Economic Geology Vol. 85, 1990, pp. 1520-1583 Geologic and Geochronologic Constraints on the Metallogenic Evolution of the Andes of Southeastern Peru ALAN H. CLARK, EDWARD ARlIAR, ANIEL J. KONTAK,* ROBERT . LANGRIDGE, Department of Geological Sciences, ueen's University, Kingston, Ontario, Canada K7L 3N6 MARLO . ARENAS F., Gedlogo Consultor, Caminos del Inca 698, Lima 33, Peru LYNNE . FRANCE,** ANDRA . MCBRIDE, RISCILLA . WOODMAN,*** HARDOLPH . WASTENEYS, HAMISH A. SANDEMAN, AND DOUGLAS A. ARCHIBALD Department of Geological Sciences, ueen's University, Kingston, Ontario, Canada K7L 3N6 Abstract The post-Paleozoic etallogenic volut ion of southeastern eru s clarified on the basis of the stratigraphic nd ithologic ettings f the majority of the known metallic ore deposits nd a regional rogram f K-Ar and 4øAr-39Ar eochronology. his central ndean ransect isplays a range of mineralization ypesunparalleled n other regions of the country. Contrasting magmatic, ectonic, nd metallogenic elationships re shown y the calc-alkaline-shoshonitic Upper Triassic-Holocene ain Arc magmatic omain, underlying he present Cordillera Oc- cidental and Altiplano, and the more restricted Triassic-Pliocene nner Arc domain of the Cordillera Oriental, which incor porates great variety of igneous suites andexhibits a cor- respondingly iverse metallogeny. Major economic mineralization ccurred simultaneously in the two domains nly during he late Oligocene o early Miocene nterval. The earliest significant ndean W, Cu, Mo, Sn, and Au mineralization s hosted argely by weakly peraluminous ranites f the U pper Triassic o Lower Jurassic 190-225 Ma) Carabay a batholith n the Inner Arc; magma genesis esulted rom sediment natexis long he margin of the Permian ensialic Mitu rift. Renewed ifting in the Middle Jura ssic ca. 170-180 Ma) in this area was associated ith the emplacement f the volcano-plutonic llinccfipac eralkaline Complex, syenitic plutons of which host minor Cu, Ag, and Zr(-REE) vein systems. esozoic mineralization n the Main Arc, weak n comparison o that in other central Andean ransects, comprises pper Jurassic 145-165 Ma) Cu-Au veins e.g., Rosa Maria), and mid-Cretaceous (ca. 95-110 Ma) Cu (Santiago, alparffiso) nd Fe (Morritos, Cerro Pelado) veins of the Ilo- Itc district. Restricted Upper Cretaceous ca. 80 Ma) Cu-Pb-Zn-Ag veins n the Crucero district of the Inner Arc are nterpreted as ecording brief episode f arc broadening r bifurcation. Large-scale orphyry Cu(-Mo, Ag) centers were emplaced n the Main Arc in the interval 52.15 (Cuajone) o 57.1 Ma (Toquepala) s he terminal stage n the evolution f the subaerial volcanic uccession f the Upper Cretaceous-Paleogene oquepala Group, which had previously experienced nly minor Cu(-Pb-Ag-Au) ein mineralization t ca. 80 (Challatita) and 62 Ma (Lluta district). he early Eocene vent epresents hemetallogenic ulminationf thePeruvian Coastal atholith and ts extension n northern Chile. n contrast, nly he northern extremity of the upper Eocene-lower Oligocene rc of northern Chile occurs n the study area, and he minorAtaspaca Cu-Mo-Pb-Zn-Ag tockwork nd skarn mineralization 39-45 Ma) is a pale reflection f the coeval array of giant porphyry opper deposits arther south. Much of south- eastern Peru lacked magmatism mmediately efore and after the ca. 40-Ma Incaic orogeny and hence experienced a metallogenic hiatus. The Main Arc was resuscitated n the Santa Lucia area at 31 to 32 Ma; at 28.5 + 1 Ma it abruptly broadened o a width of ca. 235 km. However, hydrothermal ctivity emained estricted n both scale and distribution. he mod- erate-sized Berenguela ca. 27 Ma) and Santa Bfirbara 23 .5 Ma) epithermal Ag deposits re associated with calc-alkaline ubvolcanic enters, n the latter case emplaced n the initial stages f cordilleran plift. Post-Oligocene ineralization ntheMain Arcwas also pparently * Present address: ova Scotia Department of Minesand Energy, 1496 Lower Water Street, Halifax, Nova Scotia, Canada B3J 2X1. ** Present address: Apt. 2C-4, 2665 Favor Road, Marietta, Georgia 30060. *** Present address: 56 East Haskell S treet, A pt. A, Winnemucca, Nevada, 89445; n•e Johnson. 1520
GedlogoConsultor,Caminosdel Inca 698, Lima 33, Peru
LYNNE . FRANCE,** ANDRA. MCBRIDE, RISCILLA. WOODMAN,***HARDOLPH . WASTENEYS,HAMISH A. SANDEMAN, AND DOUGLAS A. ARCHIBALD
Department of GeologicalSciences, ueen'sUniversity,Kingston,Ontario, Canada K7L 3N6
Abstract
The post-Paleozoic etallogenic volutionof southeasterneru s clarifiedon the basisofthe stratigraphic nd ithologic ettings f the majorityof the knownmetallicore deposits nda regional rogram f K-Arand4øAr-39Areochronology.hiscentral ndeanransect isplaysa range of mineralizationypes unparalleledn other regionsof the country.Contrastingmagmatic,ectonic, ndmetallogenicelationshipsreshown y the calc-alkaline-shoshoniticUpper Triassic-Holocene ain Arc magmatic omain,underlying he presentCordilleraOc-cidentaland Altiplano,and the more restrictedTriassic-Pliocenenner Arc domainof theCordillera Oriental, which incorporates great variety of igneoussuitesand exhibitsa cor-respondingly iversemetallogeny.Major economicmineralization ccurredsimultaneouslyin the two domains nly during he late Oligocene o early Miocene nterval.
The earliestsignificant ndeanW, Cu, Mo, Sn, andAu mineralizations hosted argelybyweaklyperaluminousranites f the UpperTriassico LowerJurassic190-225 Ma) Carabayabatholith n the Inner Arc; magmagenesisesulted rom sediment natexis long he marginof the PermianensialicMitu rift. Renewed ifting in the Middle Jurassicca. 170-180 Ma) inthisareawasassociated ith the emplacement f the volcano-plutonic llinccfipac eralkalineComplex,syeniticplutonsof whichhostminorCu, Ag, andZr(-REE)vein systems. esozoicmineralization n the Main Arc, weak n comparisono that in other central Andean ransects,
comprises pper Jurassic145-165 Ma) Cu-Auveins e.g., RosaMaria), andmid-Cretaceous(ca. 95-110 Ma) Cu (Santiago, alparffiso) nd Fe (Morritos,Cerro Pelado)veinsof the Ilo-Itc district.RestrictedUpper Cretaceousca. 80 Ma) Cu-Pb-Zn-Agveins n the Crucerodistrictof the Inner Arc are nterpretedas ecording brief episode f arcbroadening r bifurcation.
Large-scale orphyryCu(-Mo, Ag) centerswere emplaced n the Main Arc in the interval52.15 (Cuajone) o 57.1 Ma (Toquepala) s he terminalstage n the evolution f the subaerialvolcanic uccessionf the Upper Cretaceous-PaleogeneoquepalaGroup,whichhadpreviouslyexperienced nly minorCu(-Pb-Ag-Au) ein mineralization t ca. 80 (Challatita)and 62 Ma(Llutadistrict). he earlyEocene vent epresentshe metallogeniculmination f the PeruvianCoastal atholithand ts extensionn northernChile. n contrast, nly he northernextremityof the upper Eocene-lowerOligocene rc of northernChile occursn the studyarea,and heminor AtaspacaCu-Mo-Pb-Zn-Ag tockwork nd skarnmineralization 39-45 Ma) is a palereflection f the coevalarrayof giantporphyry opperdepositsarthersouth.Muchof south-easternPeru lackedmagmatismmmediately efore and after the ca. 40-Ma Incaic orogenyand hence experienceda metallogenichiatus.The Main Arc was resuscitatedn the SantaLucia area at 31 to 32 Ma; at 28.5 + 1 Ma it abruptlybroadened o a width of ca. 235 km.However,hydrothermal ctivity emained estricted n both scaleanddistribution. he mod-erate-sizedBerenguela ca. 27 Ma) and SantaBfirbara 23.5 Ma) epithermalAg deposits reassociatedwith calc-alkaline ubvolcanic enters, n the latter caseemplaced n the initialstages f cordilleran plift.Post-Oligoceneineralizationn the MainArc wasalso pparently
* Presentaddress: ova ScotiaDepartmentof Mines andEnergy, 1496 Lower Water Street, Halifax,Nova Scotia, Canada B3J 2X1.
sparse n comparison o the broadly contemporaryepithermalAg-Au-basemetal depositsofcentral and south-centralPeru, but it comprises he Au-rich veins of the Mafiazo camp (19Ma) and the Ag veinsof the Cacachara 6.5-7 Ma) and Compuertacamps 7 Ma).
The Inner Arc revived at 28 to 29 Ma, simultaneously ith the Main Arc broadening.Anatexis esulting rom shoshonitic asalt njection generatedstronglyperaluminousmon-zogranitestockswith which are spatiallyassociatedmajor, high-grade, ithophile and basemetal ode systems,ncludingSanRafael 23-24 Ma) andPalca11 (24-25 Ma), now he most
productive ard-rockSnandW deposits f the WesternHemisphere.However, he widespreadmiddle and ate Miocene peraluminousmagmatismn this region failed to produceSn poly-metallicmineralization f the scaledeveloped n Boliviaat this time; only the smallJhsicavein system 17.4 Ma) hasbeen confirmed o containSn, and the Sb veinsof the area (e.g.,Collpa:12.3 Ma) are alsoof restricted ize. n contrast, he uraniumstockworks6.8-8.0 Ma)associated ith the rare element-enriched,hyoliticMacusani olcanics re arge andappar-ently of high grade.
Althoughsharing everalmetallogeniceatureswith contiguous entralAndean ransects,southeastern eru differsmarkedly rom other areasof the country n the natureand age ofmineralization.Thus, the Inner Arc domaindoesnot persist o the northwest,and the radicaland commonly brupt changeswe define n the distributionof magmatism, nd hencemin-eralization,during he middleand ate Tertiary are apparentlyunrepresentedn centralPeru.The individualmetallogenic volutionof this region s ascribedo the inferredoccurrence fa markeddeflection n the westernboundaryof the SouthAmericanplate throughout heAndeanorogeny.
"Atenci6n,sefioras sefiores, n momentode aten-ei6n: Volved un instante la eabeza haeia este lado de
la republiea... E1Peregrino."Nieanor Parra, Poemasy Antipoemas
Introduction
SOUTHEASTERNeru (Figs.1 and2) displays widerrangeofmineralizationhanmorenortherly ranseetsof the PeruvianAndes. t has,however,received essgeologic crutiny, erhaps ecause f the reputation
of the PunoDepartment sbeingcharacterizedysmallore depositsPurser, 971). The variegated a-ture of the metallogenieelationshipsn this ranseetof the Mesozoic-Cenozoicndean rogenargely e-fleets the occurrence in the Cordillera Oriental of a
diverse ssemblagef peraluminousranitieplutonsand hyolitiegnimbrites ith associatedin-tungsten-polymetallienduraniummineralizationf types n-represented r rare elsewheren the country.Theoceanward art of this regionalsohas he greatestconcentrationf majorporphyrycopper -molybde-num)depositsn thePeruvian ndes, omprisingheoperating Toquepala and Cuajone mines and theQuellaveeo rospect.n contrast,he scattered pi-thermalvein systemsf the extensive ertiarycon-tinental olcano-sedimentaryerraneof the CordilleraOccidental nd contiguous ltiplanohavebeen essimportant ssources f silver,gold, ead,copper, ndzinc than those n geologically omparable reas othe northwest. roductive ed-rock ndplacergolddeposits ccur n the Cordillera Oriental and he sub-Andeanowlands, ut the primarymineralizationasgenerallybeen assigned Paleozoie ge.
The 1:1,000,000 nationalmetallogenicmap of Delas Casas nd Ponzoni 1969), revisedat a scaleof 1:
2,500,000 by Bellido et al. (1972) with a detailedexplanatoryext by Bellidoandde Montreuil 1972),and the perceptivesyntheses f Ponzoni 1980) andSoleret al. (1986) constitute n excellent ntroductionto the mineralization f the studyarea,but theyrevealthe lackof detailed nformation n the greatmajorityof the ore deposits.n the "southern"metallogeniczone of Soleret al., only the Toquepala nd Quella-vecoporphyrycoppercentershavebeenbriefly doc-umented in the international literature, and there are
few descriptions f the geologyof the mines andprospectsof the transect n national ournals. Thisproblem s particularlysevere or the CordilleraOri-ental, an area which has witnessed a marked increase
in exploration ndminingactivity n the past wo de-cades.Clark et al. (1984) and Kontak 1985) providepreliminaryaccounts f metallogenic elations n thisnorthwesterlyextensionof the Bolivian tin-silver-polymetallicbelt, Kiilsgaardand Bellido (1959) re-cord much useful information on the mines of the
transect,and Robertson 1978) contributes aluabledescriptionsf several epositsn northernPunoDe-partment. Fletcher et al. (1989) examine he broadgeologicsettingof severalmineralizeddistrictsof theCordilleraOccidentaland Altiplano.
The geology ndphysiographyf the southern e-ruvianAndeswere firstcomprehensivelyocumentedby Bowman 1916) andDouglas 1920). More recentsynthesesnclude those of Audebaudet al. (1976)and S•brier et al. (1988). In a broadercontext,Dal-mayracet al. (1980) and M(•gard 1987) documentthe overall geologicevolutionof Peru; the latter au-thoratitivelyreviews 1988) the regionalgeologyofthe Andesnorth of the Bolivian orocline, while Pitcher
et al. (1985) provide a wealth of informationon the
FIG. 1. Sketchmapsshowing elected xistinggeologic,geophysical, nd topographic eaturesof
the centralAndes n the vicinityof the Bolivianoroelineand Ariea deflection. . Locationof the studyarea relative o the major physiographic rovinces f the regionand to contours f crustal hickness(afterJames t al., 1971b, andFukaoet al., 1989). The Inner Are teetono-magmatieomain s delimited.The Main Are occupieshe entire AltiplanoandCordilleraOccidental. . Area with average levationabove3,000 m, undisseeted nd weakly eroded volcaniccenters,and depth contourson the centralpart of the subdueted lab after saeks,1988).
PeruvianCoastalbatholith. sacks 1988) advancesstimulatingmodel or the Neogene ectonicevolutionof the oroclineregion. n addition o numerous1:100,000 geologicmapsand reports or 30' quadran-gles n southeasterneru,p,•ticularly n the Cordil-
lera Occidental ndon ts Pacificslope,excellent e-connaissanceescriptions f extensiveareas n theCordilleraOccidental,Altiplano,andCordilleraOri-ental are presentedby Newell (1949), Laubacher(1978a and b), and Klinck et al. (1986).
Metallogenic researchat Queen's University hasinvolved detailed studiesof the majority of the re-cently productiveore depositsn the region Fig. 2),including the Toquepala porphyry Cu-Mo center(Zweng, 1984), the Cacachara Johnson, 986), andSantaBS.bara (Wasteneys,1990) epithermal silver-
polymetallic ein systems, nd he lithophileandbasemetalveinsof the SanRafael in (Palma,1981; Kontak,1985) and Palca 11 tungsten (Yamamura, 1990)camps, swell as econnaissancetudies f manyotherminesand prospects. hese nvestigations ave beencarried out in the contextof analyses f the regionaland ocal settingsof mineralization nd an extensivegeochronologic rogram.
Published nformationon the ageofmineralizationin this ca. 200-km-wide transect s scantyor absentin most districts. n the present paper we establishthe stratigraphic, etrologic, nd tectonicsettingofthe ore depositsof the region, and documentK-Ar
and4øAr-39Aratesdeterminedor the deposits nd/or immediately ssociatedgneousocks.Many of thegeochronologicata are otherwise ecordedonly inunpublished heses (McBride, 1977; Palma, 1981;Zweng, 1984; France, 1985; Kontak,1985; Johnson,1986; Wasteneys,1990; Langridge, in prep.). Ourfocus is on hard-rock metallic mineralization of
broadlymagmatichydrothermalcharacter,althoughknowledgeof the geneticand temporal elationsbe-tween magmatism nd local hydrothermalactivityranges romrigorous o tenuous for an object esson,seeFarrar et al., 1990b). Followingdefinitionof themetallogenicepisodes,comparisons re made with
those represented n other transectsof the centralAndes. Detailed accountsof the Toquepala Zwengand Clark, in prep.), SantaBftrbara Wasteneys ndClark, in prep.), CacacharaWoodman nd Clark, inprep.), SanRafael (Clark et al., in prep.), and Palca11 (Yamamura nd Clark, in prep.) depositswill bepresented n later publications. he factors espon-sible or the metallogenic ighs nd ows n this egionare evaluatedelsewhere Clark, in prep.) on the basisof availablepetrogeneticand geodynamic ata.
Regionalgeologic nd metallogenic ontext
The majorgeologic nitsexposedn thisAndeantransectare outlined n Figure 3. Our discussionfMesozoicand Cenozoiceventsemphasizesmagmaticand tectonicaspects, ecausewe consider edimen-tary rocks o haveplayedessentially passiveomenmetallic ore formation in this region. SoutheasternPeru exhibits he markedphysiographic ubdivisioninto CordilleraOccidental,Altiplano,and CordilleraOriental Fig. 1), characteristicf the greatAricade-flection or elbow, alsoknown as he Bolivian orocline(Carey,1958).The centralAndean ordillera volvedbeside the Pacific Ocean basin since at least the latest
Precambrian nd has experiencedconvergentplateinteractionand orogenesishroughout he Phanero-
zoic. Radicalchangesn tectonic,stratigraphic, ndmagmatic tyle n most ransectsndicate hat the on-going Andean orogenystarted n the Late Triassic,i.e., at 220 ___ 0 Ma.
We have previously advocateda distinctionbe-tween "Main Arc" and "Inner Arc" magmatic do-
mains n the post-PaleozoicentralAndes Figs.1 and2), the fundamental riterionbeing the natureof theoverall igneouspetrochemicalassemblage,.e., thepetrographicprovince (Clark et al., 1983a; 1984).Audebaudand Amosse 1981) advancea basicallysimilar subdivision of the Cenozoic Peruvian Andes
into "Western" and "Eastern" domains but do not
address he broader temporal or petrogenetic ela-tions.We consider hispersistent ipartitesubdivisionto be of fundamentalmportance o metallogenesis.
The Main Arc domain underlies the discontinuous
Cordillerade la Costa Fig. 1) and the entire Cordil-lera Occidental.The uppermost riassic o Quater-
nary Andeanvolcanicand plutonicrocksof this ex-tensive region are ultimately of mantle origin, butdisplaya significantangeof contributionsrom theupper and middlecontinental rust e.g., Harmonetal., 1984; Barreiroand Clark, 1984) and exhibitbothcalc-alkaline low to high K) and weakly alkaline(shoshonitic)ffinities Lef•vre, 1973; Dostalet al.,1977). In contrast, the areally restricted Inner Arcdomain,essentially oextensivewith the CordilleraOriental of southeastern Peru and western Bolivia
(Figs. 1 and 2), also ncorporates eralkalinerocksand moderately o stronglyperaluminous,nterme-diate to acidic,volcanic nd ntrusive uites Carlier
et al., 1982; Kontak et al., 1984, 1986; Laubacher etal., 1988;Pichavantt al., 1988aandb).Bothdomains re entirelyensialic James, 971a;
Clark et al., 1973), and the stratigraphic ecordthroughout he Mesozoic nd Cenozoic ulesout thepossibility f the dockingof allochthonouserranes.The Main Arc in southeastern Peru and northernmost
Chile sunderlain y thinPaleozoicedimentarytrataandby the ca. 1.9- to 2.0-Gagranuliteo amphibolitefaciescrystalline asement f the Arequipamassif(Shackletont al., 1979). The continentwardersis-tenceof the atter suncertain, ut upperProterozoicgranitoid ockshave been locally confirmed o un-derlie the Cretaceous-Cenozoic clastic fill of the A1-
tiplano n northernBolivia Lehmann, 978). In con-trast, the Inner Arc domain of the Cordillera Oriental
is hostedby a thick, stronglydeformedsuccessionfclasticand lessercalcareous aleozoic edimentaryrocks (e.g., Newell et al., 1953; Laubacher,1978aandb) thataccumulatedn extensiverough, he "AI-tiplanoEarly Paleozoic asinDepocenter"of Ramos(1988), whichappearso have ormedalonga long-standingzone of weakness n the Precambriansub-structure. The post-PaleozoicMain Arc-Inner Arcboundaryn southeasterneru (Fig. 2) is consideredto ie withinanextensive orphotectonicubprovince
termed the Precordillerade Carabayaby Laubacher(1978a, b), for which the igneous ock chemistry spoorly known. In contiguousBolivia, however, thewestern imit of the Inner Arc, asdefinedby our stud-ies (see also:J. Anguset al., unpub. data; Halls andSchneider,1988), clearlycoincideswith the abrupt
physiographicnterfacebetween the CordilleraOri-ental and Altiplano and does not lie at the westernmargin of the latter as indicatedby Redwood andMacintyre (1989, their fig. 6).
The intrusive and volcanic gneousrocks of theMain Arc of southernPeru were emplaced persis-tently throughout he Mesozoicand Cenozoic (e.g.,Stewart et al., 1974; Pitcher et al., 1985), with dor-mant ntervals f up to 25 m.y. n most ransects. heyexperienceda gradualcontinentwardmigration romthe latestTriassic o the Paleogene.However, in con-trast o northernChile, wherea remarkably ystematiceastwardmigrationof the Main Arc at an average ate
of ca. 0.85 mm/yr occurred rom the Early Jurassicto the early Miocene (Farrar et al., 1970; Clark et al.,1976), the superimposition f magmatismor periodsof up to 50, or even 100 m.y., in 30- to 50-km-widebelts characterized the main loci of Mesozoic and Pa-
leogenevolcanism nd granitoidplutonism n south-easternPeru. The contrasted ime-spacearc geome-tries in this and contiguousransects redictablyex-erted a direct control on the distribution of ore
deposits.Large-scaleareal expansionof the Main Arc in
southeasternPeru took place in the late Oligocene(Clark et al., 1984; Bonhommeet al., 1985; France,
1985; R. J. Langridge,n prep.).The present xtensivegeochronologic ata base demonstrateshat the arcbroadened ather than migratedat 28.5 ___ Ma, i.e.,within the limits of the applicabledating echniques(Clark and McNutt, 1982). This critical Oligoceneevent, restricted to the vicinity of the Bolivian oro-cline, resulted n the juxtaposition f Main and nnerArc igneous ithotypes n the Peruviansegmentof theCordillera Oriental and in a combined arc width of
ca. 320 to 350 km. Considered as a whole, however,
the Inner Arc displays magmatichistory differingmarkedly rom that of the Main Arc and experiencedwidely separatedbursts of post-Paleozoic ctivity(Carlier et al., 1982; Kontak et al., 1984, 1990c andd), in strongcontrast o the quasicontinuous evel-opment of the Main Arc (Clark et al., 1984). Onlyvery minormagmatism asoccurred n the Inner Arcsince he early Pliocene,while Main Arc igneousac-tivity hasbeen focusedalonga narrow zone, gener-
ating he articulated rray Fig. 1) of andesitic-daciticvolcanoes onstitutinghe axisof the CordilleraOc-cidental de SilvaandFrancis,1990) andrepresentinga northerly segmentof the central volcanic zone(15ø30•-27ø30S). The complexchangesn the con-figurationof the Cenozoicmagmatic rc in south-
eastern Peru, and in contiguousnorthern Chile-northwestern olivia, ook placeover an intervalofmajorchangesn the Pacificbasinplate boundaries(Handschumacher,976; Cande,1985), in platecon-vergence atesandsensee.g.,Pardo-CasasndMol-nar, 1987), in the geometry f subductionJordan tal., 1983), and in the thickness f the orogeniccon-tinental crust (e.g., Tosdalet al., 1984); it alsocoin-cided with the counterclockwise rotation of the Pe-
ruviansegment f the orogen o enhancehe appar-ently long-standing olivianorocline Isacks, 988;R. J. Langridge, n prep.).
The studied ransect s now underlainby a steeply
dipping ca.30ø)Wadati-Benioffeismicone Isacks,1988) but is flanked o the northwest y a domain ffiat subduction, lacking post-Miocene magmatism(Fig. 1). This s a Neogene late Miocene:Noble andMcKee, 1977) discontinuity, erhaps esulting romthe subductionof the aseismicNazca ridge (Pilger,1981) which now intersects he plate marginat lat15 ø S, but it serves o delimit the area under consid-eration ndmaycoincidewith anearlier,mid-Tertiarywarp n the subducting late (seebelow). n the im-mediatestudyarea,comparativelyhick crustprob-ably prevailedduring he Late Cretaceouso Paleo-cene accumulation f the entirely subaerial olcanic
rocks comprising he Toquepala Group (Fig. 3).However, he presentgreat hicknessca.65 km;Fig.1) of crustunderlying he Main Arc domain James,1971b; Fukaoet al., 1989) maybe shown rom strati-graphicandgeomorphologicelations Tosdal, 978;Tosdalet al., 1984) to be a largelyNeogene eature:upliftof the oundationf thevolcanic ordilleraOc-cidental commencedat 25 to 26 Ma. Isacks (1988)ascribeshe massive plift which generated he ca.3,650-m a.s.l. Altiplano aswell asa major accentua-tion of the Bolivian orocline o unusually ntense ec-tonic shortening f thermallyweakenedorogeniclithosphere uring he MioceneQuechuan rogeny(seealsoLyon-Caen t al., 1985). n contrast, therworkers e.g.,BakerandFrancis, 978) argue or adominant ole of magmatic nderplatingn crustalthickening nd henceuplift. Konoet al. (1989) ad-vancea compromisemodel on the basisof gravitystudiesn southern eru (Fukaoet al., 1989), in which
FIG.2. Locationmapof study ransect nd he area mmediatelyo the west,showing epartmentalboundaries, ajorcitiesand owns, ndselected re deposits,he latter classifiedccordingo size.Filled circles ndicatedepositsor whichgeochronologicataare presentedn thispaper;opencirclesrecordundated eposits; eposits ith bracketed ames re hosedated n otherstudies. he approximateboundary of the Inner Arc domain s shown.
crustal hickening n the Cordillera Oriental largelyresulted rom tectonicshortening nd is uncompen-sated,whereas hat beneath he Cordillera Occidentalinvolvedunderplatingby mafic magmas.
A persistent heme in Andean researchsince hework of Steinmann1929) hasbeen he delimitation
of orogenwide, ecularly iscrete, ompressionalec-tonic eventsconsidered o have been separatedbymore protracted periods of tectonic quiescenceorextension.Although his concept s accepted y mostworkers (e.g., Pardo-Casas nd Molnar, 1987), weemphasizehat definitionof the ageof suchorogeniesremainscontroversial; ompare, or example, he dis-cordantchronologies ndnomenclaturesor the laterTertiary, "Quechua," eventsrecently advanced ngeomorphologic, tratigraphic, ectonic, and geo-chronologic tudies n southeastern eru and contig-uousnorthernBoliviaby Tosdalet al. (1984), Lavenu(1986), M•gard (1987, 1988), S•brier et al. (1988),
and Ellisonet al. (1989).The mantle-derived melts of the central volcanic
zone of the Andes, and their predecessors, re con-sidered o have experienced historyof melting,as-similation,storage,and homogenizationn a deepcrustalzone (Hildreth and Moorbath, 1988). Stron-tium and oxygen sotope elations n the correspond-ing Mesozoic ndPaleogeneMain Arc rocksof, e.g.,northernChile, are interpreted McNutt et al., 1975;Longstaffet al., 1983) asevidenceor magma ourcesin the lower crustor uppermantleand or only minorupper crustal contributions hrough assimilation-fractionalcrystallization rocessesefore substantial
crustal hickeningoccurred n the Neogene. n con-trast, both upper crustaland mantle magmasourceswere directly apped n the Inner Arc (Kontaket al.,1984), and a wide rangeof true anatectic onditionswere involved n the genesisof its diverseperalu-minoussuites e.g., Pichavant t al., 1988a and b).Whereas he Main Arc resemblesmagmatic rovinceswhich are generatedas by-productsof subduction,the Inner Arc exhibitsmagmatic nd ectonic eaturescharacteristic of ensialic rift zones and continental in-
terior plutonicbelts.Dramaticvariations n Inner Arcmagma hemistry re correlatedwith radicalchangesin tectonicconditions,ndicating hat this domain s
a narrowbut persistent uffer zonebetween he An-deanorogenand the Braziliancraton.Manyworkers e.g.,Sillitoe,1972a, 1976; Ponzoni,
1980; Soler et al., 1986) have emphasized hat thisregion exemplifies he transverse re metal zonationconsidered haracteristic f Andean-typeorogens,
with a continentwardransition rom Fe-, throughCu-dominated ones o a polymetallic omainwhere Cuis oinedby Pb, Zn, andAg; all are considered ereinto lie within the Main Arc. Zentilli (1974) and Clarket al. (1976), however,emphasizehe marked ncon-sistenciesn metal zoning n the centralAndes.The
wide compositional pectrumof the Inner Arc mag-matism in southeastern Peru and northwestern Bolivia
is paralleled by an extremely diverse metallogenicmakeup,n which he economicmetals ndmetalloidscharacteristicof the hydrothermaldepositsof theMain Arc are joined by globally mportant concen-trationsof Sn, as well as by U, Li, and possibly, rand REE. Althoughwidespread n the Main Arc, W,Bi, andSbare greatlyenhancedn the Inner Arc. Thesparse adiogenic sotopedata available or igneousrocksdirectlyassociated ith ore deposits f the MainArc domainsuggest hat an increasing nvolvementof the continental rust n magmagenesiswasparal-
leled by an increasing omplexity n the ore metalassemblage f the associatedore deposits.Crustalsources, robablyargely gneous, re nferred o haveadded Ag 4- W and then Pb to a mantle metal asso-ciationcharacterized y Cu(-Mo),Au, Fe (oxideores),andminorCo, Zn, and Mn (Clark, 1982). Anatexis fmetasediments,ssentiallyestricted o the Inner Arc,wasa prerequisite or the generation f economic n,and probably U, deposits Amosseand Audebaud,1978; Audebaudand Amosse, 981). Suchvariableinteractions within the continental crust, rather than
areal and temporal changes n the conditionsofmagmaand/or fluid generationassociated ith the
subducting lab e.g., Sillitoe, 197œa, ) or the dis-tributionof specific upracrustalock ypes Petersen,1972), are consideredo underlie he transverseco-nomicmetal zonationdocumented y Sillitoe 1976)and others. Variations n the extent of magma-crustinteraction lsoaccountor the mportant berrationsfrom he accepted atterns f metaldistribution,uchas the across-orogennrichment n Cu and Au, anddepletionn Pb, exhibited y areas f northernChileandnorthwestern rgentina Zentilli,1974; Clarketal., 1976).
