Economic Geology
Vol. 62, 1967, pp. 540-550
TIN
BELTS
ON
THE
CONTINENTS
ATLANTIC
R. D.
AROUND
THE
OCEAN
SCHUILING
ABSTRACT
Tin is inhomogeneously
distributedon the continents,in relatively
narrow,
continent-sized belts.
On a reconstruction of the continents
around the Atlantic Ocean before continental drift, the belts extend un-
brokenfrom one continentto another. As the agesof the tin mineralizations vary within the belts, an argument can be derived that the source
of the tin and its associated elements must be in the crust.
It is further
speculatedthat concentrations
of workabletin depositsoccur in the intersectionof orogenicbeltswith zonesof primitive enrichmentof tin. The
ultimate causeof such primary geochemicalculminationsmay well lie
back in the early history of the earth.
INTRODUCTION
A M•.T.•LLO•ENETIC
provincemay be definedas an area characterized
by a
conspicuous
concentration
of a certainelementor groupof elements,
as comparedwith otherareas. In suchprovincesthe element,or elements,are commonlydeposited
by more than one geological
processand at differenttimes.
The conceptof a metallogenetic
provinceimpliesthe existenceof large-scale
chemicalinhomogeneities
in that part of the crustor the mantlefrom which
the ore-deposits
ultimatelywere derived. As tin seemsto be an elementthat
showsa stronglyinhomogeneous
distribution,it seemedworth while to plot
all the known economic and uneconomic occurrences of this element in North
and South America, Africa and Europe. The investigationwas restrictedto
thesecontinents,becauseit was hopedthat the data might, at the sametime,
have somebearingon the theory of continentaldrift. Furthermorea review
of this kind might be of somehelp in planningof future prospecting
for tin
deposits. The map (Fig. 1) providesthe factual basisfor the subsequent
discussion.
Acknowledgments.--Valuableinformationwas obtainedfrom the Directors
of the GeologicalSurveysof Algiers, Angola, Argentina, Cameroon,CongoBrazzaville,Congo-Leopoldville,
Dahomey,Ecuador, Liberia, Libya, Malawi,
Mauretania, Peru, Senegal,Sierra Leone, SpanishSahara,Tanzania and Zambia, for which the writer wishesto expresshis thanks. The writer is further
indebtedfor informationand assistanceto Sir Edward Bullard, Cambridge;
Dr. G. C. Brouwer, formerly of the Bureau de RecherchesC•ologiqueset
MiniSres,French Guyana; ProfessorDj. Guimaraesand Dr. J. B. Kloosterman, Brazil; Dr. Lepersonneof the Musde Royal de l'Afrique Centrale at
Tervuuren,-Belgium; and Dr. Tagini of the Organisation S.O.D.E.M.I.,
Ivory Coast. Professor W. C. Burnham of the Pennsylvania State
University kindly read the manuscript,and suggesteda number of im540
TIN BELTS ON CONTINENTS AROUND THE ATLANTIC
541
provements;ProfessorJ. Kalliokoskiof PrincetonUniversity is thankedfor
his stimulatinginterestin the subject. A grant of the Billiton Mining Company as well as the stimulatinginterest of its Chief Geologist,Dr. G. L.
Krol, is gratefullyacknowledged.The NetherlandsOrganizationfor the Advancement
of Pure Sciencegrantedthe authora NATO ResearchFellowship
at PrincetonUniversity, where most of this work was carried out.
CONSTRUCTION
OF
MAP
The heading"Tin" in the ArmoredBibliographyof EcoNoMic GEOLOGY,
1928--1963,provideda first setof references
to tin-occurrences,
whichwas expandedby a searchfor further data, both in older and in very recentliterature.
The final list of references
from whichthe map (Fig. 1) wascompiledcontains
well over 500 titles, to which new literature is still being added. From these
I have selected a shorter list of references that contains most of the data used
in the construction
of the map. The mapcontainsalsomuchunpublished
information,whichwasobtainedon requestfrom the Directorsof manyGeological Surveys, as well as a number of individuals,all mentionedin the
"acknowledgments."
