian).
Shvartsev, S.L. 1998. +\GURJHRFKHPLVWU\ RI WKH =RQH RI +\SHUJHQHVLV 2nd Edition. Moscow:
Nedra (in Russian).
Smirnov, S.S. 1955. =RQHRI2[LGDWLRQRI 6XOSKLGH 'HSRVLWV. Moscow: Academy of Science of
the USSR (in Russian).
Solovov, A.P. 1978. *HRFKHPLFDO0HWKRGVRI3URVSHFWLQJ. 1985. 2nd edition, Moscow: Nedra (in
Russian).
Solovov, A.P., Grigoryan, S.V. 1984. Geochemical Methods of Prospecting // 5D]YHGNDL2KUDQD
1HGU, N 7, pp. 49-53 (in Russian).
Tkalich, S.M., 1970. 3K\WRJHRFKLPLFKHVNLL0HWRG3RLVNRY0HVWRURMGHQLL3ROH]Q\K,VNRSDHP\NK
Leningrad: Nedra (in Russian).
Vernadsky, V.I. 1954. 6HOHFWHG:RUNV. V.1 (in Russian).
59
$QDO\WLFDODVSHFWV
*HRFKHPLFDOEDFNJURXQGDQGDQRPDO\
&ODUNHYDOXHVIRUWKHDEXQGDQFHDQGGLVWULEXWLRQLQURFNVDQGVRLOV
It is impossible to overestimate the role of the concept of geochemical background in both
science and practice. Geochemical background refers to the so-called normal chemical composition of
an earth material. The key points of its definition are that any determination is specific to a particulate
material: granite, shale, clay, soil, and so forth. Major methods used to estimate geochemical
background are based on crustal or lithologic abundances of the elements (Clarke values) published in
geologic literature.
There is a direct correlation between the abundances of elements and reserves of these elements
in deposits and concentrations in ores. The dependence of metal accumulation on the Clarkes is
exposed not only on a global scale, it is also revealed for a group of deposits, and for a separate
territory, as a continent, or a big country or an ore province, it can be disclosed even within an
individual ore formation. Dimensions and maximum reserves of the largest deposits of each metal are
limited by its Clarke. The ratio of the reserves of a metal association in an aggregate of deposits within
an ore formation or province reflects the ratios of the Clarke values of these metals in primary rocks.
Not only the degree of metal concentration in deposits , but their dispersion, i.e., any displacement in
nature depends on the Clarke as well. The amount of metals annually setting with continental and
volcanic dusts, with atmospheric precipitates, and also transported by river discharges is proportional
to their Clarkes.
These regularities can be regarded as a direct evidence indicating that the average abundance of a
chemical element in a natural geochemical system is a constant value. Any statistically significant
deviation from the Clarke is causally conditioned, and may be useful for practical applications. As
practice shows, in order to assess the significance of such applications, sometimes it is sufficient to
compare observed concentrations of an element with its Clarke in the earth crust. In other cases,
special properties of rocks containing these concentrations should be taken into account. Thus, it is
advisable to use not only crustal Clarkes, but the Clarkes of major types of rocks.
With the development of analytical methods accompanying by improving their
precision/accuracy and, mainly, sensitivity, the data on the crustal and rock Clarkes became more
exact and reliable. One of the recent summary of Clarkes values has been made by Ovchinnikiv in
1990 (Ovchinnikov L.N., 1990). In his work, numerous previous data (of A.P.Vinogradov, S.R.Taylor,
K.H.Wedepohl, D.M.Shaw, B.Mason, K.K.Turekian and others) were analyzed and generalized. Table
2-1 presents crustal abundances of elements (the Clarke values in the earth crust).
60
7DEOH&UXVWDODEXQGDQFHV&ODUNHVRIHOHPHQWVLQSSPIRUQREOHJDVHV±+H1H$U.U
DQG;H±LQFPJDIWHU2YFKLQQLNRY
Elements
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Clarkes
1,100
0.6
25
2
9
200
20
465,000
640
0.00078
23,800
22,600
80,700
279,900
1,000
330
180
0.22
21,300
38,100
17
5,300
120
93
900
53,300
23
70
Elements
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Rb
Sr
Y
Zr
Nb
Mo
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Cs
Ba
La
Clarkes
53
68
1.7
1.4
1.8
0.073
2.4
0.000042
110
370
32
160
21
1.2
0.004
0.005
0.009
0.073
0.17
0.15
2.3
0.3
0.003
0.47
0.0000034
4.3
470
30
Elements
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Th
U
Clarkes
61
7.6
30
7.3
1.2
7.2
1.9
4.7
1.5
3
0.36
3.1
0.9
2.4
2.2
1.4
0.0008
0.002
0.00065
0.0057
0.0035
0.072
0.9
1.3
0.19
10
2.6
It is generally accepted concept that the elements having mean crustal abundances (Clarkes) of
less than 200 ppm are to be considered UDUH elements, provided that they do not exhibit any significant
local concentrations. Both the low mean abundance and the tendency to disperse are connected with
the atomic structure of rare elements. Abundance is a function of nuclear stability, whereas the
tendency to disperse depends primarily on the electron structure.
Mean abundances of elements in major types of igneous rocks are given in Table 2-2, together
with their coefficients of differentiation .G = Clarkemax/Clarkemin.
7DEOH0HDQDEXQGDQFHV&ODUNHVRIHOHPHQWVLQPDMRUW\SHVRILJQHRXVURFNVSSP
DQGWKHLUFRHIILFLHQWVRIGLIIHUHQWLDWLRQ.GDIWHU2YFKLQQLNRY
Element
H
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Sc
Ti
V
Cr
Ultrabasic
Basic
Neutral (diorites,
Acidic
Acidic Syenites
(dunites and others) (basalts, gabbro)
andesites)
(granodiorites) (granites)
600
900
1,100
1,200
28
37
26
27.5
15
0.75
1
3.6
2.1
1.8
0.56
0.2
9
12.5
12.5
12
5
3
300
250
150
100
30
22
20
21
19
7
487,000
480,000
465,000
440,000
431,000
1,200
820
560
500
400
100
26,100 40,400
28,200
27,800
18,600
3,200
5,800
2,200
9,900
21,500
45,500
218,000
72,700 88,000
83,300
89,500
82,200
17,100
342,300 291,000
311,000
271,000
232,500
200,000
800
600
980
1,350
1,300
280
300
300
300
300
300
200
470
190
160
100
80
74
39,700 48,000
25,200
17,100
8,000
220
18,000
7,100
24,900
47,600
73,000
22,800
3
6.5
13
18
30
12
3,500
1,600
4,600
6,100
10.700
1,600
30
38
91
140
240
42
2
5.6
22
54
180
2,000
61
.G
2
49
18
4
3
4
12
13
99
5
1.7
5
1.5
6
218
13
10
7
8
1,000
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Rb
Sr
Y
Zr
Nb
Mo
Pd
Ag
Cd
In
Sn
Sb
Te
I
Cs
Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Th
U
1,300
93,500
150
2,000
10
46
2.2
1.3
1.3
0.05
0.9
0.7
7
2
43
13
0.3
0.05
0.06
0.05
0.01
0.5
0.2
0.001
0.3
0.1
0.8
3.9
8.6
1.4
4.8
0.83
0.24
0.93
0.2
0.28
0.16
0.35
0.06
0.48
0.068
0.46
0.41
0.3
0.14
0.006
0.007
0.15
0.46
0.0046
0.004
0.0014
1,700
85,600
48
140
92
110
16
1.4
2
0.07
3.5
37
460
23
130
19
1.4
0.016
0.11
0.19
0.2
4
0.34
0.001
0.5
1
290
17
48
5
22
5.3
1.3
5.2
0.83
2.5
0.99
2.2
0.25
2
0.5
2.6
0.74
0.8
0.0006
0.0005
0.00026
0.07
0.0035
0.07
0.18
6
0.007
3.2
0.8
1,200
53,600
14
41
43
74
18
1.4
2.2
0.095
4.5
80
410
25
170
15
1
0.00Q
0.09
0.15
0.31
1.2
0.21
0.001
0.4
1.4
410
21
45
4.7
20
4.7
1.1
5.4
0.94
5.2
1.1
2,5
0.25
2.4
0.8
2.1
0.95
1.1
0.0028
0.0021
0.025
11
0.009
6
2.2⋅
750
30,700
78
16
29
59
18
1.3
1.8
0.08
4.3
120
440
36
140
20
1
0.00Q
0.056
0.11
0.17
1.9
0.2
0.001
0.5
2.2
560
51
75
6.4
23
8.2
1.4
5.4
1.3
5.2
1.9
3.8
0.3
3.6
1.1
2.5
2.8
1.6
0.000Q
0.0000Q
0.0000Q
0.0028
0.052
0.86
15
0.01
9.9
2.7
420
85
15,600 36,700
1
3
3.5
4
10
5
39
130
18
0.3
4.4
1
1.6
14
0.07
0.05
1.7
2.7
180
110
150
200
50
17
180
500
21
35
1.5
1.1
0.00Q
0.038
0.00Q
0.17
0.13
0.22
3
0.2
0.2
0.001
0.5
0.5
5
0.6
750
1,600
48
45
72
95
7.4
10
31
42
7.5
10
1.4
1.8
6.8
10
1.1
1.6
5
7
1.3
2
3.1
4.4
0.3
0.44
4
4.3
0.9
1.2
3.9
11
3.6
2.1
2.2
1.3
0.0006 0.0003
0.00004 0.0000Q
0.00009 0.0000Q
0.008
0.002
0.0027
0.0Q
0.06
1.4
1.9
12
19
0.01
13
18
3
3.9
20
6
150
570
18
3
60
4
11
2
5
257
66
25
12
3
5
3
4
31
8
1.7
1
1.5
50
2000
13
11
7
9
12
8
11
8
25
12
13
7
9
17
24
9
7
2
12
3
18
3
33
66
41
2
4500
2785
This table shows that both radioactive elements - Th and U - are subjects of the strongest
differentiation, they have maximum .G values.
In Table 2-3 the Clarkes values for major types of sedimentary rocks – clayey shales and sands –
together with corresponding .G values are presented.
62
7DEOH0HDQDEXQGDQFHVRIHOHPHQWVSSPLQPDMRUW\SHVW\SHVRIVHGLPHQWDU\URFNV±FOD\H\VKDOHV
DQGVDQGVDQGWKHLUFRHIILFLHQWVRIGLIIHUHQWLDWLRQ.GDIWHU2YFKLQQLNRY
Elements
H
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Rb
Sr
Y
Zr
Clayey
shales
4,000
65
3
100
11,000
580
503,000
700
10,000
15,000
77,200
215,000
700
2,600
18
26,400
21,000
13
4,400
130
94
800
44,200
19
74
48
93
22
1.7
12
0.58
4.4
150
330
300
170
Sands
.G
Elements
2,500
20
0,Q
35
13,000
61
515,000
240
5,300
7,000
26,300
361,000
250
230
10
11,500
35,000
1
2,000
20
35
400
15,900
0.3
2
1
21
10
0.91
1
0.05
1
55
20
40
220
1.6
3.2
6
3
1.2
9.5
1
2.9
1.9
2.1
2.9
1.7
2.8
11
1.8
2.3
1.7
13
2.2
4.6
2.7
2
2.8
63
37
48
4.4
2.2
2
12
12
4.4
2.7
16.5
7.5
1.3
Nb
Mo
Ag
Cd
In
Sn
Sb
Te
I
Cs
Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Au
Hg
Tl
Pb
Bi
Th
U
Clayey
shales
18
2.6
0.072
0.42
0.082
6,4
1.5
0.01
1.9
6.5
660
140
63
6.3
27
6.5
1.1
6.5
1
4.8
1.4
2.7
0.23
3
0.66
3.5
1.5
1.5
0.0033
0.42
1.1
20
0.097
12
3.7
Sands
.G
0,0Q
0.2
0,0Q
0,0Q
0,0Q
0,Q
0,0Q
1.7
0,Q
180
30
92
8.8
37
10
1.6
10
1.6
7.2
2
4
0.3
4
1.2
3.9
0,0Q
1.6
0,00Q
0.03
0.8
7
1.7
0.45
360
13
1.1
3.7
4.7
1.4
1.4
1.4
1.5
1.5
1.5
1.6
1.5
1.3
1.5
1.4
1.3
1.8
1.1
1
14
1.4
1.4
7
8.2
In Table 2-4 mean abundances (Clarkes)of elements in soils are given.
7DEOH0HDQDEXQGDQFHV&ODUNHVRIHOHPHQWVLQVRLOVSSPDIWHU2YFKLQQLNRY
Elements
Li
Be
B
C
N
O
F
Na
Mg
Al
Si
P
S
Cl
K
Ca
Sc
Clarkes in soils
48
6
24
20,000
1,000
490,000
200
6,300
5,200
71,200
330,000
730
780
100
13,800
13,700
-
Elements
Cu
Zn
Ga
Ge
As
Se
Br
Rb
Sr
Y
Zr
Nb
Mo
Ag
Cd
In
Sn
Clarkes in soils
30
84
23
1
12
0.74
4
95
380
50
300
2
0.1
5.2
10
63
Elements
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Au
Clarkes in soils
50
6
-
Ti
V
Cr
Mn
Fe
Co
Ni
4,900
150
850
38,000
13
110
5
5
5.7
500
-
Sb
Te
I
Cs
Ba
La
Hg
Tl
Pb
Bi
Th
U
0.02
0.1
1.3
8
1
As it can be seen from this table, the data concerning mean abundances of several rare elements in
soils are not established reliably, so they are not included in the summary.
'HILQLWLRQRIDQDQRPDO\DQDO\WLFDOFRQWH[W
Recognition of a geochemical anomaly from background is a basic problem in geochemical
exploration. Its solving means to distinguish elevated concentrations of an element, supposed to be
induced by mineralization, from the variations of background element concentrations connected to
regional geological-geochemical processes.
Anomalous chemical composition can be induced by either mineralization of an earth material or
its industrial contamination. Background is usually expressed as the average or mean concentration of
an element. However, because the spatial distribution of concentrations of an element is never
uniform, background appears to be described more realistically by a range of concentrations. In this
case, the upper limit of the range of measured background concentrations may be used as the specific
threshold limiting the influence of mineralization or contamination processes.
In both mineral exploration and environmental characterization, the interpretation of geochemical
data has a common goal: to identify which values are from the background population and which are
from an anomalous population with elevated concentrations (such as mineralized rock or contaminated
soil). A geochemical population is the set of concentrations of an element that represents the statistical
regularities of the distribution of the element in a particular formation (Beus, A.A., and S.V.Grigorian,
1977). This definition encompasses the statistical concept of a population: each measured
concentration is a value of a random variable having a probability distribution function which is
described by certain parameters. For a population having a normal distribution, these parameters are
the mean and variance.
Thus, a geochemical anomaly is determined using the threshold , i.e. the concentration of an
indicator element &A, above which a measurement is considered anomalous. Usually, this
concentration is taken as being equal to the upper limit of background fluctuations: any higher value
are anomalies, and lower values constitute background. The upper limit of background fluctuations is
defined as
[D = [ + W6
(2.1)
where [ is the mean, 6±the standard deviation, and W determines the level of certainty of the detection
of anomalies.
In order to illustrate the role of W, one can consider the following situations. If &A is determined at
the level corresponding toW = 4, the probability of erroneous including of background fluctuations into
the category of anomalies would be quite negligible (0.003% in a normal distribution if data), however
some weak anomalies insignificantly distinguishing from the concentration of background &EJ would
be registered. If &A is taken at the level of W = 4, practically all weak anomalies would be revealed,
however an important fraction of background quantities regarded as anomalies (the probability of
registration of these fictitious anomalies induced by variations of background is about 16% in a
normal distribution. Thus, it is reasonable to put W = 2 or 3, the latter value is more common.
In the majority of analytical methods applied in geochemical exploration, errors of measurements
follow a log-normal distribution. Analytical errors enter as an item 6an into the standard deviation 6of
background. According to the rule of the addition of variances,
62 62nat + 62an,
(2.2)
where 62nat is natural variance.
The equation (2.1) can be rewritten as the dependence between logarithmic values:
~
[a = lg&A lg & [ + W6lg
64
(2.3)
making this expression free of logarithms,
~
&$ = & [ εW
(2.4)
~
where & [ = &EJ – the mean geometric concentration of an element within a background site. It is
determined as
1
∑
~
1
& [ = antlg (
lg &L )
1 L =1
(2.5)
The value ε = antlg6OJ is called “standard factor”. Taking into account the above-stated considerations
concerning the choice of W, the lower limit of anomalous concentrations of an element used for
marking out weak anomalies fixed by one point of observation, is determined by the following
formula:
& $,1 ≥ & EJ 3
(2.6)
In order to trace weak anomalies formed by a group of adjacent points of observation with increased
concentrations of an element non-reaching the level of &A,1, it is possible to bring down a threshold
amount, according to the criterion:
& $,P ≥ & EJ 3 / P ,
(2.7)
where P is a number of points which can be united into a common anomalous contour (Solovov, 1978,
1985).
'HWHFWLRQRIZHDNDQRPDOLHV
Several practical statistical procedures can be used in order to delineate weak geochemical
anomalies, assumed to be caused by mineralization, from background element concentration related to
regional geological-geochemical processes. They include the use of moving averages, Kriging (see,
for example, Clark, 1979), probability graphs, and other techniques. The methods of probability plots
permits a statistical characterization of the background populations, from which, as it has been showed
by Fleischhauer and Korte, reliable criteria of detection of anomalies may be developed (Fleischhauer
and Korte, 1990). The method of probability plots of trace element concentration is considered below
(all examples are taken from the article of Fleischhauer and Korte, 1990).
Graphical techniques were applied extensively in mineral exploration to segregate the data set
into its constituents populations. Such plots are often referred to as cumulative distribution curves,
cumulative frequency plots, or simply probability plots. In statistical applications, the cumulative
distribution is usually plotted on normal probability paper primarily for testing the assumption of
normality of the data set. Tenant and White noted that the probability plots of geochemical data
frequently consist of two straight-line segments, which they interpreted as representing different
geochemical populations (Tenant and White, 1959). This effect is easily reproduced with model data
sets generated from a table of random normal numbers (Fleischhauer and Korte, 1990).
In Fig. 2.1, curve A is the probability plot of a sample drawn from a normal population with a
mean of 10 and standard deviation of 3.
65
)LJXUH. Probability plot of model sample data from normal populations: (x) - B; ( • ) - (A+B); (+) - A
(Fleischhauer and Korte, 1990).
The values range from 2 to 17 and average of 9.6. Curve B is the probability plot of a sample drawn
from a normal population with a mean of 27 and standard deviation of 8. The values range from 10 to
49, so there is some overlapping in the two data sets. Since these two data sets are from normal
populations, their plots are straight lines. Combining the two data sets and recalculating the cumulative
frequencies results in the curve shown as curve A+B. This curve consists of two straight-line segments
connected by a steeply slopping segment in the central part of the curve. Figure 2.2 is a histogram of
the combined data.
)LJXUH. Histogram of model data simulating a mixture of two normal populations (Fleischhauer and Korte,
1990). See curve A+B in Figure 2.1.
If curve A is regarded as a sample representing the background population and curve B - as a sample
representing the anomalous population, curve A+B might represent the sample obtained at an explored
site. The threshold, or the upper limit of background, is identified as the inflection point on the
probability graph, that is the point where the concavity changes from downward to upward on curve
A+B.
In the example considered, the inflection point is at 17, and background is determined from the
curve as consisting of all samples with a concentration less than or equal to 17. Because background is
defined from the sample in this way, several (eight) values from the anomalous sample set are
included with the background data (see Fig. 2.2). The effect of these eight values on the estimated
average background is minor. The mean of the background population is defined as 10, and the mean
66
of the background sample drawn from this population is 9.6. When the eight values from the
anomalous sample set are included, the background is estimated as 9.9. In a real situation, this
difference is negligible, taking into account the magnitude of sampling error and analytical errors.
The above example is characterized by the bimodal sample distribution because both the
background and anomalous populations are represented in approximately equal proportions in the
mixed sample. However in practice, the anomalous sample set is usually smaller in comparison with
the background one. It means that the distribution of the mixed sample will generally not be bimodal,
and the anomalous (contaminated) population may not be as well defined. Fleischhauer and Korte
showed that if such situation should be simulated with a sample set consisting of 10% anomalous
population and 90% background population, the model data set could be generated by combining the
100 background values used for curve A with 11 random values from the anomalous population
represented by curve B. The values from the anomalous population range from 14 to 49, so there is
again some overlap with the background data. A histogram of the model sample set has a long tail of
values, but there is no pronounced second mode (Fig. 2.3).
)LJXUH. Histogram of model data simulating a 90:10 mixture of two normal populations (Fleischhauer and
Korte, 1990).
)LJXUH. Probability plot of model data simulating a 90:10 mixture of two distributions (Fleischhauer and
Korte, 1990).
The probability plot (Fig. 2.4) consists of two straight-lines segments joined at an angular hinge.
This hinge is the threshold and occurs at a value of about 17, the maximum value observed in the
model background data. As before, the use of the probability plot to divide the populations results in
the inclusion of some values from the anomalous population , but the effect on the estimated
background average is again insignificant. Indeed, the inclusion of these values changes the estimated
mean of background (defined as those data less than or equal to 17) from 9.6 to 9.8.
67
These two examples with model data demonstrate that different populations can be identified and
partially segregated by plotting the cumulative distribution of the sample on probability paper.
Segregation of the background and anomalous populations will always be partial because of the
possibility of overlapping. Overlap may introduce a certain bias, but this bias will remain rather small.
Rather recently, an innovative approach to separate geochemical anomalies from background was
proposed and tested, it is based on the use of fractals (Qiuming, Cheng, et al., 1994). Applications of
the fractal method to geochemical exploration were suggested by B|lviken et al (B|lviken, B. et al.,
1992). Fractals are shapes that look basically the same on various scales of magnification. They are
neither entirely regular, nor entirely random, and it may be said that fractal objects are “self-like” or
self-similar. This self-similarity is a type of symmetry that can be used to characterize disordered
geometric systems. However, the methods of fractal geometry can also be used to analyze nongeometrical objects, for example distributions in space (or time) of various types of observations or
measured values. Objects or phenomena that are created by stochastic processes where all length
scales have equal opportunity to be realized, become fractal.
According to B|lviken et al, geochemical distribution patterns may well belong to this type of
scale independent phenomena, since the processes causing such patterns have occurred throughout the
geological history of the earth, at any speed and at scales ranging from microscopic (chemical
reactions, crystal growth, melting, solidification, dissolution, precipitation, etc) to the size of
continents (river water transport, atmospheric transport, etc). Moreover, a vast amount of empirical
data shows that significant geochemical distribution patterns exist at a wide range of scales. Classes of
such patterns reflecting different scales of geochemical dispersion can be as follows: distribution of
elements in minerals as imaged by electron microprobe back-scatter X-rays – distribution of minerals
in thin sections – distribution of the contents of elements in drill cores – local to countrywide
distributions of the contents of elements in geological samples – metallogenic and geochemical
provinces at countrywide to continental scales. Major advantages of the utilization of the fractal
methods can be (1) establishing reliable criteria for a selection of geochemical anomalies detected in
low density surveys, and (2) improvement of cost efficiency in geochemical prospecting by systematic
follow-up investigations, working step by step increasing sample density within decreasing target
areas (B|lviken, B. et al, 1992).
Qiuming Cheng et al have analyzed lithogeochemical data (major oxides and trace elements)
from more than 1,000 surface samples in the Mitchell-Sulphurets precious-metal district (about 120
km2 in area) in British Columbia (Canada) using fractal and multifractal models. All samples were
analyzed for approximately 30 trace elements and 13 major oxides. Fractal models commonly result in
power-law relations between the variables of interest. Such relations plot as straight lines on log-log
paper. Therefore, log-log plots for element concentration-area were employed to separate
geochemically anomalous areas from background (Qiuming Cheng, et al., 1994).
0XOWLHOHPHQWDQRPDOLHV
The concept of multi-element anomalies is stated in Ovchinnikov’ monograph (Ovchinnikov,
1990). The formation of natural accumulations of chemical elements (ores) is a result of transition
elements from their dispersed forms into concentrated forms. In any process, significant amounts of
solutions participate extracting metals and their satellites from large volumes of primary sources.
Thus, many chemical elements become mobile, and the zone of their deposition occupies a space
which is usually much more extensive than the volume of ore bodies. Any deposit should be regarded
as a combination of an ore body and a multi-element halo around it. The ore body and its primary halo
which is a multi-element anomaly, make a whole unit, the difference between them concerns the level
of element concentrations.
According to the composition of their multi-element anomalies (haloes), all deposits can be
divided into three types: (1) deposits of lithofile elements (mainly, rare-metal pegmatitic, greisen,
apogranitic, skarn, metasomatitic) connected with acid magmatism and metasomatism; (2) deposits of
siderophile metals (mainly, magnetite and chromite); (3) deposits of a chalcophile group, which is the
vastest most various, including, besides copper and polymetals, genetically different types of deposits
of Au, W, Mo, Sn, fluorite, and others containing sulphides as admixtures.
Though geochemical spectra of haloes of these three major geochemical-genetic major types of
deposits differ significantly, there is a certain community in their element associations. Of all elements
68
presented in anomalies (haloes), the so-called “through-passing” elements have been identified. In
fact, eight indicator elements practically always behave as “through-passing” ones, they are observed
in haloes of all three types. This association is formed by three chalcophile elements (Cu, Zn, Pb), two
siderophile elements (Co, Ni), and three lithophile elements (Sn, Mo, Ba). Seven indicator elements
are present constantly in haloes of sidero- and lithophiles deposits: Sc, Ti, V, Cr, Y, Sr, Zr. Five other
elements – Be, Na, K, Bi, W – are observed simultaneosly in haloes of both litho- and chalcophile
deposits. Therefore, any geochemical halo, being a multi-element anomaly, includes numerous
enriched elements.
On the other hand, in all types of deposits, the formation of their primary haloes may be induced
not only by the supply of elements but also due to the evacuation of some other elements. Elements
with siderophile properties – Ti, V, Cr, Sc – are rather often carried out from the halo zone upwards.
From haloes of litho- and siderophile deposits, Ba, Sr, and Zr can be carried out as well, from haloes
of litho- and chalcophile deposits – B, from lithophile deposits – Cu, from siderophile deposits – V.
Thus, more than a dozen of elements may leave the anomalous zone of a halo.
As a quantitative measure of multi-element anomalies, multiplicative coefficients .P have been
proposed. They are products of the concentrations of enriched elements, for example, .P =
&Co&Ni&Zn&Cu. In order to make quantitative characteristics of multi-element more contrast, fractional
coeffocients may be used, their numerator is represented by a product of the concentrations of
enriched elements, and denominator – by a product of the concentrations of depleted elements, for
example, .P’ = &Zn&Cu&Pb/&Ti&Cr&V.
A new technique based on dry extraction of organic matter from soils to reveal secondary multielement superimposed haloes of deeply buried ore bodies has been reported in 1988 at the 4th AllRussian Conference “Theory and Practice of Geochemical Prospecting under Contemporary
Conditions” (Boev and Klos, 1988). It was described as follows. In areas overlapped by allochthonous
sedimentary covers, a vital activity of plant root systems is of significant importance in the formation
of superimposed secondary haloes of elemental dispersion. After atrophy of plants, the accumulation
of chemical elements occurs in not totally humified plant remnants, including root residues (Tkalich,
1970) that make up a significant part of humus horizon - an organic fraction of soils. In 1986 the
Central Expedition of the Geological Industrial Society "Ukrgeologiya" worked out a technique of
sufficiently complete dry extraction of an organic fraction of soils, which was called as DEOFSmethod (or soil-geochemical method). The application of this method is recommended for all "closed"
landscapes where sustained contacts of plant root systems with underground waters or with their
capillary margins have been identified.
The DEOFS-method was successfully tested at two sulphide and two rare-metal ore
manifestations. The clearest results have been obtained at a nickel-sulphide ore manifestations
accompanied by a gold-polymetallic mineralization. The use of the DEOFS-method provided to
observe the connection of primary haloes of mineralization with the surface through a sedimentary
cover having a thickness from 30 to 60 m. High-contrast multi-element haloes (about 8&EDFNJURXQG) of
Au, Ag, Ni, Cu and Mo were revealed, whereas the method of mobile forms (see 2.2.4) was capable to
provide only weak-contrast (2-3&EDFNJURXQG), mainly mono-element anomalies of those elements. As to
traditional lithogeochemical sampling, it did not show any anomalous concentrations of elements at
all. It is worth noting that anomalous concentrations of gold in samples used by DEOFS-method could
be measured by a rather insensitive analytical technique, such as semi-quantitative spectral analysis.
One of the reasons of it - a very weak influence of matrix effects (Boev and Klos, 1988).
'HWHFWLRQOLPLWV
The detection limit of an analytical method is a signal that can reliably be discerned above
background. Usually, supposing that there is a normal distribution of signals, the following
mathematical estimates of detection limits are used:
&min = 26bg (95% confidence), or &min = 36bg (99% confidence),
where 6bg – is the standard deviation of the background or blank measurements.
If the background signals follow Poisson’s law:
6bg = (&bg)1/2
where &bg the mean background.
69
Thus, it can be written
&min = 2(&bg)1/2 or 3(&bg)1/2, for 95% and 99% certainty, respectively.
(2.8)
Table 2-5 illustrates the capabilities of modern analytical methods to detect rare elements
occurring in rocks and soils in amounts close to their mean crustal abundances (Clarkes). Generally,
the elements having mean crustal abundances less than 200 ppm (0.02%) are considered as rare, so
Table www includes the elements following this concept (the summary of the Clarke values given by
Ovchinnikov in 1990 was used, see 2.1.1). The data concerning the values of detection limits
summarized by Ingamells and Pitard (1986) were used (see 2.2.3).
7DEOH$QDO\WLFDOPHWKRGVFDSDEOHWRGHWHFWUDUHHOHPHQWVSUHVHQWHG
DWWKHLUPHDQFUXVWDODEXQGDQFHV&ODUNHV
Abbreviations:
FAAS – Atomic Absorption, Flame
GFAA – Atomic Absorption, Graphite Furnace
HYAA – Atomic Absorption, Hydride Generation
CICP – Chemical Separation, Inductively Coupled Plasma
Spectroscopy
CSAA – Chemical Separation Atomic Absorption (FAAS or
GFAA)
CVAA – Cold Vapour Atomic Absorption
DCES – Direct-Current Arc Emission Spectrography
DCSW – Direct-Current Arc Emission Spectroscopy, Short
Wavelength
Elements
Li
Be
B
Cl
Sc
V
Cr
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Rb
Y
Zr
Methods
ICPS, FAAS
DCES, ICPS, CSAA
DCES, SP, DCQS
XRF, IC, ISE
DCES, ICPS, INAA
DCES, ICPS, GFAA, SP
DCES, ICPS, FAAS, XRF,
INAA
DCES, ICPS, FAAS, INAA
DCES, ICPS, FAAS, GFAA,
XRF, INAA
DCES, ICPS, FAAS, CSAA,
XRF
DCES, ICPS, FAAS, XRF,
DCSW, INAA
DCES, ICPS, RNAA
GFAA, RNAA
CSAA, HYAA, DCSW, INAA
INAA
INAA
DCES, ICPS, FAAS, XRF,
INAA, RNAA
DCES, ICPS, XRF, CICP
DCES, ICPS, XRF, INAA
Elements
Nb
Mo
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
Cs
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
DNAA – Delayed Neutron Activation Analysis
FA – Fire Assay Preconcentration (GFAA or DCES)
IC – Ion Chromatography
ICPS – Inductively Coupled Plasma Emission
Spectrometry
INAA Instrumental Neutron Activation Analysis
RNAA – Radiochemical Neutron Activation Analysis
SP – Spectrophotometry
XRF- X-Ray Fluorescence Spectrometry
Methods
DCES, ICPS, XRF, SP
DCES, ICPS, SP
RNAA
FA, RNAA
FA, RNAA
CSAA, RNAA
CSAA, DCSW, RNAA
RNAA
CSAA
CSAA, HYAA, INAA
RNAA
DCES, FAAS, INAA,
RNAA
DCES, ICPS, XRF, INAA,
RNAA
DCES, ICPS, CICP, XRF,
INAA, RNAA
ICPS, CICP
DCES, ICPS, CICP, INAA,
RNAA
ICPS, CICP, INAA, RNAA
CICP, INAA, RNAA
CICP, INAA, RNAA
CICP, INAA, RNAA
70
Elements
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Th
U
Methods
ICPS, CICP
CICP, INAA
ICPS, CICP
CICP, INAA, RNAA
DCES, ICPS, CICP,
INAA, RNAA
CICP, INAA, RNAA
INAA
INAA
INAA, SP
RNAA
RNAA
RNAA
RNAA
INAA, RNAA
CVAA
DCSW, CSAA
DCES, ICPS, CSAA
CSAA, HYAA, DCSW,
RNAA
ICPS, INAA, DNAA,
RNAA
INAA, DNAA, RNAA
3UHFLVLRQDQGDFFXUDF\RIDQDO\VHV
The following definitions are helpful in determining the terms of precision and accuracy
(Ingamells and Pitard, 1986).
• A measurement is unbiased when the mean (Pof the analytical error (AE) is equal to zero:
P(AE) = 0
•
A measurement is biased when the mean of the analytical error is not equal to zero:
P(AE) ≠ 0
•
A measurement is accurate when the absolute value of the bias P(AE) is not larger than a
certain standard of accuracy P(AE) regarded as acceptable:
P(AE) ≤P(AE)
•
A measurement is precise or reproducible when the variance of the analytical error σ2(AE) is not
larger than a certain standard of precision σ02(AE) regarded as acceptable:
σ2(AE) ≤ σ02(AE)
Depending on what is acceptable for P(AE) and σ02(AE), several sections of analytical methods
may have to be modified (e.g., sample weight, particle size, quality of standard reference materials,
etc.).
6WXGLHVRIUDUHDQGWUDFHHOHPHQWV
6SHFLILFIHDWXUHVRIDQDO\VLVIRUUDUHDQGWUDFHHOHPHQWV
In trace/rare element analysis, FRQWDPLQDWLRQ problems should be considered seriously, because
they can be of great importance. Some of the procedures that may be used in preparing samples for
analysis include washing, drying, crushing, sieving (grinding), preconcetration, wet or dry ashing,
dissolving, filtering, precipitation, etc. Opportunity exists for contamination during these processes, so
minimal treatment is best. That is why there is a tendency to develop sensitive instrumental techniques
applicable for trace and rare element determinations.
When estimating amounts to be analyzed, it is necessary to know how representative the sample
is of the bulk material to study. The requirement of UHSUHVHQWDWLYHQHVV is typical for sampling solids,
which are more or less heterogenous. Trace, rare, and ultra-rare elements can be distributed in rocks
and minerals in a very irregular manner, so the samples prepared should be representative as much as
possible. Of the three stage in an analysis – sample preparation, analysis, and data transfer – the last
two can be automated by various means, but sample preparation remains the operation requiring time
and labor. Such operations as grinding and screening are especially time-consuming, so it is desirable
to minimize them.
The problem of representativeness of samples was studied in detail, there are several sampling
theories, all they depend on the same statistical principles but differ in emphasis and applicability.