Format of data presentation
Our focus is on the Mesozoic-Cenozoic Andean
orogenyand only brief mentionwill be madeof de-monstrably lder mineraldeposits. he Precambrianand Paleozoicbasement erranesare generallyonlyweakly mineralized (Clark et al., 1976; Ericksen,1980; Sillitoe, 1988). We consider irst the available
FIG. 3. Geologicmap of the study ransect,modifiedand greatly simplifiedafter INGEMMET(1975), outliningspecific reasof study,shown n more detail n Figures4 to 10 and 14 to 16. Thedoublewavy ine is our proposed oundary etween he Arequipa ndToquepala egmentsf theCoastalbatholith. f only Albian and younger ntrusionswere considered, he boundarywould lieapproximatelymidwaybetweenArequipaandToquepala.
geochronologic ata for mineralization n the MainAre, assigned o oceanward Jurassic-Eocene)ndcontinentwardOligocene ndMiocene)subprovinceswith respect o the axisof the Cordillera Occidental(Fig. 1). Thereafter we examine he chronologyofore formation n the narrow nner Arc, subdividing
the depositsnto Mesozoic ndCenozoicgroups. helocationmap, Figure 2, indicates he majority of thedated depositsand districts, as well as those whichremain unstudied rom the geochronologic tand-point, and severalkey depositsmmediatelywest ofthe study ransect.Geologicdescriptions nd sketchmaps representedor the miningdistricts,acilitatingevaluation f the new geochronologicata;manyofthe study areasare outlined in Figure 3. In severaldistricts, he sparsityor problematic ignificance fthe agedeterminationsequiresa moredetailedeval-uationof geologic elations.The attentionwe pay toseveral mallshowingss ustifiedby the information
they provideon overallmetallogenicrendsand pat-terns,andsuchapparentlysparsemineralizationmayalsobe germane o future mineral exploration.
Geochronologic echniques
The K-Ar and4øAr/39Arotal usiondates nd heagespectra eportedare from studies e.g., McBride,1977; France, 1985; Kontak, 1985; R. J. Langridge,in prep.; H. A. Sandeman, npub.data) hat were un-dertakenover a protractedperiod duringwhich theanalytical echniques sed n the Queen'sUniversitygeochronologyaboratoryevolved significantly.
Early argon extractions (McBride, 1977) were
madeby radio-frequencynduction eating f samplesin niobiumcruciblesn a pyrexvacuumine, followingovernightbakeoutat ca. 150øC. n later K-Ar studies(France, 1985; Kontak, 1985), Ar extractionsweremade in resistively heated tantalum cruciblesmounted in a turret-type furnace connected to astainlessteelvacuum ystem.All argon sotope atioswere determined on an Associated Electrical Indus-
tries, Ltd., MS-10 massspectrometer,operatedstat-ically,using liquots f 3SAr, alibrated gainst P-6interlaboratorystandardbiotite and JC-90 internalstandardbiotite, as the spike. Potassium oncentra-tionswere determined n duplicateon separatesam-
ple aliquotswith an nstrumentation aboratory,nc.,143 flame photometer,employinga lithium internalstandard nda sodium uffer McBride,1977) or withan I.L. 251 atomicabsorption-emissionpectrometerusinga CsC1 nternal buffer (France, 1985; Kontak,1985). Potassium nalyses ere referred to Bern 4Mand LP-6 international standards.
In the later 4øAr/39Ar tudies eported herein(Kontak,1985; R. J.Langridge,n prep.;H. A. Sande-man,unpub.data),samples ndmonitorsJC90) wereirradiated n position5C of the McMasternuclear e-actor,Hamilton,Ontario.Monitorsused n the 4øAr/3•Aranalysesncluded P-6biotiteand nternal tan-
dard SP-85 biotite. The samemass pectrometer, utundercomputer ontrol,wasemployed.Otheraspectsof gasextractionand analysis emained he same. nthe incremented eating uns,a Lindberg urnacewasemployed o controlstep emperatureprecisely.
The decayconstantsnd sotope bundanceatios
used are those recommended y Steiger and J•iger(1977). Quoted errorsare at the 95 percentconfi-dence level. To obtain maximum definition of agespectra, o error wasassignedo the J values sed ocalculate øAr/3•Ar tepages. f, therefore, ompar-ison is to be made between conventional K-Ar and
4øAr/3•Arates, pproximately.5 percent f thedateshould e added o the errorsquoted or the 4øAr/3•Ar ntegrated ges.
Full analytical ataare given or conventional -Ar datesand for 4øAr/39Arotal-fusionuns Tables1-4). The resultsof 4øAr/3•Ar tep-heating xperi-ments,however,are presentedonly in the form of
apparent gespectra; omplete atamaybe obtainedfrom E. Farrar. We refer the radiometric dates to the
"Decadeof North AmericanGeology1983 GeologicTime Scale" (Palmer, 1983). Our metallogenic pi-sodes re consideredo makeup a singlepost-PermianAndeanmetallogenicpoch;we realize hat hisusagediffers rom hat of Lindgren 1933), but it is requiredby the still ncomplete eochronologicatabase orthe central Andes.
Mesozoic to Eocene Mineralization
of the Main Arc Domain
Introduction
The oceanwardlopes f the CordilleraOccidentaland the Cordillerade la Costa Fig. 1) are underlainby UpperTriassic, ndmoreextensively, urassic a-rine volcanic nd sedimentary trataandby an UpperCretaceouso Paleogeneubaerial olcanic eries,heToquepalaGroup (Fig. 3). These remnantsof asuccessionf continentalmarginmagmatic rcsandof flanking, argely shallow-water asins MSgard,1987) are underlainby a basement ominated yPrecambrianmetamorphicocks nd owerPaleozoicgraniticplutons ssigned,espectively,o the Are-quipamassif Shackletont al., 1979) and to the
southerly xtensionsf the Silurian-DevoniananNi-col/•s atholith Mukasa nd Henry, 1990; R. J. Lang-ridge, unpub.data).The Paleogene nd older unitsare overlainunconformablyy a generally hin coverof Oligoceneo Quaternary ontinental lastics ndvolcanics. he age relations nd stratigraphy f thepost-Eocene trata,and the Neogene ectonicevo-lution of the transect,are documented y Tosdaletal. (1981, 1984) and S•brier et al. (1988).
All significantypogenemetallicmineralizationnthis egionsof pre-Oligocenegeanddisplayscloseassociationith granitoid lutons ndhypabyssalel-sic stocks. he distribution nd petrography f the
intrusive ocksare well documented n the 1:100,000geologicmapsandquadrangleeportsof BellidoandGuevara 1961, 1963), Narv•ez and Garcia (1962),Wilson and Garcia (1962), Narv•ez (1964), Bellidoand Landa (1965), Jain (1965), Garcia 1968), andBellido 1979). The plutonic ocks ange n compo-sition romgabbroo alkali eldspar ranite, utquartzdiorite, quartzmonzodiorite, nd granodiorite re-
dominaten mostareas. heseauthors ecognizedhepolyphasenature of the Andean batholith, but ten-tativelyassigned Cretaceouso Paleogene ge o allgranitoid ntrusiveactivityon the basis f the contactrelationsof someplutonswith the volcanicstrataofthe UpperCretaceouso Paleoceneoquepala roup.
The first geochronologicatum or the plutonicrocksof the regionwasprovided y Laughlin t al.
(1968), but the existenceof Mesozoic ntrusionswasunconfirmedntil heK-Arstudies f McBride 1977)and Shnchez1983a andb). Beckinsale t al. (1985)present a selective review of these data and addition-ally contributeseveralwhole-rockRb-Sr sochronsorintrusive ocksof the Toquepala istrict seebelow).
They,andPitcher 1985),assignedheplutonso theToquepalasegmentof the PeruvianCoastalbatholith;given he ca. 150-m.y. ime span epresentedy therocks, his erminologys probablyoo nclusive, utit is ollowed erein.Pitcheret al. (1985) alsodelimitseveralplutonicsuperunitsn the area, followingmethodology eveloped n the better studiedLimasegment.However, no U-Pb zircon datesare availablefor Andeanplutonic ocks n the immediate ransect:Mukasa's1986) dataare for plutons o the northwestof Arequipa Fig. 3) whichonly arguably onstitutepartof theToquepalaegment. e stronglydvocateon petrographic nd geochemical, ut alsosemantic,
groundshat heboundary etween he Arequipa ndToquepala segmentsof the batholith be sited south-eastof thecityof Arequipa ather han o tsnorthwest(Fig. 3). Boily et al. (1984) interpret he Rb-Srdatato indicateca. 185 Ma asthe age for the ChocolateVolcanicsf the lo-Ite area,but theysuggestn ageof ca. 150 Ma for moresoutheasterlyequences.
The mineralization of the area includes scattered
auriferous opperveins,hematite -magnetite) eins,polymetallic einsand skarns, nd three majorpor-phyry Cu-Mo centers;only porphyrydeposits avebeen productive n the past two decades.Our dis-cussion f the age relationsof the ore deposits nd
mineralshowingss subdividednto sevendistricts nfour map areas, he locationsof which are shown nFigure 3. More detailed geologicmapsof the min-eralizedareasare included n Figures4 through7.
Ilo-Ite district
Three smallcopper mineshave been active northandnortheast f lo in the Cordillera e a Costa Figs.1-4). The Santiago, alpar•/iso,ndLiconaoperationsdeveloped orizontally xtensive eins,now deeplyoxidized, ut with a chalcopyrite-pyrite-hematitey-pogene paragenesis.The veins occur within and at
the marginof a leucocratic iotite-hornblenderano-
diorite pluton (Narvftez,1964), intrusive nto marinevolcanicand sedimentary trataof the LiassicChoc-olate Volcanics and Callovian Guaneros Formation
(Fig. 4). Iron mineralizations alsowidelydevelopedin the area. Pegmatitebodies n the roof zone of adiorite plutonnorth of Ilo containabundantmagne-tite, intergrownwith bytownite, Cl-rich (_•0.65 wt%) hastingsite, ndscapolite Clark,unpub.data),allcommon o the magnetite (-Cu, Au) mineralizationassociatedith maficplutons f theArequipa egmentof the Coastal atholith Atkin et al., 1985), but theoccurrences re apparentlyof negligiblesize. More
important Fe showings ccur near Ite where north-west-strikinghypogene hematite-quartz veins withaveragewidthsof ca. 3 m (Narv•ez, 1964) and con-taining minor magnetite and pyrite, have beentrenched on Cerro Morritos. Bellido and de Montreuil
(1972) estimate eservesof ca. 10 million metric tons
of •60 percentFe to shallowdepths.Both the Mor-ritos prospectand the less mportanthematite veinsexposed n CerroPelado rehosted y granitoid ocksranging n composition rom diorite to granodioriteand displaying oth gradational nd abrupt ransitionsfrom one ithology o the other on all scalesNarv•ez,1964). There are no recordsof iron production romeither prospect.
McBride (1977) determinedsixconventionalK-Ardates or four granitoidsamplesn the Ilo area: hedata (Table 1, a: samplesSP-112, -114, -116, and-120) were interpretedas defining wo episodes fplutonism, f LateJurassicca.151-159 Ma) andmid-
Cretaceous 96-111 ma) age. The older dateswereobtained for diorite from the immediate littoral zone
(sample P-120),and he Albianages or granodioritesand onalitesarther nland.S•nchez 1983a)obtainedsimilar Albian K-Ar dates for several granodioriticsamples ortheast f lo but also oundEarly o MiddleJurassic ates 196 and 182 Ma) for two dioritic rocksfrom the coastal one. AlthoughMcBride's (1977)data cited,but in part mislocated y S•nchez,1983a)includedconcordant ate Jurassic ates or associatedhornblende and biotite (SP-120), Beckinsaleet al.(1985) madeno reference o the possible ccurrenceof magmatism f this age in their analysis f the in-
trusivechronology f the area. nstead, hey nferredthat intrusion ook place only in the Early Jurassicand mid-Cretaceous. Because their older dates were
obtained rom the discontinuouselt of dioriticplu-tonsexposed long he coast Narv•tez,1964; Fig. 4),they furtherproposedhat suchmafic ocksconstitutea distinct Punta Coles superunit,whereas he morewidespread granodioriteswere assigned o a mid-Cretaceous lo superunit. Pitcher (1985) recorded agabbroic o dioritic compositionor the former anddescribedhe younger ocksas anging rom onaliteto granodiorite.Contrary to Pitcher's observations,the rocksof the area are not generally oliated;pen-
etrativedeformations argelyconfinedo synplutonicmaficdikes.An epizonal,but submarine, nvironmentof emplacement s inferred.
We consider he PuntaColesand lo superunitsohave been prematurelyestablished.Narv•tez 1964)emphasizedhat mafic and felsic granitoidmagmaswere intimatelyassociatedn the area, particularly nthe emplacementof the mixed diorite-granodioriteunit (Fig. 4), and the seniorauthorhasobserved on-vincingevidence cf. Vernon et al., 1988) of maficand felsicmagmamingling n the coastal rea northof Ilo, e.g., globular enclaves pillows) of diorite in
FIG. 4. Geologicmapof the Ilo-Ite area,simplified fter Narv•tez 1964). It emphasizeshe pre-Cenozoicunitsand gives he distributionof metal minesand prospect.The locations f the samplesdatedby conventional-Ar and4øAr/S9Arethods re shown,ogetherwith step-heatingpectraorsevenminerals rom five granitoidsamples. lsoshown re ocations ndK-Ar dates or samples 6.80and 17.80 from S•nchez (1983a).
cies s provided y an ongoing rogram f 4øAr/39Arstep-heating eochronologyR. J. Langridge,n prep;R. J. Langridgeet al., in prep.), sevenage spectrafrom which are presented n Figure 4. As would beexpected rom he variedK-Ar dates,mosthornblendeand biotite age spectradetermined or the intrusiverocks of the area reveal evidence of thermal distur-
bance: rue plateausare not widely displayed.Theoldest ntegrated age, 186.04 _+ 8.75 Ma, was ob-tained for hornblende n sampleSPAM-123 (Fig. 4:spectrum ) from a smallexposure f granodioriten
the upper reachesof the Rio de Ilo. Omissionof ahigh-error owest emperaturestepgenerates moreprecise ntegratedageof 184.52 _+ .76 Ma, andstepstwo through iveof the spectrum onform dequatelyto a plateauconfiguration. his date is taken to in-
dicate ntrusion n the Middle Jurassic,n permissiveagreementwith the observedcontact elationswiththe LiassicChocolateVolcanics. he pluton s appar-ently unmineralized.
A significantly ounger,Late Jurassic, øAr/39Arintegratedageof 159.32 _+4.78 Ma wasobtained orfreshhornblende rom a dioritic rock croppingoutnear the northwestcorner of the map area (Fig. 4:A). The age spectrum evealsa small degree of re-setting, ut the overlapping rrors n the threehighertemperaturestepssuggest hat the age may be ac-
ceptedwith confidence. his date s sensiblydenticalto that yieldedby conventionalK-Ar datingof nearbysampleSP-120and s consideredo confirmMcBride's(1977) inferenceof a Late Jurassicntrusiveevent nthis area.
Other agespectraobtained n the present esearch
yield mid-Cretaceous ates.Hornblende and biotitefrom SPAM-125 (Fig. 4: B and C) give essentiallyconcordant ntegrated ages of 108.83 ___ .91 and104.04 ___ .74 Ma, respectively.The spectra,andparticularly hat for hornblende,are disturbed,butthe similarity n the datessuggest hat intrusionoc-curred n the mid-Cretaceous. oth this and he pet-rographicallyimilarbiotite-hornblenderanodiorite-tonaliteSPAM-88 (Fig. 4: D andE) exhibitmoderatechloritization of hornblende and, to a lesser extent,biotite. n the caseof SPAM-88, his s probably e-flected n the markedly ighererror n the ntegratedage for the hornblende 96.38 ___2.08 Ma) than in
that for the biotite (101.36 _+2.23 Ma). However, 89percentof the gas eleasedrom he hornblende ieldsa more precise age of 97.39 ___ .86 Ma. As withSPAM-125, emplacement n the mid-Cretaceous sinferred.Bothof these ocksconform roadly o thecharacteristics f Pitcher's (1985) Ilo superunit. ncontrast, ampleSPAM-45, romthe vicinityof PuntaMeca Grande, s a maficbiotite-bearing iorite, andthe plutonhasbeenassigned n petrological roundsto the Punta Colessuperunitby both Pitcher (1985)and Beckinsale t al. (1985). The biotite, however,yieldsan almostundisturbedplateauspectrum Fig.4: G) with an integratedage of 104.65 ___ .12 Ma,
i.e., essentially dentical to those of the more felsicrocks.
We interpretheK-Arand4øAr/39Argedata orthe Ilo-Ite area as delimiting at least three distinctplutonicepisodes, f Middle Jurassicca. 185 Ma),Late Jurassicca. 160-165 Ma), andmid-Cretaceous(ca. 95-110 Ma) age.This represents compromisebetween the chronologies roposedby McBride(1977) andBeckinsalet al. (1985), but the arealdis-tribution of the intrusive age groups emains ncom-pletelydefined R. J. Langridge t al., in prep.).Theearlier two events followed shortly on the eruptionof the andesites of the Chocolate Volcanics and the
Guaneros ormation, espectively. he Albian ntru-sions aveno clear ocalvolcanic nalogues. lthoughM. Boily (in Boily et al., 1984) briefly notes he oc-currence of ca. 100-Ma volcanic strata beneath the
ToquepalaGroup, he main ocusof the late Albianvolcanism,and of the associatedMochica deforma-tional event, was far to the north, in central andnorthernPeru (M•gard, 1987). It is also nferred hatall three plutonicsuitescomprise ocks anging ncompositionrom diorite to granodiorite;hus, hePuntaColes-Ilo upergroupubdivisionhould rob-ably be abandoned.
Whereas earlier workers (e.g., Soler et al., 1986)have nferred a Jurassic ge for the Fe deposits, henew age data strongly mply that all significantme-tallic mineralization n the area s of Cretaceous ge;only the very minor magnetite-amphibole-scapolitebodies are associated ith Middle Jurassic lutons.
No datable material could be recovered from thechloritizedandsilicifiedselvages f the Santiago ndValparaiso opper veins,but traverses o the minesfrom he Ri6 de lo revealnosignificantntrusive on-tacts, and it is inferred that these and the Licona vein
system re hostedby a lithologicallydistinctive, eu-cocraticgranodiorite-tonalite luton ca. 100 to 105Ma in apparent age. No dikes are observed n thevicinity of the veinsand a mid-Cretaceous ge s alsotentatively proposed or the hydrothermalactivity,which may, however, have been coeval with thewidespread hloritization, erhaps t ca. 95 Ma. Thepotentially economichematite veins of the Cerro
Morrito area are hostedby the mixed diorite-grano-diorite unit of Narvftez 1964) which, on the upperslopesof Cerro Meca Chico, may be observed o in-trude the ca. 105-Ma PuntaMeca Grandediorite plu-ton. However, severalother total fusion4øAr/39Ardates for biotites from the mixed unit are also of this
age (R. J. Langridgeet al., in prep.), and it is thusconcluded that the iron mineralization at both Cerro
Morritos and Cerro Peladowas emplaced n the A1-bian.
Cocachacra district
The deep valley of the lower Rio Tambo (Figs. 2
and 5) exposes everalstocks f hornblende-biotitegranodioritewhich ntrude gneisses f the Arequipamassif, clastic sedimentsof the probably LowerPermianCocachacra ormationand he Upper Trias-sic YamayoGroup, and andesitic olcanic trataofthe LiassicChocolateVolcanics BellidoandGuevara,1961, 1963). A wider rangeof granitoid ockscropsout n the eastern art of the Puntade Bomb6n uad-rangle right-hand reaof Fig. 5) and ncludes iorites,monzonites,and a mixed granodiorite-dioriteunitsimilar to that of the Ilo-Ite district. Scattered Au-
bearing cupriferousmineralizationoccurs n associ-ation with the granitoid rocks, but only the now-abandoned osaMariaminehassupported ignificantproduction.
Cordaniet al. (1985) provide he only publishedgeochronologicata for intrusive ocksof the area,recordinga conventionalK-Ar date of 154 Ma forgranodiorite rom an imprecisely ocated stock.McBride (1977) dated a sample SP-149) from thegranodiorite tock mmediately orthof E1Fiscalob-taininga K-Ar ageof 156.4 ___.6 Ma for chloritizedbiotite (Table 1, a).
R. J.Langridgeinprep.) as eterminedøAr/•Arstep-heatingates,ncludinghreebiotite-hornblende
•• ••• (•)•-1• I I Units • •Hornb•nde•• •L"••."/ /•k •;;•;V • Chocolate"X•_Diorite_
•////////////• • •'•[ •VVVVVVVVVVVV IvvvvI (Liassic••//••//•(SPAM - 82)•v •' • • v v v v v v v v v v v v v __• major ault
•///////•///////• • • ] / V V V V V V V V V V V V V •:•:::•(:)•]Triassic- •- •'- road•• • • COCACHACRA v v v v v v v v v v p•=•%2;• iassic)• 7•-. • /' / /vvvvVVVVVVVVVV• '-• / / tvvvvvvvvvvvvvv ............
• /- / / •V V V• V V V V V V V V •'"'"'•?•:;•1pc•cnacra • river- VVVVVV ß
0 o,• 10 %l;gratedge593182Cumulative %39Ar released
71ø50'W 71ø40'W
I I
in{••oclaSPAMd ge44.68.0171ø30'W
I
FIG.5. Geologicmapof the Cocachacrarea,simplified fterBellidoandGuevara1961), showingthe ocations f the RosaMariamineandof samplesatedby the K-Ar and4øAr/39Ar ethods. hespectrumor sample PAM-82Gwasdeterminedor a monzonite ike ntruding ranDdioriteampleSPAM-82.
pairs, or sixspecimens f granDdiorite rom outcropsin the Rio Tambo valley between Cocachacra nd ElFiscal.Representative ata or biotite andhornblendefrom one granDdioritesample (SPAM-82), and aspectrum or orthociasarom a 2-m-wideapliticmon-zonite dike (SPAM-82G) which intrudes he granD-diorite are both given n Figure 5. All agespectra orhornblende rom this districthave similarconfigura-tions,showingairly well definedhigher emperatureplateau segmentsand low-temperaturesteps withlower apparentages,suggestive f a smalldegreeofresetting.The biotite spectraare similarbut show naddition ow maxima eparatinghe plateauand nitialsegments,yielding a saddle-shaped onfigurationsimilar o thoseof thermallydisturbedbiotite spectrarecordedby Berger 1975) andDallmeyerandRivers(1983). However, his featuremay alsobe the resultof 39Ar nternal ecoilgenerated uringneutron r-radiationowing to the presenceof fine interlamina-tionsof secondary hlorite Lo and Onstott,1989), awidespreadeatureof the biotites n the granDdioritesof the area. The integrated agesof coexistinghorn-blende (162.55 _+ 6.58 Ma) and biotite (159.73_ 1.82 Ma) in SPAM-82 (and n the other dated sam-pies)are n satisfactoryoncordance,nddespitehe
complex atureof the spectra, Late Jurassicgeofca. 160 to 165 Ma is nferred or all of the granDdioritestocks xposed long he owerRioTambo.Thesedatalendsupport o the occurrence f UpperJurassiclu-tons in the Ilo area.
Orthociasa rom the monzonitedike (SPAM-82G)cuttingSPAM-82yields nexcellent lateau pectrum(Fig. 5) with an integratedage of 144.68 _+1.00 Ma.This date is significantly ounger han both the in-tegratedagesand plateausegments btained or thegranDdiorite ost, and despite he low Ar retentiontemperatureof orthociasa,s consideredo record adistinct ntrusiveepisode n the latestJurassic. hismay havebeen responsibleor the minorresettingofthe agesof the Rio TambogranDdiorites. ellidoandGuevara 1963) observe hat the more mafic,dioriticintrusionsn the easternpart of the area coveredbyFigure 5 alsocut the granDdiorites, ut it would bepremature o infer a latestJurassic ge for them.
The RosaMaria vein system, nitially worked forgold but more recently for copper, is hostedby agranodioriticpluton (Bellido and Guevara, 1963)identicaln petrographyo thatrepresented y SPAM-82 but displaying ervasive hloriticand ocalargillicalteration, ndcut by (premineral) ndesitic nd elsic
dikes. ourmalines observedn quartzoseeinstoneson the RosaMaria dumps.Moreover,veinletswith achalcopyrite-pyrite-hematitearagenesisimilar othat whichdominateshe RosaMariaveinsare verywidelydevelopedn all of the granodiorite tocks nthe north bank of the Rio Tambo. On thisbasis,a Late
Jurassicca.160 Ma) maximum gewouldbe inferredfor the Au-Cu(-Fe) mineralization of the district.However, he monzonite ampleSPAM-82Gandsev-eralnearbydikes ontainrregular atches f a quartz-pyrite-hematite-chalcopyrite-tourmalinessemblage,indicatinghat hydrothermal ctivityoccurredn thelatest urassic,t ca. 145 Ma. The RosaMariadepositcouldbe of either age.
Toquepala-Quellaveco-Cuajoneistrict
A Paleogene gehasbeen accepted or this rio ofporphyryCu(-Mo, Ag) deposits Fig. 6) since he pi-
onceringstudyof Laughlinet al. (1968), who deter-mineda K-Ar ageof 60.2 (___.8) Ma for biotite froma premineralization diorite" from an oxidizedout-crop in the vicinity of the Toquepalaopen pit. Thisbody s one of a clusterof clearlyepizonalstocks s-signed y Pitcheret al. (1985) to the Toquepala lu-
ton.Estrada 1975) subsequentlyecorded K-At ageof 56.2 Ma for hydrothermal ericite rom a near-cen-tral Cu- andMo-rich ore zoneat the Quellaveco ros-pect, an agebroadlysupported y the whole-rockK-Ar data of Zimmermanand Kihien (1983). A latestCretaceous ge ca.70 Ma, Rb-Sr:James t al., 1974)hasbeenproposedor the ToquepalaGroupvolcanics,the eraplacement f which largely or entirely pre-ceded granitoid intrusion, whereas S•brier et al.(1983) record a late Paleocenewhole-rockK-At date(59.1 Ma) for the TinajonesRhyolite,an upper mem-ber of the group.Beckinsale t al. (1985) presenta
52.3 Ma (m)SP - 78
VVVVVV
VVVVV
.I-I-I-I-
+++++++++++++++++ VVVVVVVVVV
t?øto's v v v v v v•,Z• • v v
++++++++VW VVVv•'y,.;z.•7VVvVVVVv•/vvvvvvv
+ VVVvvvvVVvvvvvv++ + VVVVVVVVVVvvvv
.I- .I- .I- .I-
+++, VVVVVVVVVVVVV+ VVVVVVVVVVVVV
.I- .I- .I- .I- .I- .I- .I-
•++++++ 58.7 M•++++ SP - 137
::::::;:::: SPAM - 108
v'•,vvvv. MU SP-78 :;: ,•-,r•-•Upperligocene-_
VVVVV'.A.2.R3_1.70Maiii ;'•'.-;;;IPliocene*_*_*_*.1v v v v v v • • • ;• • • • JVolcanicsnd • ] • • •v v v r.:.:,:,.'..'..'..•Clastic I ...
vvvvv • **********v.[[vv ***[***•. • o/vv ***-- *** 0% •oo%V V V V V V V V V + + + + Cumul• iv•%3•r
v v v v 70o30'WVVVVVVVVV
DaciticCenters
Granite
;• Monzonite
• Gabbro-Dionzodiorite-
Granodiorite
mine;
'•,• abandonedine
K-Ar date
ß b biotitem - muscovite
(•) 39Ar4øArpectrum
•ORSPAM113)I.A.2.74___0.3a
FIG. 6. Geologicmapof the Toquepala-Quellaveco-Cuajonerea,modifiedafter BellidoandLanda(1965), showinghe ocations f the Toquepala, uajone, ndNorvillmines nd he Quellaveeo rospect,andof datedsamples. gespectra re presented or two granitoid ocks A andB) and or hydrothermalmuscovite rom the Cuajone deposit C).
16-point whole-rockRb-Sr isochron or the plutonsof the Toquepalaarea,assignedo the Yarabamba u-perunit of the Coastalbatholith,obtaining n age of61 ___ Ma. This isochron, lthough egarded ssta-tisticallyacceptable y Beckinsale t al. (p. 180) hasa mean squareweighted deviation (MSWD) of 2.6
and showsconsiderablescatter. Both the granitoidplutonsand the ToquepalaGroup are transectedbythe regionallyextensivencapuquio ault, whichcon-stituted he northeastern oundaryof the Eocene oearly OligoceneMoquegua ore-arcbasin Maroccoand Noblet, 1990) but has been inactive since themid-Tertiary (Tosdalet al., 1984).
In Table 1, b, and Figure 6 we record new K-Arand 4øAr/S9Arge data or intrusive ocks rom theToquepala rea.A latestPaleoceneK-Ar date of 58.7___.0 Ma for freshbiotite from a melanocratic uartzmonzodioritesample SP-137) taken from the 31-R-4 railway tunnel (1,500 m from its southportal), 4.5
km northwestof the marginof the Toquepalapit, issimilar o that reportedby Laughlinet al. (1968) fora surface ampleof the same ntrusion.The two datesoverlapwithin limits of error, but we favor the youn-ger date because f the higherpotassium ontentofthe analyzedmica (7.90 vs. 5.76 wt %). Significantlyolder4øAr/S9Arateswereobtainedor two samplesfrom the plutonexposed outhof the ncapuquio aultin the broader mine area. Here, biotite from SPAM-
108, representativeof the quartz-poorgranodioritewhich s the major faciesof this body, yielded an in-tegratedageof 65.40 ___.73 Ma. The spectrum Fig.6: A) exhibits convex-upwardrofilewhich, n view
of the slight chloritizationof the mica, may reflecteitherS9Arecoileffects r a minor hermal esetting.SPAM-113 s from a fine-grained, plitic monzonitedike cuttinggranodiorite imilar o the abovesample.Slightly sericitizedorthoclase degree of orderingconfirmedby X-ray powder diffractionstudies) romthis rock yieldsa clearly-defined lateau Fig. 6: B),with an integratedage of 62.74 ___.35 Ma, in per-missive greementwith the olderdate or SPAM-108.Similarmonzonite ormsa largerpluton mmediatelynorth of the Incapuquio fault and several discretestocks lsewhere n the district.Smallmiaroliticpeg-matite bodies rich in tourmaline, and with quartz
lenses ontaining yrite and chalcopyrite, re widelyassociatedwith the monzonites n Quebrada La Si-m•t. rron•l..
We conclude hat the intrusions roppingout tothe west, northwest,and southwest f Toquepalaarenot strictly coeval,despite heir broad petrographicsimilarities.nstead,our datastrongly uggesthat n-trusion n the vicinity of the Toquepalaminespannedthe latest Cretaceous o latest Paleocene nterval (ca.59-66 Ma). The excellent plateau displayed bySPAM-113 orthoclases nterpretedasevidence hatthe hostdike cooled apidly o belowca. 130øC (Har-
risonand McDougall, 1982) at 62.74 +_ca. 0.35 Ma,probably rior o theeraplacementf hepluton ep-resented y SP-137.Some f the considerablecatterin the whole-rock sochron resentedby Beckinsaleet al. (1985)may hus eflect ncorporationf rocksof significantlyifferent ges. onsideredsa whole,
thepredominantlyuartzmonzodioriticocks f thearea do not conformpetrographicallyo the grano-dioritic-monzograniticinga-YarabambauperunitoftheArequipa egmentf hebatholith)o which heyare assignedy Pitcher t al. (1985).As n the Co-cachacra istrict, the monzoniticmagmas xsolvedmetalliferousqueousluids, utnosignificantulfidemineralization has been documented within these in-trusions.