Comparedto the amountof informationpresentedon somemetallogenetic
maps(age,size,typeof deposit),on the mapspresented
hereinho distinction
is madeon the basisof sizeof deposits. The only distinctionmadeis between
thosedeposits
that havebeenor are in production,
and uneconomic
$ccurrences. By differentiatingbetweenproductiveand unproductive
locationsI
feel that somequalitativemeasureof tin concentration
is introduced.
Someobjectionmightbe raisedagainstincludingplacerdeposits
in a map
ß
• '
[l'••
0
Fro. 1, A-D.
i•
I.•
•'
TIN-BELTS AROUNDTHE ATLANTIC
OCEAN
R.D.
SCHUILING,
1966
ßTin-deposit
(limit
economic
or
marginal
)
-- Approximate
oftinbelts
+ Uneconomicoccurrence of tin minerals
A, Europe; B, Africa; C, South America; D, North America.
542
R. D. SCHUILING
I
•.l e• ß
IS
Fro.
1 B.
whichpurportsto give informationon the primarydistributionof tin. However, as it is commonexperiencethat placer depositsof tin are never, or
rarely,locatedfar from their primary source,it is felt that on the scaleof the
map this introducesno ambiguities.
TIN
BELTS
From an inspectionof Figure 1 it is obviousthat tin occurrences
showan
unevenlydistributionoverthe continents.They are concentrated
in elongated
TIN BELTS ON CONTINENTS AROUND THE ATLANTIC
543
/
+/
/
+
/
+
/
I
I
/
/
/
/
/
/
/
/
e+
//, q+/
t,/
/
/
F•G. 1C.
zonesthat can be refered to as "tin belts." Although in detail one may
havea differentopinionon whereto draw the boundariesof thesebelts (and
on this scaledetailsmay be mattersof severalhundredkilometers!), it seems
certain that the overall distribution
can be characterized as "belt-like."
It
may well be that someclustersof tin occurrences
that have not been dis-
544
R. D. SCHUILING
++
44-+
4-
D
FIG.
1D.
tinguished
asbelts,suchasthosein CanadaandCentralAfrica,will eventually
form parts of beltswhen more occurrences
are found. The followingtin
beltsare distinguished:
1. The Andeanbelt, richestin Bolivia,can be tracedfrom Argentinainto
Bolivia,Peru and probablyColombia. The age of the depositsrangesfrom
Mesozoicto Middle Tertiary, althoughin Argentina the belt containssome
small Precambrianoccurrences.The depositsare related geneticallyto
Mesozoicintrusivesor Tertiary extrusives.
2. The East Brazilian
belt extends from Rio Grande do Sul in a north-
easterlydirectionthrough the coastalstatesof Brazil up to Cear/t and Rio
Grandedel Norte, where it terminatesat the Atlantic Ocean. Many of the
depositsare in pegmatites,
associated
with beryl and lithium silicates. As far
as is known, mostor all of the depositsare Precambrianand a numberof them
in thisbelthavebeendatedat 750 m.y.
3. The Rond6nia-Guyanabelt. This area is still largely unknown,with
the tin fields of Rond6niahaving been discoveredonly in recentyears, and
someof the occurrences
to the northeastof Rond6niadiscovered
as recentlyas
1965. A large part of the connection
betweenRond6niaand Guyanais obscuredby the Tertiary of the Amazonbasin. An ageof 940 m.y. is reported
from Rond6nia (29), whereasthe agesof the granitesand pegrnatitesassociated with tin mineralizationin French Guyanaare around2,100 m.y.
TIN BELTS ON CONTINENTS
AROUND THE ATLANTIC
545
4. The Rocky Mountain belt extendsfrom Mexico through California,
New Mexico,Nevada,Washingtonand British Columbiato Alaska. It seems
to be the counterpartof the Andean belt in South America, as it contains
depositsbothrelatedto Tertiary volcanicsand to Mesozoicintrusives.
