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EconomicGeologyVol. 78, 1983, pp 514-520

OCCURRENCE AND AGE OF TIN MINERALIZATION INTHE CORDILLERA ORIENTAL, SOUTHERN PERU

ALAN H. CLARK, VICENTE V. PALMA, DOUGLAS A. ARCHIBALD, EDWARD FARRAR,Department of GeologicalSciences, ueen'sUniversity,Kingston,Ontario K7L 3N6, Canada

MARIO J. ARENAS .,Ge6logoConsultor,Caminos del Inca 698, Lima 33, Perd

AND RONALD C. R. ROBERTSONAGIP Canada,2700 ScotiaCentre, 700 2nd Street S.W., Calgary, Alberta, CanadaIntroduction

The tin-silver belt (Turneaure, 1971) of the Cor-dillera Oriental (Eastern Cordillera) of western Bo-livia has ongbeen ecognized san areally estrictedmetallogeneticsubprovinceof the central Andeanorogen.Recentgeochronologicaltudies Clark andFarrar, 1973; Evernden et al., 1977; Grant et al., 1979;McBrideet al., in press) aveshown hat felsicmag-matismand associatedydrothermalin-polymetallicmineralizationn this egionoccurred longa narrowlongitudinal belt, close to the inner (i.e., eastern)boundary f the orogen,n threeepisodes:he Middleto Late Triassic 225-200 m.y.), the late Oligoceneto early Miocene 29-19 m.y.), and the middle to lateMiocene (17-12 m.y.). The tin belt experiencedasouthwardmigrationof igneous nd hydrothermalactivity,although t 18 S there s an en echelon realoverlap McBrideet al., in press) f the two youngersubprovincesistinguished y Grant et al. (1979).Moreover, ungsten- nd antimony-bearing, ossiblyLate Tertiary, subvolcanicenters rop out along henortheastern shore of Lake Titicaca in northwesternBolivia (Ahlfeld and Schneider-Scherbina,964), atthe same atitudes s the Triassicplutonsof the Cor-dillera Real (Fig. 1).The limited southward rolongation f the Andeantin belt into northwesternArgentina is apparentlywell delimited (Ahlfeld, 1967), but its northwardex-tension nto southeasterneru is poorly defined Pe-tersen,1972). n recentyears,however, his segmentof the PeruvianCordillera Oriental, and particularlythe Cordillerade Carabayadistrict lat 14 to 14$0'Slong 70 to 7045'W:Fig. 1), hasemergedas a sig-nificant source of tin concentrates. The San Rafaelmine in northern Puno Department (lat 1412'00 S,long7020'15 W; ig. 2), operated y Minsur,S. A.,was formerly a modestcopper producer but hasyieldedover 10,000metric onsof cassiteriteoncen-trates avg. gradeca. 42.2% Sn) since1970. Produc-tion in 1981 amounted to 1,500 tons of Sn metal(Minsur,S. A., unpub. epts.).The SanRafaeldeposit