Porphyry Cu(-Mo) mineralizationat Toquepala(Richard nd Courtright,1958) is associated ith acomplex ntrusivecenter dominated y porphyriticdaciteplugs, daciticdiatreme, ndunusually xten-
sivehydrothermalreccias. weng 1984) andZwengand Clark (1984, and n prep.) presenta revisedge-netic model for the deposit,defininga sequence fmineralization-alteration events similar to that doc-
umented t E1Salvador, hile,by GustafsonndHunt(1975) but differing adically n the relative mpor-tanceof the stages. he polyphase atureof the daciteintrusionss mplicit n the earlierdescriptionsf thedeposit,but Zweng (1984) first distinguishedhreeintrusions.Of these, the Main Porphyry s the onemostextensively xposedn the openpit. This is anessentially arren ntrusion raplacedate in the de-velopmentof the early-stageA vein-type)Cu-rich
stockworkhatprecededhe mainstage B vein-type)chalcopyrite-molybdenitemineralization whichdominates he deposit. t is almosteverywhereperøvasively verprinted y quartzosericite-pyritephyl-lic) alteration, ut anareaof essentiallyreshporphyrywasencountered n he 3,070-m (northwest)evelofthe pit in 1983. Magmaticbiotite from this sample(SPTOQ83-2) ppears naltered n thin section ndyielded n earliest ocene onventional-Ar dateof57.1 ___.6 Ma (Table1, b). The micacouldhavebeendegassed y subsequent ydrothermalor intrusiveevents n the center seeMaksaev t al., 1988b), butwe tentatively ccept he date asrecording he age
of early-stage re formation t Toquepala. hus,ca.2 m.y. may have ntervened etweenmonzodioriteintrusionand mineralization, lthough he data areinsufficiento establish tatisticallyhe agedifferenceof theseevents.Beckinsale t al. (1985) presenta 10-point Rb-Srwhole-rocksochronMSWD -- 1.5) fordacite porphyries rom Toquepala,yielding an ap-parentageof 57 ___ Ma: the samples omprise re-mineralizationacite presumablyheMainPorphyry)and the postmineralization dacite agglomerate,"which fills in a diatreme (Richard and Courtright,1958). Of these ntrusions,he earlier hasgenerally
suffered lmostotaldestructionf magmaticmineralsin an environment in which both Rb and Sr were mo-
bile, and he daciteagglomerates only ocallyunal-tered.The isochrons thereforesomewhat roblem-atic, but it probably ndicates hat late-stage hyllicalteration closely followed the initial intrusive and
hydrothermalevents n the Toquepalacenter.No published eochronologicataare availableorthe Cuajonedeposit, he geologyof whichhasbeenoutlined by Manrique and Plazolles (1975) andSatchwell 1983). We record a K-Ar date (Table 1,b) and4øAr/a•ArgespectrumFig.6: C) for a singlehydrothermal uscoviteeparatesample P-78).Thespecimenwascollected rom the southernslopesofthe canyonof the R•o Torata, 400 to 500 m north ofthe northern imit of the orebody,and comprisesquartz-chalcopyrite-pyrite einletswith coarsemus-coviteselvages, uttinga plagioclase nd quartzpor-phyritic ntrusive ockassignedo the mainore-host-
ing quartz latite porphyry n the Cuajoneopen pit(Stevenson,972). The earlyEoceneK-Ar age,52.3+__ .6 Ma, is similar to, but probably significantlyyounger han, the K-Ar and Rb-Sr datesdeterminedfor Toquepala.The age difference s supported ythe 4øAr/a"rspectrum, hichyields n ntegratedageof 52.37 +_1.88 Ma. This spectrums essentiallyundisturbed, ut there are large errors n the lowestand highest emperature teps.A more preciseandreliableage,52.15 ___.2 Ma, is derived rom stepsto 5 whichdefinea plateauaccountingor 89 percentof the gas eleased. luid inclusionmicrothermomet-ric data (Clark, unpub. data) for quartz in a veinlet
borderedby the dated muscovite ndicate hat thechalcopyrite-bearingssemblagerystallized rom aboiling queousrineat 340 ø ___øCundera confiningpressureof ca. 0.14 kbars.The muscovitewas here-fore probablydeposited lose o its argon etentiontemperatureand cooled apidly.
Satchwell 1983) states hat the greaterpart of thehypogenecopper mineralization n the deeper ex-posedzonesof the deposit s associated ith quartz-sericite -illitc) alterationand predated he majorep-isodeof molybdenitemineralization. atchwell's e-scription uggestshat n its alteration-mineralizationrelations he Cuajonedepositdiffersmarkedly rom
Toquepala Zweng, 1984) and other major porphyrysystems.We tentatively accept the new latest earlyEoceneage dataasdefining he time of the mainpe-riod of chalcopyriteemplacement t Cuajone;how-ever, t is possiblehat the date mayrecordan episodeof phyllic alterationand reopeningof an earlier veinsystem.
The K-Ar dates for the Toquepala and Cuajonecenters, ogetherwith the dataof Estrada 1975) andZimmerman and Kihien (1983) for Quellavecoandthoseof Beckinsale t al. (1985), confirm hat the ma-jor depositsn thisdistrictwere emplacedn the early
Eocene,some to 2 m.y. after the contiguous, re-dominantly monzodioritic plutons. Our K-Ar and4øAr/a"r data eveal hat he mineralized acitic ndlatiticstocks onstitutedhe terminalstage,or stages,in a complex ntrusivehistory at least 8 m.y. in du-ration. We propose hat the main Cu mineralization
eventsat the three depositswere not simultaneous,the Cuajone orebodyhaving apparentlybeen em-placed ater than that at Toquepala.
Tarata region
Severalsmallgranitoidplutons,hostedmainlybyMesozoic marine strata, lie southeastof the stocksof
the Toquepala district, but these intrusionsare notconsidered y Pitcheret al. (1985) in their overviewof the southeasternegments f the Coastal atholith.The area s widely, thoughapparentlynot strongly,mineralized.Four districtsare distinguished: hal-latita, Lluta, Ataspaca, ndTarata (Fig. 7).
Challatita district:Minor coppermineralizationsdocumented rom the Challatita district by Wilsonand Garcia (1962), who report the recoveryof mal-achite ores from an adit at the foot of Cerro Mina.
Hornblendeseparated rom a sampleof biotite-horn-blendegranodioriteSPAM-132) rom the hostplutonyields complex, isturbed,øAr/a"rspectrum, ithan integrated age of 78.18 ___ .82 Ma (Fig. 7: E).Seventy-four ercentof the gas eleased steps5-8)defines a broad plateau with an age of ca. 77.40+__.17 Ma, but steps4 and 9, both with high errors,yield higher apparentages, n the former caseasso-ciated with an unusuallyhigh Ca/K ratio. We tenta-
tively interpret the spectrumas an asymptoticap-proach o an age of ca. 80 Ma. Whereas he low ap-parentagesof the first hreestepsmay eveal esettingduringchloritization, pidotization, ndcoppermin-eralization,t is moreprobable hat the superimposedthermal event was related to emplacementof thenearby ca. 60-Ma intrusionsexposed n QuebradaPalca seenextsection). he copperveinsare nferredto be ca. 80 Ma in age.
The data or sampleSPAM-132represent he firstrecord of Late Cretaceous ranitoid ntrusion n thispart of the Coastalbatholith: he age correspondsothatof theTiabaya uperunit80-81 Ma)of theAr-
equipasegmentof the batholith MukasaandTilton,1984; Beckinsaleet al., 1985), an event not recog-nized elsewhere n the studyarea.
Lluta (Cercana)district: n the minorbut extensiveLluta, or Cercana,copper (-Pb, Ag) mining district(Vargas,1975), supergene ulfide-enrichednd oxi-dized quartz veinsare exposedon both sidesof Que-bradaPalcaand havebeen workedsporadicallyFig.7). Minor acanthiteand galenaare associated iththe hypogenechalcopyrite-pyrite ssemblages.hemineralizationoccurswithin the Lluta (hornblende-biotite-) quartz monzodiorite stock which intrudes
•.• abandonedine r prosl)ectß K - Ar date b-biotite
(•) 4øAr/39Arpectrum
] BI(SPM161[,.AHB44S.P3A_+M4.01;)[ .A.9.37+0.'4a
HB (SPAM - 138)I.A. 45.21_+4.21 Ma
c
•1001
I.A. 40.22_+0.85 Ma
• 501,
D'"' 0
Cumulative %39Ar raleased
BI SPAM144)HB (SPAM - 132)
I.A. 78.18_+4.83 Ma
E69o50'W
FIG. 7. Geologicmapof the Lluta-Ataspaca-Taratarea,considerablyimplifiedromWilson ndGarcia 1962),showinghe ocationsf abandoned ines ndprospects,he ocationsf dated amples,and age spectra or four granitoidsamples.
marine sediments f the BajocianSanFrancisco or-mationand he CallovianAtaspaca ormation Wilsonand Garcia, 1962).
We collectedsamples f monzodioritico grano-dioritic intrusive rocks from Quebrada Palca 2 kmnortheast of the southwestern contact of the main
pluton (SPATA-2), and from a small outcrop, un-mappedby Wilson and Garcia (1962), in QuebradaTocuco, 7 km northeast of Pachia (SPIT-i). TheirconventionalK-Ar biotite ages, 60.33 ___ .30 and60.90 ___ .83 Ma, are almost identical. In addition,
biotite in sampleSPAM-144, from an outcrop1.5 kmsouthwestof the Lluta mine, yields an essentiallyconcordant pectrum R. J. Langridge, n prep.; Fig.
7: F) which represents closeapproach o a plateauandyieldsan ntegrated geof 62.12 ___.94 Ma. Thisisslightly lder han he conventionalate or SPATA-2, but the errors n the agesoverlap.
On the basis of these data, we infer that intrusion
of the Lluta pluton ook place n the late Paleocene;the associated ineralizationwasprobablyof similarage. Contemporaneity ith the earlier intrusionsnthe Toquepaladistrict s evident.
Ataspaca district: The inactive Ataspacaminingdistrict (Fig. 7) comprises 6 small Cu mines andprospects nd two Pb-Ag prospects Vargas,1975).The deposits lusterwithin andadjacent o the Atas-pacagranitoid lutonwhich ntrudes urassicolcanic
and sedimentarystrata of the Junerata,Pelado, andAtaspaca ormations Wilsonand Garcia,1962). TheAtaspaca tockcomprises everal acies:quartz mon-zodioritic rockspredominate,but monzonitic,grano-dioritic, and quartz dioritic facies are represented.Numerous base and precious metal prospectshave
been developedwithin the stockand ts envelopebutproduction asprobablybeen minor. CENTROMINinvestigatedhe areaasa polymetallic Cu-Pb-Zn-Mo-Ag-Au) prospect n the early 1980s. No detailedac-countsof the mineralization avebeen published, utvein and stockwork-disseminated ores have been ex-
plored in both the intrusionand its country rocks,whereasmoderatelyextensive halcopyrite -cuban-itc) skarns, ich in andraditic garnet, hedenbergiticpyroxene, nd actinolite,occur n limestones f thePeladoFormationadjacent o quartz monzodiorite.
All dates determined for this district are middle or
late Eocene France,1985; R. J. Langridgeet al., in
prep.).Unaltered oarse-graineduartzmonzodiorite(SPATA-3)roman outcrop f the Ataspacaluton3km south-southwestof the 1983 CENTROMIN camp
yields a conventional -Ar biotite date of 42.58q-0.96 Ma (Table 1, d). 4øAr/39Arge spectra representedn Figure7 (C andD) for coexistingorn-blende and biotite in sampleSPAM-138of quartzmonzodiorite rom an outcrop 200 m from sampleSPATA-3.Both spectraare only slightlydisturbed,but the ntegrated geof the hornblende45.21 ___.2Ma) is significantly reater han that for the biotite(39.92 ___.2 Ma). This discrepancyersistsf onlythe moreconcordant teps and5 of the hornblende
spectrum nd steps to 7 of that for the biotitearetaken into account apparentages,46.01 4- 1.45 vs.40.22 4. 0.65 Ma). We infer that intrusionhad oc-curredby ca. 45 to 46 Ma, i.e., the middleEocene.The youngerbiotite date probably eflectsa super-imposedhermalevent ather hanslowcooling, iventhe epizonalenvironment f intrusion.
Two furthersamplesSPATA-4 nd 6) were akenfrom CENTROMIN's exploratory udithdrift (3,780m asl),which s entirelywithin intrusive ocks.Thequartz monzodiorite s medium grainedand meso-craticand s cut by stockworks f pyrite-chalcopyriteveinlets,and thoseby chloriticshear ones.A ca. 20-
m-wide length of the drift exposes melanocraticgranodioriteporphyry comprisingplagioclase ndbiotite phenocrystsn a saccharoidal atrix rich inbiotite, quartz,albiticplagioclase,ndK feldspar. hecoarse- nd ine-grained iotite in part replaces orn-blende,and he porphyry s nferred o havesufferedweak potassicalteration. The quartz monzodioriteyields Table 1, d) a biotite dateof 39.15 4. 0.85 Ma,and the biotitized porphyryone of 40.65 4. 0.88 Ma.These are identical within the limits of error but are
probably ignificantlyounger han he dates btainedfor the main facies of the stock, suggesting hat awidespreadhydrothermalevent at ca. 40 to 41 Ma
mayhavebeen esponsibleor the hornblende-biotitediscordance n sampleSPAM-138.
These age determinations re interpreted as evi-dence for an Eocene episodeof intrusionand poly-metallic mineralization n the Ataspaca-Caplina is-trict. Our dataare in broadagreementwith thoseof
S•nchez 1983b), who recordsa 39.9-Ma K-Ar biotitedate for granodiorite rom this area.
Tarata district:S/mchez 1983b) alsoprovides heonlypublished eochronologicata or the clusteroflargelygranodioriticlutonsn thevicinityof he townof Tarata. He obtained a K-Ar date of 40.8 Ma for
biotite froman outcropnear he settlementof Ticaco.We recordsimilardates rom the 4øAr/39Arnalysis(R. J. Langridgeet al., in prep.) of coexisting orn-blendeandbiotite n granodioriteroma localitynearthe northwestern imit of the samepluton. Both spec-tra (Fig. 7: A and B) displaysignificant isturbance,that for biotite is probablya result of chloritization.
The (two-step)hornblende ntegratedage of 44.834. 4.30 Ma is probablysignificantly igher han thatof the associated mica, 39.37 4. 0.94 Ma. Omission
of the egregiously oungsecond tep of the biotitespectrumncreaseshe integrated ge o 43.53 _ 0.26Ma, in satisfactory greementwith the hornblendedate. We conclude hat intrusion ook place at ca. 44Ma, in the middle Eocene and coevallywith that inthe Ataspaca istrict o the south.
A middle or late Eoceneage s further inferred forthe probablyuneconomic opper-bearing einsandskarns t scattered ocationsn the Tarataarea (Jain,1965), particularlyat Picasa, km westof the town.
All are ocatedwithin or at the margins fgranodioritestocks.t would be premature o assume similaragefor the more important Pb-Ag vein systemswhichhave been worked farther to the west (Jain, 1965),in the Molleraco-Minaytitadistrict.
Summary
From the above data and discussion,we infer that
felsic ntrusive rockswere emplaced n at least eightepisodesn the Toquepalasegmentof the PeruvianCoastal batholith sensu lato. The Cordillera de la
Costa xposes lutons f MiddleJurassicca.185 Ma),
Late Jurassic ca. 160-165 Ma), latest Jurassic ca.145 Ma), and mid-Cretaceous ca. 95-110 Ma) age.Batholithdevelopmentmay, however,havebegun nthe Early Jurassic, t ca. 196 Ma (Beckinsale t al.,1985). The inland belt of younger ntrusions nder-lying he Precordillera ndaxialCordilleraOccidentalcomprises lutonswith Late Cretaceous ca. 80 Ma),latestCretaceous ca. 63-66 Ma), late Paleocene ca.59-62), and middle to late Eocene (ca. 40-46 Ma)ages.All but the earliestplutonsare associated ithhydrothermalmineralization, enerallyof imited ex-tent. In addition, the emplacementof subvolcanicpolyphase acite,andprobably, atite porphyrystocks
and associated orphyry copper depositsoccurredover the interval, ca. 52 to 57 Ma, i.e., in the earlyEocene.
Oligoceneand Miocene Mineralizationof the Main Arc Domain
Introduction
The terracednortheastern lopes f the CordilleraOccidental nd he contiguousltiplano reunderlainpredominantly y continental olcanic, olcaniclastic,and clasticstrataof Oligocene o Plioceneage (Fig.3), which record stagesof cordilleranuplift, inter-montane asindevelopment, nd Main Arc magma-tism.Thesestrata orma generally hin coveron owerandupperPaleozoic edimentary nd gneousocks,which crop out in severalbasement ighsor uplifts(Newell, 1949; Ellisonet al., 1989).
Tertiary stratigraphic elations in this wide areawere first documented y Jenks 1946) and Newell(1949), who delimited two major sequences f sub-aerial volcanic rocks, the "Tacaza Volcanics" and
overlying SillapacaVolcanics r Group," both withtype sectionsn the SantaLuc•adistrict Fig. 3). Ma-roccoand del Pino (1966) promoted he former togroup status.Extensive sequencesof molassicsedi-ments red beds)underlyinghe volcanic ockswereassignedo the Puno Group. Mendivil (1965) estab-lished he dominantly olcanic arroso roup,whichoverlies he SillapacaGroupandconstitutesll of thevolcanic edifices of the Cordillera Occidental which
predated he Pleistocene lpineglaciation.Klincketal. (1986) assign he modernstratovolcanoesf theCordilleraOccidental o the AmpatoGroup. Strati-graphic efinementswithin this almostentirely un-fossiliferous uccessionave been contributedbyPortugal 1974), and with the aid of K-At geochro-nology,by Kaneokaand Guevara 1984), Franceetal. (1984), France (1985), and Klincket al. (1986).The last-citedwork involvedextensive uadranglemappingsouthand southwest f Lake Titicaca and ssummarized y Ellisonet al. (1989). Klincket al. re-define he limitsof the TacazaandSillapaca roupsand propose, n addition, he establishment f an in-terveningpredominantlygnimbriticPalca Group.Wasteneys 1990) providesa detailed accountof thegeologyand geochronology f the key SantaLuciaarea,defining H. A. Wasteheys t al., in prep.) ocalformational ubdivisionsn broadconformity ith thestratigraphic chemeof Jenksand Newell. Thus, thePalcaGroup s not recognized erein; ts pyroclasticunitsare assignedo the SillapacaGroup.
Few of the scattered pithermalAg-Au-basemetalvein systemsof the region have received detaileddocumentation, ut Fletcher et al. (1989) advanceregional ectonicmodel or the mineralization,muchof which s hostedby the TacazaGroup. They argue
that vein ormationwasonlyrarelydirectlyassociatedwith shallow ntrusiveactivitybut took placewithinpre-Sillapacaroupstrata sa resultof geothermalcirculation uringor mmediatelyollowing ruptionof those mid-Miocene volcanics,and was controlled
by regionalnorthwest-trendingtructurese.g., he
Lagunillasault one: ig.3), consideredo have eenactive hroughouthe Oligocene-Pliocenenterval.The ore metals were inferred to have been leached
from the apparentlyCu- and Ag-richTacazaGroupvolcanic ocks FornariandVilca, 1977). In the pres-ent discussion, e record geologicand geochrono-logicdata for severalminingdistrictsn this regionwhich demonstratehat the metallogenicmodelofFletcher et al. is untenable.
Cacachara-Pavico district
The Cacacharaand nearby Pavico (or San Bosco)mineshave been sources f silver for over 250 years(Kiilsgaardand Bellido, 1959). The former (Fig. 3)was the major silver mine of the transect n recentdecades Benavides,1984) until its closure n 1988,and reportedreservesof 0.4 million metric tonsat 30oz/metric ton Ag and a cutoff grade of 5 oz/metricton in 1985 (unpub. ept., Colquiminas, .A.).Annualsilverproduction veraged bout22 metric ons.Theorescontainca. 5 percentZn and 2.5 percentPb, aswell as considerableCu. Only the Pavicomine is re-corded in the 1:100,000 geologicmap of the sur-roundingHuaitire quadrangle Garciaand Guevara,1975) and neither deposit s described n the quad-ranglereport by M•trquez 1978).
The geologyof this isolatedmining district (Figs.2 and 8a) and the structureand mineralogyof theCacachara deposit are documented by Johnson(1986). Whereas he PavicoAg-Pb-Znmineralizationoccursdispersed n the matrix of an andesiticdia-treme, that at Cacachara ompriseshree east-north-east-trendingquartz-rich veins, developed over avertical interval of 160 to 200 m and hostedby adacitic dome. The veins are superimposed n dikesof phreaticbreccia (Clark et al., 1986; Johnson ndClark, 1986). The major Ag-bearingmineralsarepyrargyrite, etrahedrite,andpolybasite. lectrum sabundantn an early,Ag-poor,basemetalsulfide ein
stage Johnson, 986); Au grades ocally attain 0.3oz/metric ton. The observedstratigraphic elation-shipsare illustrated n schematic orm in Figure 8b.The dacitic dome intruded a succession of subaerial
andesitic nd dacitic lowsand is itself cut by a pipeof dacitic ntrusionbreccia, which may be a feederfor a dacitic ash-flow unit which overlies the earlier
volcanics. he ore-bearing einsclearlypostdate hedaciticbrecciaand are therefore probablyyoungerthan the daciticash low. The youngest olcanicunitin the area s a crystal-lithicuff of daciticcomposition;the temporal elationships f this and he mineralized
FIG.8. Geologic apof heCacachara-Pavicoining istrict, fter ohnson1986),showingocationsof dated pecimensrom he Cacacharagneousenter.All units,with heexceptionf the probablyOligoceneunoGroup, reassignedo theupperMiocene-Pleistocene)arroso roup. . Cartoonillustratinghe mutual elationshipsf the datedunits n the vicinityof the Cacachara ine.
veins are unknown. The rocks of the mine area were
assignedo the Capillune and Llallahui Formationsby Garcia and Guevara (1975) but to the TacazaGroup n the 1:1,000,000 nationalgeologicmap IN-GEMMET, 1975); neither is correct.
New K-Ar biotite ages Table 1, e) have been de-termined France, 1985) for early andesitc "MiddleAndesitc"unit of Johnson, 986), daciteporphyry,daciticash-flow uff, and late crystal-lithicuff. Theagesdelimit a narrow nterval (8.32-6.48 Ma) in the
late Mioceneand conform o the inferred sequenceofextrusive ndhypabyssalvents.Correlation f theCacachara olcanicsuite with the regionallyestab-lishedNeogenestratigraphic roups emainsuncer-tain. However, if the BarrosoGroup of Mendlvil(1965) is consideredo extendbackat least o ca. 6.5Ma, as nferredby Kaneoka nd Guevara 1984; seealsoKlincket al., 1986), the younger, elsic, ocksofthe mine area maybe regardedas nitial manifesta-tionsof this major upper Miocene o Pleistocene ol-caniccycle.
The agedatado not fully constrainhe time ofmin-eralization.Althoughvein formationpostdated m-placementof the daciteporphyryat 7.03 _ 0.4 Ma,it is not clear whether t precededor followedem-placement f the two felsicpyroelastic nits seeTable1, e). Nonetheless, ur tentative emporalcorrelationof the dacitic intrusion breccias and ash-flow tuff im-
plies that mineralizationwas younger than 6.62__+.15 Ma, and we consider t probable hat it oc-curred before 6.48 __+.18 Ma, the time of eruption
of the crystal-lithic uff. We favor, therefore,a lateMiocenerather than Plioceneage for the Cacacharadeposit.The age of the Pavicodeposit s also ncom-pletely delimited, but the large brecciabody whichhosts he ore cuts he Middle Andesitcunit (Fig. 8),indicatinghat he mineralizationsyoungerhan8.32_ 0.59 Ma.
An association of the Cacachara-Pavico mineral-
izationwith earliestBarrosoGroup volcanismwouldbe in permissive greementwith the metallogenicmodeladvanced or the region mmediately o the
northby Fletcheret al. (1989), whostate p. 70-71)that convectiveluid circulation eneratingmineral-ization was stimulatedby "Sillapacaor Barrososub-volcanic centres." However, the Cacachara veins oc-
cur within a hydrothermallyaltered subvolcanic a-citic intrusion, and the local absence of the Tacaza
Group volcanics ules out the possibility hat theyrepresent he sourceof ore metals; n both respects,the mineralization of this district fails to conform to
the concepts f Fletcher et al.
Santa Lucia district
Numerous mall- o medium-sized aseand pre-ciousmetaldeposits re clusteredn the vicinityofthe ownof Santa uela KiilsgaardndBellido, 959;Bellidoet al., 1972). The district Figs.2, 3, and9)has ongbeena source fAg, Au, Cu, Pb, andZn ores.Presentproducers nclude the SantaB•.rbaraAg(-Cu, Pb, Au) mineof Minsur,S.A., he subject f
studies y Arenas 1977), Wasteneys1990), andWasteneys ndClark (in prep.); the smallTaeazaCu-(-Ag)mine;and he Copaeabanag(Cu-Pb-Zn) ine(Minsur,S.A.)of the Compuertaamp.The largesthydrothermalenter n the area s the BerenguelaAg-Cu deposit 15-20 million metric ons:1.2-1.4%Cu and4-5 oz/metrieonAg)which, aving roducedat least400 metric onsof silver n the earlieryearsof thiscentury, chievedenewed rominencen the1960sasa testcase or the application f the TORCOpyrometallurgieal rocess, ecausemuch of the CuandAg reserves ccur ubmicroscopicallyispersedin Mn oxides.
This area ies near the northeastern oundary fthe Cordillera Occidental and on the western flank
of the Cabanillas igh (Ellison t al., 1989) and sboundedo thesouthwesty thestrueturallyomplexLagunillasroughand aultzone.We have emappedanareaof 400 km2surroundinganta ue•aat a scaleof 1:50,000 WasteneysndClark,1986;Wasteneys,1990). Of the numerousK-Ar and 4øAr-3'gr dateswhich have been determined (France et al., 1984;France, 1985; R. J. Langridge, n prep.), we recordonly hose øAr-3"rdateswhichare nterpreted sconstraininghe ageof ocalmineralizationTable2).
Our studies efine he following ventsn the ater
Tertiary history of the area:
1. ProlongedPaleogene rosionof PaleozoieandMesozoicunits, which generated he Puno Groupmolasse.Depositionwas controlledby northwest-trending fault zonesand the elasticstrataare thin toabsent in the immediate Santa Lue•a area. Ellison et
al. (1989) dentify generally eak pisodef folding,termed the QuechuaD• phase,which affected hePuno Group strata at 30 to 32 Ma.
2. Largely quiescent, hallow-water lacustrine),
and subaerialeruption of the marie o intermediate,predominantlyshoshonitic olcanicsof the Yapocoand Piruani Formations.Volcanism,controlledby thenorthwest-trendingstructures, began in the earlyOligocene,probablyshortlybefore 31 Ma, and per-sisted o ca. 26 Ma. The Lim6n Verde monzogabbro
stock (orthoclasedate, 30.28 4- 0.61 Ma; BARB-17)is interpreted as a feeder for the earlier shoshoniticvolcanics.
3. Subvolcanic intrusion of calc-alkaline horn-
blende diorite stocks nd high K andesitcdikesandsills.The intrusions aveagesn the range28.21 4- 3.4(averageof two hornblendedates or BARB 189) to26.45 4- 2.7 Ma (averageof two hornblendedates orBARB-199), thus overlappingwith the shoshoniticvolcanism.
4. Major uplift anderosion n the latestOligoceneto earliestMiocene. The period correspondso theQuechuaD2 orogenicpulse of Ellison et al. (1989)
and was accompanied nd followed by the eruptionof the rhyolitic gnimbrites f the Churuma ndSantaLuciaFormations. he ash-flowuffs,assignedo thePalcaGroupby Klinck et al. (1986), yield ages n therange of 21.59 4- 0.88 (SPAM-228) to ca. 16.5 Ma.The main ventswere probably n the Cordillera Sil-lapaca, but distal pyroelastic acies were in parttrapped in the SantaLucia structure,a ca. 8-km-di-ameter, crudely circular basin first recognizedbyWasteheys nd Clark (1986). This is interpretedbyEllisonet al. (1989) as a calderabut was probablygenerated ectonically sa resultof extension ausedby strike-slipdisplacement n the Lagunillas ault
zone (Wasteheys, 990).5. Further short-liveduplift anderosion, ollowedby eruptionof the predominantly acitic avasof theSillapaca ormation.This volcanic vent wasbrief inthe SantaLuc•aarea,extendingonly from ca. 16.2 to14.7 Ma (Wasteheys, 990). The majoreruptivecen-ter was again in the Cordillera Sillapaca,but daciticplugswere emplaced n the preexistingSantaLuciastructure.
6. Followinga protractedapparenthiatus,volca-nism esumed n the late Miocene, with the eruptionof the shoshonitic olaoccoFormation,which overliesanerosion urfacen the eastern art of the maparea.
In the immediateSantaLuc•adistrict,monzograniticporphyrydikesassignedo the Condorpufiuna hy-olite Formation Wasteheys, 990) were emplacednan en echelonseriesaround he southernmarginofthe Santa uciastructure, robably uring enewedmovementalong he Lagunillas ault zone.
Of the aboveunits, he Yapocoand PiruaniFor-mations, the Lim6n Verde Monzogabbro, and thehornblende-dioritetocks re assignedo the TacazaGroup (overallagerange,ca. 24-ca. 32 Ma), the Sil-
• Yapocoormation.• Lim6.erdeonogabb•o• foldxisEOCENE-OLIGOCENE • dykeß•-• Puno roupCRETACEOUS '•, mine
-•--• Ayavacasst. nl. ß prospectJUIL4SSIC
]:]•..,Lagunillasroup ....•- limitfmapping
SYMBOLS
bedding
/ flow-lamination
normal fault
thrust fault
FIG. 9. Geologicmap of the SantaLucia district, showing he locationsof active and abandonedminesand prospects, nd of samples atedby the 4øAr/a9Arotal fusion echnique.Geology s afterWasteneysand Clark (1986) and Wasteneys 1990).
lapaca Formation to the SillapacaGroup (local agerange= 14.7-21.6 Ma), and he Condorpu•unaRhy-olite and TolaoccoFormation to the BarrosoGroup(<7 Ma). We differ from Jenks 1946) and Newell(1949) only in assigninghe felsic gnimbritesof theChuruma "white tuff," Jenks,1946) andSantaLucia
Formations o the Sillapaca ather than the TacazaGroup (H. A. Wasteheyset al., in prep.).
The greater part of the metallic mineralization nthe maparea s hosted y TacazaGroupvolcanic ocksor the underlyingMesozoicstrata; he best-definedstructural feature in the area, the Santa Lucia basin,
apparentlyexperienced o significant ydrothermalactivity.