Pierre Gy has developed sampling theory and promoted its application in geochemical issues (Gy,
P. 1967) He proposes that the sampling characteristics of a granular material containing a small
proportion of a valuable component, ;, depend on (1) the shape of particles, (2) the distribution of
particle sizes, (3) the mineralogical composition of each of the phases in a two-phase mixture, and (4)
the degree to which ; is liberated from the gangue. Correspondingly, Gy’s sampling constant * is the
product of the four following factors:
(1) a shape factor I, equal to 1.00 if all particles are perfect cubes, and I is the ratio of particle
volume to that of a cube that will just pass the same screen;
(2) a particle size distribution factor J, equal to 1.00 if all particles are the same size, and the
larger the proportion of fine particles, the lower the value;
(3) a mineralogical composition factor P = (SZG+TZG//TZ, where G+ and G/ are the densities of
ore mineral and gangue, respectively, and TZ = 1 − SZ is the weight proportion of the valuable
constituent (or indicator element) ;;
(4) a liberation factor E related to the proportion of ore mineral liberated from gangue,
approaching 1.00 as liberation becomes complete during the reduction process.
71
Gy describes experimental methods for estimating each of these four factors and thereby the
sampling constant *When * IJPE has been estimated for a specific material, the uncertainty in a
Z-gram sample or subsample is
±S5 =(*X¶3/Z)1/2
(2.9)
where 65 = 6/. is the absolute uncertainty divided by the true ; content, ., of the mixture, and X¶ is
the linear dimension of the largest particles, that is, the linear dimension of the screen mesh that will
pass 95% of the particles. Hence, Gy’s sampling theory permits to calculate the sample or subsample
weight required for any desired uncertainty 65:
Z= *X¶3/652
(2.10)
The product *X¶ may be estimated by repetitive assay of a granular material, avoiding a need to
find the individual factors IJPand E:
*X¶3 = Z652
where Zis the weight of each sample used in the exercise, and 65 is the relative standard deviation of a
sufficient number of assays.
Ingamells and Switzer introduced a sampling constant .V,as a measureof the sampleability of a
well-mixed granular material. They proposed to determine this measure as the weight necessary for a
1%, defined by (in grams):
3
.V = 52Zor Z = .V/52
(2.11)
where 5 (in percent) is the relative uncertainty in a Z-gram sample or subsample, related to Gy’s 65
and the standard deviation in a sufficient number of assays each using a Z-gram sample:
5 = 1006/. = 1065(.V/Z)1/2
(2.12)
Ingamells’ and Switzer’s approach depends on the following proposition: The sampling characteristics
of any mass of material may be duplicated, for a single constituent ; in a hypothetical mixture of
uniform cubes of two minerals of ; contents +and / percent and densities G+ and G/, respectively
(Ingamells and Pitard, 1986). Ingammel and Switzer have shown that, for heavy metal ores,
.V = [104(.−/)(+−/)X3G+]/.
(2.13)
where .is the overall ;content (in percent) and X is the volume of a hypothetical cube. Thus, .V may
be estimated either by repetitive determination or from physical characteristics of the material
sampled.
In order to illustrate the dependence between sample weights and sampling uncertainty in the case
of determination of one of trace elements – molybdenum, Table 2-6 shows the calculated sample
weights necessary for 1% sampling uncertainty (;= the mean ±668% confidence) for molybdenite
ores and products at various mesh sizes. These weights are the sampling constants .V for these mesh
sizes.
3
7DEOH&DOFXODWHGVDPSOHZHLJKWVQHFHVVDU\IRUVDPSOLQJXQFHUWDLQW\
,QJDPPHODQG6ZLW]HU
MoS2 content (%)
1.0
0.1
0.01
0.001
Sample weight for 1% error (g) by mesh size (effective mesh size of MoS2
in the sample)
No 35
No 100
No 200
2.4
16
360
24
160
3,600
240
1,600
36,000
2,400
16,000
360,000
If a higher sampling uncertainty is acceptable, the necessary sample weight may be calculated from
the above-cited formula Z = .V/ 52, where 5 is the acceptable uncertainty. If, for example, a 10%
sampling uncertainty is acceptable, only .V/100 grams need to taken.
72
)DFWRUVLQIOXHQFLQJRQTXDOLW\RIJHRFKHPLFDOPHDVXUHPHQWV
Development of instrumental methods is associated with difficulties due to matrix effects and
interferences. Both the former and the latter are related to the specificity of the method. The matrix
effect is relevant, in particular, when calibrating an instrument, as often the calibrant is not the same
matrix as the samples. Interferences may be chemical or instrumental. A chemical interference takes
place when one species inhibits or enhances the signal from another, because of chemical (or physical)
interactions. Instrumental interferences are induced by the inability of an instrument (which can be
presented by a spectrometer) to resolve signals from two separate species.
Factors to be considered when selecting an analytical method are as follows:
• capability for determining as many elements as possible;
• high sensitivity for many elements;
• good precision and accuracy;
• simplicity of operations and maintenance;
• suitable speed of determinations;
• freedom from interferences;
• capability to be amenable to a high degree of automation by using procedures for automatic data
acquisition and data reduction;
• possibility to execute field measurements;
• relatively low purchase and maintenance costs.
Sure, some of these requirements are in contradiction – for example, high sensitivity and good
precision are incompatible with low prices for element determinations.
0HWURORJLFDOSDUDPHWHUVRIPRGHUQPXOWLHOHPHQWDQDO\WLFDOPHWKRGV
Sensitivity, precision, and accuracy are major PHWURORJLFDO SDUDPHWHUV of every analytical
method. These parameters are of special importance in determining rare and trace elements. The term
“VHQVLWLYLW\” is a general term for the lower limits of measurement for a given analytical test and is
most often expressed as either a “detection limit” or “determination limit”. The detection limit is the
minimum concentration of analyte required for a positive decision that an analysis indicates a
qualitative detection. The determination limit is a higher level of concentration that will give a
satisfactory quantitative result with a given standard deviation (such as ± 10%). Both estimates are
dependent on the analytical “noise” associated with the measurement above the background or “blank”
level for a given analytical procedure. For multi-element analytical methods, the sensitivity limits are
often matrix dependent and, therefore, may vary from sample to sample. In geochemical studies,
sensitivity must provide determination limits that are lower than the concentration values
corresponding to local geochemical background. Another criterion is to obtain determination limits
that are lower than average abundances in the earth crust (Clarke values).
3UHFLVLRQ is a measure of the consistency of results, i.e. how close they agree with each other,
even though they may not be very accurate. $FFXUDF\ is a measure of the closeness of a result to the
true result.
Table 2-7 presents determinations limits of trace and rare elements provided by modern methods
of silicate rock analysis taken from the summary made by Baedecker (Baedecker, 1987). In order to
illustrate their sensitivity, the Clarke values for the earth crust (summarized by L.N.Ovchinnikov in
1990) are also indicated.
7DEOH'HWHUPLQDWLRQOLPLWVRIWUDFHDQGUDUHHOHPHQWVIRUGLIIHUHQWPHWKRGVRIVLOLFDWHURFNDQDO\VLV
LQPLFURFUDPVSHUJUDPRUSSP%DHGHFNHULQFRPSDULVRQZLWKDYHUDJHDEXQGDQFHVLQFUXVWDO
URFNV&(&2YFKLQQLNRY
Methods:
FAAS – Atomic Absorption, Flame
GFAA – Atomic Absorption, Graphite Furnace
HYAA – Atomic Absorption, Hydride Generation
CICP – Chemical Separation, Inductively Coupled
Plasma Spectroscopy
CSAA – Chemical Separation Atomic Absorption
(FAAS or GFAA)
DCES – Direct-Current Arc Emission Spectrography
DCSW – Direct-Current Arc Emission Spectroscopy,
Short Wavelength
73
DNAA – Delayed Neutron Activation Analysis
FA – Fire Assay Preconcentration (GFAA or
DCES)
ICPS – Inductively Coupled Plasma Emission
Spectrometry
INAA Instrumental Neutron Activation Analysis
RNAA – Radiochemical Neutron Activation
Analysis
SP – Spectrophotometry
XRF – X-Ray Fluorescence Spectrometry
Lithofile elements
Ti
V
Cr
Mn
Rb
DCES………1
ICPS……..…2
INAA……..0.01
Sc
DCES……….30
ICPS……….100
XRF………..200
SP……………10
DCES…………1
ICPS…………..2
GFAA………0.2
SP………..…..10
DCES……….1
ICPS………..1
FAAS………4
XRF……….20
INAA……….1
DCES……….1
ICPS……….10
FAAS……….5
XRF………200
INAA…….….1
&(& &(& &(& Cs
&(& DCES………..3
ICPS………100
FAAS………..4
XRF………….2
INAA………..5
RNAA……0.05
DCES……..3
FAAS
.4
INAA……0.1
RNAA……0.001
DCES………..1
ICPS…………1
FAAS…..…..20
XRF………….5
INAA……..100
RNAA….…0.05
Sr
Zr
DCES………..1
ICPS…………2
FAAS………..5
XRF………….2
INAA……….50
RNAA……..0.2
DCES………3
ICPS………..5
XRF………...5
INAA……...100
Sm
Eu
DCES……….10
ICPS……….50
CICP……….0.1
INAA……...0.5
RNAA……5⋅E−4
DCES……..….2
ICPS………….2
CICP………0.01
INAA……..0.02
RNAA……1⋅E−4
&(& &(& &(& &(& Ba
&(& Tb
&(& DCES……….30
ICPS……….20
CICP……….0.4
INAA……...0.1
RNAA……1⋅E−4
DCES…………1
ICPS…………..1
CICP………0.05
INAA……....0.2
RNAA……0.005
Yb
&(& &(& &(& La
&(& Ce
DCES……….10
ICPS………….2
XRF…………..5
CICP……….0.1
INAA…….0.02
RNAA……0.001
DCES……….40
ICPS………….4
XRF…………..5
CICP……….0.1
INAA………0.5
RNAA……0.005
&(& Th
&(& U
DCES……….50
ICPS…………4
INAA………0.1
DNAA…….…1
RNAA……0.001
DCES………500
ICPS……….100
INAA…….…0.5
DNAA………0.1
RNAA…….0.001
&(& &(& Siderophile elements:
(Mo, W and Re sometimes can behave as lithofile elements
Co
DCES………..1
ICPS…………1
FAAS………..6
INAA………0.2
&(& Ni
Mo
Ru
Rh
Pd
DCES…………1
ICPS…………..2
FAAS…………4
GFAA…………1
XRF…………..2
INAA………..50
DCES……….1
ICPS………..2
INAA……..10
SP.……….0.05
DCES………2
ICPS………30
FA………...0.1
DCES……….1
ICPS……….10
FA………0.002
DCES………1
ICPS………20
FA…….0.001
RNAA…1⋅E−4
&(& W
Re
DCES…….20
INAA…….0.1
SP………..0.1
DCES….10
ICPS…..10
RNAA..…1⋅E−6
&(& &(& &(& Os
&(& DCES….……20
ICPS………..30
RNAA..…5⋅E−6
DCES………20
ICPS………..20
FA………..0.02
INAA…….0.01
RNAA……1⋅E−6
&(& &(& Ir
&(& Pt
DCES….20
ICPS…..30
FA……0.01
&(& &(& Au
ICPS……….4
FA………0.05
CSAA……0.1
DCSW……0.2
INAA….0.005
RNAA…1⋅E−6
&(& Chalcophile elements: (sometimes Sn can behave as a lithofile element)
Cu
DCES………..1
ICPS…………1
FAAS……...10
CSAA……..0.8
XRF…………2
&(& Zn
DCES……….10
ICPS………….4
FAAS………...1
XRF……….…2
DCSW……0.01
INAA…….…..1
&(& As
DCES………100
ICPS…………10
CSAA……….0.1
HYAA………0.1
DCSW………...1
INAA………….1
&(& Sb
Te
DCES………5
ICPS………..4
CSAA………1
DCES…….100
ICPS………..70
CSAA……...0.1
HYAA…….0.2
DCSW……….1
INAA………0.1
DCES……1000
ICPS………..30
CSAA…….0.02
DCSW……….1
RNAA……0.001
&(& Ag
Cd
DCES………0.1
ICPS…………2
FAAS………..2
CSAA…….0.01
RNAA……1⋅E−5
DCES……….30
ICPS………....2
FAAS………..1
CSAA…….0.02
DCSW……...0.1
RNAA……1⋅E−5
&(& Sn
&(& Se
DCES………200
ICPS…………20
CSAA……….0.1
HYAA………0.1
DCSW………...5
INAA………….1
Hg
&(& DCES……1000
ICPS………..70
CVAA..…..0.02
DCSW………..1
&(& 74
&(& Pb
DCES………7
ICPS……….4
FAAS……..20
CSAA…….0.5
&(& &(& Bi
DCES……….10
ICPS………..10
CSAA…….0.01
HYAA……0.03
DCSW…….0.1
RNAA……5⋅E−5
&(& 'LUHFW&XUUHQW$UF(PLVVLRQ6SHFWURJUDSK\DQG6SHFWURPHWU\'&(6DQG'&6:PHWKRGV
In general, low part-per-million concentrations of most naturally occurring elements can be
measured for arced samples ranging in mass from 10 to 20 mg. Only solid-phase samples can be
analyzes conveniently by this technique, and these samples are finely pulverized (100-200 mesh)
rocks, minerals, soils, ashes from plants, etc. All analyses by this method are based on comparisons of
measured spectral signals between samples and standards. Therefore, good, naturally occurring or
synthesized reference materials are essential to high-quality analyses. Quantitative analyses that are
accurate within ± 10% can be achieved routinely by available metods for up to 55 elements (Golightly
D.W et al, 1987).
,QGXFWLYHO\&RXSOHG3ODVPD(PLVVLRQ6SHFWURPHWU\,&36PHWKRG
The ICPS technique is capable to determine most elements at trace (2-100 ppm), minor (0.010.5%), and major (greater than 0.5%) concentrations. The sample first must be dissolved and presented
to the instrument as a solution. Water solutions can be analyzed directly or after preconcentration. Up
to 44 elements can be determined simultaneously as a semiquantitative analysis. The sensitivity of the
ICPS methods varies with every element, and not all elements are compatible in a single solution. For
many elements, the detectability is adequate to measure concentrations at the crustal abundance level.
A fundamental limitation of the ICPS method arises from its greatest asset. The excitation energy
of the plasma is high enough to excite ground state and ion electron transitions for most elements.
Thus, for typical instruments employing optics of moderate dispersion, the opportunity for spectral
overlap from other elements in the sample is much greater than from less energetic sources, such as
the direct-current arc. The spectral overlap contribution from each element can be corrected
mathematically. Nevertheless, the degree of overlap and the concentration of the interfering element
combine to deteriorate the limit of detection. For example, measurement capabilities for Rb and Cs are
limited because of poor sensitivity.
The ICPS method is highly precise. The instrumental precision of measurements for
concentrations well above detection limits can be characterized by 1-2% relative standard deviation.
However, this value should be considered as an optimal limit of precision. In most cases, sampling and
dissolution stages limit the precision., so the precision of routine measurements is between ±5 and 10
% relative standard deviation. High temperatures of the plasma greatly reduce the effects of matrix
elements on the slope of calibration curves, so for most samples, the accuracy of the analysis is nearly
equal to the precision. However, because standardization of the ICPS is based on the using of
reference materials, and dissolution of their minerals is very important, those materials should match
the mineral content and the major, minor, and trace element concentrations (Lichte F.E., 1987).
$WRPLF$EVRUSWLRQ6SHFWURPHWU\0HWKRGV)$$6*)$$+<$$
The AAS method has become one of the most widely used techniques for determining major,
minor and trace elements in geologic materials. It is routinely used for the determination of 35 metallic
elements with a precision in the 1fange from 1 to 10% relative standard deviation range. Its major
advantages are: (1) capability for determining about 70 elements; (2) rather high sensitivity for many
elements; (3) comparatively good precision and accuracy; (4) simplicity of operations and
maintenance; (5) speed of determinations; (6) relative freedom from interferences; (7) relatively low
purchase and maintenance costs.
At the same time, the AAS method has the following limitations: (1) the technique is not useful
for determining nonmetals; (2) the refractory elements are determined with poor sensitivity; (3)
simultaneous multi-element analysis is not practical; (4) the precision is generally poorer than in other
modern methods (Aruscavage P.J. and Crock J.G., 1987).
;5D\)OXRUHVFHQFH6SHFWURPHWU\
X-ray fluorescence (XRF) methods are classified on the basis of two alternate methods of X-ray
spectral analysis – X-ray dispersion by crystal diffraction, or wavelength-dispersive X-ray
fluorescence, and semiconductor detectors converting X-ray spectra into electrical signals, or energydispersive X-ray fluorescence. The former methods provides comparable precision and accuracy to
traditional wet chemical methods fot the determination of major elements in rock and mineral samples
and is also applied to the determination of minor and trace elements, where the higher resolution of
wavelength-dispersive instrumentation is required to eliminate or reduce spectral interferences. The
XRF method is regarded by the majority of earth scientists as the technique preferred for determining
the major and minor rock-forming elements in bulk rocks and mineral separates, namely Na, Mg, Al,
Si, P, K, Ca, Ti, Mn, and Fe, because it provides higher precision and accuracy than alternative
methods.
75
The advantages of the XRF method are: (1) X-ray emission spectra are simple and orderly; (2) Xray spectra are relatively independent of chemical state; (3) X-ray excitation and absorption vary
uniformly with atomic number; (4) absorption and enhancement effects are predictable; (5) spectral
line interference is relatively infrequent; (6) sample preparation can be nondestructive; (7) specimen
form can be solid, powder, paste, liquid, or gas; (8) good precision and accuracy can be attained; (9)
sample preparation and analysis times can be relatively fast and are not usually labor intensive. The
disadvantages of the XRF method are: (1) sensitivity for low atomic number elements is poor; (2)
sensitivity for low abundance levels is poor without preconcentration procedures; (3) interelement
effects acting within the sample must be recognized and corrected; (4) numerous standards are
required; (5) initial cost of equipment is relatively high (Taggart Jr., J.E. et al, 1987; Johnson R.G. and
King B.-S.L., 1987).
,QVWUXPHQWDO1HXWURQ$FWLYDWLRQ$QDO\VLV,1$$
INAA with thermal or epithermal neurons is a well-tested method for the determination of over
30 elements in rock samples. The method is based on the irradiation of samples and standards in a
reactor neutron flux and the measurement of the induced radioactivity using high-resolution gammaray spectrometry. The method has good sensitivity (0.1–10 ppm) for a wide range of elements,
including many of the first-row transition elements, rare earths, alkali, and alkaline earths.
The estimation of detection limits for INAA is subject to considerable uncertainty because it is
dependent on the signal to background ration for each photopeak of each sample being counted and on
the characteristics of the detector employed. The detection limits, therefore, are dependent on sample
composition (the data presented in Table 2–7 are for samples of silicate rocks).
There are limitations in INAA induced by factors affecting both precision and accuracy. Major
factors affecting precision are: (1) nonuniform distribution of the neutron flux across the sample
irradiation position; (2) nonreprodicible positioning of the sample during counting; (3) errors due to
poor counting statistics and to photopeak baseline selection during photopeak integtration. Among
factors affecting accuracy are the following: (1)interfering nuclear reactions on other elements that
yield the same indicator radionuclide; (2) gamma-ray spectral interferences; (3) self-shielding, i.e. an
attenuation of the neutron flux by the sample; (4) dead-time errors, they occurs during gamma-ray
counting when the activity of the sample differs considerably from that of the standard.
INAA is amenable to a high degree of automation by using procedures for automatic data
acquisition and data reduction. INAA is not a rapid method, a single analysis may take 2 or 3 months
to complete because optimum results are achieved by counting the samples at various times during the
decay of radionuclides induced in the sample (Baedecker P.A. and McKown D.M., 1987).
'HOD\HG1HXWURQ$FWLYDWLRQ$QDO\VLV'1$$
The DNAA method is used for measuring uranium and thorium in a complex sample matrix
without chemical processing. It is a rapid methods, generally applicable for routine analysis of a wide
variety of geological materials, including most common silicate rocks, soils, and some moderately
mineralized materials that exhibit a Th/U ratio greater than 3. Determination limits are of about 0.1
ppm for U and 1 ppm for Th. Analytical precisions of about ± 5% for U and 10% for Th may be
achieved if U and Th concentrations are greater than about 1 ppm and 10 ppm, respectively (McKown,
D.M. and Millard, Jr. H.T., 1987).
5DGLRFKHPLFDO1HXWURQ$FWLYDWLRQ$QDO\VLV51$$
The technique of RNAA provides ultimate sensitivity for neutron activation analysis by removing
the matrix interferences that result in higher determination limits for the instrumental method. It
provides excellent results for favorable elements at levels that are inaccessible to most other methods.
Removal of major activities following neutron activation also makes the method capable to determine
more elements than are detectable by INAA. The precision and accuracy of RNAA for nearly all
measured elements is between 1 and 10%. Precision usually decreases as elemental concentrations,
mainly due to poor counting statistics. RNAA is a labor-intensive technique that limits the number of
samples that can be analyzed (Wandless, G.A. 1987).
0HWKRGVWRLGHQWLI\PRELOHDQGZHDNO\ERQGHGIRUPVRIHOHPHQWV0:%(
Exploration for deeply buried mineralization without any manifestation at the surface (“blind” ore
deposits) stimulated the development of innovative analytical methods and instrumentation. Very
76
important success has been achieved using a relatively new approach consisting in the selective
exrtraction of mobile and weakly bonded forms of elements (MWBE) from soil and air (including air
within the soil profile). Studies commenced in the former USSR in the 1960s, more recently the
methods developed by Russian scientists have been field-demonstrated in other countries such as
China, Canada, Australia and the U.S.A. Numerous anomalies revealed by the MWBE methods for
particular forms of occurrence of elements in soils at the surface, above mineral deposits located at
depths of up to 500 m or more, were described (Antropova et al., 1992; Goldberg, 1998).
The MWBE methods include the following techniques.
• A technique based on the use of organically bound forms of elements, when the fulvate-humate
fraction of the soil is analysed (MPF);
• A thermomagnetic geochemical technique based on the selective extraction of mobile elements
from iron and manganese oxides and hydroxides present in the soil (TMGM);
• An electrogeochemical technique of partial extraction of mobile elements. Electrodes placed in the
soil cause mobile elements to migrate to one of the electrodes where they enter the “element
collectors”. The element collector has a porous base, and contains an electrolyte surrounding the
sample (CHIM);
• A technique using the extraction of mobile elements from the soil by diffusion. “Element
collectors” containing an electrolyte are placed in the soil for a period of time. The electrolyte
becomes the sample, and is analyzed for MWBE (MDE).
In the MPF method, in order to extract fulvic-humic complexes (FHC), a selective solvent,
sodium pyrophosphate, is used. Sodium pyrophosphate also dissolves sorbates and water-soluble
compounds, but these are present in insignificant quantities in comparison to the amount of trace
elements in organic complexes. For a quantitative assessment of the amount of organic matter which is
contained in the pyrophosphate extract, organic carbon is determined. The concentration of a trace
element (&Me) is expressed relatively to the amount of organic carbon (&C), by the ratio &Me/&C. These
ratios show the concentrations of trace elements collected in FHC independently of the quantities of
fulvates and humates. Normalizing to organic carbon is helpful to eliminate errors arising from
incomplete humate and fulvate extraction, and allows determinations with partial extraction of FHC
from soils. To determine trace element amounts, different types of analysis (spectral, X-ray, or others)
may be carried out that are capable determinations in the range from several thousands ppm to one ppb
and less. Elements determined include Zn, Pb, Cu, Ni, Co, Sn, W, Bi, Sb, As, Ga, Ge, Mo, Ag, Cr, V,
Be, Y, Yb, Au, and C.
In the TMGM method, in order to extract mobile elements associated with iron and manganese
oxides and hydroxides (ferrimanganese forms) primary magnetic minerals are first removed and the
sample fired under reducing conditions. In the firing process, the secondary iron-bearing minerals are
reduced to strongly magnetic compounds (magnetite, maghematite, wustite) which can be extracted
from samples by magnetic separation. The extracted thermomagnetic fraction is analyzed for a wide
range of elements using spectral, X-ray or other methods.
In the CHIM method, the elements are extracted into a special receiver (collector) consisting of a
cylindrical polyethilene vessel with a capacity of 40 to 50 ml, covered on one end with an ion
permeable membrane made of parchment, into which is put an electrode and electrolyte solution
(HNO3). Extractions of ions into the element collector can be done in either cathode or anode mode.
Currently, there are cathode extraction modes for Au, Pb, Cu, Zn, Fe, Ni, Co, Sn, and an anode
extraction mode for Mo. The special CHIM station with many (up to 40) element collectors provides
simultaneous extraction of electromobile forms of elements into these collectors that can be placed
along a profile or distributed over a chosen site. Element collectors are usually spaced 20 m apart but
this may vary depending on the problem being addressed.
MWBE results obtained by geological organizations in the former USSR confirmed the potential
of new methods and their effectiveness in locating deep-seated mineralization buried beneath
unconsolidated overburden in excess of 150 m and bedrock in excess of 500 m. Deeply buried and/or
blind ore bodies can be traced at surface on the basis of trace element anomalies when the elements are
in easily mobile and weakly bonded forms of occurrence. It was demonstrated that these new methods
can be applied to exploration of various types of mineralization: copper-nickel, porphyry copper,
polymetallic, rare-earth elements, gold, and others (some case studies are given in 2.2.4).
Mineralization can be located under significant thickness of unconsolidated overburden regardless of
the age and composition of overburden. Trace element anomalies can be revealed for mineralization
beneath very permeable overburden and dense clay (for example, Quaternary moraines, river
alluviums, glaciolacustrine sediments). These anomalies over deeply buried mineralization can be
traced under different landscape-climatic situations: permafrost, swampy and boggy, arid and semiarid landscapes, etc.
77
It is worth noting that the similarities in the results obtained by the MWBE techniques within a
variety of geological and natural settings illustrates the universal character of the phenomena which
give rise to the formation of geochemical haloes at great distances above buried and blind ore bodies.
Anomalies obtained differ in a number of features: (1) they are located over the head of deep-seated
mineralization and have a local character; (2) the width of an anomaly depends on the depth of of
occurrence of mineralization to a small extent and, as a rule, does not exceed the width of the ore body
by more than 2-3 times; (3) the magnitude of the anomalies in weight and concentration of elements
within the same geochemical landscape is independent of the depth of occurrence of the ore body.
The local character of the detected anomalies suggests the presence of channel ways through
which fast migration and streaming of elements happens over great distances from depth to surface. In
some cases, such streams are observed as anomalous quantities of the mobile occurrence forms of
elements in the transported sediments covering the mineralization (Antropova L.V. et al, 1992).
In general, MPF and TMGM provide broader and less contrasting anomalies than those defined
by CHIM and MDE. Of the latter two methods, CHIM produces anomalies which are the more local
and contrasting. Therefore, the former two techniques are usually used at a preliminary (regional)
stage of exploration, whereas the latter two are applied for detailed investigations. The CHIM and
MDE methods appear to describe the behaviour of the most mobile form of the occurring element, and
can be presumed to be more closely connected with the primary source of the metal at depth. The
spatial relationship of weakly bonded forms (adsorbed onto organic matter, certain metal-organic
complexes, adsorbed onto oxides and hydroxides of Fe and Mn, etc) with sources of metal are more
complicated. This may be related to the lateral migration of the mobile forms of metals and their
interaction with the soil.
Thus, there is considerable evidence, supported by special field experiments, of vertical mobile
element migration over long distances through the geological environment. The velocity of this
migration was the subject of investigations at several sites. MWBE anomalies for Cu, Ni, and Co have
been located by the CHIM and MPF methods in surficial materials above Cu-Ni deposits in the Kola
Peninsula, Russia (Antropova, L.V., 1975) The host rocks are covered by well-dated moraines up to
100 m thick. As the age of the moraines is about 10,000 years, the velocity of mobile metal migration
must be not less than 1 cm per year. This value is much greater than would be expected using a
diffusion coefficient of 10−6 cm2⋅s−1 determined for this rocks (Zaraysky and Balashow, 1983, see
Goldberg, 1998), which would allow a diffusion front to advance at a rate of only about 2.5 cm per
10,000 years or 2.5⋅10−2 cm per year, two orders of magnitude less than based on the age of the
moraine. Thus a mechanism other than diffusion (though it is not yet well understood) was suggested
(Goldberg, 1998).
MWBE anomalies seem to occur regardless of the mineral composition, age, genesis, or
morphology of their source deposit (several case studies are given below). These anomalies also
appear regardless of the nature and composition of the deposit’s host rocks, their physical properties,
tectonic disturbance, moisture content, or the presence and nature of younger overlying rock or
uncosolidated material. The fact that MWBE occur despite the differences in conditions of the ore
body and host rocks suggests that vertical mobile element migration does exist, and can be used for a
variety of geological situations (Goldberg, 1998). Anyway, the mobile metal ion techniques become
applicable to routine geochemical exploration (Mann, A.W., 1998).
&DVHVWXGLHV
As it was said before, the CHIM and MDE techniques may reflect the influence of the most
mobile forms of elements and can be more closely connected with the primary source of the elements
at depth. That is why just the cases concerning the application of the CHIM and MDE methods will be
considered (Goldberg, 1998).
Fig. 2.5 shows CHIM results over Sn ore stockwork in Kavalerovo ore region (the Far East of
Russia). The host rocks are present in the form of migrating sandstone and argillite of Tertiary age.
The ore bodies are represented by quartz veins and veinlets with cassiterite and arsenopyrite. The ore
stockwork is intersected by boreholes at a depth of 800 m. In the upper part of the section, small
quartz-cassiterite veins make an appearance. A local anomaly of an electro-mobile form of Sn is
situated directly over the stockwork (Fig. 2.5, F). For comparison, the results of the spectrographic
analysis of the soils and rocks (taken immediately under the soil) are also shown (Fig. 2.5, D and E).
The ore body is manifested as a clear Sn CHIM anomaly detected directly above. The anomaly is
approximately 25 m wide, with an intensity of up to 17 µg of Sn with a background extraction of 0.61.5 µg.
78
)LJXUH. CHIM traverse over Sn deposit in Kavalerovo ore region in the Far East of Russia:
(D) - soil; (E) - rock; (F) - CHIM; 1 - overburden; 2 – argilite and sandstone; 3 – Sn ore stockwork;
4 – Sn ore veinlets; 5 – shear zone (Goldberg, 1998).
Mann states (Mann, 1995) that the results the results of any mobile metal ion (MMI) method,
including CHIM, can be interpreted in the framework of a new conceptual model for the formation of
geochemical soil anomalies. According to this model, a dynamic balance exists between unbound and
bound metals in the A and B soil horizons and there are three fundamental processes responsible for
the formation of geochemical anomalies in weathered terrains: I – issue of unbound metals to the soil
layer; II – creation of bound metals from unbound metals; III – lateral dispersion of (bound) metals.
This model differs from previous interpretations in that the initial weathering fluids containing
unbound metals are considered to be located close to source, and it is the bound form of metals which
is further (mechanically) dispersed. The process I may occur by either hydromorphic weathering of
79
mineralized rocks, or by gaseous transport of metals expelled from rocks to the surface, or by a
combination of both.
The works of Malmqvist and Kristiansson (1984) and Antropova et al (1992) suggest that gaseous
emanation of metals may be responsible for geochemical anomalies in snow and soil. Interestingly,
that Smith et al., describing their studies of the CHIM electrogeochemical method in Kokomo Mine in
Colorado, noted that similar anomalies could be observed when the operating current of the CHIM
technique was switched off, it means that the anomaly was inherent in the soil profile and could be
assessed by application of acid. Also Mann et al cite the work of Chao (1984) who argued that any
extractant may in fact derive metals from a variety of phases within the soil. They conclude that
different methods reveal at least one common factor – the existence at any time of a supply of easily
leachable, unbound or mobile metals in the soils.
It is worth adding that Goldberg affirms that a fixed anomaly of Sn (see Fig. 2.5) is indeed
connected with a Sn-ore stockwork, not with Sn-ore veinlets placed above, though the figure shows
that these veinlets could be also responsible for the formation of the anomaly. Antropova and coauthors give another example of anomalies over a Sn-bearing zone covered by unconsolidated
sediments (clays) Anomalous concentrations of Sn, Sb, Pb and Ag have been observed using not
CHIM, but TMGM (thermomagnetic) method which allows to reveal secondary iron and manganese
complexed forms of the occurrence of ore elements (Antropova et al, 1992)..
Fig. 2.6 presents the CHIM results of measurements above a copper deposit, represented by
massive volcanogenic sulphides.
)LJXUH. CHIM traverse over Cu deposit in Kasakhstan. 1 – overburden (clay); 2 – effusive tuff;
3 – Cu ore body; 4 – boreholes (Goldberg, 1998).
80
The intensive anomaly for the electro-mobile form of Cu is manifested directly above the head of
the ore body. Palaeozoic sedimentary-volcanic rocks host the ore body which is seated at a depth of
about 200 m and covered with clay overburden.
In some exceptional cases, additional anomalies of mobile metal forms appear alongside faults
near ore deposits. Fig. 2.7. (3) shows an example of such a complex anomaly above an electro-mobile
gold-quartz deposit in Uzbekistan.
)LJXUH. CHIM traverse over Au deposit in Uzbekistan (Goldberg, 1998). 1 – loess; 2 – tuff; 3 – coarse
sandstone; 4 – porphyry; 5 – limestone; 6 – porphyritic granodiotite; 7 – fault; 8 – Au ore body; 9 – CHIM
profile (averaged); 10 – CHIM profile (single line); 11 – CHIM anomaly (background shown by dashed line).
The Au deeply buried ore body is of a telluride type. The CHIM anomaly has an intensity of up to
2 micrograms with a background extraction of 0.3 micrograms.
The next figure demonstrates the distribution of a lead MWBE anomaly obtained by the MDE
method. Fig. 2.8 shows a Pb anomaly traced with the MDE technique over a polymetallic deposit
overlain by allochthonous clays 80-100 m thick. When the distance between measurement points is
50 m, the anomaly is marked by a single data point (Fig. 2.8, a, D).
81
)LJXUH. MDE traverses over Pb-Zn deposit, Rudny Altai, Russia (Goldberg, 1998).
a – Effect of changes in the sampling interval; 1 – loam; 2 – clay; 3 – siltstone; 4 – quartzite; 5 – pyritic argilite;
6 – argilite; 7 – ore body; 8 – MDE profiles: sample interval D = 50m; E = 20 m; F = 5 m.
b – Effect of differences in sampling depth below surface line: AB – surface; CD – 0.5 m; EF – 1m; GH – 2.5 m.
82
When the distance between measurement points is 20 m, it is represented by three points comprising
two peaks (Fig. 2.8a, E). When the distance between measurement points is 5 m (Fig. 2.8a, F), the
anomaly is represented by many points and an additional peak is added. The width of the anomaly
decreases with depth (Fig. 2.8b, sampling made at 0, 0.5, 1 and 2.5 m), but its intensity is maintained
(Goldberg I., 1998).
%LEOLRJUDSK\
Antropova, L.V. 1975. Occurrence Forms of Ore Elements in Dispersion Haloes of Ore Deposits.
Leningrad: Nedra (in Russian).
Antropova, L.V. et al. 1992. New Methods of Regional Exploration for Blind Mineralization:
Application in the USSR // -*HRFKHP([SORUDWLRQ. V.43, pp.157-166.