is one of severalcomplex polymetallic ode systemsunder developmentn the Cordillerade Carabaya.The occurrence f significant mounts f tin in basemetal ores n PunoDepartmentwas irstrecordedbyRaimondi 1878), who examinedPb- and Sb-richveinsamples rom the Vilquechico district, situatedcloseto the northernshoreof Lake Titicaca. Subsequently,at Cerro Calvario n the samearea, de Romafia 1908)observedhin veinlets,apparentlyof Sn-Pbsulfides.Although hat authorconsideredhere was ittle con-vincingevidenceof the extension f the Bolivian inbelt into southeastern eru, Petersen 1960) was ableto record seven further occurrences of tin mineralsin the region, including both bedrockand fluvio-glacial deposits.Moreover, imited productionhadtaken place from the latter. The San Rafael depositwas apparently first recordedas containing in byZambrano t al. (1965), while Rodriguez 1966) tab-ulated several new localities at which tin occurs inthe region.The CordilleraOriental of PunoDepart-ment is defined as a tin-polymetallicsubprovince nthe 1:2,500,000metallogeneticmap of Peru (Bellidoet al., 1972), but systematic reatment at that timewas hindered by the lack of reliable information oneven he locations f someof the Sn-bearing eposits.The Cordillera Oriental is bounded, to the south-west,by the northernextremity of the elevatedA1-tiplano basin, whereas,on the northeasterly lank,altitudes all abruptly to the sub-Andean angesandthe headwaters of the Rio Inambarl and its tributaries(Fig. 2). MostknownSn-bearing eposits re locatedon the southwesterlylopes f the main, ice-cladCor-dillera de Carabaya,at altitudesof up to 5,000 m.We are engaged n an investigation f the geo-chronology, etrochemistry, nd metallogenetice-lationshipsn the Cordillerade Carabaya Robertson,1978; Palma, 1981; Palma and Clark, 1982; Clark etal., 1982;D. J. Kontak,unpub.studies),nvolvingcomparisonwith the better known northern Boliviansegmentof the tin belt. In the presentcommunica-tion, we provide the first geochronologicalvidencefor the age of tin-polymetallicmineralizationn this

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SCIENTIFIC COMM UNICA TIONS 515

little known but extensivelymineralized area of thecentral Andes. ConventionalK-Ar mineral ages arepresented or the producingSan Rafael Sn-Cu veinsystems nd for the SantoDomingo Sn-Cu-Pb-Zn-Agprospect,ocateda shortdistance o the westof theformer mine (Fig. 2).The K-Ar ages by D. A. A. and Geochron abo-ratories)were determined following standard ech-niques,using he reviseddecayconstants f Steigerand Jiger 1977),and are referred o the time scaleof Van Eysinga 1975).

Geologic SettingAlthough he study area has receivedcompara-tively little detailedgeologicnvestigation,he majorrelationshipsre definedon the 1:1,000,000 eologicmap of Peru (INGEOMINAS, 1975).Recently,Lau-bacher 1978) hasprovideda 1:500,000geologicmapof part of the CordilleraOriental of PunoDepartment

and a descriptionof the pre-Cenozoic volutionofthe area, updating the pioneeringwork of Newell(1949) and Newell et al. (i955). Stewartet al. (1974),Lancelotet al. (1978), and Audebaudet al. (1979)have eported adiometric ges or granites nd otherigneous ocks n the region.The geologic istoryof the CordilleraOriental nsoutheastern Peru is summarized in Table 1 and willbe discussed nly briefly herein. The stratigraphicrecord is similar to that in the Cordillera Real of Bo-

/

take

SANRAFAEL-' 200 km

Ii I

UPPERERMIAN- ORURO& [.38 MD TRIASSIC LUTONS[MD.-UP.RIASSICLUTONS-I+W-Sn) 202-225 Ma[ UP.LIGO.-R. SMIOCENELUTONS+Sn-W) .'- R-IOCENESUB- UP. IOCENEOLCANICn

22'

Fit;. 1. Generaldistribution nd agerelations f intrusivebodiesand mineralization n the tin-polymetalliebelt of the central An-dean Cordillera Oriental, with the location of the San Rafael de-posit. Modified after, inter alia, Evernden et al. (1977), Grant etal. (1979), and Laubaeher 1978). Numberson Oligoeene-Mioeeneplutons n Bolivia are ages in m.y.) from McBride et al. (in press).

, 70:i . 69 1( ' '.d,o ' -

I / ,,-. .... -_-.-/ I -

F'-S. x .,. / ' L'%7 '.*'-' '' _

ue x O_ . -I_& -/O, ' ,

F(;. 2. Morphostructuralrovincesn southeasterneru,withlocations of the San Rafael mine and Santo Domingo prospect.Modified after Laubacher (1978).

