GEOCHEMICAL EXPLORATION
FOR POLYMETALLIC ORES IN
VOLCANO-SEDIMENTARY
ROCKS
XIPING
ZHA NG
Institute of Geosciences,
University of Oulu
Studies in China and Finland
OULU 2000
XIPING ZHANG
GEOCHEMICAL EXPLORATION FOR
POLYMETALLIC ORES IN VOLCANOSEDIMENTARY ROCKS
Studies in China and Finland
Academic Dissertation to be presented with the assent of
the Faculty of Science, University of Oulu, for public
discussion in the Auditorium of the Department of
Geology (GO 101), Linnanmaa, on December 1st, 2000,
at 12 noon.
O U L U N YL I O PI STO, O U L U 2 0 0 0
Copyright © 2000
University of Oulu, 2000
Manuscript received: 10 November 2000
Manuscript accepted: 20 November 2000
Communicated by
Professor Ouyang Zongqi
Doctor Raimo Lahtinen
ISBN 951-42-5787-1
(URL: http://herkules.oulu.fi/isbn9514257871/)
ALSO AVAILABLE IN PRINTED FORMAT
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ISSN 0355-3191
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OULU UNIVERSITY PRESS
OULU 2000
To my mother
Zhang, Xiping, Geochemical exploration for polymetallic ores in volcanosedimentary rocks: studies in China and Finland
Institute of Geoscienses, University of Oulu, P.O.Box 3000, FIN-90014 University of
Oulu, Finland
2000
Oulu, Finland
(Manuscript received 10 November 2000)
Abstract
A comparison between the two very important sulfide belts Raahe-Ladoga Ore Zone (RLZ) in
Finland and Southern Edge of Altay (SEA) in China, including geological setting, metallogenic
characters and geochemical exploration has been made.
The two sulfide belts share similarities but differ from each other in the tectonic setting and
metallogenic epoch. Polymetallic ores in RLZ and SEA are the products of the submarine
volcanism, but mainly Zn-Cu type is present in RLZ and Pb-Zn, Cu-Pb-Zn and Cu-Zn types occur
in SEA. A main Ni-Cu ore belt related to the mafic-ultramafic intrusions is also present in the RLZ.
RLZ is metamorphosed to a higher grade than SEA.
The Viholanniemi Zn-Au deposit is a veinlet-disseminated type, possibly beneath the
stratabound sulphide ores, and the Keketale Pb-Zn deposit is a stratabound sulphide ore hosted by
sedimentary rocks in the volcano-sedimentary formation. They show many differences. It is
suggested that stratabound sulphide ores overlie stratigraphically the Viholanniemi stringer ores and
Au-bearing stringers underlie the Keketale stratabound ores. Geochemical explorations of the two
deposits exhibit different methods, subjects and procedures. Boulder tracing and till geochemical
exploration proved to be very effective in finding the Viholanniemi deposit while stream sediment
and soil geochemical surveys were the major and effective tools in finding the Keketale deposit.
An extensional environment and the intensity of volcanism are the essential conditions for the
formation of polymetallic ores related to the volcanism. It is feasible to classify the ores into the
ores hosted by volcanics and sedimentary rocks in a volcano-sedimentary formation. The
stratigraphical thickness of volcanic rocks and the amount of agglomerates are the two most crucial
factors needed to be considered in prospecting. The chemical variations of the host rocks can
indicate the sulphide ores hosted by sedimentary rocks in some circumstances.
Keywords: Raahe-Ladoga Ore Zone (RLZ), Southern Edge of Altay (SEA), metallogenesis, volcanism
A short preface to the study
I was in Finland as an exchange scholar through an agreement between the Finnish
Academy and the Chinese Academy of Sciences in 1997. The invitation came from the
Geological Survey of Finland (GTK) and the Institute of Geosciences and Astronomy of
the Oulu University. Before that I knew that Finland enjoyed a high reputation in
Precambrian research and geochemical explorations.
The facts, however, are not merely as I had learned before. Two of the greatest
geologists, Sederholm, J.J. and Eskola, P. are well known over the world for their
pioneering studies and contributions to the anatexis, as well as migmatization and
experiment petrology. Before 1998, I knew almost nothing about them when I read their
famous works on the advice of Prof. Cheng Yuqi, the pioneer of metamorphic geology of
China. Of course, Finnish geologists have also made by far the most outstanding research
on Quaternary Geology and Economic Geology which resulted in the finding of many
important ore deposits e.g. the Main Sulphide Ore Belt including Outokumpu Cu-Co-ZnNi deposits.
The following study has been carrying out in the way of cherishing a feeling of great
reverence for Finland and Finnish geologists. With the results of the study, the author
would like to express his sincere thanks to Finland and Finnish friends for the invitation
and giving me the chance to do the study.
Acknowledgements
In January 1997, Geological Survey of Finland and Institute of Geosciences and
Astronomy, at the University of Oulu invited me to Finland as a junior scientist as part of
the agreement of co-operation in a scientific exchange program between Finland and
China. The Academy of Finland provided financial support. Geological Survey of
Finland and Institute of Geosciences and Astronomy, at the University of Oulu provided
support, including field, laboratory and office work, as well as analyses of samples. The
Geological Survey of Finland has also given me permission to use and publish the
valuable data including unpublished data. The Research Center of Mineral Resources
Exploration, the Chinese Academy of Sciences and the Beijing Institute of Geology and
Mineral Resources have supported me with this program. I am very grateful to all these
institutes.
I am deeply indebted to Dr. Elias Ekdahl, Professor Risto Aario, Dr. Hannu Makkonen
and Professor Vesa Peuraniemi. Dr. Elias Ekdahl and Professor Risto Aario arranged and
supervised the programs in Finland and Dr. Hannu Makkonen followed the study with
enthusiasm. Professor Vesa Peuraniemi also supervised part of the program. Their
knowledge and experiences were so invaluable both in field and subsequent discussions,
as well as in directing the course of the study. The manuscript was also checked and
reviewed by them and I acknowledge with gratitude for their numerous suggestions and
comments.
Professor Jiang Fuzhi has given me many valuable suggestions during discussions. Dr.
Raimo Lahtinen and Professor Ouyang Zongqi read and checked the manuscript and
made comments and many important suggestions. Drs. Li Yanhe and Juha Karhu
reviewed the part with the isotope studies. Mr. Rauli Lempiäinen assisted me with field
work in Finland. Mr. Gordon Roberts M.A. reviewed the English of the manuscripts.
I am additionally grateful to Professor Markku Mäkelä, the Research Director of the
Geological Survey of Finland, Dr. Anssi Lonka and Mr. Kari Pääkkönen, the Director of
the Kuopio Regional Office of the Geological Survey of Finland, Professor Risto Aario
and Professor Tuomo Alapieti, the Director of the Institute of Geosciences and
Astronomy, at the University of Oulu, for allowing me to use the facilities of institutes.
Also I wish to thank Mr. Tuomo Korkalo, the General Manager of Exploration,
Outokumpu Mining Oy, for allowing me to use some unpublished data.
The author wishes to express his specific thanks to Professors Cheng Yuqi, Huang
Dingcheng, Sun Zhaojun, Wang Jingbin, Wang Dongbo, Ms.Yin Xiuzhu, Dr. Huang
Zhen, Mr. Yang Bing, as well as many friends from Finland for their help and support in
different ways.
I would like here also to thank my mother, brothers, sister and my close friends for
their great support.
List of original publications
The following previously published papers are reviewed and revised in this study:
1. Zhang X (1992) Geochemical anomalies of rock-forming elements reflecting
precipitation environments of ore substances - an important indicator for prognosis of
blind ore deposits in geochemical exploration. Geoph Geoch Explor 16(3): 208-215
(in Chinese with English Summary).
2. Zhang X & Chen W (1995) Preliminary research on REE geochemistry of the
Keketale Pb-Zn deposit, Xinjiang. Geol Expl Non-Ferrous Metals 4(4): 219-222 (in
Chinese with English Summary).
3. Zhang X, Chen W & Wang S (1996) Geochemical investigation of the Keketale PbZn deposits in Xinjiang and its anomaly model. Geol Expl Non-Ferrous Metals 5(1):
48-53 (in Chinese with English Summary).
This thesis consists of the following parts:
Part I
Early Proterozoic metavolcano-sedimentary formation and zinc-gold deposit in
the Viholanniemi area, south-eastern Finland.
Part II Boulder prospecting and till geochemistry in the search for zinc-gold ore in the
Viholanniemi area, south-eastern Finland.
Part III Geochemical exploration and study of Keketale lead-zinc deposit hosted by sedimentary rocks in a volcano-sedimentary formation, north-western China (review
of previous studies including papers 2 and 3).
Part IV Geochemical anomalies of rock-forming elements: an important indicator of
blind ore deposits (revised version of the previously published paper 1).
Contents
Abstract
A short preface to the study
Acknowledgements
List of original publications
1 Polymetallic ores in the RLZ, Finland and the SEA, China . . . . . . . . . . . . . . . . . . . 15
1.1 Volcano-sedimentary formations and related polymetallic ores
in the Viholanniemi and Maizi areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.2 Essential genetic conditions of polymetallic ores in
volcano-sedimentary formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.3 Geochemical exploration for polymetallic ores in volcanic terrains . . . . . . . . . 20
1.4 Prospecting and interpretation of polymetallic ores in volcanic terrains . . . . . . 24
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
PART I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Early Proterozoic metavolcano-sedimentary formation and zinc-gold deposit in the
Viholanniemi Area, South-eastern Finland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Location and physiography of the study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Background to the research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Methods and objectives of the study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
The regional geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Geology of the Viholanniemi area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Lithology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Stratigraphical relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
The volcanic cycle, rock assemblage and paleovolcanic center. . . . . . . . . . . . . . . 40
Metamorphism, deformation and structural features . . . . . . . . . . . . . . . . . . . . . . . 41
Lithogeochemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Whole rock geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Classification of volcanic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Tectonomagmatic affinities of volcanic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Viholanniemi Zn-Au deposit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Wall rocks and host rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Ore occurrence and metal contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Ore mineralogy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Isotope studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Geotectonic setting of the Viholanniemi volcano-sedimentary formation. . . . . . . 64
Viholanniemi Zn-Au mineralization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Summary and conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Appendices 1-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
PART II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Boulder prospecting and till geochemistry in the search for zinc (gold) ore in the
Viholanniemi area, South-eastern Finland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Bedrock geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Glacial geology and boulder prospecting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Till geochemistry and geochemical exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Mineralogy of Till. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
Till geochemical exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Conclusions and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
PART III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Geochemical exploration and study of the Keketale lead-zinc deposit hosted by
sedimentary rocks in the volcano-sedimentary formation in North-Western China . . . 111
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
The geological setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
Ore deposit geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Geochemical exploration and the discovery of the deposit. . . . . . . . . . . . . . . . . . . . 116
Deposit geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Summary and conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
PART IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Geochemical anomalies of rock-forming elements: an important indicator
of blind ore deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
The case of anomalous models of rock-forming elements . . . . . . . . . . . . . . . . . . . . 134
Porphyry copper deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Stratabound sulfide deposits hosted by volcanic rocks . . . . . . . . . . . . . . . . . . . . 136
Stratabound sulfide deposits hosted by sedimentary rocks in the
volcano-sedimentary formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Acknowledgement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
1 Polymetallic ores in the RLZ, Finland and the SEA, China
For the author it was very useful to take part in geochemical exploration for polymetallic
ores and make studies on deposits, for instance the Keketale Pb-Zn deposit, found in
volcanic terrain within the Southern Edge of Altay (SEA) in China from 1985, and
continue the studies in the Viholanniemi Zn-Au deposit within the Raahe-Ladoga Ore
Zone (RLZ) in Finland from 1997. This made it possible to understand better the
polymetallic ores related to volcanism, their genesis and geological setting, as well as
share the experiences on exploration both in Finland and China through the studies and
comparison. The Viholanniemi Zn-Au deposit is not a typical VMS deposit but can be
considered as a stringer type (also see Makkonen 1991) with superimposition of
metamophism according to its distinct characters, while the Keketale Pb-Zn deposit is
one of the stratabound deposits hosted by sedimentary rocks in the volcano-sedimentary
formation (also see Jiang & Liu 1992, Jiang 1994). This however does not hinder the
comparison of SEA and RLZ, which both contain a variety of ores in volcanic terrains.
The studies greatly help to learn the characteristics of VHMS deposits and also the
prospecting.
RLZ and SEA seem to share similarities in many respects, although they differ from
each other in the tectonic setting and metallogenic epoch. RLZ is a boundary zone
between the Finnish Archaean and Proterozoic, which has been interpreted as a collisional zone of the Archaean continent and Palaeoproterozoic, Svecofennian lithosphere
(see Ekdahl1993, Weihed & Mäki 1997). Several epochs of mineralization and also metallogenic provinces are related to the Palaeoproterozoic intracratonic rifting (Outokumpu), island arc volcanism (Pyhäsalmi-Vihanti), locally arc-rifting (Viholanniemi) and
also the mafic-ultramafic intrusions (Kotalahti Ni-belt) (Ekdahl 1993) (Fig. 1).
16
Fig. 1. Metallogenic provinces and epochs within the Raahe-Ladoga zone, central Finland. 1.
Kotalahti Ni-Belt; 2. Pyhäsalmi Island Arc; 3. Kainuu-Outokumpu Back Arc. (Ekdahl 1993).
SEA is a part of the southern margin of the Siberia plate. The regional tectonic
evolution is characterised by splitting-collision regims from Proterozoic to Paleozoic (Li
1983, Huang et al. 1990, Han & He 1991, Xiao et al. 1990, Chen et al. 1996). According
to Chen et al. (1996), the protolith of the Proterozoic basement is a volcanic-terrigenous
formation indicating an extensional environment. Altai massif was accreted to the Siberia
plate on its southern margin in Early Ordovician. During the Early-Middle Devonian, an
epicontinental extensional rift was formed beginning at the eastern part of the area. It was
accompanied by ongoing rifting, submarine volcanism associated with massive sulphide
mineralizations along three basins Maizi (Mongku-Keketale)-Altay-Ashele (Chen et al.
1996) (Fig. 2).
Polymetallic ores in RLZ and SEA were the products of the submarine volcanism.
Volcanic rocks related to the massive sulphides in RLZ are mainly tholeiitic and calcalkaline, and also the products of bimodal volcanism, while in SEA the rocks are
tholeiitic, calc-alkaline and alkaline, and the bimodal volcanism seem to have a close
relationship with Cu-Zn ores. Deposits in RLZ are Zn-Cu type, however, in SEA, deposits
are Pb-Zn, Cu-Pb-Zn and Cu-Zn types. In addition, except for VMS deposits, a main NiCu ore belt related to the mafic-ultramafic intrusions is also present in the RLZ; these are
absent in SEA except for locally mafic intrusions and one related Cu-Ni deposit. Both
zones have experienced deformation and metamorphism, but the effects seem to be
17
stronger in RLZ than in SEA. Detailed comparison is listed in Table 1 according to the
data of Ekdahl (1993), Weihed and Mäki (1997), Jiang (1993), Jiang and Liu (1992),
Jiang (1994), Zhang (1992), Zhang et al. (1996), Wang et al. (1998, 1999), Chen et al.
(1995, 1996), Ding (1999).
Fig. 2. Metallogenic belts and epochs in the southern edge of Altay, north-western China. The
map is simplified after Chen et al. (1996) and Wang et al. (1998). The data is from Chen et al.
(1996) and Ding (1999). 1. Volcanic-sedimentary basin; 2. Fault.
18
Table 1. Comparison between the VHMS deposits in Finnish RLZ and Chinese SEA.
RLZ in Finland
SEA in China
Bimodal submarine volcanism in island arc system,
volcanics are tholeiitic and calc-alkaline
Bimodal-unimodal submarine volcanism in continental
margin rift, volcanics are tholeiitic, calc-alkaline and
alkaline
Volcanic complexes and zones are associated with
gravimetric highs or sharp gradients and medium-to
high-grade metamorphism
Volcanic-sedimentary formations are associated with
gravimetric gradients
Ores are mainly Zn-Cu type
Ores are mainly Cu-Zn, Cu-Pb-Zn and Pb-Zn types
Footwall rocks include dolomite/carbonate, calcsilicate rocks, felsic volcanics, chert, U-P horizon,
black schist, ( BIF )
Quartz-Keratophyrite-Keratophyric pyroclastics,
carbonate, tuffaceous clastics compose the footwall of
Cu-Zn ores, Na-K rich rhyolitic lava and felsic
pyroclastics compose the footwall of Pb-Zn ores.
Sericitization, Silicification and Chloritization are
general
Commonly underlain by a zone of alteration enclosing
the stringer ores, silicification, sericitization, pyritization
as well as chloritization, epidotization and
carbonatization are general
Mg, Fe, H2O and S increase towards the ore, and
conversely, Si, Ca, Na and K decrease
Si, K, H2O and S increase and Ca, Na decrease towards
Ore in Cu-Zn type; Mg, Fe, Ca increase and Na decrease
towards Ore in Pb-Zn type
Cyprus-type (Outokumpu) deposits (³1.96Ga ) are
Cyprus-type deposits absent
present
The geometry of the deposits is intensely tectonically The geometry of the deposits is tectonically controlled
controlled
c. 2.0-1.9 Ga in ages
c. 404.6-352.3 Ma in ages
Amphibolite-granulite facies metamorphism
Greenschist facies metamorphism
1.1 Volcano-sedimentary formations and related polymetallic ores in
the Viholanniemi and Maizi areas
A comparison between the Viholanniemi Zn-Au deposit and Keketale Pb-Zn deposit is
made in Table 2 (the data are from Wu 1992, Jiang 1993, Han and He 1991, Han 1992,
He et al. 1994, Jiang & Liu 1992, Jiang 1994, Zhang et al. 1990, Zhang 1992, Zhang et
al. 1996, Wang et al. 1998 and 1999, Chen et al. 1995 and 1996).
19
Table 2. Comparison between the Viholanniemi Zn-Au deposit, south-eastern Finland and
the Keketale Pb-Zn deposits, north-western China.
Viholanniemi Zn-Au deposit
Keketale Pb-Zn deposit
Bimodal submarine volcanism seen from the
stratigraphical sequence but not fractionated from the
same parent magma in arc-rifting, volcanics are
tholeiitic and calc-alkaline
Bimodal submarine volcanism fractionated from the
same parent magma in continental margin rift,
volcanics are calc-alkaline
The volcano-sedimentary formation has a relative
small stratigraphical thickness
The volcano-sedimentary formation has a
stratigraphical thickness over 300m
Volcanic breccia and agglomerate are common
Volcanic breccia and agglomerate are common
Felsic volcanics are mainly pyroclastics
Felsic volcanics including large voluminous lava
underlie the host rocks
The host rocks are mainly quartz-carbonate-tremolite The host rocks are mainly composed of biotite quartz
rocks (the protolith includes siliceous rock, tuffaceous schist, granoblasite with interlayers of marbles, metasiltstone and tuff)
tuff, meta-tuffaceous siltsone and meta-siltstone. (The
protoliths include calcareous-argillaceous sandstone,
siliceous rock and iron-bearing carbonates)
Ores are veinlet and disseminated
Ores are mainly disseminated, taxitic, massive,
banded, breccia and net-veined
Sericitization and locally epidotization are general
Sericitization, carbonatization and silicification are
general
Ore sulphide d34S values vary from -0.5‰ to 10.4‰
and no sulphate mineral is present
Ore sulphide d34S values vary from –5.4‰ to –15.3‰
and sulphate minerals are present
Calcite has d18O values of 7.6-20‰ and d13C values
of –3.6 — – 8.1‰, and graphite is present
One carbonate has d13C value of –11.6‰ and no
graphite is present
Not intense primary geochemical patterns and no
depleted Na2O
Clear and coherent primary geochemical patterns with
typical depleted Na2O
Intense metamorphic overprinting
Evident metamorphic overprinting has not been found
Comparing the two areas of Viholanniemi and Keketale, the volcanic rocks in the
Viholanniemi area seem to be the products of bimodal volcanism, if only concerning the
stratigraphical sequence, and in fact the rocks of calc-alkaline and tholeiitic series are not
fractionates from the same parent magma. The tectonic setting is interpreted as an
incipient arc-rifting, and the felsic volcanics are mainly pyroclastics. In contrast to these,
the volcanic rocks of the calc-alkaline series in the Maizi area were formed by bimodal
volcanism fractionated from the same parent magma in the continental margin rift. The
large quantity of felsic lava is peculiar to the formation. Secondly, the stratigraphical
thickness is less and the period of inactivity of volcanism is shorter in Viholanniemi area
than in Maizi area. The sedimentary rocks formed in hot water (here it means a
sedimentary basin near the volcanic center, in which the water may have been about
100oC in temperature) are present in both areas, only a small volume of siliceous rock has
been found in Viholanniemi. Siliceous rock and iron bearing carbonate rocks, however,
are common in the Maizi area, particularly in Keketale. Thirdly, ore sulphide d34S values
vary between 5.4‰ to 15.3‰, and no carbon concentration has been documented in
Keketale (Han 1992), while sulphide d34S values in Viholanniemi are mainly positive and
20
vary between -0.5‰ to10.4‰ and also graphite is very common. In addition, an intense
overprinting of metamorphism is present in Viholanniemi, but this is not evident in
Keketale.
However, although a big difference, including an economic significance, between the
two deposits is obvious, they share common features connected by stratabound sulphides
related to marine volcanism. The volcano-sedimentary formations are composed of
marine volcanics and clastics, and volcanic agglomerate and breccia are general in two
areas, which indicates that both deposits were formed in the sedimentary basin near the
volcanic center. The most important factor is that both of them were formed in an
extension environment, and this is perhaps the volcanogenic sulphide ore proper.
Therefore the Viholanniemi Zn-Au deposit could be considered as a veinlet-disseminated
type possibly beneath the strata bound sulphide ores which experienced metamorphic
overprinting, and the Keketale Pb-Zn deposit is a stratabound sulphide ore hosted by
sedimentary rocks in the volcano-sedimentary formation. It is noteworthy perhaps here to
point out the possibility of the presence of stratabound sulphide ores stratigraphically
above the Viholanniemi stringer ores and of Au bearing stringer below the Keketale strata
bound ores.
1.2 Essential genetic conditions of polymetallic ores in volcanosedimentary formation
As the geological setting of the polymetallic ores are related to the volcanism, an
extensional environment seems to be essential. In this case, the magma in the depth may
provide good conditions to differentiate and gather the volatile component needed by
intense eruption. It is easy to understand why most of important polymetallic sulphide
ores are associated with the intense felsic or felsic-intermediate volcanism.
Other essential conditions could contribute to the intensity of volcanism. According to
Jiang (1994), the intensity of volcanism in the same time with the mineralization is the
crucial factor affecting the genetic type of polymetallic ores. The ores hosted by volcanic
rocks are generally the products of intense volcanism in which the extensive fluid
activities also happened. In contrast to this, the ores hosted by sedimentary rocks in the
volcano-sedimentary formation were formed in the periods of small volcanic activity
following mainly felsic eruptions. The sedimentary basin near the volcanic center and
relative strict conditions, such as reducing environment or bacteria activity, would be
needed.
1.3 Geochemical exploration for polymetallic ores in volcanic terrains
Boulder tracing and till geochemical exploration have been proved to be very effective
tools in the prospecting of mineral deposits in Finland. One must, however investigate the
Quaternary framework before the exploration, because the erosion, entrainment,
21
transportation and depositional history and the resulting composition of sediments are
very important factors in considering sampling, analysis of glacial sediments and
interpretation of the data.
Preglacial weathering in the Viholanniemi area was intense, but its products preserved
well only in the bottommost layers, immediately above the bedrock. The till in the
bottom-most layer is composed of more local material illustrated by identical mineral
composition including the ore minerals in the mineralized sites presented both in till and
weathered bedrock. Trace elements presented in till in the area are generally related to the
adsorption of clay minerals, secondary oxides and hydroxides, but high concentrations of
Zn, Cu, Pb, Au, Ag, Ni and Co in till in the project area are mainly related to the residual
ore minerals.
The ore-bearing boulder train that indicated ores related to quartz-carbonate rocks and
felsic volcanics is composed of long and narrow boulder clusters of about 20 km (Fig. 3).
Following the till geochemical, together with geophysical exploration led to the discovery
of the Viholanniemi Zn-Au deposit. All metals detected in the till show clear and coherent
anomalous distribution patterns which reflect the mineralization sites well in the area with
Ag and Zn having the strongest anomalies (Fig. 4).
Differing from Finland, stream sediment and locally soil geochemical surveys are the
major and effective tools in prospecting of mineral deposits in China. Stream sediment
geochemical exploration is the first choice in most mountain areas and this was well
illustrated in the SEA, in NW China. Generally, the testing of selecting the fraction of
favorable size is necessary before the exploration. Stream sediment geochemical
exploration carried out in the central part of SEA exhibits an associated anomalous area
of about 200 km2 composed of Pb, Zn, Ag, As, Cu, Cd and Mn in the Maizi area (Fig. 5).
Detailed exploration of the anomalies of Cd and coherent Pb, Zn, As, Ag and Mn occur to
the south-eastern part of the Maizi area (Fig. 6) brought about the finding of stratiform
gossan at Keketale and a ring of soil anomalies of Pb and Zn corresponding to the
volcano-sedimentary formation of Lower Devonian. The Keketale Pb-Zn deposit was
found by following geochemical and geophysical anomalies.
Fig. 3. Ore boulder train from Viholanniemi, south-eastern Finland (modified after Makkonen
1991).
22
Fig. 4. Map of the areal distribution of zinc concentration in till at Viholanniemi, south-eastern
Finland.
Obviously, the Quaternary framework is the main subject of the till geochemistry in
Finland. In China, however, most exploration geochemists are not concerned with the
Quaternary framework but only the favorable sample size (and the horizon in soil survey).
The geochemical surveys of the Viholanniemi Zn-Au deposit were started with the
boulder tracing. Then, it transited to the close-spaced sampling along lines with distances
of 200 m, 50 m and 25 m, and the sample spacing of 40 m, 20 m, 10 m and 5 m.
Meanwhile, a geophysical survey was also carried out. It was composed of two main
stages before the drilling. Compared to these, the geochemical surveys of the Keketale
Pb-Zn deposit began with the stream sediment survey, and then with the anomaly tracing
and at the same time sampling with a grid of 200 m by 40 m was also carried out. At the
last step, it transited to a more detailed sampling with a grid of 100 m by 20 m and the
geophysical exploration. These two parts of detailed sampling and the geophysical
exploration should have been combined into one for economic reasons and for a rational
prospecting procedure. Trace elements, particularly Cd associated closely with the ore
minerals, were successfully applied in the interpretation of geochemical anomalies in
Keketale.
23
Fig. 5. Anomaly of lead in stream sediments in the Maizi district, north-western China
(modified after Wang et al. 1998).
Fig. 6. Anomalies of selected elements in stream sediments at Keketale, north-western China.
The sample site is marked by small point. a) Pb (solid line): 30,60,120,240ppm; Ag (dotted line):
0.05,0.1,0.2,0.4ppm; b) Zn (solid line): 120,240,480,1000ppm; Cd (dotted line): 0.6,1.2,2.4ppm.
24
1.4 Prospecting and interpretation of polymetallic ores in volcanic
terrains
Concerning prospecting and interpretation of polymetallic ores, it is feasible to classify
the sulphide polymetallic ores related to volcanism into the ores hosted by volcanics and
sedimentary rocks in a volcano-sedimentary formation (Jiang & Liu 1992, Jiang 1994).
The stratigraphical thickness of volcanic rocks and the amount of agglomerates are the
two most crucial factors. Intense alteration, including an alteration pipe in the footwall,
occurs mainly in the ores hosted by volcanics and is characterized by the absence of a
feldspar zone (Lambert 1974, Riverin & Hodgson 1980, Larson 1984, Jiang & Liu 1992,
Jiang 1994). Alteration is typically shown as enrichment of Fe and Mg (K and Si) and as
depletion of Na and Ca in chemical composition (Lambert & Sato 1974, Riverin and
Hodgson 1980, Frater 1983, Larson 1984, Peterson 1988, Ekdahl 1993, Chen et al. 1996).
The alteration present in the ores hosted by sedimentary rocks is commonly weaker and
the alteration pipe is seldom met. The chemical variations, however, are obvious: for
instance the increase of Fe, Mg and Ca and the decrease of Na correspond to the
alteration and ore bodies (Zhang et al. 1990, 1996, Zhang 1992). Consequently, the
chemical variations of the host rocks would give a good indication of prospecting of
sulphide ores hosted by sedimentary rocks in the volcano-sedimentary formation, in the
case where alteration can not be used as a good indicator of the presence of sulphide ores
hosted by sedimentary rocks.
Elements associated to the major minerals in the polymetallic ores should be given
much attention in the interpretation of geochemical exploration, for example, the
indication of Cd in the discovery of the Keketale Pb-Zn deposit. Rock-forming elements
and their variations can be used as good indicators of blind ores, no matter what type of
sulphide ore it is (Zhang et al. 1990, 1996, Zhang 1992).
References
Ekdahl E (1993) Early Proterozoic Karelian and Svecofennian formations and the evolution of the
Raahe-Ladoga Ore Zone, based on the Pielavesi area, central Finland. Geol Surv Finland, Bull
373, 137 p.
Chen Y, Ye Q, Feng J, Mu C, Zhou L, Wang Q, Huang G, Zhuang D & Ren B (1996) Ore-forming
conditions and metallogenic prognosis of the Ashele Copper-Zinc metallogenic belt, Xinjiang,
China. Geol Publ House, Beijing, 330 p (in Chinese with English Summary).
Chen Y, Ye Q, Wang J & Rei J (1995) Metallogenic conditions and evaluation of mineral resources
of Altay gold and non-ferrous metals provinces. Unpublished research report, 483 p (in Chinese).
Ding R (1999) Evolution of ore-bearing fluid and prospect forecasting in Keketale metallogenic belt,
Xinjiang. Unpubl. PhD thesis. China University of Geosciences, Beijing, 100 p (in Chinese).
Frater KM (1983) Geology of the Golden Grove prospect, Western Australia: A volcanogenic
massive sulfide-magnetite deposit. Econ Geol 78: 75-919.
Han B & He G (1991) The tectonic nature of the Devonian volcanic belt on the Southern Edge of
Altay Mountains in China. Geosc Xinjiang, No 3: 89-100 (in Chinese).
Han D (1992) Keketale lead-zinc deposit. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds)
Geological, geophysical and geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge
of Altay and the prospecting targets. Unpublished research report, 251 p (in Chinese).
He G, Li M, Liu D, Tang Y & Zhou R (1994) Paleozoic crustal evolution and mineralization in
Xinjiang of China. People’s Publ House of Xinjiang, 437 p (in Chinese with English Summary).
Huang J, Jiang C & Wang Z (1990) On the opening-closing tectonics and accordion movement of
plate in Xinjiang and adjacent. Geosc Xinjiang, No 1: 3-16 (in Chinese).