5..4 smallbeltmaybranchoff the RockyMountainbeltin the U.S., going
into Coloradoand South Dakota (Black Hills). Althoughthis belt is based
on rather few occurrences,
it is interestingto note that it would correspond
to Burnham's(3) Eastern belt, definedon the basisof high trace-element
content(especiallytin) in chalcopyrite
and to a lesserextent sphalerite. In
New Mexico and SouthDakota somepegmatiticdepositsof Precambrianage
are included in this belt.
6. The .4ppalachianbelt extends from Alabama to New Brunswick and
Nova Scotia. Its southernend disappearsunder the Mississippidelta and
the Gulf of Mexico, and it may be buriedin and aroundNew Jerseyunder a
Mesozoiccover. It containsboth Precambrian,mainly pegrnatiticdeposits,
and Paleozoicoccurrenceswhich are in somecasescharacterizedby greisen.
7. The Central .4frican belt extendingfrom Natal through Swaziland,
Transvaal,SouthernRhodesiainto EasternCongoand Uganda,containspeg-
matites,lodesandpipes,whichare definitelyPrecambrian(around2,100m.y.;
in Rwanda-BurundiandKatangabetween870 and 1,000m.y.). It is tempting
to speculate
that the recentlydiscovered
Precambriantin depositsof the Eastern Desert of Egypt and thoseto the north of I(haroum are part of this
same belt.
8. The South I/Vest.4frica-Nit7eriabelt starts at the very tip of South
Africa, wheretin was minedfrom the Kuils river, near Capetown. Most of
the numeroustin depositsin South West Africa, are related to "Younger
Granites" of late or post-Karrooage (Jurassic?), but others are related to
Precambrian
granitesandpegmatites.The beltformsa relativelynarrowstrip
alongthe Atlantic Oceanin Angola,the Congos,Gabonand Cameroon,striking almostdue north into Nigeria. Extensivetin mineralization,both Precambrianand Jurassicoccurin Nigeria, and analogousmineralizationhasbeen
discovered
recentlyin formerFrenchNigeria (Air and Zindermassives). In
southernAlgeria extensivetin mineralizationoccursin the Hoggar Massif.
The belt is probablycontinuouswith sometin occurrences
in easternAlgeria,
throughthe still poorlyprospected
Sahara,wherethe lack of water prevents
prospecting
by panning. The ageof the youngergranitesis datedas Jurassic
in Nigeria and as Eocenein Cameroon.
9..4 rather poorly definedbelt extendsfrom Liberia to Morocco. In its
southernpart tin mineralization
occursmainlyin Precambrianpegmatites,
but
in Moroccosomeoccurrences
seemto be related to Hercynian intrusives.
10. The Iberian belt strikesthrough Spain and northernPortugal. The
tin-tungstenmineralization
is relatedto late-Hercyniangranites.
11. The .4rmorican belt, in the western part of the Massif Central, extendsthroughBrittany into Cornwall. All depositsare relatedto Hercynian
granitesand consistof veins,and disseminated
cassiterite
in greisen. If, as
suggested
in Figure1 thisbeltincludes
alsotheTuscanyandElbaoccurrences,
then part of the belt is of Tertiary age.
546
R. D. SCHUILING
12. TheErzgebirge
province.Herethepredominant
deposits
aregreisentype,with associated
lithium-micas,
relatedto Hercyniangranites. It cannot
be ascertained
whetherthisprovince
is part of a largertin belt.
RoughIy90% of the occurrences,
includingall but one of the pastor
presentproducersfall into the abovebeltsthat occupylessthan half the land
surfaceunderconsideration.
A calculation
showsthat the averagedensityof
tin-occurrences
withinbeltsis morethan20 timesthe averageoutsidethebelts.