Numeroussmallmagnetite-rich ndraditicgarnetskarn bodies on the flanks ofCerro Lim6n Verde have
been mined as material for smelter flux. The orebodies
are developed n horizonsand ensesof red-bed clas-ticswhich constitute faciesof the Cretaceous ya-vacasLimestoneFormation Klincket al., 1986), ad-jacent to the subvolcanic im6n Verde monzogabbrostock.AlthoughPortugal 1974) suggestedhat ironoxidemineralswere concentrated uringdepositionof the sandstones,he epigeneticnature of the ore-bodiessclearandwe nfer hathydrothermalctivitytook place at ca. 30.3 Ma, coevalwith intrusion.Else-where in the district,minor coppermineralizationsdirectly associatedwith several small hornblendediorite stockswhich ntrude he YapocoFormation.The nameLim(•nVerde waspromptedby the brightgreen malachiteand chrysocolla xtensivelydevel-oped n outcrops f chalcopyrite-pyriteeinlets.Theveinscut Ayavacas imestoneFormationbedsadja-cent to a propylitized ine-graineddiorite plug andare intimatelyassociated ith dikesof phreaticbrec-cia.The dioritic ocksoccur n the immediate icinityof the monzogabbro tock,but the mutual relationsof the two intrusive ock ypesare uncertain.A shortdistanceo the southwest, groupof oxidized opperveinshavebeen exploited o a limited extent at Cer-rillos. The mineralization is associated with a series
of northeast-striking,ubvertical ebbledikes,whichcut YapocoFormation agglomerates djacent o a
subvolcanic stock of hornblende diorite. A late Oli-
gocene ge ca.26.4-28.2 Ma) is nferred or hydro-thermalactivityhere and at Lim6nVerde.
Severalcontrasting eneticmodelshave been ad-vanced for the BerenguelaAg-Cu deposit, whichcomprises everalwest-northwest-trending assiveostockworkbodies of manganese xideshosted byfaulted limestones f the Ayavacas ormation.Hy-pogeneandsupergene opperandsilverminerals reinvariablyassociated ith the Mn oxide concentra-tions,which are dominatedby cryptomelane nd to-dorokite.CandiottiandCastilia 1983) proposedhatthe baseand preciousmetalswere absorbed y sed-imentary Mn oxides from downward-percolatinggroundwater and were derived rom overlyingmo-rainic deposits earingsulfideclasts roded rom theLim6n Verde stock. n contrastKlinck et al. (1986)and Fletcher et al. (1989) state hat the Mn-Cu-Agbodies eplace faulted imestone, he former authorsenvisaging control by swallowholeswhich formedthroughkarsticweatheringof the limestone.
We concurwith the concept hat the Berenguelaorebodies result from fracture-controlled metaso-
matism of the carbonate rocks; however, we infer adirect relation to a subvolcanicntrusion,on the basisof the widespread ccurrencen the immediateminearea of polyphasephreatic breccia dikes and lenses.Candiotti and Castilla's "tills" and Klinck et al.'s "flu-
vio-glacialriver gravels" have been reinterpreted(Clarket al., 1986) as he surface xpressionf a largehydrothermal recciapipe. The intimateassociation
of brecciation and mineralization s shown by thepresence f Mn-rich ore concentrationslongquartz-rich fractures djacent o bodiesofbreccia.Moreover,the dominant ocksoccurring sclastsn the brecciasare, with the exceptionof limestoneand quartzite,"exotic" ine-grained uartzdiorites nd hornblende-
plagioclase-porphyriticacite,both exhibiting ntenseargillic alteration.We infer that these gneous ocksrepresent,at the least, the heat sourcewhich drovethe large-scale ydrothermalsystem. he daciticpor-phyry clastsproved too altered to date, but a lateOligocene 26.80 _ 1.3 Ma; BARB-140)hornblendeagewasobtained or a dike oftrachyandesitexposedon the northern edgeof the main open pit, in an areacut by numerousMn-rich veinlets.The unalteredna-ture of this rock strongly mplies hat it wasemplacedsubsequento mineralization,nd hus heBerengueladeposit s consideredo be late Oligocene n age,pos-siblycoevalwith the copperveins n the Lim6nVerdearea.
The SantaBftrbara ilver -Cu, Pb) mine, at presentthe most important in the Santa Lucia district, hasreserves in excess of 1 million metric tons, with a
grade of 15 oz/metric ton Ag. Production n 1988amounted to 2,342 metric tons of concentrates,with
27.5 percentCu, 12.9 percentPb, and 105.4 oz/met-ric ton Ag. The concentrate ompositioneflects heroles of argentianchalcocite,bornitc, and chalcopy-rite as the major silver hosts n the hypogene ore.Less important are argentian tennantite and minortetrahedrite,pearceitc,andbetekhtinite Wasteneys,1990; Wasteneysand Clark, 1990). A gold recovery
circuit was nstalled n 1987. As Fletcher et al. (1989)record, the vein systemas a whole has a remarkableconfiguration, ircular n plan (ca. 1.25-km-surfacediam)and with the overall orm of an invertedcone(Wasteneys t al., 1990), conforming losely o themargin of a diatreme filled with weakly stratifiedrhyodacitic uffs,assignedo the Cerro HermosoFor-mation (Wasteneys,1990). The veins are superim-posedon a polyphase eriesof concentric nd radialphreatic and phreatomagmatic reccia dikeswhich,together with the diatreme, comprise he SantaBftr-bara Complex (Clark et al., 1986; Wasteneys,1990;Wasteneys t al., 1990). Despite its clearly proximal
volcanicsetting, he vein systembearsstrongeranal-ogies o the adularia-sericitehan the acidsulfateclanof epithermalpreciousmetal deposits Heald et al.,1987). Hydrothermal alteration is dominated byphyllic assemblages.
The Cerro Hermoso diatreme is inferred to have
beenemplacedwithina northwest-trendingaultzonealong he valley of the Rio Verde, precededby intru-sion of an extensive series of hornblende andesitc
(-diorite)sills nto the YapocoFormation lows.Onesill in the immediatemine area yieldsa 4øAr/3•Arhornblende date of 26.9 _ 2.7 Ma (BARB-199). A
coeval date of 26.83 _+0.28 Ma, for an HF-leached
whole-rocksampleof rhyodacitic uff from the CerroHermoso Formation (SPAM-231), is in permissiveagreementwith the hornblendeage, but the rock ishydrothermally ltered and the geologic rror in thedate maybe high. The ageof mineralizations better
defined y the 4øAr/39Arateof 23.50 _ 0.52 Ma fora concentrate f hydrothermal ericiteseparatedromphyllicallyaltered phreaticbreccia (BARB-422)ad-jacent to the main SantaB/trbaravein on the 3,932-m level of the mine (588 m southof the main shaft).The date, at the Oligocene-Miocene oundary,con-firms that the Cerro Hermoso Formation representsthe first manifestation f felsicpyroclastic ctivity nthis region of the Cordillera Occidental, antedatingby some2 m.y. the earliestash lowsof the ChurumaFormation.A latestOligoceneor earliestMioceneageis inferred for the mineralization, which may havebeen riggeredby the initial stageof cordilleran plift
in this region.Three smallerbaseand preciousmetal depositsnthe area have been documented. The Tacaza
Cu(-Pb, Ag) mine is locatedwithin the type sectionof Jenks' 1964) andNewell's 1949) TacazaVolcanicsandworksa seriesof northeast-trendingeinshostedby plagioclase ndaugitcporphyriticshoshoniticndbanakitic lowswith agglomeratentercalations. heserocks are assigned o the YapocoFormation on geo-chronologic and petrologic grounds (Wasteneys,1990). Klinck et al. (1986) report a whole-rockK-Ardate of 17.5 ___.6 Ma for stronglyaltered "andesitc"from the mine area and assign he volcanics o a
"younger Tacaza" (i.e. post-22 Ma) sequence.Thisage is incompatiblewith analyticallymore reliablebiotite4øAr/a•Aratese.g.,21.59 _ 0.88 Ma;SPAM-228) for the tuffsof the overlyingChurumaFormation(Palca Group of Klinck et al., 1986). We thereforequestion he validity of the 17.5-Ma date, preferringto infer an age of ca. 26 Ma for the hostrocksof theTacazadepositon the basisof severaldatesobtainedfor flowsof the Auquirane ection f the TacazaGroupa short distance to the south of the mine. Subvolcanic
intrusionsof monzogabbroand hornblende dioriteoccur in the mine area but have not been delimited.
The Tacazaveinsare superimposed pon dikesof
polymictic pebble breccia. The dominanthypogeneore mineralsare chalcociteand bornitc. Copper sul-fides and galenaalsooccur n two mantos n the im-mediatevicinity of the veins.Thesequasiconcordantorebodies comprise disseminations nd patches ofsulfide n amygdaloidalnits;analogiesmaybe drawnwith the Chile-typestrata-bound u(-Ag) deposits fthe shallowmarine to subaerialJurassic f northernChile (Ruiz et al., 1971). Fletcher et al. (1989) arguethat the hydrothermal luids were pondedbeneathimpermeablewelded tuffs of the Palca Group (ourChuruma Formation), spreading aterally to form the
mantos.However, he overlying uffsare onlyweaklywelded and the major strata-bound rebody,SanSal-vador-27, lies 75 m below the unconformity.Wetherefore are not convinced that mineralization oc-
curred after accumulation of the lower Miocene tuffs
and suggesthat it couldbe older or younger han
the Oligocene-Miocene oundary.Similaritieswiththe larger SantaBirbara veins nclude he associationwith phreatic breccia dikes, the abundanceof chal-cociteandbornitc, andprobably, he association ithhornblendeporphyritic ntermediate ntrusiverocksof late Oligoceneage. The two depositsmay, there-fore, be approximately oeval.
Small-scalemining of silver-rich ores has takenplacesince he 19th century n the Compuerta amp.Two mainsetsof veins,hostedmainlyby PunoGroupclasticsediments,have been worked in the abandoned
Huiscar and San Germln mines,and contiguousothe latter, in the active Copacabanamine. The Co-
pacabana-San ermln veinsare dominated y chal-cocite, tennantite, and dolomite, whereas the Huiscar
mine worked argentian galena and sphalerite-richores.One seriesof veins Copacabana-San ermln)hasa generaleast-southeastrend (unpub.map,Kro-mar, S.A., 1986) but comprises egmentswith alter-natingeast-southeastndsoutheast trikes; he secondseries Huiscar) s very narrowand rendsnortheast.The east-southeast-trendingeins are closelyasso-ciated with an en echelon array of lensy dikes ofquartz-feldspar orphyritic hyolite,which displaysthe samealternationof segments ith east-southeastand southeast rientations.At depth, the porphyry
dikes ncreasen sizeandnumber;mostare postmin-eral, but someare cut by barite veinsassociated ithargillicalteration,demonstrating temporaloverlapof magmatism nd hydrothermalactivity. We tenta-tively infer that the emplacement f both veinsandporphyry ikeswascontrolled y transcurrentextralmovement on the regional Lagunillas ault zone,within which the deposit lies, the east-southeast-,southeast-, nd northeast-trending tructures epre-sentingR, P, and R' Riedel shears, espectively. hisis in close agreementwith the tectonic model ad-vancedby Fletcher et al. (1989) for mineralizationnthisregion.However,we favora genetic elationbe-
tween he rhyoliticdikesand he vein systems. hesedikesare inferred to belong o the CondorpufiunaRhyoliteFormation, he type area or which ies 3 to5 km to the east-northeast, nd which constitutes n
arcuatesystem f subvolcanicntrusions onformingto the southernmargin of the earlier Santa Luciastructure.The late Miocene age, 6.97 _ 0.50 Ma,obtained or biotite from the type locality (BARB-280), is thusconsideredo record he age of miner-alization n the Compuerta istrict,despite he sim-ilarities of some of the veins to the Santa Birbara veins.
No direct age dataare available or the silver-base
metal Cayachira rospect, ut discussions warrantedbecause Klinck et al. (1986) report an AlbianK-Ar date (104 _ 4 Ma) for the nearby Cerro Paco"(micro-)granodiorite"lug.The mineralization, ithan averagegrade of 15 oz/metric ton Ag, 6 percentPb, 7 percentZn, and0.3 percentCu (R. ValdiviaU.,
pers.commun., 984), formsa peneconcordant antowith an average hickness f 60 cm extending or atleast 1.2 km alongstrike n brecciatedolistostromicAyavacasFormation cherry limestones.The nearbyflow-bandedplug also intrudes the Ayavacas or-mation, for which a Cenomanian (i.e., ca. 91-97.5Ma) age is establishedNewell, 1949; Klinck et al.,1986). The K-Ar date, for altered biotite, is thereforeproblematic.However,Yoshikawa t al. (1976) recordMesozoic, ncludingCretaceous,K-Ar dates or gran-itoid intrusionsn the generalTintaya area (Fig. 2),and Marocco and Noblet (1990) infer that igneousclasts in the molasse of the Cuzco-Sicuani basin record
Late Cretaceousor Paleocenearc magmatismover350 to 400 km from the (present)Peru-Chile trench.These scatteredobservations,ogether with the rec-ord of mid- andUpper Cretaceousmafic-intermediateigneous ocks n the Inner Arc domain, end supportto the tentative suggestionsy McBride et al. (1983)and Clark et al. (1984) that the later Cretaceous awa markedexpansionor bifurcation)of the arc in thevicinityof the presentBolivianorocline. t is possiblethat both Cretaceous nd Neogene ntrusions ccurin the Cayachira rea,but we favora Tertiary age orboth the mineralizationand for the nearby subvol-canic stockwhich is juxtaposedwith a ca. 1.5-km-
wide pipe of fragmental ocks,which ncludephreaticbreccias.Although this probable diatreme systembearsmanysimilarities o the SantaBirbara Complex,we prefer to assignt to the upper MioceneCondor-pufiunaRhyolite Formation on the basisof the lith-ological imilaritiesWasteneys, 990) of the intrusiverocks.
From the precedinggeologicand geochronologicrelations,we conclude hat mostbase and preciousmetal epithermal mineralization in the Santa Luciadistrict accompanied ruption of the Tacaza Group,generally exhibiting a close associationwith upperOligocene,calc-alkaline ubvolcanicntrusions. he
SantaBarbara ein systemwasdirectlyassociated ithan apparently solated elsicexplosive enter which,from its close association with a hornblende andesitc
sill complex,we interpret to be the terminal stageofthe TacazaGroup. Both the Cerro Hermosodiatremeand he mineralizationmayalsobe regardedasbeingtransitionalbetween the dominantlymarie ate Oli-goceneand he felsicearly Miocenevolcanic egimes.Less mportanthydrothermalactivity occurred n as-sociationwith hypabyssal elsic magmatism oevalwith the earlieststage n the accumulation f the up-per Miocene-PleistoceneBarrosoGroup. None ap-
pears o have akenplaceduringSillapaca roupvol-canism cf. Fletcher et al., 1989).
Ma•azo district
The long-establishedafiazoCu-Pb-Zn-Ag amp(Figs.2, 3, and 10) has ecentlyemerged sa signif-
icant sourceof bed-rockgold (Arenas,1988; Fletcheret al., 1989). The polymetallic ein and stockworkmineralization of the area is associated with small
stocksof diorite and granodiorite,with dacitic flowdomesand a large dacite dike. Presentproduction smainly rom the LosRosales u-Cu vein, whichdis-plays downward onationromcopper- o gold-richores Fletcheret al., 1989) and which s hostedbythe Cerro Vizcachane dioritic plug, intrusive intosandstonesndred shales f the probablyOligocenePunoGroup. n addition, custommill processesresfrom the Aladino 6, SantaMestres, and Lulita ("Pal-
tapata")mines,as well as from the SanAntoniodeEsquilacheamp, ecovering g- andAu-richsulfideconcentrates.
The structuralgeologyof the area s well knownfrom the work of Newell (1949), who demonstratedthat the CretaceousAyavacasLimestone Formation
is uxtaposed ith the Paleogene unoGroupclasticsediments long a west-northwest-striking,orth-verginghrustaultand s tselfoverlain, ndprobablyoverthrustby, mid-Callovianshales, sandstones,limestones, nd quartz arenitesof the LagunillasGroup.Newell's"Maravillas"or "Mafiazo" hrust sconsidered y Klinck et al. (1986) andEllisonet al.(1989) to represent segment f the Lagunillasaultzone.Newell (1949) andotherworkers ave nferredthat the minor dacitic ntrusions n the southernpartof the Mafiazo area were controlledby the thrusts.The daciticbody underlyingCerro Caracollo s in-
MA•AZO•3926 m a.s.I.)
CERRO
CARACOLLO
San Marcpsi
Santa Carmen
i
/
• CCALAPAMPA
[]'x ,
ßSanta .'.
Mina Los
,,':':':••,':Y:'.".' ina San
VIZCACHANE •. ..:)..::
:.:. ina Santiaguito•.
'San Martin
0 I 2 3
I " I k
70'20'W
I
• 20
0: :1 km
• unconsolidatedlluvium:•._•.•'• iorite
daciticomesndikes":'•'• Punoroup
• Ayavacasimestonem.
•::..•i• agunillasroup
• thrust
...•.._•_ treamourses
•, • activemine'abandonedmine or prospect
MUSCOVITE (COCA 1804)
Integrated age 19.03 Ma
0.2 0.4 0.6 0.6. . . i . . . i , . , i , . - • . ß ß
Cumulativeraction 39Ar eleased
FIG. 10. Geologicmapof the Mafiazomining istrict,modified fterNewell 1953)andArenas(1988),withschematicrossectionA-A')hroughheLulita Paltapata)ine inset). gespectrumis for hydrothermal uscoviterom heLulitaworkings.
terpreted as a partially extrusive dome (Arenas,1988). The Pb-Zn-Agmineralization t SantaMestresis associatedwith dacitic and minette dikes, and with
a pipe of phreatic probablyphreatomagmatic)rec-cia, which may be a marginal aciesof the dome.
We have datedhydrothermallyaltered dacitepor-
phyry from the Lulita Au(-Cu,Pb,Ag)mine, which nrecent yearshasyielded ca. 200 to 300 metric tons/month of ores with ca. 1.5 percent Cu, 0.8 percentPb, 0.8 percentZn, 3 to 4 oz/metric on Ag, and3 to5 g/metric ton Au. Quartz-pyrite-chalcopyrite-ar-gentian tetrahedrite-electrum einlets compriseastockwork within a 50-m-wide dike situated 10 m
southof the thrust separating he Ayavacas nd La-gunillas ormation nddipping outh, roadlyparallelwith the thrust (inset in Fig. 10). Mineralization isassociatedwith intense quartz-sericite muscovite)-pyrite alterationof the host porphyry.The datedsample,which yielded a high purity concentrate fhydrothermalmuscovite,was aken from the north-west end (1989) of the 4,330-m sublevel.
The 4øAr/a9Ar uscovite pectrum ieldsan inte-grated age of 19.03 _4- .18 Ma. Although he spec-trum is not a true plateau, he apparentagesof themajorityof the gas ractions verlapwithin the limitsof error (2a), and the integratedage is acceptedasapproachinghe time of crystallization f the mica.This early Miocenedate differs rom all othersso fardetermined for mineralization in the Main Arc domain
in this transect.The implied age correspondso thetime of eruption of the Churumaand SantaLuciaFormation gnimbrites f the SantaLuciadistrict,andthus, o that of the PalcaGroup ofKlinck et al. (1986).Despite ts association ith dioritic ather handaciticintrusive rocks, we further infer that the Los Rosales
Au-Cu vein system s alsoof early Mioceneage.
Cabanillas district
Paleozoicmarinestrataare extensively xposednthe Cabanillas igh (Ellisonet al., 1989), which sep-arates he SantaLucla district rom the Altiplano. nthe hills o the westof the villageof Cabanillas, owerDevonian clasticsedimentsof the CabanillasGroup(Newell, 1949) are intruded by the Cerro Yaretanegranodiorite-monzogranite pluton (Laubacher,1978a; Clark et al., 1990a), probably he largestPa-
leozoicgranitoidbody in the immediate ransect.K-Ar and 4øAr/agArating Clarket al., 1990a)yieldsan Early Permian age (ca. 277 Ma) for the intrusion.
Wolframite- and molybdenite-bearing uartz veinsexploiteduntil recentlyby the smallSanJudas adeo,or Porvenir,mine (Fig. 2) are alsoof Permianage (ca.260 Ma: Clark et al., 1990a). Auriferous placers inthe valleys draining the Cerro Yaretane pluton arederived from pyrite- and gold-bearingquartz veinswhichare tentativelyconsideredo be a lateral aciesof the lithophilemetalmineralization.
The W(-Mo) and Au mineralizationof this area isassignedo the Andeanbasement.
Pucard-Putina area
Small-scalemining of antimonyand base metal-rich oreshas aken place at several ocalitieson theAltiplanonorthwestof Juliaca Figs.2 and 3). The Sbdepositsmay epresent art of the extensive, ndonceproductive Purser,1971), antimonysubprovince fthe Precordillera e Carabayao the northeastwhere,in the SantaRosaandPutinadistricts Fig. 11), stibniteveinscontaining aryingamounts f argentian alena,sphalerite,scheelite,and wolframiteare hostedbylower Paleozoic clasticstrata, forming inliers in thePutina synclinorium (Newell, 1949; Laubacher,1978a andb). The localoccurrence f cassiterite nd/or Snsulfosaltse.g.,Petersen, 960) in several f thePrecordillerandepositssuggestshat this area con-stitutes a transition between the Main and Inner Arc
domains. here are no moderndescriptions f these
deposits,but severalare associatedwith subvolcanicstocksof sanidineporphyriticrhyolite and of quartzandplagioclaseorphyriticquartz-latite.Preliminaryfluid nclusion tudiesKontak,1985) of samplesromthe San sidro deposit n the SantaRosacamp eveala complex,multistage, hermal history,and elevateddeposition emperatures >240øC), suggestive f amagmatichydrothermal ather than, e.g., a meta-morphogenic r submarine xhalative rigin.
No geochronologicata are available or the Pre-cordilleranSbdeposits, ut a K-Ar dateof 15.4 _4- .4Ma (Table 1, f) wasobtained or biotite from a stockof flow-banded,vesicular,quartz and sanidinepor-
phyritic rhyolite which forms a prominent topo-graphic eatureat Pucar•t Figs.2 and 3). This ntru-sion s cut by swarms f phreaticbrecciadikes.Nomining ctivity sevident, ut floatof quartz einstonebearingminorbarite,galena, ndstibnite s scatteredaround the foot of the hill. Ten kilometers to the
north, the Liliana-Maurillia 3 mine worked Sb(-Pb,Ag, Sn)veinscuttinga brecciated hyolitestock erysimilar in lithology to that at Pucar•t (Robertson,1978). On this basis,we tentatively nfer a middleMioceneage or at leastsomeof the antimonian einsof this district. It should, however, be noted thatKlincket al. (1986) record he occurrence fstibnite
in a quartz-cementedreccia t Ccera,50 m from hecontactof the Huisaroqueonalitestock,situated 0km eastof PucarS., nd for which a TriassicK-Ar biotite
age of 236 _4- Ma wasobtained. t is possiblehatmore than one episodeof Sb mineralizations rep-resented in this wide area.
Summary
Geochronologicoverage f the polymetallicmin-eralization of the continent-ward half of the Main Arc
FIG. 11. Mineral depositmap of the Cordilleraand Precordillera e Carabaya.Major intrusivecenters f Devonianor Carboniferous?),Triassico EarlyJurassic,ndmid-Jurassicgeare outlined(modifiedafter Laubacher,1978a, b).
The depositsre numbered s ollows those or whichdirectgeochronologicataare presentedherein are italicized,and significant astor presentproducers re asterisked): = Huscocachi;-- Ucuntaya; = PioX; 4 = SantoDomingo; = TresMadas no.2); 6 = SantaMarta;7 -- unnamed;8 = Rescate;9 = Martha; 10 = San Rafael*; 11 = Quenamari*; 12 = Minastira; 13 = Mormoroni; 14= Cantuta; 5 = Volcdn; 6 = Levans; 7 = Padua1 and2); 18 = unnamed;9 = Aurora; 0 = Calv6rio;21 = Olga;22 = Rosario;3 -- unnamed;4 -- unnamed;5 = Cunchulli;6 = SanPablo-Antonia;27 -- SanFrancisco; 8 = LilianaMaurillia*;29 = San sidro*;30 -- unnamed; 1 = Cecilia*;32 -- SanAntonio*; 3 = Jaime; 4 = Nazareth; 5 = Princesa; 6 = Nicaragua; 7 = Altura;38 = SantaAnaDos*;39 = SantaAna Uno*;40 -- Casade Plata*;41 = Cerrodel ncaAzul*; 42 -- Condoriquifia*;3-- Sol de Cobriza;44 = Coetapalo; 5 = Dominga;46 -- SanAntoniode Padua;47 -- Esquifia; 8= Sarita; 9 = unnamed;0 = San os•;51 -- Ocuara; 2 = SantaAna;53 -- SantaRosa e Patambuco*;54 = CuyoCuyo; 5 = Condoriqui6a;6 = Gavildn eOro*;57 -- AnaMaria*; 8 -- Jdsica;9 = Palca11'; 60 -- LosEspafioles;1 = Collpa*; 2 = Revancha;nd63 = Corani*.The areaoccupied y theuranium rospectsf the Quenamari esetas outlined y a vertical-lineattern;he ocation f thePicotani ranium rospect y U(P) and hat of the Coasaadiometric nomaliesy (U).
Cacachara,SantaLucia, Mafiazo and Pucarft -Putina)districtsdemonstrate hat hydrothermalactivity oc-curredepisodicallyveran ntervalof at least20 m.y.,extending rom the late Oligocene o the late Mio-cene. The substantialSantaBftrbaraand BerenguelaAg-Cu centers,aswell as he Tacazaand other smaller
Cu-rich deposits f the SantaLucia district,are con-sidered o have been emplaced n the late Oligocene(ca. 23.5-29 Ma); the Lulita Au(-Cu, Pb, Ag) stock-work is of early Mioceneage (19 Ma); the Sb-bearingveins of the Pucar•t-Putinaegion may be of middleMiocene age (ca. 15 Ma); and the Ag-Pb-Zn-Cuveinsin the Compuertaand Cacachara ampsare, respec-tively, probablyand clearly of late Miocene age (6-7 Ma). The more mportanthydrothermalsystems reage-equivalento the volcanism f the Tacaza, lower)Sillapaca or Palca), and (lower) BarrosoGroups.Theessentially onophase etaIlogenicmodelof Fletcheret al. (1989) is not supported; ndeed, the daciticSil-
lapacaGroup asdelimited by Klinck et al. (1986) andEllisonet al. (1989) wasapparently he only stageofsubaerial olcanism ot directly responsibleor me-tallic mineralization. Further, at least the Santa Bftr-
bara, Lulita, Compuerta,and Cacachara eposits reclosely associatedwith felsic (dacitic to rhyolitic)hypabyssalntrusions.Finally, hydrothermalbrecciaswith phreatic, or even phreatomagmatic, haracter-•stics see Sillitoe, 1985) occur n the immediatevi-cinitiesof the Lim6n Verde (-CerriIlos),Berenguela,Cayachira,and Tacaza depositsand containclastsoffine-grained ioriteor daciteporphyry uggestingheoccurrenceof epizonal ntrusionsat depth. We ad-
vocate a correlation between the epithermal miner-alizationof the Cordillera Occidentaland Altiplanowith Oligocene and Miocene subvolcanicstocks.However, the regional ectonicmodel of Fletcher etal. (1989) remainsplausible,with the rider that bothhydrothermal irculation nd epizonal ntrusionwerecontrolled by the major northwest-trendingstrike-slip fault zones.
Mesozoic Mineralization of the Inner Arc Domain
Introduction
The Cordillera Oriental separates he Altiplanofrom the sub-Andean owlands (Fig. 1). The 5,000-to 6,000-m-highglaciatedpeaksof thiscordilleraaretraditionallyassignedo the Cordillerade Carabaya,and n the vicinity of the Bolivianborder, o the Cor-dillera, or Nudo, de Apolobamba. hismountain hainis in part bounded o the southwestby the Crucerodepression, Tertiary intermontane asin Laubacheret al., 1988), andby the extensive plands f the Pre-cordillera de Carabaya (Figs. 11, 12, and 13). Thegeology of this abundantlymineralized region hasbeen documentedby Newell (1949), Newell et al.(19,53), and Laubacher 1978a and b), who provides
a 1:500,000 geologicmap.Francis 1956) andCarlieret al. (1982) describedaspects f the magmatism fthe Cordillerade Carabaya, orminga foundation orthe more detailed petrologicwork of Noble et al.(1984a), Kontak et al. (1984, 1985, 1986), and Pi-chavantet al. (1987, 1988a and b). Geochronologic
data for the igneous ocksare recordedby Lancelotet al. (1978), Carlier et al. (1982), Clark et al. (1983b),Bonhomme t al. (1985, 1988), Kontaket al. (1987),Laubacher t al. (1988), andPichavant t al. (1988a).Kontaket al. (1990c and d) synthesizehe availablepetrogeneticand geochronologic ata for, respec-tively, the late Paleozoic o early Mesozoicand Ter-tiary ntervalsn the region.Geochronologicndpet-rogenetic research s underway on Oligocene toMiocene volcanic-subvolcanic ocks in the region(Cheilletz et al., 1990, and n press;Sandeman t al.,1990; Yamamura,1990; Clark et al., in prep.).
The area s dominatedby a thick successionf Or-
dovician o Lower Permian,dominantlymarine, sed-imentary strata, unconformably verlain by LowerPermian molassicclastics Mitu Group) and by theCretaceous continental clastics of the Putina basin,
or synclinorium Laubacher,1978a). Ordovician oDevonian units of the San Jos•, Sandia,and AnaneaFormationsdisplay he effectsof strongcompressivetectonism,ascribed o a Late Devonian to early Car-boniferous early Hercynian)orogenyby M•gard etal. (1971), but they are widely preserved in asubgreenschistaciesmetamorphic tate. Areas ofhigh-grade,ow-pressuremetamorphism,xposednthe SanGabfro nd nambari Sandia) alleys, urround
intrusive omplexesocallyexhibiting trong oliation;they are regardedby Laubacher 1978a) as repre-sentingmetamorphic ulminations nd synkinematicintrusionsof Devonian to early Carboniferousage.The late Hercynianorogeny Laubacher,1978a), ofEarlyPermian ge Clarket al., 1990a), affected oththe lower Paleozoicstrata and units of the Mississip-pian Ambo Group and the Pennsylvanian arma andCopacabana roups Newell et al., 1953). It involvedgenerallyweak compressionnd probablyno signif-icant metamorphism, nd was immediately ollowedby continentalifting, orming he northwest-trendingMitu trough and associated lkali basalts Kontaket
al., 1985, 1990c). Renewed ectonismduring he lateEocene ncaic orogeny (Laubacher,1978a and b;Laubacheret al., 1988) generateda southwest-verg-ing foldand hrustbelt acrosshe Putinasynclinorium.Immediately to the northeast,along he presentaxisof the cordillera, coeval (ca. 38 Ma) thermal and tec-tonic activitygaverise o the Zongo-SanGabfm one(Fig. 13) within whichK-Ar dateswere radically eset(Farrar et al., 1988; Kontak et al., 1990d). The in-tensity of the thermal disturbance ncreases ystem-atically rom southwest o northeastacrosshis zone.Further compression ccurred n the latestOligocene
FIG.12. Geologicketch apof hepre-Cretaceousnits f heCordillerandPrecordilleraeCarabaya,implifiedndmodifiedfter aubacher1978a nd ),and mphasizinghemajor lutoniccenters.heboundaryetweenheMituandAllinccftpacroupssgeneralizedafterKontak t al.,1990c).