Jiang F (1993) Petrochemical characters of ore-bearing volcanic formation in massive sulfide
deposits. In: Li Z & Wang B (eds) Volcanic rocks, volcanism and related mineral resources.
Collection of Papers of Geo Soc China 1: 31-38 (in Chinese).
Jiang Q & Liu Y (1992) Geological features of Cu-polymetallic ore deposits in Southern Edge of
Altay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical and
geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospecting
targets. Unpublished research report, 251 p (in Chinese).
Jiang Q (1994) Types, evaluation criteria and geneses of the massive sulfide deposits in the volcanic
terrain. Geol Expl Non-Ferrous Metals 3(1): 4-9. (in Chinese).
Lambert IB & Sato T (1974) The Kuroko and associated ore deposits of Japan: A review of their
features and metallogenesis. Econ Geol 69: 1215-1236.
Larson PB (1984) Geochemisry of the alteration pipe at the Bruce Cu-Zn volcanogenic massive
sulfide deposit. Arizona. Econ Geol 79: 1880-1896.
26
Li C (1983) Contributions to the project of plate tectonics in Northern China. N1. Geol Publ House,
Beijing, p 3-6 (in Chinese).
Makkonen H (1991) Studies of the Viholanniemi Zn deposit in Joroinen, 1984-1988. Geol Surv
Finland, unpublished research report, 22 p.
Peterson JA (1988) Distribution of selected trace and major elements around the massive sulfide
deposit at the Penn Mine, California. Econ Geol 83: 419-427.
Riverin G & Hodgson CJ (1980) Wall-rock alteration at the Millenbach Cu-Zn Mine, Noranda,
Quebec. Econ Geol 75: 424-444.
Wang J, Qin K, Wu Z, Hu J, Deng J, Zhang J, Bian, Y & Li S (1998) Volcanic-exhalativesedimentary lead-zinc deposits in the Southern Margin of the Altai, Xinjiang. Geol Publ House,
Beijing, 210 p (in Chinese).
Wang J, Li B, Zhang J, Yin Y, Wang J, Wang Z & Zheng G (1999) Metallogenesis and prognosis of
gold and copper deposits in Ertix Metallogenic Belt, Xinjiang. Metallurgical Industry Press,
Beijing, 178 p (in Chinese).
Weihed P & Mäki T (1997) Volcanic hosted massive sulfide deposits and gold deposits in the
Skellefte district, Sweden and Western Finland. Research and exploration-where do they meet?
4th Biennial SGA Meeting, Aug. 11-13, 1997, Turku, Finland, excursion guidebook A2. Geol
Surv Finland, Guide 41, 81 p.
Wu Z (1992) The volcano-sedimentary formations of lower Devonian in major districts, Southern
Edge of Altay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical and
geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospecting
targets. Unpublished research report, 251 p (in Chinese).
Xiao X, Tang Y, Li J, Zhao M, Feng Y & Zhu B (1990) On the tectonic evolution of the Northern
Xinjiang, Northwest China. Geosc Xinjiang, No 1: 47-68 (in Chinese).
Zhang X, Chen W & Wang S (1990) Studies of the polymetallic ores, their geochemical anomalous
patterns and interpretation, Beijing Institute of Geology for Mineral Resources, China.
Unpublished research report with three accessary, 98 p (in Chinese).
Zhang X (1992) Geochemical anomalies of rock-forming elements reflecting precipitation
environments of ore substances-an important indicator for prognosis of blind ore deposits in
geochemical exploration. Geoph & Geoch Explor 16(3): 208-215 (in Chinese).
Zhang X & Chen W (1995) Preliminary research on REE geochemistry of the Keketale Pb-Zn
deposit, Xinjiang. Geol Expl Non-Ferrous Metals 4(4): 219-222 (in Chinese).
Zhang X, Chen W & Wang S (1996) Geochemical investigation of the Keketale Pb-Zn deposits in
Xinjiang and its anomaly model. Geol Expl Non-Ferrous Metals 5(1): 48-53 (in Chinese).
PART I
I
Early Proterozoic metavolcano-sedimentary formation and
zinc-gold deposit in the Viholanniemi Area, South-eastern
Finland
Xiping Zhang
Abstract
The Viholanniemi metavolcanic-sedimentary formation is composed of mainly clastics with volcanics
of a shallow marine environment. This formation includes felsic pyroclastics with minor intermediate
intercalations, mafic pyroclastics associated with pillow lava, siliceous rock and fine tuffacous
siltstone between the felsic and mafic pyroclastics, as well as flychoid clastics in the bottom and top
respectively. The volcanism began with mainly felsic explosive eruption of the central type and ended
with mafic effusive eruption of the fissure type. Pyroclastics of the Viholanniemi formation occur
concordantly with the flychoid clastic rocks of the Svecofennian. Chemical composition of the
volcanics suggests that felsic-intermediate rocks are calc-alkaline, while mafic rocks belong to
tholeiitic series of low potassium. The volcanic rocks of the area are products of mantle-derived melt
and its induced anatextic melt, and also their mixing instead of fractionates from the same parent
magma.
The mafic rocks of the Viholanniemi area are the products of volcanism within plate. Evidence
includes: (1) chemical variations share a few features of arc-tholeiite but display a clear trending of
alkalic; (2) high contents of TiO2 of mafic volcanics differ clearly from those of island arc as well as
outside the RLZ and are similar to ridge tholeiite; (3) multi-element distribution patterns including
REE patterns exhibit characteristics both of volcanism related to subduction and within plate basalts;
(4) discrimination diagrams using immobile elements indicate affinities to within plate setting and
MORB. The inference has been deduced that an incipient arc-rifting system was presented in the
Viholanniemi area.
Viholanniemi Zn-Au deposit shows distinctive features that are not typical of VHMS deposits in
many respects. These features include: (1) ore host rocks are mainly vein like quartz-carbonatetremolite rocks and ore is disseminated, or is as open fillings. Sulphur contents in the ore are very low
and no sulphate mineral has been found; (2) ore sulphide d34S values are mainly positive and vary in a
relatively wide range: d34Ssp 0.2 -10.4‰, d34Spy -0.5 -10.2‰. Sulphur came from mainly a magmatic
source mixed with a sea water source; (3) Calcite analysed has d18O values of 7.6-20 per mill and
d13C values of -3.6 – -8.1 per mill showing a clear affinity of mantle-derived carbon and possibly
mixed carbon coming from marine sediments and organic materials, and also considerable
involvement of meteoric water and metamorphic water; (4) ore bearing fluids have relatively low
salinities of 0.7-9.2wt% NaCl and different Th temperatures ranging from 170°C to 335°C (not
corrected for pressure); (5) ores experienced intense deformation and superimposition of
metamorphism, and part of the metals were remobilized; (6) geochemical patterns of the deposit do
not show intense anomalies and the typical Na2O depletion of the massive sulphides proper. The
deposit is considered as a veinlet-disseminated type that experienced intense metamorphic
superimposition.
The mineralization involves possibly convective cells developed immediately after the felsic
eruptions in the early stage of the arc-rift environment, driven by ascending mafic magma, and then
superimposed by metamorphism. A tentative geological model of the Viholanniemi Zn-Au deposit has
been established.
29
I
Keywords: Palaeoproterozoic, metavolcanic-sedimentary formation, pyroclastics, within-plate,
MORB, island arc, subduction, incipient arc-rifting, Viholanniemi Zn-Au deposit, veinlet, carbon
isotopes, oxygen isotopes, sulphur isotopes, carbon sources, sulphur sources, superimposition of
metamorphism, geological model, Finland.
Introduction
The Main Sulphide Ore Belt (Kahma 1973) or the Raahe-Ladoga Ore Zone (see Ekdahl
1993), which runs diagonally across central Finland from Lake Ladoga to the northern
coast of the Gulf of Bothnia, is a typical belt occurring at ancient convergent plate
boundaries. Within the belt occur many sulphide deposits such as Outokumpu Cu-Co-ZnNi deposits, Vihanti and Pyhäsalmi as well as Virtasalmi stratabound Zn-Cu (-Pb)
deposits, Hitura and Kotalahti Ni-Cu deposits and small occurrences including porphyry
type Cu±Mo±Au occurrences, stratiform U-P occurrences and epigenetic Au-As
occurrences etc. (Simonen 1980, Ekdahl 1993).
The Viholanniemi Zn-Au deposit is a small deposit in the belt hosted by felsicintermediate pyroclastic rocks and was interpreted as the possible representation of dyke
systems under a massive ore (Makkonen 1991). Due to its unique features, the
Viholanniemi deposit can be distinguished in many respects from sulphide Zn-Cu-Pb
deposits within the Pyhäsalmi volcanic arc (Ekdahl 1993), although it is a small one. It is
really worthy of further study due to varied and interesting metallogeny in the Main
Sulphide Ore Belt between the two main geotectonic units of the Finnish Precambrian.
This study represents the results of field and laboratory works carried out by the writer
in Finland and later in China during 1997 and 1998-1999 respectively, in the course of
executing the agreement of co-operation in a scientific exchange program between
Finland and China.
Location and physiography of the study area
The Viholanniemi Zn-Au deposit is located in Joroinen village and covers a total area of
about 70 km2. The area is a flat terrain consisting mainly of till with heavy forest
covering and boulders on the surface. There are many drumlins and lakes with northwest
orientation due to the influence of glaciation and these in turn result in a slightly variable
topography with general level of 85-100 m and the highest 130.9 m above the sea level
within the area. The outcrops, therefore, are not abundant, but it is easy to find them in
places such as drumlin tops and lake banks.
30
I
Fig. 1. Location of the study area on the geological map of Finland (simplified after the bedrock
map of Finland 1:1 000 000, Korsman et al. 1997).
Background to the research
According to the report of the Viholanniemi Zn deposit (studied in 1984-1988, Makkonen
1991), the Geological Survey of Finland (GTK) carried out exploration that led to the
discovery of the Viholanniemi Zn-Au deposit.
The first three ore bearing boulders were found on the west bank of Lake Kolkonjärvi
about 20 km southeast of the Viholanniemi deposit in 1971 with significant contents of
Zn (1.65-2.25%), Au (3.2 ppm), Cu (0.42-1.08%), Ag (133 ppm). In autumn 1984, four
31
I
more boulders of the same rock type (Zn: 4.15-24.16%, Au:0.21-1.50 ppm, Cu:0.030.51%, Ag:10-63 ppm, Pb:0.05-1.65%) were discovered at Pirttiselkä, about 7 km
northwest of the first boulders.
After this initial period of boulder tracing, a multimethod program including boulder
tracing, mapping, geophysical and geochemical exploration, pitting and deep drilling and
also research work had been executed by GTK from 1985 to 1988. Dr. E. Ekdahl and Dr.
H. Makkonen were responsible for the overall supervision of the program and fieldwork,
respectively.
It was in spring 1985 that a galena-sphalerite boulder (Zn: 1.66%, Au:0.93 ppm,
Cu:0.10%, Pb:1.66%, Ag:130 ppm) was found at Viholanniemi after discovering a
sphalerite and galena-bearing quartz-carbonate rock (Zn:1.04%, Au:7.30 ppm, Cu:0.06%,
Pb:0.43%, Ag:12 ppm) in an outcrop at the north-western end of Vuotsinsuo mire. Thus,
the boulder fan starting from the Viholanniemi deposit is about 20 km in length. The
result of bedrock mapping carried out in 1985-1986 confirmed that the bedrock in the
Viholanniemi area is mainly composed of volcanics, although they have been marked as
mica schists on the 1:100 000 bedrock geology map (Korsman 1973). The majority of the
volcanics is felsic-intermediate pyroclastics and associated with mafic volcanics
(Makkonen 1991). A geophysical survey (1985-1988) made it possible to distinguish
mica schists from volcanics (magnetic, EM, gravimetric). The ore can be distinguished in
some way by IP-surveying. Based on information of outcrops, boulders and geophysics,
totalling 886 geochemical samples of till and weathered bedrock were collected in an area
of about 6 km2. All elements detected (Zn, Au, Cu, Pb, Ag, Co, Ni) show clear and
coherent anomalies and reflect the deposit well.
In addition to the all information shown above, four pits were dug and 22 drill holes
totalling 3759.00 m were drilled in 1986-1987; the Viholanniemi Zn-Au deposit
composed of a southern part (600 m´100 m´1.1 m) and a northern part (100 m´100 m´2
m) was then discovered. The quartz-carbonate rock is the major host rock and other
mineral assemblages such as quartz, quartz-carbonate-tremolite, tremolite-carbonate,
quartz-tremolite-chlorite and quartz-sericite rocks are the minor host rocks. The amount
of ore was estimated to be about 250 000 tonnes.
Methods and objectives of the study
The objective of this study is to compare and describe the metallogenic environment and
the type of the Viholanniemi Zn-Au deposit. The study area is one part of the RaaheLadoga ore zone which is the most important ore zone in Finland running near the
Archaean margin in the south-eastern part. In some respects, the Viholanniemi deposit is
different from the stratabound Zn-Cu-Pb sulphide deposits within the belt, and the
Kuroko deposits as well, and demonstrates some unique features.
One specific aim of the present study is also try to make a contribution to establishing
the metallogenic diversity in this main ore belt in central Finland. A comparison between
the main sulphide deposits of RLZ in Finland and a selected belt in China will also be
made.
32
I
The methods involved in this study include mainly bedrock mapping, lithogeochmistry
and deposit geochemistry. All thin sections (47) examined were prepared at the GTK in
Kuopio and Espoo. Samples (98) were collected by the author from metavolcanics,
metasedimentary rocks, ore and host rocks in the study area for geochemical analyses. All
of those samples were also analyzed at the GTK in Kuopio and Espoo.
X-ray fluorescence spectrometry (XRF: SiO2, Al2O3, TiO2, Fe2O3, MgO, MnO, CaO,
Na2O, K2O,P2O5, Rb, Ba, Sr, Pb, Th, Zr, Ga, Sc, La, Ce, Nb, Y, V, Cr, Cu, Zn, S, see
Appendix 1) and inductively coupled plasma mass spectrometry (ICP-MS: REE, Nb,
Rb,Sc, Ta, Th, U, Y, Zr, see Appendix 2) as well as inductively coupled plasma atomic
emission spectrometry (ICP-AES), graphite-furnace atomic absorption spectrophotometry
(GAAS) and infrared spectroscopy (IR) (see Appendix 3) analyses were performed at the
GTK in Espoo and Kuopio. The sulphur isotope analyse was made at the Technical High
School in Espoo. Carbon and oxygen isotopes and fluid inclusions were analyzed at the
Chinese Academy of Geosciences and the Institute of Geology, at the Chinese Academy
of Sciences in Beijing, respectively. The electron microprobe analysis was performed at
the University of Oulu.
In addition, there is much material from the GTK and the Exploration Department of
Outokumpu Mining Company, which includes thin sections and unpublished data. All of
them are employed in the present study.
The regional geological setting
As all rocks in the study area are metamorphic the prefix meta has been dropped.
According to studies and descriptions of Finnish geologists (Simonen 1980, Korsman
et al. 1984, Vaasjoki & Sakko 1988, Kilpeläinen 1988, Korsman et al. 1988, Luukkonen
& Lukkarinen 1986, Ekdahl 1993, Lahtinen 1994, Makkonen 1996, Nurmi & SorjonenWard 1996, Weihed & Mäki 1997), the Precambrian in southern and central Finland is
mainly composed of Archaean basement and the Palaeoproterozoic Svecofennian
supergroup. The latter comprise ca. 1.9 Ga old orogenic terrains in southern and western
Finland including volcanic-sedimentary belts and migmatitic gneiss belts. The
Viholanniemi area belongs to this supergroup and lies within the south-eastern part of the
RLZ which has already been regarded as a representation of Palaeoproterozoic collisional
suture (Koistinen 1981, Korsman et al. 1988, also see Ekdahl 1993). The collision of
Proterozoic oceanic and Archaean continental plates is responsible for the generation of
new Svecofennian crust between 1930Ma and 1850 Ma ago (Vaasjoki & Sakko 1988) and
the Kolkonjärvi shear zone (Kosman et al. 1984, 1988) that passes through the eastern
part of the Viholanniemi district.
According to Ekdahl (1993) and Nurmi and Sorjonen-Ward (1996), continued
volcanism within Svecofennian oceanic island arc at 1920-1890 Ma resulted in the
formation of Kuroko-type deposits; the synorogenic basic and ultrabasic intrusions at
about 1890-1880 Ma led to syngenetic Ni-Cu deposits; and the late phase calc-alkaline
intrusions host porphyry type occurrences and epigenetic Au-As deposits.
33
I
There are several deposits surrounding the Viholanniemi area such as the Virtasalmi
stratabound Zn-Cu-Pb deposit (about 15 km west) (Ekdahl 1993), the Pirilä Au-bearing
quartz vein (about 18 km southeast, Makkonen & Ekdahl 1988), Osikonmäki Au deposit
occurring in a shear zone (about 24 km southeast, Kontoniemi & Ekdahl 1990), and some
smaller mineral occurrences.
Geology of the Viholanniemi area
Lithology
Mica schists and mica gneisses are the major rocks in the eastern-south-eastern parts of
Viholanniemi (Fig. 2). The primary sedimentary characteristics of turbidites include grading, graded bedding, and cross bedding. Some thin but discontinuous intercalations of
pyroclastics and carbonate occur within the turbiditic sequences, and graphite-bearing
pelitic intercalations can also be observed.
Fig. 2. Principal geological features of the study area (based on the mapping and the data from
Papunen 1990, Makkonen 1991).
Within the study area, the mineral composition of the pelitic component shows some
trends of decreasing in the amount of muscovite to east and south, although biotite is
present together with muscovite. To the south-eastern outside of Fig. 2, in the Pirilä district, sillimanite, garnet and K-feldspar are common. Pegmatites with coarse grain beryl
34
I
and quartz veins also can be met. According to Korsman et al. (1984, 1988), there are
progressive metamorphic zones towards the south: andalusite - muscovite, K-feldspar-sillimanite, cordierite-K-feldspar, garnet-cordierite-sillimanite-biotite and garnet-cordieritesillimanite (Fig. 3). As a result of this progressive metamorphism, mica gneisses or granites are present in south-eastern and south-western-southern parts of the area.
Fig. 3. Location of the study area on the tectonometamorphic map of southern Savo (Korsman
et al. 1988).
In addition, a narrow iron formation has been observed in Pirilä, which includes
silicate, oxide, and sulphide facies (Makkonen & Ekdahl 1988).
Volcanics are the predominant rocks in the study area and most of them are felsicintermediate and mafic. The felsic and also sometimes the intermediate volcanics together
show a pale weathering surface. In most circumstances, they are changed into another
gradually or appear in the form of intercalations instead of clear boundaries between
them.
35
I
Lapilli and agglomerate structures are common in the study area (Fig. 4, 5a). In many
places the primary structure is nevertheless destroyed by the strong S2 schistosity so that
the stretched ejectae can be as much as 50 cm long and the intermediate ejectae have also
been stretched to be longer than the felsic ejectae (Makkonen 1991).
a
b
Fig. 4. a) Intermediate volcanic rock with lapilli structure containing disseminated pyrite,
R305/46.10, single nicol. b) Felsic porphyrite volcanic rock with plagioclase phenocrysts, HVM86-M3.4, single nicol (Makkonen 1991).
b
a
Fig. 5. a) Felsic agglomerate with stretched ejectae from the Suurisaareke. b) Basaltic pillow
lava with recognizable fumaroles and deformed pillow from the Lahnalahti.
Quartz and biotite are generally the major minerals in felsic rocks but in intermediate
rocks plagioclase and amphibole are additional major minerals. The minor minerals are
sericite, chlorite, K-feldspar, epidote, actinolite, carbonate, and sometimes amphibole and
garnet. Accessory minerals include opaques, apatite, zircon, sphene. In felsic porphyritic
volcanics, phenocrysts are plagioclase (An10 and quartz, and quartz or plagioclase alone
(Fig. 4). The phenocrysts are usually >2 mm in size. The groundmass is mainly composed
of quartz and biotite or quartz alone. The minor minerals are plagioclase, K-feldspar,
chlorite, sericite, carbonate, epidote, amphibole with accessory minerals such as zircon,
apatite, rutile and sphene. In intermediate intercalations the porphyritic or porphyritic-like
textures are also present. The phenocrysts are plagioclase and quartz as well as amphibole
36
I
(biotite and garnet mainly as the porphyroblasts), and the groundmass contains
plagioclase, quartz, biotite, sericite, chlorite, and carbonate with accessories of apatite,
opaques and occasionally cordierite.
Mafic volcanics usually occur as intercalations but in the southern part of the area
relative thick mafic layers can be encountered. They seem to connect mainly with felsic
volcanics. Basaltic pillow lava has been observed in Lahnalahti (Fig. 5b). Occasionally,
the pillow structure can also be found in amphibolites, but the pillows are elongated and
sometimes become obscure due to the intense deformation. Hornblende, biotite,
plagioclase, as well as diopside and quartz are the main minerals. Chlorite, epidote,
carbonate, hypersthene are the minor composition and opaques, zircon, apatite and
sphene are the accessories. Most of these rocks are homogenous in texture but there are
some porphyritic-like and porphyroblastic types with phenocrysts of diopside and
porphyroblasts of hornblende and biotite as well. An amygdaloidal structure appears
occasionally and is filled by carbonate.
Agglomeratic, breccia and tuff textures as well as the relict structure of sedimentary
such as bedded structure are general in volcanic rocks. Thus the majority of volcanic
rocks of the area are volcaniclastic rocks.
Sericitization, epidotization, chloritization and disseminated pyrite are also very
common in the volcanics (Fig. 6). Particularly, the sericitization and disseminated pyrite
mainly occur in felsic-intermediate and epidotization and chloritization in intermediatemafic volcanics. Potassium feldspathization was observed in the western-south-western
parts of the area.
The majority of rocks in the study area therefore can be named as follows according to
the observations:
æ
ç
Sedimentary rocks í
ç
è
pelitic siltstone
turbidite
tuffaceous siltstone
intermediate-felsic crystal-lithic tuff
siliceous rock
æ
Volcaniclastic rocksí
è
stratified tuff (basic-intermediate-felsic)
breccia tuff (basic-intermediate-felsic)
agglomerate (intermediate-felsic)
Volcanic rocks
æ
í
è
basaltic lava
dacitic-(ryodacitic) lava (?)
Mica gneisses and migmatite together with quartz veins and pegmatitic veins were
found to be associated with the diopside-bearing amphibolites in the south-western part of
the area. Amphibolite is possibly metamorphosed from the volcanogenic rocks
(Makkonen 1996). The diopside-bearing amphibolites show features of granulite by their
homeoblast structure and minerals.
37
I
b
a
Fig. 6. a) Sericitized volcanic rock with disseminated pyrite, R301/33.75, crossed nicol. b)
Epidotised intermediate volcanic rock, HVM-86-M3.1, crossed nicol (Makkonen 1991).
Granite intrusions are present in the western part of Viholanniemi (Papunen 1990).
Granodiorites intruded on the mica schist and granite gneisses in the south-eastern and
south-western parts.
Diabase, possibly comagmatic, with mafic volcanies intruded on the intermediatefelsic volcanics in the southern part of the area.
Stratigraphical relationships
According to Luukkonen and Lukkarinen (1986), the rocks of the area belong to the
lower Bothnia subgroup which consists of mica schist and mica gneisses, mafic and acid
volcanics and their weathering products, and also arkosites, limestones and skarns.
Many stratigraphical interpretations for the surrounding areas of Viholanniemi
considered the mica schist and mica gneisses (with emphasising on pelitic lithologies) as
the lower-most rocks (see Luukkonen & Lukkarinen 1986, Makkonen & Ekdahl 1988,
Makkonen 1996). Hyvärinen (1969; see Makkonen 1996) delimited the stratigraphical
sequence in the Virtasalmi district as follows: mica gneisses with graphitic schist
intercalations in the bottom, overlain sucessively by diopside-and quartz-feldspar
gneisses including calc-silicate intervals, amphibolites, principally diopside amphibolites,
and finally by more mica gneisses (top). Makkonen (1988, 1996) proposed two similar
stratigraphical sequences which include mica schist (bottom), iron formation, felsic
volcanics, intermediate volcanics, mafic volcanics and komatiite (top) in Pirilä and mica
gneisses and mica schists (bottom), marbles and cherts and iron formations, felsic
volcanics (quartz-feldspar gnesses), mafic volcanics (diopside amphibolites) ultramafic
volcanics (top) in Juva.
The author proposes a tentative stratigraphical sequence in the Viholanniemi area
based on mapping and observations as well as above sequences as following:
38
I
mica schist and gneisses
æ basic tuff
ç basaltic lava
basic volcanics
í basic tuff (with weak sulphide mineralization)
è basic breccia tuff
felsic volcanics
æ
ç
ç
í
ç
è
siliceous rock (with minor tuffaceous siltstone) üZn-Au
ýoccurrence
felsic-intermediate breccia tuff +tuff
þ
felsic-intermediate agglomerate
felsic-intermediate breccia tuff
intermediate-felsic stratified tuff
mica schist
metaturbidite
æ
ç
í
è
intermediate-felsic crystal-lithic tuff
tuffaceous siltstone
turbidite
pelitic siltstone
It is worth mentioning here about the observations made by Makkonen (1991) and
Makkonen and the present author that include:
1. There are some thin pyroclastic intercalations in the mica schist area, which are
mainly intermediate-felsic. The tuffaceous material can be observed in fine clastic
rocks.
2. Volcanics in the area overlay directly the so-called mica schist and begin with main
intermediate stratified tuff. The aeromagnetic map of the area also shows a clear
anomalous magnetic belt but not very high in intensity corresponding to those
intermediate (including thin mafic intercalations) volcanic rocks that contact with the
mica schist (Fig. 7).
3. The majority of volcanics is mainly felsic and mafic with minor intermediate felsic.
The felsic volcanics are mainly pyroclastic rocks, and the mafic are mainly composed
of basaltic lava with pillow structure and pyroclastic rocks.
4. Mica gneisses (and migmatite) with diopside amphibolite intercalations were
observed to be contacted with the mafic volcanics in the southwestern part of the
study area.
5. Basaltic lava with pillow structure and mafic pyroclastic rocks suggest a relatively
shallow eruptive environment (Condie 1986).
39
I
Fig. 7. Aeromagnetic map of the study area (Geological Survey of Finland, compiled by J
Lerssi).
Isotopic age determinations in samples from the areas surrounding Viholanniemi have
provided some reasonable U-Pb ages which are very helpful to understand the
stratigraphical relationships of the area. The 207Pb/206Pb ages of the zircons from the
metasediments in the mica schist area of the Vuotsinsuo range from 2200 to 2300 Ma and
one felsic metavolcanic rock from Viholanniemi has a zircon age of 1906±4 Ma (Vaasjoki
& Sakko 1988). To the south-eastern part, Tuusmäki tonalite which intrudes the mafic
volcanics (Makkonen & Ekdahl 1988) has the U-Pb zircon age of 1888±15 Ma (Korsman
et al. 1984).
The volcanic cycle, rock assemblage and paleovolcanic center
The above mentioned geological features of the study area suggest that the volcanic cycle
of the area began with minor intermediate and major felsic eruptions and terminated with
mafic eruptions. The volcanic cycle can be described as:
mafic
intermediate
felsic
ö
ý
ø
alternating
felsic
felsic
intermediate
ö
ý
ø
alternating
40
I
The volcanic rocks in the area can be sorted into two facies of explosion and overflow in
which the explosion facies includes mainly volcanic agglomerate, breccia tuff and tuff
and the overflow facies are composed of basaltic lava. According to outcrop and thin
section investigations, the volcanic rock assemblage is of basalt, andesite, dacite and
(rhyolite).
From the occurrences of volcanic agglomerate and pillow lava in the area, it can be
said that there is a paleovolcanic center in the Viholanniemi area. Obviously, the site of
the center is not easy to recognize now due to the complex and strong tectonism.
Metamorphism, deformation and structural features
According to Korsman et al. (1984) and Korsman et al. (1988), the Viholanniemi area is
an area in which the metamorphism is characteristic by the transition of metamorphosed
blocks in the north to progressive metamorphosed belts in the southern (Fig. 3). The
metamorphism in the northern part of the area is characterized by intensely
metamorphosed and migmatized areas often separated from the environment by faults.
Accompanied with the granulite facies metamorphism in the so-called complex areas, the
progressive stage of metamorphism was associated with the D1 and D2 deformations (see
Korsman et al. 1988). From the Viholanniemi area to the Sulkava area, well-developed
zones caused by progressive metamorphism have been established by Korsman et al.
(1984); the metamorphic grade is increasing towards the Sulkava thermal dome. The
evolution of the zonal metamorphism took place mainly during the D2 deformation (1880
Ma ago) and was affected and culminated during D3 deformation at 1830-1810 Ma ago.
The D3 deformation is cut by the ca.1800 Ma post-tectonic granites (Vaasjoki & Sakko
1988) and the later in turn were partly folded by the D4 deformation (Kilpeläinen 1988).
The D3 deformation has manifested itself as asymmetric folds of varying size and
shear zones that locally disrupt metamorphic zoning. The primary axial planes of the
folds trend northwest-southeast and the axis plunges southeast at 45o. F1 folds occurring
only in the andalusite-muscovite zone are tight and usually of 10-20 m in amplitude with
a few degrees of S1 schistosity on their limbs. F2 folds are also tight and their wave length
is a few hundred metres and S2 schistosity is penetrative throughout the K-feldsparsillimanite zone (Kilpeläinen 1988, Makkonen 1996).
Lithogeochemistry
Whole rock geochemistry
The chemical compositions of volcanic rocks in the Viholanniemi area are listed in Table
1. The data of intermediate and acid rocks are mean values, c.f. details in Appendix 1.
Acid rocks are those of SiO2 > 63%. The values of Na2O, K2O as well as Na2O+K2O
are the highest in three groups. Average An values calculated from CIPW norms are 3-34.
Intermediate rocks have SiO2 of 52-63% and the highest average values of Al2O3, P2O5
and TiO2 in the groups. Na2O+K2O=3.69-5.39 and average An values are 19-32.
41
I
Basic rocks are those of SiO2 < 52%. Considering the effects of alteration, sample
hvm-86-24.5a, xz-97-4.2 as well as xz-97-4.1 should be excluded here. The contents of
Fe2O3*, CaO and TiO2 are very high, while K2O is very low; Na2O+K2O=2.15-5.02. All
samples contain normative di, mt, il, ap and some samples have normative ne, hy and ol.
Q valnus are almost zero, except one is 9.1, and the average An values vary from 36 to
100. These suggest that the basic rocks of the area show some distinctions such as Ca, Fe,
Ti-rich and alkalic trend.