The actualnumberof occurrences
anddeposits
withinthe beltsis evenhigher
than indicated,becauseit is necessary
to representcloselyspaceddeposits
in tin-fieldsby only one point, whereasoccurrences
outsidethe belt are commonlysingle,isolatedlocalitiesrepresenting
mineralogical
curiositiesin some
well-studieddepositof otherminerals. The lithologicalmap of the Republic
of Ruandafor exampleshowsover100tin localities
whichare represented
by
only 5 pointson Figure 1. This is one of the reasonswhy a methodof
contouring
to establish
the outlinesof the belt wouldbe ratherunsatisfactory.
A countof the numberof occurrences
and depositsshowsthe following:
452 points
54 points
One could argue that the belts representmountainousareas where discoveryof depositsis madeeasierby the work of erosion. This is only part of
the explanationof the belt-likepatterns,as tin depositsare absentfrom areas
that are rich in other mineral deposits,and as the belts themselvesinclude
large segments
coveredby youngersediments
or extrusives. Someexamples
of this have beennoted above,and severalexamplescould be given to show
that the beltsare not simplythe morefavorablyexposedpartsof the continents
under consideration. It must be recognized,however,that the belts cannotbe
tracedon an absolutely
objectivebasis,because
our samplingof the continents
is still very uneven. The discoveryof two tin occurrencesin Antarctica is
more significant,with possibleties to Tasmaniaand Eastern Australia, than
the discoveryof two tin occurrences
in Western Europe. It is interestingto
note that the accompanying
maps would have shownmore blank spaceonly
a few yearsago; someof the major discoveries
in the last decadesincludethe
Rondtnia tin fields,the Eastern Egypt occurrences,
the stanniferousgranites
in northern Nigeria, the cassiteritefind north of Khartoum and the tin
depositat Mount Pleasant,New Brunswick.
TIN
BELTS
AND
CONTINENTAL
DRIFT
The foregoingsectiondealsmainly with the directly observabledistribution of tin occurrencesand points to a possiblepracticaI applicationof the
observeddistributionpattern in prospecting. In this sectionthe observed
distributionof thesecontinent-sized
phenomenais consideredin their relationshipas evidencefor continentaldrift. The tin beltsof Figure 1 are replotted
on Bullard'sreconstruction
of the continentsbeforedrifting (2). As can be
seenfrom this Figure 2, there are someremarkablecoincidences.
TIN BELTS ON CONTINENTS AROUND THE ATLANTIC
547
a. The East Brazilianbelt seemsto be the directcounterpartof the SouthwestAfrican-Nigeriabelt.
b. The Rond6nia-Guyana
belt seemsto have its extensionin the LiberiaMorocco belt on the African
side.
c. The Appalachianbelt seemsto join the Armoricanbelt.
d. The Late-HercynianIberianbelt joinsmorecloselythe late-Hercynian
Armoricanbelt, if the Gulf of Biscayis closed.
e. The Iberian belt seems to be the continuation of the Southwest Africa-
Nigeriabelt.
f. The Andeanand Rocky Mountainbeltsare continuous
and tin-free;
CentralAmericais missing.
g. The groupof occurrences
in southwestGreenlandformsthe continuation of the Armorican
and the Iberian belt.
The remarkablepattern of beltsin Figure 2 alonecannotconstituteconvincing evidencefor continentaldrift, but it is safe to say that the concept
of tin concentration
in belts and the theory of continentaldrift derive some
strengthfrom each other. If we assumefor the moment that continental
drift is supportedsufficientlyby independentevidenceof paleomagnetism,
paleoclimatology,
and otherlinesof geologicalreasoningto be usedas a working hypothesis,
let us seewhere this leadsin connection
with the tin belts.