Aruscavage P.J. and J.G. Crock. 1987. Atomic Absorption Methods // 86 *HRORJLFDO 6XUYH\
%XOOHWLQ 1770, pp. C1-C6.
Baedecker, P.A. 1987. Introduction. Methods for Geochemical Analysis. // 86 *HRORJLFDO
6XUYH\ %XOOHWLQ 1770, pp. IN1-IN3.
Baedecker, P.A. and McKown, D.M. 1987. Instrumental Neutron Activation Analysis of
Geochemical Samples //86*HRORJLFDO6XUYH\%XOOHWLQ1770, pp. H1-H14.
Beus, A.A., and S.V.Grigorian. 1977. *HRFKHPLFDO ([SORUDWLRQ 0HWKRGV IRU0LQHUDO 'HSRVLWV.
Wilmette, Illinois: Applied Publishing.
Boev, N.I. and V.R.Klos. 1988. A Technique to Reveal Secondary Superimposed Haloes Using
Organic Fractions of Soils. In: 7KHRU\DQG3UDFWLFHRI*HRFKHPLFDO3URVSHFWLQJXQGHU&RQWHPSRUDU\
&RQGLWLRQV (Abstracts of the 4th All-Union Conference, Uzhgorod, October 10-12, 1988). Part 21HZ
0HWKRGVRI*HRFKHPLFDO3URVSHFWLQJ. Moscow: IMGRE, p.17 (in Russian).
B|lviken, B. et al. 1992. The Fractal Nature of Geochemical Landscape // -RXUQDO RI
*HRFKHPLFDO([SORUDWLRQ. V.43, pp.91-100.
Clark, I. 1979. 3UDFWLFDO*HRVWDWLVWLFV. London: Applied Science Publishers, Ltd.
Fleischhauer, H., and N.Korte. 1990. Formulation of cleanup standards for trace elements with
probability plots // (QYLURQPHQWDO0DQDJHPHQW, v.14, N 1, pp. 95-106.
Goldberg, I. 1998. Vertical Migration of Elements from Mineral Deposits -RXUQDO RI
*HRFKHPLFDO([SORUDWLRQ. V. 61, pp. 191-202.
Golightly, D.W et al. 1987. Analysis of Geologic Materials by Direct-Arc Emission
Spectrography and Spectrometry //86*HRORJLFDO6XUYH\%XOOHWLQ1770, pp. A1-A13.
Gy, P. 1967. L’Echantillonage des Minerals en Vrac // 5HY,QG0LQ. N 1 (Special Issue).
Johnson, R.G. and B.-S.L. King. 1987. Energy-Dispersive X-Ray Fluorescence Spectrometry 86*HRORJLFDO6XUYH\%XOOHWLQ 1770, pp. F1-F5.
Ingamells, C.O. and F.F. Pitard. 1986. $SSOLHG*HRFKHPLFDO$QDO\VLV. NY: John Wiley & Sons.
Lichte, F.E. et al, 1987. Inductively Coupled Plasma-Atomic Emission Spectrometry // 86
*HRORJLFDO6XUYH\%XOOHWLQ 1770, pp. B1-B10.
Mann, A.W. et al. 1998. Application of the Mobile Metal Ion Technique to Routine Geochemical
Exploration // -RXUQDORI*HRFKHPLFDO([SORUDWLRQ. V.61, pp.87-102.
McKown, D.M. and Millard, Jr. H.T. 1987. Determination of Uranium and Thorium by Delayed
Neutron Counting // 86*HRORJLFDO6XUYH\%XOOHWLQ 1770, pp. I1-I12.
Ovchinnikov, L.N. 1990. 3ULNODGQD\D*HRNKLPL\D$SSOLHG*HRFKHPLVWU\. Moscow: Nedra (in
Russian).
Qiuming, Cheng, et al. 1994. The Separation of Geochemical Anomalies from Background by
Fractal Methods //-RXUQDORI*HRFKHPLFDO([SORUDWLRQ. V. 51, pp.109-134.
Smith, D.B. et al. 1993.Preliminary studies of the CHIM electrogeochemical method in Kokomo
Mine, Russel Guich, Colorado //-*HRFKHP([SORU. V.46, pp.257-268.
Solovov, A.P. 1978. *HRFKHPLFDO0HWKRGVRI3URVSHFWLQJ. 1985. 2nd edition, Moscow: Nedra (in
Russian).
Taggart Jr., J.E. et al. 1987. Analysis of Geological Materials by Wavelength Dispersive X-Ray
Fluorescence Spectrometry //86*HRORJLFDO6XUYH\%XOOHWLQ1770, pp. E1-E19.
Tenant, C.B., and M.L.White. 1959. Study of the Distribution of Some Geochemical Data //
(FRQRPLF*HRORJ\, V. 54, pp 1281-1290.
83
Tkalich, S.M. 1970. 3K\WRJHRFKLPLFKHVNLL0HWRG3RLVNRY0HVWRURMGHQLL3ROH]Q\K,VNRSDHP\NK
Leningrad: Nedra (in Russian).
Wandless, G.A. 1987. Radiochemical Neutron Activation Analysis of Geological Materials // 86
*HRORJLFDO6XUYH\%XOOHWLQ1770, pp. J1-J8.
84
*HRFKHPLFDODQRPDOLHVDQGWKHLUH[SUHVVLRQRQWKH(DUWKVXUIDFH
*HQHUDOFKDUDFWHULVWLFV
*HRFKHPLFDOILHOGVWKHLUFKDUDFWHULVWLFVDQGDQRPDOLHV
In exploration geochemistry, primary and secondary JHRFKHPLFDOILHOGV are considered. 3ULPDU\
ILHOGV are fields of concentration and/or redistribution of chemical elements, whereas VHFRQGDU\ILHOGV
are fields of dispersion of elements. Both primary and secondary geochemical fields usually cover the
territory of a region explored.
3ULPDU\ JHRFKHPLFDO KDORV are zones with enhanced concentrations of ore elements and their
satellites, formed simultaneously with the ore body as a result of the same ore-forming processes endogenous, epigenetic (initially sedimentary), metamorphogenic, etc.
6HFRQGDU\JHRFKHPLFDOKDORHVRIGLVSHUVLRQ are formed as a result of disintegration of ore bodies
or their primary haloes and subsequent migration of elements. Amounts of chemical elements in
secondary haloes are usually (but not always) intermediate between their high concentrations in ore
bodies and low quantities corresponding to a local geochemical background.
Primary geochemical fields are characterized by the following properties: (1) abundance of
genetically interconnected deposits, ore bodies, certain kinds of mineralization, and haloes of all
enumerated objects; (2) presence of numerous sites of “rudimentary” ore-formation which are zones of
dispersed mineralization; (3) appearance of relatively large sites with elevated (at different levels)
background concentration of certain indicator elements in certain rocks; (4) presence of leaching
zones, with significantly decreased concentrations of indicator elements; (5) availability of a number
of very non-uniformly distribute indicator elements.
Processes of weathering and disintegration of ores and rocks acting within fields of concentration
and redistribution of elements lead to the formation of secondary geochemical fields of dispersion and
zones of higher concentrations of indicator elements formed at the expense of weathering of rocks
with raised background amounts of these elements. Geochemical features of secondary fields of
dispersion are determined, firstly, by inherited peculiarities of primary geochemical fields, and
secondly, by the characteristics of migration of elements in specific landscape-geochemical
conditions. Major properties of secondary geochemical fields are as follows: (1) their dimensions
exceed dimensions of corresponding primary fields; (2) a set of indicator elements, in most cases, is
similar to the set of a primary field, however it strongly depends upon the type of dispersion field,
sometimes serious changes in these sets are possible; (3) in comparison to primary fields, indicator
elements in secondary fields are distributed more uniformly; (4) different indicator elements are
usually concentrated at different sites of a secondary field, although sometimes such sites can overlap
each other; (5) distribution of elements in secondary fields is influenced essentially by landscapegeochemical characteristics of a region.
*HRFKHPLFDODQRPDO\ is a meaningful deviation from geochemical norms which are peculiar to a
region considered, or a certain geochemical landscape, or a given type of rocks, waters, plants, etc. As
a rule, geochemical anomalies imply elevated concentrations of elements, in comparison with their
background concentrations. Negative geochemical anomalies imply lowered concentrations of
elements, relatively to their background quantities. Geochemical anomalies differ in their dimensions.
Anomalies with dimensions corresponding to dimensions of individual ore bodies or deposits and their
haloes (primary or secondary) are called ORFDODQRPDOLHV. Anomalies with dimensions corresponding
to dimensions of primary or secondary geochemical fields are called UHJLRQDODQRPDOLHV.
Depending on the area of halo development, the following hierarchy of geochemical haloes in a
geochemical fields can be considered:
Q⋅0.1 km2 - a halo of an ore body;
Q⋅1 km2 - a halo of an ore deposit;
Q⋅10 km2 - a halo of an ore field;
Q⋅100 km2 - a halo of an ore zone;
Q⋅1000 km2 – of an ore region.
85
)ORZVRIGLVSHUVLRQare formed as a result of river transportation of chemical elements along the
valleys, and also due to glacial and atmospheric transport, enveloping the totality of slopes. There are
three groups of conditions determining the formation of flows of dispersion: (1) structural and
mineralogical-geochemical settings; (2) climate environments; (3) landscape properties. Most of flows
of dispersion are linked with aqueous run-off at the land. They can be divided into mechanical, salt
and mixed (salt-mechanical). Indicator elements can join a flow of dispersion: (1) from an ore body
(which is in the state of disintegration) and its primary halo, (2) or from secondary lithochemical and
hydrochemical haloes of dispersion. The first way usually leads to the formation of mechanical or
mixed haloes, whereas the second induces salt flows of dispersion. Salt flows of dispersion can be
formed also as a result of the discharge of ground waters, this yields the so-called “torn off”
lithochemical flows, having no direct linkage with neither ore bodies nor their primary and secondary
haloes. Anomalous amounts of chemical elements in flows of dispersion (i.e. bottom sediments)
depend on: (1) mineralogical and geochemical properties of ores and their host rocks; (2) the mode of
migration of indicator elements; (3) landscape environments.
4XDQWLWDWLYHFKDUDFWHULVWLFVRIJHRFKHPLFDODQRPDOLHV
$YHUDJHDQRPDO\FRHIILFLHQWRIDQHOHPHQW within a halo:
.D & D &B,
where & D - average concentration of the element within a halo, &B - its concentration out of halo
limits (local geochemical background).
&RQWUDVWLQGH[RIDQDQRPDO\ is determined by the following expression:
γ = (&PD[−&B)/6B,
where &PD[ - maximum concentration of the element within a halo, &B- its concentration out of halo
limits (local geochemical background), 6B - standard deviation of background.
Sometimes contrast index of an anomaly is determined by the following ratio:
γ = &PD[&B,
This is not always correct, because any right evaluation of this index requires a comparison of
anomalies not only with a background level, but as well with its steadiness. The measure of this
steadiness is standard deviation of background. If local geochemical background is constant in all
points (6B = 0), it would be easy to reveal any even very weak anomaly on rather high background.
That is why, it is necessary to use the signal/noise ratio, where 6B plays the role of “geochemical
noise”. Only in the case of strong anomalies the ratio &PD[&B can be used to quantify their contrast
indexes.
$UHDOVXUIDFHSURGXFWLYLW\RIDQDQRPDO\ is the following product
3 6( & D −&B),
where 6 - surface area of the halo, & D -average concentration of the element within a halo, &B- its
concentration out of halo limits (local geochemical background).
If there is an one-dimensional anomaly (after measurements along some direction), OLQHDU
SURGXFWLYLW\RIDQDQRPDO\ can be used, it is determined by the formula:
0= D( & D −&B),
where Dis the width of an anomaly (usually it is determined as the width of a maximum at half of its
height).
86
,QWHUUHODWLRQVKLSRIJHRFKHPLFDODQRPDOLHVLQWKHJHRVSKHUH
The scheme illustrating interrelationship and interdependence of geochemical anomalies in he
geospheres put forward by Solovov (Solovov A.P., 1985) is presented in Fig.3.1.
$70263+(5(
Atmochemical
(gaseous) halos and
dispersion fluxes in
under-ground and
near-surface atmosphere
II – III
LITHOSPHERE
Ore bodies and their
primary halos
I – II
HYDROSPHERE
BIOSPHERE
Hydrochemical
halos and dispersion
fluxes in groundwaters and surficial
waters
II - III
Biogeochemical
anomalies:
in plants in animals
IV
V
Secondary
lithochemical halos
and dispersion
fluxes in the
products of
weathering and
overlying.rocks
)LJ Interrelationship and interdependence of geochemical anomalies in the geospheres
(Solovov A.P., 1985)
I – V – relative gradations of the removal of elements from their original ore bodies; the arrows show direct and
feed-back relationships
Ore bodies located in the lithosphere and their primary haloes are capable to form directly, firstly,
secondary haloes of dispersion in eluvial-diluvial products of weathering and overlying rocks and,
secondly, flows of dispersion in alluvial sediments of a drainage system. This corresponds to the first
(I) and second (II) gradations of relative removal of elements from an ore body. In the atmosphere,
gaseous anomalies and dispersion haloes represent second (II) and third (III) gradations of this
removal. Similarly, hydrochemical haloes and flows of dispersion are characterized by second (II) and
third (III) gradations as well. Biogeochemical anomalies are connected with maximum element
removal from their source - gradation IV for anomalies in plants, gradation V for anomalies in animal
organisms. It means that all relations between ore bodies and manifested anomalies can be very
complex, so adequate interpretation of observed anomalies would be difficult.
6SHFLILFIHDWXUHVRIUHYHDOLQJZHDNDQRPDOLHV
The issues connected with detection of weak anomalies, including their “amplification” by means
of using geostatistics and multi-element anomalies have been considered above, in the section 2.1.
“Geochemical background and anomaly” (see 2.1.3 and 2.1.4). Additional methods of such
amplification are given below (see 3.2.5.3. “Coefficients of zoning of primary haloes”).
87
*HQHUDOUHJXODULWLHVLQWKHFRPSRVLWLRQRIJHRFKHPLFDOKDORHV
0RUSKRVWUXFWXUHDQGGLPHQVLRQVRIKDORHV
In general, lithochemical primary and secondary haloes have greater dimensions compared to
their ore bodies. Both dimensions of haloes and their configuration are determined by geological
conditions (see 3.2.2). Depending on geological-structural conditions, and taking into account a role of
conformable and cross-cutting perturbations (dislocations), haloes in the following structures can be
distinguished: gently pitching, steeply dipping, and combined. For dimensions and forms of haloes,
the direction of solution movement relatively a concrete setting where the process of ore deposition
occurs. In simple cases, a primary halo of an ore body repeats its form (shape) having expanded
dimensions (borders).
Morphology and often very complicated internal structure of haloes are determined basically by
hydrothermal conditions existed at a site of the formation of a deposit and its haloes. A major factor of
both hydrodynamic conditions and mechanism of a flow of halo-forming solutions, is permeability of
host rocks, the degree and character of its changeability in the direction of solution movement. The
process of halo-forming, as in the case of ore-forming, proceeds under the conditions of a combination
of convective transfer of substances through joints, joint zones, fractures, faults and other dislocations,
with solution spreading within a porous medium surrounding these dislocation. The more is
permeability of host rocks, the more intensively a flow spreads from a fault (fractures) into these
rocks. Any change of permeability of a fault (fractures) and hosting rocks along an ascending flow
induces the change of its direction. This gives rise to a rhythmic-banded, “torn” and “scrappy”
structure of haloes in supra-ore rock masses of many deposits, their dendritic configuration (in
connection with dykes) and other kinds of complication of the form and shape of primary haloes.
)LJ. Primary geochemical haloes of Pb, Ba and Ag; cross-section of polymetallic deposit Yaman-Sai in
Tajikistan (Ovchinnikov, 1990).
1–3 – decreasing gradations of concentrations of indicator elements in the halo; 4 – ore body; W - borehole
88
According to Ovchinnikov (Ovchinnikov, L.N. 1990), particular attention should be given to the
so-called frontal penetration of solutions into host rocks. Frontal or “digger”-like penetration of an
ore-forming solution in the zone of deposition can cause the formation of sharply different
morphogenetic types of both ore bodies and their primary haloes. The process of “digger”-like
penetration leads to percolation of solution along narrow released zones and to simple circulation
along open fractures. As a result, narrow plano-elongated haloes are formed, in connection with
veined ore bodies or the zones of schist formation with elevated concentrations of ore elements. In a
cross-section, the width of these haloes is not large, however indicator elements, being distributed
within a fracture zone, form very long extensive haloes, their length can be of several hundreds
meters. The development of haloes of this sort is manifested at polymetallic deposit Yaman-Sai in
Tajikistam (see Fig. 3.2).
The haloes of Pb, Ba, and Ag are not of the great width, but they go far upwards above the ore
body reaching the day surface at the distance of more than 320 m from the ore body.
As to vertical dimensions of secondary haloes, they depend strongly on landscape environments,
usually they are different in different landscape zones. However, vertical dimensions of secondary
haloes of indicator elements are more or less constant within a single region. Some details concerning
dimensions and forms of haloes are considered below (see 3.3.1.)
&RQGLWLRQVRIWKHIRUPDWLRQRIKDORHV
Geological conditions determining a halo’s attributes (type, dimensions, shape, internal structure,
contrast, zonality) are as follows (Ovchinnikov, 1990,):
• geological construction of an ore field, dimensions and shape of ore bodies, specifically their
vertical extension;
• elements of disjunctive tectonics: shape, dimensions, density of spreading, and position of orefeeding and ore-distributing channels;
• the presence of dykes, their dimensions, density of distribution, elements of bedding, age
relationships with ore bodies;
• conditions of bedding of ore bodies, their structural-tectonic and age interrelationships with
hosting and overlying rocks;
• physical properties of ore-hosting, underlying and overlapping rocks, contrast and directions of
alterations of porosity and permeability, the degree of jointing of an ore field, its blocks and zones;
• lithological and chemical composition of hosting, underlying and overlying rocks, the degree of
their alteration, quantity and thickness of individual layers in benches;
• direction of solution movement relatively the horizon, superposition of hosting rocks, bedding of
ore bodies, elements of joint tectonics and dykes.
&RPPRQIHDWXUHVRIFRPSRVLWLRQ]RQLQJRISULPDU\KDORHV
Accordind to Alexeenko (Alexeenko, V.A., 1989), succession of crystallization of minerals from
melts and solutions should , as a rule, be governed (in the first approximation) by the energy of their
crystalline lattices. According to Fersman (see (Alexeenko, V.A., 1989), this energy depends on the
values of energetic coefficients of ions EC, which increase with the valence increasing and the ionic
radius lowering:
ECcation = (:2/205L)⋅[0.75(105L + 0.20],
ECanion = :2/205L,
where : – valence, and 5L – ionic radius (in nanometers).
Ions having larger values of EC should be deposited from a solution earlier than others, they
usually form first compounds in the course of crystallization. In the processes of weathering, these
ions, being less mobile, are accumulated in eluvium.
89
Considering ionic radius as one of major factors migration, it is necessary to mind that in the
course of free migration, the more is the value of ionic radius, the greater is the range of migration,
whereas in the process of diffusion, migration range would be inversely proportional to ionic radius.
Even taking into account an important role of complex compounds in water migration, a significant
portion of elements always occurs in the form of simple ions, and upon some geochemical barriers the
majority of elements turns into this form.
Alexeenko claims that by the arrangement of ions in the order of their dimension increasing, it is
possible to get a schematic series of deposition succession of elements migrated as simple ions.
However, migration of ions is under the significant influence of energetic coefficients as well. Thus,
the range of migration should be inversely proportional to the EC values.
Series of the range of migration corrected with taking into account the values of energetic
coefficients is presented in Table 3-1.
7DEOH6HULHVRIGHSRVLWLRQVXFFHVVLRQRILRQVLQWKHFRXUVHRIWKHLUIUHHPLJUDWLRQ
$OH[HHQNR
Ions
Ni3
Cr6
Cr3+
Co3+
W6+
Sn4+
Mo4+
Fe3+
As3+
Sb3+
Ni2+
Mg2+
Co2+
Fe2+
Bi3+
Cu2+
Zn2+
Cd2+
Pb2+
Sn2+
Hg2+
Cu+
Ag+
I−
Main series
5 ,10−8 cm
0.35
0.52
0.64
0.64
0.65
0.67
0.68
0.67
0.69
0.9
0.74
0.74
0.78
0.80
1.20
0.8
0.83
0.99
1.26
1.02
1.12
0.96
1.13
2.2
Accessory series
EC
L
Mg
Fe
As, Fe, Ni
7.9
8.5
5.1
4.3
4.0
2.18
2.0
2.15
2.12
3.9
2.1
2.2
2.0
1.85
1.8
1.7
0.7
0.6
1.18
(Co)
Fe
Ca, As
Zn
As
Co
Bi, Ag, Sn, Sb
As, Sb, Bi, Sn
Hg
Besides a main series, there is an accessory one, the position of elements in the latter depends on
the “co-participation” of elements in the composition of minerals, isomorphic entries in forming nd
early formed minerals, and also their volatility. The series of successive precipitation of ions proposed
by Alexeenko for the case of their free migration, in many details conforms to the generalized series of
geochemical zoning established by Ovchinnikov and Grigoryan after intensive studies of
hydrothermal, magmatic and pegmatite deposits (see below). Thus, a model put forward by Alexeenko
is capable, in certain extent, to explain zoning of primary haloes around ore bodies observed in field
investigations.
3ULPDU\KDORVDURXQGRUHGHSRVLWV
As it was said above, primary geochemical halos are zones with enhanced concentrations of ore
elements and their satellites, formed simultaneously with the ore body as a result of the same oreforming processes - endogenous, epigenetic (initially sedimentary), metamorphogenic, etc.
90
=RQDOVWUXFWXUHRISULPDU\KDORV
Zoning of primary haloes is their very important feature, it is expressed by regular spatial changes
of different haloes’ characteristics and parameters along some direction. Zoning of geochemical haloes
is a vector concept, its parameters are not the same along different directions. Relatively to an ore
body, three basic types of zoning are considered: axial, longitudinal, and transversal. Their mutual
orientation is presented in Fig.3.3.
)LJ Axial (I), transversal (II), and longitudinal (III) zonalities of a primary halo
developed around a steeply dipping ore body.
$[LDO]RQLQJ corresponds to the movement direction of ore-bearing solutions, in cases of steeply
dipping (subvertical) ore bodies, it coincides with vertical zoning, and in cases of subhorizontal ore
bodies – with horizontal zoning. /RQJLWXGLQDO]RQLQJreflects a zonal structure of haloes DORQJ their
strike, whereas WUDQVYHUVDO ]RQLQJ shows this kind of structure DFURVV the strike of haloes and ore
bodies conformable with them. For ore bodies of subhorizontal seating, in the case of conformable
development of haloes, longitudinal zoning is manifested as horizontal (perpendicular to axial zoning,
but disposed in the same plane), and transversal zoning coincides with vertical zoning.
If some sort of “blind” mineralization should be discovered by means of using its primary halo,
axial zoning is the most important, because for the majority of deposits, axial zoning with vertical
zoning or is very close to it. Vertical zoning is of decisive significance for determination of an erosion
shear (section) of a mineralization studied.
Independently of a geological setting, zoning of a primary halo repeats zoning of its ore body.
However, as compared with zoning of ore bodies, zoning of haloes is more contrast and informative,
because a peri-ore space is larger and its structure is more uniform. In addition, the conditions of
mineralization are more uniform within this space as well, whereas ore bodies are formed at the sites
with sharp changes of physical-chemical conditions of element deposition, they are characterized by
anomalous, often very high concentrations of ore components accompanied by elevated variances of
the concentrations and other geochemical parameters. Taking into account all these factors, it is very
difficult to discover zoning of ore bodies.
For water haloes a special kind of zoning is often typical, it is characterized by successive
changes of anomalous concentrations of elements in accordance to their migration ability in a given
medium, dilution by surrounding background waters, and the processes of ion exchange, hydration,
sorption and co-precipitation. This causes spacious zoning which means the appearance of haloes with
different positions relatively an ore body; correspondingly, supra-ore, near-ore and sub-ore haloes are
considered (see Fig. 3.4).
91
)LJ Geochemical zoning of hydrochemical haloes of a buried copper-pyrite deposit.
Contours of water haloes: 1 – Cu; 2- Mo; 3 – Pb; 4 – Bi and Co; 5 – Zn; 6 – direction of movement of halo
waters in a weathering crust and along the faults in host volcanogenic rocks; 7 – ore body; 8 – level of groundfracture waters; 9 – endogenous halo and its zones (I – supra-ore; II – near-ore; III sub-ore); 10 – boreholes
(from “Instruction on geochemical methods of ore deposits prospecting”, 1983).
,QGLFDWRUHOHPHQWVLQSULPDU\KDORHV
All primary haloes are multi-component, their chemical composition includes trace elements
playing a role of geochemical indicators. Each type of ore deposits has its own set of indicators,
special observations covering different types of deposits allowed to recommend these sets for
geochemical prospecting, they are presented in Table 3-2.
7DEOH(OHPHQWFRPSRVLWLRQRISULPDU\KDORHVRIGLIIHUHQWGHSRVLWV
IURP³,QVWUXFWLRQRQJHRFKHPLFDOPHWKRGVRIRUHGHSRVLWVSURVSHFWLQJ´
Types of deposits
Rare-metal pegmatites
Copper-nickel
Copper-pyrite
Tungsten-molybdenum in skarns
Bismute in skarns
Tin
Polymetallic in skarns
Gold
Copper-porphyry
Copper
Copper-molybdenum
Polymetallic
Uranium
Stratiform lead-zinc
Antimony-mercury
Mercury
Indicator elements of primary haloes
Li, Rb, Cs, Nb, Sn, Ta, W, Be, As, F, B
Cu, Ni, Co, Ba, Pb, Zn, Ag, Bi, Sn, Be, W, I, Br
Ba, Ag, Pb, Cd, Zn, Bi, Cu, Co, Mo, As, Hg, I, Br
Ba, Ag, Pb, Zn, Sn, Cu, W, Mo, Co, Ni, Be, B
As, Pb, Ag, Zn, Co, Cu, Bi, Ni, B
Sn, Pb, As, Cu, Bi, Zn, Ag, Mo, Co, Ni, W, B, F, I
Ba, As, Sb, Cd, Ag, Pb, Zn, Cu, Bi, Ni, Co, Mo, Sn, W, Be, B, I
Ba, Au, Sb, As, Ag, Pb, Zn, Mo, Cu, Bi, Co, Ni, W, Be, I
Ba, As, Sb, Ag, Pb, Zn, Au, Bi, Cu, Mo, Sn, Co, W, Be, I
Sr, Ba, As, Pb, Zn, Ag, Sn, Cu, Bi, Co, Ni, Mo, Hg, I
Cu, Mo, As, Ag, Pb, Zn, Bi, Co, Ni, Be, W
Cd, Ba, Sb, As, Ag, Pb, Zn, Cu, Bi, Mo, Co, Sn, W, Sr, Hg, I
U, Ag, Pb, Zn, Cu, Mo, Co, Ni, V, As
Ba, As, Cu, Ag, Pb, Zn, Cu, Co, Ni, Sn, Mo, W, As
Ba, Sb, Hg, As, Cu, Ag, Pb, Zn, Be, Co, Ni, W, Sn
Sb, Hg, Ba, Ag, Pb, Zn, Cu, Co, Ni, Sn, Mo, W, As
92
In Table 3-3, series of indicator elements showing axial and transversal zoning of primary haloes
for several types of deposits are presented.
7DEOH6HULHVRIHOHPHQWVVKRZLQJD[LDODQGWUDQVYHUVDO]RQLQJRISULPDU\KDORHVRIPHWDO
GHSRVLWVIURP³,QVWUXFWLRQRQJHRFKHPLFDOPHWKRGVRIRUHGHSRVLWVSURVSHFWLQJ´
Types of deposits
Series of axial zoning
Tungsten (scheelite
in skarns)
W – Ba – Sn – (Bi,Mo) – Zn – (Pb, Ag)
Tin (quartzcassiterite)
(As, Be, W) – B – Sn – Cu –(Zn, Ag, Pb)
W – Mo –Cu – Ba – Zn – Pb
Copper-porphyry
(B, W, Co, Sn) – (Mo, Cu) – Bi – Au –
– (Zn, Pb, Ag) – Sb – As – Ba – I
Au – Cu – Mo – Ag – As – Pb
Be – Ni – Co Zn – Pb – Ag, Cu – As – Ba
Ag – Pb – Cu – As – Ba – Cu – Zn – Ni
Zinc-lead
form)
Mercury
Series of transversal zoning
As – W – Ag – Sn – Cu – Zn – Pb
(strati-
(Bi, Mo) – Cu – Zn – Pb – Ag – (Hg, As, Sb) Hg – As – Ba – Cu – Pb – Zn – Ni – Ag –Co
It can be seen that there are certain distinctions between the two types of zoning, they concern
both the number of elements involved in series and the arrangement order of elements in them.
&RHIILFLHQWVRI]RQLQJRISULPDU\KDORHV
In order to assess quantitatively geochemical zoning of primary haloes, several indicator ratios
are used. These ratios are chosen, taking into account a contrast position of compared elements in a
zoning series considered. The following coefficients of zoning can be used (they are recommended for
geochemical prospecting in Russia ("Instruction on geochemical methods of ore deposits prospecting",
1983):
&, /
& , Additive coefficient .A =
∑
V L
Multiplicative coefficient .M =
∑
X M
M
L
∏& , / ∏ &
L
V L
M
X
,
M
where index Vrefers toelements enriched in the halo, and index X– elements evacuated from it.
It was proved that multiplicative coefficients can be very effective tools in revealing different
kinds of ore deposits, including “blind” and deep-seated ones.
Figure 3.5 shows how the value of multiplicative zoning coefficient .M = &Pb&Ag&Sb/&Cu&Bi&W
changes with the depth at nine different tin deposits of the Far East of Russia.
)LJ Change of the multiplicative zoning coefficient .M = &Pb&Ag&Sb/&Cu&Bi&W of primary haloes with
the depth at tin deposits of the Far East of Russia (1- Yuzhnoe; 2 – Smirnovskoe; - Zimnee; 4 – Vernoe; 5 –
Vetvistoe; 6 – Ivanovskoe’ 7 – Dal’netaezhnoe; 8 – Trudnoe; 9 – Obychnoe), (Ovchinnikov, 1990).
93
The depth change which is only 500-600 m, corresponds to .M changes covering ten orders of
magnitude – from 10−5 to 105. The values of .M > 105 mark out supra-ore haloes which could belong to
“blind” ore bodies or haloes developed at the level of upper parts of ore bodies (a weakly eroded
mineraliation). The values of .M < 10−3 correspond to strongly eroded anomalies.
Similar contrast variations of the value of another multiplicative coefficient .M =
= &Pb&Ag&Zn/&Cu&Bi&Co were observed in haloes of polymetallic deposits (Figure 3.6).
)LJ Change of multiplicative zoning coefficient .M = &Pb&Ag&Zn/&Cu&Bi&Co of primary haloes with
the depth at polymetallic deposits of Russia (1- Garpenberg, 2 – Altyn-Topkan, 3 – Kurusai, 4 – Vostochnyi
Kanimansur; 5 – Kansai, 6 – Aktash, 7 – Sadon), (Ovchinnikov, 1990).
*HQHUDOL]HGVHULHVRILQGLFDWRUHOHPHQWVLQSULPDU\KDORHV
The most complete studies of vertical zoning in the distribution of elements in primary halos have
been carried out by Ovchinnikov and Grigoryan (Ovchinnikov, L.N., 1990). They established zoning
series of indicator elements in different deposits (hydrothermal, magmatic, and pegmatitic), and
introduced the so-called generalized zoning series for primary halos of hydrothermal deposits. This
series (reflecting vertical zoning) which has been proposed after exploring more than 400 deposits, is
as follows (elements are indicated from below upwards):
W1 – Be – As1 – Sn1 – Au1 – U – Mo – Co - Ni – Bi - W2 – Au2 – Cu1 –
– Zn – Pb – Sn2 – Ag – Cd – Au3 – Cu2 – Hg – As2 – Sb – Ba.
Indexes 1, 2 and 3 mean that some elements can hold different positions in the zoning series,
depending on their mineral species and associations with other elements. For example, Sn1
corresponds to deposition of tin as cassiterite SnO2, and Sn2 implies the form of stannite Cu2FeSnS4
formed at lower temperatures. Authors underline statistical character of this series; every concrete
deposit , depending on its origin, can reveal certain rearrangement of elements in its primary halo,
without violation of the essence of their general succession. Solovov argues that the listed series can
be added at the left by such easily volatile elements as Cl, Br, I. Tl (Solovov, 1985).
Ovchinnikov marks out eight “always present” elements – Ba, Mo, Sn, Ni, Co, Pb, Zn, Cu,
forming primary halos of endogenous deposits of the majority of genetic types. On the other hand, the
withdrawal of iron and their satellites (Ti, V, Cr, Sc, etc) from primary halos of many deposits is
possible. Observed zoning of hydrothermal deposits is complicated by multi-stage character of ore
deposition and following metamorphism, however there is no doubt about the existence of general
settled regularity.
There were numerous attempts to explain observed zonal structure of primary halos including
various physical-chemical grounds, such as solubility constants of element compounds, stability
indexes of simple and complex ions under different values of pH and Eh, differences in the rate of
mobility of hydrated ions in solutions, energy values of crystalline lattices and so on. Alexeenko
94
claims that one can observe a very good compliance when the generalized zoning series is compared
with the series of consecutive ion precipitation, calculated for their free migration (infiltration) in ionic
solutions (Alexeenko V.A., 1989). He declares that comparison of these series shows that for the most
of cases calculated position of elements coincide with the positions observed in the study of primary
halos of hydrothermal deposits. This good agreement would allow to propose (in general outline) the
following model of the formation of both hydrothermal ore bodies and their primary halos. Metals are
transported from a source along ore-conducting channel-ways, mainly in a complex mode, and partly
in an ionic form. When they reach some geochemical barrier, complex compounds dissociate, so from
this moment migration performs having only ion species. The process of metal concentration depends
strongly on the type of geochemical barrier, the amount of metal approached to the barrier, and
different conditions of migration. When the barrier reveals its action, precipitation of principle ore
elements (their concentration in the solution should be the largest) can occur firstly. This model would
explain the zonal structure of primary halos around ore bodies.
However, there was a serious critics of this approach. According to Solovov, deposition of ore
elements from hydrotherms, undoubtedly, depends on many simultaneously acting reasons, so any
effort to explain the zoning ore-formation in the light of decisive role of a single factor appears to be
fruitless (Solovov, 1985). One may suppose that just a variety and commensurability of factors acting
at the same time determine the observed stability of series of zonal deposition of elements, when
obvious manifestations of different particular conditions do not change (or change in a very small
extent) a final result.