The variation diagrams (Fig. 8) show that, Fe2O3*, MgO, CaO and MnO decrease
coherently with the increasing of SiO2. Na2O and K2O display scattered characters
instead of clear positive correlation relationships with SiO2. The inflections however, can
be observed in Al2O3, TiO2 and P2O5 variations correlated with SiO2. TiO2 is similar to
the case of tholeiitic basalts by increasing and reaching maxima between 50% and 57%
SiO2 (Gill 1981). They may also imply here that volcanics of the area are not fractionates
from the same parent magma otherwise a clear negative correlation relationships with
SiO2 should be present (see Liu et al. 1984). Variations of Na2O and K2O might partly be
affected by the weak alterations such as sericitization, chloritization as well as potassium
feld spathization presented in the volcanics, on the other hand, they may also confirm
what has been indicated by TiO2 and P2O5 as a lack of clear positive correlation
relationships with SiO2 (also see Liu et al. 1984).
The trace elements Rb, Ba, Zr, Nb and Y have their highest values in acid rocks, while
elements Sr, V, Cr and Ni are mainly concentrated in basic rocks. K-group elements (K,
Rb, Ba, Sr, Gill 1981) in the basic rocks correlate positively with each other except for Sr
which in contrast has a negative correlation with others. The basic rocks also have low
Rb/Sr and high Ba/Rb ratios respectively.
Concentrations of REE of volcanic rocks and their chondrite normalized distribution
patterns (Table 2, Fig. 9) show varied total REE contents (61.5-201.6 ppm) and åCe/åY
ratios (3.72-16.19) with a small negative Eu anomaly. Acid rocks have relatively high
åREE and åCe/åY with an apparent Eu negative anomaly showing slightly strong
fractionated patterns. In these respects, they represent those rocks of modern arc volcanics
(Jakes & Gill 1970, Jakes & White 1971, Garcia 1978, Cullers & Graf 1984, Condie
1986). In contrast, mafic rocks have flat and weak fractionated patterns.
42
I
Table 1. Representative analyses and average chemical compositions of the volcanic rocks
of the Viholanniemi area.
1
2
3
hvm-86- hvm-86- hvm-8624.2
24.3
24.4
wt%
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2 O
P2 O5
total
ppm
Rb
Ba
Sr
Pb
Zr
La
Ce
Nb
Y
V
Cr
Ni
Cu
Zn
S
Na2O+K2O
Na2O/K2O
K/Rb
Rb/Sr
Ba/Rb
Q
or
ab
an
ne
di
hy
ol
mt
il
hm
ap
47.3
1.5
16.3
9.6
0.399
7.75
11.1
2.74
0.813
0.23
97.76
54.7
1.82
16.1
11.4
0.29
4.81
6.77
3.08
0.508
0.244
99.75
22
66
325
37
146
18
44
16
19
251
74
38
45
545
50
3.55
3.37
306.77
0.068
3.00
0
4.97
22.68
30.74
0.67
20.03
0
15.3
2.15
2.94
0
0.56
8
105
306
78
166
24
49
17
24
365
22
23
35
473
30
3.59
6.06
527.13
0.026
13.13
9.13
3.04
26.39
28.99
0
2.94
22.96
0
2.51
3.5
0
0.59
49.8
1.65
12.9
12.9
0.223
6.47
10.5
3
0.292
0.29
98.06
4
hvm-8624.5a
43.4
1.02
9.46
16
1.04
5.71
18.1
0.16
0.019
0.253
95.38
7
1
150
34
305
446
<30
<30
241
145
32
23
74
45
21
14
28
20
300
204
22
17
53
34
18
2024
194
290
40
590
3.29
0.18
10.27
8.42
346.28
157.72
0.023
0.002
21.43
34.00
0
0
1.78
0.12
26.19
1.44
21.55
26.7
0
0
25.05
56.52
17.86
8.8
0.79
0
2.89
3.71
3.23
2.06
0
0
0.71
0.64
5
6
7
8
9
xz-97- xz-97- xz-97- xz-97- xz-974.1
4.2
8.1
20.1
22.1
46.4
1.74
14.1
7.86
0.137
3.74
13.2
5.1
0.125
0.184
92.62
37.7
1.18
9.16
12.3
0.194
9.47
17.5
1.69
0.085
0.244
89.66
3
2
98
21
319
179
<30
<30
113
100
6
10
37
48
17
9
20
23
264
267
85
1216
99
569
86
67
50
115
310
370
5.23
1.78
40.80
19.88
345.89 352.81
0.009
0.011
32.67
10.50
0
0
0.81
0
23.47
0
16.56
19.4
12.72
8.75
37
39.06
0
0
0
17.12
1.86
3.02
3.59
2.53
0
0
0.47
0.65
45.1
1.38
14.9
12.3
0.162
7.73
12.8
2.08
0.071
0.173
96.78
10
11
57.75
1.52
15.50
9.45
0.19
4.46
5.33
4.02
0.73
0.40
70.18
0.63
13.65
4.30
0.12
1.82
2.72
4.34
1.24
0.15
49.3
1.74
14.9
12.8
0.168
4.71
9.34
4.29
0.726
0.342
98.37
48.3
1.19
13.9
12
0.225
5.8
12.3
3.32
0.396
0.117
97.59
10
189
423
<30
172
11
68
20
26
345
64
33
222
115
180
5.02
5.91
602.67
0.024
18.90
0
4.42
33.92
19.82
1.85
21.43
0
11.52
2.86
3.4
0
0.83
8
5
21.90
161
26 116
154
689 191
<30
<30 <30
74
80 278
10
13
29.10
33
46
76.60
5
15
24.70
23
18
29.50
363
305 226
88
557
27.60
82
321
38.20
77
180 114
130
97
93.40
90
1370 105
3.72
2.15 4.75
8.38 29.30 8.34
410.91 117.88 279.25
0.052
0.007 0.125
20.13
5.20 5.44
0
0
2.43
0.44
24.78 18.4
22.65 32.55
2.34
0
32.95 26.94
0
0.97
9.55 14.67
2.7
2.8
2.34
2.74
0
0
0.29
0.43
37.35
246
116
<30
370
41.77
99.08
30.65
34.81
56.46
15.92
7.62
61.19
68.96
856
5.58
6.18
308.95
0.408
7.77
Total iron as Fe2O3. 1-9 are mafic rocks, 10=mean value of intermediate rocks (10 samples), 11=mean value of acid
rocks (26 samples), Sampling sites see App. 4.
43
I
Fig. 8. Harker diagrams showing compositional ranges of selected major elements in volcanic
rocks from the study area.
44
I
Table 2. Representative analyses of trace elements (ppm) of volcanic rocks of the
Viholanniemi area.
1
hvm-8511.1
2
r312/
183.15
3
r321/
132.0
4
r359/
234.0
5
hvm-8511.2
La
30.9
41
40.3
21.3
16.7
Ce
63.5
83.1
77.5
41.8
35.7
Pr
Nd
7.16
25.7
9.47
35.7
8.56
30
4.8
17.4
4.37
16.9
6
xz-975.3
63.5
134
16.4
61.5
29
59.9
7.13
27.3
8
xz-974.1
8.07
20.4
2.89
12.9
9
10
xz-97xz-97-8.1
4.2
10.1
17
24.2
40.4
3.51
15.7
5.52
22.2
Sm
4.94
6.88
4.93
3.13
3.98
5.5
3.21
3.98
5.02
Eu
1.21
1.77
1.37
0.59
1.32
2.76
1.69
1.01
1.19
1.59
Gd
4.64
6.93
4.01
2.72
4.27
7.79
5.17
3.65
4.59
4.79
Tb
0.71
1.09
0.54
0.38
0.65
0.98
0.82
0.57
0.66
0.73
Dy
3.86
6.26
2.42
2
3.87
3.89
4.41
3.56
3.9
4.55
Ho
0.75
1.24
0.43
0.38
0.78
0.68
0.88
0.71
0.78
0.86
Er
2.34
3.64
1.23
1.03
2.25
1.74
2.56
2.04
2.14
2.38
Tm
0.35
0.55
0.18
0.17
0.33
0.22
0.38
0.3
0.28
0.35
Yb
2.44
3.44
1.09
1.04
2.03
1.47
2.41
1.9
1.86
2.26
Lu
0.38
0.53
0.15
0.16
10.7
7
r312/
142.3
0.31
0.22
93.46
305.85
147.5
89.02
78.97
288.86
130.52
48.48
58.68
91.73
7.88
14.49
16.99
16.98
13.02
14.45
16.22
16.19
11.30
5.45
17.00
7.69
3.72
4.06
5.66
0.92
0.61
0.98
0.89
0.96
0.90
0.85
0.98
11.92
36.97
20.48
8.23
43.20
12.03
4.25
5.43
39.6
14.1
11.9
20.9
27.3
SREE
148.88
201.6
172.71
96.9
SCe
133.41
177.92
162.66
SY
15.47
23.68
10.05
SCe/SY
8.62
7.51
dEu
0.76
0.78
La/Yb
12.66
Y
23.4
23
0.35
0.29
61.5
21.1
0.24
0.3
73.13
107.95
22.1
7.52
24.3
Th
6.51
5.29
5.4
6.13
1.93
6.17
2.52
0.76
1.01
1.4
U
2.14
2.14
2.52
1.84
0.74
3.63
0.89
0.3
0.37
0.59
Zr
Nb
Ta
261
20.8
1.58
353
25.2
1.65
198
18.1
1.12
51.4
115
4.75
0.4
73.9
161
13.3
0.89
Rb
44.1
21.3
Sc
8.6
11.8
8.57
5.42
La/Th
4.75
7.75
7.46
3.47
8.65
La/Nb
1.49
1.63
2.23
4.48
1.26
173
14
0.65
194
16.7
1.04
76.6
78.2
120
13.9
6.97
0.9
0.44
15.5
0.96
2.13
0.49
9.2
30.3
86.9
30.7
25.7
15
21.7
30.2
25.4
32.5
10.29
11.51
10.62
10.00
12.14
4.54
1.74
0.58
1.45
1.10
1-4: felsic, 5-7: intermediate, 8-10: mafic. Sampling sites see App. 4.
45
I
Fig. 9. Chondrite-normalized rare-earth element patterns of selected volcanic rocks from the
study area. a) felsic rocks; b) intermediate rocks; c) mafic rocks.
Classification of volcanic rocks
Considering the cases of low grade metamorphism and non visible strong alteration in the
salmpes studied, it should be feasible to classify volcanic rocks by means of geochemical
schemes. This in turn will show some relationships between elements which have
resulted from the varied geochemical processes.
46
I
Fig. 10. Geochemical characteristics of Viholanniemi volcanics on (a) TAS diagram (Le Maitre
et al. 1989) showing subalkaline (tholeiitic) series and (b) the Jensen cation plot (Jensen 1976).
Volcanic rocks of the area are mainly of the subalkaline (or tholeiitic) series in the TAS
diagram (Fig. 10a). According to Rollinson (1993), the Jensen plot has a distinct
advantage over other classification schemes for volcanic rocks especially for those that
experienced metamorphism. Thus the volcanic rocks of the area are mainly basalt,
andesite and dacite of calc-alkaline series and high-Fe tholeiite basalt (Fig. 10b).
On the AFM diagram, the volcanic rocks display a calc-alkaline trend in most of the
felsic and intermediate volcanic rocks, while mafic volcanic rocks show a tholeiitic
affinity (Fig. 11a). On the K2O vs. SiO2 diagram, the rocks fall in the low-K and mediumK areas (Fig. 11b). The number of the rocks falling in the low-K area are more than that
of medium-K area particularly those that are mafic and intermediate, and thus, they can
be considered to mainly belong to the low-K tholeiite magma series.
47
I
Fig. 11. Geochemical characteristics of Viholanniemi volcanics on (a) AFM diagram after
Irvine & Baragar (1971) and (b) K2O vs silica diagram after Le Maitre et al. (1989). Symbols
as in Fig. 10.
Tectonomagmatic affinities of volcanic rocks
Before considering the use of the chemical composition of volcanic rocks for their
tectonomagmatic affinity discrimination, it is necessary to evaluate the rock alteration
first, even though the low grade metamorphism in the area has been established. On the
MgO/10-CaO/Al2O3-SiO2/100 diagram, which has been suggested by Davies et al.
(1978), most of mafic and intermediate rock samples studied fall within the field of
unaltered magmatic rocks (Fig. 12). Three mafic rock samples (xz-97-4.1, xz-97-4.2 and
hvm-86-24.5a) and also a few intermediate samples show an alteration trend (also see
Table 1).
48
I
Fig. 12. Field for unaltered magmatic rocks (Davis et al. 1978). Symbols as in Fig. 10.
Compared with the volcanic rocks from the arc system, the mafic and intermediate
rocks of the study area (Table 2) have a unique La/Yb ratio (Jakes & Gill 1970), and they
also show affinities to those of the back arc or MORB by La/Th and La/Nb ratios (Gill
1981, Table 5.4). The mafic samples of the area may be considered further by their
slightly LREE enriched patterns and La/Nb ratio as the E-MORB (Saunders 1984, Gill
1981).
Considering the MORB-normalized multi-element diagram, some elements such as Sr,
K, Rb and Ba might have been enriched during metamorphism (Saunders & Tarney
1984); the rest of the elements however belong to those unaffected or immobile (Saunders
& Tarney 1984, Brewer & Atkin 1989) which are mainly controlled by the chemistry of
the source and the crystal/melt processes (Rollinson 1993). The mafic rocks excluding xz97-4.1,xz-97-4.2 and hvm-86-24.5a showing alteration trend on figure 12 exhibit some
notable features resembling those basalts of within plate (Pearce 1983, Condie 1986) by
their patterns and lack of Nb depletion which is proper for volcanic arc basalts (Pearce
1982) (Fig. 13). In Virtasalmi (about 15 km west), Lawrie (1992) observed basalts with
similar MORB-normalized multi-element patterns.
49
I
Fig. 13. MORB-normalized trace element patterns for the different metavolcanic rock types: a)
felsic rocks; b) intermediate rocks; c) mafic rocks.
The discriminating diagrams are presented with trace elements such as Cr, Ni, Ti, Y,
Zr, Ta, Nb which were considered to be immobile during secondary processes (Condie
1982, Saunders & Tarney 1984, Brewer & Atkin 1989). On the Cr-Ti diagram (Fig. 14a),
50
I
Fig. 14. Composition of mafic rocks on tectonomagmatic discrimination diagrams. a) Ocean
floor basalts (OFB) and low potassium tholeiites after Pearce (1975). b) Ocean floor basalts
(OFB) and island arc tholeiites after Beccaluva et al. (1979). c) Arc volcanics (ARC) and ocean
floor basalts (OFB) after Shervais (1982). d) Mid ocean ridge basalts (MORB),within plate
basalts (WPB) and arc lavas (AL) after Pearce (1982). e) Fields for island arc tholeiites (A),
ocean floor basalts (B), calc-alkali basalts (B,C) and within plate basalts (D) after Pearce &
Cann (1973). f) Fields for within plate basalts (AI), within plate alkaline basalts and within plate
tholeiites (A), E-MORB (B), within plate tholeiites and volcanic arc basalts (C) and N-MORB
and volcanic arc basalts (D) after Meschede (1986). g) Fields for MORB and volcanic arc
basalts (dashed line) and within plate basalts after Pearce (1982), Thol=tholeiitic basalts,
Trans=transitional basalts, Alk=alkaline basalts. h) Fields for within plate basalts (A), island
arc basalts (B) and mid-ocean ridge basalts (MORB) after Pearce & Norry (1979).
51
I
the mafic samples are divided into ocean-floor basalts and low potassium tholeiites. The
latter group includes mainly the mafic pyroclastics indicating that some differences may
be present between them and those of basaltic lava. The same situation is also obtained
on Ni-Ti/Cr diagram (Fig. 14b), but almost all samples are ocean-floor basalts and not
island arc tholeiites. The Ti-V diagram (Fig. 14c) shows that all mafic samples are within
the field of Ti/V ratios of 20-50 and are those of MORB and back arc basin basalts.
Further indication is shown on plots of Zr-Ti (Fig. 14d), Ti-Zr-Y (Fig. 14e), Zr-Nb-Y
(Fig. 14f), Nb/Y-Ti/Y (Fig. 14g) and Zr-Zr/Y (Fig. 14h), they not only display the main
affinities to within-plate basalts with the samples studied, but the Nb/Y-Ti/Y also
subdivides most samples into the transitional basalts area. The latter three diagrams
clearly show that the basalt and basaltic rocks of the study area differ from those of the
volcanic arc and MORB.
Obviously, the varieties of chemical composition are present among the volcanic rocks
and particularly those of mafic rocks. These features imply the compositional character of
magma on the one hand, and the character of tectonic setting on the other. In conclusions
the affinities to within plate suggested by the majority of the samples of mafic volcanic
rocks in the study area seem to be clear and these show further a possible enriched mantle
source.
Viholanniemi Zn-Au deposit
Wall rocks and host rock
The wall rocks are mainly siliceous rock and tuffaceous siltstone that were
metamorphosed to quartz (-feldspar) schist with a recognizable blastobedding structure,
and felsic-intermediate volcanics as well with some lapilli, agglomerate and also
blastobedding structures. The strong sericitization and abundant disseminated pyrite are
characteristic in the rocks particularly in the felsic ones. Less abundant carbonate and
local epidotization is also present, and casually disseminated magnetite occurs in
intermediate rocks. The wall rocks are sometimes crushed by shearing.
Makkonen (1991) has named the majority of host rock as quartz-carbonate rock. The
most common mineral assemblage is quartz-carbonate-tremolite and the others include:
quartz, quartz-carbonate-tremolite-chlorite-biotite, tremolite-carbonate, quartz-tremolitechlorite, quartz-sericite, quartz-biotite-chlorite and chlorite. Other accessory minerals are
opaques, epidote, garnet, titanite and tourmaline. Sometimes graphite is abundant. In the
host rocks, carbonate and amphibole are mostly of about 1 mm in grain size and quartz is
more fine-grained, coarse-grained types are about 5 mm in grain size. The orientation and
plastic deformation of quartz can be observed frequently in host rocks. In most
circumstances the host rocks occur as conformable dykes and sometimes as stockwork
veinlet. They vary in thickness from under 1 cm to 5 m.
The microanalyses of carbonate carried out (Makkonen 1991) indicate that the
carbonate is a manganese-bearing calcite. The composition of the center of some
carbonate grains is probably different because it is fractured while other parts of the grain
are whole and gold is often present in this part of the grain.
52
I
Ore occurrence and metal contents
Ore occurs in the host rocks as mainly disseminated and veinlet. The ore bodies strike
along the directions from NW to NNW and dip into SW. According to Makkonen (1991),
the form of ore bodies is defined by F3 folds and partly in the depth the dip is nearly
horizontal. In the southern part, the ore body extents up to over 300 m in the depth and its
average thickness in the first 100 m is c. 1.1 m (Fig. 15, 16). The length was assumed to
be 600 m. In the northern part, the dimensions of the ore body were assumed to be
100´100´2 m (Fig. 17).
Fig. 15. Cross-section of the southern ore body on profile R301-303, 320. The ore (quartzcarbonate rock) is marked with black. Other rocks consist of felsic to mafic volcanics
(Makkonen 1991).
The most important elements in the ore are Zn and Au, and then Pb, Cu, Ag and S. The
average contents of Zn and Au are 2.31% and 0.7 ppm in the southern part, and 1.97%
and 1.11 ppm in the northern part. Zn and Au have their highest concentrations in a one
meter drill core of 12.26% and 10.48 ppm in the southern part and 11.61% and 7.84 ppm
in the northern part, respectively. Cu, Pb and Ag are nevertheless low in the ore
occurrence but Pb has its highest content of 11.17% and the highest Ag is in the northern
ore body. However, with regard to the economic benefits, the very important factor is that
the sulphur concentration in both the southern and northern ore bodies is low, and thus the
metal contents are high in the sulphide fraction (Table 3). Estimated ore amounts of
190 080 and 57 600 tonnes in the southern and northern parts, respectively, were obtained
(Makkonen 1991).
53
I
Fig. 16. Cross-section of the southern ore body on profile R304-305, R321. Rock types as in
figure 15 (Makkonen 1991).
54
I
Fig. 17. Cross-section of the northern ore body on profile R310-312. Rock types as in figure 15
(Makkonen 1991).
Table 3. The thickness of ore intersections and their main composition.
borehole
301
302
303
304
305
306
307
308
321
mean in southern part
311
311
312
316
mean in northern part
thickness(m)
1.95
3.00
1.85
0.85
1.00
0.70
0.90
0.40
1.00
1.29
7.35
1.20
0.90
1.55
2.75
Zn %
3.31
0.23
3.50
1.17
3.09
6.49
3.05
0.04
1.88
2.31
1.34
1.97
8.28
1.27
1.97
Cu %
0.36
0.04
0.23
0.05
0.05
0.07
0.19
0.71
0.01
0.19
0.09
0.26
0.27
0.06
0.12
Pb %
0.03
0.00
0.02
0.62
0.4
0.12
0.01
0.00
0.00
0.10
0.95
0.02
0.05
0.00
0.64
Ag ppm
22
3
15
16
16
64
140
14
2
26
140
41
86
2
105
Au ppm
0.2
1.8
0.1
<0.1
<0.1
1.2
<0.1
1.7
<0.1
0.7
1.29
1.55
0.60
0.19
1.11
S%
3.98
2.47
4.03
3.09
3.34
3.88
2.29
2.09
n.d.
3.21
0.37
2.15
n.d.
n.d.
0.62
Ore mineralogy
Sphalerite is the most important and most common ore mineral. It occurs as a
disseminated form and dykes that brecciate the silicate and carbonate material. In most
circumstances, the grain size of sphalerite in the dykes is coarse and the grain boundaries
are not observable. Haematite often replaces sphalerite from the rims of the grains.
Galena appears as small xenomorphic inclusions in sphalerite and dykes but is more
rare than sphalerite. Chalcopyrite occurs either as single grains (<0.1 mm) in
xenomorphic form, or most often as inclusions in sphalerite. Cubanite is associated with
some chalcopyrite grains and haematite is also presented as the replacement of
chalcopyrite. Pyrite occurs most often as idiomorphic grains (<2 mm) in sphalerite dykes
55
I
and disseminated in the host rocks. It is sometimes slightly altered to marcasite or
hydrated pyrrhotite. Pyrrhotite grains are also xenomorphic and appear as inclusions in
sphalerite. Ilmenite is present as acicular grains (£1 mm long) and usually as mixed
grains consisting of ilmenite and rutile. Gold is present as small (<10µ) grains of electrum
within silicates and carbonate. Silver can be observed as metallic silver and dyscrasite
inclusions in galena (Ag3Sb) and possibly other compounds (Fig. 18).
Besides the previously mentioned ore minerals, magnetite, mackinawite, covellite,
arsenopyrite and tetrahedrite can also casually be found.
a
b
c
d
Fig. 18. Ore minerals and their occurrences. a) Sphalerite (brown in quartz-carbonateamphibole rock, R302/79.70, single nicol. b) Chalcopyrite-bearing sphalerite, R312/83.10,
single nicol. c) Gold-electrum grains in carbonate, R301/37.25, single nicol. d) Metallic silver in
strongly altered volcanic rock, R311/96.75, single nicol. (Makkonen 1991).
Isotope studies
Sulphur
Sulphur isotope measurements have been made on different disseminated sulphide
minerals from the Viholanniemi Zn-Au deposit. The results are shown in Table 4 and Fig.
19. The sulphides of the deposit have d34S values in a relative wide range from 1.7 to
10.4 per mil, with a median value around 5 per mil (average value 5.13 per mil).
56
I
Table 4. Sulphur Isotope Composition of Sulphides from Ore Occurrences in the
Viholanniemi Area.
d34S
Sample
Location
Rock* Minerals*
ga
sp
R311/99.6
Viholanniemi inter
ga+sp+py** 8.7
8.2
8.5
strongly altered (ep+ca),
filling ores
R311/101.8
Viholanniemi c-a
ga+sp
7.0
8.4
filling ores
R312/82.8
Viholanniemi q-a-chl py
10.2
disseminated py ( sp )
R312/83.5
Viholanniemi q-a-chl py
6.5
disseminated py ( sp )
R319/95.1
Viholanniemi felsic
py
-0.5
strongly altered ( ser ), disspminated py
R319/96.35
Viholanniemi felsic
py
-1.7
strongly altered ( ser ), disseminated py
disseminated py ( ch )
py
po
Notes*
ch
R319/188.1
Viholanniemi inter
py
6.0
R319/196.5
Viholanniemi mafic
py+ch
4.6
disseminated py ( ch )
R319/203.0
Viholanniemi felsic
py
4.7
disseminated py
R306/229.95
Viholanniemi q-c
sp
R301/33.75
Viholanniemi q-c-a
ga+sp
R303/71.80
Viholanniemi q-c
sp**
R304/101.00
Viholanniemi q-c
py+ch
ZX-97-6.1
Joroisenniemi
po
ZX-97-6.2
Joroisenniemi
po+py
disseminated sp ( ga )
7.4
disseminated sp ( py+ch )
0.2
disseminated sp ( ga+ch )
disseminated ga+sp
sp
HVM-86-24.5b Viholanniemi mafic
10.4
-0.5
2.2
disseminated py ( ch )
-4.6
-6.3
disseminated
disseminated
Rock and Mineral abbreviations: inter=intermediate, C=carbonate, a=amphibol, chl=chlorite, q=quartz,
ga=galena, sp=sphalerite, py=pyrite, ch=chalcopyrite, ep=epidotization, ca=carbonatization, ser=sericitization. **
Mixed sample. Analytic precision: ±0.2‰ -: the amount of mineral is not enough.
Fig. 19. The d34S values for sulphides in Viholanniemi Zn-Au deposit. Comparison data from
Rollinson (1993).
57
I
Similar ranges of d34S are presented in pyrite and sphalerite, between 1.7 and 10.2 per
mil and 0.2 and 10.4 per mil, respectively. These d34S values of sulphides are similar to
those of the massive sulphide deposits of the Kuroko type (Rye & Ohmoto 1974, Ohmoto
& Rye 1979, Hoefs 1980, Rollinson 1993) and of the later Archaen (Ohmoto 1986, Taylor
1987). The relatively wide range of d34S and mainly positive values of sulphides is
nevertheless distinguished.
The disseminated pyrite from strongly sericitized felsic volcanies have d34S values of
1.7 to 0.5 per mil differing from that of sulphides in quartz-carbonate rock or volcanies
with a strong carbonatization and epidotization. The later group of sulphides including
pyrite, sphalerite and galena have d34S values of 0.2 to 10.4 per mil. It shows that the
sulphur of pyrite in volcanies with only sericitization is more reduced sulphur coming
from the rock itself, and sulphur of sulphides in quartz-carbonate rocks may come from
mainly a magmatic source mixed with sea water. Two samples of pyrite and pyrrhotite
from meta-sedimentary rocks in the south-eastern part of the area have d34S values of 6.3
and 4.6 per mil showing quite clear sulphur source of rocks themselves.
A narrow variation of d34S in sulphides from the northern part of the deposit are
distinguished from that of the southern part of the deposit. With calculations using
sphalerite-galena pair (Hulston 1980, see Wei et al. 1988), the crystallization temperature
is 473°C.
Carbon and Oxygen
Eight calcite samples from the deposit were analysed for carbon and oxygen isotopes
(Table 5 and Fig. 20). Carbon isotope compositions vary in a quite narrow range: the
d13C range between -3.6 and -8.1 per mil, but oxygen isotope vary in a wide range: the
d18O range between 7.6 and 20.0 per mil. Most of the calcite analysed has d18O values of
7-11 per mil and d13C values of -3 -5 per mil.
Table 5. Carbon and oxygen isotope composition of calcite from the Viholanniemi Zn-Au
occurrence.
Sample
Rock*
R312/82.95-83.35
q-a-chl
-8.1
R315/84.25-84.75
q-c
-4.0
R316/81.55-82.05
q-c
-6.1
-12.8
17.7
disseminated py
R301/37.00-37.50
q-c-a
-5.0
-10.8
20.0
disseminated sp+py+ch
R303/70.90-71.40
q-c
-4.2
-22.0
8.2
disseminated sp+py+ch
R304/100.80-101.30
q-c
-4.7
-20.0
10.2
disseminated sp+py+ga+ch
d13CPDB
(‰)
d18OPDB
(‰)
d18OSMOW
(‰)
Notes*
-22.5
7.6
disseminated sp+py
-21.8
8.4
disseminated py
R302/79.70
q-c-a
-4.0
-20.5
9.8
disseminated sp+py
R306/229.85
q-c
-3.6
-19.7
10.5
disseminated sp+ga
* Rock and mineral abbreviation see table 4. Analytic precision:±0.2‰
58
I
Fig. 20. Carbon and oxygen isotope composition of carbonate from the Viholanniemi Zn-Au
deposit.
Comparing the northern part to the southern part of the deposit, the d13C values vary
from -4.2 to -8.1 per mil in the northern part, and in contrast, the d13C values are quite
homogeneous in the southern part varying from -3.6 to -5.0 per mil. In combining the data
of d13C with d18O, the majority of samples fall in the field of carbonatites in Rollinsons
(1993) d18O-d13C plot (Fig. 21). Two samples fall within the hydrothermal calcite area,
showing mixing between mantle-derived carbon and seawater and within the Mississippi
Valley-type hydrothermal area respectively, as well as one within the ordinary chondrite
field. These characteristicss indicate a main deep-seated origin of the carbon and also the
possible mixing with carbonate-derived and organically derived CO2 (Ohomoto & Rye
1979, Hoefs 1980, Taylor 1987).
The d18O range between 7.6 and 20.0 per mil in calcite may reflect the effect of
metamorphic fluids with a wide range of d18O due to different rock types and
metamorphic grade (Hoefs 1980, Wei et al. 1988).
59
I
Fig. 21. d18O vs d13C plot showing the composition of carbonates from a variety of
environments after Rollinson (1993). d18O is plotted relative to both the SMOW and PDB scales
and the isotopic composition of a number of different carbon is plotted along the right-hand
side of the diagram.
Fluid inclusions
Fluid inclusion measurements were carried out on quartz from the quartz-carbonate rock
of the deposit and the results are listed in Table 6. The results show that the small
inclusions presented in quartz include liquid inclusion, pure CO2 inclusion, CO2-H2O
60
I
inclusion and gas-liquid inclusion. Inclusions distributed randomly, especially those
isolated are the oldest (Crawford & Hollister 1986) and most possibly original, while
those appearing as clusters or oriented along recognizable planes of healed fractures are
clearly later, possibly pseudosecondary or secondary (Fig. 22). Homogenization
temperatures (Tn) were found to have three ranges of 170ºC-175ºC, 318ºC -335ºC and
268ºC -272ºC (not corrected for pressure). The original inclusions have the highest
homogenization temperature range in measured samples and they concentrate mainly
arround 320ºC. Middle salinities were also obtained in original inclusions by 8.4-9.2 wt%
NaCl. Possibly secondary inclusions have lower temperatures of 170ºC-175ºC and
salinities of 0.7-1.1 wt% NaCl.
Table 6. Measurement results of fluid inclusion in quartz from the Viholanniemi Zn-Au
occurrence.