Continentaldrift is usually consideredto have taken place either from
the Permian to the Tertiary, or, alternatively,is still taking place. If the
agesof the tin depositsin the SouthwestAfrica-Nigeria belt are considered,
a numberare Precambrian(pre-drift), an importantpart are Jurassic(during
drift) and someare Eocene(after drift or at a later stageduringdrift). This
is interpretedto mean that throughoutthis time the sourceof the tin must
havebeencarriedalongby the movingcontinents. Hence this sourcemustbe
locatedin the crust,or in that part of the uppermantlewhich adheredto the
crust during drifting. Otherwiseif the sourceof tin is somelinear zonein
the mantle, mineralizationwould have taken place in successivelydisplaced
belts as the crust slid over this sourceof tin. It seemsreasonableto suppose
that the idea of a crustal sourceholds also for the commonlyassociatedelements W, Ta, Nb, Be, Li, F.
CAUSES
OF
TIN-CONCENTRATIONS
There is anotherpoint that meritssomespeculation.It is rather obvious
that in a generalway severalof the tin beltsfolloworogenictrends(Andes,
RockyMountains,Appalachians,
Armoricanbelt). It is onlyin muchsmaller
segments
of thosebelts,however,that largeconcentrations
of occurrences
and
workabletin depositsare found. There may be someindicationon Figure 2
that for economicconcentrationsto occur, a combinationof a geochemical
culminationand an "event" is necessary. A geochemical
culminationis consideredto be a continent-sized,
lower-crustalbelt along which a particular
elementhasbeenenrichedrelativeto its normalabundance.An "event"is any
geological
process,
by meansof whichthisenriched
materialis broughtup, or
further concentrated
as for exampleby the development
of graniteintrusions
548
R. D. $CHUILING
:::::::::::::::::::::::::::::::::::::::
...............
. ..::i:i::.
...............
....•.•.:,:.:.;.:..
.......,.-,................
.,
..........
..:.:.•.:...•.:.•q.:..
............
........i:i:i:i:i:iiiii2!i
.........
DARKER AREAS
IN TIN-BELTS
INDICATE
CONCENTRATIONS
WORKABLE
OF
DEPOSITS
POSITION
OF TIN-BELTS
RECONSTRUCTION
ON A
OF THE CONTINENTS
R, D. SCHUILING, 1966
Conhnentolfit after Bullordet ol. (1965)
Fz•.
2.
TIN BELTS ON CONTINENTS
AROUND THE ATLANTIC
549
accompanyingan orogeny. Each of these factors alone is not sufficientto
produceworkable deposits. A geochemicalculmination is passive,whereas
certain eventslike pegmatiteformation, granite intrusion, or volcanicextrusions,may under favorableconditionsproducesometin minerals,even when
starting with materialsoriginally poor in tin. Such occurrenceswill rarely
exceedthe statusof mineralogicalcuriosities. Only if the appropriateprocess
actson alreadyenrichedstartingmaterialwill economicconcentrations
of tin
minerals result.
These conceptsfind somesupportin the data in Figure 2. The rich
Boliviantin deposits
are foundwherethe Rond6nia-Guyana
belt strikesinto
the Andes, whereaselsewherein the Andes the same apparentgeological
processes
produced
onlyinsignificant
concentrations
of tin minerals. The same
relationshipmay hold true for Mexico, where the Appalachianculmination
joins the RockyMountainbelt. Anotherexamplemight be Cornwall,where
the Iberian and the Armoricanbelt cometogether.
Clearly,with only 12 beltsand provinces,and with evenfewer intersections,argumentslike thesecan neverbe completelyconvincing. The idea of
an interactionbetweengeologicalevent and geochemicalculminationdoes
seemlogical,and it is consistent
with the smallamountof availabledata. The
significant
pointis that the ultimatecauseof the geochemical
inhomogeneities
may be due to someprocessaccompanying
the earliestformationof the
sialiccrust.
-•,
•
VENING•V•EINESZ
LABORATORY
OFGEOPHYSICS
ANDGEOCHEMISTRY,
UTRECHT,
•lpri124, 1967
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