6XEEDFNJURXQGKDORHVRIK\GURWKHUPDOGHSRVLWVRIXUDQLXP
Specific haloes have been identified at peripheral areas of hydrothermal uranium deposits. The
study of numerous deposits has shown that at the periphery of a hydrothermal field, there is a zone
within which the concentration of U does not exceed the level of a local background, but the
parameters of non-uniformity of the concentration distribution are anomalous in comparison with
corresponding parameters of this background. These parameters include the coefficient of asymmetry
of concentration distribution, variance, and the coefficient of variation. The values of all these
parameters are clearly increased within specific haloes called “subbackground haloes” were observed
at all investigated deposits of U (Gurevich, V.L. and Kantzel, A.V. 1984). For example, the coefficient
of variation averaged over a typical subbackground halo is 3-4 times the corresponding value of a
local background. The extent (competence) of haloes of this kind usually accounts for 30-80% of the
extent (competence) of the so-called effective portion of primary uranium haloes.
A mechanism of the formation of subbackground haloes is supposed to be induced by the
processes of redistribution of U at peripheral zones of a hydrothermal field. In the course of these
processes, the substance balance seems to remain invariable, however uranium variance appears to be
increased at the expense of its efflux from local separate sites and subsequent deposition at
neighbouring sites.
Subbackground haloes can be regarded as a new sort of manifestation of deep-seated uranium
bodies at the earth surface. Their use provides a new tool for detecting the zones of primary haloes and
fixation their border-lines. Moreover, subbackground haloes allow to enlarge the border-lines of
detectable primary haloes.
6HFRQGDU\OLWKRFKHPLFDOKDORVRIGLVSHUVLRQ
Secondary dispersion halos are zones with enhanced concentrations of ore elements or their
geochemical satellites in surrounding rocks adjacent to ore bodies; these zones were formed due to
hypergenetic migration of chemical elements. Numerous types of secondary lithochemical haloes have
been identified, they were subjects of a special classification.
&ODVVLILFDWLRQRIVHFRQGDU\OLWKRFKHPLFDOKDORV
Classification of secondary litochemical halos put forward by Kvyatkovsky E.M. is presented in
Fig. 3.7. As Fig. 3.7 shows, there are seven levels of this classification.
95
7KHILUVWOHYHO refers to a medium enclosing a halo. Autochthonous and allochthonous sediments
can enclose secondary haloes, autochthonous ones are usually formed at the sites of ore bodies or their
primary haloes. Allochthonous sediments are subdivided into aquatic, englacial and aeolian (windlaid).
7KH VHFRQGOHYHO implies interrelation (basically, through time) of a halo within its medium. In
autochthonous sediments, syngenetic (residual) haloes are predominant. Their formation is due to
weathering and evacuation of easily soluble components from ore bodies and their primary haloes. In
allochthonous sediments, on the contrary, epigenetic (superimposed) haloes are predominant, at their
contemporary contours there was no elevated concentrations of indicator elements before weathering
of ores or primary haloes.
ATTRIBUTES
HALO TYPES
Autochthonous sediments
1.Environment
Eluvial
Allochthonous sediments
Aquatic
Hillside
2. Relation to
the environment
3. Dispersion
process
4. Correlation of
productivities
Residual (syngenetic)
Englacial
Aeolian
Superimposed (epigenetic)
Mechanical (physical)
Chemical (salt)
Enriched
Depleted
Inherited (normal)
5. Halo
morhology
6. Position relatively
to an ore body
7. Availability for
discovering
Train-like
Supra-ore
Displaced
Torn off
Uncovered
Covered
Buried
)LJ Classification of secondary lithochemical haloes (Kvyatkovsky E.M.)
7KH WKLUG OHYHO deals with a prevalent process of dispersion which depends on phase states of
migrating elements. Just at this level a basic type of migration is considered. Correspondingly, all
secondary haloes are divided into mechanical (physical),salt (chemical) and mixed (physicalchemical). Mechanical haloes are formed in the process of displacement of shattered mineralized ores
and rocks. The formation of salt haloes is connected with dissolution of minerals of ore deposits,
transportation of indicator elements in solutions and following deposition in new mineral forms.
Mixed haloes represent a combination of mechanical and salt haloes, such haloes are typical for
sulphide deposits of some non-ferrous and rare metals. Formation of salt and mixed dispersion haloes
is possible when, firstly, water soluble salts of indicator elements are available and, second, if the
96
medium of migration is impregnated by water at a sufficient extent. There are several reasons of
deposition of indicator elements: chemical reactions of solutions with host rocks; isomorphic entries
into minerals of host rocks; sorption; decay of complex compounds. By the mechanisms of formation,
the haloes considered belong to infiltration haloes. Indicator elements in infiltration haloes can occur
in mineral and isomorphic forms.
7KH IRXUWK OHYHO of classification reflects the process of relative enrichment or depletion of
secondary haloes, in comparison with destroying ore bodies and their primary haloes. The majority of
secondary haloes are depleted, however sometimes these haloes (mechanical, not salts) can be
enriched. Some details concerning mechanical and salt haloes are given below (see 3.2.6.2 and
3.2.6.3).
7KHILIWKOHYHOtakes into account morphological properties of haloes. Inherited haloes repeat (in
the plan) the form of outcropping bodies in original rocks. “Train-like” haloes are elongated along the
direction of run-off of the products of decay of ore bodies and primary haloes. These haloes can be
enriched by ore elements, the limit case of their enrichment is the formation of placer deposits.
At tKHVL[WKOHYHO, the position of a halo relatively an original outcrop of ore bodies is considered.
Accordingly, supra-ore, displaced and “torn off” are included in the classification. Supra-ore haloes
can be subdivided into diffusive (they are inseparably linked with ore bodies) and accumulative (they
are formed upon a certain geochemical barrier, above an ore body or a deposit. “Torn off” haloes have
no linkage with ore bodies, they are usually displaced from them in the direction of element migration
(as a rule, downhill). Displaced haloes are intermediate between supra-ore and “torn off” haloes. Their
minor part is located over an ore body, whereas major part is displaced in the direction of element
migration.
At WKHVHYHQWK OHYHO secondary haloes are divided by their availability for discovering: opened
(uncovered), closed (covered or blind) and buried. Opened haloes crop out at the contemporary day
surface. Covered (blind) haloes had not reach the surface in the course of their development. Buried
are haloes which had been outcropping out earlier, but were overlapped by contemporary
allochthonous sediments.
Classification of secondary haloes has been developed by Solovov, he considered their major
groups presented in Fig. 3.8.
Fig.3.8. Major groups of secondary lithochemical haloes of dispersion at ore deposits
(a – opened haloes; b – closed haloes); (Solovov, 1985).
I – residual (eluvial-diluvial); II – superimposed diffusional; III – superimposed accumulative supra-ore; IV
– superimposed accumulative “torn off”; V – residual (eluvial-diluvial) leached and impoverished; VI – residual
buried; VII – superimposed buried.
1 – contemporaneous eluvial-diluvial sediments or crusts of palaeoweathering of ore-bearing rocks; 2 –
overlying sediments brought from far away; 3 – ore-bearing rocks; 4 – ore bodies and their primary haloes; 5 –
secondary haloes of dispersion.
Opened secondary haloes are observed at the earth surface, they are divided into four groups:
residual (eluvial-diluvial); superimposed diffusional; superimposed accumulative supra-ore; and
superimposed accumulative torn off away. Buried secondary haloes did not reach the earth surface in
97
the process of their development, they include also secondary haloes which were opened earlier and
overlapped recent allochthonous sediments. Buried secondary haloes are divided into three groups:
residual (eluvial-diluvial), leached and extremely depleted; residual buried; superimposed residual.
0HFKDQLFDOGLVSHUVLRQKDORV
According to Solovov, the decisive role in the formation of secondary residual halos of dispersion
belongs to a solid phase (Solovov, 1985). Simultaneously with physical disintegration of ore body and
host rocks bearing its primary halo, the fragments formed in the zone of weathering acquire the ability
to move away from the site of their original bedding. This mobility of rock “particles” in the zone of
weathering can be manifested by three independent modes: (1) the whole mass of all particles can
move under the force of gravity, this induces either plastic deformations of a loose rock mass or local
fractures of its continuity; (2) individual particles of rocks can be displaced from the surface of a loose
(unconsolidated) rock mass and then can be deposited again, in particular, after being displaced
towards relief lowering, to the base of denudation and into the site of sedimentation; (3) particles
themselves within unconsolidated rocks can undergo mutual displacements .
The roles of these modes of mobility are essentially different in the formation of a dispersion
field. Displacement of the whole mass of particles, without their mutual redistribution can not lead to
the formation of a mechanical dispersion halo. Its results will be only displacement and deformation of
the halo. Moving away of particles and their transport to the base of denudation determine the
formation of a lithochemical dispersion flux and the rate of continuous renewal of the halo. With
selective moving away of particles, this process leads to depletion or enrichment of the halo. Anyway,
the halo formation is induced by mutual displacements of particles within a loose rock mass of the
products of weathering. Driving forces of this process are the agents of physical weathering:
expansion and contraction due to temperature changes, water freezing and thawing out, crystallization
of salts, dynamic actions of rains and winds, the influence of root systems of plants and such animals
as shrews.
Within a limited site of unconsolidated deposits formed after disintegration of some single rock
body, all particles have the same chemical composition. Under these conditions, mutual displacements
of rock particles will not lead to the changes in the concentrations of elements, because the place of
any particle will be taken by other particle with the same chemical composition. At the border of two
different rocks and, in particular, at the contact of ore body with its host rock, the place of any moved
particle would be occupied by a particle having another chemical composition. It means that
geochemical mobility of elements (the rate of mechanical dispersion) in the direction [ will be
proportional to the concentration gradient along this direction ˜&[/˜[. Thus mutual mobility of the
particles of unconsolidated sediments leads to the displacement of ore particles from the sites with the
highest concentration to the sites of lower concentrations. So mechanical dispersion of ore substances
occurs (Solovov, 1985).
6DOWGLVSHUVLRQKDORV
The formation of secondary lithochemical salt halos is subordinated to the following basic
conditions: (1) the occurrence of ore elements in the species of water-soluble compounds; (2) watersaturation of the environment where dispersion is developed. Both these conditions are always kept in
the zone of hypergenesis. Loose (unconsolidated) rocks always contain water, even frozen rocks do
not make exclusion. Indeed, it is established that the freezing of capillary water in dispersed rocks of
the zone of weathering occurs even at − 13.6 0C if capillary is 0.24 mm, and at − 18.5 0C if capillary is
0.06 mm, whereas usual temperature of steady permafrost in North Russia is 5-6 0C below zero.
The behaviour of water-soluble salts in the field of dispersion is governed by complex processes
of chemical and physical-chemical exchange reactions, phenomena of diffusion and capillary lifting of
solutions from deep layers of rocks to the day surface. This behaviour is associated with evaporative
and biogenic accumulation of salts by atmospheric precipitation. Due to very long periods of
geological time, even hardly soluble ore minerals participate in the formation of a salt halo. Salt
dispersion is connected usually with the formation of weakly mineralized solutions in the zone of
contact of groundwater table with an ore body, by means of direct dissolution of primary minerals or
98
in the process of their hypergenic alteration up to the transformation into their stable secondary
generations.
0DWKHPDWLFDOPRGHORIDVHFRQGDU\KDOR
In 1957, Solovov put forward a model of the formation of a residual mechanical halo over a thin
vertical ore body. In the process of weathering, a chaotic displacement of ore and vein minerals,
together with clay particles, develops at the earth surface. This happens in the course of water freezing
and thawing, extension and contraction of unconsolidated rock masses, temperature changes, activities
of worms, insects and other animals, mechanical influence of plant roots, hydration, salt
crystallization, etc. Such displacement can be liken to Brown’s movement of particles or thermal
movement of molecules, where an average length of free path corresponds to the coefficient of
mechanical dispersion. Naturally, the particles near by the surface are most mobile, that is why a
mechanical halo gains the form of a fan.
Taking into account that halo formation occurs during a very long period of time, in the
accordance with the theory of similarity, unconsolidated rocks can be regarded as a continuous
medium analogous to a viscous liquid, where diffusion phenomena develop. Taking into consideration
that the movement of each particle is of random character, the number of particles being extremely
large, and the time of movement – extremely long, Solovov got a model of mechanical dispersion, as a
solution of Fourrier’s differential equation describing heat spreading from a source of heating.
Suggesting that concentration of an element in an ore body and its background concentration are
constant, the integration of Fourrier’s equation yields the following formula:
&[ = (0/σ 2π )⋅exp (−[/2σ2) + &B,
where σ is the coefficient of dispersion which represents the standard removal of ore particles from
their initial position within an ore vein. Thus, the distribution of ore particles and, correspondingly,
chemical elements in a residual mechanical halo of a thin vertical ore body (vein) follows a normal
distribution with parameters M and σ depending on the properties of mineralization and other local
conditions. This halo is presented in Fig. 3.9.
)LJ Vertical section and graph of an opened secondary residual lithochemical halo of dispersion developed
above a thin ore body (vein).
1 – eluvium; 2 ore body; 3 – host rocks; 4 – concentration isolines (Solovov, 1985).
99
/LWKRFKHPLFDOIOX[HVRIGLVSHUVLRQHTXDWLRQRIDQLGHDOGLVSHUVLRQIOX[
/LWKRFKHPLFDOIOX[HVRI GLVSHUVLRQ are characterized by the areas of enhanced concentrations of
ore elements or their satellites on the ways of solid, soluble (aquatic) or gaseous run-off, superficial or
underground, from land. In the theory of formation of lithogeochemical flows of dispersion worked
out by Solovov, there is a basic equation of an ideal dispersion flux. (TXDWLRQRIDQLGHDOGLVSHUVLRQ
IOX[ allows to calculate the amount of some metal(s) in lithochemical dispersion flux for a deposit
having a residual dispersion halo which is subjected to denudation on a hillside of a river valley.
The theory uses the following approach. Any river (creek, valley) without lateral inflows is called
a flux of the first (I) order. Two conflowing rivers form a river of the second (II) order; two rivers of II
order, after their conflowing, form a river of the III order, which can get as lateral inflows only rivers
of the I and II orders. This is illustrated by Figure 3.10.
)LJ Illustrating the calculation of lithochemical flux of dispersion.
a - position of an ore body in the basin of a drainage system; b – graphs of dispersion fluxes
1 – secondary residual halo of dispersion with productivity 3; 2 – points of sampling of alluvial sediments;
3 – direction of run-off; 4 – borders of a drainage system 6 .
Roman numerals designate intervals limited by the points of start (5 ) and finish ® of element fetching
from the halo into the river-bed. (Solovov, 1985).
[
Basins of drainage systems of river-beds of the I order are usually “pear-shaped”, and their area
6[ for any point of a river-bed is proportional to the second power of the distance [ from a drainage
system head 0 (see Fig.3.10, D). Suppose that on the slope of a valley, a secondary halo is located, with
areal (surface) productivity 3 The goal is to identify the dependence of the amount of metal in riverbed sediments &¶[ from the coordinate of the point of sampling [:
&¶[ = I([) I(3, 6[),
(3.1)
where 6[ ϕ ([), and 3plays the role ofa local parameter.
Suppose that all the formation of dispersion flow is determined by a solid run-off. For the riverbed shown by Fig. 3.10, D , three intervals should be distinguished: interval I which is up-stream from
the point 5 ,ore material from a secondary halo does not in this interval; interval II which is between
the points 5and 5 , where halo material removed from the left slope into the river-bed in the form of
eluvium-deluvium determines the appearance of anomalous amounts of ore elements in alluvium;
interval III which is down stream of the point 5, where this alluvium is replenished only by the
material removed from both ore-free slopes, so anomalous concentrations descend gradually (see
Fig.3.10, E).
In all points of the interval I of the river-bed, concentrations of an element considered remain at
the level of local background, so the expression (3.1) becomes identical:
&¶[ = &¶B .
100
(3.2)
Within the interval III of the river-bed, concentrations of the element in alluvium will exceed
background concentrations by the following quantity:
∆&[ = (TM/TR)⋅100%,
where TM - an additive amount of element coming in the river-bed at the expense of denudation of the
halo of dispersion; TR – total amount of rock material removed from all area of the drainage system 6[,
duringthe same time interval. If ∆K is an average width of a denudation layer, then:
TM = 3∆KG⋅10−2,
TR = 6[∆KG,
where Gis volumetric mass of a removed eluvium-diluvium into the river-bed.
Therefore,
∆&¶[ = 3/6[,
&¶[ = (3/6[) + &¶B .
(3.3)
In the interval II, different amounts of the element will be transported in the river-bed, they
depend on the productivity 3[ of the part of the dispersion halo which participates in the formation of a
solid run-off at the sampling point [. Assuming that linear productivity of the halo remains constant
upon the interval (5−5)we have:
3[/3 = ([−5)/ (5−5).
Thus, according to (3.3):
&¶[ = (3/6[) + &¶B = [3([−5)/6[(5−5)] + &¶B.
(3.4)
The identity (3.2) and equations (3.3), (3.4) describe the distribution of an element in an ideal flux of
dispersion. Each of these expressions deals with a certain interval of a river-bed and they are not
compatible analytically.
From (3.3) , we have
(3.5)
3 = 6[(&¶[ − &¶B).
This formula characterizes an ideal flux of dispersion, for natural conditions it is replaced by
proportional dependence. Designating the right part of (3.5) by 3¶and calling it SURGXFWLYLW\RIDIOX[
RIGLVSHUVLRQ, it is possible to write:
3¶[ = 6[(&¶[ − &¶B) = N¶3 = const,
where N¶ can be >1 or <1, it is a coefficient of proportionality depending on a local orohydrographical
setting and individual properties of chemical elements.
Expressions (3.3), (3.4) and following from them equation 3¶[ = 6[(&¶[ − &¶B) = const if [!5(see
Fig.3.10, E) are of fundamental importance in the theory of formations of lithochemical flows of
dispersion of ore deposits (Solovov, 1985).
'LVSODFHPHQWRIVHFRQGDU\KDORHV
Unconsolidated eluvial-diluvial sediments on a hillside are in the state of continuous movement
towards a foot of the hill, even if an angle of inclination is small. This process is induced by the force
of gravity, it is very slow. Secondary geochemical haloes of dispersion formed on slopes are involved
in this process, so they become displaced relatively their initial position above an ore body (see
Fig.3.11).
101
)LJ Displacement of a secondary residual lithochemical halo of dispersion upon a plane slope
(Solovov, 1985).
1 – eluvium – diluvium; 2 – ore-bearing rocks; 3 – ore body.
The problem concerning the displacement of secondary haloes of dispersion was studied by
Solovov, he put forward a formula to calculate the value of this displacement 6D (see Fig. 3.11) which
is as follows:
6D $Ksinα,
where $ is a parameter depending on local conditions; K – thickness of covering sediments; α - an
angle of inclination.
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Primary haloes are formed simultaneously with ore bodies, and they are genetically connected
with the processes led to concentration of elements. The formation of primary haloes accompanies the
formation of deposits induced by crystallization of magmas, postmagmatic and metamorphic
alterations of rocks, and also by sedimentary ore deposition. Primary haloes should be called haloes of
concentration, not dispersion.
)RUPVDQGGLPHQVLRQVRISULPDU\KDORHV
Each type of ore deposits − magmatic, intermediate (transitional), and postmagmatic − has its
own morphology of primary haloes. However, primary haloes of steeply dipping (subvertical) ore
bodies are always elongated along the strike and up the dip, in the site plane they have an ellipsoidal
form, sharply elongated along the strike of ore bodies. Along the strike, dimensions of haloes of
steeply dipping ore bodies significantly exceed dimensions of these bodies. Primary haloes of dipping
at low angles ore bodies are elongated along the strike, in the cross-section they look as bands parallel
to ore bodies.
According to V.I.Smirnov, three classes of deposits can be formed as a result of crystallization of
magmas: early-magmatic, late-magmatic and liquation. Primary haloes are typical for all these three
classes. However, both their dimension and composition of indicator elements are different not only
for the classes, but for the groups belonging to the same class. These distinctions are caused by both
102
external conditions of deposit formation (temperature, pressure) and geochemical properties of an
injected melt and its host rocks.
Among liquation deposits, a group of sulphide Cu-Ni deposits confined to ultrabasic and basic
rocks is the most widely distributed. Formation of primary haloes of deposits of this group is induced
mostly by the processes of partition of a melt into silicate and sulphide components, and subsequent
migration of a sulphide portion under the action of gravity. It means that some indicator elements of a
future halo migrate in a magmatic melt. Occurrence forms of these elements are mineral and
isomorphic. Formation of haloes with a mineral form depends on the following factors: (1)
crystallization of the magma up to the total settling of all “drops”; (2) crystallization of a sulphide melt
in the fissures of an earlier formed silicate melt and host rocks; (3) breakdown of isomorphic mixtures
with temperature lowering. In the course of magma crystallization, before total settling of its sulphide
component, haloes of diffused drops are formed above ore bodies (see Figure 3.12).
)LJ. Scheme of placing of ore bodies and “drop haloes” at a liquation-type deposit.
1 – underlying rocks; 2 – overlying rocks; 3 – host (ore-bearing) rocks; 4 – ore bodies; 5 – ore veins; 6 –
haloes of “pendent” phenocrysts.
Dimensions of such haloes ,in a large extent, depend on the duration of cooling of a prevailing silicate
portion of a melt and, therefore, on the depth and dimensions of an intrusion. Dimensions of “drop
haloes” corresponding to the ores by their mineral composition are, as a result, not large (they rarely
exceed several tens meters).
Haloes of a final (pegmatite) stage of the magma crystallization are different from the abovementioned. They appear as intermediate (transitional) to postmagmatic haloes. Morphology and
dimensions of primary haloes of pegmatite deposits depend on both the pegmatite type and the
structure of ore fields and the character of host rocks. Rare metal pegmatites are the most significant
among all types of pegmatites. According to G.G.Kochemasov, several element form haloes around
tantalum-bearing pegmatites: Li, Cs. Rb, Sn, Be and Nb. All they are direct indicators of “blind” ore
bodies. These elements have been supplied into pegmatite bodies and host rocks in the process of NaLi-metasomatosis. The broadest and most contrast primary haloes in hosting rocks and sedimentary
host rocks are formed by lithium (Alexeenko V.A. and Voitkevich G.V., 1979). Dimension of Li
haloes along the strike of dipping at low angles ore veins in slates exceed 500 m, their magnitude in
granites reach 250 m. At the same deposit, similar by their dimensions and very intensive primary
haloes are formed by Cs. Other elements have significantly lesser haloes.
Dimensions and forms of postmagmatic deposits depend on several factors. Major factors are: (1)
structural properties and dimensions of ore bodies. (2) lithological composition of rocks; (3) features
of fissure tectonics of the site. The dimensions of haloes of uranium, as all primary haloes, are always
exceed the dimensions of ore bodies. Both uranium and its geochemical satellites can form primary
haloes of the same form and dimensions. S.V.Grigoryan and E.M.Yanishevsky studied primary haloes
at one of uranium deposits of the former USSR. This deposit is confined to greisened granites (see
Fig.3.13).
103
)LJ Primary haloes of uranium deposit confined to greisened granites.
1 – alluvial sediments; 2 – granites; 3 – greisens; 4 and 5 – concentrations of elements expressed in the
values of local geochemical background of the element &B: 4 – from 3 to 10&B; 5 - > 10&B.
It was shown that uranium itself and its indicator elements Pb, Mo, Cu, and Zn have formed similar
broad primary haloes around ore-bearing greisened zones. The formation of all considered haloes was
induced by the action of uranium-bearing hydrothermal solutions upon both greisened (altered) and
unaltered rocks. That is why dimensions of haloes are many times dimensions of ore bodies and
greisens.
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Zoning of primary haloes of U deposits depends of many factors including the properties of haloforming elements and the characteristics of geological settings. It was shown that haloes of Pb are
usually disposed above ore bodies, whereas primary haloes of U itself and Mo can be traced under ore
bodies. The values of ratios Pb/U, Pb/Mo and U/Mo decrease with the depth, from supra-ore towards
sub-ore horizons.
0DMRULQGLFDWRUHOHPHQWVLQSULPDU\KDORHVRIXUDQLXPRUHV
Among endogenous deposits of uranium, hydrothermal deposits are of the most importance, their
primary haloes are well studied. By the element composition of their primary haloes, all hydrothermal
U deposits are divided into four groups (Grammakov A.G. et al., 1969), according to their leading
indicator elements: lead-molybdenum, lead-nickel-arsenic, molybdenum and arsenic (see Table 3-4).
For the first group, lead is the most significant indicator (both for surface, “blind” and buried ore
bodies), it is followed by molybdenum. Copper and zinc are usually present as well. In the haloes of
the second group, Pb is also the most important satellite, Ni and As follow it; Mo is present in small
amounts, but sometimes it is absent at all. The third group is presented basically by U-Mo deposits,
their ores and primary haloes usually contain Mo in very large quantities. Lead and Cu are typicalfor
the haloes of this group. The fourth group includes mainly low-temperature uranium deposits, arsenic
haloes of this group are intensive and extensive; haloes of Pb and Mo are characterized by lesser
dimensions and concentrations.
104
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*UDPPDNRYHWDO
Groups of uranium deposits
Pb – Mo
Pb – Ni – As
Mo
As
Major satellites of U in primary
haloes
Pb, Mo, Cu, Zn
Pb, Ni, As, (Mo)
Mo, Pb, Cu
As, Pb, Mo
Minor satellites of U in primary
haloes
Be, Zr, Th, P
Zn, Co, Ag
As, Tl, Y
Tl, Sb, V, Sr
Table 3-4 shows that Pb is present as a major indicator in all primary haloes of U deposits. It is
worth noting that isotope studies have proved that this Pb is not radiogenic, it is usual lead of
hydrothermal origin which convoys uranium mineralization.
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Primary haloes of uranium not affected by erosion are rarely manifested at the surface. If primary
haloes around “blind” uranium bodies are more or less stripped by erosion, their secondary haloes of
dispersion of U and its satellites become important. Such secondary haloes of U are typical for
endogenous (hydrothermal) uranium deposits, where ore bodies are disposed in an echelon-like
manner, following one another with the depth increasing, and when primary haloes of these bodies are
at different stages of stripping by erosion. In the process of formation of secondary haloes, relations
between elements which were typical for primary haloes, can be disturbed. Thus, the leading role of
Pb which is present in all primary haloes of U hydrothermal deposits, can be broken, for example, due
to very low solubility of its sulphate formed as a result of chemical weathering (oxidation of
sulphides). In fact, the value of PbSO4 solubility is only 0.04 g/l, whereas solubility of ZnSO4 – 531
g/l, NiSO4 – 275 g/l, CuSO4 266 g/l.
)LJ Secondary dispersion haloes of U and Pb at an uranium deposit with blind ore bodies
(Grammakov et al, 1969).
1-5 – concentrations in eluvial-diluvial sediments expressed in the units of local geochemical background &B:
XUDQLXP: 1 - <2&B; 2 – from 2 to 4&B; 3 – from 4 to 8&B; 4 – from 8 to 20&B; 5 - >20&B;
OHDG 1 <3&B; 2 - from 3 to 10&B; 3 - from 10 to 30&B; 4 - from 30 to 100&B; 5 - >100&B;
6 – uranium ore bodies cropping out; 7 – projection of a blind U body up the dip to the day surface; 8 – a site of
the anomaly recommended for reconaissance in detail; 9 – blind U ore zones stripped at one of deep horizons
and projected (up the dip) to the surface.
105
Superficial manifestation of primary and secondary haloes of an uranium deposit with blind ore
bodies was considered by A.I.Grammakov et al (Grammakov et al, 1969) Ore bodies of this deposit
are confined to steeply dipping zones of crushing and their feathering fissures, in acid effusive rocks
and tuffs. Major ore minerals are pitchblende and closely associated with it molybdenite and galenite.
Up the dip of blind ore bodies, carbonatization, albitization, and weak hematization are developed. At
low horizons of the deposit, sericitization and silicification of ore-bearing rocks are observed. Primary
haloes are formed by U, Pb and Mo. After the study of primary haloes above known ore bodies, it was
established that only most extensive of them (280 m up the dip) crop out. Over the north-east section
of the deposit (see Fig. 3.14), an anomaly with relatively high quantities of Pb and low concentrations
of U was discovered. This anomaly belongs to a secondary halo above the blind body which has been
developed at the expense of a primary halo stripped by erosion. Thereupon, secondary dispersion
haloes of U, Pr and Mo were revealed, they agree with primary haloes of these elements.
+\GURFKHPLFDOKDORHVRIEOLQGXUDQLXPGHSRVLWV
Hydrochemical haloes of dispersion of U and its satellites are formed above blind uranium
bodies, at the expense of oxidation of these bodies and their primary haloes. The conditions of
formation of hydrochemical haloes are favourable, if deep and intensive washing of ore bodies is
possible. The scheme of formation of a hydrochemical halo connected with blind uranium bodies in
one of mountain regions of the former USSR is given in Fig. 3.15.
)LJ. Scheme of a hydrochemical halo of a blind hydrothermal uranium deposit discovered after
revealing its radiohydrochemical anomaly (Grammakov et al, 1969)
1 – granites and granosyenites; 2 – sedimentary effusive rocks; 3 – ore bodies; 4 – meteoric precipitation and
underground non-radioactive waters; 5 –radioactive underground waters; 6 – radioactive spring; 7 – prospecting
wells.
Uranium ore bodies are located in granites and granosyenites, they are washed by underground
waters. These waters become radioactive and form a vast hydrochemical halo. A radiohydrochemical
anomaly has been discovered in the course of gamma survey, a radioactive spring was its first
indicator.
Earl and Drever investigated hydrochemical haloes of unconformity-related uranium deposits
(Earl, S.A.M. and Drever, G.L., 1983). Athabasca uranium deposits (Northern Saskatchewan, Canada)
are characterized by relatively simple mineralogy. In most deposits the only important minerals are
pitchblende and coffinite, along with nickel-arsenides and nickel-sulphides. The average underground
water flow rate is in the order of a few centimeters to a few meters per year. Anomalous levels of
uranium, radium, radon and helium have been detected in underground waters from the vicinity of U
mineralization. The results are as follows: U (µg/l): range: 0.1-2000, median – 0.4, anomaly threshold:
10; Ra (pCi/l): range: 1-170; median: 16, anomaly threshold: 10; Rn (pCi/l): range: 80-204 000,
106
median: 1700, anomaly threshold: 300. These anomalies have been detected in drill holes several tens
of metres away from known mineralization.
The rate of “success” have been determined for some of the constituents studied (Fig. 3.16).
Percent of samples from
mineralized areas which
have anomalous concentration
Percent of samples from
unmineralized areas which
have anomalous concentration
)LJ Relative “success” rates, in distinguishing mineralized from unmineralized areas, for underground
water samples from the Athabasca Basin (Earl and Drever, 1983). The “slashed” part of the He and Ra bars
represent false anomalies that can be accounted for (see text).
”Success” was defined as an anomalously high level from a drillhole which is within 100 m of a
uranium mineralized zone. It was established that radon has the highest rate of success, with
anomalous levels found in about 80% of the samples from known mineralized zones. Success rates for
U, Ra and He are slightly lower, and those for As and the hydrocarbon gases (CH4) are below 50%. As
to false anomalies, only about 10% of the samples from presumed unmineralized areas have
anomalous Rn ad U. For He the false anomaly rate is about 60%, but many of these anomalies can be
attributed to long residence times (due to accumulation of He in old ground waters) and can be
eliminated. For Ra the false anomaly rate is 40%, but again some of these can be eliminated as being
of high radium solubility, especially under conditions of low Eh. Arsenic and the hydrocarbon gases
have high false anomaly rates. Some of the samples which were classified as being false anomalies,
particularly those for Rn, U and Ra, are from areas which have a good potential for uranium blind
mineralization.
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Primary lithochemical haloes of U can be buried both in rocks of a folded basement and in crusts
of paleoweathering. These crusts can be overlaid by a very tick cover of unconsolidated deposits. All
diversity petrographical composition of rocks (magmatic, metamorphic, sedimentary) is usually
reflected in the formation of three horizons of a weathering crust (from below upwards): breakstone
(rock debris), particoloured argillaceous (clayey) and kaolin. The full section of a weathering crust is
rarely observed. On elevated sites, only a lower (breakstone) horizon is present; for depressions and
plain sites, a middle horizon is typical; a kaolin horizon can be developed at local sites.
In regions confined to contemporary or ancient river valleys and sea costs of abrasion, a crust
weathering can be completely eroded. Therefore, only those primary haloes which are buried in the
rocks of a basement are symptoms of a deep-seated uranium deposit.
107
6HFRQGDU\UHVLGXDOEXULHGOLWKRFKHPLFDOKDORHVRIGLVSHUVLRQ
Secondary residual buried lithochemical haloes of dispersion are developed within paleocrusts of
weathering, these haloes are abundant and can be observed in any contemporary climatic conditions
(taiga, steppes, deserts). The process of formation of weathering crust was accompanied by the
dispersion of U and its satellites, so secondary haloes in different horizons of the weathering crust
have been generated. Buried secondary haloes are usually mixed (salt and mechanical), with a certain
prevailing of salt haloes. Secondary lithochemical haloes can be also buried in a lower structural stage
(rocks of a folded basement).
The dimensions of buried secondary haloes are, as a rule, several times the dimensions of
corresponding primary buried haloes. This means that buried secondary haloes are closer to the earth
surface than primary ones. Figure 3.17 presents an example of a secondary residual buried
lithochemical halo of dispersion of uranium in a particoloured argillaceous (clayey) crust of
weathering.
)LJ Buried secondary halo of dispersion of U in a particoloured argillaceous (clayey) crust of weathering
(Grammakov et al, 1969).
1 – crust of weathering; 2 – tuffs, 3 – tuffs-conglomerats; 4 – ore body; 5 – primary halo of dispersion; 6 –
secondary halo of dispersion; 7 – boreholes.
6HFRQGDU\VXSHULPSRVHGRSHQHGDQGEXULHGOLWKRJHRFKHPLFDOKDORHVRIGLVSHUVLRQ
Opened secondary superimposed lithochemical haloes of dispersion of U can be developed in
certain climatic environments, and when a thickness of covering unconsolidated rocks is small. Buried
secondary superimposed lithochemical haloes of dispersion of U have been formed in corresponding
paleoclimatic conditions (during the intermission in sedimentation) in sediments of a rather large
thickness.
The formation of superimposed haloes of dispersion depends on many factors: thickness and
composition of unconsolidated sediments, the depth of bedding of superficial and underground waters,
climate, neotectonics, physical-chemical properties of host rocks, etc.
%XULHGOLWKRFKHPLFDOIOX[HVRIGLVSHUVLRQ
Within plains and low-mountain topography, buried lithochemical fluxes of dispersion are rare.
More frequent can be exogenous accumulations in unconsolidated sediments. A typical sign of a flow
of dispersion is its selective cofining to diluvial-proluvial and alluvial-proluvial deposits. Sometimes,
mechanical and salt paleofluxes of dispersion are fixed, usually within old plains.
108
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The following factors are favourable for the development of hydrochemical haloes and fluxes of
dispersion: (1) availability of well-soluble compounds and minerals of U in the zone of hypergenesis;
(2) presence of deeply-washed structures promoting the access of underground waters to ore bodies
and their haloes; (3) certain chemical composition of waters and slow water exchange providing long
contacts of underground waters with ore bodies and water-bearing rocks.
In the areas with a well-developed drainage system, groundwater discharges can be fixed
sometimes as radioactive hydrochemical anomalies in peat bogs, lakes, springs. So,
radiohydrochemical survey of springs along the shores of a lake in one of the regions of the former
USSR (see Fig.3.18) allowed to contour a perspective site, the concentration of U in water within it
exceeded 0.00005 g/l.