livia but is generally more complete.Large areasareunderlainby lower and upper Paleozoic trata Lau-bacher, 1978) and record tectoniceventsof both An-dean (i.e., Middle Triassicand younger)and pre-An-dean (Hercynian: M6gard et al., 1971) orogenies. tis evident that intrusive and volcanic rocks were em-placed both in the Carboniferous-Triassicnterval,i.e., at the closeof the younger of the pre-Andeantectoniccycles,and in the Cenozoic,as an integralpart of the Andeanorogeny.Each igneous uitedis-playsa wide compositionalange, from gabbros nddiorites to monzogranitesStreckeisen, 967). Thepre-Andean volcano-plutonicbodiesare more volu-minous han the Andean, and all large granitoid n-trusionsare of Permo-Triassicage (Stewart et al.,1974; Lancelot et al., 1978; Laubacher, 1978).The ages of intrusionof the probably numerous(Laubacher,1978) Andean plutons n this region arein part constrainedby their stratigraphic elation-ships,as in the Precordillerade Carabaya (Fig. 2;Laubacher, 1978), where severalsmall stocks ntrudeCretaceous sediments. In the main Cordillera de Car-abaya,however, he graniticrockswere emplaced nPaleozoic trataand could, therefore, be of any post-Paleozoicage. It has been assumed hat the majorityof plutons re of Oligoceneor Mioceneage (Petersen,1960;Laubacher, 978)becausehey are inferred opostdate he postulatedmiddle to late Eocene Incaic)episodeof Andean deformation.This interpretationis not convincingly upported y stratigraphic r tec-

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516 SCIENTIFIC COMM UNICA TIONS

TABI.E1. SimplifiedStratigraphic olumn,CordilleradeCarabaya, Southeastern eruModifiedafter Laubacher, 978;plutonic ocksomitted.Approx.thickness

Formations nd lithologies (m)Miocene-PlioceneCretaceous

Late Permian

Pennsylvanian-Early PermianMississippian

Siluro-DevonianCaradocian

Llanvirnian-Llandeillian

Felsic gnimbrites 2,500Sandia Formation (shales, :3,500quartzites)SanJos( ormation (shales) :3,500

Basementnot exposed

tonic relationships n the immediate study area buthas nevertheless een confirmedby our geochrono-logicalstudies.The mostvoluminous ndean gneous odies n theCordillera de Carabaya are probably the thick andareallyextensive equencesf felsicperaluminousg-nimbrites (Francis, 1959; Laubacher, 1978), whichare of Miocene o Plioceneage (Barnes t al., 1970;Noble et al., 1982).Mineralization

A wide range of metallic mineralization s repre-sented in the Cordillera Oriental of Puno Depart-ment, but production o date has been limited. Inaddition to the San Rafael Sn-Cu deposit, here haslongbeena modest ecoveryof gold from veinsand,more widely, fiuvioglacial gravels. Several smallminesare currentlyproducingPb-Zn-Agconcentratesin both the Cordillera de Carabaya and the Precor-dillera de Carabaya, as well as in the contiguousAI-tiplano.The great majority of the deposits re vein type,although everal trata-bound b-Zn-Ag,Cu, and Mncentersare known. Baseand preciousmetal vein sys-

rems, particularly those n which copper and tin areabundant,showa spatialassociation ith granitic n-trusions. everalof thesedistrictsdisplaymetal zona-tion patterns, howing, or example,Cu and Sn con-centratedwithin and adjacent o the plutons,whereasPb, Zn, and Ag occur n peripheralareas D. Kontak,unpub.studies). everal mallvein and skarndeposits,includingsomeof tungstenand copper,are locatedwithin or adjacent o large granitoidplutonsof Perm-ian or Triassic ge, suchas the Coasabatholith Lau-bacher,1978),but the magnitudeof the Permo-Trias-sic metallogenetic pisode s undefined.The knowntin-polymetallicdepositsof proven or probable po-tential in the Cordillera de Carabaya are associatedwith youngergranitic ntrusions mplacedduring theAndean orogeny.These nclude the San Rafael Sn-Cu deposit and, almostcertainly, the nearby Quen-amari, or Mina Carabaya,Sn-Cu-Pb-Zn-Ag istrict)and the SantoDomingoSn-Cu-Pb-Zn-Agvein system.San Rafael district