Sample
Type
Form
Size(µ)
GLR*
(%)
Distribution
liquid
elliptical
major 1-2
minor 4-6
<10
orientated
4-8
100
random
Genesis
R305/126.20
elliptical
Pure CO2 negative
crystale
4-8
20-30
random
gas-liquid elliptical
3-6
10
orientated
Fp*
(°C)
Salinity
(wt% NaCl)
-0.6~-0.8
-0.6
-0.8
0.7-1.1
original
R307/37.90
CO2-H2O elliptical
Th*
(°C)
172
170
173
174
174
175
original
318
320
321
321
320
335
330
265
268
268
270
272
272
8.4-9.2
* GLR=gas liquid ratio, Th=homogenization temperature, Fp=freezing point.
a
b
Fig. 22. Fluid inclusions and their distributions. a) CO2-H2O inclusions isolated; b) CO2
inclusions distribute along fractures.
61
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Observations of the several generations of fluid inclusions suggest that the
mineralization of the deposit originated through mixing of fluids, or there were multistage fluid activities and the maximum temperature was about 335ºC (Crawford &
Hollister 1986). The ore-bearing fluids are therefore middle salinity and of high
temperatures of 268-335ºC if original inclusions are related to the mineralization. In
connection with the plastic deformation of quartz, the observations may also reflect the
presence of metamorphic fluids accompanied by recrystallization of quartz.
According to Ohmoto (1986), the sphalerite-galena pair usually gives isotopic
temperatures very close to the fluid inclusion temperatures in low P environments. If this
could be used here in combining with the observations of inclusion temperatures, the orebearing fluids in which the major sulphides were precipitated from might have
temperatures of more than 300ºC.
As already mentioned above, if the temperature is 318ºC -335ºC, the d18O value of
water in the fluids can be calculated using the d18O value of calcite. The calculation gives
the d 18O value varying in a range of 1.9per mil to 15.37 per mil but most of which vary
from 1.9 per mil to 5.87 per mil. Similarly, the calculation with the temperature of 268ºC 272ºC gives the results of the d18O value varying from 0.99 per mil to 13.53 per mil and
most of which range in 0.99 per mil to 4.03 per mil. Also the d18O values reached by
temperatures of 170ºC -175ºC are 3.68 per mil to 9.36 per mil with most of the negative
values. Those calculated d18O values of water in the fluids may be tentative. Considering
the facts of d 18O values of calcite and the inclusion features mentioned above, all these
imply that metamorphic fluids could have been involved during the whole mineralization.
Geochemical patterns
Most of the metals analysed (see Appendix 1 and 2) are very low in their concentrations
in the volcanic rocks of the Viholanniemi area. Taking away the samples near the ore
occurrences and some abnormally high data, the average contents of Zn, Pb and Cu
calculated in felsic-intermediate volcanics are 63 ppm, 23 ppm and 22 ppm, respectively.
Only Pb is somewhat higher, Zn and Cu are lower compared to their abundances in the
earth crust. It is noteworthy that Zn is lower in felsic rocks than intermediate rocks.
Figure 23 shows geochemical patterns of selected elements on the section of R312R311-R310 in the northern ore body (see Fig. 2, 17). Zn and Cu show anomalies with
partly correspondent concentration patterns, whereas Pb and Mn display weak anomalous
patterns. Unfortunately, although the weak anomalies of Zn, Cu and Mn can reflect the
places where ore bodies occur, these primary geochemical patterns especially those of
major oxides do not show intense anomalies. Coherent patterns are those of CaO and
MgO as well as Fe2O3 with good correspondance to that of Zn. Concentrated SiO2
appears mainly both in the upper and lower sides of the enriched Zn, CaO and MgO parts.
K2O and Na2O have the patterns showing banded concentration and indistinguishable
depletion of Na2O.
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Fig. 23. Geochemical patterns of selected elements on profile R312-311-310.
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Apparently the patterns of CaO, MgO, Fe2O3, SiO2, K2O and Na2O with unclear
variations in their concentrations are possibly a reflection of the protolith. In addition,
SiO2, Na2O (and K2O) may also indicate the alteration.
Discussion
Geotectonic setting of the Viholanniemi volcano-sedimentary formation
An island arc system, including the Pyhäsalmi Island Arc (PIA) and Kainuu-Outokumpu
back-arc related to the subduction in the Raahe-Ladoga Zone (RLZ) has been suggested
(see Ekdahl 1993). A totally opposite model with subduction from the NE without any
connection to Kainuu-Outokumpu area was also interpreted (e.g. Ward 1987, Lahtinen
1994, Nironen 1997). Geochemical studies of early Proterozoic volcanic rocks in the
RLZ display considerable varieties in their chemical compositions (Kousa et al. 1994,
Viluksela 1994, Vaarma & Kähkonen 1994, Lawrie 1992, also see Ekdahl 1993) and
possibly very complex geological processes.
The Viholanniemi volcanic cycle began with minor intermediate pyroclastic eruption,
succeeded by major felsic productions with an intermediate interlude; it ended with mafic
productions. The majority of volcanics are volcanic clastics with minor lava. Pyroclastics
of the cycle contact concordantly with the sequence of flychoid clastic rocks which are
now called mica schist in the eastern side of the Viholanniemi area. A clear temporary
break after the felsic eruptions is now confirmed by the presence of siliceous rock
accompanied by fine tuffaceous rocks. All this, together with the pillow structure,
indicates a shallow marine environment on the one hand, and, on the other hand, the
explosiue eruption of central type in the early stage, and an effusive eruption of a possible
fissure type in the later stage. According to their chemical compositions, felsic and
intermediate rocks are calc-alkaline, and mafic rocks are of low potassium tholeiitic series
with Fe-enrichment. The volcanic rock association is basalt, andesite, dacite and rhyolite.
A notable factor that should be mentioned here is that the majority of the volcanics in
the area are felsic and mafic rocks and they connect directly in the southern area.
Together with the variations of major elements, especially TiO2 and P2O5 in the rocks,
they may imply that the volcanics are not fractionates from the same parent magma.
Jakes and White (1971) subdivided the calc-alkaline series related to the subduction
zone into three sub-series: the arc-tholeiite, calc-alkaline and shoshonite sub-series.
Compared to arc-tholeiite (Jakes & White 1971, table 2), the mafic rocks of the study
area, particularly those occurring in the southern-most area (late products) exhibit some
differences by their very high TiO2, MnO, P2O5, Sr, La, Ce, Na2O/K2O, La/Yb values. It
seems that the mafic rocks of the area did not share the features of arc-tholeiite. Condie
(1982) considered that tholeiites may be mixed with calc-alkaline volcanics from the arc
proper in a relatively small back-arc basin. In addition, the Cr, Ni contents in the mafic
rocks obviously increase from earlier products to later ones. Particularly, two samples
(Table 1) have surprisingly high values of Cr and Ni as well as very high MgO and CaO
contents. One sample (xz-97-4.2) is the cement of pillow lava and the other (xz-97-22.1)
is amphibolite. If these contents are absolutely true, they may imply that some material
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came from the mantle at shallow depths. Unfortunately, from this two samples, it is
difficult to confirm the presence of mafic cumulate. Lawrie (1992) however, has
considered some amphibolites in Virtasalmi (about 15 km west) as tectonised relics of
high-level magma chambers.
Considering the bulk chemical compositions of the volcanics in the area, the content of
Na2O is very high in almost all rocks. Plagioclase phenocrysts in felsic rocks are mainly
albite (An 10) (Makkonen 1991) and the Ti, Fe, Ca bearing minerals such as diopside,
ilmenite are also general in mafic rocks. Average An values of the mafic rocks calculated
by CIPW norms range mostly from 22 to 47, and particularly, normative nefeline is
present in some samples. It should be noted here that the volcanics particularly those of
mafic share a clear trend of alkalic features, although they are not alkaline series. We
know that the alkaline series occur usually within a plate environment (Condie 1982,
Cong 1978, Qiu 1985). Smellie (1987) has interpreted the volcanic rocks with distinctly
alkaline composition in the Antarctic Peninsula as the products of a post-subduction
tensional environment.
Another distinct characteristic of the mafic (including intermediate) rocks of the study
area is their high TiO2 content (mostly>1.5%). These values are near to or higher than
that of the average composition of ridge tholeiite (Condie 1982, table 7.3). Mafic
volcanics in the arc are generally thought to be characterised by low contents of Ti
(Pearce & Cann 1973, Pearce & Norry 1979, Wood et al. 1979) and rarely have
TiO2>1.3% (Gill 1981). Augustithis (1978) connected Ti to the petrogenic significance.
Chaye’s (1964, 1965; also see Augustithis 1978) data showed that the circum-oceanic
basalt usually has TiO2 of <1.5%, and ocean basalt has TiO2 of >2.0%. The same cases
are also presented in the mafic volcanics in south-eastern Finland and the Tampere Schist
Belt (Lawrie 1992, Viluksela 1994). Kähkonen (1987, see Viluksela 1994) has attributed
this feature to a temporary extensional stage during the geological evolution of The
Tampere Schist Belt. Pekkarinen and Lukkarinen (1991) documented the metalava and
lava with TiO2 of >1.5% in the Koljola formation, the Kiihtelysvaara-Tohmajärvi district
which was interpreted as a rift environment. Similarly, Lawrie (1992) suggested an
intracratonic rift in Virtasalmi where the amphibolites have also high TiO2. However, in
the Pielavesi and Rautalampi areas the content of TiO2 in the mafic rocks is varied
(Ekdahl 1993, Lahtinen 1994).
The mafic volcanics of the Viholanniemi area are characterised by enrichment of Sr,
K, Rb, Ba, Nb, Ce, and P on MORB-normalized plots. They show features similar to
those basalts within the plate by their distribution patterns and absence of Nb depletion
which is proper for volcanic arc basalts (Pearce 1982). The chondrite normalized REE
patterns of the volcanics suggest the calc-alkaline rocks in modern island arc (Garcia
1978, Jakes & Gill 1970, Jalles & White 1971) on one hand, and on the other, mafic rocks
have their REE patterns with a slight enrichment of LREE similar to those of within plate
such as Hawaiian basalts, ridge basalts and E-MORB (Condie 1982, Jakes & White 1971,
Jakes & Gill 1970, Saunders 1984).
Discrimination diagrams using elements Cr, Ni, Ti, Y, Zr, Ta and Nb which were
considered to be immobile during secondary processes (Condie 1982, Saunders & Tarney
1984, Brewer & Atkin 1989) indicate that most mafic samples (including intermediate
samples in some case) have affinities to the setting within the plate and MORB or E-
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MORB on Ti-Zr, Nb/Y-Ti/Y, Zr-Zr/Y and Nb-Zr-Y diagrams. On Cr-Ti, Ni-Ti/Cr and TiV diagrams, the mafic rock samples are also subdivided into MORB or back arc basin
groups and low-K tholeiites.
Korsman et al. (1988) have established a clear tectono-metamorphic discordance
between the northern and southern parts of the Savo schist belt. The discordance,
particularly the abrupt changes in metamorphic facies can be encounted in the
Viholanniemi area which belongs to the Rantasalmi-Sulkava progressive metamorphism
area (Fig. 3). According to Korsman et al. (1988), the isolated Haukivuori area was thrust
over the blocks of the Kiuruvesi-Haukivesi complex. The conglomerate with plutonic
clasts of 1885±6Ma encountered in the Haukivuori area indicate that the sedimentation
might still have been going on in the Rantasalmi-Sulkava area when erosion was already
affecting the Kiuruvesi-Haukivesi complex. Therefore the Viholanniemi area could be
part of a possible subsiding basin.
The mafic and ultramafic sill-like intrusions of c.1.9Ga in the Juva district representing
mantle-derived magma intruded into metapelitic sediments prior to deformation and
reorientation into their present steeply dipping attitudes (Makkonen 1996). These
intrusions, together with volcanics in the Viholanniemi area, should be the products of comagmatism caused of similar geochronological and compositional characters. In this
respect, the volcanism of the study area could be explained as the basaltic magmainduced crustal melting so that felsic melts erupted first, followed by the mafic melts.
In fact, Svecofennian basalts of the early Proterozoic seem to be identical in the LIL
element enrichment and slightly enriched LREE concentration (Colley & Westra 1987,
Ekdahl 1993, Lahtinen 1994, Kousa et al. 1994, Vaarma & Kähkönen 1994, Kähkönen &
Nironen 1994, Viluksela 1994, Makkonen 1996). However, not only in the Viholanniemi,
but also in the RLZ, especially in the southestern part, the negative anomaly of Nb (Ta) in
the basalts can not be observed (Ekdahl 1993, Viluksela 1994), but they appear in the
basalts in the TSB (Tampere Schist Belt). This also may indicate here that the crustal
involment in magma of RLZ at least in its south-eastern part is limited.
It is clear from the discussion above that the volcanics of the Viholanniemi area exhibit
considerable variety in their compositional characteristics. This could contribute to the
hybrid magma resulting from the mixing of mantle-derived melt with its induced
anatextic melt (Fyfe 1981). The volcanic cycle developed mainly from explosive eruption
of the central type in the early stage to effusive in the later stage. The volcanism most
possibly took place in a temporary tensional environment.
Allen et al. (1996) considered the Bergslagen and Skellefteå areas in Sweden as a
continental back-arc region and a transitional area between renewed arc volcanism of a
more continental character to the north and subsidence basin to the south, respectively.
Lawrie (1992) interpreted the Virtasalmi area as an intracratonic rift (passive margin?).
Considering the cases of post-subduction tensional events in the Antarctic Peninsula
(Smellie 1987), intra-arc rifting in the Skellefteå district in Sweden (Rickard 1987,
Vivallo & Claesson 1987) and an aborted marginal basin in the Western Peruvian
(Aguirre & Offler 1985), it could be envisaged here that an incipient arc-rifting system
was presented in the Viholanniemi area and the subsiding basin was aborted shortly after
it formed. The rift might have developed in the temporary period of stress changing due
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to the decreasing subduction rate and this in turn induced a transtension stress regime.
Thus, the Viholanniemi volcanic-sedimentary formation was formed in an incipient arcrifting environment.
Viholanniemi Zn-Au mineralization
Distinctive characteristics
The Viholanniemi Zn-Au deposit is not a typical volcanic host massive sulphide deposit
(VHMS) because there is no stratified or massive ore. However, the deposit shares some
similarities with VHMS deposits on the one hand, and displays distinctive characteristics
in many respects on the other.
With regard to the VHMS deposits, the Viholanniemi Zn-Au deposit have characters in
general as follows: (1) the volcanic-sedimentary formation is the production of an arc-rift
environment; (2) the deposit occurs in those places where the felsic pyroclastics transits
to sedimentary rocks; (3) Sericitization, disseminated pyrite as well as chloritization and
secondary quartz are very common; (4) Cu-Pb-Zn metal relationships in ores represent
those of VHMS deposits (Ekdahl 1993); (5) Ore sulphide d34S is between 1.7 to 10.4 per
mil similar to that of VHMS deposits (Rye & Ohmoto 1974, Ohmoto & Rye 1979, Hoefs
1980, Ohmoto 1986, Taylor 1987).
On the other hand, the deposit shows its distinctive characteristics in many respects
that include:
– The ore host rocks are mainly vein like quartz-carbonate-tremolite rocks and the ore
occurs disseminated or as open fillings.
– The sulphur contents in the ore are very low and no sulphate mineral has been found.
– Ore bearing fluids have been observed to be extensively but less intensely activated
in the area. Apart from the Viholanniemi Zn-Au occurrence, there are also small
occurrences elsewhere surrounding Lahnalahti both in mafic and felsic rocks.
– Ore bearing fluids were possibly composed mainly of CO2 and H2O with relatively
low salinity. However, the values of 8.4-9.2 wt% NaCl of the fluid inclusion may
resemble that of stockwork beneath the massive ore (Sawkins 1990). Clearly, there
were different fluids with variety of temperatures which range from 170ºC to 335ºC
(not corrected for pressure).
– Ore sulphide d34S values are mainly positive and vary in a relatively wide range:
d34Ssp 0.2–10.4‰, d34Spy -0.5–10.2‰.
– Carbon and oxygen isotopes together show a clear affinity of mantle-derived carbon
(Hoefs 1980, Kerrich 1989, Rollinson 1993) and also possibly another carbon source
coming from the mixing between marine sediments and organic materials. The
d18OSMOW values of calcite vary greatly and may indicate a wide range of temperatures. Calculated d18OSMOW values of water in the fluids varying from 3.68 per mil
to 15.37 per mil suggest a considerable involvement of atomspheric water and metamorphic water.
– Ores experienced intense deformation and overprints of metamorphism. The remobilization of metals during the metamophism is present.
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– Geochemical patterns of the deposit do not show typical Na2O depletion of the massive sulphides proper, particularly in the altered footwall.
Sulphur and base metal sources
Due to no sulphate mineral present in the ores, the ore sulphide d34S values could be
considered as representative of d34SåS of fluid. The positive and varied sulphide d34S
values of ores indicate that the sulphur came from mixed sources including mainly
magmatic, seawater and partly sulphides in the rocks (Hoefs 1980, Ohmoto 1986,
Rollinson 1993). Disseminated sulphides in volcanics derived clearly their sulphur from
the rocks themselves. The variations of sulphide d34S values might also be the result of
the various degrees of mixing between sulphur of magmatic and ocean water. A wide
spread of disseminated pyrite in the volcanics in the study area and lower contents of Zn
and Cu, especially in the felsic volcanics, imply that the main base metals of the deposit
possibly came from those volcanics.
Carbon sources
Marine limestones have d13C values close to 0 per mill and decarbonation of the
limestones would produce CO2 with d13C values between +3 per mill and +5 per mil
(Hoefs 1980). The marine carbonates and also the organic origin should not be considered
as the major carbon sources of the deposit. Considering the presence of graphite in the
host rock and also the high concentration of MnO in carbonate of the deposit however,
part of the carbon coming from sediments and organic materials cannot be absolutely
excluded.
Calcite from calc-silicate has mean d18O and d13C values of +16.5 per mill and -6 per
mill (Hoefs 1980). Stakes and ONeil (1982, see Rollinson 1993) documented calcite in a
greenstone breccia having mantle-like d13C values and forming in a rock-dominated
environment (low water/rock ratio) at high temperature. The diagram after Rollinson
(1993) (Fig. 21) shows the characteristics of carbonatites in most of samples. Considering
the alkalic trend of the mafic volcanics of the area, the main carbon sources of the deposit
could be (1) mantle-derived and partly mixed with carbonate-derived and organic
originated CO2, and possibly (2) mixing between carbonate-derived and organic
originated CO2.
Water in the fluids
The calculated d18O values of water in the fluids range in three groupes: 1.9–15.37 per
mil, 0.99–13.53 per mil and 3.68–9.36 per mil corresponding respectively to the
temperatures of 318ºC-335ºC, 268ºC -272ºC and 170ºC -175ºC. Regardless of the d18O
values of ocean water at that time, it could be deduced that the water in the fluids from
which the major sulphides precipitated was mainly composed of ocean water and also
some magmatic water. During the metamorphism, the meteoric water and also the
metamorphic water might have been involved.
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Superimposition of metamorphic fluids
Although the majority of carbon of the carbonate in the deposit can hardly be expected to
be derived from the decarbonation of marine limestones during the metamorphism, the
superimposition of metamorphic fluids on mineralization is significant. The evidence is
as follows:
(1) Fluid inclusions measured in the deposit exhibit obvious multi-stage fluid activities
according to inclusion types, distributions and different salinities and temperature along
with the plastic deformation of quartz. (2) The presence of graphite in the host rocks and
possibly part of carbon coming from the mixing of morine carbonate-derived and organic
originated CO2. (3) Involvement of meteoric water and also the metamorphic water
suggested by the d18O values of calcite. (4) Some sulphides (e.g. chalcopyrite and
sphalerite) have been remobilized and reprecipitated along the fractures in garnet during
metamorphism (Fig. 24).
Therefore, many of the distinctive characteristics of the Viholanniemi Zn-Au deposit
could be the results of metamorphic superimposition.
a
b
Fig. 24. Remobilized sulphides in the Viholanniemi Zn-Au deposit. a) Chalcopyrite fillings in
the fractures of garnet, R301/36.55, single nicol. Magnification x 200. b) Sphalerite and
chalcopyrite fillings in the fractures of garnet R301/36.55, single nicol. Magnification x 200.
Mineralization type
All the above mentioned factors indicate that the Viholanniemi Zn-Au deposit is a
veinlet-disseminated type deposit related to volcanism, and it experienced intense
metamophic superimposition. Compared to the mafic volcanics, the relatively smaller
volume of felsic volcanics in the study area and surroundings may be considered to be the
main reason of the limited mineralization. If there are typical stratabound massive ore
bodies, not yet found in the area, the sedimentary rocks stratigraphically overlying felsic
volcanics should be considered further.
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Summary and conclusion
The Viholanniemi metavolcanic-sedimentary formation is composed of mainly clastic
rocks with volcanics of the shallow marine environment. The formation includes felsic
pyroclastics with minor intermediate intercalations, siliceous rock and fine tuffacous
siltstone, mafic pyroclastics associated with pillow lava, as well as flychoid clastics in the
bottom and top respectively. The volcanism of the Viholanniemi area is characterised by
an explosive eruption of the central type in the early stage and effusive eruption of a
fissure type in the later stage. Volcanics of the area are products of mantle-derived melt
and its induced anatextic melt as well as their mixing instead of fractionates from the
same parent magma. Pyroclastics of the formation occur concordantly with the flychoid
clastic rocks of the Svecofennian. Chemical compositions of the volcanics suggest that
the felsic-intermediate rocks are calc-alkaline, while mafic rocks belong to a tholeiitic
series of low potassium with a trend of Fe-enrichment.
The tholeiitic rocks of the Viholanniemi area are the products of volcanism within
plate. Evidence includes: (1) chemical variations share few features of arc-tholeiite but a
clear alkalic trend; (2) high contents of TiO2 of mafic volcanics differ clearly from those
of the island arc and are also outside the RLZ, but are similar to those of ridge tholeiite;
(3) multi-element distribution patterns including REE patterns exhibit characteristics both
of volcanism related to subduction and within plate basalts; (4) discrimination diagrams
using immobile elements indicate affinities to within plate setting and MORB. The
conclusion could be deduced here that an incipient arc-rifting system was presented in the
Viholanniemi area and the basin was aborted shortly after it formed. Therefore the
geotectonic setting of the Viholanniemi volcanic-sedimentary formation is of an incipient
arc-rifting system.
Observations of the presence of siliceous rock and fine tuffaceous rocks indicate a
temporary break between the mainly felsic and mafic volcanic eruptions. The
Viholanniemi Zn-Au mineralizations started during this short period.
The Viholanniemi veinlet-disseminated Zn-Au deposit shares some features of VHMS
deposits on the one hand, and exhibits also distinctive features in many respects on the
other. The mineralization involves possibly convective cells developed immediately after
the felsic pyroclastic eruptions in the early stage of the arc-rift environment, driven by
ascending mafic magma, and then superimposed by metamorphism. Those distinctive
characteristics of the Viholanniemi Zn-Au deposit lead the author to assume a tentative
geological model as follows:
(1) In the early stage of the arc-rifting, extrusion of mainly felsic pyroclastic material
accumulated a relatively thick volcanic pile. Infiltrated and inverted seawater along the
synvolcanic faults downflowed into the deep and led to the initial development of
convective cells.
(2) As the ongoing of temporary extension, the initiatially convective cells were driven
by the ascending mafic magma. Thus, the convective hydrothermal systems were formed
and circulated throughout the volcanic pile. Ore bearing fluids might reach the seafloor
forming small scale stratified ores, or they formed mainly vein type sulphide ores and
disseminated sulphides in volcanics.
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(3) During the metamorphism, the deposit experienced intense superimposition,
sulphides present in volcanics and ores were partly remobilized. Some distinctive
characeristics of the deposit may also be attributed to this secondary processing.
Acknowledgements
Dr. Elias Ekdahl and Professor Risto Aario arranged and supervised the programs, and
Dr. Hannu Makkonen followed the study in Finland. The manuscript was also checked
and reviewed by them and I acknowledge with gratitude their invaluable suggestions and
comments.
Professor Jiang Fuzhi checked part of thin sections that I had examined in Finland and
gave me many valuable suggestions during discussions. Dr. Li Yanhe reviewed the part of
isotope studies. Mr. Rauli Lempiäinen assisted me with field work. Dr. Jouko Paaso
helped me with electron microprobe analysis. Mr. Heikki Puustjärvi, senior geologist, and
Dr. Lauri Pekkarinen introduced me to the geological background of the Outokumpu
district and Lahnalahti area. Mr. Li Shengqi helped me with the data processing. I would
like to express my heartfelt thanks to them all.
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74
Appendices 1-4
1
65.4
1.13
14.8
5.87
0.088
2.18
3.91
4.32
1.54
0.327
99.57
0.22
0.0037
0.0279
0.0149
0.0020!
0.0004!
0.0506
0.0031
0.0010!
0.0055
0.0148
0.005
0.0047
0.0061
0.0012!
0.0005!
0.0003!
0.012
0.009!
0.0003!
0.0000!
0.0000!
0.0002!
0.0003!
0.007
0.0000!
2
53.3
2.47
14.7
12
0.165
5.35
5.56
4.27
0.779
1.04
99.63
0.03
0.0022
0.0072
0.0166
0.0023!
0.0000!
0.0326
0.0025
0.0017!
0.0033
0.0118
0.0036
0.0035
0.0269
0.0011!
0.0013!
0.0008!
0.0175
0.006!
0.0002!
0.0000!
0.0000!
0.0000!
0.0002!
0.004!
0.0000!
6
70.7
0.701
13.9
4.48
0.103
1.74
0.769
5
2.17
0.182
99.75
<0.01
0.0051
0.0675
0.007
0.0015!
0.0007!
0.0325
0.0020!
0.0004!
0.0037
0.0092
0.0026
0.0023
0.0077
0.0023!
0.0017!
0.0016!
0.0137
0.003!
0.0000!
0.0000!
0.0000!
0.0000!
0.0003!
0.006
0.0000!
7
55.1
1.64
15.5
11.2
0.22
4.43
5.25
4.32
1.28
0.284
99.22
0.06
0.0033
0.0221
0.0202
0.0020!
0.0000!
0.0193
0.0027
0.0020!
0.0021!
0.0053
0.0018
0.0024
0.0323
0.0019!
0.0023
0.0171
0.0125
0.032
0.0000!
0.0000!
0.0000!
0.0001!
0.0002!
0.004!
0.0001!
14
47.3
1.5
16.3
9.6
0.399
7.75
11.1
2.74
0.813
0.23
97.73
0.01
0.0022
0.0066
0.0325
0.0037
0.0000!
0.0146
0.0025
0.0031
0.0018!
0.0044
0.0016
0.0019
0.0251
0.0074
0.0038
0.0045
0.0545
0.005!
0.0001!
0.0000!
0.0000!
0.0000!
0.0000!
0.003!
0.0000!
15
54.7
1.82
16.1
11.4
0.29
4.81
6.77
3.08
0.508
0.244
99.72
<0.01
0.0008!
0.0105
0.0306
0.0078
0.0000!
0.0166
0.0027
0.0029!
0.0024!
0.0049
0.0017
0.0024
0.0365
0.0022!
0.0023
0.0035
0.0473
0.003!
0.0000!
0.0000!
0.0000!
0.0000!
0.0002!
0.004!
0.0000!
16
49.8
1.65
12.9
12.9
0.223
6.47
10.5
3
0.292
0.29
98.03
<0.01
0.0007!
0.015
0.0305
0.0024!
0.0003!
0.0241
0.0019!
0.0026!
0.0032
0.0074
0.0021
0.0028
0.03
0.0022!
0.0053
0.0018!
0.0194
0.004!
0.0000!
0.0000!
0.0000!
0.0000!
0.0000!
0.004!
0.0000!
17
43.4
1.02
9.46
16
1.04
5.71
18.1
0.16
0.019
0.253
95.16
<0.01
0.0001!
0.0034
0.0446
0.0027!
0.0003!
0.0145
0.0018!
0.0028!
0.0023!
0.0045
0.0014
0.002
0.0204
0.0017!
0.0034
0.2024
0.029
0.059
0.0002!
0.0000!
0.0000!
0.0006!
0.0000!
0.003!
0.0000!
21
66.8
0.859
13.9
6.62
0.197
2.55
1.6
4.38
2.55
0.212
99.67
<0.01
0.0067
0.0298
0.0071
0.0016!
0.0005!
0.045
0.0027
0.0005!
0.0046
0.0099
0.0035
0.0041
0.0053
0.0009!
0.0000!
0.0009!
0.018
0.001!
0.0002!
0.0000!
0.0000!
0.0002!
0.0001!
0.012
0.0001!
22
77
0.148
12
2.23
0.287
1.09
1.45
2.51
2.76
0.014
99.49
0.02
0.0064
0.0847
0.0047
0.0015!
0.0010!
0.0179
0.0022
0.0000!
0.0057
0.0115
0.0025
0.0032
0.0009!
0.0018!
0.0000!
0.0018!
0.0038
0.000!
0.0000!
0.0000!
0.0000!
0.0001!
0.0001!
0.004!
0.0004!
23
65.4
0.738
12.9
6.03
0.193
1.14
6.44
3.68
1.3
0.162
97.98
0.92
0.0043
0.0372
0.0157
0.0023!
0.0005!
0.0315
0.0023
0.0010!
0.0042
0.0102
0.0033
0.0039
0.0093
0.0028!
0.0021
0.0009!
0.0105
0.022
0.0002!
0.0000!
0.0000!
0.0000!
0.0000!
0.012
0.0000!
24
71.3
0.926
11.9
5.75
0.096
0.73
3.41
3.78
0.954
0.28
99.13
0.33
0.0038
0.0214
0.0149
0.0020!
0.0002!
0.0279
0.0016!
0.0006!
0.0032
0.0066
0.0028
0.0028
0.007
0.0015!
0.0005!
0.1037
0.0083
0.175
0.0004!
0.0000!
0.0000!
0.0001!
0.0001!
0.01
0.0000!
25
76.8
0.255
9.16
2.81
0.098
0.56
3.8
2.71
0.955
0.044
97.19
0.62
0.0039
0.0324
0.0117
0.0018!
0.0006!
0.0292
0.0015!
0.0000!
0.0038
0.0089
0.0025
0.0027
0.0033
0.0016!
0.0002!
0.015
0.005
0.022
0.0000!
0.0000!
0.0000!
0.0000!
0.0000!
0.01
0.0000!
26
64.8
0.8
12.2
4.9
0.166
1.2
6.42
3.46
1.75
0.215
95.91
0.94
0.0049
0.0323
0.0171
0.0024!
0.0003!
0.0263
0.0018!
0.0010!
0.0026!
0.0082
0.0022
0.0027
0.0124
0.0020!
0.0018!
0.004
0.0181
0.041
0.0000!
0.0000!
0.0000!
0.0000!
0.0000!
0.008
0.0000!
27
46.4
1.74
14.1
7.86
0.137
3.74
13.2
5.1
0.125
0.184
92.59
1.73
0.0003!