)LJ Localization of a perspective area according to the data of radiohydrochemical survey in one of the
regions of the former USSR (Grammakov, 1969).
1 - Paleozoic sediments; 2 - granitoids; 3 - tectonic dislocations; 4 - points of sampling; 5 - anomalous
concentrations of uranium in water; 6 - perspective area delineated by the data of radiohydrochemical survey.
This site was recommended for further exploration.
&DVHVWXGLHV
Below are some examples of studying buried uranium deposits in different geological settings in
the course of prospecting and exploration in the former USSR.
Figure 3.19 refers to the situation where both uranium bodies and their secondary dispersion
haloes are buried. The site is located within a steppe region which is developed upon an accumulative
diluvial-proluvial plain filled by contemporary loams and mid-Ouarternary clays having thickness of
5-8 meters. In a particoloured clayey weathering crust (its thickness varies between 40 and 80 m)
formed upon tuffogenic-sedimentary rocks, residual haloes have maximum dimensions which are five
times dimensions of ore bodies and their primary haloes. In loose (unconsolidated) sediments, released
superimposed dispersion haloes are developed, they do not reach the day surface ending at the distance
of 5-7 m from it. These haloes have not been observed by previous airplane, automobile or pedestrian
gamma-surveys. Only by in the course of blasthole survey, an anomaly has been discovered. Its
detalization has shown that secondary haloes are represented as two zones with the length between
300 and 580 m and the width of 80-120 m. Thereupon, it was established that several benchs of
alternated aleurites, aleurolites (siltstones), litho- and crystalloclastic tuffs of andesite composition
which are broken through by dykes of plagiogranite-porphyries and andesite porphyrites of midPaleozoic. Uranium ores are concentrated in shatter zones and their feathering fissures. Ore
109
mineralization consists mainly of uranium salts of orthophosphoric acid associated with pyrites, iron
oxides, and ankerite. Ore bodies of U are accompanied by the haloes of P2O5.
)LJ Residual and superimposed secondary haloes of dispersion at the site of buried uranium deposit
(Grammakov et al, 1969).
1 – contemporary loams; 2 – particoloured clayey crust of weathering; 3 – rock debris crust of weathering;
4 – alteration of litho- and crystalloclastic tuffs of andesite composition ; 5 – andesite-porphyrites; 6 –
plagiogranite-porphyries; 7 – shatter zone; 8 – ore bodies; 9 – isoconcentrations of U in ppm; 10 – wells (a) and
blastholes (b).
Zones of haloes with U concentrations exceeding 100 ppm are shown by different styles of shading.
Another case deals also with buried secondary haloes (see Fig.3.20). The site is settled on a gently
sloping accumulative plain formed by contemporary clayey sediments with the lenses of
inequigranular sands. Thickness of unconsolidated sediments varies from 5 to 10 m. This overburden
screens completely secondary haloes of dispersion, so they are not manifested at the day surface.
Unconsolidated sediments overlay clayey and rock debris weathering crust of quartz-micaceous rocks.
Average thickness of weathering crust is about 4 m.
An anomaly has been discovered by a blasthole gamma-survey. Subsequent works, using core
drilling, have shown that uranium mineralization is located within crystalline schists of early
Paleozoic. Host rocks are silicificated, they are superimposed by sulphide mineralization consisting of
pyrite, arsenopyrite and sphalerite. Contrast uranium ores are at the depths from 2 to 30 m. They
consist of pitchblende closely associated with pyrites and chlorite. Ore bodies are convoyed by the
haloes of arsenic and copper, they are more extensive than uranium haloes. Migration of U appears as
a result of not recent ongoing, but of older processes. Haloes of As and Cu are also buried.
110
)LJ Cross-section of residual and superimposed secondary buried haloes of dispersion at an uranium
deposit (Grammakov et al, 1969).
1 – clays and loams; 2 – particoloured clayey and rock debris weathering crust; 3 – crystalline schists; 4 –
diorites; 5 – granodiorites; 6 – ore bodies; 7 – isolines of gamma activity in microroentgens per hour; 8 – wells
(a) and blastholes (b).
Zones of haloes with U concentrations exceeding 100 ppm are shown by different styles of shading.
The next example illustrates one of the most difficult prospecting case when a hypogenic uranium
deposit underlies exogenous accumulations in a sedimentary cover (see Fig. 3.21).
)LJ An example of exogenous accumulations of U in unconsolidated sediments and of buried U
mineralization (Grammakov et al, 1969).
1 – Quaternary sediments; 2 – Oligocene sand-clayey sediments; 3 – Triassic-Jurassic weathering crust; 4 –
granites; 5 – lamprophyres; 6 – isolines of gamma-activity in microroentgens per hour; 7 – ore body; 8 – wells
(a) and blastholes (b).
111
The deposit is confined to a neotectonic cavity in the roof of a granite intrusion. It was developed
due to accumulation of uranium in clays of upper Oligocene. Elevated concentrations of U in humusbearing clays are confined to coastal zones of an Oligocene lake basin. The form of the ore body is
lens-like, its thickness does not exceed 2 m. Secondary haloes along the roof of a weathering crust
have the length of 800 m (that it is perpendicular to the image plane) and 300 m in the direction of its
width. Hypogenous mineralization is presented by relatively small lenses of contrast ores. Uranium in
them is in the form of salts of orthophosphoric acid. In the case considered, exogenous accumulations
of U and hypogenic U mineralization are not related genetically. Their spacious correlation appears as
a result of neotectonic movements along earlier formed released zones (to which are confined uranium
mineralization) when a subsidence of the site has happened. A system of lakes with the reductive
environment was formed over here in Oligocene. From underground waters draining granodiorites
with highly elevated concentrations of U, uranium was precipitating in coastal zones of lakes, this has
led to the formation of exogenous accumulations.
Isolines of gamma-activity at the isolated halo on the left represent one of exogenous
accumulations of U in unconsolidated sediments, there are several of them within this site located in
near-shore zones of an Oligocene lake basin, they do not have any economic value. The authors
underline that exogenous accumulations of U and its hypogenic mineralization are not genetically
related in the case considered (that is why this is an example of rather difficult situation). Spacious
relation is caused by neotectonic movements resulted in a subsidence of the site, a system of lakes
formed in Oligocene had a reductive environment, uranium was precipitated from underground waters
which drained granitoids with high concentrations of U, its deposition at near-shore zones of lakes
yielded the formation of exogenous accumulations.
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All easily discovered deposits of metals are usually divided into three groups depending on what
namely is exposed at the earth surface: (1) primary ores and their haloes; (2) secondary (oxidized) ores
and their secondary or mixed haloes; (3) secondary haloes only. An example of primary haloes of rare
metals (Pb, Ba, Ag) clearly exposed at the earth surface was considered above (see 3.2.1).
Uranium deposits characterized by their primary ores cropping out are rather rare. Uranium
deposits with cropping out of their oxidized ores are more usual, but also rare. The most abundant are
cases where only secondary haloes of U deposits are exposed at the surface (opened secondary
haloes). Their properties strongly depends on landscape characteristics.
2SHQHGKDORHVRIXUDQLXPLQWKH]RQHVRIWDLJDZLWKFRQWLQXRXVSHUPDIURVW
In the zones of taiga with continuous permafrost, both ore bodies and their primary haloes can be
exposed at the surface, due to the predominance of physical weathering of the ores. It occurs mainly
upon steep and denuded slopes, where hillside wastes of ores go down as narrow bands. The areas of
these mechanical halo can be many times the dimensions of radioactive sites in original rocks.
On gentle slopes covered by silt, the upper border of permafrost approaches the surface, and an
active layer, which is thawed out in summer, can reach 1-1.5 m. The processes of leaching proceed
basically just within this active layer, where podzolic leached soils are developed. Leaching of the
uranium outcrops leads to the evacuation of U and Ra, the former is evacuated more intensively than
the latter. The processes of leaching do not promote the formation of epigenetic opened haloes, even in
a thin layer of silt. In unconsolidated eluvial-diluvial material, mechanical haloes are formed, due to
the input of radioactive fragments. In this case, a coarse fraction is the most radioactive, whereas
radioactivity of a fine fraction is low. Maximum thickness of an unconsolidated cover providing the
formation of opened dispersion haloes, which can be easily and reliably detected, is called critical
thickness of covering sediments in considered cases is about 1 m (Grammakov, 1969).
112
2SHQHGKDORHVRIXUDQLXPLQWKH]RQHVRIWDLJDZLWK³LQVXODU´SHUPDIURVW
In the zones of taiga with “insular” permafrost, thickness of thawing out layers is increased, so
the processes of leaching and transport of ore material become more intense. As a result, near-surface
depletion of ores and haloes in original rocks is enhanced, it penetrates more deeply. Thus, in the
direction from northern to southern regions, there is a growing tendency of halo depletion at deposit
outcrops. At the same time, however, the possibility of the formation of new haloes in bogs adjacent to
slopes and in flows of dispersion become more significant. The appearance of taliks, mainly on the
slopes of south exposition, stipulates the outcrop of under-permafrost waters at the surface. Therefore,
opened hydrochemical haloes are not limited by a thin over-permafrost layer over here (Grammakov,
1969).
2SHQHGKDORHVRIXUDQLXPLQWKH]RQHVRIWDLJDZLWKRXWSHUPDIURVW
In the regions without permafrost (south taiga), the conditions of uranium accumulation in
dispersion flows are still more favourable than in taiga with “insular” permafrost. And the possibility
of accumulation of ore elements in subordinate landscapes is more important, at the expense of rocks
with elevated radioactivity (salt haloes and dispersion flows of granites and other acid and alkaline
rocks). This makes the interpretation of detected anomalies more difficult. On the other hand, in the
regions of southern taiga, additional opportunities arise, connected with the availability of displaced
and “torn off” haloes (haloes in diluvial trains, flows of dispersion, accumulations in bogs located in
the vicinity of slopes, hydrochemical haloes). But again, interpretation of revealed anomalies can be
difficult, due to the distant removal of ore elements from their deposits and the formation of salt
accumulations of uranium (Grammakov, 1969).
2SHQHGKDORHVRIXUDQLXPLQIRUHVWVWHSSH]RQHV
In forest-steppe zones, flows of dispersion of ore elements (including uranium) are usually well
formed, their extension can reach several hundreds or even thousands meters (see Fig. 3.22). Foreststeppes sites appear to provide the most favourable conditions for formation of dispersion flows, in
comparison with the regions located to the north and especially to the south of them. Sometimes,
accumulations in humus-bearing bottom sediments of rivers and mort-lakes (oxbow-lakes, crescentlakes, blind channels)are developed in such extent that they can be of an economic significance.
Forest-steppes represent a transition type of landscapes. At sites covered by forests, grey podzolic
soils are formed, whereas in steppes – leached chernozems. Significant quantities of atmospheric
precipitation and warmth, unstable alternated humidity of soils and grounds, frequent fluctuations of
the level of ground-water table – all these factors , at rocky sites with low-humus soils, create
favorable conditions for leaching of U from a rather large thickness of washed rocks and its evacuation
in the form of carbonate complexes into river valleys. At the same time, humus-bearing muds of rivers
and lakes promote accumulation of U. This explains the above-mentioned intense development of
dispersion flows. Their discovering is rather simple, however interpretation can be difficult, due to
long ways of U migration. In forest-steppe regions, slopes of hills are usually overlaid by a
sedimentary cover. The most denuded are watersheds and the bands of near-river sandstones. At these
sites, surface manifestation of uranium is clear, so discovery of U deposits is possible by means of
opened secondary haloes, especially by those formed by Ra (Grammakov et al, 1969).
113
)LJ Scheme of haloes and dispersion fluxes at a stratified uranium deposit in a forest-steppe region
(Grammakov et al, 1969).
1 – granites; 2 – effusive-sedimentary rocks (MZ); 3 – Quartenary eluvial-diluvial sediments; 4 – ore
bodies; 5 – uranium haloes in original rocks (a dotted line in the plan shows a halo part which is not exposed at
the surface); 6 – haloes of U (a) and As (b) in original rocks in the cross-section; 7 – uranium haloes in
Quartenary eluvial-diluvial sediments; 8 – uranium dispersion flow in bottom sediments.
2SHQHGKDORHVRIXUDQLXPLQWXQGUD]RQHV
Tundra landscapes are characterized, compared to taiga, by more intensively development of
mosses and lichens, proximity of frozen rocks to the surface, more humidity of soils and grounds (due
to weak evaporation of atmospheric precipitation and water-impermeability of frozen rocks). Tundra
soils are basically gleyish, weakly podzolic with a narrow humus layer (2-5 cm). They are practically
absent upon rocky hills. Relief hollows are usually enriched by rock debris which have been almost
not exposed to oxidation. The slopes are covered by silt (aleurite) and rock debris.
The character of soils, presence of permafrost, low activity of chemical processes promote
conservation of ores and haloes just under the earth surface. The formation of opened haloes can be
induced by vertical displacements of grounds in an active layer under the influence of such processes
as swelling, solifluction, stone freezing out. Solifluction also stretches haloes along the slopes. Mosses
and lichens which are saturated by water, can screen radioactive haloes.
%LRJHRFKHPLFDOKDORHV
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Table 3-5 presents the results of measurements of the concentration of elements in the ash of
plants growing over different types of ore deposits (Alexeenko, 1989). It shows that there are specific
114
associations of elements occurring at raised concentrations in plants associated with the type of
deposits. Uranium ore bodies are manifested by elevated concentrations of U, Th, TR and sometimes
of Mo, Pb, and Zn in plants.
7DEOH$VVRFLDWLRQVRIHOHPHQWVRFFXUULQJDWUDLVHGFRQFHQWUDWLRQVLQSODQWVJURZLQJRYHU
GLIIHUHQWW\SHVRIRUHGHSRVLWV$OH[HHQNR
Types of ore deposits
Rare metal pegmatite
Tantalum-bearing apogrnites
Skarn copper-cobalt
Skarn berillium
Skarn copper
Skarn molybdenum-tungsten
Greisen sulphide
Greisen rare metal
Hydrothermal gold-quartz
Hydrothermal gold-sulphide
Hydrothermal uranium
Hydrothermal tin
Hydrothermal copper
Hydrothermal molybdenum
Hydrothermal polymetallic
Sphalerite-polymetallic
Sphalerite
Stratified lead-zinc
Nickel-bearing crusts of weathering
Associations of elements
Li, Cs. Ta, Nb, (Rb, Be)
Rb, Li, (Sn)
Co, Ni, Cu, As, (Ag, Pb, Zn)
Be
Mo, Cu
Mo, W, (Bi)
Be, Mo, Bi
Be, F, Zr, (Cu, Mo, Pb)
Zn, Au, (Pb, Cu)
Au, Cu, As, (Ag, Pb, Mo)
U, (Mo, Pb, Zn), Th, TR
Sn, Pb, Cu, Zn
Mo, Cu, Zn
Mo
Zn, Pb, (Ti, Mn)
Pb, Zn, Mo, Ag, (Sn, Cu)
Mo, Cu, Zn, Co, (Ag)
Pb, Zn, (Ag)
Ni, (Co, Cu)
&RQWUDVWLQGH[HVRISK\WRJHRFKHPLFDODQRPDOLHV
Tkalich proposed to use two contrast indexes of a phytogeochemical anomaly: its index relatively
a local ($OS) and general ($JS) phytogeochemical background (Tkalich, 1970):
$OS = &D/&OS,
$JS = &D/&S,
where &D – the element concentration in the plant ash; &OS – local phytogeochemical background of
the element; &S – general phytogeochemical background of the element.
The values of $OS and $JS are related to the coefficients of biological accumulation. These
coefficients are determined as follows:
.EO = &D/&V,
.EJ &D/./
where &V – the element concentration in substratum (soil), ./ – the element concentration in the
lithosphere (Clarke value).
Thus, contrast indexes are determined by the following expressions:
$OS= .EO⋅&V/&OS,
$JS= .EJ⋅.//&S.
Contrast indexes are proportional to the coefficient of biological accumulation of the element .EO
(or .EJ), the concentration of this element in substratum &V (or the Clarke value ./), and inversely
proportional to local (&OS) or general (&S) phytogeochemical background. According to a contrast
degree, phytogeochemical anomalies are divided into weak-contrast ($OS = 4-10; $JS = 4-50)and highcontrast ($OS ≥ 10; $JS ≥ 50).
115
+LJKFRQWUDVWSK\WRJHRFKHPLFDODQRPDOLHV
According to Tkalich, high-contrast phytogeochemical anomalies can be formed in the following
cases.
(a) When a deposit (1) consists of minerals that are capable to be altered in the zone of
hypergenesis into substances more or less soluble in water; (2) is characterized by significant
concentrations of ore elements; (3) is localized in the environment which is favorable for chemical
weathering at the depth available for plant roots.
(b) When a deposit (1) consists of minerals that are capable to turn into secondary substances
soluble in water; (2) is characterized by comparatively low concentrations of ore elements; (3) but
occurs in the environment which is favorable for chemical weathering near the earth surface, so plant
roots are in direct contact with the ore material.
(c) When the formation of phytogeochemical anomalies is induced by a partial or total nutrition
of plants by mineralized groundwaters.
As an example of the case (a), Karaftite deposit of gold in Eastern Siberia can be considered.
It is composed by Proterozoic crystalline schists crumpled into complicated folds, broken down by
faults. Concordant quartz veins occur within schists. Ore mineralization is presented by gold and
accompanying sulphides. The thickness of elluvial-delluvial overburden is of 2-3 m. The conditions
for chemical weathering are rather favorable. There is a mixed forest over the deposit, with a wellformed circle of bushes. Determinations of gold in the ash of different plants revealed
phytogeochemical anomaliesthat delineate clearly quartz gold-bearing veins. The largest amounts of
gold (10-50 ppm) were fixed in the ash of marsh tea (/HGXP SDOXVWUH). Local phytogeochemical
background established by this plant of 0.3 ppm. The contrast indexes are: $OS 33-166; $JS = 10-50.
Phytogeochemical anomalies of molybdenum at Balbagarskoye deposit in Buryatiya (Russia)
demonstrate an example of the case (b). This deposit is composed by Proterozoic binary micaamphibole, biotite-cordierite, andalusite and sericite schists, burst by biotite-and aplitic granites. In the
site of the deposit, schists are gently pitching. They are mineralized in the zone of contact with
granites. Schists are silicified, they contain molybdenite and pyrite. The zone of oxidation is well
manifested, it contains limestone and ferrimolybdenite. The molybdenum ores of Balbagarskoye
deposit are poor. At the top of Rudnaya mountain, sediments are almost absent, however their
thickness increases downhill up to 10 m. At the outcrops of ore-bearing schists, plant roots are in
direct contact with minerals. There is a mixed forest over the deposit, where birches %HWXODYHUUXFRVD
are prevalent. By the concentrations of Mo in the ash of birch wood, phytogeochemical anomalies of
this metal have been revealed, well coinciding with the outcrops of ore-bearing schists. Local
phytogeochemical background of Mo in the ash of birches is between 1 and 10 ppm. Anomalous
concentration is of 500 ppm. The contrast indexes of anomalies are: $OS≥ 50; $JS = 25.
As an example of the case (c), phytogeochemical anomalies at one of uranium deposits in the
former Soviet Central Asia can be regarded (they have been described in the book of Malyuga ).
Uranium mineralization is localized along the fractures in a sandstone layer which is interbedded
between sand-argillite and argillite Permian suites, dipping to South at an angle of about 400.
Secondary uranium minerals occur in the fault zone, crossing the deposit in the latitude direction. The
overburden thickness is between 2 and 5 m. The soil layer is practically absent. The deposit surface is
covered by moving aeolian loads. At this deposit, underground waters are unwashed. Near the surface,
they are weakly mineralized, their mineralization increases with the depth. The concentrations of U in
underground waters is between 5⋅10−6 and 4⋅10−4 mg/l. The climate in the district of the deposit is dry,
semi-arid, unfavourable for chemical weathering. The vegetation over the deposit consists of different
xerophytic species (plants of dry landscapes) and phreatophytes (plants nourished by groundwaters).
By the concentrations of U in the ash of these plants, phytogeochemical anomalies were observed,
they coincide well with the ore zones. Local phytogeochemical background of U in the plant ash was 3
ppm. Maximum anomalous concentration of U which was of 80 ppm, has been fixed in the ash of
astragal $VWUDJDOXVYLOORVLPXV. The contrast indexes of this anomaly were: $OS= 27; $JS = 160.
116
%LRJHRFKHPLFDOH[SUHVVLRQRIGHHSO\EXULHGXUDQLXPPLQHUDOL]DWLRQ
Biogeochemical expression of deeply buried uranium mineralization in Saskatchewan, Canada
was investigated by Dunn (Dunn, C.E., 1981). The study concerned biogeochemical haloes of highgrade U mineralization (about 27% U3O8) buried 150 m beneath the surface at the unconformity
between the Athabasca and crystalline basement, buried under barren Precambrian Athabasca
Sandstone. The study has shown that abnormally high U concentrations are present in some of the
vegetation. It is important to underline that no other geological or geological surface manifestation of
mineralization was discernible. A biogeochemical survey of the area sampled different soil horizons,
peat moss, and plant organs from the dominant species, viz. Black spruce (3LFHDPDULDQD), jack pine
(3LQXVEDQNVLDQD), labrador tea (/HGXPJURHQODQGLFXP), and leather leaf (&KDPDHGDSKQHFDO\FXODWD).
Uranium concentrations in the ash of various media were very high: in spruce twigs up to 154 ppm; in
labrador tea and leather leaf stems around 100 ppm U. The background concentration of U in plant ash
was estimated to be 0.6 ppm. It is noteworthy that the soils within which the plants were growing had
only background concentrations of U (1-2 ppm). There was no correlation between the U content of
the ashed plants and the soils or peat within which they were growing. Upward migration of ions along
steeply inclined fractures was invoked to explain the U anomalous accumulation in plants.
)DOVHSK\WRJHRFKHPLFDODQRPDOLHV
High concentrations of an element in the ash of plants, not related to their selective ability and not
corresponding even to low concentrations of this element in a soil, rock or water, but depending on the
concentrations of some other elements in these media, represent false phytogeochemical anomalies.
For example, at Shipilinskoye deposit of copper in Chakassiya (Russia), it was noted that the ash of
birch leaves %HWXOD YHUUXFRVD growing on ore-bearing skarns and skarned rocks has unnatural
raspberry colour. Chemical analysis showed that this ash contains up to 10-16% of manganese. Using
these concentrations, a phytogeochemical map has been drawn, which revealed clearly rather contrast
anomalies of Mn. Control surveys showed that they confined to the rocks containing no more than
0.33% of Mn and, hence, are false.
The reason of the formation of false anomalies seems to be induced by differences of mobility of
certain chemical elements relatively to other elements under given values of pH and Eh of soil waters.
The formation of false phytogeochemical anomalies do not relate to a selective ability of plants.
However, when a chemical element forming a false anomaly in the plants of a given species is
accumilated selectively by them, their selective ability intensifies the contrastness of false anomalies
(Tkalich, 1970).
8UDQLXPUDGLXPGLVHTXLOLEULXPLQELRJHRFKHPLFDOF\FOLQJDQGLWVFRQVHTXHQFHV
Numerous studies demonstrate that the values of plant-soil concentration ratio (CR) for U and Ra
differ significantly. In his book “Natural Radioactive Elements in the Plants of Siberia”, Kovalevsky
notes that the uranium CR value depends on U concentrations in soils. If U concentrations in soils are
close to the Clarke value (Q⋅10−4%), its CR value is usually around 0.02-0.2 However, when the
amounts of U in soils are near ore concentrations (Q⋅10−2 – Q⋅10−1%), its CR values are lowered to be
within the range of 0.03 - 0.0001. The radium CR values for the same plant species are one or two
orders of magnitude higher than the uranium CR values. Under favourable conditions, the radium CR
value can be of 20-30.
The same regularity is observed if instead of plant-soil concentration ratios, one considers the
mean value of plant-rock concentration values defined as CR’ = Cp/CL, where Cp – mean concentration
of an element in the ash of plants; CL – mean abundance (Clarke) of this element on the lithosphere.
Tkalich reported the following values of CR’ averaged over many plant species: U – 0.2; Ra – 2.0
(Tkalich S.M., 1970). Compared to the ratio CR’Ra/CR’U, the ratio CRRa/CRU is always increased.
Essential differences in the values of both CR and CR’ for U and Ra are induced by the violation
of radioactive equilibrium. This violation takes place mainly in overground organs of plants
(Kovalevsky A.L., 1966). Radium is a chemical congener (analogue) of calcium, these elements show
similar features in their biogeochemical behaviour. So, in the study of uptake by vegetables from soils
117
located in regions of high natural radioactivity in Brazil, it was reported that the highest 226Ra and Ca
concentrations were found in the same plant species (Vasconcellos, 1987).
For many plant species, the Ra uptake is a linear function of the concentration of its mobile forms
in soils, this kind of dependence was observed in a wide interval of Ra amounts in soils On the
contrary, the U uptake is a non-linear function of its concentrations in soils, the response of most
plants appears as a typical saturation curve showing a certain absorption limit. According to
Kovalevsky, the role of anticoncentration physioloigical-biogeochemical barriers is essential in the
response of the majority of plants to U presence in soils. Anticoncentration barriers are common in
living organisms, they are established for 76 chemical elements (Kovalevsky A.L., 1987).
The existence of a limit in the U uptake by plants can be explained by its strong toxic properties.
According to Hodge, U acts on the surface of cells, it blocks up their hydrocarbonic exchange
including the supply of glucose. This blockade seems to be induced by the action of U on the ferment
system of plants which provides normal metabolism functioning (Hodge H.C. et al., 1973).
Thus, Ra “outruns” U in their pathway from rocks to soils and then into plants and foodchains.
This regularity concerns not only 226Ra and 238U, but also 228Ra in 232Th decay series. Average
concentrations ratio values for different vegetable species collected from the Pocos de Caldas Plateau,
Brazil, which is regarded as a natural analogue for the disposition of transuranic elements, are as
follows: 228Ra – 0.0236; 232Th – 0.00011; i.e. the uptake of 228Ra into edible plants is about 200 times
that of 232Th (Linsalata P. et al, 1989). Thus, radioactive equilibrium is violated in Th series as well,
and its shift is also in the favour of Ra.
2QGLHWDU\LQWDNHV IRUQDWXUDOUDGLRQXFOLGHVLQQRUPDOEDFNJURXQGDUHDV
Harley summarized estimates of dietary intakes for natural radionuclides in normal background
areas of the world (Harley, 1980). Mean human dietary intakes (in mBq/day) are the following: 238U –
19; 226Ra – 56; 232Th – 4.2; 228Ra – 43. Thus, the sum of Ra isotope intakes is about 100 mBq/day,
whereas the sum of U and Th intakes is 4-5 times less. As in their uptake by plants, Ra and Ca tend to
be correlated in human foodchains. So, Ra intake and bone Ra concentrations were shown to be
directly proportional to dietary Ca intake {Hallden, N.A. and Harlet, J.H., 1964). Linsalata et al.
reported strong correlations between edible vegetable Ca concentrations and 226Ra and 228Ra (Linsalata
P. et al, 1989). It is worth noting that data from adult human autopsy tissues indicate skeletal
percentage of 95% for 226Ra, this value is the largest among those of other radionuclides (Linsalata P.
et al, 1994). This underlines the preferential role of Ra incorporation into human bone where it
remains for a long time.
The following conclusions can be made.
(1)
Toxic properties of U together with severe disequilibrium between Ra and U allow to consider
the latter as an element which is practically eliminated from biological circulation in the majority of
natural biogeochemical communities. On the contrary, Ra is involved in this circulation, and just vital
activity of plants appears to be a cause of the shift in radioactive equilibrium in the favour of Ra. The
mechanisms relating to Ra uptake and translocation in plants appear to be similar to those of Ca.
(2)
Phytogeochemical anomalies of Ra over U deposits are manifested in a much more degree
than phytogeochemical anomalies of U. Sometimes, Ra biogeochemical anomalies/haloes are clearly
marked, whereas U anomalies in the same plant species are not observed. Anyway, detection of Ra
anomalies in plants is more effective (“radiophytometry” is more effective compared to
“uranophytometry”).
(3)
Despite the great differences in the litosphere Clarke values between U and Ra (more than
seven orders of magnitude), the role of Ra isotopes in the rock-soil-plant-human pathway is more
important than the role of U and Th: in normal background areas of the world, the contributions of
226
Ra and 228Ra into human radionuclide dietary intake (expressed in Bq/day) is 4-5 times that of 238U
plus 232Th.
118
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VLWHV
Very interesting regularities have been revealed after comparison of different uranium deposits of
the former USSR. Lisitsyn has analyzed well-preserved (isolated from the earth surface without any
manifestation on it) deposits with deposits that are in the state of destruction (Lisitsyn A.K., 1994).
These results are presented in Table 3-6.
7DEOH6WDWLVWLFDOUHODWLRQVKLSEHWZHHQZHOOSUHVHUYHGLVRODWHGIURPWKHGD\VXUIDFH
XUDQLXPGHSRVLWVDQGGHSRVLWVRI8ZKLFKDUHJRLQJWREHGHVWUR\HGIRUWKHIRUPHU8665
/LVLWV\Q$.
Genetic group of
deposits
Endogenous
Intermediate
Exogenous
All deposits
Number of deposits
Number of wellpreserved deposits
14
5
54
73
54
8
66
128
Percentage of wellpreserved deposits
26
62
82
57
Table 3-6 is based upon the analysis of the manifestation of the most well-known uranium
deposits of the former USSR located in Russia, Ukraine, Kazakhstan, Uzbekistan, Kyrgyzstan and
Tajikistan. Among the total amount of 128, more than half (57%) are completely isolated from the
earth surface. Among endogenous deposits, only 14 from 54 (26%) do not generate geochemical
anomalies directly connected with their ore mineralization, while exogenous deposits having no direct
connection of the ore mineralization with the earth surface number 54 of 66, i.e. 82%. These data
show an essential and contrast distinction of exogenous deposits from endogenous ones, regarding the
degree of their manifestation at the day surface and, correspondingly, reflects much better isolation of
exogenous deposits.
Above-indicated results are in good agreement with generic geological considerations.
Exogenous deposits, representing the products of the differentiation of the earth crust matter , were
influenced by exogenous factors and preserved in interior part of the earth under the conditions of their
isolation and geochemical conservation mainly in sedimentary rock basins, i.e. in depression
structures. Endogenous deposits are connected with the regions of tectono-magmatic activization
leading to a sharp differentiation of relief with its subsequent erosion. Naturally, endogenous deposits
have the greater probability of moving their ore-bearers or indicators towards the earth surface.
Thus, Lisitsyn et al insist that exogenous U deposits are more preferable for modelling than
endogenous ones. Indeed, a very essential difference between exogenous and endogenous deposits
leads to the fact that endogenous deposits are characterized by the greater probability of driving their
ore bodies towards the surface. It is worth noting that Lisitsyn et al propose to consider exogenous U
deposits not only as natural analogues for modelling, but as possible sites already ready for disposal. It
means that a repository would be just near U bodies, within their host rocks that demonstrating
excellent isolating properties.
Exogenous deposits of uranium are usually sudivided into V\QJHQHWLF DQG HSLJHQHWLF deposits.
Syngenetic concentrations were formed together with their host rocks, epigenetic concentrations
appeared as a result of ore-forming elements supply by underground waters into earlier formed
sediments and rocks. Geological environment of the localization of syngenetic uranium deposits, due
to low permeability of their host rocks, may be regarded as analogues of repositories of solid and
solidified wastes. Epigenetic uranium deposits which were formed in water-permeable layers and
fracture zones may be considered, in certain conditions, as analogues of repositories of liquid wastes
(Lisitsyn, 1994).
Two Russian exogenous uranium deposits, one – syngenetic and another – epigenetic, are briefly
described below.
([RJHQRXVV\QJHQHWLFGHHSVHDWHGXUDQLXPGHSRVLW
Stepnovskoye deposit (Ergeninsky ore region, Kalmykiya, Russia) is an example of sedimentarydiagenetic deposits, preserved within a powerful clayey rock mass of the Oligocene- Lower Miocene
age (Fig.3.23).
119
)LJ Schematical section of Stepnovskoye deposit (Ergeninsky ore region, Kalmykiya, Russia).
1- sandy-clayey rock mass; 2- carbonate aleurolite; 3 – aleuritic clay; 4 – carbonate clay; 5 – clay with fish
remnants (flake, bony detritus); 6 – clay; 7 – ore lode of fishery bony detritus.
The lodes of metal-bearing fishery bony detritus in a lower part of the rhythm of Oligocenic
aleurolite-clay strata has been revealed by drilling at accessible depths within elevated Elinistinsky
block of Karpinsky in Ergeninsky ore region (Stolyarov A.S. and Ivleva E.I., 1991). In the reducing
environmnent of clays with heightened concentrations of sulfur, phosphate matter of fishery bony
detritus accumulated rare-earth elements, uranium and scandium up to economic-level of ore amounts.
In the association with disulfides of Fe, such elements as Ni, Co, Mo, Re are present constantly, while
Cu, Zn, Pb and As can be met more or less often. This multi-element association has been created in a
calm hydrodynamic environment of rather deep-water sediments at the distance of some tens
kilometers from the shore area of island ensembles of an external zone of the shelf of an Oligocene
sea.
Such sedimentary-diagenetic accumulations of U in black clays and shales are usually wellisolated in sandy-clayey sedimentary formations so they do not influence appreciably on the
surrounding environment, until they are moved to the earth surface. In the zone of surface oxidation,
sedimentary-diagenetic concentrations of radioactive elements have an influence upon the surrounding
environment, mainly by the transformation of primary minerals into newly-formed ones, with a
limited expansion of the volume of their dissemination and formation of salt fluxes of dispersion of
ore mineralization.
Exogenous epigenetic concentrations of U and associated elements are formed by the infiltration
of underground waters , mainly of bedded (stratified) aquiferous horizons. The most general
geochemical reason of the formation of ore-bearing solutions is oxidizing leaching of chemical
elements from aquiferous rocks. A sharp change of oxidation conditions into reducing ones at the
terminations of the zones of stratified oxidation leads to the precipitation of chemical elements
forming in their low-valence states weakly soluble compounds. At reducing barriers, such elements as
Se, U, Re, Mo, V are accumulated up to ore concentrations. When a reducing environment is created
by hydrogen sulphide, the accompanying accumulation of sulphides of Zn, Pb and some other metals,
not changing their valence state in natural conditions, takes place.
Taking into account its influence on the environment, the process of ore formation by infiltration
can be regarded as a process of cleaning of infiltrated underground waters from heavy metals and such
elements as Se, some of them being highly toxic.
120
([RJHQRXVHSLJHQHWLFGHHSVHDWHGXUDQLXPGHSRVLW
The formation of uranium deposits of the type considered above occurs under the input
domination of oxidants over reducing agents into an ore-bearing horizon, this is expressed by
extension of the zones of stratified oxidation controlled by the permeability of rocks. The change of
the balance of the input of oxidizing and reducing agents in the favour of the latter leads to the ceasing
of the ore-forming process and to the conservation of epigenetic mineralization formed in the reducing
environment. Such deposits appear to be the closest analogues of that geological situation which is
required to provide a reliable burial of radioactive waste. Dalmatovskoye deposit (Transural region)
illustrates just such geological environment of hydrodynamic isolation of ore-bearing palaeo-valley
sediments under transgressively overlapping four continental and sea water-resisting layers divided by
three aquiferous horizons. Reliable isolation of palaeo river-bed sediments from the ecosphere allows
to consider these sediments beyond the limits of the deposit as a possible collector for both solidified
and liquid wastes (Lisitsyn, 1994).