This intenselymineralizeddistrict Fig. $) hasbeenmappedby N. Roldn (unpub. ept.) and, more com-prehensively,by Arenas (1980). Palma (1981) hascarriedout a mineralogical nd fluid inclusion tudyof the mineralization (see Palma and Clark, 1982).The SanRafaeland Quenamari Carabaya)minesaresituated at altitudes of over 4,500 m above sea levelon the slopes f the snow-capped evadoBartolom(de Quenamari, in Melgar Province. At San Rafael,mineralizationhas been exploitedover a vertical in-terval of 500 m.All known mineralizationat San Rafael and Quen-amari is localized n steeply nclined veinsand struc-rurally complex odes,with longitudinal xtensionsfup to $ to 4 km. Mostof the veins rend northwesterlyand, althoughconcentratedn the immediate vicinityof two small

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SCIENTIFIC COM M UNICA TIONS 517

Palma 1981)distinguishesour majorstages f veindevelopmentn the largeSanRafael ode,as ollows:(1) early, essentially arren, quartz-tourmalinevein-lets and brecciabodies; 2) a botryoidalcassiterite-quartz-chlorite tage,n which he bulk of the tin wasdeposited; ((3) a chalcopyrite- needle in -quartzchlorite stage;and (4) minor, unmineralized, atequartz-calcite eins. n the SanRafael ode theseep-isodes f mineralizationwere superimposed,eadingto the developmentof complex vein fabrics, withwidespread ine brecciationand wall-rock replace-ment, similar in many respectso thoseof the majorSn-Cu odesof Cornwall-Devon,England (Hosking,1969). Asnotedpreviously, he mine beganoperationsas a copperproducer,and only began o yield sub-stantialamountsof cassiteriten the early 1970s.Thetrend reflects an unusually clear-cut vertical metalzonation (Arenas,1980) in which copper overlies in,againas ocally n Cornwall,England.The transitionfrom the tin to the copper zones n the San Rafaellode s at ca. 4,600 m abovesea evel, and stopinghasbeen carried out from the 4,555-m level to just below5,000 m above sea level.Fluid inclusionstudiesby Palma (1981) demon-strate that the bulk of the tin and copper were de-posited rom nonboiling ow-salinity luids at mod-erate emperaturesca.220-$90C)and at very shal-low depths (confining pressures

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/

LEGENDUPPERLIGOCENELOWERMIOCENE GRANITC)D INTRUSIONSGRANITOIDIKESPALEOZOICETASEDIMENTSVEINSRIVERS

SKETCH MAPOF

SANTO DOMINGO PROSPECT

o 1 2 Ikm

FI(;. 4. Geologic ketchmap of the SantoDomingoprospectarea. Modified after M. J. Arenas unpub. rept.).

the interval between magmatic and hydrothermalevents. Three samplesof magmatic biotite in thegranitewere dated (Table 2); thesewere taken as aras possiblerom the main San Rafael lode or subsid-iary veins,on the 4,660- and 4,555-m levelsof themine. Although biotite in the stock widely shows

marginalchloritization, he potassium ontents f theanalyzed fractionssuggest hat these micas are ac-ceptably fresh.The three biotite ages,determinedat Queen'sUni-versity (24.0 and 23.7 _ 0.6 m.y.; error expressed s2a), and by GeochronLaboratories 25.9_ ca. 1.0m.y.; recalculated,ollowingSteigerandJiger,1977,from Arenas,1980), althoughnot identical,suggestthat intrusionof the San Rafael stock ook place inthe latest Oligocene.All three age determinationsappear valid from the analytical standpoint,and theminor discrepanciesetween hem may reflect ther-mal resetting, erhaps uringquasi-pervasive,reore,high-temperature hydrothermal activity (Palma,1981).The depthof emplacement f the granitecan-not be directlyestimated ut is unlikely o havebeengreat, and it is inferred that intrusionand consoli-dation of the pluton occurredat 25 to 26 m.y.The age of hydrothermalmineralizationat SanRafael is estimated rom analysisof a specimenofmassivemilky-white adularia. The unaltered eldsparis ntergrownwith quartz and is associated ith chal-copyrite,sphalerite,galena, and chlorite; t was col-lectedduring July 1979 from the north end of the4,820-m adit on the Jorgevein. Crystallization f thefeldspar ook place late in the emplacementof thethird Cu-rich stage of lode development Palma,1981).The adulariahasa monoclinichighsanidine)crystal tructure,ndprobablyesisted I, Siorderingowing o rapid cooling rom its depositionalemper-ature of ca. $00C.The apparent geof the adularia, 2.6 _ 0.5 m.y.(Table 2), falls at the Oligocene-Mioceneoundarybut snotsignificantlyoungerhan he apparent geof at least one of the magmatic biotites. Theshallowdepth of emplacementof the San Rafael oresand the moderate emperatureof mineralization m-ply that the adularia K-Ar age providesa reliableestimate of the time of ore formation. If the oldest