0.0098
0.0319
0.0020!
0.0002!
0.0113
0.0012!
0.0036
0.0006!
0.0037
0.0017
0.002
0.0264
0.0085
0.0099
0.0086
0.005
0.031
0.0001!
0.0000!
0.0000!
0.0003!
0.0000!
0.006!
0.0000!
Appendix 1 Whole rock chemical compositions of selected rocks in the Viholanniemi area. Oxides and others are all in wt%. Sampling sites are presented at the App.4.
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
total
C
Rb
Ba
Sr
Pb
Th
Zr
Ga
Sc
La
Ce
Nb
Y
V
Cr
Ni
Cu
Zn
S
U
Sb
Sn
As
Bi
Cl
Mo
76
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2 O
P2O5
total
C
Rb
Ba
Sr
Pb
Th
Zr
Ga
Sc
La
Ce
Nb
Y
V
Cr
Ni
Cu
Zn
S
U
Sb
Sn
As
Bi
Cl
Mo
28
37.7
1.18
9.16
12.3
0.194
9.47
17.5
1.69
0.085
0.244
89.52
1.97
0.0002!
0.0021
0.0179
0.0018!
0.0000!
0.01
0.0020!
0.0035
0.0010!
0.0048
0.0009!
0.0023
0.0267
0.1216
0.0569
0.0067
0.0115
0.037
0.0001!
0.0000!
0.0003!
0.0000!
0.0000!
0.007
0.0000!
30
49.3
1.74
14.9
12.8
0.168
4.71
9.34
4.29
0.726
0.342
98.32
0.16
0.0010!
0.0189
0.0423
0.0013!
0.0001!
0.0172
0.0023
0.0030!
0.0011!
0.0068
0.002
0.0026
0.0345
0.0064
0.0033
0.0222
0.0115
0.018
0.0000!
0.0000!
0.0000!
0.0002!
0.0001!
0.008
0.0000!
31
60.1
1.08
15.7
8.01
0.076
3.4
3.17
2.96
2.72
0.5
97.72
0.02
0.0171
0.0247
0.0441
0.0036
0.0005!
0.0204
0.0029
0.0009!
0.0049
0.0136
0.0016
0.0025
0.0172
0.0057
0.0046
0.0074
0.014
0.317
0.0003!
0.0000!
0.0000!
0.0000!
0.0000!
0.004!
0.0000!
32
57
0.742
19.1
7.9
0.039
2.98
0.381
1.36
5.17
0.093
94.77
0.21
0.0222
0.0686
0.0111
0.004
0.001
0.0164
0.004
0.0015!
0.0031
0.0097
0.0017
0.0029
0.0169
0.0144
0.0066
0.0051
0.0164
0.063
0.0003!
0.0000!
0.0000!
0.0008!
0.0002!
0.006
0.0000!
33
56.8
1.24
15.9
8.94
0.138
4.11
6.69
2.3
1.52
0.61
98.25
0.02
0.0095
0.0604
0.1303
0.0032
0.0006!
0.0214
0.0026
0.0014!
0.0069
0.0164
0.0016
0.0021
0.0202
0.0046
0.005
0.0083
0.0134
0.334
0.0001!
0.0000!
0.0000!
0.0001!
0.0000!
0.004!
0.0000!
36
76.1
0.6
12.1
3.54
0.024
0.99
0.574
1.76
3.54
0.118
99.35
0.03
0.0134
0.0688
0.0119
0.0026!
0.0007!
0.0255
0.002
0.0000!
0.0038
0.0085
0.0016
0.0023
0.0079
0.0104
0.0023
0.0010!
0.0072
0.035
0.0000!
0.0000!
0.0000!
0.0000!
0.0000!
0.006!
0.0000!
37
67.8
0.618
14.4
5.58
0.07
2.42
2.45
3.44
2.19
0.166
99.13
<0.01
0.0105
0.0313
0.0248
0.0033
0.0008!
0.0178
0.0025
0.0010!
0.0032
0.0066
0.0012
0.0022
0.0117
0.0157
0.0051
0.0037
0.0082
0.154
0.0002!
0.0000!
0.0000!
0.0000!
0.0002!
0.005!
0.0000!
38
72.9
0.503
12.3
4.78
0.059
1.99
1.72
3.31
2
0.148
99.71
0.02
0.0091
0.0423
0.0233
0.0029!
0.0013
0.0216
0.0023
0.0007!
0.0036
0.0108
0.0008!
0.0024
0.0106
0.0132
0.0037
0.0017!
0.0057
0.127
0.0000!
0.0000!
0.0000!
0.0008!
0.0000!
0.004!
0.0000!
39
68.7
0.686
13.5
5.98
0.074
2.8
1.7
2.8
3.24
0.139
99.62
0.03
0.0146
0.0756
0.0177
0.0027!
0.0008!
0.0197
0.0024
0.0010!
0.0032
0.0087
0.0012
0.0023
0.0127
0.0106
0.0036
0.0003!
0.0084
0.008!
0.0003!
0.0000!
0.0000!
0.0003!
0.0000!
0.007
0.0000!
Appendix 1 Continued.
34
71.9
0.508
12.6
4.35
0.042
2.42
0.861
1.69
3.23
0.136
97.74
0.63
0.0103
0.0535
0.0111
0.0017!
0.0010!
0.0181
0.0023
0.0008!
0.0029!
0.0084
0.0009!
0.0017
0.0106
0.0079
0.0046
0.0055
0.0069
1.56
0.0000!
0.0000!
0.0000!
0.0003!
0.0000!
0.006
0.0000!
40
48.3
1.19
13.9
12
0.225
5.8
12.3
3.32
0.396
0.117
97.55
0.23
0.0008!
0.0161
0.0154
0.0017!
0.0000!
0.0074
0.0022
0.0047
0.0010!
0.0033
0.0005!
0.0023
0.0363
0.0088
0.0082
0.0077
0.013
0.009!
0.0002!
0.0000!
0.0000!
0.0002!
0.0004!
0.004!
0.0000!
41
61.9
0.708
17
7.01
0.061
2.66
1.01
2.09
4.1
0.086
96.63
0.36
0.0173
0.0989
0.0197
0.0041
0.0015
0.0193
0.0027
0.0013!
0.0052
0.012
0.0015
0.0026
0.0128
0.0111
0.0036
0.0019!
0.0128
0.031
0.0003!
0.0000!
0.0000!
0.0000!
0.0002!
0.003!
0.0000!
42
45.1
1.38
14.9
12.3
0.162
7.73
12.8
2.08
0.071
0.173
96.70
0.33
0.0005!
0.0026
0.0689
0.0015!
0.0000!
0.008
0.0024
0.004
0.0013!
0.0046
0.0015
0.0018
0.0305
0.0557
0.0321
0.018
0.0097
0.137
0.0001!
0.0000!
0.0000!
0.0006!
0.0003!
0.002!
0.0000!
43
75.9
0.353
11.8
3.33
0.083
1.55
1.35
2.79
2
0.053
99.21
0.05
0.0062
0.0202
0.005
0.0018!
0.0006!
0.0367
0.0019!
0.0002!
0.0049
0.0106
0.0032
0.0041
0.0027!
0.0018!
0.0007!
0.0016!
0.0095
0.004!
0.0000!
0.0000!
0.0000!
0.0001!
0.0000!
0.003!
0.0000!
44
74.4
0.044
14.7
0.78
0.057
0.19
1.32
5.95
1.83
0.036
99.31
0.21
0.0044
0.0651
0.02
0.0027!
0.0000!
0.0037
0.0026
0.0000!
0.0009!
0.0036
0.0007!
0.0001!
0.0006!
0.0014!
0.0005!
0.0007!
0.0027
0.011
0.0000!
0.0000!
0.0000!
0.0000!
0.0002!
0.004!
0.0000!
77
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2 O
P2O5
total
C
Rb
Ba
Sr
Pb
Th
Zr
Ga
Sc
La
Ce
Nb
Y
V
Cr
Ni
Cu
Zn
S
U
Sb
Sn
As
Bi
Cl
Mo
45
64.3
1.09
15.1
6.88
0.17
4.41
2.64
4.24
0.715
0.238
99.78
0.02
0.0027
0.0065
0.0112
0.0027!
0.0005!
0.0298
0.0022
0.0013!
0.0035
0.0074
0.0024
0.0028
0.0141
0.0025!
0.0018!
0.0005!
0.0074
0.003!
0.0001!
0.0000!
0.0000!
0.0000!
0.0002!
0.004!
0.0000!
46
56.1
1.09
16.6
9.32
0.223
5.33
5.19
5.21
0.18
0.267
99.51
0.03
0.0004!
0.0053
0.0219
0.0021!
0.0000!
0.022
0.0024
0.0015!
0.0025!
0.0055
0.002
0.0026
0.0195
0.0063
0.0096
0.0009!
0.0081
0.003!
0.0000!
0.0000!
0.0000!
0.0000!
0.0003!
0.006!
0.0000!
47
74.8
0.38
13.3
3.01
0.048
1.02
1.14
4.75
1.13
0.044
99.62
0.06
0.0025
0.0339
0.0086
0.0014!
0.0006!
0.0557
0.0020!
0.0000!
0.0052
0.0138
0.0044
0.0049
0.0019!
0.0010!
0.0010!
0.0088
0.0016!
0.002!
0.0000!
0.0000!
0.0000!
0.0001!
0.0006!
0.003!
0.0000!
48
69.7
0.612
14.3
5
0.076
1.73
1.78
4.7
1.12
0.14
99.16
<0.01
0.0035
0.0192
0.009
0.0031
0.0007!
0.0365
0.0024
0.0003!
0.0047
0.0102
0.0027
0.0029
0.0062
0.0020!
0.0015!
0.0095
0.0022
0.907
0.0001!
0.0000!
0.0000!
0.0002!
0.0002!
0.005!
0.0011
49
68.6
0.609
14.4
5.28
0.127
2.02
4.04
2.25
1.84
0.143
99.31
0.02
0.0062
0.0256
0.0127
0.0023!
0.0006!
0.0352
0.0024
0.0004!
0.0045
0.0101
0.0031
0.0039
0.0057
0.0023!
0.0009!
0.0054
0.0023
0.031
0.0002!
0.0000!
0.0000!
0.0001!
0.0002!
0.006!
0.0000!
51
71.6
0.465
13.7
4.51
0.129
1.43
2.13
4.62
1.07
0.087
99.74
0.11
0.0036
0.0186
0.0069
0.0016!
0.0007!
0.0448
0.0033
0.0004!
0.0041
0.0088
0.0035
0.0055
0.0024!
0.0016!
0.0001!
0.0000!
0.0023
0.000!
0.0000!
0.0000!
0.0000!
0.0001!
0.0001!
0.003!
0.0000!
52
72.2
0.483
13.9
2.69
0.133
2.45
1.46
5.56
0.467
0.086
99.43
0.02
0.0014
0.0048
0.008
0.0020!
0.0006!
0.0468
0.0025
0.0003!
0.0051
0.0109
0.0035
0.0043
0.0031
0.0010!
0.0001!
0.0000!
0.0098
0.001!
0.0000!
0.0000!
0.0000!
0.0000!
0.0005!
0.004!
0.0000!
53
67.7
0.85
15.1
4.15
0.086
2.18
3.5
5.86
0.14
0.241
99.81
0.06
0.0001!
0.0036
0.0193
0.0025!
0.0004!
0.0401
0.0026
0.0009!
0.004
0.0093
0.0034
0.0035
0.0065
0.0006!
0.0002!
0.0002!
0.0023
0.004!
0.0000!
0.0000!
0.0000!
0.0002!
0.0002!
0.006!
0.0000!
54
59.5
1.79
14.6
9.38
0.192
3.87
5.67
3.59
0.712
0.459
99.76
0.03
0.0027
0.0058
0.0179
0.0029!
0.0001!
0.028
0.0025
0.0023!
0.0031
0.007
0.0026
0.003
0.0249
0.0016!
0.0010!
0.0005!
0.0134
0.003!
0.0001!
0.0000!
0.0000!
0.0001!
0.0002!
0.006!
0.0001!
Appendix 1 Continued.
50
72.8
0.564
12.9
4.14
0.083
1.68
2.77
3.42
1.18
0.125
99.66
0.02
0.0034
0.023
0.013
0.0016!
0.0003!
0.0373
0.0021
0.0001!
0.0035
0.0101
0.0027
0.0032
0.0051
0.0021!
0.0010!
0.0007!
0.0028
0.003!
0.0000!
0.0000!
0.0000!
0.0000!
0.0003!
0.005!
0.0000!
55
59.2
1.33
15.1
9.03
0.218
4.32
3.76
4.02
1.02
0.238
98.24
0.04
0.0034
0.0309
0.015
0.0031
0.0001!
0.031
0.0027
0.0017!
0.0033
0.0077
0.0026
0.0033
0.0225
0.0011!
0.0023
0.0854
0.0105
0.038
0.0001!
0.0000!
0.0000!
0.0000!
0.0003!
0.006!
0.0000!
56
62.1
1.09
15.4
7.53
0.15
4.28
3.61
4.01
0.689
0.28
99.14
0.01
0.002
0.0084
0.0172
0.0029!
0.0002!
0.034
0.0026
0.0015!
0.0042
0.0091
0.0027
0.0032
0.0133
0.0024!
0.0036
0.0005!
0.0091
0.004!
0.0000!
0.0000!
0.0000!
0.0000!
0.0000!
0.006!
0.0000!
57
68.1
0.826
14.6
5.54
0.107
1.74
2.67
4.66
1.33
0.234
99.81
0.05
0.0045
0.0259
0.0124
0.0032
0.0005!
0.04
0.0025
0.0011!
0.004
0.0112
0.0031
0.0034
0.0067
0.0010!
0.0003!
0.0011!
0.0031
0.005!
0.0000!
0.0000!
0.0000!
0.0000!
0.0003!
0.005!
0.0001!
58
54.8
1.47
16.2
10.9
0.263
5.16
5.79
4.17
0.296
0.367
99.42
0.05
0.0012
0.0047
0.0194
0.0019!
0.0001!
0.0228
0.0025
0.0019!
0.0020!
0.0065
0.0022
0.0025
0.0234
0.004
0.0077
0.007
0.0075
0.009!
0.0001!
0.0000!
0.0000!
0.0000!
0.0003!
0.006!
0.0000!
59
64.7
0.889
15.1
5.19
0.152
3.26
5.15
4.13
0.635
0.217
99.42
0.06
0.0022
0.0055
0.0225
0.0021!
0.0005!
0.0256
0.0023
0.0013!
0.0036
0.0078
0.0022
0.0025
0.0131
0.0026!
0.0029
0.0000!
0.0045
0.002!
0.0000!
0.0000!
0.0000!
0.0001!
0.0003!
0.004!
0.0000!
78
SiO2
TiO2
Al2O3
Fe2O3
MnO
MgO
CaO
Na2O
K2O
P2O5
total
C
Rb
Ba
Sr
Pb
Th
Zr
Ga
Sc
La
Ce
Nb
Y
V
Cr
Ni
Cu
Zn
S
U
Sb
Sn
As
Bi
Cl
Mo
60
61.3
1.16
15.7
6.35
0.152
3.76
5.63
4.17
0.6
0.28
99.10
0.06
0.0017
0.0053
0.0238
0.0022!
0.0004!
0.0348
0.0026
0.0016!
0.0032
0.0091
0.0028
0.003
0.0147
0.0049
0.0043
0.0000!
0.0045
0.000!
0.0002!
0.0000!
0.0000!
0.0002!
0.0000!
0.005!
0.0000!
61
71.3
0.496
14.3
3.8
0.077
1.34
1.93
5.92
0.445
0.099
99.71
0.09
0.0018
0.0057
0.0087
0.0017!
0.0005!
0.0475
0.0026
0.0000!
0.0046
0.0108
0.0037
0.0041
0.0030!
0.0013!
0.0000!
0.0009!
0.0022
0.001!
0.0000!
0.0000!
0.0000!
0.0004!
0.0000!
0.004!
0.0001!
62
72.8
0.463
13.1
2.82
0.154
1.37
3.29
3.6
1.11
0.096
98.80
0.2
0.0052
0.0065
0.0102
0.0048
0.0005!
0.0441
0.0019!
0.0003!
0.0054
0.0104
0.0036
0.0041
0.0024!
0.0016!
0.0002!
0.0000!
0.0062
0.003!
0.0000!
0.0000!
0.0000!
0.0000!
0.0000!
0.005!
0.0003!
63
70
0.473
13.7
3.25
0.166
3.48
1.83
2.96
1.58
0.099
97.54
0.02
0.0058
0.0075
0.0081
0.0087
0.0007!
0.0456
0.0019!
0.0000!
0.0043
0.0114
0.0034
0.0042
0.0033
0.0012!
0.0007!
0.0005!
0.0262
0.004!
0.0000!
0.0000!
0.0000!
0.0000!
0.0001!
0.006!
0.0001!
64
67.6
0.816
14.7
5.53
0.059
1.56
2.18
6.09
0.557
0.22
99.31
0.03
0.0012
0.0189
0.0117
0.0016!
0.0005!
0.0392
0.0023
0.0000!
0.004
0.0108
0.0032
0.0031
0.0074
0.0013!
0.0003!
0.0010!
0.0019!
0.963
0.0004!
0.0000!
0.0000!
0.0005!
0.0000!
0.007
0.0000!
66
57.5
1.31
15.9
9.84
0.197
4.63
5.56
3.19
1.33
0.33
99.79
<0.01
0.0033
0.0242
0.0132
0.0020!
0.0001!
0.0249
0.0027
0.0020!
0.0027!
0.0069
0.002
0.0025
0.0219
0.0028!
0.0049
0.0007!
0.0052
0.005!
0.0000!
0.0000!
0.0000!
0.0000!
0.0002!
0.004!
0.0000!
67
73.4
0.481
13.5
2.83
0.063
1.85
1.31
5.75
0.479
0.081
99.74
<0.01
0.0014
0.0089
0.0094
0.0016!
0.0005!
0.05
0.0019!
0.0000!
0.0051
0.011
0.0034
0.0035
0.0026!
0.0010!
0.0001!
0.0000!
0.0031
0.002!
0.0000!
0.0000!
0.0000!
0.0002!
0.0001!
0.004!
0.0004!
68
66.6
0.855
15.9
4.49
0.089
2.74
2.48
5.74
0.647
0.241
99.78
0.02
0.0022
0.0075
0.0107
0.0030!
0.0004!
0.0412
0.0018!
0.0004!
0.0039
0.0101
0.0031
0.0041
0.008
0.0010!
0.0007!
0.0000!
0.0033
0.007!
0.0000!
0.0000!
0.0000!
0.0000!
0.0003!
0.005!
0.0000!
69
61.8
0.69
15.3
5.98
0.087
5.64
4.77
4.3
0.908
0.18
99.66
<0.01
0.0026
0.0338
0.0612
0.0033
0.0003!
0.0166
0.0019!
0.0010!
0.0026!
0.006
0.0011
0.0012
0.0127
0.0274
0.0157
0.0034
0.0076
0.006!
0.0003!
0.0000!
0.0000!
0.0183
0.0003!
0.005!
0.0000!
Appendix 1 Continued
65
58.6
1.84
15.3
8.98
0.144
3.44
7.32
3.25
0.444
0.456
99.77
<0.01
0.0017
0.0023
0.0261
0.0025!
0.0002!
0.0288
0.0023
0.0018!
0.0027!
0.0077
0.0024
0.0035
0.0265
0.0015!
0.0012!
0.0009!
0.0051
0.005!
0.0001!
0.0000!
0.0000!
0.0000!
0.0000!
0.004!
0.0000!
70
61.6
0.699
15.2
6.21
0.093
5.88
4.71
4.15
0.969
0.176
99.69
<0.01
0.0031
0.037
0.0655
0.0041
0.0001!
0.0162
0.0025
0.0008!
0.0020!
0.0067
0.001
0.0013
0.0126
0.0282
0.0173
0.0014!
0.0074
0.004!
0.0001!
0.0000!
0.0000!
0.029
0.0004!
0.005!
0.0000!
71
65.5
0.883
15.8
5.34
0.047
2.07
3.28
4.02
2.11
0.285
99.34
<0.01
0.0058
0.0458
0.0698
0.0024!
0.0005!
0.0234
0.0029
0.0000!
0.0047
0.0108
0.0023
0.0015
0.013
0.0069
0.0034
0.0049
0.0063
0.037
0.0003!
0.0000!
0.0000!
0.0004!
0.0003!
0.006
0.0000!
72
67.6
0.661
14.9
5.94
0.075
2.33
1.58
3.46
3.04
0.142
99.73
<0.01
0.015
0.0495
0.0253
0.0036
0.0007!
0.0143
0.0025
0.0009!
0.0027!
0.0078
0.0013
0.0023
0.0109
0.0104
0.0045
0.0038
0.0096
0.012
0.0002!
0.0000!
0.0000!
0.0000!
0.0000!
0.006!
0.0000!
73
59.7
0.765
16.7
8.54
0.061
3.71
0.959
2.22
3.67
0.154
96.48
<0.01
0.0179
0.0506
0.0159
0.0045
0.0007!
0.0151
0.0029
0.0015!
0.0034
0.0072
0.0015
0.0026
0.0175
0.0149
0.0079
0.0074
0.0153
0.014
0.0004!
0.0000!
0.0000!
0.0003!
0.0004!
0.074
0.0001!
74
81.6
0.246
8.91
2.28
0.03
0.7
0.699
1.92
3.25
0.072
99.71
0.03
0.0081
0.0824
0.0169
0.0048
0.0005!
0.0144
0.0015!
0.0000!
0.0023!
0.0073
0.0007!
0.0013
0.005
0.0057
0.0024
0.0002!
0.0055
0.002!
0.0000!
0.0000!
0.0000!
0.0012!
0.0000!
0.005!
0.0000!
79
Sc
Rb
Pr
Nd
Nb
Lu
La
Ho
Gd
Eu
Er
Dy
Ce
4.94
8.6
44.1
7.16
25.7
20.8
0.38
30.9
0.75
4.64
1.21
2.34
3.86
63.5
6
3.98
25.7
30.3
4.37
16.9
13.3
0.31
16.7
0.78
4.27
1.32
2.25
3.87
35.7
7
3.21
30.2
2.13
2.89
12.9
13.9
0.29
8.07
0.71
3.65
1.01
2.04
3.56
20.4
27
3.98
25.4
0.49
3.51
15.7
6.97
0.24
10.1
0.78
4.59
1.19
2.14
3.9
24.2
28
5.02
32.5
9.2
5.52
22.2
15.5
0.3
17
0.86
4.79
1.59
2.38
4.55
40.4
30
9.31
14.4
157
14.7
56
13
0.22
57.2
0.7
7.24
2.4
1.97
3.84
118
31
6.26
23.7
206
9.34
33.5
12.5
0.37
40.6
0.86
5.1
1.17
2.43
4.44
77.6
32
10.7
15
86.9
16.4
61.5
14
0.22
63.5
0.68
7.79
2.76
1.74
3.89
134
33
5.1
10.5
117
7.72
28.1
10.6
0.28
32.1
0.65
4.75
1.04
1.89
3.31
64.8
36
5.31
15.1
133
7.63
29.4
9.01
0.26
32.8
0.69
4.62
1.02
1.85
3.44
66.6
39
6.89
18
159
10.4
36.5
14
0.34
44.7
0.87
5.81
1.18
2.32
4.53
87
41
5.5
21.7
30.7
7.13
27.3
16.7
0.35
29
0.88
5.17
1.69
2.56
4.41
59.9
66
6.88
11.8
21.3
9.47
35.7
25.2
0.53
41
1.24
6.93
1.77
3.64
6.26
83.1
68
1.12
4.93
8.57
51.4
8.56
30
18.1
0.15
40.3
0.43
4.01
1.37
1.23
2.42
77.5
71
0.66
0.81
5.32
22.5
161
7.32
27.1
10.7
0.29
31.1
0.76
4.54
1.08
2.05
3.88
62.4
73
0.4
3.13
5.42
73.9
4.8
17.4
4.75
0.16
21.3
0.38
2.72
0.59
1.03
2
41.8
74
Appendix 2 Geochemical compositions of selected rocks in the Viholanniemi area. Elements
are in ppm. Samplins sites are presented at App.4.
Sm
0.54
0.38
1.65
0.17
6.13
1.09
0.29
8.84
1.04
0.18
5.4
0.82
0.55
5.29
0.95
0.38
2.52
0.83
0.35
14.4
0.66
8.86
0.61
0.28
0.6
8.84
0.77
0.25
0.98
6.17
0.65
0.22
0.78
10.9
0.97
0.36
0.85
6.5
0.73
0.26
0.73
1.4
0.96
0.35
0.66
1.01
0.44
0.28
11.9
1.84
0.57
0.76
22.5
2.95
0.9
0.3
2.52
0.65
1.93
14.1
0.89
0.33
2.14
0.71
6.51
39.6
1.58
0.35
0.89
Ta
Th
27.3
Tb
Tm
26
115
1.04
3.49
2.09
20.6
134
2.28
1.09
20.2
198
3.18
3.44
20.9
353
3.63
2.41
25.5
194
3.56
169
2.27
3.53
175
1.77
20.9
218
1.76
24.3
173
1.47
0.59
140
2.68
22.1
1.7
0.37
178
21.1
2.26
0.3
120
23
78.2
1.86
0.74
76.6
1.9
23.4
161
2.03
2.14
261
2.44
U
Yb
Y
Zr
80
1
<1.0
<30
0.94
<0.5
5
<5
8
3.45
1.23
327
<5
5
1310
<10
<0.01
10.7
2490
20
90
<10
<25
<50
<50
2
<1.0
<30
1.38
<0.5
16
5
5
3.78
1.51
226
<5
7
4120
<10
<0.01
9.3
2860
120
75
<10
<25
<50
<50
3
2.6
<30
1.03
<0.5
31
8
46
4.79
1.86
1030
<5
32
1420
<10
<0.01
6.3
3950
145
97
<10
<25
<50
<50
4
<1.0
<30
1.97
<0.5
28
7
61
4.25
1.54
1360
<5
27
1260
<10
<0.01
13.6
3400
150
73
<10
<25
<50
<50
5
<1.0
<30
0.41
<0.5
14
7
6
3.78
0.91
438
<5
11
1270
<10
<0.01
3.3
2900
96
75
11
<25
<50
<50
6
1.2
<30
0.21
<0.5
13
8
22
2.84
0.98
535
<5
17
785
<10
<0.01
<2.0
2930
44
120
<10
<25
<50
<50
7
<1.0
<30
0.92
<0.5
19
6
161
3.04
1.12
347
<5
14
1200
<10
0.03
4.5
2680
144
49
<10
<25
<50
<50
8
1.6
<30
1.02
<0.5
18
6
70
3.8
1.89
991
<5
10
1020
15
0.19
19.2
3830
96
133
<10
<25
<50
<50
9
<1.0
<30
0.34
<0.5
6
<5
31
1.15
0.69
851
<5
4
185
<10
0.02
4
885
<5
28
<10
<25
<50
<50
10
<1.0
<30
1.83
<0.5
27
13
29
6.4
2.74
1230
<5
9
3880
<10
0.05
16.6
6180
148
184
<10
<25
<50
<50
11
1.5
<30
0.32
<0.5
4
5
38
2.52
0.25
320
<5
8
239
<10
0.04
4.2
541
<5
44
<10
<25
<50
<50
12
<1.0
<30
0.27
<0.5
18
12
10
6.79
2.29
958
<5
9
1400
<10
<0.01
<2.0
5090
255
291
<10
<25
<50
<50
13
<1.0
<30
0.57
<0.5
2
,5
7
0.53
0.16
216
<5
3
192
<10
<0.01
13.9
98
<5
31
<10
<25
<50
<50
14
<1.0
<30
1.55
<0.5
13
17
49
1.52
1.13
617
<5
12
907
<10
<0.01
34.5
2660
53
179
<10
<25
<50
<50
15
<1.0
<30
1.11
<0.5
26
11
35
4.32
1.33
625
<5
11
1010
20
<0.01
26.1
2000
171
256
<10
<25
<50
<50
16
<1.0
<30
1.57
<0.5
16
7
14
3.16
1.19
449
<5
20
1240
<10
<0.01
43.6
3350
88
55
<10
<25
<50
<50
17
<1.0
<30
3.91
<0.5
11
<5
1990
3.27
0.33
1330
<5
7
1130
<10
0.06
74.6
3090
72
34
<10
<25
<50
<50
18
5.9
<30
1.24
1.6
22
10
7250
4.87
1.28
1010
<5
11
721
31
0.61
45.5
2030
169
295
<10
<25
<50
1360
19
<1.0
<30
0.3
<0.5
4
<5
39
1.5
0.47
349
<5
2
150
<10
<0.01
17.1
831
5
30
<10
<25
<50
<50
Appendix 3 Geochemical compositions of rocks in the Viholanniemi area. Ca, Fe, Mg and S in
wt%; Au, Pd, Pt, Te in ppb; others in ppm.Sampling sites are presented in App.4.
Ag
As
Ca
Cd
Co
Cr
Cu
Fe
Mg
Mn
Mo
Ni
P
Pb
S
Sr
Ti
V
Zn
Au
Pd
Pt
Te
81
<1.0
20
<1.0
21
<1.0
22
<1.0
23
4.8
24
<1.0
25
<1.0
26
<1.0
27
6.91
<30
<1.0
28
1.71
<30
<1.0
29
2.36
<30
<1.0
30
0.53
<30
<1.0
31
0.07
<30
<1.0
32
2.18
<30
<1.0
33
0.13
<30
<1.0
34
0.16
<30
<1.0
35
0.1
<30
<1.0
36
0.18
<30
<1.0
37
<30
<1.0
38
Appendix 3 Continued.