Exogenous epigenetic deposit Dalmatovskoye was formed during the progressive
development of ground-stratum oxidation of alluvial water-permeable deposits containing organic
(humus) substances. Under transgressive overlapping of ore-hosting rocks by clayey water-resisting
continental and, later, sea sediments, the ceasing of the input of exogenous oxidants led to regression
of the process of oxidation and to epigenetic reduction of earlier oxidized rocks (Fig.3.24).
Geochemical signs of preservation of Dalmatovskoye deposit are its reducing environment and
the absence of heightened amounts of uranium in underground waters of the ore-bearing horizon.
However, reducing environment does not hinder migration of radium and radon, that is why their
concentrations within the limits of ore bodies reach, respectively, several tenths of nanogram and
several thousands emans in 1 l of water. Extremely slow water exchange (the gradient of piezometric
level is about 0.0003) predetermines mainly diffusion mechanism of migration and re-distribution of
radioactive elements. The differences in geochemical properties of U and Ra provoke here specific
violations of radioactive equilibrium. The value of a coefficient of radioactive equilibrium between U
and Ra (.UH) in ore samples varies from 0.33 to 5.75.
Discrete distribution of uranium minerals of rocks in geochemical environment which is
unfavourable for migration of U but favorable for migration of Ra, caused rather narrow variation
limits of Ra concentration in ore samples in comparison with their U concentrations. This has resulted
in a statistically revealed greater probability of samples having a disequilibrium shift towardsRa
excess. Radium deficiency is observed only in samples that are strongly enriched in U. The modal
value of .UH averaged on several hundreds of measurements is 1.08, while in relatively waterproof
(strongly mudded by clay) samples this value is practically 1. Using a group of 236 samples where .UH
varies between 0.9 and 1, i.e. samples related to minimal diffusion dispersion of Ra, the Pb isotope
method has yielded the modal value of age equal to 140 million years, this corresponds to the
boundary of Jurassic and Cretacious periods.
121
)LJ Schematized section of Dalmatovskoye deposit (Transural region).
1 – permeable, mainly terrigenic rocks; 2 – water-resisting, mainly clayey sediments; 3 – products of
the weathering of clayey crust; 4 – rocks of lithified basement; 5 – ore intervals crossed by boreholes.
A lowered degree of oxidation of U in the ore of Dalmatovskoye deposit which is only about
10% of hexavalent uranium of its bulk content, also agrees with geologically long being of ore bodies
in geochemically reducing environment. This distinguishes the ores of Dalmatovskoye deposit from
other late-Alpine stratified infiltrated deposits with an uncompleted ore-forming process (Lisitsyn,
A.K. et al., 1984), the latter reveals an equal probability of uranium occurrence in all oxidation states,
from U (IV) to U(VI).
(QGRJHQRXVGHHSVHDWHGXUDQLXPGHSRVLW
The section of Grachevskoye deposit in Northern Kazakhstan (Fig. 3.25) is an example of an
endogenous deposit isolated from the earth surface.
Hydrothermal uranium mineralization placed in compound-dislocated and metamorphised rocks
of Vendian age was partially eroded and was later isolated from the earth surface by a screen of a
clayey weathering crust of Mesozoic age together with mainly clay Cenozoic sediments that have been
overlapped an ore-bearing series. Uranium mineralization has been discovered by well-logging of
hydrological holes for a water supply (Lisitsyn, A.K., 1994)
122
)LJ Schematized section of Grachevskoye deposit (Northern Kazakhstan)
1 – clayey crust of weathering of Mesozoic age; 2 – medium- and coarse-grained leucocratic and
porphyraceous granites; 3 – gabbro; 4 – carbonate-schist series of Vendian age; 5 – terrigenic (guartz) Vendian
series; 6 – basic faults; 7 – uranium mineralization; 8 – mine workings.
It is worth underlying that Figure 3.25. does not show an example of a non-preserved endogenous
deposit. This is an example of an endogenous deposits which is very well isolated from the surface. It
has been discovered by chance, accidentally. People wanted to have more water in the region, so they
were drilling boreholes to search water-beating horizons. These holes were not deep, the deposit is
rather near the surface. So, they failed in their water search, but a new U deposit has been discovered,
though previous special surface surveys for U were unsuccessful.
%LEOLRJUDSK\
Alekseenko, V.A. 1989. *HRFKHPLFDO 0HWKRGV RI ([SORUDWLRQ. Moscow: Vysshaya Shkola (in
Russian.
Alexeenko, V.A. and Voitkevich, G.V. 1979. *HRFKHPLFDO 0HWKRGV RI 3URVSHFWLQJ RI 0LQHUDO
'HSRVLWV. Moscow: Nedra (in Russian).
Dunn, C.E. 1981. Biogeochemical Expression of Deeply Buried Uranium Mineralization in
Saskatchewan, Canada // -RXUQDORI*HRFKHPLFDO([SORUDWLRQ. V.15, pp.437-452.
Earl, S.A.M. and Drever, G.L. 1983. Hydrogeochemical Exploration for Uranium within the
Athabasca Basin, Northern Saskatchewan // -RXUQDORI*HRFKHPLFDO([SORUDWLRQ. V.19, pp.57-73.
Grammakov A.G. et al., 1969. 0HWKRGVRI3URVSHFWLQJRI8UDQLXP'HSRVLWV. Moscow: Nedra (in
Russian).
Gurevich, V.L. and Kantzel, A.V. 1984. Subbackground Haloes of Hydrothermal Deposits of
Uranium // *HRORJL\DUXGQ\KPHVWRURMGHQLL*HRORJ\RI2UH'HSRVLWV N 4, pp.65-75.
Harley, J.H. 1980. Naturally Occurring Sources of Radioactive Contamination. In: M.W.Carter
(ed.). 5DGLRQXFOLGHV LQ WKH )RRGFKDLQV cited by Linsalata P. 1994. Uranium and Thorium Decay
Series Radionuclides in Human and Animal Foodchains – a Review // -(QYLURQ4XDO V.23, pp.633642.
123
Hallden, N.A. and Harlet, J.H. 1964. Radium-226 in Diet and Human Bone from San Juan, Porto
Rico // 1DWXUH (London). V. 204, pp.240-241.
Hodge, H.C. et al. 1973. Uranium, Plutonium and the Transplutonic Elements +DQGERRN RI
([SHULPHQWDO3KDUPDFRORJ\. Vol.36. NY: Springer-Verlag.
,QVWUXFWLRQ RQ *HRFKHPLFDO 0HWKRGV RI 2UH 'HSRVLWV 3URVSHFWLQJ. 1983. Moscow: Nedra (in
Russian).
Kovalevsky, A.L. 1966. 1DWXUDO 5DGLRDFWLYH (OHPHQWV LQ WKH 3ODQWV RI 6LEHULD Ulan Ude (in
Russian).
Kovalevsky A.L. 1987. Biogeochemical Prospecting for Ore Deposits in the USSR // -*HRFKHP
([SORU. V.21, pp.63-72.
Kvyatkovsky, E.M. 1977. /LWKRFKHPLFDO0HWKRGVRI([SORUDWLRQRI(QGRJHQRXV2UH'HSRVLWV.
Leningrad: Nedra (in Russian).
Linsalata, P. et al. 1994. Uranium and Thorium Decay Series Radionuclides in Human and
Animal Foodchains – a Review // -(QYLURQ4XDO V.23, pp.633-642.
Linsalata, P. et al. 1989. An Assessment of Soil-to-Plant Concentration Ratios for Some Natural
Analogues of the Transuranic Elements // +HDOWK3K\V.V.56, pp.33-46.
Lisitsyn, A.K., et al. 1984. Geochemical Features of Ore Lodes at the Terminals of the Zones of
Stratified Oxidation of Grey-Colored Rocks // /LWKRORJL\DL3ROH]Q\H,VNRSDHP\H, N 1, pp.49-61 (in
Russian).
Lisitsyn, A.K., 1994. Exogenous Uranium Deposits – Possible Burial Sites of Radioactive Waste
// /LWKRORJL\DL3ROH]Q\H,VNRSDHP\H, N 6, pp.89-100 (in Russian).
Ovchinnikov, L.N. 1990. 3ULNODGQD\D*HRNKLPL\D$SSOLHG*HRFKHPLVWU\. Moscow: Nedra (in
Russian).
Solovov, A.P. 1978. *HRFKHPLFDO0HWKRGVRI3URVSHFWLQJ. 1985. 2nd edition, Moscow: Nedra (in
Russian).
Stolyarov, A.S. and Ivleva E.I. 1991. Metalliferous Lodes of Bony Detritus of Fishes in Maikop
Sediments of Ergeninsky Ore Region // /LWKRORJL\D L 3ROH]Q\H ,VNRSDHP\H. N 6, pp.70-83 (in
Russian).
Tkalich, S.M., 1970. 3K\WRJHRFKLPLFKHVNLL0HWRG3RLVNRY0HVWRURMGHQLL3ROH]Q\K,VNRSDHP\NK
Leningrad: Nedra (in Russian).
Vasconcellos, L.M.H. 1987. Uptake of 226Ra and 210Pb by Food Crops Cultivated in a Region of
High Natural Radioactivity in Brazil // -(QYLURQ5DGLRDFWV.5, pp.287-302.
124
$SSHQGL[
1$785$/$9(5$*(*(2&+(0,&$/)/8;(62)5$',2$&7,9($1'
&+(0272;,&(/(0(176
6HOHFWLRQRIHOHPHQWV
The goal of this part of the report is to evaluate the natural average fluxes of elements and
radionuclides that are relevant to both radioactive and possible toxic waste disposal. As Miller
et al state, the fluxes methogology can be transposed directly from the area of radioactive waste
disposal to that of toxic waste disposal (Miller 1997. W.M.Miller, G.M. Smith, P.A. Towler, D.
Savage, SITE-94, Natural elemental mass movement in the vicinity of the Äspö hard rock
laboratory. SKI Report 97:29). It means that natural background levels of both radiotoxic and
chemotoxic hazards should be considered. Accordingly, the list of elements selected in this
report can be divided into two groups:
(1) Elements mostly inherent to radioactive waste disposal: K, Rb, Sr, Cs, Ce, Th, U
(2) Elements mostly inherent to toxic waste disposal: Cr, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd,
Sn, Sb, Ba, Hg, Pb.
The above-indicated division is conditional, because heavy radioactive elements (Th and U)
exhibit chemotoxic hazards, and many of the second group elements are stable analogues of
their radionuclides (such as 60Co, 59Ni, 79Se, 113mCd, 126Sn, 125Sb, etc). The second croup covers
both heavy metals and toxic metalloids (As, Se, Sb). In the first group, potassium and rubidium
are considered because their radionuclides (40K and 87Rb are the most important naturallyoccurring beta-emitters and can produce significant contributions to natural radiation doses and
associated risks. Strontium and cesium are stable analogues of corresponding radionuclides
(90Sr, 135Cs, 137Cs). Cerium represents the group of rare earth elements (RRE), it is of special
importance. Historically, it has been believed that the REEs are immobile during rock
weathering and alteration processes. That is why the REEs have been used as analogues for the
actinide elements (including transuranic Am, Cm, etc) in studies related to radioactive waste
disposal (Barretto and Fujimori, 1986; Lei et al., 1986) in order to demonstrate their general
immobility in the weathering environment. However, recent investigations revealed that most
alteration processes gave a net REE loss from the rock, and their release to groundwater was
clearly demonstrated (Smedley, 1991). It is known that the REEs occur in natural waters in the
trivalent state, but cerium also occurs in tetravalent form. REE solubility is strongly controlled
by pH, but Ce is also influenced by Eh. Tetravalent Ce is highly insoluble and hence under
oxidising conditionsm dissolved Ce concentrations could be low. Besides, stable Ce has its
radioactive analogue 144Ce (that is why it is included into the first group here). All this shows
that the REEs in general and Ce in particular might be very useful in the evaluation of natural
elemental fluxes.
125
6HOHFWLRQRIQDWXUDOSDWKZD\VRIHOHPHQWDOIOX[HV
It is possible to indicate numerous natural pathways of elemental fluxes. Some natural fluxes are
more relevant than others in the context of comparisons with radioactive of toxic waste
repositories releases. Miller et al have discussed four criteria to identify the most important
pathways for consideration (Miller et al, SITE-94, 1997). They note that, strictly speaking, no
natural fluxes is likely meet all four criteria. Nevertheless, four fluxes appear to be the most
relevant and should be considered in detail. Accordingly, Miller et al. propose to take into
account four driven forces responsible for natural fluxes as being the most relevant ones in the
light of the problem studied:
*URXQGZDWHUWUDQVSRUW. Groundwaters may not be associated with large natural elemental
fluxes, but this flux is significant because it is the principal pathway to the biosphere
available to repository-derived radionuclides and toxic elements. In addition, this kind of
transport deliver to the biosphere the elements in a more readily assimilable physical form
for human uptake.
*ODFLDOHURVLRQ. Glacial erosion provides a flux which is relevant to the glacial environment
only. The elemental fluxes due to this process appear to be the largest of the natural fluxes;
therefore, glacial will control the total natural flux even in the case of time-periods longer
than the glaciation.
1RQJODFLDOZHDWKHULQJ. Non-glacial weathering’s fluxes are important in different
environments: periglacial, coastal and inland, it is formed by mechanical disintegration and
chemical decomposition of the near-surface rock. These natural fluxes will be dominant
until the onset of the next glaciation. The elemental fluxes due to chemical weathering are
of specific importance, because this process yields a portion of the dissolved substances in
river waters which may be large.
5LYHUWUDQVSRUW. The flux connected with river transport is essential in the periglacial and
inland environments. The material transported by river waters may be in solid (suspended)
or in dissolved form, the former results from mechanical disintegration of the rocks, the
latter is caused by chemical breakdown of the rocks, by leaching of soils and discharge of
groundwaters. Both dissolved and suspended material in rivers supplies a large fraction of
the total natural flux available for human uptake, so this flux may control the total dose and
risk associated with natural elemental fluxes.
These four pathways are considered in the following sections of this part.
*URXQGZDWHUWUDQVSRUW
Groundwater dissolves element compounds (minerals) from the rock flowing through fractures,
if the element considered occurs in a soluble form under the existing environment, and if the
groundwater is not saturated with respect to minerals containing the element. The flux of
elements carried by the groundwater is dependent on the concentration of elements in the
126
groundwater and the groundwater flow rate. Miller et al proposed to use a groundwater flow rate
of 4.23⋅10−12 m/s which is typical of the regional steady-state groundwater flow field in the
crystalline basement in the Aspo area (Sweden) [SKI, 1996]. This value of groundwater flow
rate is equivalent to 1.33⋅10−1 l/m2/y, it was regarded to be representative of the present-day
coastal and inland environments. This value corresponds to groundwater flows in deep
crystalline rocks.
This report deals with natural fluxes in the zones of hypergenesis and active water exchange, so
it is preferable to consider underground water flow rates of these zones. That is why the values
of underground water flow rates in major landscape zones of moderate climate calculated by
Shvartsev (Shvartsev S.L. Hydrogeochemistry of the zone of hypergenesis, M., 1978) were
used, they are presented in Table 1.
Table 1. Underground water flow rates in major landscape zones of moderate climate (from
Shvartsev, 1978)
Landscape zones
Tundra
Northern taiga
Mixed forests
Southern taiga
Forest-steppes
Steppes
Underground
water flow
rates,
(l/km2/s)
0.5-2.5
1.0-3.0
3.0-6.0
1.5-3.5
1.0-2.0
0.1-0.5
Average
underground
water flow
rates,
(l/m2/yr)
47.4
63.2
142.2
79.0
47.4
9.5
The average value of underground water flow rates for all zones presented in this Table is XJZ
64.8 l/m2/y. This value and average element concentrations in groundwaters of the zones of
moderate climate recommended by Shvartsev were used in this report in order to calculate
natural elemental fluxes IJZin groundwaters of the zones of moderate climate:
IJZ FJZ⋅XJZ
whereFJZ - the values of average concentrations of elements in groundwaters of moderate
climate (from Shvartsev).
The results of calculations are presented in Table 2.
127
Table 2. Natural elemental fluxes in groundwaters of the moderate climate zones
Elements
Average concentrations in
groundwaters of moderate
climate (from Shvartsev)
FJZ, (µg/l)
3040
K
40 *
0,359
K
1.87
Cr
42
Mn
0.42
Co
2.35
Ni
4.85
Cu
25.2
Zn
2.64
As
0.87**
Se
Rb
2.35
87
Rb***
0.654
245
Sr
1.04
Mo
0.15
Cd
0.58
Sn
1.05
Sb
0.64
Cs
16.7
Ba
1.8****
Ce
Hg
0.61
Pb
1.94
Th
0.08
U
2.1
*) 40
K – 0.000118 (Bowen, 1979)
**)
from Zyka (1972), see Shvartsev (1978)
***) 87
Rb – 0.2765 (Bowen, 1979)
****)
from Smedley (1991).
Natural elemental fluxes in
groundwaters of moderate
climate, IJZ
(mg/m2/yr)
197
0.023
0.121
2.72
0.027
0.152
0.314
1.63
0.171
0.056
0.152
0.042
15.9
0.067
0.0097
0.038
0.068
0.041
1.08
0.12
0.040
0.126
0.005
0.136
*ODFLDOHURVLRQ
Glacial erosion of rocks is manifested by different processes: crushing, fracturing, abrasion
(induced by both ice itself and embedded rock fragments), cavitation and chemical
decomposition (Drewry, 1986). The relative contributions of these processes are governed by
several factors, the most important of them are the thickness of ice, the nature of rocks, the
speed of the glacier over the rock, and the temperature of the glacier base. The total mass of
material eroded per unit area from the glacier bed includes the mass of crushed and fractured
material, the mass of material eroded by abrasion, the mass of material removed by meltwater
erosion, and the mass of material removed by chemical decomposition of the rock by the
meltwater.
Usually, glacial erosion rates are calculated from measurements of the sediment transport in
rivers. Numerous investigations, using this approach, have evaluated erosion rates for various
glaciers around the world. Table 3 presents the results of indirect measurements. These
measurements may provide underestimated values of the glacial erosion rate because the
128
technique based on estimating sediment transport does not take into account discharges of
dissolved substances or sediment incorporated in and on the ice. However, as Miller et al note,
these discharges appear to be small in relation to total river transport, and they may be even less
then the errors associated with this method (Miller et al, 1997).
Table 3. Indirect measurements of glacial erosion rates (reported by Drewry in 1986, from
Miller et al, 1997)
Glacier
Rate, (mm/yr)
Source and publication date
Muir, Alaska
19.0
Reid (1892)
Muir, Alaska
5.0
Corbel (1962)
Hidden , Alaska
30.0
Corbel (1962)
Engabreen, Norway
5.5
Rekstad (1911)
Storbreen, Norway
0.1
Liestøl (1967)
Heilstugubreen, Norway
1.4
Corbel (1962)
Hoffelsjökull, Norway
from 2.8 to 5.6
Thorarinsson (1939)
Kongsvegen, Norway
1.0
Elverhoi HWDO (1980)
St. Sorlin, France
2.2
Corbel (1962)
Imat, USSR
0.9
Chernova (1981)
Ajutor-3, USSR
0.7
Chernova (1981)
Fedchenko, USSR
2.9
Chernova (1981)
RGO, USSR
2.5
Chernova (1981)
The median of these values is 2.5 mm/yr.
Few direct measurements of glacial abrasion rates are available, for some glaciers in France and
Iceland. These direct values are presented in Table 4.
Table 4. Directly measured glacial abrasion rates (published by Boulton in 1974, from Miller et
al, 1997)
Locality
Glacier d’Argentiere
Breidamerkurjøkull
Breidamerkurjøkull
Breidamerkurjøkull
Breidamerkurjøkull
Breidamerkurjøkull
Rate, (mmr/y)
36.0
3.75
3.40
0.90
3.00
1.00
Ice velocity (m/yr)
250
15
20
20
10
10
Platten
Marble
Marble
Marble
Basalt
Marble
Basalt
The median of these values is 3.2 mm/yr.
Ostrem has assessed erosion rates for Norwegian glaciers [1975], his smallest value was 0.073
mm/y, and the largest one was 0.610 mm/y. Miller et al used Ostrem’s median erosion rate
which was 0.34 mm/y noting that this value would be the most appropriate to the Aspo island
129
(Southern Sweden). Assuming that the density of the Aspo granite is 2.5⋅103 kg/m3, this means
that the median erosion rate is equivalent to 0.85 kg/m2/y. For a global estimate, it would be
more correct to use the average of the two above-mentioned medians, this yields the glacial
erosion rate of 2.85 mm/y. Taking the average density of major surface sedimentary rocks as
2.3⋅103 kg/m3, the glacial erosion rate will be 6.55 kg/m2/yr.
There is one more approach to estimate erosion rates for the last few glaciations, using the
volume of glacial sediments (moraines, tills, etc.) and the depth of glacial valleys. The data in
the frame of this approach indicate that in mountainous areas, the floor of a glacial valley can be
lowered as about 600 m in one glacial cycle (Hamblin, 1982). If a single glaciation event may
last 10 or 20 thousand years, this gives an erosion rate of several centimeters per year. As Miller
et al note, this is clearly an overestimated estimation. Thus, though the value of 2.85 mm/y is
several times higher than the erosion rate used for the Aspo island, it appears as an adequate
estimate averaged over many localities around the world.
Given the glacial erosion rate YH 6.55 kg/m2/yr, and the average values of elemental
abundances in surface (sedimentary) rocks (FVU), it is possible to calculate the natural fluxes of
individual elements due to erosion:
IH = FVU⋅ YH
Average concentrations in surficial rocks exposed to weathering have been calculated by Martin
and Meybeck, their goal was to evaluate the river particulate matter content (Martin J.M.,
Meybeck M. (1979), Elemental mass balance of material carried by major world rivers. 0DULQH
&KHPLVWU\, , 173-206). These calculations were performed on the basis of a proportion of 52
shales, 15 sandstones, 7 limestones and 26 composite igneous rocks, and revealed the marked
similarity between river suspended material and shales (for shales the data of Wedepohl
published in 1968 were used). Indeed, this similarity can be seen from Table 5, where the data
of Martin and Meybeck for surficial rocks are compared with the data of Ovchinnikov
(Ovchinnikov, Applied Geochemistry, 1980) for clay shales (these data are more recent
compared with Wedepohl’s data).
In order to evaluate natural fluxes due to glacial erosion, the calculations have been performed,
using the data of Martin and Meybeck; because in their data there is no values for Se, Sn and
Hg, Ovchinnikov’s values for these elements were used. The results are given in Table 5.
130
Table 5. Natural elemental fluxes due to glacial erosion (the average element concentrations in
surficial rocks are taken from Martin and Meybeck (1979) and the average concentrations in
clay shales - from Ovchinnikov, 1980)
Elements
Average concentrations
in surficial rocks (from
Martin and Meybeck),
FVU
K
40
K
Cr
Mn
Co
Ni
Cu
Zn
As
Se
Rb
87
Rb
Sr
Mo
Cd
Sn
Sb
Cs
Ba
Ce
Hg
Pb
Th
U
(mg/kg)
24 400
2.88
71
720
13
49
32
127
7.9
112
31.2
278
1.7
0.2
0.9
3.6
445
86
16
9.3
3
Average concentrations
in clay shales (from
Ovchinnikov),
FVU
(mg/kg)
26 400
3.12
94
840
19
74
48
93
12
0.58
150
41.8
330
2.6
0.42
6.4
1.5
6.5
660
63
0.42
20
12
3.7
Natural fluxes due
to glacial erosion,
IH
(mg/m2/yr)
159 820
18.86
465
4716
85.2
321
209.6
831.8
51.7
3.8
733.6
204.3
1821
11.1
1.3
41.9
5.9
23.6
2915
563.3
2.8
104.8
60.9
19.6
1RQJODFLDOZHDWKHULQJ
Non-glacial weathering (or erosion) may be regarded as the result of two kinds of processes –
physical (mechanical) disintegration and chemical decomposition of rocks. Mechanical
processes are associated with the removal of an overlying load (for example, ice), expansion and
contraction of the rock due to changes in temperature (including the formation of ice in rock
fractures and grain boundaries causing the rock to be split apart), heat from fires , activities of
plants and animals, etc. Chemical reactions that may occur are hydrolysis, oxidation, reduction,
carbonatization, hydration, cation exchange, dialysis, etc (see 1.1.2.1).
Mechanical and chemical weathering processes may proceed independently of each other,
however they are coupled almost always. Climate is the principal factor that controls the relative
importance of each kind of weathering. In environments where both rainfall and temperature are
low, mechanical processes are dominant. High temperature and high rainfall promote the
dominance of chemical processes. Coupling between mechanical and chemical weathering
occurs because: (1) mechanical disintegration of rocks increases the available surface area
131
leading to an increase of the rate of chemical reactions; and (2) certain minerals are more
susceptible to chemical decomposition than others causing the surface of rock outcrops to
become pitted which enhanced mechanical breakdown (Miller et al, SITE-64, 1997).
Bluth and Kump showed an important role of a balance between physical and chemical
weathering (Bluth G.J.S. and Kump L.R. Lithologic and climatologic controls of river
chemistry, *HRFKLP&RVPRFKLP$FWD v.58. N 10, pp. 2341-2359 (1994)). It means that a
warm, wet climate , or the presence of abundant vegetation cannot guarantee high rates of
chemical denudation unless accompanied by high rates of physical removal. In this connection,
they note the impact of biological processes on continental denudation. These processes can
affect chemical weathering in a number of ways: by supplying acidity (through production of
CO2 and organic acids) to the subsurface, by generation of chelating ligands, by the transfer of
nutrients from the soil to the surface during growth cycles, by physically working the soil
through root growth, etc. Alteration of the physical properties of soils leads to both chemical
and mechanical weathering.
There are rather inconsistent points of view concerning quantitative estimates of biological
acceleration of weathering. Schwartzman and Volk affirmed that the biotic enhancement of
weathering rates is a factor of the order of at least 100 to perhaps more than 1,000
(Schwartzman D.W. and Volk T. Biotic enhancement of weathering and the habitability of
Earth, 1DWXUH, 457-460 (1989); Schwartzman D.W. and Volk T. Biotic enhancement of
weathering and surface tempertaures on Earth since the origin of life, 3DOHRJHR3DOHRFOLP
3DOHRHFRO, 357-371 (1991)). Drever concludes that the biological effect of changes in soil
physical properties can be dominant (Drever J.I. The effect of land plants on weathering rates of
silicate minerals, *HRFKLP&RVPRFKLP$FWD, v.58, N 10, pp. 2325-2532, 1994). By binding
fine particles, land plants can greatly increase weathering rates, this is their direct effect.
Besides, the indirect physical effects are possible, for example through alteration of
precipitation patterns on the continents. Nevertheless, according to Drever, the earlier evaluation
of biotic enhancement of weathering made by Schwartzman and Volk appears to be
overestimated.
Many estimates of global chemical denudation have been given in recent years. The chemical
denudation rate is given as 0.014 mm/y by Meybeck (Meybeck M. (1988) How to establish and
use world budgets of riverine materials. In 3K\VLFDODQG&KHPLFDO:HDWKHULQJLQ*HRFKHPLFDO
&\FOHV(ed. A.Lerman and M.Meybeck) pp. 247-272. Kluwer); Stallard (Stallard R.F. (1988)
Weathering and erosion in the humid tropics. In 3K\VLFDO$QGDQG&KHPLFDO:HDWKHULQJLQ
*HRFKHPLFDO&\FOHV(ed. A.Lerman and M.Meybeck) pp. 225-246. Kluwer)gives a range of
0.005 to 0.03 mm/y for continental shields and sediments; Holland (Holland H.D. (1978) 7KH
&KHPLVWU\RIWKH$WPRVSKHUHDQG2FHDQV. Wiley) puts the global estimate as 0.008 mm/y. The
most recent estimate of the global FKHPLFDO weathering rate has been made by Lasaga et al :
0.009 mm/yr. It is generally agreed that SK\VLFDO weathering is about VL[WLPHVODUJHU than
chemical weathering (Holland, 1978; Lasaga et al, . *HRFKLP&RVPRFKLP$FWD, N 10, pp.
2361-2386, 1994), so the global rate of mechanical disintegration is 0.054 mm/yr, and the rate
of global non-glacial weathering is 0.063 mm/y.
The total flux can be calculated by determining the mass of rock eroded per unit area per unit
time and a density of the rock. According to Miller et al, the total non-glacial weathering rate in
Southern Sweden is 0.0015 mm/yr, so for the rock considered (schists and fine-grained
132
gneisses) with the density of 2.5⋅103 kg/m3, the total flux of material released by post-glacial
erosion is 3.75⋅10−3 kg/m2/yr, where the proportion of chemical weathering of the rock is
2.4⋅10−3 kg/m2/yr. They underline that chemical erosion appears as the most important driving
force for erosional processes in Southern Sweden (Miller et al. 1997).
In this report an erosion rate is supposed to be equal to the rate of global non-glacial weathering
(0.063 mm/y), and the average density of surfacial rocks is assumed to be 2.3⋅103 kg/m3, so the
total mass flux of eroded material will be XQJ 1.45⋅10−1 kg/m2/yr. Using this total rate of postglacial weathering and the average elemental abundances in surficial rocks FVU, it is possible to
calculate the total fluxes of individual elements due to total (physical plus chemical) erosion:
IQJ FVU ⋅ XQJ.
The calculations have been performed and the results are given in Table 6.
Table 6. Natural elemental fluxes due to total (physical plus chemical) weathering based on the
global total rate of post-glacial erosion
Elements
K
40
K
Cr
Mn
Co
Ni
Cu
Zn
As
Se
Rb
87
Rb
Sr
Mo
Cd
Sn
Sb
Cs
Ba
Ce
Hg
Pb
Th
U
Natural fluxes due to
non-glacial weathering
IQJ, (mg/m2/y)
3538
0.418
10.3
104.4
1.88
7.1
4.64
18.4
1.15
0.084
16.24
4.52
40.3
0.246
0.029
0.928
0.130
0.522
64.5
12.5
0.061
2.32
1.35
0.435
5LYHUWUDQVSRUW
The major driving force of both dissolved and solid material transported to the oceans is the
rivers draining the continents. There are two distinct methods to use in order to estimate the
mass of river sediment entering the oceans: the first takes into account the mass being carried by
rivers, while the second evaluates denudation of the continents. Sediment loads calculated on
the latter method give much higher estimates than those based on the former because they
133
include large amounts of eroded matter that never reaches the oceans. Following the first
method, Meybeck determined the total masses of material carried by all the worlds rivers to the
oceans, they are 15.5⋅1012 kg/yr for the solid load and 4.0⋅1012 kg/yr for the dissolved load,
giving a total of 19.5⋅1012 kg/yr (Meybeck M. 1976. Total dissolved transport by world major
rivers. Hydrol. Sci. Bull., 21: 2, 265-284. Erratum 21, 4, 651). Some trace elements are
transported preferentially in suspended forms. For example, it was established, using neutron
activation analysis, that 90% of Cs in the water of rivers and lakes is bound on suspended matter
(Lieser K.H. et al. -5DGLRDQDO&KHP, 17 (1977); Calmano W. and Lieser K.H. -
5DGLRDQDO&KHP 335 (1981);
Using more accurate data regarding major world rivers, many of which have been unavailable,
Milliman and Meade gave in 1983 a new approach to a world-wide delivery of river sediment to
the oceans (Milliman J.D. and Meade R.H. (1983) World-wide delivery of river sediments to
the oceans. 7KH-RXUQDORI*HRORJ\, 1-21). They calculated the values of drainage area,
sediment discharge and sediment yield for world rivers, their results are presented on Table 7.
Table 7. Drainage areas, sediment discharges and sediment yields for the rivers on different
continents (from Milliman and Meade)
Area
N. & C. America
South America
Europe
Eurasian Arctic
Asia
Africa
Australia
Large Pacific Islands (Japan,
Philippines, Indonesia, Taiwan,
New Zealand, New Guinea)
17.50
17.90
4.61
11.17
16.88
15.34
2.20
Sediment
Discharge,
(106 t/yr)
1462
1788
230
84
6349
530
62
Sediment Yield,
(t/km2/yr =
g/m2yr)
84
97
50
8
380
35
28
3.00
3000
1000
Drainage Area,
(106 km2)
13 505
150
18 300*
15 500**
*
According to Holeman (1968) (Holeman J.N. 1968. Sediment yield of major rivers of the world: Water
Resources Res., v.4, pp.737-747).
**
According to Martin and Meybeck (1979).
Totals
88.60
Estimates of Milliman and Meade include neither bed load, nor the sediment transported during
catastrophic floods, nor sediment discharge due to small river basins (particularly those draining
mountains and high standing islands).They note that bed load and floods may increase the
average annual input by 1-2⋅109 t, this will raise an average annual total sediment (suspendedbed) input up to 16⋅109 t. The value of 15.5 109 t/yr appears to be a reasonable estimate of total
sediment discharge (it is just in the middle of the two extreme values of 13 505 and 18 300
t/yr),that is why it was used for calculations in this report.
Martin and Meybeck estimated the elemental composition of average river particulate
(suspended) matter together with average concentrations of dissolved species (Martin J.M.,
134
Meybeck M. (1979) Elemental mass balance of material carried by major world rivers. 0DULQH
&KHPLVWU\, , 173-206). Their data are presented in Table 8. This table also shows earlier results
of Livingston and Turekian concerning average concentrations of dissolved loads in all the
world rivers.
In order to compare the dissolved and suspended loads, Martin and Meybeck calculated for each
element the so-called 'LVVROYHG7UDQVSRUW,QGH[ (DTI), which is the ratio of dissolved loads to
total loads. This calculation was based on the average dissolved content of rivers and on a world
river discharge to the ocean of 37 400 km3/yr (according to Baumgartner A., and Reichel E.
1975. The World Water Balance. Elsevier, Amsterdam, 179 p.). The values of DTI are
presented in Table 8 as well. As Martin and Meybeck note, there is a correlation between the
DTI values and the ionic potential of elements ϕ: high DTI values correspond either to the
lowest ionic potentials (ϕ < 2.02) or to very high potentials (ϕ >9.66). This correlation is not
strong, because numerous exceptions are manifested in the intermediate ionic potentials (for Zn,
Cu, As, Sb which have DTI between 17 and 45 %), or in the extremely low potentials (for Rb
and Cs, their DTI values are only 3% and 1.4%, correspondingly).
Martin and Meybeck underline that their DTI values are averaged on a global scale, so wide
geographic variations can be observed. Nevertheless, the DTI may be considered as the
expression of the global vulnerability, for a given chemical element, in the earth’s outcropping
rocks, rather than a direct estimate of its solubility. According to Strakhov, it is possible to use
the DTI as the relative mobility of elements in the weathering mantle (Strakhov N.M. 1967.
Principles of Lithogenesis, part I, chapter 1. Consultants Bureau and Oliver and Boyd,
Edinburgh, 245 p.). Anyway, such elements as the rare earths (their only repressentative – Ce –
is considered here) are almost entirely carried by the river particulate matter (DTI < 1%).