TABLE . K-Ar Age Determinations, an Rafael and Vicinity, PeruAnalysis Specimen Mineral 4hr rad) % 4Ar Age andno. no. analyzed % K cm NTP/g (arm.) error (m.y.)San Rafael deposit

1 B-4850 Biotite 7.209 7.115 )< 10 4, 52.2 25.9 1.02 SARL-457 Biotite 7.216 6.767 )< 10 ' $6.2 24.0 0.6$ SARL-259 Biotite 7.446 6.911 )< 10 4' 41.1 23.7 +__ .64 SARL-4$4 Adularia 11.464 10.141 )< 10 ' 10.2 22.6 +__ .5

Santo Domingo deposit5 SD-7 Biotite 7.189 6.841 X 10 -4' 13.9 24.3 0.6

Analysis by Geochron aboratories,emainderby D. A. Archibald; nalysis is for vein adularia,othersamples re for magmaticbiotite in monzograniteAgeswerecalculated sing he constantsuggestedy Steiger ndJiger 1977); rrors epresenthe analytical recisiont 2a

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SCIENTIFIC COMMUNICATIONS 519.biotitedate (25.9 +_1 m.y.) may be regarded spro-vidinga minimumage or intrusion,headulariadatewouldbe in permissivegreementwith a model n-volvinga hiatusof ca. 2 m.y. betweengraniteem-placement nd stage mineralization.Santo DomingoAt thisprospect e haveobtained n ageonly ormagmaticbiotite.The analyzedspecimenTable 2)wascollectedrom a narrow,coarse-grained,on-zogranitedike located near the southern imit of themineralized istrict.This rock s slightly hloritized,but the biotite is fresh.The K-Ar biotiteage of 24.$+_ .6 m.y. is verysimilar o thoseeported bove or the magmatic io-tites rom SanRafael, mplying hat ntrusionn thetwo centerswas essentiallycontemporaneous. hesimilaritiesn the styleof mineralizationn thesedis-trictsalsosuggesthat they may be assignedo thesamemetallogenetic pisodeand district.

Discussion:Regional RelationshipsThe K-Ar age data presented erein demonstratethat, although omemineralizationn the Cordillerade Carabayas certainly f Permo-Triassicage, hemost mportantmetallogeneticvent so far recog-nized n the regionoccurredn the late Oligiocene(ca.26-25 m.y.).No otherdates avebeen eportedfor ore depositsn thisregion,but Audebaud t al.(1979)havedetermined -Ar agesn the range 5.6to 28.$ (+_1)m.y. for basaltic nd trachytic olcanics