Ag
<30
0.16
5.72
14
<0.5
<30
18
<0.5
2.99
8
<0.5
<30
24
1.8
2.01
12
<0.5
<30
25
<0.5
1.41
17
<0.5
<30
23
<0.5
3.18
20
<0.5
<30
22
<0.5
0.18
19
<0.5
<30
18
<0.5
0.27
17
<0.5
<30
8
<0.5
0.92
11
<0.5
Ca
17
<0.5
As
6
23
112
<0.5
133
12
40
<0.5
77
32
28
<0.5
26
Cd
73
Co
47
3.23
24
381
1.21
18
439
1.45
33
<5
162
<5
685
17
123
0.49
47
<10
14
<5
826
<5
361
1.52
24
<10
<5
<5
508
15
247
1.19
91
<10
4.4
0.12
<5
<5
640
4.8
0.15
<5
368
1.54
39
<10
0.04
10
219
1.62
<5
637
<2.0
85
2600
Cr
<5
44
<10
2.34
3100
45
37
64
12
2490
<2.0
1990
100
<10
3.74
370
1.97
557
3.9
1.45
804
29
69
<25
10
<5
<10
502
0.37
642
198
52
<10
<50
2.13
428
1.11
44
0.06
2210
28
241
<10
<25
<50
149
<5
<10
2080
<2.0
97
52
<10
<25
<50
<50
3.68
379
1.24
17
0.34
2460
74
<10
29
<50
<50
62
1.1
<5
<10
1440
22.6
80
<10
<25
123
<50
2.85
510
25
0.02
2440
138
<25
68
<50
79
431
0.52
<5
<10
1590
28.7
141
<10
<50
3.67
<5
150
0.02
4090
115
<25
<50
46
945
0.71
42
<10
1120
23.3
130
<10
<50
4.94
<5
722
0.04
3630
44
<25
<50
72
566
0.31
19
<10
81.7
135
<10
<50
5.08
<5
873
0.03
1260
56
<25
<50
216
4
<10
41.4
47
<10
<50
3.47
398
0.43
241
0.04
2000
15
<25
<50
248
946
0.62
<5
<10
18.2
49
<10
<50
3.76
0.59
<5
8
0.03
2720
9
<25
<50
72
1010
19
<10
1180
18.3
90
<10
<50
1.74
1.52
<5
752
0.2
489
152
<25
<50
88
1050
2
<10
17.5
15
<10
<50
1.32
<5
136
0.02
1680
38
<25
<50
51
788
2.84
3
<10
19.4
32
<10
<50
3.15
Mg
965
1590
63
<25
<50
153
Mn
<5
<10
2.4
0.01
58
<10
<50
1.78
Mo
14
0.01
473
88
<25
<50
3.46
Ni
<10
1440
<2.0
<5
<10
<50
1020
P
3620
33
<25
<50
18
Pb
8.5
0.04
18
<10
<50
3.74
S
4460
154
<25
<50
35
Sr
119
<10
<50
1.29
Ti
277
<25
<50
22
V
<10
<50
4.29
Zn
<25
<50
5.9
Au
<50
554
Pd
<50
Fe
Pt
Cu
Te
82
<1.0
39
1.87
<30
<1.0
40
0.04
<30
<1.0
41
3.09
<30
<1.0
42
0.34
<30
<1.0
43
0.65
<30
<1.0
44
0.36
<30
<1.0
45
0.83
<30
<1.0
46
0.28
<30
<1.0
47
0.24
<30
1.1
48
1.35
<30
<1.0
49
0.39
<30
<1.0
50
0.53
<30
<1.0
51
0.25
<30
<1.0
52
0.62
<30
<1.0
53
1.21
<30
<1.0
54
0.86
<30
6.2
55
0.66
<30
<1.0
56
<30
<1.0
57
Appendix 3 Continued.
Ag
<30
0.46
0.12
12
<0.5
Ca
21
<0.5
As
28
18
<5
<0.5
13
20
15
1.8
11
4.04
7
847
<0.5
8
4.87
7
8
<0.5
<5
4.22
5
4
<0.5
<5
2.43
11
13
<0.5
<5
1.79
13
11
<0.5
8
2.8
12
16
1.6
9
2.8
7
59
<0.5
9
3.37
17
93
<0.5
<5
3.16
19
93
<0.5
37
1.84
2
17
<0.5
13
2.98
6
9
<0.5
<5
4.16
20
13
<0.5
<5
0.42
10
27
<0.5
97
2.01
15
162
<0.5
84
1.73
17
17
<0.5
22
4.55
Cd
87
72
Co
Cr
1.89
3.42
9
438
0.97
3.91
567
2.07
Fe
833
2.09
Cu
638
3
<5
1.47
<5
949
295
<5
27
<10
0.71
<5
17
<10
1180
725
<5
5
<10
1130
1.38
<5
2
<10
1890
696
3
<10
1010
0.74
<5
424
443
2
<10
1.02
<5
387
578
9
<10
1.17
<5
580
361
11
<10
1.01
7
692
282
<5
13
<10
0.52
2
13
660
484
<5
251
1.32
<5
44
<10
639
<5
13
<10
1200
2.36
2
<10
1040
295
<5
157
0.06
5
<10
468
<5
265
0.84
132
<10
231
<5
693
0.84
26
<10
367
<5
411
1.51
20
<10
7
<0.01
443
<5
529
13.8
<0.01
0.76
35
<10
16.1
0.04
441
Mo
639
18.8
<0.01
1.66
Ni
<10
15.5
<0.01
Mg
P
3.4
<0.01
Mn
Pb
5.2
<0.01
36
2080
11.4
1560
24
<0.01
2490
75
<10
36.2
2270
157
63
<25
0.04
1340
131
71
<10
<50
2.0
974
33
75
<10
<25
<50
0.98
1090
7
8
<10
<25
<50
<50
3.6
1890
7
76
<10
<25
<50
<50
<0.01
1860
33
15
<10
<25
<50
<50
8.7
1290
37
16
<10
<25
<50
<50
<0.01
287
34
17
<10
<25
<50
<50
4.1
1330
<5
12
<10
<25
<50
<50
<0.01
1990
93
8
13
<25
<50
<50
9.9
24
98
29
<10
<25
<50
<50
<0.01
1120
<5
55
<10
<25
224
<50
3.9
1290
8
16
<10
<25
<50
<50
<0.01
3250
49
76
<10
<25
<50
<50
308
2170
99
13
<10
<25
<50
<50
0.14
3360
97
104
<10
<25
<50
<50
7.4
103
42
<10
<25
<50
<50
0.03
Ti
70
<10
<25
<50
<50
8.9
V
<10
<25
<50
<50
<0.01
Zn
<25
<50
<50
3.8
Au
<50
<0.01
Pd
<50
S
Pt
Sr
Te
83
As
Ag
1.14
<30
<1.0
58
1
<30
<1.0
59
1.14
<30
<1.0
60
0.43
<30
<1.0
61
1
<30
<1.0
62
0.24
<30
<1.0
63
0.37
<30
<1.0
64
1.94
<30
<1.0
65
1.24
<30
<1.0
66
0.2
<30
<1.0
67
0.34
<30
<1.0
68
0.33
171
<1.0
69
0.33
281
<1.0
70
0.33
<30
<1.0
71
0.12
<30
<1.0
72
0.13
<30
<1.0
73
6
<0.5
0.14
<30
<1.0
74
Appendix 3 Continued
Ca
23
9
38
<0.5
62
129
19
85
0.43
1.73
<0.5
80
2.03
5.45
13
57
3.88
<0.5
48
1.37
19
3.45
<0.5
17
158
1.18
16
1.42
<0.5
35
144
1.21
11
1.31
<0.5
12
<5
1.08
7
9
<5
1.5
2.77
<0.5
1.84
23
19
20
1.07
<0.5
5
5.06
15
17
2.07
<0.5
3.54
11
14
<5
1.02
<0.5
18
<5
0.9
3.57
9
2.16
<0.5
15
<5
1.92
7
1.7
<0.5
11
<5
0.73
<5
208
7
2.4
<5
382
<0.5
12
27
0.73
<5
466
12
9
3.01
<5
283
<0.5
12
1.57
83
10
2.13
<5
<0.5
88
20
1.26
77
22
Cr
3.85
<5
<0.5
Cu
1.48
<5
413
Cd
Fe
<5
337
Co
Mg
<5
23
668
312
<5
75
<10
507
46
683
<0.01
<5
34
521
<10
239
104
1170
<0.01
<5
92
742
<10
942
3
745
0.01
<5
2
959
<10
753
41
363
0.03
<5
6
1400
<10
368
<2
1820
<0.01
<5
2
925
<10
575
3
493
<0.01
<5
<2
412
<10
545
35
450
<0.01
<5
21
1200
<10
530
43
888
<0.01
Mn
Ni
1530
<10
Mo
P
<0.01
5.4
<10
1100
<0.01
<2.0
<10
3980
1.15
4.3
15
3280
<0.01
25.4
14
3620
<0.01
24.2
<10
1960
<0.01
21.6
<10
1850
<0.01
<2.0
<10
1550
<0.01
2.2
<10
1140
<0.01
20.7
S
2990
Pb
53.9
44
45
2980
125
153
4.5
80
93
1900
92
3.8
116
1100
20
65
12.5
15
62
1290
19
35
2.7
17
10
730
32
151
28.6
20
120
2000
11
38
27.2
10
1700
210
11.6
7
1940
51
Ti
7
Sr
16
<25
<10
26
<25
<10
76
<25
<10
21
<25
<10
61
<25
<10
28
<25
<10
126
<25
<10
V
<25
<10
Zn
<25
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
<25
<50
<50
<10
<50
<50
Pd
Pt
Au
Te
84
Appendix 4 Sample sites and rock types.
SAMPLE
LOCATION
X
Y
1
hvm-85-33.1
viholanniemi
6893.850
3541.550
ROCK TYPE
felsic
2
hvm-85-33.2
viholanniemi
6893.850
3541.550
intermediate
3
hvm-85-32.1
viholanniemi
6893.400
3541.290
felsic
4
hvm-85-32.2
viholanniemi
6893.400
3541.290
intermediate
5
hvm-85-24.1
viholanniemi
6893.300
3541.250
intermediate
6
hvm-85-11.1
viholanniemi
6893.290
3541.120
felsic
7
hvm-85-11.2
viholanniemi
6893.290
3541.116
intermediate
8
hvm-85-3.1
viholanniemi
6893.170
3541.210
felsic
9
hvm-85-2.2
viholanniemi
6893.112
3541.230
felsic
10
hvm-85-2.3
viholanniemi
6893.112
3541.228
intermediate
11
hvm-85-37.a.1
viholanniemi
6891.430
3540.330
felsic
12
hvm-85-37.b.1
viholanniemi
6891.390
3540.330
intermediate
13
hvm-86-24.1
viholanniemi
6891.110
3540.085
felsic
14
hvm-86-24.2
viholanniemi
6891.110
3540.055
mafic
15
hvm-86-24.3
viholanniemi
6891.110
3540.035
mafic
16
hvm-86-24.4
viholanniemi
6891.170
3539.910
mafic
17
hvm-86-24.5a
viholanniemi
6891.180
3539.925
mafic
18
hvm-86-24.5b
viholanniemi
6891.180
3539.925
mafic
19
hvm-86-26.1
viholanniemi
6891.050
3539.900
felsic
20
hvm-86-29.1
viholanniemi
6890.900
3540.160
mafic
21
xz-97-13.1
viholanniemi
6891.240
3540.320
felsic
22
xz-97-17.1
viholanniemi
6890.360
3540.300
felsic
23
xz-97-18.1
viholanniemi
6890.650
3541.245
felsic
24
xz-97-18.2
viholanniemi
6890.650
3541.245
felsic
25
xz-97-18.3
viholanniemi
6890.650
3541.245
felsic
26
xz-97-18.4
viholanniemi
6890.615
3541.230
felsic
27
xz-97-4.1
lahnalahti
6888.680
3541.520
mafic
28
xz-97-4.2
lahnalahti
6888.680
3541.520
mafic
29
xz-97-9.1
lahnalahti
6889.380
3540.360
mafic
30
xz-97-8.1
lahnalahti
6888.750
3540.560
mafic
31
xz-97-5.1
joroisniemi
6892.685
3544.190
graywacke
32
xz-97-5.2
joroisniemi
6892.665
3544.200
pellitic
33
xz-97-5.3
joroisniemi
6892.700
3544.190
intermediate
34
xz-97-6.1
joroisniemi
6892.910
3546.030
sedimentary
35
xz-97-6.2
joroisniemi
6892.910
3546.030
sedimentary
36
xz-97-7.1
joroisniemi
6892.020
3545.540
sedimentary
37
xz-97-14.1
kotkatlahti
6888.280
3544.380
sedimentary
38
xz-97-14.2
kotkatlahti
6888.280
3544.380
sedimentary
39
xz-97-19.1
katajamäki
6889.730
3536.840
gneiss
40
xz-97-20.1
katajamäki
6888.700
3537.700
mafic
41
xz-97-21.1
katajamäki
6887.920
3538.260
gneiss
42
xz-97-22.1
katajamäki
6886.500
3539.540
mafic
43
r306/20.40
viholanniemi
felsic
44
r306/174.45
viholanniemi
felsic
45
r310/11.85
viholanniemi
felsic
46
r310/41.70
viholanniemi
intermediate
85
Appendix 4 Continued.
47
r310/79.35
viholanniemi
felsic
48
r310/118.75
viholanniemi
felsic
49
r310/135.40
viholanniemi
felsic
50
r310/162.55
viholanniemi
felsic
51
r311/11.00
viholanniemi
felsic
52
r311/31.80
viholanniemi
felsic
53
r311/51.70
viholanniemi
felsic
54
r311/70.70
viholanniemi
intermediate
55
r311/88.65
viholanniemi
intermediate
56
r311/109.65
viholanniemi
intermediate
57
r311/128.90
viholanniemi
felsic
58
r311/140.80
viholanniemi
intermediate
59
r312/24.70
viholanniemi
felsic
60
r312/42.70
viholanniemi
intermediate
61
r312/68.15
viholanniemi
felsic
62
r312/81.40
viholanniemi
felsic(gr)
63
r312/84.40
viholanniemi
felsic
64
r312/103.60
viholanniemi
felsic
65
r312/122.10
viholanniemi
intermediate
66
r312/142.30
viholanniemi
intermediate
67
r312/164.10
viholanniemi
felsic
68
r312/183.15
viholanniemi
felsic
69
r321/7.50
pirilä
intermediate
70
r321/12.85
pirilä
intermediate
71
r321/132.00
pirilä
felsic
72
r321/204.10
pirilä
mic schist
73
r359/38.15
pirilä
mic schist
74
r359/234.00
pirilä
felsic
86
PART II
II
Boulder prospecting and till geochemistry in the search for
zinc (gold) ore in the Viholanniemi area,
South-eastern Finland
Xiping Zhang
Abstract: Preglacial weathering proved to be intense in the study area and also the weathering
products variated but were well preserved in the bottommost layers immediately above the bedrock.
As a result of transportation and deposition, but not very much erosion of the last glacial processes,
the till in the bottommost layer has a high proportion of local material in the Viholanniemi area.
The fines of till and weathered bedrock have identical mineral composition. They contain
primary rock-forming minerals such as quartz, albite/microcline, hornblende/tremolite, muscovite/
phlogopite, calcite; clay minerals such as chlorite in general, as well as some ore minerals including
sphalerite, pyrite and magnetite in the mineralized sites. The chemical composition of till shows
some similarities to that of weathered and unweathered bedrock. Elements Na and Ca were
removed during the decomposition of primary minerals and the formation of clay minerals, but Al,
Na, Ca were enriched in till. Fe, Mg, Mn, P might be partly lost during the weathering. The mode of
occurrence of trace elements Zn, Cu, Pb, Au, Ag, Ni and Co in till in the non-anomalous area is due
to the adsorption onto clay minerals, secondary oxides and hydroxides, but high concentrations of
those elements in the area are related mainly to the residual ore minerals.
Till geochemical prospecting showed a clear and coherent anomalous distribution pattern of Zn,
Ag, Au, Pb, Cu, Ni and Co that reflect the Viholanniemi Zn(Au) ore occurrences well. Ag and Zn
are the best indicators of the ore occurrences. The anomalies proved to be local and related to the
deposit.
Introduction
Boulder prospecting and till geochemical exploration in the glaciated terrains of
Fennoscandia, Canada and mountainous areas of South America have long been
extensively adopted and proved to be very effective tools in prospecting for mineral
deposits since the beginning of the 20th century (Peuraniemi 1982,1990a, Ekdahl 1982,
Stigzelius 1987, Koljonen 1992, Saltikoff 1992, McClenaghan et al. 1993, 1997,
McClenaghan 1994, Gustavsson et al. 1994, Salminen & Tarvainen 1995, Salminen
1995, Klassen 1997). The famous Outokumpu Cu-Ni-Co deposit in Finland was found by
boulder tracing and also the earliest Finnish till geochemical investigation was carried out
there (Kauranne 1951, 1959, Stigzelius 1987, Koljonen 1992, Saltikoff 1992).
Unlike other geochemical methods, till geochemical prospecting needs knowledge of
the glacial history, morainic landforms as well as till characteristics, i.e. Quaternary
framework (Klassen & Murton 1996). The erosion, entrainment, transportation and
depositional history, and the resulting composition of sediments are the crucial factors,
not only in the sampling and analysis of glacial sediments (McClenaghan et al. 1997), but
also in the interpretation of prospecting results. A detailed investigation of the glacial
history, and especially of the ice movement directions is the only way that can lead to the
source.
89
II
The Viholanniemi Zn-Au deposit is located about 5 km southwest of the Joroinen
village, in south-eastern Finland (Fig. 1, 4) and the flat terrain in the area consists mainly
of till. From the year 1985 to 1988, exploration in the Viholanniemi area including
boulder tracing, till geochemical exploration, bedrock mapping and drilling was carried
out by the Geological Survey of Finland (GTK) (Makkonen 1991, unpublished research
report). The main objective of the present study is to make further investigation of the till
geochemistry, and in connection with ore prospecting, to make the plausible
interpretations of till geochemical survey in the area. All the samples and data involved in
the study were provided by GTK.
Bedrock geology
The Viholanniemi area is within the Raahe- Ladoga zone, which forms part of the so
called Savo schist belt (Fig. 1), a transition belt between the Svecofennian and Karelian
supracrustal domains in Finland (Vaasjoki & Sakko 1988, Ekdahl 1993). The bedrock is
composed mainly of meta-volcanics, metasediments and granitoids with the strike of
NNW-SSE to NW-SE. The volcanics are chiefly felsic-intermediate pyroclastics with thin
mafic intercalations in the northern and central part of the area. In the southern part, there
occur more mafic volcanics which have been metamorphosed to amphibolite. Also pillow
lava can be found there. Mica schist and turbidity greywacke occur in the eastern part,
and granite, granite gneiss and mylonite (Papunen 1990) in the western and south-western
part. Sericitization, disseminated pyrite are widespread in volcanics especially in felsicintermediate volcanics; in mafic volcanics epidotization is general.
The sulphide Zn-Au mineralizations were observed to be associated mainly with
felsic-intermediate pyroclastics and the host rocks are quartz-carbonate-tremolite veins
and lenses, that can be called the skarn-like rock, as well as felsic (- intermediate)
volcanics with sericitization, carbonatization and pyritization. Ore mineralization occurs
as two main parts: the northern and southern ore occurrences having about NW-SE trends.
The average contents of metals in the ore bodies are as follows: southern ore-body: Zn
2.31%, Cu 0.19%, Pb <0.1%, Au 0.7 ppm, Ag 26 ppm; northern ore body: Zn 1.97%, Cu
0.12%, Pb 0.64%, Au 1.11 ppm, Ag 105 ppm (Makkonen 1991).
Postglacial weathering resulted in the pale surface of the bedrocks and the colour
change in the surficial parts of the drift. Preglacial weathering however, had affected
greatly both the bedrock and glacial deposits as it was throughout Finland. For example,
the occurrences of weathered bedrock have been found immediately underlying
Pleistocene till deposits all over Finland and the entire eastern part of Fennoscandia had
been covered by an old weathering crust before the Pleistocene glaciations (see Nenonen
1995). As a result of intense preglacial chemical weathering, the occurrences of Kaolin
and other clay minerals have been found in many places in Finland (Peuraniemi 1990c,
Peuraniemi et al. 1993, 1997, Saarnisto & Salonen 1995, Lintinen 1995, Nenonen 1995,
Sarapää 1996).
90
II
Fig. 1. Location of the study area on the geological map of Finland (simplified after the bedrock
map of Finland 1:1 000 000, Korsman et al. 1997).
In the study area, Niemelä (unpublished research report 1992) observed the kaolin
occurrences at Tervajoensuo and also at places around Virtasalmi (also see Nenonen
1995, Sarapää 1996). In order to confirm the observation, some samples were re-analysed
by X-ray diffraction (Siemens Diffractometer D5000), differential thermal (DTA) and
thermogravimetric(TGA) techniques (Netzsch Simultaneous Thermal Analyzer STA 409
Ep) at the University of Oulu. The XRD traces and DTA curves of samples are shown in
Figs 2-3. Kaolinite gives two XRD peaks at 7.1 and 3.5Å (Fig. 2) and typical DTA curves
(Norton 1939, Huang 1987) with a sharp endothermic peak at 520-530 oC and exothermic
peak at 990-1000 oC (Fig. 3), and is amorphous or less crystallized (Huang 1987). It is
also possible that kaolinite was formed mainly by the weathering of plagioclase because
the latter can not be detected in the case of the presence of kaolinite (Fig. 2 a,b,d) but is
detectable in the absence of kaolinite (Fig. 2 c). From the TG curves showing about 3%7% weight loss it can be estimated that the total content of water bearing secondary
minerals in the weathered bedrock is not very high.
91
II
Fig. 2. X-ray diffraction traces of fines of the weathered bedrock samples from Viholanniemi.
Mc=muscovite, K=kaolinite, Ch=chlorite, Q=quartz, M=microcline, Ab=albite, a=R374/12.8m13.8m, b=R248/13.4m-14.5m, c=R373/17.8m-18.4m, d=R373/10.8m-12.8m.
Fig. 3. DTA-TGA graphs of fines of the weathered
bedrock samples from Viholanniemi. Solid line=DTA,
dashed line=TGA, a=R373/10.8m-12.8, b=R248/13.4m14.5m, c=R374/12.8m-13.8m.
92
II
Glacial geology and boulder prospecting
The study area belongs to the area covered by the activity of the Finnish Lake District Ice
Lobe during the Later Weichselian Deglaciation (Punkari 1980, Glückert 1987, Salonen
1986). According to Saarnisto and Salonen (1995), there was a long ice-free period in
southern and central Finland in the Early Weichselian period. During the deglaciation of
southern and central Finland, the ice sheet was divided into six different ice lobes
(Punkari 1979, 1980). An actively flowing ice of the Finnish Lake District Lobe flowed
towards the Salpausselka ice-marginal belt and created strong drumlinisation (Glückert
1987). The Pieksamäki drumlin field (Glückert 1987) inside of the former ice lobe with
11000 drumlins is one of the largest in the world. The Viholanniemi area is a part of the
drumlin field (Fig. 4, 5).
Fig. 4. Ice lobes of the Scandinavian ice
sheet in Finland during deglaciation
(from Nenonen 1995). Fan shaped lines
indicate major ice flow directions.
Location of Viholanniemi area is
outlined by rectangle.
The drumlins have been extensively investigated in Finland by Aario et al. (1974,
1979a,b, 1990a, 1992), Glückert (1987), Salonen (1987), Peuraniemi (1990a), Nenonen
(1995) and many others.
Till sampling carried out by GTK during 1986-1987 (Makkonen 1991) indicated that
the thickness of till in the Viholanniemi project area can reach 16 m. The thickness of till
varies greatly and the drumlins in the study area appear often to be rock- cored. The
ridges of those drumlins have the same trend of NW-SE. This direction is related to the
ice movement direction of the last advance of the Weichselian Ice Sheet that moved from
the northwest and north (300-360°) (Glückert 1987).
The first ore-bearing boulders with high concentrations of Zn, Au, Ag, Cu were found
on the west bank of lake Kolkonjärvi, about 20 km southeast of the Viholanniemi deposit.
During the following years of 1984-1985, several boulders which were quartz-carbonate
rocks and felsic volcanics containing sphalerite were found in Pirttiselkä, at the north-
93
II
western end of the Vuotsinsuo mire and the western side of Highway 5 respectively, and,
finally, a sphalerite bearing exposure at Viholanniemi by GTK (Makkonen 1991).
Together with an ore boulder at the west side of the exposure found during the bedrock
mapping, it showed a boulder train that is long and narrow with the length of about 20km
and composed of separate boulder clasters (Fig. 6). It can be estimated from the boulder
train that the direction of ice movement in the area is about 310°. A narrow ore boulder
train about 50 km long at Virtasalmi had been reported by Glückert (1973) (cf., Aario &
Peuraniemi 1992) (Fig. 5). Salonen (1986) also estimated that the boulder transport
distance in drumlin areas is about 5-17 km.
Fig. 5. Copper ore boulder train in a drumlin landscape (after
Glückert 1973 and cf Aario & Peuraniemi 1992) at Virtasalmi in
Pieksämäki drumlin field, central Finland.
Fig. 6. Ore boulder train from Viholanniemi
(modified after Makkonen 1991).
94
II
All the above suggest on the one hand an active ice flow from the northwest (about
310°) with a relatively long transport distance in the study area, and obviously the
dominant transportation and deposition of this ice flow on the other.
Till geochemistry and geochemical exploration
Mineralogy of Till
Extensive research into the mineralogy of till in Finland has been published by
Peuraniemi (1982, 1987, 1990b,c, 1991), Aario and Peuraniemi (1990), Peuraniemi and
Islam (1993), Peuraniemi and Pulkkinen (1993), Lintinen (1995), Peuraniemi et al.
(1997) and also many others. In order to investigate the composition of fines of till in the
area, and then to determine the origin of till material, and also to get a detailed and
reasonable interpretation of the prospecting results, some chosen samples of till and
weathered bedrock were analyzed further by XRF and XRD in the University of Oulu.
The minerals observed in fines of till and weathered bedrock can be classified into
three groups: (1) primary rock-forming minerals; (2) clay minerals; and (3) ore minerals
(Fig. 7, 8).
Fig. 7. X-ray diffraction traces of fines of the till samples from Viholanniemi. H=hornblende,
T=tremolite, Ph=phlogopite, Sp=sphalerite, Ca=calcite, the rest of the symbols are the same as
in Fig. 4.
95
II
Fig. 8. X-ray diffraction traces of fines of the weathered bedrock samples from Viholanniemi.
H=hornblende, T=tremolite, Sp=sphalerite, Py=pyrite, Ma=magnetite, the rest of the symbols
are the same as in Fig. 4.
Rock-forming minerals are quartz, feldspars, amphiboles and micas. The presence of
quartz is shown as peaks at 3.34Å and 4.26Å in almost all the samples studied. Feldspars,
which are also common minerals in the samples, are mainly albite that has the peaks at
3.19Å and sometimes 4.03Å, and microcline that has the peaks at 3.25Å and 3.47Å.
Amphiboles present in some samples appear at 3.12Å and 8.42-8.51Å as hornblende and/
or tremolite. Muscovite was detected on the basis of peaks at 10.1Å, 5.0Å, as well as
3.31Å in some samples and phlogopite was recorded in one sample at 10.1Å and 5.1Å.
Clay mineral detectable in samples is mainly chlorite which was found in some samples
with the d values of 7.1Å, 4.7Å and 3.5Å. From the case of kaolin occurrences showed in
Fig. 2-3, it is clear that the partial resolution of two peaks of kaolinite and chlorite at
3.58Å and 3. 55Å, respectively (Duance & Robert 1989) is present when both of them
were detectable in the samples. It can be inferred that the kaolinite is possibly absent or
undetectable in the samples from the project area although it is present in surroundings
(Niemelä 1992, Sarapää 1996).
Ore minerals found are sphalerite, pyrite and magnetite that could be measured in
some weathered bedrock and till samples. All of the samples were collected in or near the
mineralized sites and the concentrations of base metals in them all are very high. Calcite
was detected in one sample from the mineralized site by its d values of 3.86Å, 3.03Å and
2.46Å (Fig. 7, 30837).
According to the investigations of Finnish tills (Lintinen 1995, Peuraniemi et al. 1993,
1997), the mineral composition of till and its variation are mainly controlled by the
composition of the bedrock from which the till material was derived. The till material in
96
II
the bottommost layer just above the bedrock in the Viholanniemi area shared a high
proportion of local material because the mineral compositions of till and weathered
bedrock in the area are quite the same. Generally, the till material in the higher levels of
the drumlins have been transported far.
Chemical composition
The chemical compositions of the samples studied are listed in tables 1, 2, and 3. They
show that the till has contents of SiO2, K2O and TiO2 similar to that of weathered
bedrock, and the contents of SiO2, Al2O3 and TiO2 similar to that of mainly felsic rocks.
Compared to felsic-intermediate volcanics, the weathered bedrock from the
mineralized area has lower contents of Al, Na, Ca and Ti, but higher of K, Mn and Mg. In
spite of the mixed mineral composition including stable and undecomposed primary
minerals and also secondary minerals (Fig. 7, 8), it is obvious that the removal of the
relatively soluble elements Na and Ca accompanied the formation of clay minerals (see
Rose et al. 1979) during the weathering. Probably, the decomposed mineral is dominantly
plagioclase. This is evident in the XRD traces of samples with kaolin occurrences in Fig.
2 and in their chemical composition. Silicon, Al and K were relatively enriched, whereas
Mg, Fe, Na, Ca, Mn, Ti and P depleted while the kaolinite (and also possible illite)
formed.
On the other hand, the contents of Al, Ca, Na, K and Ti are higher and Fe, Mg, Mn and
P are lower in till compared to the weathered bedrock. This is possibly the result of a
relative gathering of primary minerals including secondary minerals as well as a small
amount of calcite while the leaching of Fe, Mg, Mn and P as soluble products of
weathering. Åström and Björklund (1995) reported the case of extensive leaching and
high concentations of Mg, Mn, Fe in solution in western Finland.
The fact is, however, that the preglacial weathering in the study area was relatively
intense but areally varying, particularly variated and controlled by the rock types and
topographic relief and also drainage (Rose et al. 1979).
The presence of trace elements Zn, Cu, Pb, Ni, as well as Au and Ag in till can be
attributed to the residual primary ore minerals and to their adsorption onto clay minerals
and secondary oxides and hydroxides (Rose et al. 1979, Jenkins et al. 1980). But those
elements in the area of no anomalies are related mainly to biotite/phlogopite, feldspars
and secondary minerals. Peuraniemi (1991) reported gold occurring inside goethite in
Kotkajärvi, southern Finland. Nikkarinen (1991), Lestinen et al. (1991) also cited the
possible supergene gold in Ilomantsi, eastern Finland and Seinäjoki, western Finland.
Dilabio (1985) (see Bernier et al. 1989) has documented gold related to the oxidized
fractions of till in Canada. Almost all of the high concentrations of trace elements in the
study area were detected in the weathered bedrock and only a few till samples had high
trace element contents in the anomalous areas (Table 1, Fig. 7, 8).