(ca. 24 Ma: Clark et al., in prep.) during he initialstagesof the protractedQuechuaorogeniccycle(Laubacheret at., 1988).
The lowerandupperPateozoic trataare ntruded(Fig. 12) by severalargeplutonsof weaklyperalu-minous monzograniteassigned o the Carabayabathotithby Kontaket at. (1990c), and for whichPermian Lancelot t al., 1978) andTriassicKontaket al., 1990c)ages reproposed. catteredeldspath-oid-bearing yeniteplutonsandperalkaline olcanicunits regrouped s heprobably urassicllincc/tpacPeralkalineComplex,or Group, by Kontak et at.(1990c).With the exception f the local ntrusion fsmallgranodiorite tocksn the mid- and Late Cre-taceous, he Inner Arc domain was thereafter mag-maticallyquiescent ntil the late Oligocene ca. 28.5Ma), whenperatuminous onzogranitelutons nd
rhyodacitic sh-flowuffswereemplacedn close s-sociation with mafic-intermediate shoshonitic volca-
nism Clark et al., 1983b; Bonhomme t at., 1985;Kontak et at., 1986, 1987; Laubacheret at., 1988)along west-northwest-trendingelt surroundingheCrucerodepressionndextendingo the west-north-
west. n the Miocene,a resumption f peratuminousvolcanism, ut with a significantly ifferentcompo-sition, eneratedherhyolitic sh lows f thePicotani(Kontak, 985;Laubacher t at., 1988;Sandemantal., 1990)andQuenamariorMacusani)Nobleet at.,1984a;Pichavant t al., 1988a;Cheilletzet al., 1990)fields (Fig. 13). The area has been magmaticaltyquiescentince a.3 Ma (Bonhommet al., 1988).
The location numbers, distribution, and great va-
riety of the ore deposits f this area are shown nFigure11. Thisregionhas ongbeena significant
FIG. 13. Sketchmapshowinghe Tertiaryunitsof the Cordillera ndPrecorditlerae Carabaya,the CrucerodepressionndAnanea-Ancocataasin, nd he approximate oundaries f the Zongo-SanGabSnectono-thermatone ZSGZ: fterFarraret at., 1988, andKontak t at., 1990d).Agesof ntrusiveandvolcanic ocksare mainly rom Clark et at. (1983b), Kontaket at. (1986, 1987), and Bonhommeet at. (1988). AR -- Aricoma luton;CO = Coasa luton;LI -- Limbanipluton;LM = Limacpampapluton;MS = MacusaniSyenite;SG -- SanGabancomplex--all Jurassic r older.
source f gold(Fornariet al., 1988) frombothbed-rock ndplacer perations,utbasemetal roductionfrom he Cecilia loc31), SanRafael loc10), andCarabaya"Quenamari"r "Nazareth":oc11)mineshasbeenmore mportantn recent ears.Moreover,sincehe 1970s, he region asemerged sa majorlithophilemetalprovince; t the present ime, the
SanRafaelandPalca11 (loc 59) minesare the largestsources f, respectively,in and ungstenn the Andesand he mostproductivebedrockoperationsor thesemetals n the WesternHemisphere. he rhyolitic uffsof the Macusani ield hostseveralpotentially mpor-tant concentrationsf high-grade raniumstockworks(Flores et al., 1983).
The metallogenic istoryof the region s summa-rized by Clark et al. (1984) and Kontak (1985), andgeologicguidelines or tin and tungstenexplorationare proposed y Kontakand Clark (1988). The con-clusions f thosepapers equire modificationn thelight of recently acquiredage data. The mineral de-
positsof the region are herein subdivided nto Me-sozoicand Cenozoicgroups.Discussion f the oldermineralization includes an evaluation of a series of
Au-, Sn-,andW-bearingquartzveinswhichhave ra-ditionallybeen regardedas of Paleozoicage, a con-clusionwhichwe question.
Cerro Condoriquiria-Limacpampaistrict
The Condoriquifia "Condoriquefia")deposit loc55), the first significant in-dominantbedrock min-eralization o be recognizedn Peru (Petersen,1960),comprises seriesof cassiterite-rich onesof massivegreisen nda groupof narrow,but laterallyextensive,
cassiterite-bearing, uartz-chloriteveins,containingabundantwolframite, sphalerite,and arsenopyrite swell as erraticallyhigh Au grades Petersen,1960).The deposit, nCerroCondoriqui•a,shosted y two-mica monzogranites nd muscovite eucogranites fthe smallLimacpampa luton Figs.12 and 14), whichintrudes tourmaline-rich andalusite-biotite hornfelses
derived from Siluro-Devonian clastics of the Ananea
Formation Laubacher,1978a and b). Both the veinsand the granitesare affectedby variably ntense o-liation, locally approaching neissic. he tectonizednature of the granites, and the wide extent of themetamorphic ureole, ed Laubacher 1978a and b)
to assignhe center a possibleCarboniferous ge.The peraluminous imacpampa ranite ies within
the ca. 38-Ma Zongo-SanGabSnzone (Farrar et al.,1988; Kontak et al., in pressb) and is therefore dif-ficult to date in the absence of U-Pb zircon data.
However, our Rb-Sr studies Kontak et al., 1990c)show hat a negative nitial Sr isotope atio would bedefined f the granitic rockswere as old as Carbon-iferous. Muscovite rom the granite yields an Rb-Srage of 199 Ma at a reasonable ssumednitial ratio of0.710. ConventionalK-Ar data are given in Table 3for a muscoviteLMP-2A) anda muscovite-biotiteair(LMP-1) from the vicinity of the Condoriqui•apros-
pect. The dates range from 112.4 to 37.1 Ma, andthere is extremediscordance etween he coexistingmicas n sampleLMP-1.
The conclusion hat these sampleshave sufferedintense hermaldisturbances stronglysupported ythe4øAr/a9ArgespectrumorLMP-1muscoviteFig.14, b; Kontak et al., 1990d), which yields an inte-gratedageof 81.04 _ 1.48 Ma. This spectrums typ-ical of thermally overprintedmicas e.g., York andLopez Martinez, 1986), andwith the exception f thesaddle,crudely approximates profile that would beexpected f extensive olume diffusionof argonhad
occurred Turner, 1968). If a crystallization ge of200 Ma is assumedor the muscovite, 70 to 75 per-cent Ar loss is indicated. The considerable local vari-
ation n muscovite pparent gesuggestedy the datamay be a functionof grain size and/or the extent ofinteraction of the micaswith the 300 ø to 400øC H20-
CO2-CH4-NaC1 luids mplicated n the evolutionofthe Zongo-S•tnGab/•nzone (Kontaket al., 1990d).
The available -Ar and4øAr/39Arata or thisdis-trict demonstratehat mineralizationookplacepriorto 112.4 _ 2.4 Ma, whereas he Rb-Sr isotope ela-tionsstronglysuggest post-Carboniferousge.Themostconservativenterpretationwould be to assignthe Condoriqui•a Sn(-W, Zn, Au) veins to the LateTriassic-EarlyJurassicmetallogenicepisode ecog-nized elsewhere n the Cordillerade Carabaya. f so,the foliation of the Limacpampa ocks could resultfrom their locationclose o the northeasternmarginof the Zongo-San Gab/•n zone (Figs. 13 and 14).
However, similar fabrics n the Triassic Heinrich etal., 1988) two-mica eucogranitesf the Zongoplutonof the Cordillera Real, northwest Bolivia, are inter-preted (Heinrich, 1988; Clark et al., in prep.) asre-cording ntrusionat depths of ca. 10 to 15 km, i.e.,in the upper mesozone.Exhumationof the deeperpartsof the CordilleraRealbatholithduring he ncaicorogeny s considered o have occurred owing to aca. 90 ø rotation (up to the northeast)during devel-opment of a crustal-scale duplex" (Farrar et al.,1990). A similarmodelmaybe suggestedor the An-anea-Limacpamparansectof the Zongo-SanGab•tnzone (Kontak et al., 1990d).
Ananea district
Alsosituatedwithin the Zongo-SanGab/•n one sthe Ananea,or La Rinconada, istrict Figs.11-14),which hasbeen a gold camp sinceat least he 17thcentury when placer mining flourished n the Cha-quiminasarea. Production rom the fiuvio-glacialgravels of the Ananea-Ancocala asin at the south-western oot of the Cordillera de Apolobamba aspersisted pisodicallyo the presentday (Fornarietal., 1982, 1988). The source f the placergold,andof the intimately associated etrital cassiteriteandwolframite,wasundoubtedlyn bedrockdeposits x-
posed at elevationsof ca. 5,000 to 5,250 m on theslopes f the NevadoAnanea-NevadoNacariamassif.The geology f the miningdistricthasbeendescribedby Fornariet al. (1988). Of the two mainestablishedunderground operations, he Ana Maria mine hasprobablyyielded no more than 1 metric ton of goldi• recent years,but the extent of the workingsandthe high gradesof the ores to 25 g/metric on Au)suggest hat long-term productionhas been signifi-cantlyhigher. The nearbyGavil/•nde Oro workingshave supported populationof up to 2,500 garim-peiros and dependentsduring the past decade.No
F•G.14. Sketchmapof southeasternegmentf theCarabayaatholith, howingocationsf minesandprospectsiscussedn the text,andof samplesatedby the K-Ar and øAr/a9Artep-heatingtechniques spectra -c). The Zongo-SanGabhn one s outlined.
goldproductionigures re availableor this mine,but a singlemeter-wide einyielded metric onsofwolframitend1 metric onof cassiterite,onthly,in the early1960s Robertson,978).Old workingsshowingvidence f considerableroductionxtendfor several kilometers to the east of the Ana Maria
mine J.C. Kovaf•ik, ers.commun., 990).The age of the Au-lithophilemetal-basemetal
mineralizationemains roblematic,ut geologic
considerationslacesome onstraintsn the environ-mentand imingof hydrothermal ctivity.Fornarietal. (1988) recorded hat the Ana Maria mine has ex-ploited up to eight separatemantoorebodies--lat-erally extensive, ut thin (max.20 cm), systems fgray quartzveinsbroadlyconformablewith the bed-ding of the east-northeast-striking,emi-isoclinallyfolded, Lower Devonian turbidites of the Ananea
Granodiorite Whole rock 2.811 9.37 8.5 83.8 _+ 3.1
Granodiorite Whole rock 2.426 7.31 10.3 74.4 _+ 1.6
Diabase Whole rock 0.665 3.25 22.9 121.5 _+ 2.6
of white quartzveinscuttingbedding s also ecorded.Native gold is associated ith arsenopyrite,pyrite,pyrrhotite, and particularly,galena.The folded andboudinaged atureof the mantoss ascribed y Soleret al. (1986) and Fornariet al. (1988) to deformationduring he early Hercynianorogeny, .e., in the LateDevonianor early Carboniferous.n addition o thequartzveins,a broadlyconcordant,aminated,weaklyauriferous ca. 2 g/metric ton) body of arsenopyrite,
pyrrhotite,andpyrite,with ca. 15 percent detrital"quartz, s nterpretedasa sedimentary xhalative o-rizon (Fornari and Bonnemaison, 984). The quartzveins are considered o represent suboceanicluidconduits.
Preliminary ield and petrographic tudies nder-takenduring he present esearch efine he followingstages n the developmentof the San Jorge manto(level 2, 5,200 m) of the Ana Maria mine:
1. Emplacementf the mantoof grayquartz.Thisdipsca.20ø SSE,subparallelo thebedding ndweak
axial-planar leavage f the turbidites.The vein cutsboth of those abricsand alsoa north-northwest-dip-ping spacedcleavage the S1 oliationof Fornari etal., 1988); somevein segments re controlled y theintersectionof the bedding and the spacedcleav-age. The host sedimentary rocks, which exhibitsubgreenschist,nchimetamorphicaciesconditions,displayno widespreadhydrothermalalteration,butwithin ca. 5 to 10 mm of the vein, the rocks are con-
verted to extremely ine grained,melanocratic el-vagescomprisingwhite mica,quartz, andTi(-Fe) ox-ides leucoxene),which surviveaswispyseptawithinthe vein quartz. The irregular contactsand anasto-mosing atureof the mantos re thusascribedn partto their emplacementhrough eplacement f the hostrocksby hydrothermal luids; he Ti oxidesare re-gardedas refractoryphases.Although, n the seniorauthor'sopinion,neither native gold nor sulfidemin-erals can be demonstratedo be directly associatedwith this stageof quartz ntroduction, . C. Kova•ik(pers. commun.,1990) records hat ore-grademin-
possibly, ativegold where they transect he manto.Brecciascomprisingangular ragmentsof metasedi-mentaryhost ock are ocallydeveloped.Sulfidemin-erals,andapparently,goldwere introduced nto con-tiguous areas of the manto. Fluid inclusions n themilky quartz displayhighlyvariable iquid/vapor a-tios andvariableamounts f CO2 (or CH4 .9).
5. Extensivedissolution f the milky quartz.Thedissolutioneneratedmegascopicavities hichwerepartially illed in by the millimeter-scale latesandeven euhedra of gold which characterize he ores.Inclusionsof sperrylite and micheneritehave beenobservedn one coarsegold grain (J. Kova•ik, pers.
commun., 1990, has confirmed the occurrence of Ptalloys n the nearbyAu placers).Vug developmentwasassociated ith pseudomorphousrowthof pyriteafter pyrrhotiteand he deposition f minorankerite.
Similar elationsare evident n the larger Gavil•nde Oro depositwhere early, sinuous ut extensive,mantos f grayquartzare cut by severalmilky quartzveins rich in muscovite, cassiterite, and wolframite,
striking ca. 60 ø and dipping 20 ø SE (Robertson,1978). Handspecimensrom he dumps isplay ein-lets of white vuggy quartz, rich in sulfidesand withtraces of gold, cutting wolframite- and cassiterite-bearingquartz veinstone.As at Ana Maria, the bulkof the goldat Gavilftn e Orowas herefore pparentlyintroduced ate in the history of the veins and wasassociated ith extensive issolution f quartzwherebrittle fractures intersected the mantos.
From the above data, it is concluded that the em-
placement f at least he high-grade oldmineraliza-tion was separated rom turbidite sedimentation nthe Early Devonianby a complexseriesof tectonicand hydrothermal vents.Like manyother gold de-posits e.g., Tourigny et al., 1989), the vein systemsof the Ananeadistrictare multiphase, omprising
varietyof formsandattitudeswith respect o regionalstructures.The exhalativemodel advocatedby For-nari et al. (1988) thereforecannot atisfy ll observedfeatures f the deposits. he anchimetamorphicradeof the hostrocksand the occurrenceof muchgold ncavities ndicate that all mineralization ook place at
relatively shallowdepths.Whereaswe are not con-vincedby the evidence or truly exhalativeprocesses,we accept hat the mantosdeveloped n a late kine-matic, and possibly, ate metamorphic nvironment.In contrast, he crosscutting eins were emplacedduringan episodeof brittle fracturing n a very shal-low environment. t is implicit that hydrothermalac-tivity overlappedwith a transitionrom compressionalto extensional ectonics and with probably abruptuplift and erosional xhumation f the area.The An-anea veins displayclosesimilarities o the bedding-parallelauriferous uartzveinswarms f the PaleozoicMeguma terrane, Nova Scotia. These controversial
depositsKeppieet al., 1986) are considered y Kon-tak et al. (1990b) to have formed n association ithlate kinematic plutonismduring the rise of deep,metamorphically erived luids.The only exposedn-trusive body in the immediateAnanea district is asmall lens of strongly deformed and chloritizedgranodiorite,but a similarmodel may be applicable.
The age of the gold-bearingveins emains ncom-pletely defined. n Table 3, a, we record a conven-tional K-Ar date of 143 _ 10 Ma for hydrothermalmuscovite irectlyassociated ith cassiteriterom heGavilfm de Oro workings.This earliest Cretaceousdatum s tentatively interpreted as ndicatinga min-
imum age for the veins.Thus, it is clear that at leastthe Sn mineralizationwas not generatedduring theEocenedevelopment f the Zongo-SanGab•n zone.The compressionalectonicenvironmentof the earliermineralization tagesmayhavebeen hat of the earlyHercynian orogeny, as proposedby Fornari et al.(1988), but it could alsohave developedduring thelate Hercynian EarlyPermian) ectono-thermalvent(Laubacher,1978a and b). The superimposed pi-zonaleventwhich,we infer, was esponsibleor muchof the ore grade Au, may have occurredduring theuplift and rifting which generated he Mitu trough,also n the Early Permian. However, the closeasso-ciation of lithophile metal (Sn,W) associations ithgold n the Ananeacamppromptsanalogieswith thenearbyCerro Condoriquifia istrict Fig. 14). In par-ticular, the markedly changing ectonic conditionsimplied by the earlier and later veins at Ana Mariamay directly reflect the transition from initial em-placementof the Carabayabatholithat ca. 225 Ma,throughuplift, to the intrusionof the younger,moreintensely mineralized stocksat ca. 190 to 200 Ma.Petersen 1960) indeedproposed genetic elationbetween he two centers,suggestinghat the Au-richveins n the vicinity of Ananeaand the Condoriquifia
Sn(-W, Au) veins constitute, espectively,distal andproximal aciesof a large-scale ydrothermal ystemrelated directly to emplacementof the Carabayabatholith; in contrast,Fornari et al. (1982, 1988) donot consider the occurrence of cassiterite and wolf-
ramite in the Ananea bedrock mineralization, and
therefore, do not address hese relations. We concurwith Petersenand cite analogieswith the PermianSanJudasTadeo district (seeabove),where Au-richveins similarly appear to represent (Clark et al.,1990a) a peripheral zone arounda W(-Mo) core, andthe lateral zonation from wolframite- to gold-richveins in the Pacollo district of the Cordillera Real,Bolivia AhlfeldandSchneider-Scherbina,964). Thegold-bearing luids may have been derived from thegranitoidmagmas r from the extensivemetamorphicaureoles hichare nferred o surroundhe Carabayabatholith at mesozonal epths.On this basis,we ten-tatively avor a Jurassic ge for the golddeposits.
Ollachea district
Despite the groundwork aid by Douglas (1920)and Francis (1956), the geologyof the precipitousvalley of the Rio SanGab in,which ransectshe axialCordillera Oriental north of Macusani Figs. 11 and12), remains ll-defined. Laubacher (1978a and b)providesa sketchmap approximately elimiting hetwo major igneoussuiteswhich are incisedby theriver: the San Gab in Complex, north of Ollachea(Kontak t al., 1990c), and he Allinccfipac eralkalineComplex to the south (Francis, 1956; Laubacher,1978a; Kontaket al., 1990c). Clarificationof the age
relations n this area s hinderedby its ocationwithinthe Zongo-SanGab inzone,preventing recisedatingof the numerous,once productive, metallic mineraldeposits ssociated ith the two complexes.
The scatteredplutonsof the SanGab in Complex(the Corani batholith) ntrude clasticstrataof the Or-dovicianSan Jos• and SandiaFormationsand are inpart surrounded y an extensive ureoleof low-pres-sure metamorphism Kontak, 1985) culminating nsillimanite-bearing ssemblagesefiningconditionscorrespondingo the bathozone1-2 transitionof Car-michael 1978), i.e., P = ca. 2.2 kbars.The intrusiverocks, anging n compositionrom olivine-pyroxene
gabbro o two-mica eucogranite, re variably, andlocallystrongly, oliated.Compositionalrendssug-gesta comagmatic rigin through ractionalcrystal-lization of a maficparent but with extensivecontam-ination by aluminoussedimentary ocks. These fea-tures are not sharedby other granitoid suites n theCordillerade Carabaya.Only K-Ar dates or biotitesare available or the SanGab inComplex: hese angefrom 123 to 38 Ma (n = 5) and, ogetherwith biotitedates rom the enclosingmetapelites, ecrease ys-tematically rom south o north acrosshe Zongo-San
Gabfinzone (Kontak et al., 1990d). On this basis,wecan only infer that the plutonsare Early Cretaceousor older.
Bedrockquartzveins asat Huscocachi;oc 1) havebeen significant ources f gold (Soler et al., 1986)but have apparently not been geologicallydocu-
mented; hese and other deposits n the San Gab inintrusions re tentatively nterpretedas he sourceofthe placer gold which is still being recovered romseveralsitesbelow Ollachea.As in the broadlycom-parablesettingsn the Cerro Condoriquifia rea (seeabove)and n the Zongodistrictof Bolivia Farraretal., 1990a; Clark et al., in prep.), we envisage hatthe foliated granitoid rocks of the complexrecordbatholithemplacement onditions t depth; he sparsenatureof the primarymineralizationmayreflect hehigh pressures nder which the hydrothermal luidsevolved.
An extensive area south of Ollachea is underlain
by alkaline ndperalkaline yenitic ocks, onstitutingthe Macusani yeniteof Francis 1956), oneof severalcenters of silica-undersaturated agmatism n thewestern Cordillera de Carabaya (Kontak, 1985).These phaneritic intrusive rocks grade upward intocompositionallyquivalentvolcanics, hichunderlieNevadosAllinccfipac nd Japuma o the east of theupper Rio San Gab in. The extrusiveunits were as-signed o the Lower Permian Mitu Group by Lau-bacher (1978a and b), but we elsewhereargue forthe existenceof a distinct AllinccfipacPeralkalineComplex n this area (Kontak et al., 1990c). The al-kaline rocks range in composition rom gabbro,
through diorite to nepheline- and amphibole bar-kevikite and hornblende)-pyroxeneaegirine-augite)syenites,and have compositionsargely in the plu-masiticand miaskitic ieldsof Sorensen 1974).
Mining activity within the AllinccfipacGroup hasbeen restricted to scattered silver-rich veins: the
largestmine, at Ucuntaya loc 2), worked Cu-Ag ores(Zambranoet al., 1965). Francis (1956) documentsnumerousColonialor olderbedrockworkings or sil-ver along the Rio San Gab in and records high Augrades rom one ocality.The smallPio X Pb-Ba(-Mn)veinsystemloc3), southof the mainsyenite lutons,may also epresenthydrothermalactivity associated
with the alkaline magmatism.Ore samples rom aprospect n the vicinity of JuroJuro, ca. 9 km south-southwest f Ollachea,comprise einletsof analcime,1 to 2 cmwide andcontaining isseminationsf nativesilver, acanthite,and cuprostibite Cu2Sb),a sulfur-poor assemblageimilar n some espectso thosede-scribed rom the Ilimaussaqperalkaline syenitebyKarup-Moller (1974). However, other Ag mineral-ization n the syenitic ocksappears o havebeen richin pyrite, galena,and argentian etrahedrite.
intrusions lsooccur n the mainbodyof the MacusaniSyenite.Robertson 1978) tentatively dentifiedeu-dialyte as a constituentof veinlets n at leastone lo-cation.This hasbeen confirmed n the presentwork;alluvial cobblesof pyroxene-rich yenite n the JuroJuroareahaveat least wo stages f irregular ractures
in which he mainminerals re apatite,eudialyte C1rich), and steenstrupine.Semiquantitativeelectronmicroprobe ndproton-induced -ray analysis f theeudialyte shows t to containca. 4 to 5 wt percentBE•O3 (Y > Ce > La > Nd). This steenstrupine on-tainsonly racesof uranium.Noneof theseapparentlyhydrothermalmineralshasbeen observedn the hostsyenite (cf. Bailey et al., 1981). Kontak (1985) hasreported veinlets of tugtupite from the nephelinesyenitenear the baseof the intrusivecomplex.Ourmore recent work has shown that sodalite occurs
widelyasveins, ocally5 to 6 cm n width,but proton-induced gamma-rayanalysis detection imit ca. 10
ppm) reveals no significantBe in the feldspathoid(J.D. MacArthur,pers.commun., 990). The sodalitealso acks he intenseblue color of the long-minedandprobablycoevalCerro Sapooccurrencen Bolivia(Brendler, 1934; Ahlfeld and Schneider-Scherbina,1964), but similarly forms veins cutting nephelinesyenite. Stronglysaline,weakly saline,and gaseousaqueousluid nclusions re abundantn the Ollacheasodalitevein material. The veinlets are bordered byzones of intense microbrecciation and sodalite re-
placement f feldspar ndnepheline.A hydrothermal,possiblyexplosive,origin is favored, as in the com-parableDitro Complex,Romania Streckeisen, 960).No metallic minerals have been observed in the so-
dalite veins.The extent of the eudialytevein system,andhence, he potential or economic r or REE min-eralization, is unknown.
Much of the main syenitic ntrusivecenter appar-ently iessouthof the Zongo-SanGab•tn ectonother-malzone,but foliation s ocallydeveloped ndbiotitefrom these ocksyieldsvariableK-Ar dates, angingfrom 184 (Stewartet al., 1974) to 156 Ma (Kontaketal., 1990c). The mica datesshowa broad nversecor-relation with the intensityof foliation.Exposures fquartz-free yenite outhof Ayapata xhibitapparentgradational elationswith the monzograniteof the
western obe of the Coasapluton (Robertson, 978;Kontak, 1985), for which a Late Triassicage is in-ferred Kontak t al., 1990c). t is, herefore, ossiblethat the syenites,and the Allincc•tpac eralkalineComplexas a whole, may be essentially oevalwiththe granitoid plutons of the Carabaya batholith.However, in the absenceof other geochronologicdata, we accepta Middle Jurassic ge (ca. 170-180Ma) for the alkaline ocksand or their associated g-rich and Zr-REE mineralization.
Coasa district
Hydrothermalmineralization emonstrablyelatedto the granitoid rocks of the extensive Carabayabatholith s widely dispersed Figs. 11, 12, and 14)but rarely of significant xtent or grade. The large
(ca. 1,300 km2) Coasamonzogranitic-granodioriticpluton (Laubacher, 978a andb; Kontaket al., 1984,1985, 1990c) is host to severalsmall ithophile andbasemetal deposits, oneof whichhassustainedma-jor production.Contactmetamorphicmineralassem-blagesn the aureole ndicate mplacementt a depthof ca. 6 to 8 km (Kontak, 1985), possibly oo greatfor the development f extensive rittle fracturing nthe immediatepostmagmatic eriod. Our K-Ar andRb-Sr data for the intrusive rocks and the U-Pb zircon
date (238 _+11 Ma) of Lancelot et al. (1978) are in-terpreted asrecording nitial batholithemplacementin the Late Triassic,at ca. 220 to 230 Ma (Kontak et
al., 1990c). The Triassicgranitoids,althoughpre-dominantlyperaluminous nd with initial Sr isotoperatios of >0.7082 (Kontak et al., in pressa), arebroadly comparable n chemistryand mineralogy othe I-Caledonianclan of Pitcher (1983).
Skarn mineralization occurs at several locations
along he southand west marginsof the pluton. Asmalldeposit,comprising yroxene-rich ndoskarn,greisen-bordereduartzveinlets, ndamphibole-ep-idote-rich exoskarn n adjacentTarma Group lime-stone, s exposed t the southern ontactnearQueafi-ani (loc 18). The intrusionshows n abrupt outwardtransition from coarse-grained, apakivi-textured
monzograniteo tourmaline-richeucograniten thevicinity of the skarns.The mineralizationcompriseschalcopyrite, alena,acanthite, nd pyrrhotite.Hy-drothermal muscovite BAR-16) from this prospectyielded a Late TriassicK-Ar age of 212.7 _+4.3 Ma(Table 3, b).
The more extensive Cu skarns and veins of the Vol-
c•mprospectloc 15; Robertson, 978; Kontak,1985)occurat the contactof the western obe of the pluton,in an area where the granitoid rocks show abrupttransitionsrom hornblende-biotitemonzogranite ndsyenogranite locally tourmalinized) o quartz-poordiorite, monzonite,and syenite Kontaket al., 1984,1985). The deposithasnot been directly dated,butthe presence of endoskarnmineralization suggeststhat hydrothermalactivity occurredcontemporane-ouslywith intrusion, or which Late Triassic o EarlyJurassic -Ar biotite agesof 198 to 210 Ma havebeendetermined (Kontak et al., 1990c). Minor scheeliteoccurs in the Volcftn ores.
Severalmineraldeposits avebeenexploredwithinthe Coasapluton, mainly for tungsten.The Levans,or Huarachani, wolframite-(molybdenite)-quartzveins (loc 16) are rich in specularite nd pyrite, av-
erage50 to 60 cm wide, and trend at 158ø to 162ø,parallel to a regionallydeveloped,steeply nclinedjoint system.The country rocks comprisecoarse-grained monzogranite ut by swarmsof aplitic andquartz porphyriticrhyolite dikes; ocal float displayslaminated pegmatitic-apliticcomplexeswith unidi-
rectional growth textures. These features stronglyimply that the Levansveins ormedclose o the apexof a stock nternal to the large monzogranitic luton;the laminated ocksare interpreted as representinga stockscheider.
Vein-selvage muscovite from the level 1 adityieldeda K-Ar ageof 186.7 ___.8 Ma, whereas iotitefrom unalteredmonzogranite 00 m southwest f theworkingsgavea significantly lder ageof 193.4 ___.9Ma (Table 3, b). This part of the intrusion i•es loseto the southwestern imit of the Zongo-San Gab•tntectono-thermal zone (Kontak, 1985; Farrar et al.,1988; Kontaket al., 1990d). Thermal overprinting s
recorded y a 4øAr/39Arge spectrumFig. 14, b)determined for biotite from COCA-268, a monzo-
granite collected 6.25 km east-northeast f Huaramchani Kontak,1985). The spectrum,which yieldsanintegratedage of 179.5 ___.7 Ma, displays saddlecharacteristic f disturbance. hermal modeling, ol-lowing Turner (1968) and Dodson 1973), suggeststhat the mica experienced relativelybrief (ca. 1-3m.y.) thermal pulseat a temperatureof ca. 160ø to175øC, in conformitywith microthermometric atafor fluid inclusions reserved n microfabrics evel-oped during he overprinting Kontak,1985; Kontaket al., 1990d). It is estimated hat the biotite lostonly
ca. 4 percent adiogenic rgon,and romthe apparentagesof the plateausegmentslanking he saddle, hatoriginal ntrusionoccurredat ca. 190 Ma (seeDall-meyer, 1975). The Levans deposit s located n anareaof the pluton essaffectedby the Zongo-SanGa-bftn event than the above sampleand we estimatethat only ca. 3 percent radiogenicargon loss ookplaceat this time in the mine area.We conclude hatthe Eoceneactivity hasnot significantly ffected hetwo K-Ar mica dates from the Huarachani area and
that their "reversediscordance" i.e., muscovite ateless hanbiotite date) s evidence hat the Levans einsformed at least 7 to 8 m.y. after the Coasamonzo-
granitehad cooledbelow ca. 250 ø to 300øC (the Ar-blocking emperatureof biotite). On this basiswe in-fer that lithophile metal mineralization n this areawas probably not directly associated ith the em-placement f the voluminousmonzogranitest ca.220to 230 Ma, but with younger ntrusionsof approxi-mately 190 to 195 Ma, i.e., of Early Jurassic ge.Southwestof Coasavillage, there is an extensivebutundelimited outcrop of cordierite-biotite granite,distinctlymore peraluminoushan the main monzo-granites ndwith a muchhigherS7Sr/S6Srnitial atio(0.7241 versus .7082-0.7087: Kontaket al., 1990c).