near the southwestern arginof the CordilleraOri-ental,andof 22.0 to 26.0 m.y. for several mallstocksof gabbroicr granitic ompositionn thesame en-eral region.Thus, he Sn-polymetallic ineralizationwas associated ith a magmaticepisodewhich af-fected wide areasof the Cordillera Oriental of south-easternPeru. Volcanism ersistedn this regionthroughhe Neogene nd, ocally,nto he Quater-nary (S. L. McBride,unpub.data),but asyet thereis no definite videnceor post-Oligoceneineral-ization; hus, he middle o late Miocene pisode fCu-Pb-Zn-Ag-Aure ormation istinguishedn cen-tral Peru e.g.,McKee t al., 1979)has etto becon-firmed in this area.Simultaneouslyith the late Oligocenenitiationof magmatic ndhydrothermalrocessesn the Cor-dilleraOrientalof the studyarea, hereoccurredregionaleactivationf thecentralAndeanmagmaticarc in areas as widely separatedas southernPeru(Nobleet al., 1974;Tosdal t al., 1981),and north-ernmost Mortimeret al., 1974)and northern Clarket al., 1976;Quirt, 1972)Chile.At this ime (ca.26-20 m.y.) hepreviouslyarrow,ongitudinal,olcano-plutonic elt of the CordilleraOccidentalwesterncordillera)xperiencedradical realbroadening,

penetrating in some transects o over 500 km fromthe continentalmargin (Clark et al., 1976;Clark andMcNutt, 1982).Thisepisode asbeen entatively s-cribed o the immediately recedingeorganizationof plateconfigurationsn the contiguousastern a-cific basin, nd coincided ith widespreadhysio-graphicuplift throughout he westernand easterncordillera R. M. Tosdal,A. H. Clark, and E. Farrar,unpub.data). There is, however,only limited evi-denceof metallicmineralizationf this age n theCordilleraOccidental f southern eru, perhaps e-flecting he restricted xposure f intrusivebodies.Asnotedn the ntroduction,he northern egmentof the tin belt in Bolivia was reactivated in the lateOligocene28-29 m.y.), presaging broadsouthwardmovement f magmatic nd hydrothermal ctivitythrough he Miocene (Everndenet al., 1977; Grantet al., 1979;McBride et al., in press).However, heages eterminedor the importantSanRafaeldepositand or theSantoDomingo rospecthow learly hatthis time-spacepattern is not extrapolatednorth-westwardalong the Peruviansegmentof the belt.Thesepolymetallic ein systems re coevalwith themostproductive f the tin vein depositsn the plu-tonic subprovinceof northern Bolivia, i.e., in theCordilleraQuimsaCruz (McBrideet al., in press)some450 km to the south.As far as is known, therearenosignificant ligocene-Miocenein-bearingen-ters n the northwesternmostegment f the Boliviantin belt, so that the mid-Tertiary in veinsof Perumay be widely separatedrom thoseof northernBo-livia. Acknowledgments

Field studiesn Peru were fundedby grants oA.H.C. from the NationalSciencesnd EngineeringResearchCouncil of Canada, as part of the CentralAndean Metallogenetic roject (CAMP). The samebodysupportedaboratorytudies,hrough rantsoE.F. and A.H.C.Field work in the Cordillerade Carabayawouldnot have been possible ithout he generous oop-erationof Minsur,S. A. We are particularlyndebtedto FaustoZavaleta,GerenteGeneral, or permissionto undertake his research nd to publish his contri-bution. At San Rafael, we received he kind assistanceof NestorRoldftn,Adolfo Mdico, JulverAlvarez,Hugo Cruz, and PastorLuque.The earlier stages fthe programwere carried out in collaborationwithFlavio Estrada,of the former InstitutoCientificoyTecno16gico inero del Per6.August 6, December 1, 1982

REFERENCESAhlfeld, F., 1967, Metallogenetic pochs nd provinces f Bolivia:Mineralium Deposita,v. 2, p. 291-$11.

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520 SCIENTIFIC COMMUNICATIONSAhlfeld,F., and Schneider-Scherbina,., 1964, Los yacimientosminerales de hidrocarburose Bolivia:BoliviaServicioGeol.,Bol. 5, 888 p.Arenas,M. J., 1980, E1distrito minero San Rafael, Puno:estafio nel Per6: Soc.Geol. Per6 Bol., v. 66, p. 1-12.Audebaud, ., Bernard,D., Vatun-Perignon,., and Vivier,G.,1979,Quelques gesK/Ar sur es ochesgn6es nozoiquesu

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