97
63.26
73.32
(%)
0.61
0.73
0.42
(%)
12.54
12.23
12.71
12.24
(%)
7.68
5.50
5.45
6.38
2.92
(%)
0.32
0.29
0.23
0.38
0.05
(%)
4.62
3.42
3.01
4.27
1.15
(%)
Al2O3 Fe2O3 MnO MgO
2.53
3.60
2.26
4.24
2.59
(%)
CaO
1.62
2.65
3.00
2.37
3.26
(%)
Na2O
2.10
2.35
2.19
2.50
1.99
(%)
K2 O
0.22
0.17
0.18
0.18
0.13
(%)
P2O5
99
74
16
14.3
Co
Zn
Pb
Ag
Au
17
17.7
6
1985
703
24.7
6158
18.2
6.3
11.3
1.21
0.40
5
2.33
0.667
(ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppb)
24
32.3
105
(%)
SiO2
0.16
0.82
(%)
TiO2
15.80
14.10
13.64
19.68
(%)
Al2O3
1.29
1.75
0.33
1.79
(%)
Fe2O3
0.01
0.02
0.00
0.01
(%)
MnO
1.62
2.60
0.36
1.89
(%)
MgO
0.08
0.04
0.03
0.18
(%)
CaO
0.19
0.33
0.06
0.17
(%)
Na2O
2.51
2.78
2.36
2.38
(%)
K2O
0.03
0.03
0.03
0.04
(%)
P2O5
18.2
1462
68.39
0.18
6.48
17.6
79.38
0.39
41.8
1
75.36
1010
R373/10.8-12.8m
1
74.38
10
26
n
57.8
70.2
(%)
SiO2
1.52
0.63
(%)
TiO2
15.5
13.6
(%)
Al2O3
9.45
4.30
(%)
Fe2O3
0.19
0.12
(%)
MnO
4.46
1.82
(%)
MgO
5.33
2.72
(%)
CaO
4.02
4.34
(%)
Na2O
0.73
1.24
(%)
K 2O
0.40
0.15
(ppm)
P 2O 5
114
61.2
(ppm)
Cu
38.2
7.62
(ppm)
Ni
19.3
9.69
(ppm)
Co
93.4
69
(ppm)
Zn
23.9
24.4
(ppm)
Pb
1.07
0.72
(ppm)
Ag
5
5.11
(ppb)
Au
II
3
65.35
10.90
Table 1. Arithmetic mean and variation of the chemical elements in the till and weathered bedrock samples from the project area.
9
0.60
0.65
Ni
Till from non-anomalous area
2
65.71
Cu
Till from anomaly area
66.21
TiO2
Till from anomaly area
5
14
SiO2
Mean
n
Weathered bedrock from anomaly area
R374/12.8-13.8m
3
1
Table 2. Chemical composition of weathered bedrock with kaolin occurrences.
R248/13.4-14.5m
n
Mean
Felsic rocks
Table 3. Arithmetic means of the chemical elements in the volcanics in Viholanniemi area.
Intermediate rocks
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II
Till geochemical exploration
Till geochemical exploration in Viholanniemi was carried out in the winter of 1986 by
GTK. All samples were taken by a percussion drilling machine (Cobra) and total of 886
samples was collected in an area of about 6 km2. The sampling lines were chosen on the
basis of information shown by outcrops, ore boulders and geophysics. The line distances
were 25, 50 or 200 m, and the sample spacing along the lines 5, 10, 20 or 40 m. Till
material was the main sampling media but the weathered bedrock, sorted materials and
glaciofluvial sand might be taken in some places as the substitution. Sampling always
tried to reach the interface between the till and underlying bedrock. It gave the depths of
0.4-5.4 m. Sample size was small (100-200 g).
Samples were first dried at room temperature in open bags and then in +70oC in the
laboratory. A sieving procedure was not employed, only the large bedrock pieces were
taken away for storing. The rest of the sample was ground in a carbon steel vessel.
Hot aqua regia leaching was adopted for all elements except for Au that was leached
by aqua regia at room temperature before analysis. Cu, Zn, Pb, Co, Ni and Ag were
analysed by atomic absorption spectrometry (AAS) and Au by graphite-furnace atomic
absorption spectrometry (GAAS). Sulphur was determined with a Leco-sulphur-analyser.
Statistical parameters of the metals measured in the till are presented in Table 4. All
elements seem to be positively skewed, amongst which the marked skewness of Zn, Cu
and Pb are notable. It suggests the anomalous distributions of those metals, especially Zn,
Cu and Pb in the project area.
Table 4. Statistical parameters for metals in the till at Viholanniemi (x= arithmetic mean, s
= standard deviation, c = coefficient of variation, n = number of samples).
min
max
x
Co(ppm)
1
54
12
Cu(ppm)
5
8700
75
Ni(ppm)
0.5
439
25
s
c
8.1
0.7
886
431
5.7
886
31
1.3
886
Pb(ppm)
1
12300
26
416
Zn(ppm)
10
11600
129
534
Ag(ppm)
0
127
0.87
Au(ppb)
0
198
2.8
4.5
10 3
16
4.1
n
886
886
5.2
886
6
886
The areal distributions of various metals are presented as maps in Fig. 9-15.
Apparently, all the metals detected show quite clear and coherent anomalous distribution
patterns and the main parts of those patterns reflect well the Zn mineralization sites in the
Viholanniemi area. Anomalous contents are also found outside the presently known
mineralization. The main anomalies have dispersal trends of NW to SE, and the total
length of the anomalous area, which is composed of many different local anomalies, is
about 3.4 km.
The strongest anomalies of almost all elements analysed, except for Pb, were found in
the mineralized areas. Silver and Zn are the best two of all, by which their coherent and
strongest anomaly patterns delineate precisely the ore occurrences and the highest
99
II
contents are 127 and 11600 ppm, respectively. A less coherent anomaly belt of Ag and Zn
parallel to the ore occurrences is located in the eastern part of the area and the highest
contents of them in the belt are 21.4 and 3060 ppm. Pb, Ni and Co have about the same
anomalous patterns of which the main parts not only reflect ore occurrences well, but also
extend north-west from the northern ore occurrence for about 250 m. In addition, Pb, Co
and Ni also show another anomalous belt in the same area with the eastern anomalies of
Ag and Zn. Lead gives its highest content of 12300 ppm there. The anomaly patterns of
Au and Cu can be divided into two parts: the southern part is stronger and corresponds
well to the southern ore occurrences with the highest contents of 198 ppb and 8700 ppm;
the northern part appears as discontinued but widely distributed anomalous points in the
northern area including the northern ore occurrence.
Fig. 9. Map of the areal distribution of zinc concentration in till at Viholanniemi.
It can be deduced that the principal parts of anomalies which reflect well the
mineralized sites are related directly to the ore materials coming from ore bodies of the
Viholanniemi Zn (Au) deposit. In addition, those anomalies did not show evident
displacement. Apparently, the materials from the bottom-most layer of till and the
weathered bedrock have been well preserved. It is consistent with the reflections of till
composition and thus favour the till geochemical prospecting of ore. The practice of
finding a deposit in the area has already corroborated the effectiveness of the till
geochemical survey.
100
II
Fig. 10. Map of the areal distribution of silver concentration in till at Viholanniemi.
.
Fig. 11. Map of the areal distribution of gold concentration in till at Viholanniemi.
101
II
Fig. 12. Map of the areal distribution of copper concentration in till at Viholanniemi.
Fig. 13. Map of the areal distribution of lead concentration in till at Viholanniemi.
102
II
Fig. 14. Map of the areal distribution of cobalt concentration in till at Viholanniemi.
Fig. 15. Map of the areal distribution of nickel concentration in till at Viholanniemi.
103
II
Conclusions and discussion
The ore boulder train in the Viholanniemi area is about 20 km long and composed of
narrow and separate boulder clusters with a direction of about 310°. The trends of
drumlin ridges and also some of the distal axes of lakes in the area are about the same as
the boulder train (Fig. 5, 6). Long and narrow boulder trains are general in the drumlin
fields resulting from an active ice flow. The ice movement direction in the area is about
310°.
Rock-cored drumlins (Glückert 1987) composed of mainly basal till (also see Nenonen
1995) at least at the bottom are dominant in the Viholanniemi area. The preservation of
kaolin occurrences reported by Niemelä (1992) and confirmed by the present study
suggests an intense preglacial chemical weathering and the glacial deposition prevailing
over erosion. The relatively small amount of water-bearing minerals (Fig. 3) and the
compositional variation of weathering products suggest that the intensity of the preglacial
weathering is areally varied. It is also possible that preglacial weathering products are
preserved only in fracture zones where weathering reached deeper down than in the
surroundings (cf. Sarapää 1996).
The fines of till samples from the project area contain primary minerals such as quartz,
microcline, hornblende and/or tremolite, muscovite or phlogopite; clay minerals such as
chlorite. Some till samples collected in the mineralized sites also contain sphalerite, or
pyrite, or magnetite and calcite. The weathered bedrock has about the same mineral
composition as till. It is apparent that minerals which are unsusceptible to weathering or
are undecomposed during the weathering are presented together with the new minerals
such as clay minerals and secondary Fe-Mn minerals (see Tarvainen 1995) in till.
Till and weathered bedrock samples have similar contents of SiO2, K2O and TiO2, and
the similar levels of SiO2, Al2O3 and TiO2 are also obvious between till and unweathered
felsic rocks. During the weathering process, the relatively soluble elements Na, Ca were
removed while rock-forming minerals decomposed and secondary minerals formed (see
Rose et al. 1979). Particularly, Si, Al and K were concentrated, whereas Mg, Fe, Na, Ca,
Mn, Ti and P depleted when kaolinite formed in places. Due to the relative concentration
caused by mixed mineral composition (possibly including carbonates) and the leaching of
Fe, Mg, Mn and P, elements Al, Na and Ca were enriched in till in the project area.
The conclusion is that the till in the bottom-most layer just above the bedrock in the
project area consists mainly of local material, although the till materials in the drumlin
fields are overal far-transported (Glückert 1987, Aario & Peuraniemi 1992).
Trace elements Zn, Cu, Pb, Au, Ag, Ni and Co are related to residual primary minerals
and secondary minerals. The main part of those elements present in till in the nonanomalous area can be attributed mainly to the adsorption onto clay minerals, secondary
oxides and hydroxides. The high contents of those elements in the project area were
detected in weathered bedrock samples and a few till samples, and they are related
directly to the ore material.
Boulder tracing, and till geochemical exploration in the area, proved to be effective in
prospecting for ore. All metals show clear and coherent anomalies in till and well reflect
the Zn mineralization bodies in the Viholanniemi. The anomalies occur as a belt
composed of different local anomalies with a dispersal trend of NW to SE and a total
104
II
length of about 3.4 km. Almost all elements, except Pb have their strongest anomalies just
on or near to ore sub-outcrops. Ag and Zn are the most crucial indicators of ore
occurrences compared to Au, Cu, Pb, Ni and Co.
The anomalies are of quite a local nature and they closely reflect the ore occurrences,
anomalies in the eastern part of the project area are worth further study, because Zn, Ag,
Pb, Ni and Co altogether show anomalies there. Moreover, the highest content of Pb is
also there.
However, it should be taken into account also that most of the strongly anomalous
samples in mineralized sites are from the weathered bedrock, while only a few of them
are from till. In contrast, the anomalous samples in the eastern anomaly are mainly from
till. Besides, Au and Cu show no regular distribution patterns, as in mineralized sites.
Thereby the differences between two anomalous areas are appreciable.
In addition, it is obvious that the coherent anomalous distribution patterns of Ag, Zn,
Pb, Au, Cu reflecting the mineralized sites are well correspondent to the anomalous
patterns of IP if we consider the geophysical exploration in the area carried out by GTK.
Unfortunately, these identically anomalous patterns outside the mineralized sites cannot
be found. So, as far as the information goes, the clear potential significance of the eastern
anomalies is still difficult to figure out.
On the other hand, however, from the prospecting point of view, those anomalies in the
eastern part and northern part shown by Cu and Au are all still worth detailed
investigation. Most anomalous points of Cu and Au in the northern area were detected in
the weathered bedrock samples and there appears no evidence to connect those of Au to
the "nugget effect".
Acknowledgements
The Geological Survey of Finland has given me the permission to do the study and
provided all samples and data involved, bedrock samples were also analysed there.
Mineralogical and geochemical analyses have been performed in the laboratories of the
Departments of Geoscience and Electron Optics of the University of Oulu. I wish to
express my sincere thanks to the institutes involved.
I would like to thank Dr. Elias Ekdahl, Prof. Risto Aario, Prof. Vesa Peuraniemi and
Dr. Hannu Makkonen for their invaluable help. Risto and Vesa instructed me in doing this
study and made useful comments on the text. Elias and Hannu also made many useful
suggestions and checked the manuscript. Dr. Kauko Holappa and Mr. Olli Taikina-Aho
assisted me with my laboratory work. Ms. Fan Jiao, Ms. Li Chunxia and Ms. Qu Lili
helped me to draw the figures. I also wish to express my gratitude to all other persons
involved.
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108
PART III
III
Geochemical exploration and study of the Keketale leadzinc deposit hosted by sedimentary rocks in the volcanosedimentary formation in North-Western China
(A review of previous studies including papers 2 and 3)
Xiping Zhang
ABSTRACT: The Keketale Pb-Zn deposit is a stratabound sulphide deposit hosted by sedimentary
rocks in the volcano-sedimentary formation of the Devonian age in the Maizi syncline within the
Southern Edge of Altay. Volcanic rocks of a calc-alkaline series are the products of bimodal
volcanism and the Pb-Zn mineralization is related to the felsic eruptions in the early stage of
volcanism. The original host rocks are those of sedimentary rocks such as silicalite and iron bearing
carbonate rocks formed in hot water. Meta-volcanic breccia, meta-agglomerate, meta-breccic tuff
and meta-felsic lava as well as meta-tuff and mica quartz schist underlie the host rocks.
Disseminated ores dominate and other types include taxitic and massive, also banded, breccia as
well as net-veined. The alteration includes carbonation, sericitization, silicification and
disseminated pyrite. Epidotization appears outside the ore bodies.
Stream sediment and soil surveys showed a geochemical anomaly area of about 200 km2
composed of coherent Pb, Zn, As, Ag, Cu, Cd and Mn and a ring anomalous belt of Pb and Zn
corresponding to the Maizi syncline and the volcano-sedimentary formation respectively. The
appearance of a Cd anomaly together with a concentrated center of Pb, Zn, As, Ag and Mn indicates
in most circumstances the ore outcrop. The element concentrations of volcano-sedimentary
formation and the chondrite-normalized REE patterns of ores and felsic lava below the host rocks
suggest clearly a leaching out of Pb, Zn etc. and the metal sources of the deposit thus could be
connected to this leaching process. The deposit was formed in the sedimentary basin near the
volcanic center with extensive bacterial activity.
Coherent primary geochemical anomalies of the deposit include (1) Pb, Zn, Ag, As, Sb, Hg, Mn,
Cd, Mo, TFe, CaO and MgO; and (2) depleted Na2O.The rock-forming element patterns reflect the
main wall-rock alteration and also possibly the environment characters of ore precipitation. The
anomalies of Cd, Mo and Na2O have their distinct significance on ore deposit siting and also on
prospecting.
Introduction
Several important deposits have been found in the Southern Edge of Altay (SEA) in
north-western China during extensive explorations in the past twenty years. Those
deposits include Ashele Cu-Zn deposit, Tiemierte and Abagong polymetallic ore deposits,
Keketale Pb-Zn deposit, Duolanasayi Au deposit, Saerbulake and Saidu Au deposits.
Keketale Pb-Zn deposit was found by China National Non-ferrous Metals Industry
Corporation (CNNC) in 1986. In 1985, a project of stream sediment geochemical
exploration over 3250km2 in SEA was carried out by CNNC and an associated
geochemical anomaly of Pb, Zn, Ag, As, Cu, Cd and Mn, which is about 3-8 km wide
and 40 km long in the Maizi district was discovered. At the same time as detailed
geochemical exploration in the Maizi district, a stratiform gossan was met in the district.
It was corroborated later, by drilling, that the existence of a stratabound Pb-Zn sulphide
111
III
deposit hosted by sedimentary rocks in the volcano-sedimentary formation of Lower
Devonian. Now the reserves of the deposit have been estimated at about 300 0000 t
(Pb+Zn) (Wang et al. 1998).
The author took part in the geochemical exploration in 1985 and made geochemical
study after the deposit had been found.
Fig. 1. Location of the study area (outlined by rectangle) on simplified geological map of the
Altay area, north-western China (after Chen et al. 1996). 1, Cenozoic; 2, Cretaceous; 3,
Jurassic; 4, Permian; 5, Carboniferous; 6, Devonian; 7, Devonian-Silurian; 8, SilurianOrdovician; 9, Proterozoic; 10, Paleoproterozoic(1-10 are all supracrustal); 11, Granitoids; 12,
Diabase; 13, Faults.
The geological setting
SEA is one of the most important metallogenic belts of Hercynian orogeny in China and
has attracted the attention of geologists from the 80's. During the past twenty years, it has
been considered to connect to the island arc and continental margin although the views
are divergent on geotectonic setting. Li et al. (1982) and Li and Wang (1983) suggested
that SEA is an active continental margin accreted from the southern part of the Siberia
plate; Liu (1984) interpreted the belt as an island arc of active continental margin
produced by subduction of Junggar paleo-oceanic crust. Based on these interpretations,
112
III
the Ashele Cu-Zn zone related to the marine bimodal volcanism of the early-mid
Devonian has been considered as the island arc belt, and also the extension of marginalErtix belt of Kazakhstan; the Keketale Pb-Zn zone related to the marine felsicintermediate volcanism of the early Devonian was considered as the northern edge of the
back arc basin (Jiang & Liu 1992, Jiang 1994, Zhang 1987). Recently, however, the
volcano-sedimentary formation of the late Paleozoic in SEA was interpreted as the
production of continental margin rift (Han & He 1991, He et al. 1994, Chen et al. 1995,
1996, Wang et al. 1998, 1999).
Polymetallic ore deposits found in SEA occur mainly in four volcano- sedimentary
basins of the Devonian. From east to west, those basins are Maizi, Kelang,Chonhuer and
Ashele (Fig. 2). The Keketale Pb-Zn deposit is situated in the south-eastern part of the
Maizi syncline, about 95 km southeast to Aletai. The volcano-sedimentary formation in
Keketale has its greatest stratigraphical thickness in the basin, and volcanic breccia and
agglomerate are also mainly found there. According to Jiang and Liu (1992) and Chen et
al. (1995), the thickness of the formation in the north-western part of the basin is less than
that in Keketale, and the sedimentary rocks, particularly those of carbonate, are dominant
there.
Fig. 2. Metallogenic belts and epochs in the southern edge of Altay. The map is simplified after
Chen et al. (1996) and Wang et al. (1998). The data is from Chen et al. (1996) and Ding (1999).
1. Volcanic-sedimentary basin; 2. Fault.
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Volcanic eruption in the Maizi basin is mainly felsic in early stage and felsic,
intermediate and mafic in later, and the rocks are of bimodal assemblage of calc-alkaline
series (Wu 1992, Jiang 1993). Volcanic rocks include felsic breccia, agglomerate, lava
and pyroclastics, as well as mafic lava and pyroclastics. There was a relative long period
of inactivity between the early and later eruptions. The volcano-sedimentary formation is
about 3000 m in stratigraphical thickness (Wu 1992). The Keketale Pb-Zn deposit occurs
in the sedimentary rocks with several thin layers of volcanics formed during the inactive
period of volcanism. The stratigraphical thickness of the sedimentary rocks is up to 300m.
The deposit has been suggested as a transitional type between the stratabound deposits
hosted by volcanics and sedimentary rocks (Jiang & Liu 1992, Jiang 1994). The volcanosedimentary formation experienced regional metamorphism of greenschist-low
amphibolite facies (Wu 1992).
Ore deposit geology
The host rocks of the Keketale Pb-Zn deposit are mainly composed of biotite quartz
schist with granoblasite (contains calcite, diopside and garnet locally) intercalations, and
intercalated also diopside marble, garnet epidote marble, meta-tuff, meta- tuffaceous
siltstone and meta-siltstone (Han 1992, Wang et al. 1998). The protoliths are sedimentary
rocks such as calcareous-argillaceous sandstone, and siliceous rock and iron bearing
carbonate rocks formed in hot water (Jiang,1992, 1994) (see the explanation in Synopsis).
Meta-volcanic breccia, meta-agglomerate, meta-breccia tuff and meta-felsic lava as well
as meta tuff and mica quartz schist underlie the host rocks (Han 1992, Wang et al. 1998)
(Fig. 3).
Fig. 3. Simplified geological map of the Keketale area (after Han 1990 and Wang et al. 1998).
C=Granite; CT=Meta crystal tuff; FL=Meta felsic lava; BA=Volcanic breccia and agglomerate;
Tu=Tuff; Ss=Meta calcareous sandstone and siltstone; Mb=Marble; Bsc=Biotite schist;
PbZn=Pb-Zn ore.
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III
Ore bodies that occur as stratiform and stratiform-like with the NE direction of dip
(turning to SW in deep) are 50-1350 m in length, 5-80 m in breadth and extend down to
200-750 m in inclined depth (Fig. 4). On the surface, they appear as gossan of reddish and
yellowish brown and the gossan belt extends up to 810 m along its strike. Disseminated
ores are dominant and then taxitic and massive, and also sometimes banded, breccia as
well as net-veined. Pyrite, pyrrhotite, sphalerite and galena constitute major ore minerals
and arsenopyrite, chalcopyrite, tetrahedrite, bornite and marcasite make up the minors.
Quartz, calcite, plagioclase, sericite, diopside, tremolite, epidote, biotite and less barite,
fluorite and gypsum compose the gangue. Metal contents are Pb: 0.379-4.95%, Zn: 0.4010.79% and associated elements are S, Ag (max:222g/t) and Cd as well (Han 1992, Wang
et al. 1998).
Fig. 4. Cross-section of the ore body on profile of No.7 in the Keketale lead-zinc deposit, northwestern China (after Han, 1990 and Wang et al, 1998). 1, Meta felsic lava; 2, Meta breccia tuff;
3, Meta tuffite; 4, Leucogranoblasite; 5, Biotite granoblasite; 6, Biotite-quartz schist; 7, Marble;
8, Meta calcareous sandstone; 9, Meta sandstone; 10, Mica schist; 11, Plagioclase-biotite schist;
12, Biotite-epidote granoblasite; 13, Pegmatite; 14, Garnet, epidote, tremolite, actinolite,
chlorite and diopside; 15, Silification, muscovite and calcite; 16, Oxidized zone of Pb-Zn ore;
17, Pb-Zn ore; 18, High-grade Pb-Zn ore; 19, Inferred primary Pb-Zn ore.
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III
Carbonation, sericitization, silicification and disseminated pyrite occur with the
mineralization. Epidotization appears outside the ore bodies and sericitization as well as
potassium feldspar are present in the volcanics below the host rocks (Han 1992, Wang et
al. 1998).
Geochemical exploration and the discovery of the deposit
Stream sediment geochemical exploration in an area more than 3250 km2 in the central
part of SEA was carried out by CNNC in 1985. A total of 12250 samples were taken,
mainly in the first-order and second-order streams, and a few in the third-order streams
,with average density of about 4 samples/km2. After taking away big fragments of rocks,
the samples were dried outside and sieved. Part of the <0.42mm fraction was ground to
0.097mm and the rest stored. Samples were analyzed by inductively coupled plasma
atomic emission spectrometry (ICP-AES: Zn, Cu, Cd, Mn, V, Ti, Cr, Co, Be, Ba and Sr),
atomic absorption spectrophotometry (AAS: Pb, Ag, Au, Ni,), atomic fluorescence
spectrometry (AFS: As and Hg), polarography (POL: W and Sn) as well. Some rock
samples were analyzed by ICP-AES for TFe, SiO2, CaO, MgO, MnO, Na2O, K2O and
Al2O3. Before analyses, HF+H2SO4 and HF+HNO3 leaching for ICP-AES and AAS
respectively, hot aqua regia leaching for AFS as well as Na2O2 leaching for POL analyses
were employed. For deposit geochemical study, except for the elements mentioned above
the samples were also analyzed Se and REE(ICP-MS), Tl, In, Ga and Ge(AAS), Sb and
Bi(AFS), Mo(POL), S and Fe(Volumetry).
The elements analyzed were calculated for their average values using 2000 random
samples (excluded very high and low values) and thresholds using the average value plus
two times the standard deviation. An anomaly area of about 40 km long and 3-8 km wide
composed of Pb, Zn, Ag, As, Cu, Cd, Mn was found in the Maizi district (Fig. 5,6).
Extremely coherent anomalies of Pb, Zn, As, Ag, Mn correspond in their concentrated
center to small anomalies of Cd. The eastern part of the anomaly area is about 27 km by
4-8 km and the concentrated center of Pb, Zn, Ag, As anomalies (max: 270 ppm, 1608
ppm, 0.476 ppm, 59 ppm) correspond well to Cd anomalies appearing in six sites evenly
spaced (Fig. 7). Because a similar anomalous association was met in the Tiemuerte Pb-Zn
polymetallic occurrence about 80km northwest of Keketale and also a Pb occurrence is
present near to the anomalies, the attention of the explorers was therefore by analogy
attracted to the anomalies in Keketale.
116
III
Fig. 5. Anomaly of lead in stream sediments in the Maizi district (modified after Wang et al.
1998).
Fig. 6. Anomaly of zinc in stream sediments in the Maizi district (modified after Wang et al.
1998).
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III
Fig. 7. Anomalies of selected elements in stream sediments at Keketale. The sample site is
marked by a small round point (modified after Zhang et al. 1990). a) Pb (solid line): 30, 60, 120,
240 ppm; Ag (dotted line): 0.05, 0.1, 0.2, 0.4ppm; b) Zn (solid line): 120, 240, 480, 1000 ppm; Cd
(dotted line): 0.6, 1.2, 2.4 ppm.
Detailed explorations including a soil geochemical survey with a grid of 200 m by 40
m and mapping were made in 1986. The results not only showed a round anomalous belt
of Pb, Zn related to the volcano-sedimentary formation of the lower Devonian in the
Maizi syncline (Fig. 8), but also indicated a clear correlation between the anomalous area
of the stream sediment survey and the syncline. At the same time, a stratiform gossan of
reddish and yellowish brown colour was found some hundreds of meters northeast to a Cd
anomaly. A gossan sample gave the metal contents of Pb+Zn>10%, and thus it was
concluded that the anomalies of the area originate mainly from a Pb-Zn mineralization.
Explorations followed, such as trenching, a geochemical survey with a grid of 100m by
20m and geophysical survey (SP) indicated the anomalies of high polarization, low
resistivity, negative SP and concentrated Pb and Zn above the gossan. The information
above led to the first drilling and the primary Pb-Zn sulphide ore body was met.
Fig. 8. Anomaly of lead (solid line) and zinc (dotted line) in soil at Keketale (modified after
Wang 1996).
118
III
Deposit geochemistry
An interesting phenomenon is seen from the element variations in the time-strata profile
within the area of 3250 km2. The major ore-forming elements including Pb, Zn, Cu, (Au)
and some trace elements such as Sb, Cr, Ni, Co display a clear valley floor corresponding
to the Lower Devonian in variation curves of elements in the time-strata profile. A similar
situation is also seen from the variations of TFe, MgO and MnO. However, the curve of
SiO2 has its highest point at the Lower Devonian (Fig. 9) (Zhang et al. 1990). Because
the Pb-Zn mineralization related to the volcanism of the Lower Devonian is very
common, it is reasonable to assume that the eluviation of sediments by leaking sea-water
was general in the region at that time.
Fig. 9. Variation of elements in the time-strata profile within the exploration area (3250 km) in
Southern Edge of Altay. S2-3 =Mid-upper Silurian; D1=Lower Devonian; D2=Mid Devonian;
C3K=Upper Carboniferous; P=Permian (data after Zhang et al. 1990).
119
Rock
Marble (5)
Meta tuff (8)
Epidote biotite quartz schist (7)
Garnet biotite quartz schist (4)
Meta tuff (5)
Meta breccia tuff (4)
Meta felsic lava (8)
Regional average value (1000)
Crustal abundance (Taylor, 1964)
Cu
14.2
35.5
74.7
22.1
19.6
15.2
16.2
20.2
55
Pb
219
27.9
49.9
220
22.2
20.5
19.4
40.5
12.5
Zn
425
235
334
708
299
78
36
65.2
70
W
Sn
Mo
2.43 0.508 0.3
3.34 2.78 0.391
2.49 2.84 3.50
4.14 2.2
1.21
4.21 1.39 0.98
2.27 2.83 1.59
2.75 2.62 1.66
1.15 2.83 0.64
1.5
2
1.5
As
14
3.59
7.54
12.2
13.3
17.3
5.05
3.92
1.5
Sb
Be
2.18 0.786
0.675 2.57
2.47
3.33
2.04
2.30
1.35
1.10
2.8
3.36
0.958
0.343
0.244
0.37
0.2
Sn As Tl
Sb
In
Cd
Bi
Co
3.39
11.7
21.5
21.1
13.0
11.7
5.87
12.7
25.0
Cd
2.22
0.439
2.43
0.259
0.259
0.034
0.045
1.28
0.2
Co/Ni
0.6
Ni
10.7
18.5
25.7
34.0
19.6
18.6
15.5
24.4
75.0
S/Se
439273
Cr
19.3
42.7
60.2
79.2
41.5
32.6
20.3
46.0
Fe(%) V
20
Ga Ge Mo Cu Mn
105 480
>20
Hg
Au
Ag
Ba
Mn
43.6 0.48 0.48 235 4046
37.2 <0.3 0.121 504
945
22.7 0.807 0.283
1671
38
1.39 0.851 1696 2285
20
0.24 0.083 616 1281
32.5 0.538 0.103 119
568
26 0.269 0.071 644
462
40
0.6 0.043 346
80
4.00 0.07 425
950
Table 1. Averaged element contents of rocks from the No. 7 profile in the Keketale ore district. Number of samples in parentheses (Zhang et
al. 1990).
No
1
2
3
4
5
6
7
8
Au and Hg: ´10-9, K2O and Na2O: %, Others: ´10-6, 4 and 5 are hanging wall and footwall rock respectively.
Ag Pb
Zn
6
>3000 4050
Ni
15
587625
9.6 66
42 45
13.2 43
36 30
S(%) Se Co
48.32 1.1 9
21
>4.0
>2.0
1.57
0.38
4.2
<2
3.6
3
102 2100
48270
50905
791744
188346
25
25
750
<20
10.5 >3000 >3000
<10
<10
<10
<10
<3 34.5
0.45 150
0.3 810
1.1 450
1.2 <3
<1 <3
1.98 24
3.9 <3
48.27
48.36
49.09
48.97
48
114
780
480
0.47
3.6
87
72
10.0 >200 51
9.5 >200 90
0.62 33 21
2.6 39 102
<10 232714
<10 60886
2.1 168 2.4 <3
<2 30 1
<3
42
42
180
99
<3 0.51 450
75
19 12 9600 2040
<3 >30 >10000 126
<100
>10000 <10
>10000 <10
1.0
3.18
2.35
<10 242000 1.0
<10 685571 1.58
<10 >1314000 1.0
48.40 2.0 3
47.99 0.7 30
13.14 <0.1 <3
<3 >30 >10000 20
4.2 330 12 >300 20
>100
1
38
6.6 2.7 5400 >10000 <2 6.9 7.5 15.6 >30 >300
<3 <1 192 66
10.2 <0.3 72
>10000 <2 3
1
3
19 >300
<3 <1 15.6 78
<10 633500
33 617800
<10 261250
78 <10
24.6 60
<1 27 <100
0.45 870
<0.3 42
>100
12.67 0.2 <3
30.89 0.5 21
31.35 1.2 24
<2 315 1.2 <3
2
840 9
51
33 120 >30 >300 <1
48.87 2.1 21 45
48.10 7.9 162 45
47.01 0.8 >300 15
Table 2. Representative analyses of trace elements in sulphides of Keketale Pb-Zn deposit (ppm).