Such rocks may be parental to the W(-Mo) mineral-ization developed within, and perhapsadjacent to,the Coasapluton.
Aricoma district
The 150-km Aricoma luton s the hostof the Sa-
rita polymetallic rospectFigs.11, 12, and 14). Thebiotite monzogranitesnd granodiorites f this ntru-sionyield biotiteK-Ar agesof 211 to 217 Ma (Kontaket al., in pressa). Dalmayracet al. (1980) presentedin a preliminary orm a 234 ___-Ma U-Pb zircondatewhich we interpret to record a contribution rom aninherited Pb component,and we suggest hat, as inthe Coasaarea, initial intrusion took place at 220 to230 Ma rather than earlier. A muscovite geof 225.0___4.8 Ma (Table 3, c) was obtained or greisenas-sociatedwith a systemof quartz-tourmaline-pyriteveins exposeda short distancesouthof the south-easternmarginof the Aricoma ntrusion loc 49); the
economicpotential of this hydrothermalzone is un-known.
The Sarita, or Oscoroque,Cu-W-Mo(-Sn) depositin the northernsectorof the Aricomapluton (loc 48),by far the most mportantbaseand lithophile metalmineralization known to be associated with the Cara-
baya batholith,has been briefly describedby Rob-ertson 1978), Guerrero 1980), Candiottiand Guer-rero (1983), and Kontak 1985). Severaldistincthy-drothermal aciesare represented,ncludingswarmsof pipelike bodiesrich in W, Mo, and Sn and sur-roundedby zonesof potassic feldspar-rich lterationsuperimposed n an intenselyalbitizedgranite,and
at a lower altitude, chalcopyrite-richodeswith vari-ably epidotized, ericitized, lbitized,andchloritizedenvelopes. umerous pliticandbasaltic ikesoccurin the district.
A conventional -Ar age of 194.1 ___.9 Ma (Table3, c) was obtained or biotite (OSC-1) from monzo-granite n the lowerpart of the mineralized rea.Thesamplewas aken from an outcropadjacent o a Cu-rich vein and contains isseminatedhalcopyrite. hisage s distinctly ounger han othersdetermined orgranitoid ocksof the Aricoma istrict.A 4øAr/39Arstep-heatingun on this biotite yields a weakly dis-turbed age spectrum Fig. 14, c), with an integrated
age of 187.11 ___ .18 Ma. The Saritaprospect iesclose o the southwesternimit of the Zongo-SanGa-b•tnzone and the spectrum ecordsan Ar lossof nomore han 5 percent.This may eflect he late Eocenetectono-thermalvent,but the ageprofilediffers romthose of disturbed micaselsewhere n the zone (cf.spectrum for LMP-1, Fig. 14, and Kontak et al.,1990d). The configuration f steps3 through 12 issimilar to those recorded by Lo and Onstott (1989)for chloritized biotites and interpreted by them asresultingrom3"r recoil.SampleOSC-1biotiteap-pears resh n thin section nd contains a. 7 percent
K (Table 3), but it is from a site close o a vein withirregularlychloritizedselvages.We tentativelypro-pose hat granitoid ocksdating rom ca. 205 to 210Ma were invadedby younger ntrusions nd hydro-thermal fluids in the Early Jurassic, t ca. 185 to190 Ma.
Crucero district
A small mill formerly operated by the BancoMinero at Puncotira processed silver-bearingPb-Cu(-Zn) sulfide, and more recently, oxide oresfrom severalvein depositsn a districtcenteredca.15 km north-northeast f the town of Crucero Figs.3 and 11). The veins,amongwhich hoseof the Cerrodel ncaAzul (loc41) andCasade Plata loc40) mines(sometimes rouped as the Tambopatamine) havebeen the mostproductive,are hostedby strataof theCarboniferouso Lower PermianTarma and Copa-cabanaGroups n the vicinity of severalsmallstocks
of hypabyssalranodiorite. he Altura loc37), SantaAna Uno (loc 38), and SantaAna Dos (loc 39) oper-ationshavealsoproducedmixedsulfideconcentrates;the first wo deposits rehosted y fine-grained orn-blende granodiorite.These vein systems re domi-nated by quartz and carbonates: arly periods ofbrecciation, and of silicification and chloritization of
the wall rocks,were followedsuccessivelyy quartz-chalcopyrite-pyritend carbonate-galena-acanthite-sphalerite)stages Kontak, 1985). Whole-rockK-Ardates or the intrusions osting he Altura and SantaAna Uno deposits re, respectively,74.4 and 83.8 Ma(Table 3, d). Whole-rockdatesof such ocksare sub-ject to uncertainty,but the agesare tentatively ac-cepted sevidenceor a LateCretaceous etallogenicepisode.
One sulfidic Cu, Zn, Pb) veinsystemn the district,that of Condoriquifialoc42), not to be confused iththe Sn-W depositnear Limacpampa, asbeen shown(Bateman,1982; Kontak, 1985) to containacicularcassiterite nd is comparablen its paragenetic vo-lution to the chloritic lodes of the San Rafael and other
ca. 25-Ma districts e.g., Clark et al., 1983b). Kontaket al. (1990a) have, moreover,shown hat the Pb iso-tope composition f the ores s identical o that of theSn-bearing ein systems, hereas hose rom the Snofree depositsn the Cruceroareadiffermarkedly.
The smallSol de Cobrizacoppervein system loc43), is developedn limestones djacent o a diabasicintrusion, which yields an Early CretaceousK-Arwhole-rock ateof 122 Ma (Table3, d; Kontak,1985).The Pb isotopecomposition f this ore hasno equiv-alent in the region, lendingsupport o the isolatedapparent age.
Bonhomme t al. (1985) report five whole-rockK-Ar dates n the range, 66 to 169 Ma, for largely n-termediateepizonalgranitoid ocks rom an east-westbelt betweenAjoyaniandMina SantoDomingo Fig.
11). These rocksare considered o be of Hercynian,i.e., Paleozoicage, and the dates o reflect Andeanresetting,but we consider t probable hat the agedata record a westward extension of the Cretaceous
intrusive ctivitywe identify n the Cruceroarea.Theonlymineralization ocumentedn thisbelt, however,
is of Cu and Sn (the Tres Marlas and Rescatepros-pects: ocs5 and8), of a type unlikely o be associatedwith intermediate calc-alkaline stocks. The intrusions
of the Crucero districtmay representpart of an ex-pandedCretaceous rc (Clark et al., 1984).
Summary
Definitionof the agerelations f the mineralizationemplaced n the earlier stages f development f theInner Arc domain is far from complete. However,granitoidmagmatism f the polyphase, pper Triassicto Lower Jurassic,Carabayabatholith is implicatedin a wide range of lithophile (W, Sn, and Mo) andbasemetal deposits,mostof modestsize. We favor agenetic relation between the batholith and the Aulithophilemetal veinsof the broaderAnaneadistrict.The limited extent of much of the bedrock mineral-
ization may directly reflect the generallydeep levelof exposureof the magmatichydrothermalsystem.We consider the evidence for the occurrence of Pa-
leozoicmineralization nconvincing.Minor argentianbase metal vein systems re associatedwith UpperCretaceous I-type" stocks n at least one area.
Cenozoic Mineralization of the Inner Are Domain
Introduction
In contrast o the restrictedscaleof hydrothermalactivity associatedwith the Carabayabatholith, thesmallerepizonalgraniticstocks f Tertiary age n theCordillera and Precordillerade Carabayageneratedseveralargeandhigh-gradeithophileandbasemetaldeposits Kontakand Clark, 1988). The geochrono-logic data base or the intrusions nd ore deposits fthe area has been documentedelsewhere (Clark etal., 1983b, 1984; Kontak et al., 1987; Farrar et al.,
1990b) and requires only brief summary.However,we include new data for two mineralized districts in
the region.
Mineralizationassociated ith upper Oligocene
granitic plutonsSmall,composite, pizonal ntrusivecenters n the
SanRafael-Quenamariand SantoDomingodistricts(Figs. 11 and 13) are associated ith, respectively,Sn-Cu(-Ag)and Pb-Zn-Ag(-Cu,Sn), and Zn-Pb-Cu-Sn(-Ba)vein systems, xhibiting ateral (QuenamariandSantoDomingo)andvertical SanRafael)zonationfrom early Sn o later baseandpreciousmetalassem-blages (Arenas, 1980; Kontak, 1985; Kontak andClark, 1988; Clark et al., in prep.). The host mon-zogranites are markedly peraluminousand petro-
graphically distinctive, with phenocrystsof alkalifeldspar, iotite, andcordieriteandmicrophenocrystsof sillimanite,and are interpreted as productsof va-por-absent, iotite-mediated, artialmeltingof semi-pelitic protoliths n the continentalcrust (Kontaketal., 1984; Clark et al., in prep.). Intrusionwasaccom-
panied,andprobablycaused y, injectionof mantle-derived shoshonitic asalt magmas nto the crust(Kontaket al., 1986). The stocks xposedwest andnorthwestof the Crucerodepression re disposedna broadly circulararray, inferred to delimit a largepluton at depth (Kontakand Clark, 1988; M. J. Ar-enas,unpub. data; Clark et al., in prep.). This, andthe flagrantlycrosscutting ontacts f the intrusions,impliesemplacementn an extensional r neutral ec-tonic setting.
K-Ar datesof magmatic iotites n the SanRafael,Quenamari,and Santo Domingo stocks ange from23.1 ___.7 to 27.1 ___.0 Ma (Fig. 13), whereasun-
mineralizedstocksof this provincewere emplacedover the interval,20.0 ___.5 to 24.9 _ 0.5 Ma (Kontaket al., 1987; Sandeman t al., 1990). However, K-Ardates or hydrothermalmuscovite nd adularia romthe SanRafael veins (Clark et al., 1983b; Kontak etal., 1987) indicate that mineralization ook place atca. 22.6 ___.5 to 23.6 ___.6 Ma, perhaps ignificantlylater than monzogranitentrusion n the SanRafael-Quenamari rea.At the southeasternxtremityof theregion affectedby this late Oligocenemetallogenicepisode, øAr/39rdating f hydrothermaliotiteandadularia rom the large Palca 11 W-base metal veinsystem Farrar et al., 1990b; Yamamura,1990) dem-onstrates hat ore formation is essentiallycontem-poraneous, t 24-25 Ma, with that at SanRafaelandis considerablyearlier than emplacementof thenearby Cerro Corimpataand Pucaorco micro-)gra-nitic stocks 8.4 and 12.4 Ma, respectively:Kontaket al., 1987; Laubacher et al., 1988; Farrar et al.,
1990b).In addition to the Condoriquifia Crucero) Sn-
bearing veins, other mineralization n the Carabayaregionwhich may havebeen contemporaryncludesthe manganese epositsormerlyworkedat the Min-astira (loc 12) and San Francisco loc 27) mines.Atboth locations,broadly strata-bound ensesof man-ganReand other Mn oxidesare hostedby limestonesof the Pennsylvanian-lowermostermianTarma andCopacabana Groups. Audebaud and Laubacher(1969) concluded hat these depositsoccur withinkarst cavernsdevelopedbeneathan erosionsurfacenow overlainby continentalclastics f the PermianMitu Group. However, at least he Minastiradepositis situatedadjacent o a smallplug of cordierite-bio-tite-(sillimanite)granite Kontak,1985), and samplesfrom the mine show that Mn oxide replacementoflimestonewas controlled by thin dikes of phreatic
breccia, as at Berenguela.Similar relationsmay per-tain at the smallMartha (loc 9) andCerro Moromoroni(loc 13) hematite deposits.Each occurs n mixedlimestoneand clastic aciesof the Tarma-CopacabanaGroups; t Cerro Moromoroni, he iron mineralizationis concentrated ith chalcedonic ilica n crosscutting
fragmentalbodies,describedas sandstone ikesbyKontak (1985) but perhaps epresentingmultistagephreatic breccia bodies.Barite is abundant n bothdeposits, nd at Cerro Moromoroni orms_•15-cm-wide veinscutting he hematite-cementedreccias.The latter deposit ies a shortdistancebelow an un-conformably verlying uccessionf upperOligocenevolcanicbrecciasand flows of shoshonitic omposi-tion, intrudedby the 24.9 _ 0.5-Ma Antautagranite,a wide dike of cordierite-biotitemonzogranite.
The Mn and Fe(-Ba)depositswest of the Crucerodepression re interpreted as havinga geneticrela-tionshipwith the upper Oligocene o lower Miocene
peraluminous ranite ntrusions, eing either distalfaciesof Sn-basemetal veinsor, more probably, heproductsof small-scaleluid circulationunassociatedwith other mineralization.The latter is preferred be-cause he associatedranites t MinastiraandAntautashow none of the hydrothermal alteration effectswhich are widely developed n the SanRafael,Que-namari,andSantoDomingostocksKontakandClark,1988). The lead isotopecompositions f the Marthaand Minastiraores (Kontaket al., 1990a), extremelyradiogenicwhen compared o thoseof the SanRafaeland allied vein systems, re interpretedasreflectingthe dominance of host-rock over magmatic metalsources.
Also possiblyof mid-Tertiary age is the RosarioMo(-W, Sn, Cu) mineralization loc 22), comprisinga series of molybdenite-wolframite-pyrite-quartzveinsassociated ith a phyllicallyaltered felsicpor-phyryplug.Althoughmolybdenite ccurs nlyrarelyin the Tertiary veinsof the region, being more char-acteristicof the Permianand Triassic-Jurassicepos-its, the ore-lead sotopecomposition f the mineral-ization s very similar o that of undoubtedmid-Ter-tiary systems (Kontak et al., 1990a). Moreover,textural relationssuggest hat much of the pyrite inthe veins s pseudomorphousfter athsof pyrrhotite,as at SanRafael-Quenamari.
The most mportantmineralizationof problematicage n the region s that of the Cecilia-SanAntonioZn-Pb-Ag district (loc 30-32), in which the Ceciliamine was the major producer,reportingreserves f1.2 millionmetric onsat 6.8 percentZn, 2.68 percentPb, and 2.35 oz/metric on Ag prior to its closure n1985 (Sassos, 984). The deposit compriseswideveins (to 12 m) of essentiallymassivesulfide andstrata-bound mantos of sulfide veinlets, both hosted
beneath the contact with the Tarma-CopacabanaGroup. Whereaswe originally nterpreted he min-eralization o be of "sandstoneead" type (Clark etal., 1984), inferringemplacement uring he diagen-esisof the clastic ocks,petrographic tudydemon-strateshat the ore mineralswere introduced ot only
after diagenesis ut following the developmentoffabricsndicative f intense ressure olutionGirard,1984; Kontak, 1985). Bothvein and mantoorescon-tain abundantmarcasite, seudomorphousfter eu-hedralpyrrhotite,aswell asdelicately onedsphal-erite crystals strongly suggestiveof open-spacegrowth.Moreover,stannites a widespread ccessoryconstituent f the ores.These eatures re suggestiveof a shallowmagmatic ydrothermal rigin,prompt-ing analogieswith the mineralogically imilar aterstages f the tin-bearingvein systems t SanRafaeland elsewhere Clark et al., in prep.). Kontaket al.(1990a) show hat the ead sotope omposition f theCecilia sulfides s very similar o that at SanRafaeland SantoDomingo.Moreover, he Cecilia-SanAn-tonio camp ies only 1.5 km northwestof an outlierof the volcanicield of the PicotaniMeseta Fig. 15),which exposes arge volumesof upper Oligocenerhyodacitic sh-flow uffsmineralogically nd chem-ically similar to the monzogranites t San Rafael-Quenamariand SantoDomingo (Laubacheret al.,1988; Sandemanet al., 1990). Cordierite-biotitegranite float occurs n a streamvalley 0.6 km northof the Ceciliamine. On the basisof theseobservations,we tentativelyassign he Cecilia baseand preciousmetaldepositso the ate Oligoceneo earlyMiocenemetallogenic pisode epresentedn thoseother dis-tricts.
Picotani district
An extensive reaof essentiallyiat-lyingsubaerialvolcanic rocks, the Picotani Meseta, lies at the north-
ern marginof the Precordillerade Carabaya nd inpart separateshe Crucero depressionrom the An-anea-Ancocalaasin Figs. 13 and 15). The eruptiverocksof the area were assignedo the rhyolitic Ma-cusaniVolcanics y Laubacher 1978a and b), butmore recent studies Laubacheret al., 1988; Sande-manet al., 1990) haveshown hat, n addition o felsicash-flow uffs similar n some espects o the ignim-
britesof the MacusaniQuenamari)ield, he Picotaniareaexposes ubstantial olumesof basaltandof san-idine, biotite, andcordieriteporphyritic hyodacitictuffs.Laubacher t al. (1988) problematicallyssignall units n the area to the CayconiFormation,witha type section n the Cruceroarea (Fig. 13).
ConventionalK-Ar ages or the Picotanivolcanicsare presentedby Kontak (1985, in Pichavantet al.,1988a) and by Bonhomme t al. (1988) and Lau-bacheret al. (1988). Datesof 22.9 to 24.8 Ma were
obtained or the basalts nd rhyodacites nd of 16.7___.4 to 17.9 ___.6 Ma for the overlying hyolites.4øAr/39Artep-heatinggedeterminationsSandemanet al., 1990) demonstratehat major eruption n thearea persisted o 15.99 ___.48 Ma, terminatingpriorto the initiation of large-scale yroclastic ctivity n
the Macusani Quenamari)ield at ca. 10 Ma. Sande-manet al. (1990) distinguishwo faciesn the youngerrhyolitesof the area,neither dentical o the ash-flowtuffs of the Macusani ield: a lower unit with promi-nent muscovite ndbiotite phenocrysts,ndan upperwith biotite and sillimanite.
Preliminary investigationsArenas, 1985) haveshown hatCerroLintere (ca. at 14ø32'; ong69o45 )is underlain y a ca. 1-km-diameter,rudely lliptical,intensely ractured stock of muscovite-richeuco-granite, associatedwith previouslyundocumentedmineralization Fig. 15A). The north and southcon-tactsof the stockare gently ransgressiveo the bed-dingof the surrounding sh-flowuffs.The latter dis-playalteredphenocrystsf biotitebut ackmuscovite,and are thus petrographically imilar o the earlierrhyodacitic gnimbritesof the meseta Sandeman tal., 1990). At the westernmarginof the leucogranitestock, a small faulted enclave of fiuviatile conglom-erates ntercalatedwith sandstoness disconformablyoverlain y a subhorizontalasalt lowwith a vesicularupper facies.This basalthas phenocrysts f olivineand clinopyroxene, nd its high K20 content (2.10wt %) andsanidine-rich atrixpermit tsclassificationas an absarokite. Contacts between the basalt and the
graniteare not well exposed:o the west he formeris overlain, roadly onformably,y rhyodaciticuffs.
Mineralized veinscut both the sedimentary ocksand the leucogranite Fig. 15A). On the southernslopesof Cerro Lintere, the veinscontainspecularhematite,kaolinite,andcarbonatesveinD), or pyriteandquartz veinC). In contrast,he majorveinof thedistrict B), exposed t lower altitude n the valley othe west of Cerro Lintere, contains massiveFe-rich
sphalerite ntergrownwith acicularand tabularcas-siteriteandminorpyrite,marcasiteafterpyrrhotite),arsenopyrite, halcopyrite,luorite,andquartz.VeinB and the thinnerbut mineralogically imilarvein Adip steeply o the southeast nd penetrate,as thinfractures, he westernmargin of the Cerro Lintere
intrusion Arenas,1985). The main segmentof veinB, which strikes at ca. 80 ø and is 2 to 4 m wide, ter-
minates bruptlyat its southwest nd and s nferred(A. Cheilletz and G. Arroyo Pauca,pers. commun.,1989) to occupy short ensionalracturedelimitedhorizontally by northeast-strikingdextral shearplanes.None of the veins s observedo cut the ash-flow tuffssurroundinghe intrusion,but Laubacheret al. (1988) record the existenceof tourmalinizedtuff on the northernslopes f Cerro Lintere, and ex-
/,,, . :'............... I mine;bandonedine';::::::... :E::: v v v v v v .... v.
/ ":"' ":;::•i *****vv,•v. o 1
./ ............. 69o46,W
• 4øAr/3•Arotalusionge
• 4øAr/39ArpectrumFIG. 15. Geologic elations n the PicotaniMesetaarea mainlyafter Arenas,1986; Laubacher t
al., 1988; and Sandeman t al., 1990). District map (top left) shows utlineof the PicotaniOligocene-Miocene volcanic ield, locationof the Cecilia mine (see ext), and of a singledated sample.Local mapA, of the Cerro Lintere area, llustratessurroundings f the J•sicaSn(-Zn) prospect,and the locationsof two samples atedby the 4øAr/a•Arotal usionmethod, ocalmapB showshe northeastern arginof the meseta,with the locationsof the Huacchanealluvial Au-Snworkingsand the Picotaniuraniumprospect,rom whichwasobtained he sanidine gespectrum.
tensivekaolinizations evidentsouthof the mountain,suggestinghat hydrothermalactivity may have af-fecteda wide area.The veinshavebeen exploredbyMinsur, S.A., as the J•sica (or Jessica) rospect loc58) and gradesof 2 to 3 percent Sn have been re-ported.
We havedetermined øAr/a9Arotal fusiondates(Table 4) for biotite in the rhyodacitic uff exposedimmediately orthof HaciendaPicotani nd or mag-matic muscovite n the Cerro Lintere leucogranite(100 m west of vein D outcrop;Fig. 15A). A thirddate, on a whole-rocksampleof the absarokite 120m northeast f the J(•sica orkings),s tentatively n-terpreted as recording he time of crystallization fitsabundant anidine. he datesdefine ateOligoceneages or the basaltic low (26.86 +__.17 Ma) andPi-cotanirhyodacite 23.99 +__.07 Ma), and a signifi-cantly younger, early Miocene, age (17.40 4- 0.14Ma) for the leucogranite. he dates or the absarokite
and rhyodaciteare similar o but slightlyolder thanthe conventionalK-Ar ages ecordedby Bonhommeet al. (1988) and Laubacheret al. (1988) for com-parable rock types n this district.
Thus, we conclude that the Cerro Lintere leuco-
granite is a lower Miocene subvolcanic ntrusion,probably ssociatedith he earliest hase f peralu-minous hyoliticpyroclastic ruption n the Inner Arcdomain.The rhyolitic ash-flow uffs of the PicotaniMeseta Sandeman t al., 1990) differ from thoseofthe Macusaniield (Pichavant t al., 1988a,b), andmore dramatically,rom the underlying hyodacitictuffswhich,with theirbiotiteandcordieritc heno-
crysts,are interpretedas extrusive nalogues f theSanRafael-typemonzogranites.heapparentlymall
J•sica vein system s assumed o be ca. 17.4 Ma inage, and thus to represent he first recordedSn min-eralization associated with the Miocene two-mica
granites nd rhyolitesof the region,and with mag-matism iffering ignificantlyn compositionndpet-rogenesisrom the precedingSanRafaelcycle.How-
ever, cassiterite asnot been observedn vein seg-mentsdefinitelyhosted y the stock.
Uraniummineralization asbeen explored J. Va-lenciaHerrera,pers.commun., 989) in the LlojaraniGrandeareanear he northernmarginof the PicotaniMeseta (Fig. 15B). Disseminations f autunite, pre-sumably fter pitchblende,occur n a muscovite ndsanidineporphyritic felsicash-flow uff, characteristicof the earlierrhyolites f the district.A phyllicallyalteredandpyritized hyolitestock ropsout 1.5 kmto the northeast.øAr/agArtepheating f fresh an-idine from the weaklyalteredhost ock n the mainPicotaniprospectpit yieldsa plateauspectrumwith
an integratedage of 16.73 4- 0.36 Ma. On thisbasis,an earlyMioceneage s nferred or thismineralization(Sandemant al., 1990). Fluvio-glacial eposits avebeenexploited or manyyears or gold,and o a lesserextent,cassiteriteRobertson, 978) in the vicinityof Hacienda Huacchani. A short distance to the
northeast, Lower Devonian turbidites of the Ananea
Formation are intruded by a sheetedseriesof thickmicrodioritic ikeswhichare segmented y north-northeast-trendingextralstrike-slipaults ssociatedwith laterally extensivequartz veins (Laubacher,1978a). Theseundatedveins,or the nearbyCerroCarabarcunamantos Fornari et al., 1988), could
representhe source f the Au andSn n the gravelsof the Huacchani istrict, ut derivationhroughe-
workingof the fluvio-glacial eposits f the Ananea-Ancocola asin s alsopossible. sourcen the gnim-brites is considered mprobable.
Uranium, antimony, and basemetal mineralizationof the Macusanidistrict
The MacusaniVolcanics,a thick sequenceof Mio-cene to Plioceneperaluminoushyoliticash-flow uffswhich fills n the northwesternpart of the Macusaniintermontane asin, orming he Mesetade Quena-marl (Figs.13 and 16), hostseveraluraniumdeposits,someof considerable izeand grade.The mineraliza-tion in most of the showings omprises itchblende-(melnikovitic) pyrite veinlet stockworks, he indi-vidual veinletsshowing controlby both steeply n-clined ointsandgentlydippingshear ractures Flores
et al., 1983; Arribas and Figueroa, 1985; Valenciaand Arroyo, 1985). Supergenealteration o oxidateassemblagesnutunite,meta-autunite, ummite, tc.)is widespreadand intense. Minor mineralization oc-curs n interflowsediments. he major uraniumcon-centrations,which display similarities o the Lake-
view, Oregon,depositsCastorandBerry, 1981), areconfined o specific lows and are thus both stratabound and stratiform. Hydrothermal activity was,however, most intense close to the northern and
northeastern oundaries f the gnimbrite ield,wherethe generallynortheasterly ipping lowsare warpedupward against aultswhich were active during vol-canism nd husdelimited he basin,andwhichprob-ably reactivateda zone of uplift originallygeneratedwithin the Zongo-SanGab•n zone. The Macusani
--- I'.'.a,._. I Ma - 89 -151 '•v•9¾v• (.•,z-z-•9v./ -%•x', I •-_ I %•'•Z.• "" 30,
12.260.14Ma S)
I MAC2 I BI (Ma- 89- 15)• P 20., • I.A. 24.18+_0.72 a
I I •-
to Nunoa km • 15-0 10C
70140'W 70i30, Cumulative39AreleasedFIG. 16. Geologicsketchmap of the Tertiary rocksof the Mesetade Quenamari,modifiedafter
Flores et al. (1983), showing he locations f the uraniumprospects nd radiometricanomalies ostedby the Macusani hyoliticash-flow uffs,andof the mineraldeposits ssociated ith subvolcanictocksat the southernmargin of the ignimbrite field. Also shownare the locationsof two samples ated bythe 4øAr/a•Arotal fusionmethod,and an agespectrumor a micrograniterom the Ninahuisa tock.
Volcanics re (Noble et al., 1984a; Kontak, 1985; Pi-chavant t al., 1987, 1988a andb) strongly nrichedin numerousithophileandalliedelementse.g.,F,Li, P, B, Sn,W, andBe), andunmineralizedhyolitescontain to 19 ppm U (Pichavant t al., 1988b). Con-ventionalK-Ar dating (Barneset al., 1970; Kontak,
1985;Pichavantt al., 1988a)has uggestednoverallagerangeof ca. 4 to 10.5 Ma for the mainMacusani(Quenamari)gnimbrite ield. A comprehensivero-gramof 4øAr/39Artep-heatingineral gedetermi-nationacrosswell-defined ectionsCheilletzet al.,1990;and n press) assince larifiedhestratigraphicrelations f the volcanic uccession,efining eveneruptive cycles,with agesof 10.0 _ 0.5, 7.8 to 8.0___ .1, 7.5 ___.1, 7.3 ___ .1, 6.8 to 7.0 ñ 0.1, 6.7
_ 0.1, and4 _ 1 Ma, anddemonstratinghat all sig-nificant uranium mineralization occurs in flows 8.0
_ 0.1 Ma or younger.The most mportantdeposits(ChapiAlto,Pinocho, ndChilcuno I) arehosted y
tuffswith ages n the range6.8 to 7.0 _ 0.1 Ma. Themineralization as not been directly dated but isclearly no older than the latest Miocene, and themodels enerally cceptedor deposits f this type(Goodelland Waters, 1981; Valenciaand Arroyo,1985) suggesthat hydrothermal ctivitywasessen-tially contemporaneous ith volcanism.
The clusterof uraniumshowingsndradiometricanomaliesn the Chaccaconiza rea (Flores et al.,1983) occurs n Macusani ash-flow uffs less than 1km from a rhyoliticstock,with stronggeochemicalaffinitieswith the volcanics Cheilletz et al., 1990),whichyieldsa 4øAr/39Arotal usionmuscovite ate
of 7.51 ñ 0.14 Ma (Table4; Sandemant al., 1990).The intrusion s inferred to have controlledhydro-thermal circulation in this area, but intrusive bodies
havenot beendelimited n the vicinityof the largeruranium-enriched areas to the north and northeast.
The little-knownsouthernmarginof the Macusani(Quenamari) field has been a modestsourceof Pb-Zn-Ag ores Coranicamp)and of stibnite Revanchaand Collpa (Kolpa) camps).There are no moderngeologic escriptionsf thesedeposits, ut they areof vein type and occur n an area in which severalhypabyssalelsicstocksntrudeboth he marginofthe Macusanignimbrite ile and he adjacentAmbo
Groupsedimentary trata the area s erroneously s-signedentirely to the Macusani olcanics y Lau-bacher,1978a andb).
We have dated intrusive rocks from the vicinities
of the two antimonymines.The recentlyabandonedCollpamine (loc 61) workedstibniteveinscuttingAmboGroupstrata n closeproximityo a swarm frhyoliticdikes,someshowingntense ydrolytic l-teration. The dikes are offshoots of a flow-banded
total-fusion ate of 12.26 _ 0.14 Ma (Table 4), im-plyinga middleMioceneage or the Collpavein sys-tem. The Revancha ntimonymineralization loc 62)is hostedby ash-flow uffs,but it is not clearwhethertheseare of MacusaniVolcanicsype and age. Thedeposits situated lose o the northeasternxtremity
of an extensive utcropof cordierite-biotitemonzo-graniteof SanRafael ype, he Ninahuisa tock,whichyieldsa 4øAr/•"r biotiteage spectrum losely p-proaching plateauand with an integratedage of24.18 _ 0.72 Ma. This intrusionmay have been pa-rental to the Revancha veins, but the intrusive rocks
closesto the deposit re extremely resh,containingabundant lass,ranslucent anidine, ndmauve,un-pinitizedcordierite.There features trongly uggestthat (seeKontak and Clark, 1988) the granitewasuninvolvedn hydrothermal ctivity,andby analogywith the Collpadeposit, middleMiocene ather hanlate Oligoceneage s nferred or the Revancha eins.
Stibnitehas not been observedn the Sn-W poly-metallic veins associated ith the upper Oligoceneintrusions n this region.
The ageof the Coranideposit loc 63) remains n-certain. The Pb-Zn-Ag veins are hosted by AmboGroup psammites Flores et al., 1983), but it is notknown whether the veins predate or postdate henearby MacusaniVolcanics.