Table 8 gives characteristics of dissolved and particulate (suspended) material in world rivers.
Both Martin and Meybeck’ data and the earlier data of Livingston (1963) and Turekian (1969)
concerning average world values of dissolved elements in rivers are presented. Because the
values for Se, Cd, Sn and Hg are missing in the estimates of Martin and Meybeck, the data of
Livingston and Turekian were used in this report to calculate natural fluxes of these elements by
river dissolved transport.
135
Table 8. Characteristics of dissolved and particulate (suspended) material in world rivers
Elements
Average concentrations of dissolved
species, FUG
(10−6 g/l)
Martin &
Livingston (1963)
Meybeck (1979)
& Turekian,
(1969)
K
Cr
Mn
Co
Ni
Cu
Zn
As
Se
Rb
Sr
Mo
Cd
Sn
Sb
Cs
Ba
Ce
Hg
Pb
Th
U
1350
1
8.2
0.2
2.2
10
30
1.7
1.5
60
0.5
1.0
0.035
60
0.008
1.0
0.1
0.3*
2300
1
7
0.2
0.3
7
20
2
0.2
1
50
1
0.1
0.5
1
0.02
10
0.07
3
0.1
0.04
Average
concentrations in
suspended
material, FUV
(10−6 g/g)
(Martin &
Meybeck, 1979)
20 000
100
1050
20
90
100
350
5
0.58**
100
150
3
1
6.4**
2.5
6
600
95
0.42**
150
14
3
DTI (Dissolved
Transport Index),
%
(Martin &
Meybeck, 1979)
14
2.5
2.0
2.5
5
19
17
44
3
41
0
45
1.4
19
0.2
2
2
3
Table 7 shows that, compared to rivers on other continents, European rivers carry rather low
sediments loads, their average sediment yield is 7.6 times less than the average sediment yield
of Asian rivers. On the other hand, several European rivers carry suspended loads which are less
than their dissolved loads. Meybeck has given data concerning both the suspended and
dissolved loads for the Baltic Sea as a whole. According to his estimations, the Baltic Sea has a
total water flow of 158 km3/yr which carries a total 2.22⋅1010 kg/yr of material consisting of
1.92⋅1010 kg/yr of dissolved matter and 3.0⋅109 kg/yr of solid substances. This is due to the slow
water movement providing insufficient energy to transport much suspended material (Meybeck
M (1977) Dissolved and suspended matter carried by rivers, ,Q Colterman H.L(GLWRU
Interaction Between Sediments and Freshwater. Pp. 25-32). These circumstances make
necessary to consider European rivers apart from all the world rivers.
Natural elemental fluxes in European rivers )UG and )UV calculated in this report are given in
Table 9. The values of )UG and )UV were calculated using the following expressions:
)UG = FUG⋅4U
)UV= FUV⋅0U
where 4U– annual water discharge of European rivers; according to Alekin, 4U 2845⋅109 t/yr
(Alekin O.A. Fundamentals of Hydrochemistry, 1970); 0U – annual sediment discharge of
European rivers, according to Milliman and Meade, 0U = 230⋅106 t/yr, (see Table 7); FUG⋅average concentrations of dissolved species in river water; FUV– average concentrations of
suspended material in river water; the values of FUG⋅and FUV are given in Table 8.
136
Table 9. Natural elemental fluxes in European rivers
Elements
K
40
K
Cr
Mn
Co
Ni
Cu
Zn
As
Se
Rb
87
Rb
Sr
Mo
Cd
Sn
Sb
Cs
Ba
Ce
Hg
Pb
Th
U
Natural elemental
fluxes due to dissolved
loads in European
rivers, )UG
(106 kg/yr)
3841
0.452
2.8
23.3
0.57
6.3
28.4
83.4
4.84
0.569
4.3
1.19
170.7
1.42
0.28
1.42
2.84
0.012
171
0.23
0.199
2.8
0.28
0.85
Natural elemental
fluxes due to
suspended loads in
European rivers, )UV
(106 kg/yr)
4600
0.543
23.0
241.5
4.6
20.7
23.0
80.5
1.15
0.133
23.0
6.41
34.5
0.69
0.23
1.47
0.58
1.38
138
21.8
0.097
34.5
3.22
0.69
Total natural elemental
fluxes in European
rivers, )U
(106 kg/yr)
8441
0.005
25.8
264.8
5.17
27.0
51.4
163.9
6
0.7
27.3
7.6
205.2
2.1
0.51
2.9
3.4
1.4
309
22
0.3
37.3
3.5
1.54
This table shows that all elemental natural fluxes in European rivers are divided into three
groups: (1) As, Se, Sr, Mo, Sb, and Hg are presented mainly in their dissolved forms; (2) Cr,
Mn, Co, Ni, Rb, Cs, Ce, Pb, and Th are represented mainly by their suspended forms; (3)
contributions of K, Cu, Zn, Cd, Sn, Ba, and U into corresponding dissolved and suspended loads
are comparable.
Natural elemental fluxes in world rivers calculated in this report are given in Table 10. The
same formulas for )UG and )UV have been used.
137
Table 10. Natural elemental fluxes in world rivers
Elements
Natural elemental
fluxes due to dissolved
loads in world rivers,
)UG
6
K
40
K
Cr
Mn
Co
Ni
Cu
Zn
As
Se
Rb
87
Rb
Sr
Mo
Cd
Sn
Sb
Cs
Ba
Ce
Hg
Pb
Th
U
(10 kg/yr)
50 490
5.95
37.4
307
7.5
82
374
1122
63.6
7.5
56
15.6
2244
18.7
3.7
18.7
37.4
1.3
2244
3
2.6
37
3.7
11.2
Natural elemental
fluxes due to
suspended loads in
world rivers, )UV
(106 kg/yr)
310 000
36.6
1550
16 275
310
1395
1550
5425
77.5
9.0
1550
431.7
2325
46.5
15.5
99.2
38.8
93
9300
1472.5
6.5
2325
217
46.5
Total natural elemental
fluxes in world rivers,
)U
(106 kg/yr)
360 490
42.55
1587.4
16 582
317.5
1477
1924
6547
141.1
16.5
1606
447.3
4569
65.2
19.2
117.9
76.2
94.3
11 544
1475.5
9.1
2362
220.7
57.7
This table shows that, in opposite to European rivers, in elemental natural fluxes carried by
world rivers there is no division into groups. None of the elements is predominant being
transported in its dissolved form, all elements considered, except As, Se, Sr and Sb, demonstrate
the leading role of their suspended loads. Only As, Se, Sr and Sb have comparable contributions
of dissolved and suspended forms into the natural fluxes. Obviously, this difference is due to the
higher average suspended loads in all the world rivers compared to European rivers.
6XPPDU\RIUHOHYDQWQDWXUDOHOHPHQWDOIOX[HV
Table 11 gives a summary of natural average elemental fluxes calculated in this report. The data
on river transport can not be included in this table because their fluxes are in kg/yr and not in
mg/m2/yr as are the others, so the comparison would not be valid. Table 11 shows that all of the
elements are characterized by the same order of the relative magnitude of the fluxes: glacial
erosion > total non-glacial weathering > chemical decomposition > groundwater transport. This
order is the same as reported by Miller et al in 1997. However, Miller et al note a very specific
behavior of Se, which does not follow the general regularity, due to its very high concentration
in groundwater: according to Stenhouse, this concentration is of 0.1 mg/l or 100 µ/l (Stenhouse,
1979). This value appears to be doubtful, because it conforms neither with abundances of Se in
other segments of the hydrosphere (sea water, rivers) nor with the values of such ratios as
138
As/Se, Se/Sb, etc. In this paper, the average concentration of Se in groundwater of the zones of
hypergenesis was taken as 0,87 µ/l (see Table 2, from Shvartsev, 1978).
Table 11. Summary of natural average elemental fluxes
Elements
K
40
K
Cr
Mn
Co
Ni
Cu
Zn
As
Se
Rb
87
Rb
Sr
Mo
Cd
Sn
Sb
Cs
Ba
Ce
Hg
Pb
Th
U
Natural elemental
fluxes in groundwaters
of moderate climate,
(mg/m2/yr)
197
0.023
0.121
2.72
0.027
0.152
0.314
1.63
0.171
0.056
0.152
0.042
15.9
0.067
0.0097
0.038
0.068
0.041
1.08
0.12
0.040
0.126
0.005
0.136
Natural fluxes due to
glacial erosion,
(mg/m2/yr)
Natural fluxes due to
non-glacial weathering,
(mg/m2/y)
159 820
18.86
465
4716
85.2
321
209.6
831.8
51.7
3.8
733.6
204.3
1821
11.1
1.3
41.9
5.9
23.6
2915
563.3
2.8
104.8
60.9
19.6
3538
0.418
10.3
104.4
1.88
7.1
4.64
18.4
1.15
0.084
16.24
4.52
40.3
0.246
0.029
0.928
0.130
0.522
64.5
12.5
0.061
2.32
1.35
0.435
The ratio of maximum and minimum magnitudes of natural fluxes obtained in this report is
more than 1,000 for the following elements: Cr, Mn, Co, Ni, Rb, Sn, Ba, Ce, Th. This ratio is
less than 200 for Se, Sr, Mo, Cd, Sb, Hg, and U. Obviously, this reflects a relatively enhanced
role of dissolved forms of these elements in groundwaters (for Se, Sb, and Hg the abovementioned ratio is less than 100).
139
$VVHVVPHQWRIUDGLRWR[LFLW\GXHWRDYHUDJHQDWXUDOIOX[HVRIUDGLRDFWLYHHOHPHQWV
Table 12 contains the values of conversion factors that are necessary in order to calculate
activity and effective equivalent doses (from Miller et al 1997, based on ICRP
recommendations from 1991). The value 27 Bq/mg used for 238U corresponds to natural
uranium.
Table 12. Conversion factors
Conversion from activity to effective equivalent
dose, (Sv/Bq)
Inhalation
Ingestion
3.4⋅10−9
5.1⋅10−9
8.7⋅10−10
1.3⋅10−9
−4
4.1⋅10
7.4⋅10−7
−5
3.1⋅10
6.3⋅10−8
Conversion from mass
to activity, (Bq/mg)
Radionuclide
40
209
3.2
4.1
27
K
Rb
232
Th
238
U
87
Table 13 presents the values of specific activity due to natural average fluxes of radioactive
elements calculated in this report.
Table 13. Specific activities due to natural average fluxes of radioactive elements
Radionuclide
Specific activity
Specific activity
Specific activity
Total specific
of natural fluxes
of natural fluxes
of natural fluxes
activity of natural
due to
due to glacial
due to non-glacial
fluxes,
groundwater
erosion,
weathering,
Bq/m2/yr
transport,
Bq/m2/yr
Bq/m2/yr
2
Bq/m /yr
40
4.81
3941.7
87.4
4033.9
87
0.13
653.8
52.0
705.9
Th
0.02
249.7
5.5
255.2
U
3.67
529.2
11.7
544.6
Totals
8.63
5374.4
156.6
5539.6
K
Rb
Of course, the order of specific activity magnitudes is the same as the order of the relative
magnitude of the fluxes expressed in mg/m2/yr: glacial erosion > total non-glacial weathering >
groundwater transport. Glacial erosion is responsible for the lion’ share of total specific activity
of natural radionuclide fluxes.
As it was said, activities of natural radionuclide fluxes due to river transport should be
considered separately. Table 14 shows the values of activity of natural fluxes of radioactive
elements in dissolved and suspended loads of world rivers.
140
Table 14. Activities of natural fluxes of radioactive elements in dissolved and suspended loads
of world rivers
Radionuclide
Activity due to
Activity due to
Total activity,
dissolved loads,
suspended loads,
(1012 Bq/yr)
(1012 Bq/yr)
(1012 Bq/yr)
40
1244
7649
8893
87
50
1381
1431
Th
15
890
905
U
302
1256
1558
Totals
1611
11176
12787
K
Rb
Activity due to suspended loads is almost seven folds higher compared to activity due to
dissolved loads. The relative orders of contributions of radionuclides into total activity are
different in suspended and dissolved river loads: suspended loads show the series 40K > 87Rb >
U > Th, and dissolved loads – the series 40K > U > 87Rb > Th. The value of total activity of
12787⋅1012 Bq/yr is equivalent to 345 940 Ci/yr.
Table 15 presents effective equivalent doses induced by radionuclide natural fluxes due to
groundwater transport, glacial erosion and non-glacial weathering calculated in this report.
Table 15. Effective equivalent doses induced by radionuclide natural fluxes due to groundwater
transport, glacial erosion and non-glacial weathering
Radionuclide
40
K
Rb
232
Th
238
U
87
Groundwater transport
Inhalation,
Ingestion,
(Sv/m2/yr)
(Sv/m2/yr)
1.6⋅10−8
2.4⋅10−8
−9
1.1⋅10
1.7⋅10−10
8.2⋅10−6
1.5⋅10−9
−4
1.1⋅10
2.3⋅10−7
Glacial erosion
Inhalation,
Ingestion,
(Sv/m2/yr)
(Sv/m2/yr)
1.3⋅10−5
2.0⋅10−5
−7
5.7⋅10
8.5⋅10−7
1.0⋅10−1
1.8⋅10−4
−2
1.6⋅10
3.3⋅10−5
Non-glacial weathering
Inhalation,
Ingestion,
(Sv/m2/yr)
(Sv/m2/yr)
3.0⋅10−7
4.5⋅10−8
−8
4.5⋅10
6.7⋅10−8
2.3⋅10−3
4.1⋅10−6
−4
3.6⋅10
7.4⋅10−7
Again, glacial erosion is dominant in the formation of effective equivalent doses, and the
contribution of U and Th are much more higher compared to the contributions of 40K and 87Rb.
This table shows also that contributions of radionuclides into effective equivalent doses follow
the following orders:
groundwater transport (inhalation): 238U >> 232Th >> 40K > 87Rb
groundwater transport (ingestion): 238U > 40K > 232Th > 87Rb
glacial erosion (inhalation and ingestion): 232Th > 238U >> 40K >> 87Rb
non-glacial weathering (inhalation): 232Th > 238U >> 40K > 87Rb
non-glacial weathering (ingestion): 232Th > 238U > 87Rb > 40K.
141
In Table 16 the values of effective equivalent doses due to radionuclide natural transport by
world rivers calculated in this report are given.
Table 16. Effective equivalent doses due to radionuclide natural transport by rivers
Radionuclide
40
K
Rb
232
Th
238
U
87
Dissolved loads
+HG(inhalation),
(Sv/yr)
4.2⋅106
4.4⋅104
6.2⋅109
9.4⋅109
+HG(ingestion),
(Sv/yr)
6.3⋅106
6.5⋅104
1.1⋅107
1.9⋅107
Suspended loads
+HV(inhalation),
(Sv/yr)
2.6⋅107
1.2⋅106
3.6⋅108
3.9⋅107
+HV(ingestion),
(Sv/yr)
3.9⋅107
1.8⋅106
6.6⋅108
7.9⋅107
One can see that in the case of dissolved loads the values of dose due to inhalation of Th and U
are much more than doses due to ingestion of these elements. In the case of suspended loads, the
doses formed by inhalation and ingestion are comparable for all the radionuclides considered.
This table also shows that for dissolved loads the order of +HG decreasing is: 238U > 232Th > 40K
>> 87Rb – for both inhalation and ingestion. For suspended loads, the order of +HG decreasing is
a little bit changed: 232Th > 238U > 40K >87Rb – for both inhalation and ingestion.
142
$33(1',;
1$785$/+($9<0(7$/62,/6
The objective of this chapter is to elucidate the problem if and how geochemical cycles can cause concentrations
of elements in the biospere that exceed limits that have been set to protect the health of humans. How frequent
are heavy metal concentrations in soils that reach or exceed toxic limits? The principal questions are: what are
the sources (anomalies), what are the transport or migration pathways and is dispersion and dilution or reconcentration and secondary enrichment dominating. The latter is a key issue in the evaluation of safety analyses of geological repositories for high-level radioactive waste. In most cases in repository performance assessments in the course of radionuclide migration from the geosphere to the biosphere dispersion and dilution is
assumed to prevail. Thus understanding the behaviour of elements within cycles in natural systems and the processes, parameters and conditions that may lead to dispersion or enrichment is an indispensible prerequisite for
the evaluation of any repository safety case.
+HDY\PHWDOEDFNJURXQGLQURFNVDQGVRLOV
The trace elemental composition of the parent rock types from which soils form can vary widely. In particular, in
certain sedimentary rocks some elements can be conspicuously concentrated. Examples are As, I, Mo and Se in
shale and clay or As, Cu, Mo, Zn and U in organic-rich shale (enrichment up to factors of several thousand).
However, in igneous rocks variations are mostly within one, exceptionally two orders of magnitude, if ultrabasic
rocks are excluded which normally show significant enrichment of Cr, Co and Ni. The composition of a soil
cannot be predicted precisely from the fact that it lies within an area of a certain rock type, because of variations
in rock composition and because soil-forming processes can be highly varied even within the same climatic
regimen and uniform source rock (Tourtelot 1971). In general, one must expect a marked anomaly in the parent
rock as a source when a soil anomaly is observed. The more mature a soil, particularly under conditions of high
temperature and rainfall, the less is the influence of the parent material on the chemical composition of the soil.
When uptake into vegetation is considered the situation becomes even more complex as the fractions of various
mobile forms of metal ions accessable to plant uptake depend very much on the properties and processes in various layers of more or less drained soils (Mitchel 1972).
Median elemental compositions and ranges of composition of soils are given in Table A2.1 (Bowen 1979). The
data shall only serve as a guideline for orientation; some data have been revised in more recent compilations.
Data for soils near ore bodies, polluted soils and serpentine soils have not been used for compilation of these
tables. Insufficient data is available to compare different soil types. The means agree fairly well with the mean
values for igneous and sedimentary rocks. On the average, As, Br, Cd, Hf, I Pb, Sb, Se, Sn and Zr may be somewhat enriched in soils, while i.a. Hg, Sr, Tl and U may be slightly depleted. Attempts to correlate elemental
contents with factors such as the clay or carbon content were mostly without clear-cut results. Heavy metals such
as Ag, As, Cu, Hg, Pb, Sb and Zn are often found to be enriched in the upper layers of soils. Elements which are
reported to be enriched in layers where clay minerals and hydrous oxides accumulate, include i.a. Al, Fe, Mg, Ni,
Sc, Ti, V, and Zr.
Large-scale comparitive studies of background concentrations of elements in large countries, e.g. China and
USA, extending over a wide range of climatic zones from extremely cold, over moderately humid to dry desert
and subtropical areas have contributed significantly to the understanding of the relation between soil composition and the nature of the parent rock under various climatic conditions (Chen 1991). Heavy metal concentrations
were found to be very similar in corresponding climatic zones in both countries; only four elements (Be, I, Mo
and Sn) showed deviations between the two countries by a factor of 2-3. Values from Alaska were comparable to
those from the Tibetian highland despite great differences in geomorphology and latitude. The largest differences
were within a factor of two-to-three for five elements. For the other climatic regions similar results were found.
The apparent geochemical and geographical patterns in elemental composition of soil orders were attributed
mainly to the effect of climate on soil development. In general, the sequence for the metal content of soil types
decreased from lithosol (mostly cold climate; reduced weathering and leaching) to oxisol (warm, humid climate;
heavily leached). Lithosol reflects still more enhanced concentrations in the parent rocks.
Even in central Europe the scientific basis for the assessment of the risks formed by heavy metals in soils and
for setting limits for heavy metal contents was begun to establish not much more than a decade ago; see e.g.
(Kuntze 1986) for the situation in Germany as an example. In that publication numerous geological formations
are listed which have locally higher natural heavy metal contents than would be tolerable according to the sewage sludge decree which states roughly ten times higher limits than the limits for soils, although the list covers
only a part of the country. Among these metals are Zn, Pb, Cu, Cd, Ni, Cr and Co. The difficulty to set reasonable limits that take into account the change in the availability to the bioshere when heavy metals are released
143
from the parent rocks by weathering and enter various soil horizons and in dependence of soil properties and
composition (content and type of clay minerals, content of Fe- and Mn-oxides, content and type of humic substances, pH, etc.) is discussed.
Tab. A2.1: Medians and ranges of elemental composition of soils in mg X/kg soil; k, x 1000; µ, x 10-6.
+HDY\PHWDOVRLOV
Heavy metals such as Zn, Cu, Pb, Ni, Co, Cd and Cr occur practically in all soils at concentrations between
about 0.0001% and 0.065%. Naturally heavy metal-rich soils are connected with ore bodies which crop out at the
surface or reach to at least about 30 m below the surface of the earth. Heavy metal concentrations above 0.1%
exert a strong selecting effect on vegetation: In extreme cases concentrations of Zn, Cu, Pb, Ni, Co or Cd can
reach 10% or even more, U up to 0.5%, Th up to 0.6% (Ernst 1974). In areas covered by vegetation heavy metal
anomalies find expression in enhanced metal contents in certain plants or parts of these, in specific types of vegetations or in the complete absence of vegetation due to poisoning (Fig. A2.1, Bölviken 1974)). Because of the
144
world-wide occurrence of heavy metal-rich parent rocks, heavy metal soils cover all climatic zones from polar to
tropical.
In Europe and North America most natural heavy metal soils have been destroyed by mining activities and their
original extension can no longer be estimated. But, it seems that they were bound to outcrops of ore bodies in the
same way as elsewhere. Already in medieval times miners were guided by certain vegetation known to indicate
the presence of metals like e.g. Cu and Zn. Scandinavians were familiar with "pyrite plants" ("kisplant") which
grow on Cu ores (Malyuga, 1964). Locally anthropogenic heavy metal soils cover up to three orders of magnitude larger areas as natural ones. In other parts of the world numerous examples of undisturbed heavy metal soils
can be found. In Tab. A2.2 (Ernst 1974) metal concentrations in some of these soils are given. There are numerous cases known where the metal concentrations are so high that toxicity prevents growth of certain species or
even causes bare areas.
The highest metal concentrations are normally found at the outcrop of the metal-rich rock. Along the transport
direction secondary metal enrichments can occur at some distance. A few typical examples from Scandinavia
will be treated in some more detail below. The total metal contents in soils do not represent the fraction available
to plant roots, although the availability can be enhanced by acids released from the roots or by microbial activity.
Optimum availability to plants exists where metal-rich groundwater is discharged; an example of pure and naturally contaminated groundwater from an ore body is given in Tab. A2.3 (Ernst 1974). Compared to normal soils
water-soluble heavy metal concentrations can be 10-10,000 times higher in heavy metal soils (Tab. A2.4 (Ernst
1974)). Because of the stability of organic complexes of many heavy metals, e.g. Cu, Pb, Ni, very often up to
100% of the soluble fraction were reported to be organically bound while at the same location the organically
bound fraction of Zn was less (28-100%). The exchangeable amounts of metals (measured by using extraction
with 1 n ammonium acetate) can reach about ten times higher values than the water-soluble values. However,
even this fraction represents only a minor part of the total amount (in case of Zn about 1.4-12% of the total).
Fig. A2.1: Naturally poisoned area at Tverrfjellet, Hjerkinn, Norway. Light patches in the front are stones and
boulders in barren soil.
145
Tab. A2.2: Heavy metal contents of some natural heavy metal-rich soils in mg/kg dry soil.
Tab. A2.3: Heavy metal content in heavy metal-rich and heavy metal-poor spring water in a valley near an ore
deposit at Ramsbeck/Germany (values in µg/l).
heavy metal-rich
heavy metal-poor
Zn
70,000
1.0
Cd
85
0.3
Cu
20
0.3
Ni
20
0.4
Pb
0.1
0.0
Tab. A2.4: Water-soluble heavy metal contents in some normal and heavy metal-rich soils (values in mg/kg dry
soil; nb., not determined).
146
%LRJHRFKHPLFDODVSHFWV
The growth of indicator species or the occurrence of morphological changes and the metal content in plant species has become the basis of botanical and geobiochemical prospecting methods (Cannon 1960). Many deposits
of, in particular Ni, Cu, Cr, W, Sn, U, could be found in this way. In Russia areas where there is a unique reaction of plant life in a region of high metal concentrations from ore deposits is called a biogeochemical province
(Malyuga 1964). Although root penetration makes deeper layers accessable than soil sampling, accumulation of
metals by plants is a complex phenomenon which is dependent on many factors that require interpretation. Biogeochemical element information has penetration depths depending very much on geological, climatical and
other factors. In arid, warm regions the root system penetrates to 20-30m or even deeper, in temperate coniferous forest zones 2-5 (10) m, while in tundra and taiga regions where permafrost is present penetration is limited to
1-3 m. Uranium mineralizations have been detected under up to 20-25 m thick covering rocks when roots
reached water-bearing horizons at greater depths along rock fractures (Malyuga 1964). However, the U concentrations in plant material were generally only 1-2 orders of magnitude above background concentrations and thus
far below toxic limits.
A systematic study in Finland on trace elements in vegetation in which habitats representing diverse rocks such
as silicic, ultrabasic and calcereous rocks and, on the other hand, exceptional habitats such as pegmatites or areas
of ore mineralization revealed that most trace elements studied were at least within the same order of magnitude
in parent rock and associated soil (Lounamaa 1967). No further details can be discussed here, but the enrichment
of Cu and, in particular, Pb in soils over silicic rocks was remarkable. Heavy metal soils exceeding about 1000
ppm for Zn and Cu were found only at outcrops of ores. In plant ash elements (total contents) were either enriched (Mn, Cu, Zn, Mo, Pb), at the same level (Co, Ni) or depleted (Cr) as compared to rocks and soils. Exceptional concentrations in plants over ore outcrops reached 10,000 ppm Zn, 6000 ppm Pb and 3000 ppm Cu in ash,
but marked poisoning effects are not described.
)UDFWLRQDOUHOHDVHVIURPRUHV0RUURGR)HUURFDVHVWXG\
In addition to chemical toxic effects also radiation effects on plants in regions rich in U and Th and their decay
products are known. The most famous sites are the monazite sands in Kerala (India) and Brazil, the Morro do
Ferro in Brazil (Th and U in volcanic intrusives) and various locations in the SW-USA (U). In connection with
these anomalies the behaviour of these elements in food chains has been investigated and the health risk of the
population has been assessed. It is however beyond the scope of this work to review the vast literature related to
these locations or on so-called biomedical investigations. The monazite sands are an example of a weatheringresistent mineral forming the final residue of rock degradation. Even uraninite could be found locally in sands.
Morro do Ferro is a hill exposed above the surroundings due to its greater erosion resistence. Within the frame of
natural analogue projects the dissolution of uranium and its transport in groundwater has been extensively investigated at Morro do Ferro and, in particular, the nearby location Pocos de Caldas. These cases are exceptions in
that respect that usually very little quantitative or even qualitative information on element migration and mass
balances is available from ore deposits.
At Morro do Ferro, Brasil where an ore body containing, in addition to large amounts of rare earths (about
69,000 t of La), about 20,000 t Th and 100 t U is cropping out at the surface, already in early studies mobilization rates were estimated (Eisenbud 1982). The Th mobilization rate due to surface erosion was estimated to 5.9 x
10-7/a corresponding to a Th flux of about 12 kg/a while a rate due to groundwater dissolution of only 7.5 x 1010
/a was estimated. However, it was estimated that uranium has been removed already to more than 90% (about
1,300 t). Later, the values were revised to 30,000 t of Th inventory and the annual Th mobilization to 27.2 kg
(9.1 x 10-7/a) in particulate form and 0.015 kg (5.0 x 10-10/a) in soluble form during periods of rainfall. For La a
mobilization rate of 11 x 10-7/a is given which is in close agreement with the Th rate (Eisenbud 1984).
&DVHVWXGLHV
In the following chapters a few cases of two types of studies are taken from the literature: (1) cases showing how
geochemical mapping can reveal formational anomalies even in old mining provinces and (2) cases of heavy
metal poisoning are elucidated where it could be shown how elements migrate from ore outcrops and are casually enriched again in the biosphere.
Besides pollution caused by processes of low-temperature weathering, in numerous regions on the earth there is
significant natural heavy metal pollution related to active volcanism and associated hydrothermal springs, wells
and vents. Critical elements are in these cases, amoung others, Hg and As. For example, in aquatic plants near
geochemical discharges in New Zealand As up to 650 mg/kg dry mass was found (Förstner 1979). In Europe
147
similar pollution problems are known from Italy. The issue is interesting for comparison what kind of natural
pollutions can occur, but has little relevance to waste repository conditions and is therefore not treated further.
*HRFKHPLFDOPDSSLQJ
Baseline geochemical maps produced by using groups of chemical compatible elements and a methodology
giving more emphasis to the weight of the local value rather than smoothing the data to a regional average were
combined with thresholds defined by intervention criteria for agricultural, residential/recreational and commercial/industrial land uses (in this example for Canada; Tab. A2.5 (De Vivo 1998) to produce risk maps. These
maps allowed to distinguish formational anomalies from anthropogenic/mining pollution even in an ancient
mining region such as Sardinia which was selected as a typical example. The distribution of the highest values of
the element group Cr-Ni-Mg and of As corresponded perfectly to outcrops of metal-rich formations. Also Co
was found to correlate mostly with outcrops of specific rock types (Fig. A2.2, De Vivo 1998) while Pb was more
related to mining activities. The distinction between formational (V, Co, Ni, Cr, Mo) and mining pollution (Pb,
Zn, Ag, Ba) anomalies was found to be scale depended. For some elements there was not yet sufficient data
available to make interpretations. Detailed geochemical mapping results from Finland are given and discussed in
a parallel report.
Tab. A2.5: Intervention criteria for agriculture, residential/recreational and industrial/commercial land uses in
Canada.
148
Fig. A2.2: Co risk map from stream sediment samples in Sardinia.
1DWXUDOPHWDOSRLVRQHGVRLOVLQ6FDQGLQDYLD
Few occurrences of naturally metal-poisoned soils in Europe have been described in sufficient detail to understand the behaviour of the metals in the rock-groundwater-soil-surface water system. The pioneer studies using
anomalies of vegetation or plant contents in Scandinavia date back to the 1940’s (Ni, Cu in Finland; Cu in Sweden and Norway; for Lit. see Cannon 1960) which means that we cannot expect quantitative information on
dispersion and migration mechanisms. From the beginning of the 1970’s in Norway areas naturally poisoned by
lead and copper were investigated. The first case which has been studied in detail was a fan-shaped vegetation
anomaly exhibiting also complete absence of plants in an area untouched by human activity (Låg 1970). Near the
poisoned area, but not along the drainage line of the slope, was an outcrop of rock containing galena (PbS) (Fig.
A2.3, Låg 1970). In the top layers of the soil Pb concentrations of up to 10 g/kg were found in an area consistent
with the vegetation anomaly (Fig. A2.4, Låg 1970). From these observations it was concluded that the sparsity
and effected state of the vegetation was a consequence of lead poisoning. It was found that the high metal content in the soil lead to increased contents in the plants and thus must also be a thread to the local fauna. From the
local conditions it was concluded that the metal must have been transported from the weathering ore outcrop
149
some distance downhill by near-surface groundwater and then continuously accumulated in the upper humusrich soil layer. Numerous similar examples were found and investigated thereafter. The result of a typical profil
measurement over an ore body showing downslope displcement of the anomaly is shown in Fig. A2.5, Björlykke 1973).
Geochemical drainage dispersion from sulphide mineralization in glaciated terrain at Hjerkinn, Norway (Pb, Zn,
Cu anomalies) gave evidence that dispersion patterns were entirely controlled by groundwater movements and
groundwater chemistry changes (Mehrtens 1973). Stream sediment anomalies were more pronounced than
groundwater anomalies. Lead anomalies were largely confined to the vicinity where mineralized groundwater
reached the surface. At the location early stage development work for mining had not caused yet any environmental contamination, but the shaft allowed to take groundwater passing the ore body. The metal contents in
these waters were low, indicating that the water had not passed the oxidation zone of the ore. Groundwater from
the till overlying the ore sub-outcrop had enhanced but not extremely high metal contents, in particular Pb was
low. The highest values were found in groundwater in till downdrainage from the ore, which decreased over a
distance of about 2 km downhill. Without going into more detail of the significant differences in migration/retardation behaviour of the three elements it could be concluded from simulation of the change of water
chemistry upon dilution along the flow path that the decrease of the metal concentrations could not be explained
by a simple dilution effect. More rapid decrease was accounted to coprecipitation or sorption by ion oxides where Fe(II) oxidized or at higher pH to sorption on clays. In stream sediments fixation by coprecipitation and ion
exchange was inferred. The complexity of the mobilization and secondary enrichment processes working in
surface/near-surface rock-soil-water systems was further evidenced by results from extracted metal fractions and
from peat bogs downhill.
Investigations at other locations discovered in Norway often showed a very scattered pattern of the metal concentrations in soil despite the existence of extended known mineralizations (Låg 1974). In Fig. A2.6, (Låg 1974)
the toxic soil pattern is shown which is caused by a mineralization about 2 km long and mostly covered by till.
The metal enrichments reflect the groundwater discharge pattern in lower parts of the terrain.
Recently, the development of analytical and modelling tools enabled considerable progress giving a better understanding of heavy metal behaviour at natural soil anomalies (Säther 1988). At a location in Norway with a
rather simple geological setting: Pb occurring as only one mineral (PbS) disseminated in a monomineralic rock
(quarzite); the rock striking perpendicular to the slope of a hillside; 0.5-2.0-m-thick till cover, the concentration
of Pb reached up to 11% in the upper soil layer and up to 1000 ppm at depths of 25-50 cm. Measurement of Pb
in groundwater sampled (directly and through dialysis tubes) along the fall-line (Fig. A2.7, Saether 1988) showed the highest metal concentrations at the locations of groundwater discharge (Kastad: 2A, 2B, about 5200
ppm Pb) which were more in downhill direction at the other location (rising from about 160 to 950 from sample
4 to 7 and from 780 to 2400 ppm from sample 10 to 12). From the distribution coefficient of nearly 1 between
groundwater and dialyzed water and calculated distribution of inorganic species it was concluded that more than
97% of the migrating Pb was present as Pb2+ and about 2% as PbSO4. However, in this study fixation
mechanisms of the metal in the humus-rich soil layer were not investigated.
In the work cited above and other investigations covering numerous similar locations in Scandinavia it was
found that:
- small heavy metal-contaminated areas connected to sulphide ore outcrops or sub-outcrops were more common
than believed earlier,
- metals can be transported over considerable distances under hydraulic gradients,
- when metal-loaded groundwaters meet variations in the chemical environment, e.g. pass through material rich
in humus the metals can be precipitated and enriched to concentrations far greater than those at the place where
they originated, reaching even toxic levels,
- secondary enrichment can eventually lead to poisoning occuring even at relatively low heavy metal concentrations in the parent rock,
- the time scale for transport and secondary deposition of the metals has been the period since the end of the last
glaciation.
150
Fig. A2.3: A lead-poisoned, barren area at Kastad, Norway
151
Fig. A2.4: Lead in top soil (depth 2-4 cm) in the same area as Fig. A2.3.
152
Fig. A2.5: Geology, lead in mineral soil (B2 horizon) and lead in humus at a profile in the Snertingdal anomaly
area, Norway.
153
Fig. A2.6: Patterns of naturally lead-poisoned areas, Nössmarka, Snertingdal, Norway.
Fig. A2.7: Sketch maps of the sampling stations in lead-poisoned areas at Kastad (a) and Nössmarka (b), Norway.