Sample
Mineral Position
Notes
1
5-8607
pyrite
ZK7-7,412.39- massive
466.0m
2
5-8601
pyrite
ZK7-7,136.66- massive
149.15m
3
ZK7-9-26 pyrite
ZK7-9,585.49m banded
4
ZK93-3-5 pyrite
ZK9-3,277.40m banded
5
ZK7-9-18 pyrite
ZK7-9,420.0m massive
6
ZK7-2-2 pyrite
ZK7--2,64.0m disseminated
7
ZK15-3-10 pyrite
ZK15-3,284.68m banded
8
ZK7-9-28 pyrite
ZK7-9,622.10m disseminated
9
ZK7-2-1 pyrite
ZK7-2,53.9m
veined
10 ZK15-7-26 pyrite
ZK15-7,404.52m massive
11 ZK15-7- galena
ZK15-7,425.0m veined
27A
12 ZK3-7-9 galena
ZK3-7,232.0m veined
13 ZK7-0-4 sphalerite ZK7-0,33.25m veined
14 ZK15-7- sphalerite ZK15-7,399.0m massive
25A
1-2 from Zhang et al. (1990), 3-14 from Han (1992).
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III
The geochemical cross-section (Table 1, excluded the samples above the ore bodies)
displays in most of the rocks in the volcano-sedimentary formation high contents of Pb,
Zn, As, Sb, Cd, Ba, Mn and W, and low contents of Cr, Ni, Co, Cu, Mo and Sn.
Compared to the average concentrations of unmineralized rocks taken within the area of
3250 km2, Pb, Zn, Ag, As, Sb, Ba and W are concentrated in the rocks of the upper part
of the formation including the host rocks (Table 1:1-5); Pb, Zn, Sb, Cd, however, have
their lowest contents particularly in felsic meta-lava below the host rocks. It clearly
suggests a leaching out of Pb and Zn etc. from the felsic volcanics (Zhang et al. 1990,
1996).
Trace elements in the ores are listed in Table 2. Ag, Tl, Sb, Bi are mainly found in
galena and In, Cd and Mn in sphalerite. Pyrite in the ore bodies has varying Co/Ni ratios
and high S/Se ratios, which indicates on one hand a variety of origins of pyrite and on the
other dominantly sedimentary origins (Tu et al. 1984, Tu 1987, Xu & Shao 1980). It is
also confirmed that Ag, Sb, Cd, Tl, Bi, Mn, As, In, Cu, Mo, Hg are associated with the
Pb-Zn mineralization (Zhang et al. 1990, 1996, Han 1992).
Except for the fluorite and barite bearing ore which have the highest åREE, ores have
lower åREE than rocks. The taxitic and massive ores that are mainly composed of
sulphides show the lowest åREE. The chondrite-normalized patterns of ores (most have
dEu<1 and two have dCe<1, Table 3, Fig. 10a) (Zhang et al. 1990, Zhang & Chen 1995)
are clearly different from each other due to their geneses and compositions. Massive and
disseminated ores have similar patterns with those of felsic lava (dEu<1, dCe<1) below
the host rocks in the Maizi area (Fig. 11) although their åREE differ greatly( mostly
caused of added sulphides). It has been found that the lava below the host rocks is
characterized by negative anomalies of Eu and Ce, however the lava above the host rocks
has positive Ce and negative Eu anomalies (Wang et al. 1998). Rocks, including altered
ones, nevertheless show quite similar patterns (Fig. 10b), but altered rocks display the
trend of depletion of Eu (Fig. 10c) relative to unaltered ones. These characters imply
further a close relationship between the Pb-Zn mineralization and felsic lava below the
host rocks, and also possibly the leaching of Eu during the wall-rock alteration.
121
III
Fig. 10. Chondrite-normalized REE patterns of (a) ores, (b) rocks and (c) Curves showing REE
ratio of altered rocks to unaltered rocks (r1: to hanging wallrock; r2: to the bottom-most rock
of the volcano-sedimentary formation) from the Keketale Pb-Zn deposit (data after Zhang et
al. 1990 and Zhang & Chen 1995).
122
III
Fig. 11. Chondrite-normalized REE patterns of volcanics in the Maizi district (after Wang et al.
1998).
Statistical data of the elements analysed in the rock samples of drill cores shows that
the variations of Pb and Zn are related to that of rock-forming elements: from the rocks
® wall rocks near ores ® ore body, Na2O drops, and CaO and MgO increase gradually
as Pb and Zn increase (Table 4, Fig. 12).
The primary geochemical anomalies of the deposit are composed of concentrated trace
and major elements such as Pb, Zn, Ag, As, Sb, Cd, Mo, Hg, Mn, Au, Cu, W, Be, Ca , Mg
and (TFe), and depleted major elements of Na (Fig. 12, 13).
Fig. 12. Variation of selected elements in the drill core of ZK7-7 at the Keketale Pb-Zn deposit.
1=Meta tuffite; 2=Plagioclase-biotite schist; 3=Biotite schist; 4=Granoblasite; 5=Marble;
6=Mica schist; 7=Garnet, epidote, silification; 8=Pb-Zn ores (after Zhang et al. 1990).
123
Table 3. Representative analyses of REE in the samples from the Keketale district (ppm) (Zhang et al. 1990).
1
2
3
4
5
6
7
8
9
10
11
La
3.98
4.47
11.29
15.72
76.71
20.56
17.13
19.57
16.62
18.62
15.66
Ce
7.55
9.98
25.21
36.60
139.62
48.16
40.00
48.87
42.86
45.25
35.92
Pr
0.83
0.98
3.01
4.02
15.25
4.73
4.37
4.82
5.09
4.34
3.86
Nd
3.23
4.33
14.64
16.20
57.12
19.59
18.33
19.65
20.99
20.26
16.78
Sm
0.79
1.16
3.73
3.14
10.28
3.93
4.27
4.11
3.96
4.69
3.92
Eu
0.15
0.37
1.27
0.39
4.64
0.71
0.93
0.69
0.79
1.07
0.97
Gd
0.91
1.25
3.60
3.23
9.81
4.53
5.01
5.03
3.68
5.12
4.39
Tb
<0.3
<0.3
0.67
0.47
1.08
0.57
0.88
0.67
0.46
0.71
0.62
Dy
0.66
0.98
3.58
2.38
4.52
3.85
5.29
4.65
2.22
4.18
3.82
Ho
0.11
0.21
0.77
0.51
0.73
0.88
1.08
0.97
0.52
0.88
0.84
Er
0.45
0.63
2.00
2.10
1.44
2.93
3.46
3.05
2.26
2.77
2.76
Tm
<0.1
<0.1
0.28
0.37
0.13
0.45
0.51
0.45
0.41
0.41
0.40
Yb
0.35
0.59
1.63
2.43
0.60
3.02
3.22
2.83
3.07
2.58
2.74
Lu
<0.1
<0.1
<0.1
0.20
<0.1
0.40
0.58
0.51
0.22
0.29
0.25
Y
3.42
4.74
19.54
14.58
27.72
24.42
33.49
27.01
15.36
22.75
22.53
SREE
22.68
29.94
91.27
102.34
349.70
138.73
138.55
142.88
118.51
133.92 115.46
LREE/HREE
2.69
2.46
1.84
2.90
6.59
2.38
1.59
2.16
3.20
2.37
2.01
dCe
0.95
1.10
1.02
1.08
0.93
1.13
1.09
1.18
1.11
1.17
1.08
dEu
0.54
0.93
1.05
0.37
1.39
0.51
0.61
0.46
0.62
0.66
0.71
1. massive ore, 2. taxitic ore, 3. banded ore, 4. disseminated ore, 5. fluorite and barite bearing disseminated ore, 6. hanging wall rock (garnet-biotite-quartz
schist), 7. silicificated mica schist, 8. footwall rock (altered granoblasite), 9. footwall rock (leucogranoblasite), 10. biotite quartz schist (in the bottom of the
formation), 11. meta sandstone (in the top of the formation), chondrite values from Boynton (1984).
K2O(%)
0.n~5(±)
0.1~4
Na2O(%)
0.n~6
<6
5~14
A12O3(%)
11~13.5
>20
>6
TFe(%)
2~10
>5
>3
>3
1~4
>3000
>100
>3000
>100
Zn(ppm)
nx10~100
2~8
<0.1
CaO(%) MgO(%) Pb(ppm)
0.n~4
0.n~4
nx10~100
0.n~4
Table 4. Statistical data of elements in the Keketale Pb-Zn deposit (Zhang et al. 1990).
wall rocks
wall rocks
near ores
orebodies
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III
Fig. 13. Geochemical patterns of selected elements in the profile of No.7 in the Keketale leadzinc deposit, north-western China (after Zhang et al. 1990, 1996). 1=Meta felsic lava; 2=Meta
breccia tuff; 3=Meta felsic lava and tuff; 4=Biotite-quartz schist and Biotite granoblasite with
carbonate and meta tuff intercalations; 5=Pb-Zn ore.
Strongly concentrated Pb, Zn, Ag, As, Sb have a broad anomaly area respectively. The
patterns of Pb, Ag, As, Sb are also quite similar (Fig. 13). A distinct pattern is seen from
the element As, which exhibits clear trends of high concentration both in the hanging wall
and foot wall rocks immediate to ores. Similar trends but mainly appearing in the hanging
wall rocks are shown by Sb and Cu (Fig. 12). Cd, Mo, Hg and Mn distribute in a
relatively narrow area corresponding to ores, particularly, Cd and Mo illustrate a narrow
but coherent pattern confined exactly to the shape of ore bodies. Major elements CaO,
MgO and (TFe) show anomalies of enrichment and TFe correspond well to ores. CaO
(and Mn) also seems to reflect the character of the host rocks: iron bearing carbonate
rocks. Depleted and coherent Na2O patterns are nevertheless typical of strata bound
sulphide deposit related to volcanism, particularly the depletion of Na2O well reflects a
whole stratiform space where the ores are enveloped (Fig. 13).
The variations and the patterns of rock-forming elements are clearly the reflections of
the main alteration although the alteration in the deposit is not intense, and possibly
reflections of the environmental characteristicss of ore precipitation (also see Zhang
1992). Obviously, the host rocks are characteristic of unusually high Fe, Ca and Mg
125
III
bearing sediments. From the point of view of prospecting, therefore, high concentrations
of Ca and Mg can lead the attention to the promise of the strata position; and the
anomalies of Cd, Mo and Na2O however have a great significance on ore deposit siting
and also ore body finding.
According to Han (1992), sulphides in the deposit have d34S values, varying between
–5.4 to –15.3 per mill and high S/Se ratios (also see Zhang et al. 1990). Such data suggest
a main sulphur source of sea water sulphate reduced by bacteria. One carbon isotope
analysis gave the d13C values of –11.6 per mill, and lead isotope data showed the same
age as the host rocks. Also no carbon concentration has been found both in ores and host
rocks. All this data, together with the characteristics above lead to the conclusion that the
Keketale Pb-Zn deposit was formed in the sedimentary basin near the volcanic center
during the sedimentary process of the host rocks. At the same time of the processing, the
bacteria activity was also extensive. As one type of the stratabound sulphide deposit
related to the volcanism, the Keketale Pb-Zn deposit may imply that the deposit hosted by
the sedimentary rocks in the volcano-sedimentary formation would prefer relatively strict
conditions for the sedimentary basin in addition to the volcanism during their formation.
Summary and conclusions
1. The Keketale Pb-Zn deposit is a stratabound sulphide deposit hosted by sedimentary
rocks in the volcano-sedimentary formation (Jiang 1992, 1994). The deposit occurs in
the south-eastern part of the Maizi volcano-sedimentary basin within the SEA in the
place with the greatest stratigraphical thickness of the basin. Volcanic rocks of the
calc-alkaline series including felsic breccia, agglomerate, lava and pyroclastics, as
well as mafic lava and pyroclastics are the products of bimodal volcanism (Wu 1992).
The Pb-Zn mineralization took place after the felsic eruption in the early stage of the
volcanism.
2. The host rocks of the Keketale Pb-Zn deposit are mainly composed of biotite quartz
schist and granoblasite intercalations with interlayers of diopside marble, garnet
epidote marble, meta-tuff, meta- tuffaceous siltestone and meta-siltestone (Han 1992,
Wang et al. 1998). The protoliths are those sedimentary rocks including calcareousargillaceous sandsone, siliceous rock and iron- bearing carbonate rocks formed in hot
water (Jiang 1992, 1994). Meta-volcanic breccia, meta-agglomerate, meta-breccic
tuff and meta-felsic lava as well as meta tuff and mica quartz schist underlying the
host rocks (Han 1992, Wang et al. 1998).
3. Ore bodies are present as stratiform or are stratiform-like. Dominant ores are
disseminated and then taxitic and massive, also banded, breccia as well as net-veined.
Carbonation, sericitization, silicification and disseminated pyrite appear with the
mineralization. Epidotization occurs outside the ore bodies and sericitization as well
as potassium feldspar are met in the volcanics below the host rocks (Han 1992, Wang
et al. 1998).
4. Stream sediment and soil surveys showed a geochemical anomaly area of about 200
km2 composed of coherent Pb, Zn, As, Ag, Cu, Cd and Mn and a round anomalous
belt of Pb and Zn corresponding to the Maizi syncline and the volcano-sedimentary
126
III
5.
6.
7.
8.
9.
formation of the lower Devonian in the syncline, respectively. The appearance of the
Cd anomaly together with a coherent concentrated center of Pb, Zn, As, Ag and Mn
indicate in most cases the ore outcrop.
The major ore-forming elements including Pb, Zn, Cu, (Au) and some trace elements
such as Sb, Cr, Ni, Co display a clear valley floor corresponding to the lower
Devonian in variation curves of elements in the time-strata profile. Because the Pb-Zn
mineralization related to the volcanism of lower Devonian is very common, it is
reasonable to assume that the eluviation of sediments by leaking sea-water was
general in the region in that time.
The volcano-sedimentary formation has high contents of Pb, Zn, As, Sb, Cd, Ba, Mn
and W and low contents of Cr, Ni, Co, Cu, Mo and Sn. Pb, Zn, Ag, As, Sb, Ba and W
are concentrated in the rocks of the upper part of the formation, including the host
rocks. On the other hand, Pb, Zn, Sb, Cd have their lowest contents particularly in
felsic meta-lava compared to the average concentrations of unmineralized rocks
within the area of 3250 km2. The similar chondrite normalized REE patterns
especially the values of dEu and dCe of ores and felsic lava below the host rocks in
the Maizi area (Wang et al. 1998) suggest clearly a leaching out of Pb and Zn etc. and
the metal sources of the deposit thus could be connected to the leaching of felsic
lavas. The leaching of Eu in the rocks during the alteration is also possible.
The coherent primary geochemical anomalies of the deposit are characteristic of (1)
broad and strongly concentrated of Pb, Zn, Ag, As and Sb; (2) concentrated but
narrow Cd, Mo, Hg, Mn especially for Cd and Mo corresponding exactly to the ore
bodies; and (3) concentrated CaO and MgO and depleted Na2O; (4) a distinct trend of
As which exhibits clear trends of high concentration both in the hanging wall and foot
wall rocks immediate to ores, and similar trends but mainly appearing in the hanging
wall rocks of Sb and Cu.
The variations and geochemical patterns of rock-forming elements reflect the main
wall-rock alteration and also possibly the environment characteristics of ore
precipitation such as Ca and Mg bearing sediments formed in hot water. The
anomalies of Cd, Mo, Na2O have a great significance on ore deposit siting and also
ore body finding.
Sulphides in the deposit have d34S values varying between –5.4 to –15.3 per mill and
high S/Se ratios, showing a main sulphur source of sea water sulphate reduced by
bacteria. One carbon isotope with the d13C values of –11.6 per mill and lead isotope
data showing the same age as the host rocks, and also no carbon concentration both in
ores and host rocks (Han 1992), together with the characters of the deposit suggest
that the Keketale Pb-Zn deposit was formed in the sedimentary basin near the
volcanic center with extensive bacterial activity.
Acknowledgements
The author would like to express appreciation to the Xinjiang Geochemical Exploration
Team of Geology for Nonferrous Metals for providing some data, and Dr. Hannu
Makkonen for reviewing the manuscript.
127
III
References
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conditions and metallogenic prognosis of the Ashele Copper-Zinc metallogenic belt, Xinjiang,
China. Geol Publ House, Beijing, 330 p (in Chinese with English Summary).
Chen Y, Ye Q, Wang J, Rei J and the research group (1995) Metallogenic conditions and evaluation
of mineral resources of Altay gold and non-ferrous metals provinces. Unpublished research report,
483 p (in Chinese).
Han B & He G. (1991) The tectonic nature of the Devonian volcanic belt on the Southern Edge of
Altay Mountains in China. Geosc Xinjiang, No 3: 89-100 (in Chinese).
Han D (1992) Keketale lead-zinc deposit. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds),
Geological, geophysical and geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge
of Altay and the prospecting targets, unpublished research report, 251 p (in Chinese).
He G, Li M, Liu D, Tang Y & Zhou R (1994) Paleozoic crustal evolution and mineralization in
Xinjiang of China, Peoples Publ. Hose of Xinjiang, 437 p (in Chinese with English Summary)
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deposits. In: Li Z & Wang B (eds) Volcanic rocks, volcanism and related mineral resources.
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Jiang Q & Liu Y (1992) Geological features of Cu-polymetallic ore deposits in Southern Edge of
Altay. In: Jiang Q, Liu Y, Wen H, Deng Y & Chen H (eds) Geological, geophysical and
geochemical studies of Cu-Fe-polymetallic ore belt in Southern Edge of Altay and the prospecting
targets. Unpublished research report, 251 p (in Chinese).
Jiang Q (1994) Types, evaluation criteria and geneses of the massive sulfide deposits in the volcanic
terrain. Geol Expl Non-Ferrous Metals, Vol 3, No 1: 4-9. (in Chinese).
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(in Chinese).
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Publ House, Beijing: 3-6 (in Chinese).
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Geochemistry. Shanghai Sci. & Tec. Publ. House, Shanghai, 447 p (in Chinese).
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Wang J, Li B, Zhang J, YinY, Wang J, Wang Z & Zheng G (1999) Metallogenesis and prognosis of
gold and copper deposits in Ertix Metallogenic Belt, Xinjiang. Metallurgical Industry Press,
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Wang Z (1996) Exploration and discovery of Keketale Pb-Zn deposit. In: Xong G, Deng Z & Xie D
(eds) The discovery of important metal deposits in Xinjiang, Geol Publ House, Beijing, pp 105114 (in Chinese).
Wu Z (1992) The volcano-sedimentary formations of lower Devonian in major districts, Southern
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129
PART IV
IV
Geochemical anomalies of rock-forming elements: an
important indicator of blind ore deposits
(Revised version of previously published paper 1)
Xiping Zhang
Abstract. Traditionally, geochemical explorationists have relied overwhelmingly on trace elements
and ignored major rock-forming elements. It is, however, the major rock-forming elements that
dictate the physio-chemical parameters of the ore-forming system which favors or prevents the
precipitation of ore elements. The much researched wall-rock alteration is the result of
redistribution of rock-forming elements to form new minerals under changed conditions. A certain
portion of wall rock alteration is actually the product of ore forming processes. Wall rock alteration
that took place before ore-forming processes may have created a favorable condition for ore
precipitation.
Major element anomaly patterns are well developed and best investigated in porphyry Cu
deposits and Kuroko type deposits, where the distribution and quantitative variation of the major
elements show a close spatial relationship to the extent of mineralization and the rich ore beds. The
factor that rock-forming elements control the migration, accumulation and precipitation of ore
elements is confirmed by the following observations: the composition of fluid inclusions in both ore
minerals and gangue, the theory of transportation in complex ions, the mass exchange between ore
fluids and wall rocks and the existence of metasomatic plumes at the early stages of ore forming
processes in a number of pyrite deposits. Geochemical anomaly of rock-forming elements is
therefore not only a subject of academic interest, but a practical indicator in geochemical
prospecting, especially in the search for blind ore deposits.
Introduction
Geochemical prospecting in the past was almost always direct. Essential and associated
elements were used for finding blind deposits and these were mainly trace elements.
Geochemical prospecting is now developing in new directions, which involve studying
closely the geochemical reflection of ore precipitation environments, conditions and oreforming processes.
The ore-forming system, a very complex system, not only concentrates useful
elements but also leaves information and marks of the ore-forming process. Anomalies of
ore-forming elements and associated elements comprise part of, but not all, the
information and marks. Information on environmental changes before and during the
precipitation of ore-forming elements can be useful in finding blind deposits.
Experienced geologists commonly consider the wall rock alteration to be a useful ore
deposit indicator since it plays a part in mineralization. Geochemically, wall rock
alteration reflects the environmental preconditions for ore substance precipitation. On
relationships of alteration and ore, Burt (1972, see Rose & Burt 1979) indicated that
alteration and ore probably have closer relationships if early stage alteration enlarged the
porosity and permeability of rocks, and thus provided the feeder for mineralizing fluid; or,
the mineral assemblage of early stage alteration made it possible in chemistry to accept
the precipitation of ore substances. Actually, the most important factor in the relationship
133
IV
between early stage alteration and ore is that the mineral assemblage of the former can
chemically accept the precipitation of the latter. It is impossible that ore will precipitate
when there is a chemical balance between the hydrothermal solution and wall rocks (Rose
& Burt 1979). Thus the mineral assemblage of early stage alteration is essential to ore
precipitation.
Because it is so essential to alteration, the re-allotment of rock-forming elements must
be related to element anomalies. So studying rock-forming elements and their anomalies
will enrich the study of deposit geochemistry, and at the same time reveal the
mineralization process and the geochemical environments favorable to the settling of ore,
as well as establishing a most useful indicator for prospecting. Alterations around ore
reflect that mineral assemblage necessary for the precipitation of ore substances and
media, and indicate geochemical environments favorable to the precipitation of ore
substances.
The case of anomalous models of rock-forming elements
The relationship of wall rock alteration to ore shows clear patterns of lateral and vertical
zoning, and one or two types of these are intimately associated with ore.
Alterations studied thoroughly are porphyry copper deposits and a Kuroko deposit.
The closed alteration zoning of the San Manuel Kalamazoo porphyry deposit is a typical
example (Lowell & Guilbert 1970), the ore bodies were located on the border of potassic
alteration of the central zone, and toward the outside it transits to a sericitization zone and
propylitization zone.
The alteration enveloped Kuroko deposit can be divided into four zones (Matsukuma
1970): from the wall rock to the ore body there are: 1) the montmorillonite and zeolite
zone (zone of transition to unaltered rocks), 2) the sericite, chlorite and pyrite zone (inside
of strata above ore bodies), 3) sericite, chlorite and quartz zone (in the ore bodies), and 4)
silication zone (footwall and middle part of ore bodies).
The Baiyin massive sulphide deposit (Gansu, China), Jiang et al. (1968) indicated that
the features of alteration were no feldspar zone (silication and sericitize) +
decolourisation process (chloritization, decolourisation and titanic hematite became
rutile) + pyrite (pyritization).
Carbonation, sericitization, silicification and disseminated pyrite occur with the
mineralization of the Keketale Pb-Zn deposit, one strata bound sulfide deposit hosted by
sedimentary rocks in the volcano-sedimentary formation in Xinjiang (NW China).
There must be regular anomalous patterns of rock-forming elements in response to the
typical alteration zoning.
Porphyry copper deposits
The Fujiawu porphyry copper deposit (Jiangxi, China, Li et al. 1978) shows
concentration of K2O and depletion of Na2O in response to metallogenic elements Cu
and Mo. The K2O/Na2O ratio shows low value(<1) in the centre no ore body zone,
134
IV
medium value (1-10) in the ore bodies, and high value (10-30) on the periphery of the ore
bodies. It indicates an intimate relationship between alkaline alteration and concentration
of copper and also the precipitation of ore substances (Fig. 1).
Fig. 1. Geochemical patterns of selected elements in the Fujiawu porphyry copper deposit
(modified after Li et al. 1978).
The Duobaoshan porphyry copper deposit (Heilongjiang, China, Li et al. 1979) shows
the same patterns and that K2O/Na2O³1, by means of a plan view. The study carried out
by The Research Group (1978) had also showed the enrichment of K, OH and the loss of
Na, Ca, (Al) in each alteration zone, and concentration of Si only in the silication zone
(Fig. 2).
Fig. 2. Geochemical patterns of selected
elements in the Duobaoshan porphyry
copper deposit (modified after Li et al.
135
IV
Obviously, anomalies of rock-forming elements of porphyry copper deposits are not
only clear, but also typical. Actually no exceptions to this type deposit have been found in
the world.
Stratabound sulfide deposits hosted by volcanic rocks
We are all familiar with the depletion of sodium in Kuroko ore. It was documented that
the content of Na and Ca is decreased but Fe and Mg (K and Si) is increased from wall
rock to the centre of ore body (Lambert & Sato 1974, Riverin & Hodgson 1980, Frater
1983, Larson 1984, Peterson 1988, Chen et al. 1996).
Stratabound sulfide deposits hosted by sedimentary rocks in the volcanosedimentary formation
In studying the Keketale Pb-Zn deposit, the author devoted much attention to the
distribution of rock-forming elements in the deposit. The deposit is a volcanogenic Pb-Zn
ore deposit related to the mainly felsic marine volcanism of the lower Devonian.
Anomalies of rock-forming elements are regular (Fig. 3). The ore bodies are in the zone
of CaO and MgO enrichment and Na2O depletion. The patterns of depletion are very
special, but the anomaly of K2O is not regular.
Fig. 3. Geochemical patterns of selected elements in the Keketale lead-zinc deposit (modified
after Zhang et al. 1990).
136
IV
According to the anomalous models of Na2O, Pb and Zn, an inference about deep ore
body and the occurrence of deposit was made and confirmed by drilling.
Discussion
The concentration and precipitation of ore substances is due to the change of physiochemical conditions in the ore solution and environment. It is impossible to induce the
concentration and precipitation of a large scale and complex component without changing
the chemistry and exchange of chemical components.
Rei (1984) calculated the exchange capacity of chemical components in rock pillars at
a depth of 1 km from altered porphyry bodies in Yulong, Malasongduo and Tongchang. It
shows that the amount of SiO2 added to the pillars is about hundred million tons, twenty
million tons and forty million tons, respectively. The amount of K2O added to the pillars
of Yulong and Malasongduo is about six million tons, and the amount of Na2O depleted is
fifty million tons, ten million tons and forty million tons, respectively. As a result of the
exchange, the amount of Cu and Mo added to the porphyry bodies is five million tons,
one million tons, three million tons and three hundred thousand tons, seventy thousand
tons and fifty thousand tons respectively.
The composition of fluid inclusions shows that the ore solution contains a great deal of
Cl, K, and Na etc., with mostly heavy metal such as Cu, Pb and Zn etc. These can form
complexes and move stably under acid or slightly acid conditions, and low concentrations
of H2S. The complexes can be decomposed and heavy metals precipitated in some ways
when the conditions change.
In discussing the mineralization epoch of pyrite deposits, Smirnov (1970) indicated
that: True vaporous solution with high temperatures in the initial stage of mineralization
changed the mineral composition of volcanic rocks as it moved through, and formed the
hydrothermal altered rock pillar. The temperature reduced from 400 to 200 degrees
Celsius from the quartz zone to the chlorite zone, the acidity-alkalinity (Ph) increased
from 4-5 to 6-7-8, and rock-forming elements were diluted from or added to the different
zones (Fig. 4). The following pyrite stage caused the iron sulfide to dissociate from the
flowing strongly leached quartzite and quartz-sericitelite hydrothermal solution, and then
formed sediment. The Ural-orefield terrain proved that the porosity of altered rocks had
been enlarged by 2-4 times, and showed a direct ratio with the increase in the amount of
sericite and chlorite.
137
IV
Fig. 4. General sketch of reallotment of elements in the replacement pillar of volcanic rocks
caused by fell off in energy (t°C) and acidity (pH) in the replacement front of the early period
of pyrite mineralization (after Smirnov 1976).
Actually, heavy metal mineralization (Cu, Pb, Zn etc.) works in the same way. The
hydrothermal altered rock pillar of the initial stages of mineralization of pyrite ore
deposits is significant, because it always takes place before the ore precipitation and is
necessary for this precipitation. Therefore the rock pillar shown in figure 4 is just a
preparation stage of the concentration and precipitation of pyrite; it not only produces a
new mineral assemblage favorable to pyrite precipitation but also greatly enlarges the
porosity of protolith. The major cause of formation of altered mineral assemblage is the
decrease in the temperature and acidity of the solution. Decreasing acidity is due to the
chemical exchange between solution and wall rock, especially for the replacement of ions
of alkaline metals, alkaline-earth metals and iron.
The formation of sericite, chlorite (and quartz) is as follows (Department of Geology
1979):
3KAl3SiO8 + 2H+ ® KAl2AlSi3O10 (OH)2 + 2K+ + 6SiO2
(1)
(orthoclase)
(sericite)
(quartz)
2K(Mg,Fe)3AlSi3O10(OH)2 + 4H+ ® Al(Mg,Fe)5AlSi3O10(OH)8 + 2K+
(biotite)
(chlorite)
+ (Mg,Fe)2+ + 3SiO2
(quartz)
(2)
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IV
Action (1) shows that the OH-/H+ ratio increases with the H+/K+ exchange, and thus the
acidity drops. At the beginning of the exchange, the decrease in acidity and the
continuing action are interdependent. The result of action (2) is the same as (1). The
exchange causes the recombination of the component of the protolith, changes the
character of the solution, and also breaks the chemical balance between the solution and
the wall rocks. As a result, the complexes with ore elements are dissociated, and the
released elements together with the elements from wall rocks are precipitated. The
recombination of components of the protolith causes the enlargement of porosity of the
protolith and geochemical anomalies of rock-forming elements. In this way, the favorable
conditions for ore-forming element precipitation come about, confirming the intimate
relationships of wall rock alteration and ore substance precipitation.
Conclusions
Early stage alteration can have a significant effect on mineralization. The altered mineral
assemblage makes it chemically possible to accept the precipitation of ore substances,
and the alteration can enlarge the porosity of rocks. That is to say early stage alteration
has created chemical and physical conditions favorable to the precipitation of ore.
The second significant effect of the alteration is that it can promote the concentration
of ore further through chemical material exchange.
Wall rock alteration is the re-allotment of rock-forming elements, and thus causes
anomalies of the elements. That is to say the anomalies of rock-forming elements are the
reflection of geochemical environments favorable to ore precipitation.
Rock-forming elements control the geochemical behavior of ore-forming elements,
and therefore merit further study.
Anomalies of rock-forming elements are practical indicators of deposit particularly
blind deposits.
Acknowledgement
The author expresses his thanks here to Ms. Tracy Lyons Shupp for checking the English
of the manuscript.
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