Summary
The most mportantore deposits f the Inner Arcdomainwere emplaced uring he earlieststageof
Cenozoicperaluminousmagmatismn the late Oli-gocene, epresentedby epizonal cordierite-biotite(-sillimanite) onzogranitictocks. he metallogenicsignature s complex--tin occurring ogether withcopper, ead,zinc,silver,barium,andprobably,man-ganese--perhaps reflecting intimate petrogeneticrelations etween he anatecticmagmas ndmantle-derivedbasalticmelts Kontaket al., 1986; Clark etal., in prep.). Gold is conspicuouslybsent.Whereasthe Palca11 veins ormedat this ime (Farraret al.,1990b), t is not clearwhy tungsten,whichoccursnonly raceamountsn the SanRafael-QuenamarindSantoDomingodeposits,s so enriched.The major
difference etween he Sn- and W-bearingveins sthe stronglyeduced ndcomparatively-poor atureofthe ormer withnoprimary e oxides ut abundantpyrrhotite) and the oxidizedand S-richnature of thelatter (rich n hematiteandpyrite). The intrusion n-ferred to be parental o the Palca11 veins s not ex-posedand t maybe petrochemically ifferent romthe S-type, lmenite-series onzogranitesssociatedwith the Sn mineralization.
Subsequentpisodes f crustalmelting n the re-gionwere much ess ecund, he only majordepositsbeing he upper Mioceneuraniumveinsof the Ma-cusaniield (Quenamari). he small •sicaSn-Zncen-
ter probably epresents n earlyMiocenecontinuationof the SanRafael-typeSn-basemetal mineralization,but despite he extreme enrichment n Sn and otherlithophilemetals f the rhyolites f the mainMacusanifield, the subvolcanic tocks ssociated ith the ig-nimbrites appear to host no tin mineralization of
Mexican type (Burt and Sheridan, 1988). The anti-monydeposits, owever,were probablyemplaced nthe middle Miocene at the outsetof this major py-roclasticactivity.
The major ate EoceneZongo-SanGab•tn one ec-tono-thermal ventwasnot demonstrably ssociatedwith crustalmelting, and despite he large-scale ir-culationof saline fluids triggered by the tectonism(Kontaket al., 1990d), played no significantminer-alizing role. Only the weak radiometricanomaliesalong he strongly aultedandcataclasticLaubacher,1978a) northeastern ontactof the Coasapluton (G.Arroyo Pauca, pers. commun., 1989) may record
metal concentration t this time (Fig. 11).
Synthesis nd RegionalCorrelations
Lacunae and uncertainties
For the first ime,ourgeologic ndgeochronologicdatapermit a coherentoverviewof the metallogenicevolution of southeasternPeru, and hence, a com-parisonwith relationships stablishedo the north-west, in central and south-central Peru, and to thesouth, n BoliviaandnorthernChile.The groundworkis laid for the development f models elatingmetal-logenesis nd the magmatic nd tectonichistoryof
the post-Paleozoicontinentalmargin.Definitionofthe mineralizationage in this extensive egion is,however, ar from comprehensiveFig. 2). Severalsignificant re depositsemainundated.These ncludethe Norviii and CanauraCu(-Au) depositsn the Cre-taceouso Paleogene rcof the CordilleraOccidentalfor which we assume gesof ca. 60 and 40 Ma, re-spectively, y analogy ith the nearby oquepala ndAtaspaca enters.A more important acuna s repre-sentedby the once-productive an Antonio de Es-quilache,Mantode Laycacota, nd Condoroma-KataAg-basemetal epithermaldistrictsof the CordilleraOccidentaland Altiplanoandby the smallerHuacul-lani and Pizacoma mines close to the Bolivian border
(Fig. 2). At least he first four of theseare hostedbyvolcanic trataof the TacazaGroupandare thereforeno older han ate Oligocene, ut their minimum gescannot e delimited; here s ittle evidence o supportFletcher et al.'s (1989) model ascribing he hydro-thermalactivityentirely o thermalgradientsmposedduring eruption of the middle Miocene SillapacaGroup.
Equallysignificant, ndpotentially ritical,are theassumptionsnderlying he present esearch.Gran-itoid plutonsand subvolcanicntrusions re inferred
to be parental o, and henceessentially oevalwith,mineral depositswithin them. That this is not nec-essarilyrue is shownby the settingof the RosaMariadeposit n the Cocachacra istrict; he hostgranodi-orite date is ca. 165 Ma, but there is evidence for
hydrothermalactivity in direct association ith the
ca. 140-Ma monzoniticdikes.Clearly, the uncertain-ties are greaterwhere the mineralizationoccursnear,but not in, the dated intrusions see Farrar et al.,1990b). Further work on direct datingof vein or al-teration minerals is indicated.
Perhaps the most serious uncertainties concernthosedepositsor which there are no significantlye-strictive stratigraphicor geochronologic ata (e.g.,Cecilia)or where he mineralageshavebeenmodifiedby later tectono-thermal vents e.g., GavilS. de Oro).Our coverageof the Au(-W, Sn, Sb, platinum-groupelement,basemetal)veinsof the CordilleraOrientalis particularlyscanty. hus, he ageof the largeSanto
Domingovein system Fig. œ),which yielded 500 to1,000 kg of Au annuallybetween 1896 and 1930(Fuchs,1898; Soler et al., 1986) is constrained nlyto the post-Cambrian. he geologic elationships fthe veins of the Ananea district also remain conten-
tious. We present here and elsewhere Clark et al.,in prep.) our reasonsor favoringa Mesozoic atherthan Paleozoicage for this mineralization, ut morereliablegeochronologicataare required.At present,the only significantmetallic depositsof pre-Andeanorigin are the San JudasTadeo W(-Mo, Au) veins(Clark et al., 1990a) and the Aurorared-bedcopper-barite deposit, espectively,definitely and probably
of Permianage.Despite heseproblems,we consider hat the geo-chronologic ata sufficiently elimit the majorityofthe metallogenicpisodesepresentedn the transect.
Metallogenicepisodes f southeastern eru
Metallic mineralization n this ca. 90,000-km2 re-gionof Peru wasassociated ith Andean ntermediateand elsicmagmatic ctivity anging n age romLateTriassic o at least he latestMiocene. Major ore de-posits,however,were emplacedat widely spaced n-tervalsand are geographically cattered.The majorandminormetallogenic pisodes efined,or implied,by our studies nd thoseof previousworkers n theMain and Inner Arc domains are summarized in Table
5 andFigure 17. The increasedrequencyof miner-alization n the Tertiary is consideredo be real andnot a functionof the dating echniques.t is almostcertainly nfluenced y the exposureevel of the as-sociatedgneous odies,but there is probablyno re-lationshipbetween the size of the ore deposits ndthe amounts f intrusive ndvolcanic ockspreservedfrom each epoch.Only during the late Oligocene oearliest Miocene did demonstrable economic miner-
Ollachea district (AgoPb-Zn)(? r, REE)SARITACu-W-Mo-Sn); Levans W-
Mo); Volc•tn Cu(-W)); [?Au(-Sn,W)veins of Ananea-Limacpampa rea]
• Major episodesnd argerore depositsre capitalized;ueriesndicate ncertaintiesegardinghe ageassignmentsr thepresenceof economicmineralization
Despite he markedlyepisodicncidence f magma-tism in the Inner Arc, contrastingwith the quasicon-tinuousactivity in the more extensiveMain Arc, sig-nificanthydrothermalevents ook place with com-parable frequency n the two environments.
As in Figure 2, the rankingof the importanceofthe deposits ndepisodesn Table 5 is in part globaland n part nternal o the region.Thus, he porphyrycopperdeposits f the Cuajone-Toquepalaistrictareworld class n terms of tonnageand grade: the SanRafael deposithas yielded over 36,000 metric tonsof metallic tin and the Palca 11 deposit, although atan early stageof development,has producedover4,500 metric tons of ferberite and scheelite concen-
tratesand clearly epresents considerableoncen-tration of high-grade ungstenores (Willig and Del-gado,1985). All maybe consideredo be majorde-posits. n contrast, he most mportantrecent sourcesof Ag-Au-base metal ores in southeasternPeru,namely, heAtaspaca, acachara, antaBfirbara, er-
enguela,Mafiazodistrict, ndCeciliadeposits,swellthe several undated districts of the Cordillera Occi-
dental, are almost certainly smaller than many Ag-Au-Pb-Zn(-Cu) centersof central and south-centralPeru (Petersen, 965). They are consideredo be ofmoderate scale n the present context but probablywould not achieve his rankingeven in the nationalarena;Benavides1984) ranks he Cacachara eposit,recently he most mportantsilverproducerof thetransect, sonly the 24th in the country.Finally, nu-merousdeposits, .g., thoseof Cu(-Au) and Fe in the
Ilo-Ite district,are probablyof only minor economicimportance in any context.
We conclude hat two majormetallogenic pisodesare representedn thisAndean ransect, oth allingwithin the Tertiary. The one of earlyEoceneageem-placed he Toquepala,Quellaveco, ndCuajonepor-phyry copperdeposits,he Cerro Verde-SantaRosa
porphyry,andprobably he Chapivein-replacementdeposit,a short distance o the west (Fig. 2). Thisepisode, elimitedby the K-Ar age data for the To-quepala 57.1 Ma) andCuajone 52.15 Ma) deposits,affected a restricted swath of the Cordillera Occiden-
tal and was apparently unrepresented n the InnerArc domain, where there is no record of Paleogenemagmatic ydrothermalctivity.The episode f lateOligocene to earliestMiocene)age, generated m-portantmineralizationn both the Main and InnerArcs. In the former, we cite 23.5 Ma for the SantaBfirbaraAg-Cu-polymetallicein system nd, essse-curely, nfer that the Berenguela g(-Cu,Mn) deposit
formedshortlyprior to 26.8 Ma. Thus,we concludethat he oldersignificant ilverandbasemetaldepositsof this area were associated either with intermediate
(ca. 26-28 Ma) stagesn the evolutionof the region-ally extensiveTacaza Group, and particularlywithhigh K calc-alkalinemagmatism,or with the earlystages f the ensuingatestOligoceneo middleMio-cene nterval of felsicexplosive olcanism Franceetal., 1984; France, 1985; Klinck et al., 1986; Waste-
neys, 1990). In the Inner Arc, the mostproductivelithophile-basemetalvein systems f the Cordillera
FIG. 17. Tabular summaryofmetaliogenicepisodesn the southeastern eru studyarea (B) and ncontiguous outh-central eru (A) and northernmostChile-northwesternBolivia (C). Sources f geo-chronologicdata are summarized n text. Major episodes re in black, minor in white; gradationallyshaded pisodes re those or which the intensityof mineralizations inferred o have ncreased rdecreased ith time (see ext). Episodes eaklyconstrained y either geochronologicr stratigraphicdata are delimited by dashed ines (BM = basemetals).The Au mineralizationof the Inner Arc ofsoutheastern eru is not shownbut is tentativelyassignedo the Jurassic.
and Precordillerade Carabaya ormed at this time.These nclude he SanRafael and Palca 11 deposits,the veinsof the smallerQuenamari Carabaya) amp(Hannington, 983), and hoseof the SantoDomingoprospect, or which K-Ar ages n the range 22.3 toca. 25 Ma havebeen determinedor inferred (Clark
et al., 1983b; Kontak et al., 1987; Farrar et al.,1990b). Moreover,we advocate similarage or theundatedbut mineralogically omparableCondori-quifia Crucerodistrict)polymetallic eins, he minorMn and Fe oxidedeposits f the area, and the exten-sive veins and mantos of the Cecilia-San Antonio Zn-
Pb-Ag district. The supergeneenrichmentof thelower Eoceneporphyry copperand vein deposits,n-cludingCuajone,Quellaveco,and Toquepala Clarket al., 1990b)alsooccurred uring he ateOligoceneto early Miocene. Geomorphologic nd geochrono-logicstudiesn thisareahavedemonstratedhat chal-cocitedevelopment egan n the late Oligocene at
ca. 25-26 Ma) and persisted nto the mid-Miocene(ca. 12 Ma). Supergene ctivitywasstimulated y asuccessionf majoruplifteventsAymara r Quechua91 and heir successors)hichaffected he oceanwardfrontof the Oligo-Miocene olcanic rc (Tosdal t al.,1981, 1984).
Metallogenic volutionof the centralAndes:A comparativeanalysis
The ongitudinal iscontinuityf many entralAn-dean ectonic,magmatic, ndmetallogenicubprov-inces or "belts" has been emphasized y Sillitoe(1974), Soler et al. (1986), and other workers. This
is seen n significantifferencesn the metallogenicevolutionof the various rogenic ransectsClark etal., 1976; Sillitoe,1988). n thiscontextwe are par-ticularlyconcernedwith temporalaspects:he defi-nitionof heextento which hemetallogenicpisodesoutlined n our studies rerepresentedn areas o thenorthwesti.e.,centralPeru, ncorporatinghecentralandsouth-central etallogenicegmentsf Soleretal., 1986) and o the south i.e., northernmost hile--north of lat 25ø S, the norte grande--and north-westernBolivia).
The episodes f mineralization n transectso thenorthandsouthof the study reaare given n Figure17; the approximate reas ffected y the episodes,aswell as he broadercoevalmagmatic rcs,are out-lined in Figure 18. These mineralizeddomainsarenot strictly metallogenic ubprovinces,inceno ac-count s takenof the intensityof hydrothermal ctiv-ity. The majorprimaryandsecondaryources f geo-chronologic ataare Pitcheret al. (1985) and SolerandBonhomme1988a, andnumerous apers itedtherein) for central and southern Peru; McBride(1977),Sillitoe 1988),andMaksaev t al. (1988aandb) fornorthernmosthile; ndMcBride1977),Grant
et al. (1979), McBride et al. (1983), and RedwoodandMacintyre 1989) for Bolivia. n addition, efer-ence is made to Chilean transectssouth of lat 25 ø S,
particularly he generalCopiap6 or E1Salvador) is-trict (lat 27o-29 ø S) of the norte chico, where theagesof the ore deposits re well establishede.g.,
Clark et al., 1970, 1976; Clark and Zentilli, 1972;Quirt, 1972; Zentilli, 1974; Haynes,1975). However,despite he expansionn geochronologicesearchnthe past decade, considerableuncertainty persistswith regard o the ageof ore depositsn manyareasof the Andes.Thus, he metallogenic istoryproposedby Vidal (1985) for the Mesozoic nd Paleogene fcentralandsouthern eru s argelyunconstrainedydirect ore depositdating.Selection f the successivetime frames n Figure 18 was nfluenced y our in-evitablysubjectiveecognition f discretemagmatichydrothermalevents. The ensuingdiscussions inchronological rder.
Although the initiation of the Central Andeanorogenyn the Late Triassicmaybe recorded y theminor submarinevolcanismof the YamayoGroup(Petersen, 1954; Bellido and Guevara, 1963), pre-served long he littoralof southeasterneru, he firstimportantAndeanmetallogenic vent wasrestrictedto the orogen, n the presentCordilleraOriental ofsoutheastern eru and northwesternBolivia Figs. 17and 18a). Predominantly vein-type W-Sn(-basemetal),andprobablyAu, mineralizations associatedin both areas of the tin belt with Upper Triassic oLowerJurassicranitoidntrusions hichwereclearlyfocused y the northeasternoundary f the Permian
Mitu ensialic ift (Laubacher,1978a; McBride et al.,1983; Clark et al., 1990a), probablyduringpersistingor renewed crustalextension.These plutonic rocksrepresenta rangeof crustalpartial melts nferred ohavebeen riggered y mantle-derivedlkalibasalticmagmatismKontaket al., 1985, 1990c). Hydrother-mal activitywasbroadlysynchronousn the Peruvianand Boliviansegments f this areally restricteddo-main:K-Ar and4øAr/39Arates or granitoid ocks nthe CordillerasReal and Mufiecas or Apolobamba)of Bolivia ange rom 202 to 225 Ma (outside f theZongo-San ab•tn one), and K-Ar dates or hydro-thermal muscovitesrom 195 to 210 Ma (McBride etal., 1983). Miller andHarris 1989) reportRb-Srdatesof 284 4- 16 to 300 4- 48 Ma for Boliviangranites orwhich either Late Triassic o Early Jurassic r lateOligocene o early MioceneK-Ar dateshave beendetermined Everndenet al., 1977; McBride et al.,1983). Details of the Rb-Sr studiesare not given,however, and although here is evidence or LatePermian intrusive activity in the Cordillera Real(McBrideet al., 1987; Clark et al., 1990a), we seenocompelling eason o accepta Carboniferouso EarlyPermianage for the mineralizedplutons.
FIG. 18. Sketchmaps howing reasn the centralAndes ffected y selectedMesozoic ndCenozoicmagmatic ndmetallogenicpisodes. hading elimits pproximateolcano-plutonicomains ndblackareas epresent he more important,or in somecases,metallogenically ignificant,mineralizations.Radiometricages are given (18f) for the severalregionscontributing o the critical 30ø to 46-Maepisode;ZSGZ represents he Zongo-SanGab•tn ectono-thermal one of Farrar et al. (1988). Map "a"incorporateshe locationof the Permo-Triassicolcano-plutonicelt of northernChile, emplacementof which had terminatedprior to the intrusionof the Carabayabatholith n the study ransect.
Whereasepizonal evelsof the plutonsare widelyexposed n the Cordillera Real of Bolivia, and majormineralizationcoincidentwith the earliest stagesofmagmatisms preserved Fig. 17), the deepererosionof several of the intrusions in the Cordillera de Cara-
baya (Kontak, 1985) may have obliterated most oftheir significantepizonal ithophile metal deposits.Conversely,we suggesthat abruptuplift and major
rotationof batholithsduring he late EoceneZongo-SanGab/inevent (Farraret al., 1988, 1990a) exhumedwidespread,n part mesothermal, u(-W-Sn-Sb) einsystemswhich have given rise to important Quater-nary placerdepositsn both Boliviaand Peru. Thus,the gold (-scheelite-stibnite) eins of the easternslopes f the CordilleraRealclearlyoverprint hermalmetamorphic ssemblageshich developed t depthsof ca. 5 to 14 km around he Zongoand Yani plutons,the former definitelyof Late Triassicage (Heinrichet al., 1988; Farrar et al., 1990a), and the mineral-
ization s similarly nferred to be no older thanTrias-sic. Comparable rguments re applied o the studytransect,where the more importantareasof Au min-eralization Ananea-SantoDomingoand Ollachea-SanGab/in)occur n areasdisplaying xtensive igh-temperaturemetamorphism.
We also nfer that the most significantMesozoicSn-W-Modeposits f the Cordillerade Carabayawere
emplaced n the Early Jurassic, n associationwithstronglyperaluminous tocksntruded nto the UpperTriassicplutons.This Cu and W, Mo, Sn mineraliza-tion was coeval with the establishment of the Main
Arc in littoral Peru and Chile. It may record the in-cursionof alkali basaltmagmasnto metaclastic tratapreviously naffected y anatexis, erhaps riggeredby a tectonicevent which affected he entire orogenas a result of larger scaleplate interactions.
In the Main Arc, Middle to Late Jurassic, asic ointermediateplutonismaffecteda narrow but longi-
tudinallyvery persistent elt (Fig. 18b) which maybe traced at least from south-central Peru to central
Chile (e.g.,Farrar et al., 1970; McBride, 1977; Paradaet al., 1988). Important Fe skarn mineralization nsouthernPeru (Marcona: njoque et al., 1988) andChile-type Cu mantosand Cu(-Fe, Co, Au, Mo, U)
vein systemsn northern CarrizalAlto:Zentilli, 1974;Clark et al., 1976) andnorthernmoste.g.,BuenaEs-peranza,MantosBlancos:Maksaev t al., 1988a) Chileare associated with this shallow-marine to subaerial
•nagmatism.e infer hat heRosaMar•aAu-Cu(Fe)veinsof the Cocachacra istrictare part of this me-tallogenic omain,but it is apparent hat mineraliza-tion of thisage n southeasterneruwasminor elativeto that in areas to the north and south. No strata-
boundCu deposits avebeendocumentedromeitherthe ChocolateVolcanicsor the GuanerosFormation,evenwhere theseunitsare intrudedby maficstocks.The probablyminor Cu-Ag-dominatedeinsof the
Middle Jurassic acusani yeniteconstitutehe onlyeconomic metallic mineralization known to be asso-
ciated with the peralkalinemagmatism f the InnerArc domain f southeasterneruandBolivia. he po-tential for Zr and REE depositswhich may be asso-ciatedwith theseJurassicntrusions asnotbeensys-tematicallyassessedn either country.
Voluminousgranitoid ntrusive activity occurredduring the mid-CretaceousFig. 18c) alongalmostthe entirecentralAndean onvergent lateboundary.This ncluded he initialstages f the Coastal atholithproper (Beckinsale t al., 1985) andoverlappedwithmarinevolcanism ndwith attenuation nd ncipient
breakupof the continentalmargincrust n northernChile e.g.,Zentilli,1974; •berget al., 1984),andin centralPeru, with the eruptionof the marinevol-canicsof the Albian-CenomanianasmaGroup n alongitudinalmarginalbasin Athertonet al., 1983).On a broaderscale, he intensemagmatismoincidedwith the initiationof sea-floor preadingn the SouthAtlantic. Major mineralizationdefinitely associatedwith the Albian granitoidplutons ncludes he an-desite-hosted Fe (-Cu, Au) skarns and someAu(-Cu)veinsof northernChile (Haynes, 975; Clarket al., 1976; Colley et al., 1989) and ourmalinebrec-cia and Au-rich porphyry copper mineralization n
north-central hile, o the south f theareaof Figure18 (Munizagaet al., 1985; Sillitoe, 1988). In south-centralPeru,Vidal (1985) proposes n Albianage orthe Monterrosas, •o Seco,Acar•,andotherCu(-Fe,Co, Au) vein deposits, ut geochronologicataspe-cificallyor the mineralizationre acking.However,Vidal (1987) convincingly rgues or a submarine x-halativeorigin, and hencemid-Cretaceousge, forthe productiveLeonila-Gracielamassive arite-Zn-(-Pb,Ag) deposits f centralPeru,and eportsK-Ar(sericite)agesof 106 and 116 Ma for alterationas-sociatedwith the nearbyAurora Augustadiscordant
deposit (see Figs. 17 and 18c). To our knowledge,there are no confirmed mid-Cretaceous mineral de-
posits n northernmostChile, but we infer that thesmallCu(-Fe, Au) veinsof the Ilo districtand he he-matite veins in the Ite area of southeastern Peru con-
stitute a link, albeit weak, in this chain of mineraliza-
tion.A transition rom dominantlysubmarine o domi-
nantlysubaerial olcanism,ndassociatedlutonism,or from a Marianas o a Chilean type of subduction(Uyeda and Kanamori,1979), occurred hroughoutthe central Andes in the later Cretaceous and is in-
terpreted as initiating the developmentof thickercrust hanhad prevailed n the preceding100 to 120m.y. This engendered Clark et al., 1976) a diversi-fication of the ore metals and associated metalloids:
economic r subeconomiconcentrations f copper,molybdenum,ron, gold,cobalt,zinc, and manganesewere now oined in many areasof the Main Arc do-
main by crustallyderived silver, tungsten,arsenic,bismuth,antimony,mercury,and ead.Although he SantaRosaandHuantajaya ilverde-
positson the Chilean coastnear Iquique may be ofLate Jurassic r Early Cretaceousage (Clark et al.,1976), the Caracolesdeposit, also in northernmostChile, is the oldestsilver-richvein systemconfirmedin the Main Arc in the regioncoveredby Figure 18;Maksaevet al. (1988b) consider his mineralizationto have formed between 75 and 85 Ma. A similar Late
Cretaceous ge maybe inferred for several mportantAg-Cu depositsn the Copiap6district arther south(Zentilli, 1974; Clark et al., 1976), andVidal (1985)
has entativelyassignedges n this ange o numeroussmall Cu(-Au, Mo, W) vein-, skarn-and porphyry-type deposits ssociated ith the Coastalbatholith ncentral and southernPeru (Figs. 17 and 18d). Thethick subaerialvolcanic -hypabyssal) uccession fthe largely Upper CretaceousToquepalaGroup inthe study ransect s extensively xposed, ut no sig-nificant base or precious metal mineralization sknown to be directly associated ith theserocks,al-though numeroussubvolcanicntrusionshave beendocumented A. PlazollesValdivia, pers. commun.,1986). Only the very minorCu veins n the Challatitaarea may be broadlycoevalwith the main period of
ToquepalaGroup eruption. However, scatteredPb-Zn-Ag(-Cu) vein systemsormed at this time in theInner Arc domain Fig. 18d), as n the Crucerodistrictand n the Monolito Sorata) reaof the northwesternBolivian Cordillera Oriental, where McBride et al.(1983) reportwhole-rockK-Ar datesof 82.7 and78.8Ma for shoshonitic andesitic and dacitic dikes asso-
ciated with minor Pb-Zn-Ag mineralization. Thisevent remainspoorly defined, but the recent sedi-mentologic tudies f Marocco ndNoblet (1990) inthe Cuzco-Sicuanintramontaneasin trengthenursuggestionClarket al., 1984) that he centralAndean
are experienceda marked broadening n the LateCretaceous.The available adiometricdatessuggestthat this putative event immediately followed theSantonianPeruvian orogeny (Steinmann,1929; Vi-cente,1981). However,our observationsuggesthat,unlike the late Oligocenearc expansion,t did not
cause nner Arc anatexis, and hence, no lithophilemetal mineralizationwas emplaced.
Epizonalmonzodioritic o granodioritic lutonismof late Paleocene ge (ca. 59-64 Ma) in southeasternPeru, as n the Lluta (Cercana),and probably, Norviiidistricts,had associatedminor Cu(-Pb, Ag, Au) min-eralization,contemporaneous ith comparably mallCu(-W, Mo, Au) deposits n the Campanani (Lluta)district in northernmost Chile, from which McBride
(1977) reportsa 62.6-Ma K-Ar age or a mineralizedgranodiorite.Farther south, Maksaevet al. (1988b)infer similar ges 60-63 Ma) for Cu veins n the SierraGorda-Copuchadistrict.This widespread pisodeof
minor Cu mineralization probably persisted to thenorthwestof the study area, but unambiguous eo-chronologic ataare acking Fig. 17). In Figure 18e,this late Paleocene event has been combined with the
immediately succeeding, ar more important, earlyEocene ca. 52-58 Ma) episodeof porphyryCu(-Mo,Ag) emplacementwhich dominateshe Main Arc do-main of southeastern eru, extending from CerroVerde to Toquepala Fig. 2). Again, he extentof thisepisoden south-central eru s poorlydefined Vidal,1985), but its persistence outhward nto northern-mostChile sconfirmed y ca.58-Ma ages eterminedby Quirt et al. (1971; see alsoSillitoe, 1981) for the
medium-sizedMocha porphyry copper deposit,andby similarages eported or the E1 nca and Cachinalde la Sierra silverveinsby Maksaevet al. (1988a) andfor the argeE1Guanaco pithermal old -Cu)depositby Puiget al. (1987). Still arthersouth, he Paleoceneto early Eocenebelt (Sillitoe, 1988) assumes morepolymetallic nature: copper-rich veins and brecciapipes ocally containsignificantW, Au, and Bi (Ruizet al., 1965) and ca. 50- to 65-Ma agesare recordedfor severalAg-rich depositsof the Copiap6 districtby Zentilli (1974), Haynes (1975), and Clark et al.(1976).
Despite their apparentlyerratic mineralization n-
tensity, he Mesozoic ndPaleogene olcano-plutonicarcs display a remarkable continuity from at leastsouthernPeru to central Chile (Fig. 18b-e), with ex-tensivesuperimposition f magmaticactivity of dif-ferent ages n Peru contrastingwith a more orderlycontinentwardmigration n Chile (Farraret al., 1970;Clark et al., 1976; Colley et al., 1989). The oldestbelts,of Jurassic ge,are apparently runcatedby thepresentcoastlineof the Africa deflection,but withthe exceptionof the still poorly definedCretaceousactivity n the Tintaya area and n the Cordillera Ori-ental,magmatism asconfinedo a narrowzonesub-parallel and close o the presentcontinentalmargin.
The coherenceof the ensuingmagmatic-metallo-genicevent n the vicinityof the orocline s ess learlydefined. In Figure 18f we follow Sillitoe (1988) ingrouping ogether all late Eocene o mid-Oligoceneigneous ndhydrothermal ctivity,embracinghe n-terval 30 to 46 Ma. In Chile, this belt incorporates
the greatestknownconcentration f giant porphyryCu(-Mo) centers, ncludingChuquicamata, 1 Abra,andLa Escondida, swell asa largenumberof smallerCu (and/or Mo)-dominateddeposits.An extensiveK-Ar geochronologicdata base (Quirt et al., 1971;McBride, 1977; Sillitoe, 1981, 1988) has been aug-mented y the detailed øAr/39Artudies f Maksaevet al. (1988a) on severalof the porphyry deposits nnorthernmost Chile. Porphyry mineralization oc-curred from 31 to 41 Ma between latitudes 27 ø and
20 ø S, in associationwith a narrow magmatic arc,generallyof only modestvolume,coincidingn partwith the West Fissure fault zone, a continental-scale
structure. In southeastern Peru, Yoshikawa et al.(1976) andNoble et al. (1984b) presentK-At agesof31 to 38 Ma (Fig. 18f) for intrusions ndCu-Fe skarnand stockwork mineralization in the inland Anda-
huaylas-Yauri subprovince (Bellido et al., 1972),which many authorshave recognizedasconstitutingan anomalyn the metallogeniconation f the centralAndes (Sillitoe, 1976), where the great majority ofsignificantFe deposits ie close o the continentalmargin. n west-centralPeru, Soler and Bonhomme(1988a and b) report discordantK-Ar datesof 25.9to 29.3 Ma which are interpreted as ndicatinga ca.31-Ma age for the Atacochaand Milpo polymetallic
vein and skarncenters; hey tentativelyascribea sim-ilar age o the Uchucchacua ilverdeposit.The abovemineralization lies within a ca. 125-km-wide upperEocene o Oligocenemagmatic rc, delimitedby No-ble et al. (1979) andothers, he emplacement f whichbeganat ca. 40 to 41 Ma following he majorepisodeof thin-skinnedcrustalshortening nd uplift consti-tuting the Incaic orogeny Steinmann,1929; Nobleet al., 1979; M•gard, 1984). Maksaevand Zentilli(1988) similarly mphasizehat he richlymineralizedcoevalarc n northernChile wasgenerated n the af-termath of the Incaic compression.
The greater part of the southeastern eru transect
is demonstrated o constitutea significant iatus nthis mportantupper Eocene o mid-Oligocenemag-matichydrothermal omain n the vicinityof the Aricadeflection. The Ataspacagranodioriticcenter, withits Cu polymetallic, n part porphyry-style,mineral-ization, located 320 km north-northwest of the
northernmostdocumented,broadly coeval (39 Ma:McBride, 1977), Chilean porphyry copper-typede-posit, Queen Elizabeth (Sillitoe, 1988), clearly ex-tends this richly endowed belt into southernmostPeru. However, only minor Cu mineralization s re-corded from the upper Eocene stocksnear Tarata,and his argelygranodioritic rc s apparently evered
farther o the northwest.Althoughcalc-alkalineelsicintrusive activity persisted nto the mid-Oligoceneboth in northernmostChile and n the Andahuaylas-Yauri belt of south-centralPeru, the initiation of maficshoshonitic volcanism in the Santa Lucia area at ca.
31 to 32 Ma (Wasteneys, 990; thispaper) s nferred
to reflect a radicallydifferent ectono-magmaticon-text, despite ts locationon the stronglycurved tra-jectory of the mid-Tertiaryarc overall.