154
2WKHUKDORV
While outcrops and sub-outcrops of ore bodies often lead to accumulation of toxic metal concentrations in soils,
more deeper buried anomalies generally do not lead to enhanced concentrations except near open pathways such
as e.g. faults. Obviously the existence of geological structures enabling migration of metal ions in groundwater
play a more important role than the thickness of the overburden. A typical example studied systematically are
genetically identical sulphidic Cu, Zn mineralizations (containing up to 4.5% Cu and 10% Zn) seated at various
depths of 20, 30, 40 and 100m (Friedrich 1984). The only clear anomalies of Cu and Zn in soils observed above
the 100 m and 40 m deep mineralizations were coupled to faults (7400 ppm Zn, 2500 ppm Cu, respectively,
3000 ppm Zn, 5900 ppm Cu). Even at the more shallow mineralizations the maximum soil contents (>1% Zn,
about 2700 ppm Cu) were connected with faults.
8UDQLXPKDORV
Any review of geochemical case histories shows the high success in locating U deposits by soil, sediment and
plant surveys which is favoured by the relatively low geochemical background of U in soils and plants, so that it
is easy to detect even relatively low accumulations of U. However, also other factors such as the relatively high
mobility of U under certain environmental conditions and its tendency to form secondary enrichments play an
important role. Such issues are treated in other chapters of this work. Here we are mainly interested in the formation of anomalies in soil and vegetation reaching harmful levels.
The effects of U on the vegetation in arid and semi-arid regions has been extensively studied in the western parts
of the USA. Uranium-tolerant flora has been recognized and described, but symptoms of uranium poisoning
were masked by excessive amounts of V, Se and Mo present in the ore (Connan 1952). The leaves of plants that
were rooted in ore contained 2-100 ppm U while the normal background was less than 1 ppm. Environmental
factors and ore and soil composition determined U uptake. Poisoning was observed mainly on dumps and disturbed ground where the ore was exposed to weathering and U availability to plants was increased while no noticeable effects occurred on undisturbed ground.
In the humid mountainous region of the Alps high U contents of the Rhone river and its tributaries have been
explained by the presence of U-rich granites and a sreies of U mineralizations. U uptake in plants has been observed on a very local scale at outcrops of pitchblende veins, but no damage of the observation is known. An
example is at an outcrop at a very steep slope causing contamination of an area of about 50 x 100 m decreasing
downslope from 2500 ppm near the vein to 15 ppm in the soil layer 0-20 cm (reference value 3 ppm) (Pfeifer,
1994). The migration mechanism discussed consists of oxidation of pitchblende fragments at and near the soil
surface, transport downwards within the profile and immobilization of U by adsorption on Fe-oxyhydroxides.
The U concentrations in springs and surface waters in the wider area are around 3 ppb which suggests that the
retention capacity may be exceeded by CO2-rich solutions leading to U transport into river systems.
'HHSO\EXULHGXUDQLXPRUHV
Extensive experience is available from the U occurrences of the Athabaska type in Canada. From these the conclusion can be made that deply buried U mineralizations form detectable anomalies at the surface practically
only if channelways for U migration are existing, but even here U concentrations mostly remained below 50-100
ppm (Hoffman 1983). In some cases described in that work the age of the glacial overburden and movement of
surface anomalies downslope indicated recent U migration processes (Fig. A2.8, Hoffman 1983). A U-rich mineralization with locally up to 27% pitchblende under 150 m of sandstone gave as the only surface expression
slightly increased U contents in plant ash. At other locations in the region upward migration of U was interpreted
as facilitated by fractures but no time constraint could be given. It is a typical feature of many of these types of
deposits that U has been mobilized by hydrothermal processes in the past and these anomalies can now be exposed at the surface. Near-surface expression corresponding to about 8-13 times the background of the U deposits at Cigar Lake and other similar sites ranging from about 100 to 430 m burial depth were reported (Clark
1987). Association with hydrothermal alteration channels was mentioned but no further discussion of migration
mechanisms and time scales involved was given. Extensive investigations which far exceed the frames of prospecting work are necessary to distinguish unambiguously the roles of various paleo and more recent events in the
formation of a halo. At Cigar Lake such investigations have been conducted which exclude at least U migration
from the bulk ore body (Cramer 1994).
155
Fig. A2.8: U anomalies associated with faults; young age of till and downhill displacement of geochemical
anomaly indicating postglacial U migration.
6RLODQRPDOLHVUHODWHGWR8ULFKJURXQGZDWHU
Very few examples of anomalies exist which are predominantly related to be caused by metal-rich groundwaters.
A unique but somewhat mysterious U (and He) anomaly in a region of permafrost of 300 m thickness has been
found on a lake bottom (Dyck 1987). Consistence of U and He contents in sediments and water as well as concentration profiles in the water column give sufficient evidence of groundwater origin. The problem is that the
discharging water is oxidizing, rich in U and poor in Fe which is in contrast to general experiences from
groundwaters at that depth. However, the U contents in sediment (57 ppm median and up to 396 ppm) and lake
water (up to 35 ppb above groundwater entry points) were below toxic levels.
Direct influence of uraniferous groundwater on U contents in vegetation was suggested from the absence of
correlation between the U contents in soil of the root zone and vegetation (douglas-fir) in a small drainage basin
at a site in the NW-USA where enrichment of U in late Quaternary, organic-rich valley-bottom sediments
reached as high values as 0.9% on a dry weight basis, the values correlating with organics content. The most
organic-rich parts of the sediments were peat with 50-60 wt.% organic matter. U content in fir is obviously controlled by pathways of near-surface groundwater which include subsurface runoff in 1-2 m thick glacial till at
steep slopes and emergence of uraniferous groundwater (100-150 ppb U) at slope springs in a structurally controlled (fractures in underlying bedrock) zone (Fig. A2.9, Zielinski 1987). Age determinations suggest dominantly syndepositional or early post-depositional emplacement of U; the age of the host sediments is given as
younger than 15,000 a (Zielinski 1986). Young, surficial U enrichments of that type are so wide-spread that they
form a significant U resource.
156
Fig. A2.9: Generalized cross section of drainage system showing hypothetical flow paths of subsurface uraniferous water, and the effect on the U content of slope vegetation. Localities of anomalously uraniferous douglas-fir
are indicated as shaded trees.
8UDQLXPLQSHDW
Uranium in peat bogs has received considerable attention. The conditions to be met and the enrichment
mechanisms have been studied at a typical location fulfilling most requirements for enrichment of U (Idiz 1986).
The prerequisites found there were: granitic bedrock relatively rich in U (around 10 ppm) looses U upon weathering (weathered rock contains half as much U as fresh rock); groundwater flow is driven by mountenous relief;
groundwater discharges continuously at a topographical expression of a fault; groundwater has high U content
(average, 100 ppb; max. 293 ppb) and favourable pH and Ca/U ratio to give optimum enrichment in peat. The
enrichment factor was estimated to be about 10,000 giving U values up to 1100 ppm in peat. The fundamental
requirement seemingly is an elavated U content in circulating ground- and surface waters.
Similarly, it was demonstrated at a location in northern Sweden that even low concentrations of U in bedrock can
lead to significant U mobilization, migration and secondary enrichment when the rock is exposed to weathering.
At the mentioned location, no ore could be identified as U source. Granite and pegmatite in the potential source
region had U contents of 30 and 180 ppm, respectively. U in streams was 0.2-7 ppb and the background in
springs was about 6 ppb, but, 2% of the 230 springs which were analyzed had an average U concentration of 730
ppb (Armands 1967). Obviously the springs carrying U were related to fracture systems in the bedrock which
channelized the groundwater. The quantity of U transported into the peat bog by only one of these springs was
estimated to be 6 kg/a. Consequently, in the peat a heterogeneous enrichment of U was measured with an average U content of 600 ppm in dry matter and a maximum of 3.1% U. From the results an enrichment factor for U
of 9000 was derived which is consistent with the results of the previously cited field study and laboratory measurements. In plant ash in the area up to 860 ppm U were determined.
8UDQLXPLQSHDWLQ)LQODQG
A very similar site in northern Finland where uranium mobilization and fixation processes leading to significant
U levels are presently working was described more recently (Peuraniemi 1991). U is leached from surficial volumes of granitic rock (about 8 ppm U), transported by groundwater (up to 380 ppb in one spring) and locally
enriched in a peat bog (up to 3.1% U in peat ash in a groundwater discharge area). Groundwater at the only ra-
157
dioactive spring discharged at a river bank. The final dispersion pattern is complex due to a multicyclic history
with several clastic (glacigenic) dispersion phases, each followed by postglacial weathering and groundwatermediated dispersion. Obviously the more pronounced topography in the northern regions of Scandinavia has
favoured U cycling in both cases described before which are, however, examples of very local phenomena. The
part of the catchment in northern Fimland, where U migration is occurring, has so small dimensions with a radius of below 2 km, that the anomaly did not stand out on reconnaissance scale geochemical maps.
In peat bogs sampled in other areas of Finland only in 7 of 131 bogs the U content in ash exceeded the 1000 ppm
limit; the background was 30 ppm (Yliruokanen 1980). All peat bogs with high U content were on granite bedrock; bogs on rapakivi granite were not included in that study. The maximum content at one location was 2.4%
U in peat ash corresponding to 830 ppm in dry mass: The highest contents usually were found in the basal layers.
The conclusion was that high U contents are not widely found in peat in Finland in spite of the capacity of peat
to collect U.
+DORIRUPDWLRQLQSHQHSODLQVHWWLQJLQ)LQODQG
The few examples described above imply that the morphology governing groundwater flow plays an important
role in the formation of halos around geochemical anomalies. Under comparable climatic conditions, but, in the
peneplain situation in Finland anomalies caused by sub-outcrops even under only a few metres glacial till cover,
often, cannot be recognized on the surface. An example to illustrate this is given in (Wennervirta 1973). The suboutcrop of a Cu mineralization buried under till of between about 2 and 6 m could not be found by samples from
the till from a depth of 2 m. Only locally where the rock surface reached the same level enhanced Cu values
were found. The mineralization left a chemical halo only in the basal till layer adjacent to the rock surface (Fig.
A2.10, Wennervirta 1973).
Another "typical" example, a very limited halo formation over an arsenopyrite vein cropping out below about 2
m of glacial till during the geologically relatively short postglacial period, here even in a terrain of rather marked
topography exhibiting steep-sided valleys, is shown in Fig. A2.11 (Kauranne 1967).
The example in Fig. A2.12 (Salmi 1967), represents the "typical" low-relief setting in Finland with thin covers of
peat and glacial till. The highly mobile Mo from the ore outcrop is manifested in a local halo in the surface
layers of the peat probably due to the fact that evaporation exceeded precipitation during the summer months.
Other water-soluble elements such as Zn, Cu and Pb showed similar behaviour in the water-saturated settings.
In the following a brief summary and evaluation of the findings from natural heavy metal soils is given without
repeating details treated in the different paragraphs.
158
Fig. A2.10: Till samples extracted from three different depths with their copper abundances in -0.074-mm fractions: sample obtained by percussion drilling at a depth of 2 m (1) and corresponding content (4); percussion
drill sample at depth of maximum penetration (2) with corresponding content (5); drill sample from close to
surface of bedrock (3) and corresponding content (6). Cu in core from diamond drill hole (7) in same profile and
estimated footwall contact of mineralization (8).
Fig. A2.11: Distribution of total As, total Cu and exchangeable Cu in a vertical section of glacial till over an
outcrop of a 5-10 cm thick arsenopyrite vein.
159
Fig. A2.12: Distribution of Mo in peat and glacial till cover over ore outcrop, Susineva bog, Finland.
6XPPDU\DQGFRQFOXVLRQV
- Heavy metal levels in soils which may exceed even toxic limits are very common in all parts of the world
- Heavy metal soils are mostly connected to near-surface sources such as outcropping or sub-outcropping metal
anomalies (ore bodies), more rarely to somewhat deeper seated ore bodies when suitable migration pathways
(faults) exist
- Metals are transported by near-surface groundwater or surface water
- Heavy metal soils due to naturally contaminated deep groundwaters are more rare; but, even low concentrations in water can cause significant anomalies due to high enrichment factors
- Mobilization of metals is favoured by rock weathering under oxidizing conditions
- Secondary enrichment preferentially in organic-rich soil layers is very common, in particular for uranium
- Little quantitative information on mass transport is available from ore bodies; an exception is the Morro do
Ferro natural analogue study site and e few similar sites
- Soil anomalies are very difficult to predict due to the complexity of processes and the multitude of parameters
involved
- Morphological factors (relief) play a dominant role in soil anomaly formation
- Surface anomalies can be the result of paleoprocesses; evidence of postglacial to recent migration and accumulation is more easy to obtain in young sediments/soils
- In peneplain situation in Finland no toxic soils were observed: outcrops have only very local halos due to
limited transport by water or strong dilution; groundwater-mediated heavy metal soils occur only in a few peat
bogs (mostly U); migration of metal ions is often limited to immediate rock-till contact zone
- In Scandinavia the geochemical relationship between surface sediment/soil and mineralized bedrock is complicated by both weathering and glacial processes
- In areas where the soil cover and crust of weathered rock has been removed recently (in the Quarternary) by
glaciation the exposed fresh rock generally gives cause of enhanced weathering and, locally, enhanced heavy
metal transport and secondary enrichment.
- The simple assumption in repository performance assessments of simple dispersion and dilution of ions released from the waste, transported through the geosphere by groundwater and finally reaching the biosphere is
not supported by any observation from natural anomalies.
- In nature complex mobilization, migration and, in particular, reconcentration (eventually remobilization) processes prevail.
160
- The more near to the top soil layers the metal ions migrate the more complex becomes their behaviour and the
more difficult predictions can be made.
- The settings of most of the natural heavy metal soils found would be comparable to a waste repository with
spent nuclear fuel disposed without protective canister and buffer in horizontal holes cropping out at the surface
or under a few meters till cover at more or less steep slopes.
5HIHUHQFHV
Armands 1967: G. Armands, Geochemical prospecting of a uraniferous bog deposit at Masugnsbyn, northern
Sweden. In: A. Kvalheim, Geochemical prospecting in Fennoscandia, Interscience, New York, 1967, pp. 127154
Björlykke 1973: A. Björlykke, B. Bölviken, P. Eidsvig, S. Svinndal, Exploration for disseminated lead in southern Norway. In: M.J. Jones, Prospecting in areas of glacial terrain, Trondheim, 1973, 111-126
Bowen 1979: H.J.M. Bowen, Environmental chemistry of the elements, London, 1979, p.60-61
Cannon 1952: H.L. Connan, The effect of uranium-vanadium deposits on the vegetation of the Colorado plateau,
Amer. J. Sci. (1952) 735-770
Cannon 1960: H.L. Cannon, Botanical prospecting for ore deposits. Science 132 (1960) 591-598
Chen 1991: J. Chen, F. Wei, C. Zheng, Y. Wu, D.C. Adriano, Background concentrations of elements in soils in
China. Water, air and soil pollution, 57-58 (1991) 699-712)
Clark 1987: L.A. Clark, Near-surface lithogeochemical halo as an aid to discovery of deeply buried unconformity-type uranium deposits, Athabaska Basin, Canada, J. Geochem. Explor. 28 (1987) 71-84
Cramer 1994: J. Cramer, J. Smellie, Final report of the AECL/SKB Cigar Lake analog study, SKB Technical
Report 94-04, Stockholm, 1994
De Vivo 1998: De Vivo, M. Boni, S. Costabile, Formational anomalies versus mining pollution: geochemical
risk maps of Sardinia, Italy. J. Geochem. Explor. 64 (1998) 321-337
Dyck 1987: W.Dyck, D. Car, Detailed geochemical studies of a He-U lake anomaly in permfrost, Baker Lake
area, N.W.T. J. Geochem. Explor. 28 (1987) 409-429
Eisenbud 1982: M. Eisenbud, et al, Studies of the mobilization thorium from the Morro do Ferro. In: W. Lutze,
Scientific Basis of Nuclear Waste Management - V, Boston, 1982
Eisenbud 1984: M. Eisenbud, K. Krauskopf, E.P. France, W. Lei, R. Ballad, P. Linsalata, Natural analogues for
the transuranic actinide elements: an investigation in Minas Gerais, Brasil, Environ. Geol. Water Sci. 1 (1984) 19
Ernst 1974: Schwermetallvegetation der Erde (Heavy metal vegetation of the earth), Stuttgart, 1974
Förstner 1979: U.Förstner, Metal pollution in the aquatic environment, Springer, Berlin, 1979
Friedrich 1984: G. Friedrich, P. Herzig, S. Keyssner, G. Maliotis, The distribution of Hg, Ba, Cu and Zn in the
vicinity of cupriferous sulfide deposits, Troodos complex, Cyprus, J. Geochem. Explor. 21 (1984) 167-174
Hoffman 1983: S.J. Hoffman, Geochemical exploration for unconformity-type uranium deposits in permfrost
terrain, Hornby Bay basin, NW Territories, Canada. J. Geochem. Explor. 19 (1983) 11-32
Idiz 1986: E.F. Idiz, D. Carlisle, I.R. Kaplan, Interaction between organic matter and trace metals in a uranium
rich bog, Kern County, Ca, USA, Appl. Geochem. 1 (1986) 573-590
Kauranne 1967: L.K. Kauranne, Prospecting for copper by geochemical and related methods at Kotanen, Viitasaari, central Finland. In: A. Kvalheim, Geochemical prospecting in Fennoscandia, Interscience, New York,
1967, pp.255-271)
161
Kuntze 1986: H. Kuntze, U. Herms, Bedeutung geogener und pedogener Faktoren für die weitere Belastung der
Böden mit Schwermetallen (The importance of geogenic and pedologic factors for the further burden of soils by
heavy metals), Naturwissenschaften 73 (1986) 195-204)
Lounamaa 1967: J. Luonamaa, Trace elements in trees and shrubs growing on different rocks in Finland. In: A.
Kvalheim, Geochemical prospecting in Fennoscandia, Interscience, New York, 1967, pp. 287-317
Låg 1970: J. Låg, O.Ö. Hvatum, B. Bölviken, An occurrence of naturally lead-poisoned soil at Kastad near Gjövik, Norway. Norges Geologiske Undersökelse 266 (1970) 141-159
Låg 1974: J. Låg, B. Bölviken, Some naturally heavy-metal poisoned areas of interest in prospecting, soil chemistry and geomedicine. Norges Geologiske Undersökelse 304 (1974) 73-96
Malyuga 1964: D.P. Malyuga, Biogeochemical methods of prospecting, New York, 1964
Mehrtens 1973: M.B. Mehrtens, J.S. Tooms, Geochemical drainage dispersion from sulphide mineralization in
glaciated terrain, central Norway. In: M.J. Jones, Prospecting in areas of glacial terrain, Trondheim, 1973, 1-10
Mitchel 1972: R.L. Mitchell, Trace elements in soils and factors that affect their availability. In: H.L. Cannon,
H.C. Hopps, Geochemical environment in relation to health and desease. Geol. Soc. Amer., Special Paper 140
(1972) 9-16
Peuraniemi 1991: V. Peuraniemi, R. Aario, Hydromorphic dispersion of uranium in a surficial environment in
northern Finland, J. Geochem. Exploration 41 (1991) 197-202
Pfeifer 1994: H-R. Pfeifer, M. Vust, N. Meisser, R. Doppenberg, R.C. Torti, F-L. Domergue, C. Keller, J. Hunziker, Uranium-enrichment in soils and plants in the vicinity of a pitchblende vein at La Creusaz/Les Marecottes
(W of Martigny, Valais, Switzerland). Eclogae geol. Helv. 87/2 (1994) 491-501
Salmi 1967: M. Salmi, Peat prospecting: Applications in Finland. In: A. Kvalheim, Geochemical prospecting in
Fennoscandia Interscience, New York, 1967, pp. 113-126
Säther 1988: O.M. Säther, B. Bölviken, J. Låg, E. Steinnes, Concentration and chemical form of lead during
natural transportation in groundwater. Chem. Geol. 69 (1988) 309-319
Tourtelot 1971: H.A. Tourtelot, Chemical composition of rock types as factors in our environment. In: H.L.
Cannon, H.C. Hopps, Environmental geochemistry in health and desease. Geol. Soc. Amer., Memoir 123 (1971)
13-29
Wennervirta 1973: H. Wennervirta, Sampling of the bedrock-till interface in geochemical exploration, in: M.J.
Jones, Prospecting in areas of glacial terrain, Trondheim, 1973, 67-71
Yliruokanen 1980: I. Yliruokanen, The occurrence of uranium in some Finnish peat bogs, Kemia-Kemi (1980)
213-217
Zielinski 1986: R.A. Zielinski, C.A. Bush, J.N. Rosholt, Uranium series disequilibrium in a young surficial
uranium deposit, NW Washington, USA, Appl. Geochem. 1 (1986) 503-51
162
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The geology of Finland is characterized by the almost complete absence of paleozoic and mesozoic sediments.
Mainly due to the Quaternary glaciations such sediments, if they had existed, have been removed. As a consequence the Precambrian basement rock is exposed or covered with a thin layer of glacial till. The rock basement
is mostly fresh and also the till contains predominantly fresh crushed rock in addition to some remains of older
weathering crust. Postglacial weathering is restricted to the upper layers of the till cover; in poorly drained areas
peat bogs have formed. Under these conditions ore enrichments related to processes of external (exogeneous)
geochemical cycles such as products of physical and chemical weathering, oxidation and hydrolysis products,
transport residues, precipitates, evaporates and biogenetic sediments are missing. The only exception are socalled lake ores which were historically the earliest ores used. Lake ores are in some areas common precipitates
at lake bottoms and in peat bogs of iron oxihydroxides containing variable amounts of manganese and humus.
The occurrence is related to discharge of near surface groundwaters.
All ore deposits in Finland are of endogeneous origin; they belong to the Precambrian and are connected to early
magmatic, hydrothermal, and pegmatitic-pneumatolytic processes. Sedimentary ores from the Precambrian are
so highly metamorphosed that they seem intrusive in relation to their country rocks. The mostly intrusive character of the anomalies has implications on location, size and geometry of the ore bodies, which often form lenses, fracture fillings or deformed and inclined layers. Many ore zones and single deposits are bound to structural
units such as joints and fracture zones or certain lithologies, mostly shists and basic intrusions. Migmatitic and
granitic units are almost devoid of ore enrichments.
A look at exploration geochemical case studies in Finland leads to the preliminary conclusion that the situation
of a nearly peneplane relief and mostly fresh old crystalline bedrock under a thin young till cover in combination
with the small dimension of ore bodies has led to only limited formation of halos around anomalies after the end
of the last glaciation. Chemical migration of elements is locally constrained to the immediate vicinity of outcrops
and suboutcrops under the till cover. The dominating dispersion mechanism, however, was mechanical transport
of weathered and fresh rock material from ore outcrops. Consequently the majority of ores in Finland were found
by studying the fans of glacially transported boulders, so-called boulder trains followed by geological and
geophysical methods. Geochemical investigations, however, were used increasingly during the last three decades. Outcropping or suboutcropping ore bodies usually give a chemical anomaly which, however, can be surprisingly weak and is normally below toxic concentration limits. Deeper lying ore bodies were only found by
geophysical and geological methods.
In the following a number of examplary case studies including some of the largest ore bodies which are mined
and locations which are typical for the Finnish situation are cited; the locations are indicated on the map in Fig.
A3.1 (Simonen 1984). Details of the measured concentrations in the halos at some of these sites and conclusions
concerning geochemical fluxes are treated in a parallel report.
Because of the particular relevance to the safety indicator project uranium anomalies are treated first. The only
uranium ore ever mined in Finland is located in North Karelia at Paukkajanvaara. It is a very typical setting,
minor mineralisations bound to fracture zones, steeply inclined and cropping out (Fig. A3.2 (Piirainen 1968)).
The area is well drained and geochemical anomalies caused by fluvial transport were found in stream sediments
and the organic fraction of lake sediments, although the anomalies were rather weak with only a few local values
exceeding 100 ppm (Björklund 1976a). In till and glaciofluvial sediment layers uranium was not found in the
upper 1 m although the deposit was found by tracing uranium-mineralized boulders at the surface. The uppermost layer has usually been transported longer by the glacier and the material has been derived from a wider
area. Therefore the share of local material is minor. The U concentration in till rarely exceeded 100 ppm, the
highest concentrations being near the rock-till interface (Björklund 1976b).
The famous Outokumpu sulphide ore deposit containing Cu, Zn and Co was discovered by tracing back a glacial
boulder of 20 t weight found exceptionally far from its origin. Several similar deposits in the area were found
also by investigating boulder trains. All these ore bodies were outcropping. Only lithogeochemical halos were
studied in the course of the exploration work (drilling) which led also to the discovery of one blind ore body
(Vuonos) which lies more than 100 m below ground surface. One of the outcrops (Luikonlahti) has long before
been known due to rusty weathering products (Isokangas 1975). Later, geochemical halos caused by the serpentinite rock in the area were easily detected by enhanced Ni contents in till. As in large parts of the Outokumpu
area the transport distance of the fine fraction of till was found to be below 300 m and the soft host rock has been
rapidly crushed to small grain sizes, the Ni distribution in till reflected well the bedrock beneath. The Cu anoma-
163
lies, however, were from two different sources, the ore itself and black shales. The ore occurs in very resistant
quartz rock weak and therefore the anomalies caused by the ore were not stronger than those by the black shales;
both had to be distinguished by their Cu/Zn ratios (Salminen 1981).
The Ni-Cu sulphide ore bodies of Kotalahti, Makola and Hitura were also found by tracing glacially transported
ore boulders. At Kotalahti discoveries during road works helped finding the ore. The outcrop of the pipe-shaped
ore at Kotalahti had dimensions of only about 400 x 5-30 m which is very typical for most ore bodies in Finland.
The outcrop at Hitura was buried under 10-20 m till and clay (locally 40 m at the present mine).
The large Pyhäsalmi sulphide ore body, which was under a till cover a few meters thick, was not detected until
the 1950's. Glacially transported surficial ore boulders had been weathered away already. When digging a well
on his yard a farmer hit on massive Zn- and Cu-bearing pyrite ore at a depth of only 2.5 m. The suboutcrop was
found to be 650 m long and 80 m wide at its center. At this ore body some supergene alteration products were
found associated to fracture zones and areas of intensive jointing (Isokangas 1975). The nature of the secondary
phases leads to the conclusion that most alteration products were still formed under relatively reducing conditions (chalcosite, covelline, bornite) while only minor amounts of oxidation products such as goethite and various sulphates formed probably during the postglacial period.
Due to a flat topography, rock outcrops are rare and extensive peatlands dominate in the area of the Vihanti mine. The thickness of the overburden fluctuates between 10 and 30 m. Consequently also here the first indication
of this large ore body containing Zn, Cu and Pb was the presence of sulphide-rich boulders. But, at Vihanti later
a geochemical analysis of the expression of the ore anomaly in the overlying till (in an area where it was 1-20 m
thick) was conducted. Routine till-geochemical mapping carried out in the Vihanti area at a density of 10 sites
per km2 did not indicate any large ore body. Surprisingly, in more detailed investigations the Vihanti ore deposit
gave a low-contrast, incoherent and areally restricted anomaly down-ice in the till. The lithological and geochemical correlation between the till and underlying bedrock appeared to be non-existent. Vihanti represents a model of restricted secondary dispersion of the elements from a mineralization in bedrock into overlying drift
(Björklund 1976c). As an example the results of a 2400 m long investigation line crossing the Vihanti ore are
given in Fig. A3.3 (Salmi 1967). The overburden is 1-10 m, being thickest at the eastern end. The known ore
bodies of the area lie between 1700 and 2700 m on both sides of the investigation line where the overburden is
composed of watery peat. The Zn ore containing Cu and Pb is mainly mined between 2300 and 2500 m. Pyrite
suboutcrops are found between 2000 and 2700 m. In the western part Cu and Zn contents in peat ash are so low
that they do not give any hint as to the location of the ore, but the Pb content is higher than the background.
Background values in Finnish peat ashes are < 100 ppm for Cu and Pb and < 50 ppm for Pb. Plant samples (given are the contents in ash) indicate the proximity of the ore whereas the thin peat layer does not. In the thicker
eastern peat layers Cu and Pb anomalies were found, but Zn was sparse. No ore body was known to exist there.
The Precambrian, sulphidic lead ore at Korsnäs had been localized by geophysical methods and drilling after
lead ore boulders (galena) had been found in the area in the 1950's. The terrain was flat former seabed with
height differences normally less than 5 m and thus very few exposures existed. The sub-outcropping ore which
contained 3.5 to 5.5% Pb and 0.9% rare earths was connected with a calcite-rich, weathered fracture zone; its
size was about 300 m length, 5-30 m width and 160 m depth. The carbonate rocks were eroded deeper than the
surrounding. The observations that the wall rock near the contact zone was kaolinized in combination with the
mineral pargenesis points to hydrothermal alteration. Only near the surface more recent weathering and oxidation has occurred leading to formation of e.g. limonite. Rare earth elements were enriched in the clay-rich weathering products in the form of mineral grains of e.g. monazite, orthite and bastnäsite which allows the conclusion that obviously no chemical mobilization took place (Isokangas 1975).
The same conclusion concerning the rare earth elements can be drawn from similar observations at the Sokli
carbonatite intrusion, a much younger (350 Ma) plug of about 5 km diamater in Lappland which forms a topographic depression. At Sokli chemical weathering of the carbonate rock has reached a depth of several tens of
meters (max. 60 m) producing regolith beds enriched in iron, niobium and rare earths (Isokangas 1975).
At Korsnäs much later (during 1968-70) systematic geochemical lead prospecting was conducted. The area is
covered by a continuous layer of glacial till, normally 1-4 m thick. In erosional basins higher thickness is
reached. Locally, the till is covered by postglacial marine and lacustrine sediments. The results were complex:
following the pattern of the boulder train down-ice from the lead ore the main anomaly was found, but surface
samples gave only irregular patterns. In Fig. A3.4 and A3.5 (Björklund 1976d) the distribution of Pb-bearing
boulders and, respectively, of Pb contents in till from a depth of 1 m in the Korsnäs area are shown. An outstanding feature was the lack of an anomaly close to the ore in till at depths of 1 m. In the deep samples (2-4.5 m), on
the other hand, an anomaly occurred close to the ores as expected. The displacement from the main ore was less
164
than 400-600 m. The Pb contents in the till at depth were at maximum 45 ppm (95th percentile) (Björklund
1976d).
The examples mentioned before were restricted to the major deposits of non-iron metals in Finland. In the Finnish literature numerous case studies are described from small anomalies which are not economically interesting,
but show minor local halos. These will be reviewed in a parallel report on results of the compilation of natural
metal concentrations in Finland.
The total amounts of toxic metals in the ore deposits mined in Finland are huge, although the mines have mostly
modest size on a global scale. For example, the total reserves of the Vihanti mine were estimated to be 600,000 t
Zn, 70,000 t Cu and 43,000 t Pb, while at Outokumpu the reserves were 106 t Cu. At the Korsnäs mine mentioned above 27,500 t of Pb were mined (Isokangas 1975).
Although these ore bodies usually reached up to the ground surface or to the rock-till interface and although they
consisted of minerals highly unstable when exposed to weathering conditions, there were surprisingly weak and
areally limited chemical dispersion halos found in surface materials. Even at outcrops the metal concentrations
did not reach levels toxic to plants. No other reports of plant communities typical for soils enriched in certain
heavy metals are known to the author than those generally known for serpentinite rocks due to their Ni tolerance.
Sinks where reconcentration processes occur, such as peat bogs, are very common in Finland, but the levels of
metals reached in these rarely exceed toxic levels; only a few cases of enhanced U contents in peat are reported.
A more detailed evaluation and comparison of the risks associated with these heavy metal enrichments in dependence on the use of the land or the peat material will be done later.
Summarizing the numerous observations from natural ore enrichments in Finland, it seems that the dominating
dispersion processes at the outcrops of ore bodies where mechanical processes related to the latest glacial periods. The greatest transport distancies were due to boulders shifted by the moving ice and fluvial transport of
clay fractions. These boulders when left on the surface of the till cover weathered easily and left a local chemical
halo while clay fractions were dispersed and diluted over larger areas. Within the unsorted till cover groundwater
movement is limited due to a low permeability as compared to sorted fluvial and glaciofluvial sediments. Therefore, weathering within deeper layers of till is slow and elemental migration mediated by groundwater is limited,
which in term explains the common finding of local anomalies confined mostly to the till adjacent to the bedrock surface.
There is obviously no clear indication of surface expressions caused by ore bodies deep in the bedrock or contradictory the opinions prevail over such cases, although theoretically migration of metal ions carried by oxidizing
groundwater should be possible at least along fracture zones under favourable flow conditions. Obviously the
amounts transported by groundwater are so small that the metal ions liberated by surface weathering mask their
contribution. At least without thorough investigation of groundwater flow and composition a more quantitative
estimation of the role of groundwater transport seems impossible.
5HIHUHQFHV
Björklund 1976a: A.J. Björklund, M. Tenhola, R. Rosenberg, Regional geochemical uranium prospecting in
Finland, In: Exploration for uranium ore deposits, IAEA-SM-208/26, Vienna, 1976, p. 283-295
Björklund 1976b: A.J. Björklund, Use of till in geochemical uranium exploration, In: Exploration for uranium
ore deposits, IAEA-SM-208/26, Vienna, 1976, p. 297-309
Björklund 1976c: A. Björklund, M. Kontio, M. Nikkarinen, Vihanti: The geochemical response of bedrock and
ore in the overlying till. In: L.K. Kauranne (Ed.), Conceptual models in exploration geochemistry, J. Geochem.
Explor. 5 (1976) 370-373
Björklund 1976d: A. Björklund, Korsnäs: lead prospecting by till geochemistry. In: L.K. Kauranne (Ed.), Conceptual models in exploration geochemistry, J. Geochem. Explor. 5 (1976) 253-258
Isokangas 1975: P. Isokangas, The mineral deposits of Finland, Licentiate thesis, Geological Survey of Finland,
1975, 128 pp.
Piirainen 1968: T. Piirainen, Die Petrologie und die Uranlagerstätten des Koli-Kaltimogebiets im Finnischen
Nordkarelien. Bull. Comm. Geol. Finlande 237 (1968) p.57
165
Salmi 1967: M. Salmi, Peat prospecting: Applications in Finland. In: A. Kvalheim, Geochemical prospecting in
Fennoscandia, Interscience, New York, 1967, pp. 113-126
Salminen 1981: R. Salminen in: P. Lindroos (edit.) The importance of surface till in the transport of ore boulders. GSF, Report of Investigation No. 55, Espoo, 1981, 95-104
Simonen 1984: A. Simonen, The Precambrian in Finland. Geol. Survey of Finland, Bull. 304 (1980) 5-58
Fig. A3.1
166
Fig. A3.2: Cross-section of U occurrence at Paukkajanvaara, Karelia. 1. till, 2. metadiabase and spilite 3. orthoquarzite, 4. quartz-containing conglomerate, 5. sericite-quartz shale, 6. satrolite and granite gneiss, 7. uranium
ore
167
Fig. A3.3
168
Fig.A3.4: Distribution of Pb.bearing boulders in the Korsnäs area, Finland
Fig. A3.5: Distribution of Pb in till samples from a depth of 1 m in the Korsnäs area
169