As in transects o the south and northwest, the Main
Arc domainbetween, approximately, arata andTin-taya experienced plift and crustalshorteningn thelate Eocene to mid-Oligocene.The uncomformitybeneath the fore-arc basinalsuccession onstitutingthe continentalMoqueguaFormation Bellido,1979;MaroccoandNoblet, 1990), whichnowunderlies heLlanuras Costaneras between the axial Cordillera Oc-
cidental and the Cordillera de la Costa, could have
been generatedduring the Incaic orogenyat ca. 40
to 43 Ma and may extendacross he submarine on-tinental slopeas the well-definedEocene-Oligoceneerosionsurface van Huene and Lallemand, 1990).Erosionof the •52-Ma ToquepalaGroup, however,probablycommenced arlier and the on-landstrati-graphic record may be incomplete.Farther inland,physiographic ifferentiationof the emergingCor-dillera Oriental and Altiplano occurredas a result ofthin-skinned,argelysouthwest-verginghrusting ndfolding Newell, 1949; M•gard, 1988; Ellisonet al.,1989) in the vicinity of Lake Titicaca (the Huancan•thrust and fold belt of M•gard, 1988; Fig. 3). How-ever, we infer that the greatestuplift took place to
the northeast, longand mmediatelycontinentwardof the presentaxisof the Cordillera Oriental. Herethe Zongo-SanGab•tn ectono-thermal one records(Farraret al., 1988;Kontak t al., 1990d)major hick-skinnedcompressionnvolvingbasement plift, andprobably, rotation acrosscrustal-scale uplexes nsome ransectsFarrar et al., 1990a), shortlyprior to38 Ma, the time of Ar retention in biotites at the rootof the zone.
Broadanalogieswith the Mio-Pliocenebasementupliftsof the SierrasPampeanasf the northwestAr-gentinian oreland Jordan t al., 1983) suggesthatsoutheasterneruexperiencediat subductiont this
time. No magmatism asbeen recognizedn associ-ation with the Incaic orogenicevents n much ofsoutheasterneru, accountingor the absence f up-per Eocene o lower Oligocenehydrothermalmin-eralization. teepsubductions,however,nferred ohavepersistedn centralPeru. Noble et al. (1984b)suggestedhat the Andahuaylas-Yauriranitoid eltresulted from shallowsubduction,but we believe that
it occupies transitional osition,possibly crossmajor warp in the subducting late, along whichmagmasosewith minimal ssimilationf crustalma-terials, eading o majormineralization ith a mantlegeochemical ignature Cu, Fe ___u).
A dramaticchange n the magmatic nd tectonicactivityof the study ransect nsuedn the ate Oli-gocene, t 28.5 ___Ma. Geochronologictudiese.g.,Tosdalet al., 1981; Clark et al., 1983b; Franceet al.,1984; Bonhomme t al., 1985; Kontak et al., 1987;R. J.Langridge,n prep.)demonstratehatat this ime
magmatismbruptly evived cross widthof 320 to350 km, extendingrom he Pacific lopeof the pres-ent Cordillera Occidental. The Main Arc alone, en-
compassinghepresent ordillera ccidentalnd heAltiplano,attained width of ca. 230 km. Felsic g-nimbrites, nferred o haveerupted rom he locationof the modern olcanic rc Tosdal t al., 1981), dom-inated he oceanward ortionof the late OligoceneMain Arc, whereas mafic and intermediate calc-al-kaline mediumo highK) andshoshoniticuites re-dominated across ts continental areas. The coeval
suscitation f the contiguousnner Arc involvedcrustalmeltingwhich esulted, t east n southeastern
Peru, from the emplacement f mantle-derivedshoshoniticabsarokitic)magmas Kontaket al.,1986).Broadeningas ensiblynstantaneousClarkandMcNutt,1982),and heavailable -Arand øAr/39Ardata reveal no clear transversesecularmigrationof the inner and outer limits of the arc.
Majorupliftat ca.25 to 26 Ma (Tosdal t al., 1984;Wasteneys,990) clearly ollowedhis adical evivalof magmatism. rc broadeningn southeasterneruthereforepreceded he initiationof the Aymar•torQuechuaD• episodeof regionalcrustalshortening(S•brieret al., 1988;Ellison t al., 1989). Arcbroad-eningprobably lso recededhedevelopmentf thecentral Andean foreland thrust and fold belt in the
Miocene,but the two features learlycoexistedor aprotractedperiod.
A strictlycontemporaneous28-29 Ma) reactiva-tion of both mafic and peraluminous ranitoidmag-matism occurred in the Illimani volcano-plutoniccenterof the BolivianCordilleraReal (McBrideet al.,1983), but the still scanty ge data or the northernBolivianAltiplano (Everndenet al., 1977; Naeseretal., 1987; Swansonet al., 1987; Lavenu et al., 1989;Clark et al., in prep.) suggest hat arc expansion tthis latitude was not coherent until ca. 24 to 25 Ma,
i.e., until the latestOligoceneorogenicevent. Red-wood and Macintyre (1989) recognizeonly a mid-Miocene ca. 17 Ma) arc expansionn this area. Re-stricted arc broadeningalso occurred n the south-western Bolivian Altiplano in the late Oligocene(Kussmault al., 1975). n south-centraleru ca.13øS), the K-Ar dataof McKeeand Noble (1982) dem-onstrate that Main Arc volcanism revived at ca. 27
Ma, although he majormagmaticlare-up here wasassignedo the period 17 to 23 Ma (seealsoNobleet al., 1974). There wasa markeddiminution f ig-neousactivity n centralPeru (ca. 11ø S) in the mid-Oligocene,eadingSolerandBonhomme1988b,p.175) to conclude rroneouslyhat "[a] lack of mag-
matic ctivity hroughout id-to-late ligoceneimesis generalover the PeruvianAndes."
The significancef the arcbroadenings problem-atic, argelybecause irectlycomparable vents avenot been documented in other Mesozoic to Recent
orogens: hus, the large-scaleMesozoic-Cenozoic
displacement f the cordilleran arc in the westernUnited States Coney and Reynolds,1977) involvedmigration ca. 1000 km) of the arc front over a pro-tracted period (90 my), rather than instantaneousbroadening.However, from the age, areal distribu-tion, andchemistryof the igneous ocks n the studyarea, we infer that, followinga late Eocene o mid-Oligocene pisode f fiat subduction, steeper ngleof oceanicplate descent bruptlyensued n the lateOligocene.
The late Oligocene o early Miocene interval ofbroad arc activity gave rise to extensivemineraliza-tion, particularlyn the Inner Arc domain,where arge
and high-grade edrock in depositswere emplacedin Boliviaand southeastern eru (Figs.17 and 18g).Detailed K-Ar studiessuggest hat Sn and W veinmineralization commenced at ca. 24 to 26.5 Ma in
spatial ssociation ith 25- to 28.5-Ma peraluminousgranitoidstocksn both the Cordillerade Carabayaand Cordillera Real segments f the tin belt (Clark etal., 1983b; McBride et al., 1983; Kontak et al., 1987;Farrar et al., 1990b). Also n Bolivia,at latitude 19050S, minor Sn-W mineralization was associatedwith theKumuranapluton (25.25 Ma), representing he initialmagmatism f the richly mineralizedLos Frailes-Po-tosl area (Schneider, 1987; Halls and Schneider,
1988). Vein formation hereafter persisted o ca. 22Ma in the Cordillera de Carabayaand, southof theCordillera Real, in the CordillerasQuimsaCruz andSantaVera Cruz. Subsequently, t ca. 20 to 21 Ma,the major focusof mineralization n the Bolivian inbelt migratedsouthalong he proto-CordilleraOri-ental to generateLlallaguaand other large subvol-canic in deposits f west-centralBolivia Grant et al.,1979). Schneiderand Halls (1985) also emphasizethat the Kumarana-Azanaques agmatichydrother-mal episode ca. 20-25 Ma) of the Potos• rea maybe distinguishedrom ater events n the centralseg-ment of the Bolivian tin belt.
Clark et al. (in prep.) argue that, whereas hegranitoidstocks f the Cordillerade Carabayawereemplaced n a structurallyneutral (postkinematic)environment, he immediatelyensuing ormationofSn- and W-rich veins (ca. 24 Ma) occurredduring acompressionalectoniceventwhichmaybe assignedto either the QuechuaD• or, preferably, he Aymar•torogenic hase seealsoLaubacher t al., 1988; S•-brier et al., 1988).
In the Main Arc, we recognize significantmetal-logenicepisode t ca. 23.5 to 28 Ma, responsibleorthe SantaB•trbara g-basemetaland,probably,Ber-
enguelaAg-Cu deposits. he areal extentof this ateOligocene o earliestMioceneevent, unrecognizedin previousmetallogenic yntheses f the PeruvianMain Arc (e.g.,Petersen ndVidal, 1983; Soleret al.,1986), is poorly defined. However, Robertson's(1978) conclusionhat the Ag-basemetalmineraliza-
tion of the Manto de Laycacotacamp (Fig. 2) incor-porates hallow-waterlacustrine) xhalative orizonsin the TacazaGroup >_ a. 25 Ma: Franceet al., 1984;Wasteneys,1990) suggestshat other Ag-rich epi-thermal centers n the CordilleraOccidentalmay beof this age. The SantaB•trbara eins (23.5 Ma), inparticular,displayan ntimateassociation ith initialuplift n the Santa ucia egion n the atestOligocene,and with the first ocal outbreakof felsicpyroclasticactivity,both manifestationsf the Aymar•t,QuechuaD1, or QuechuaD2 (Ellison et al., 1989) orogeny.The ignimbrite-dominated ceanwardportion of thearc is apparentlybarren, but few eruptive centers
havebeen recognized o date (Tosdalet al., 1981).The Au- and Ag-rich veinsand stockworks f theMafiazodistrictare inferred o be ca. 19 Ma in ageon he basis f the datedphyllicalteration ssemblagefrom the Lulita deposit,and thus,representa metal-Iogenic episodeslightly younger than that of thenearbySantaLucia area.This mineralization ecordsthe only hydrothermalactivity n southeastern eruknown to be coevalwith the early Miocene (ca. 18-20 Ma) episodeof uplift (Tosdal t al., 1984) andvo-luminous gnimbriticvolcanism Tosdalet al., 1981;Wasteneys,1990) in the Cordillera Occidental,con-sideredby Tosdalet al. (1984) to represent he final
phaseof the tectonic cycle initiated in the late Oli-gocene. Supergene enrichment of the Cuajone,Quellaveco, ndprobably, oquepala orphyrycop-per depositswas nterruptedat ca. 18 to 18.5 Ma byabrupt uplift of the oceanward lopeof the Precor-dilleraandattendantmanfling y rhyoliticgnimbrites(Clark et al., 1990b).
In northwestern Bolivia, on the eastern shores of
Lake Titicaca, a 23.3-Ma (biotite) K-Ar age hasbeendeterminedMcBride,1977) for the smallPfilpitodelDiablo rhyodacitic tock,which s associated ith mi-nor Pb-Sb (-Sn, as eallite and berndtite) mineraliza-tion (Clark et al., in prep.), possibly epresentingtransition between the Main and Inner Arc metallo-
genic domains.Elsewhereon the BolivianAltiplanothe majorityof the red-bedandalliedcopperdepositsincludingCorocoro, ormed n this nterval (ca. 18-23 Ma: Clark et al., in prep.), as did probably therestrictedmineralization f this ype n the SantaRosa(Desaguadero) istrict in the study area (Fig. 2).However, there is no evidence for the occurrence of
epithermal veins in association ith the scatteredsubvolcanic tocks f early Mioceneage on the Bo-livian Altiplano. Whereas late Oligoceneto earlyMiocenevolcanism nd shallowplutonism ersisted
in the Main Arc south nto northernmostChile, onlythe large La Coipa Ag-Au epithermalcenter in theCopiap6 (or E1 Salvador)district of northern Chile(Rivera-Cabello,1988; Colley et al., 1989) hasbeenconfirmedo fall in thisage ange 23-24 Ma: Zentilli,1974; Clark et al., 1976).
The geochronologicata for the study ransectdonot permit delimitation of the area of the Main Arcin southeastern eru that experienced he succeedingmiddle (ca. 17 Ma) to late (ca. 7 Ma) Miocenemetal-logenic pisode, r episodes, hichgeneratedhe vastmajority of the large Ag and basemetal depositsofthe centraland southern reasof the country Erick-son et al., 1987; Candiotti, 1988; Soler and Bon-homme, 1988a and b; alsoPetersen and Vidal, 1983,
and references herein), including he rich veins ofthe Puquio-Cailloma g district (16.3-17.1 Ma) im-mediately to the west of the area under discussion(Fig. 2). Someof the baseand preciousmetal epi-
thermal depositsof the northern BolivianAltiplano(e.g.,La Joya,Viscachani) re alsoof middleMioceneage (ca. 12-16 Ma; McBride, 1977; RedwoodandMacintyre,1989). Volcanism f thisage s representedin the area of study by the SillapacaFormation, thepredominantlydacitic eruptive centersof which arepreserved n the SantaLucia district (14.7-16.2 Ma:Wasteneys,1990) and elsewhere n the inner Cor-dilleraOccidental ndAltiplano Klincket al., 1986).The sparse vailabledata suggesthat at leastsomeof the antimony-rich mineralization on the south-easternPeruvianAltiplano, and perhaps, n the Pre-cordillerade Carabaya,may have been emplacedat
this time (e.g., Pucar•t:15.4 Ma). However, mosteruptivecenters f middleMioceneage n the transectarenot known o hostsignificant pithermal eins cf.Fletcheret al., 1989); this snot a functionof erosionallevel and s nterpretedasrepresenting true metal-logenic ull.
The smallJ•sica Sn-Znprospect 17.4 Ma) consti-tutes he only ocalbroadcontemporary f the seriesof very large Sn-Ag -Bi, basemetal) epithermalde-posits eneratedn the centralandsouthern egmentsof the Bolivian tin belt in the later early Miocene,including Oruro (16.3 Ma; McBride et al., 1983),Chorolque (16.2 Ma), Tatasi (15.6 Ma), and Tasna
(16.4 Ma; Grant et al., 1979). This contrast n min-eralization ntensity s striking,given he broad sim-ilarities n petrochemistryKontak,1985; Schneider,1987) of the coevalperaluminousgneous ocks nthe two areas,but we emphasize hat the Cerro Lin-tere microgranite tock s the onlysubvolcanicenterof this ageso ar recognizedn the Cordillerade Ca-rabaya,and hat significant olcanism t this ime waslargelyrestricted o the PicotaniMeseta Sandemanet al., 1990). However, there are alsono knownPe-ruvian equivalents f the important ate-middleMio-ceneBolivianSn-Ag-basemetalcenters Potosl, 3.8
Ma; Chocaya, a. 12.5 Ma; Grant et al., 1979; Schnei-der, 1987). The extremeenrichmentsn Sn _•53ppm)and other ithophileelements xhibitedby the rhyo-litic ash-flow uffs of the main middle to upper Mio-cene (ca. 4-10 Ma) Macusani olcanics Pichavant tal., 1988b; Cheilletz et al., in press)andby the scat-
tered subvolcanic tockswith similar geochemicalfeatures Farraret al., 1990b;Yamamura, 990) raisesexpectationshat concentrationsf thesemetalsmaybe locally developed.However, the majority of thestocks nown o be of this age andpetrochemical f-filiation displayno evidenceof interactionwith high-temperaturemagmatogeneluids Yamamura, 990).
In contrast, he uraniummineralizationdevelopedextensively in the Macusani Volcanics, and lessstrongly n the _•8-Ma (Schneider,1987) Los Frailesignimbrite field of Bolivia (Michel and Schneider,1978), displays irect geochemical ongruencewiththe host rocks,and the derivation of the uranium from
the rhyolites s indisputable. he deposits elimitedin the Quenamari Macusani)ield nclude he argestandrichestof thisclanyet recognizedworldwide cf.GoodellandWaters,1981) andrepresent significantlate Miocenemetallogenic poch,one that was esswell developed n Bolivia.
Whereas a transition to Sb-dominant mineralization
tookplace ocally n the Bolivian in belt in the latestMiocene (ca. 8 Ma: Schneiderand Halls, 1985), ourdata for the Collpa districtsuggesthat this had oc-curred by 12 Ma in the studyarea. Both in Boliviaand Peru, however, t is probable hat theseclearlyepithermalstibnitedeposits epresentmuchweaker
concentrations f antimony than the mesothermalSb(-W, Au) veins (e.g., Ahlfeld, 1974) and have cer-tainly been lessproductive.
The most mportantsilver depositof recent yearsin southeastern eru, Cacachara,was emplaced,co-evallywith the veinsof the less mportantCompuertacamp,at ca. 7 Ma, in the later stages f the Oligoceneto Mioceneexpanded rc, associated ith the earliesteruptionsof the BarrosoGroup. Broadly contempo-rary Main Arc epithermal mineralization on thenorthern BolivianAltiplano includes he Laurani Ag-Au-Cu-Pb-As-Sb enter (8.0 Ma; McBride, 1977) andprobably he minorPb-Zn-Ag-Sb einsof the Patricia-
Pacuni area (ca. 8.1 Ma; Redwood and Macintyre,1989). To the northwest of the study transect, theextremely ich Ag(-Au)veinsof the Arcataminehavebeen nterpretedasca.5 Ma in age Candiotti,1988),but Fornari and Viica (1977) and Soleret al. (1986)bracket the timing of mineralizationbetween 3.66and 3.73 Ma. Although upper Miocene epithermalbaseandpreciousmetalveins,and ocally,porphyryCu(-Mo, Au) centers are known from the SierrasPampeanasof northwestern Argentina (McBride,1972; Clark et al., in prep.; see alsoEricksonet al.,1987), and coevalmineralization lmostcertainlyex-
ists n western Bolivia and northernmost Chile, there
is a strikingpaucityof geochronologicata or centralAndean ore deposits n this time interval. This pre-vents delimitation of the area of the Main Arc affected
by late Miocenehydrothermal ctivityand an assess-ment of the importanceof this period. t is, however,
clear that severaladequatelydissected olcaniccen-ters of the Lower BarrosoGroup n southeastern eruexhibit no evidence of metallic mineralization.
Plio-Pleistocene geshave been reported for epi-thermal vein systemsn more northerly transectsofthe Peruvian Andes, as at Atunsulla, in Nevado Por-
tugueza Noble andMcKee, 1982; Petersen ndVidal,1983) and Ccarhuaraso D.C. Noble, in Candiotti,1988). Metallicmineralization f thisagehasnotbeenconfirmed from the contracted Pliocene-Holocene
volcanicarc of southeastern eru, despite the widerange of erosional evel displayedby the stratovol-canoes f the Barroso nd (lower) AmpatoGroups.
ConcludingStatement
The southeasternmost area of Peru embraces the
entire array of geologicand physiographic rovinceswhich constitute the Central Andean orogen and isan ideal setting n which to elucidate he overall re-lationships f hydrothermalprocesses nd the mag-matic and tectonic events which define this classic
convergent lateboundary nvironment. ur aimhasbeen to provide a detailed and unified geologicandgeochronologic ata base for the ore deposits ndtheir hostrocks,a prerequisite or the elaborationofmetallogenicmodels.Our coverageof the known
mineralization s not complete, particularly in theNeogeneprovinceof the Cordillera Occidentalandin the Precordillerade Carabaya,and several mpor-tant groupsof ore deposits, uchas he gold veinsofthe Ananeaand SantoDomingodistricts, learlymeritmore detailed attention. However, the observations
in thispaperconsiderably mplify he earlysynthesesof De las Casasand Ponzoni (1969), Bellido and deMontreuil (1972), Bellido et al. (1972), Ponzoni(1980), and Petersenand Vidal (1983), and demon-strate that the more recent metallogenicschemes fClark et al. (1984), Soler et al. (1986), and Fletcheret al. (1989) require significantmodification.
Aswould be expected,southeastern eru displaysmany similarities n its metallogenicevolutionwithother transects of the central Andes. However, it is
equallyapparent hat the regionof the Arica deflec-tion, considered sa whole,hasbeen metallogenicallydistinctivesince the initiation of Andean orogeny nthe Late Triassicand, moreover, that the study areahas commonlydiffered n the timing and nature ofmineralization rom the contiguous roclinal ransectextending rom northernmostChile to northwesternBolivia.Thus, egionalgeodynamicelationships ay
be inferred to have controlled the Triassic-Jurassiclithophilemetalvein systems f the Inner Arc domainin both Peru and Bolivia, and the major Paleogeneporphyrycopperdepositarraysof the Main Arc; im-portantcontrasts re apparentbetween he intensityof such mineralization in southeastern Peru and in
adjacent reas, ndpresent oncepts f the transversesegmentation f Andean metallogenic ubprovincesare probably nsufllciently efined.
The persistentmetallogenic ndividualityof theregionsurroundinghe Aricadeflection, swell as tsinternal variability, mplies hat for the past220 m.y.this segment f the orogenhas ncorporated first-order discontinuityn the plateboundary. t is hopedthat the present esearchwill contribute o the de-velopment f moresophisticatedndpredictiveme-tallogenicmodels or: the Andes and other, morecomplex,ensialicconvergentorogens.
Acknowledgments
The field and laboratory studieswhich form thebasis for the research summarized herein were funded
throughNatural Sciences ndEngineeringResearchCouncilof Canada rantso A.H.C. andE.F. Logisticalassistancen the field was generously rovidedbyMinsur, S.A., Southern Peru Copper Corporation(SPCC), he InstitutoGeo16gico, ineroy Metalfir-gico INGEMMET), the nstitutoPeruano e EnergiaNuclear (IPEN), and the United NationsRevolvingFund (UNRF) for Natural Resources xploration nPeru. We are particularlygrateful or the assistanceand advice of: Fausto Zavaleta, the late Adolfo M•-
dico, FortunatoBrescia,PastorLuque, SixtoParedes,Nestor Rold•tn, Rafil Valdivia, and Vidal Ayque ofMinsur, S.A.; Armando Plazolles, Jorge Manrique,Frank Stevenson, and Paul Satchwell of SPCC; Guido
del Castillo, Felix Espinoza, and Rafil Rosas ofColquiminas,S.A.; FernandoArias and JorgeTaipeof Sociedad n6nimaMineraRegina; ommyCinzanoand Elias Mestos of Compafila Minera Altiplano;GuillermoAbele of CENTROMIN; Joseph . Kova•ik,formerly of UNRF, Arequipa; Gregorio Flores andGuillermo Diaz of INGEMMET; Ralph Ellison,formerlyof Proyecto ntegradodel Sur (BritishGeo-logicalSurvey/INGEMMET);Alain Cheilletz of the
Centre de RecherchesP•trographiqueset G•ochi-miques,Nancy;and Crist(>balMiletich, JuanSaldar-riaga,Guido Arroyo,andJacintoValenciaof IPEN.
An early report and samples ollectedby RonaldC. R. Robertson rovedof greatvalue o ourresearch.Alain Cheilletz alsoprovided wo samplesrom theMacusanirea.Samplesor 4øAr/3•Aratingwere r-radiatedat the McMaster University,Hamilton, Can-ada,reactor.Pirjetta Atva, Ela RusakMazur, and Mi-chaelGerasimoff repared he illustrationsndSheilaMcPherson,Linda Anderson, nd particularly,Diane
Parrpatientlyyped hemanuscript,he nitialversionof which was mprovedby the comments f threeEconomicGeology eviewers.
This paper s a contributiono the Queen'sUni-versity Central Andean MetallogeneticProject(CAMP).
REFERENCES
Aberg,G., Aguirre, ., Levi, B., andNystr6m, . O., 1984,Spreading-subsidencendgeneration f ensialiemarginal asins:An example rom the Early Cretaceous f central Chile: Geol.Soc.LondonSpec.Pub. 16, p. 185-193.
Ahlfeld,F., 1974, Neue Beobachtungeniber die Tektonikunddie Antimonlagerst•ttenoliviens: eol.Bundsehau,. 9, p.125-131.
Ahlfeld,F., andSehneider~Scherbina,., 1964,Losyaeimientosminerales de hidroearburose Bolivia: a Paz,Depto.Nae.Geolog•a, ol. 5, 388 p.
Amosse, ., and Audebaud,E. J. M., 1978, Corrblations ntre lesmin•ralisations u Sud p•ruvien et les tencursen •l•mentstraces es oches•ruptives: eol.Bundschau,. 67, p. 253-270.
Arenas, M. J., 1977, Minas Santa Barbara, reservasde mineral,posibilidades,lande exploracionesdesarrollos:ima, Peru,Minsur, S.A., unpub. rept., 44 p.
-- 1980, E1 distrito minero San Rafael, Puno: Estafio en el
Per6: Soc.Geol. Per6 Bol., v. 6, p. 1-12.-- 1985, Prospecto (•sica: ima, Peru, Minsur,S.A., unpub.
rept., 4 p.
-- 1988,Evaluaci6n eoecon6micae aspropiedades inerasde J. S. Ortega Reyes: Mina Lulita, Sta. Mestres, Aladino 6,Mina Santiaguito, Carmen Lorena 2, Puno: Lima, Peru, Minsur,S.A., unpub. rept., 45 p.
Arribas,A., andFigueroa,E., 1985, Lasmineralizacionese uranioen as ocas olcanicaseMacusani,uno Peril): studios eol.,v. 41, p. 323-341.
Atherton, M.P., Pitcher, W. S., and Warden, V., 1983, The Me-
sozoicmarginal asinof centralPeru:Nature,v. 305, p. 303-
306.Atkin, B. P., Injoque-Esquinoza,. L., andHarvey,P. K., 1985,
Cu-Fe-amphibole ineralizationn the Arequipa egment,nPitcher,W. S., Atherton,M.P., Cobbing,E. J., andBeckinsale,R. D., eds., Magmatism t a plate edge:The PeruvianAndes:Glasgow, lackie,p. 261-270.
Audebaud,E. J. M., and Amosse, ., 1981, Distributionof traceelementsn igneousocksof PeruvianAndes--metallogenicimplications:ssoc. etroleumGeologiststudies eology, .12, p. 55-61.
Audebaud,E. J. M., andLaubacher,G., 1969, Surune discordancetardihercyni•nne dans a Cordill,re Orientale du Sud P•rou:Acad.Sci., Paris]Comptes endus, . 269, p. 2163-2166.
Audebaud,. J.M., Laubacher,., andMarocco, ., 1976,Coupeg(•ologiqueesAndes u Sudde P•rou de l'Oc(•an acifiqueaubouclierBr•silien:Geol.Rundschau,. 65, p. 213-264.
Bailey, .C., Larsen, . M., andSorensen,., 1981,The limaussaqintrusion, outhGreenland: progresseporton geology,min-eralogy, eochemistryndeconomiceology: ronlands eol.Unders6k.Rap., no. 103, 130 p.
Baker,M. C. W., andFrancis, . W., 1978,UpperCenozoic ol-canism n the centralAndes--agesandvolumes: arth Planet.Sci. Letters, v. 41, p. 175-187.
Barnes,A. E., Edwards,G., McLaughlin, W. A., Friedman, F.,andJoensuu, ., 1970, Macusanite ccurrence, ge,andcom-position:Geol. Soc.AmericaBull., v. 81, p. 1539-1546.
Barreiro,B. A., and Clark, A. H., 1984, Lead sotopic videncefor evolutionary hangesn magma-crustnteraction,centralAndes, outhern eru:EarthPlanet.Sci.Letters,v. 69, p. 30-42.
Bateman,P. W., 1982, Mineralogy,vein texturesand fluid inclu-sionstudiesof the Condoriquifia nd SantoDomingo in-basemetal deposits, E Peru, with a comparisono the SanRafaeltin-copper deposit:Unpub. B.Sc. thesis, Kingston,Queen'sUniv., 158 p.
Beckinsale, . D., Sanchez-Fernandez, . W., Brook,M., Cobbing,E. J., Taylor, W. P., andMoore, N. D., 1985, Rb-Srwhole-rock
isochron ndK-Ar agedeterminationsor the Coastalbatholithof Peru, in Pitcher, W. S., Atherton, M. P., Cobbing,E. J., andBeckinsale, . D., eds.,Magmatism t a plateedge:The PeruvianAndes:Glasgow,Blackie,p. 177-202.
Benavides, ., 1984, Ocurr•nciade la plataen el Peril:Minerla,no. 180, p. 5-10.
Berger,G. W., 1975, 4øAr/a9Artepheatingof thermallyover-printedbiotite,hornblende ndpotassiumeldsparromEldora,Colorado:Earth Planet.Sci. Letters, v. 26, p. 387-408.
Boily, M., Brooks,C., andJames,D. E., 1984, Geochemical har-acteristics of the late Mesozoic Andean volcanics, in Harmon,
R. S., and Barreiro,B. A., eds.,Andeanmagmatism: hemicaland isotopic constraints:Nantwich, U.K., Shiva Pub. Ltd., p.190-202.
Bonhomme, M. G., Audebaud, E., and Vivier, G., 1985, EdadesK-Ar de rocasherclnicasy ne6genasde un perfll E-W en elPeril meridional:Univ. Chile, Dept. Geologla,Commun. no.35, p. 27-30.
Bonhomme, M. G., Fornari, M., Laubacher, G., S•brier, M., andVivier, G., 1988, New Cenozoic K-Ar ageson volcanicrocksfrom the eastern High Andes, southern Peru: Jour. SouthAmericanEarth Sci., v. 5, p. 179-183.
Bowman, I., 1916, The Andes of southern Peru: New York, Am.Geog. Soc., 336 p.
Brendler,W., 1934, Sodalite rom Bolivia:Am. Mineralogist, .19, p. 28-31.
Burt, D. M., and Sheridan,H. F., 1988, Mineralization associatedwith topaz rhyolitesandrelated ocks n Mexico:Canadiannst.Mining MetallurgySpec.Vol. 39, p. 303-306.
Cande,S.C., 1983, Nazca-South merica late nteraction: 0m.y.B.P. to present abs.: AmericanGeophys.UnionTrans.,v. 64, p. 865.
Candiotti, ., 1988,Progresosn el conocimientoe a geologlay tf•cnicase exploraci0n e yacimientose Ag y Au en am-bientes olcanicosenozoicos:oc.Geol.PerilBol.,v. 78, p.1-21.
Candiotti,H., and Castilia,F., 1983, G•nesisdel yacimiento eCu y Ag, Berenguela, ampa,Puno:Soc.Geol. Per6 Bol., no.71, p. 79-90.
Candiotti,H., and Guerrero,T., 1983, Ocurr•nciade un yaci-miento ipo albita-greisene Cu-W-Sny Mo--Carabaya-Puno:Soc.Geol. Peril Bol., no. 71, p. 69-78.
Carey, S. W., 1958, The oroclineconcept n geotectonics: oyalSoc. Tasmania Proc., v. 89, p. 255-288.
Carlier, G., Grandin,G., Laubacher,G., Marocco,R., and M•gard,F., 1982, Presentknowledgeof the magmaticevolution of theEasternCordillera of Peru: Earth-Sci.Rev., v. 18, p. 253-283.
Carmichael, D. M., 1978, Metamorphic bathozonesand batho-grads:A measureof the depth of post-metamorphic plift anderosion on the regional scale:Am. Jour. Sci., v. 278, p. 769-797.
Castor, S. B., and Berry, M. R., 1981, Geology of the Lakeviewuranium district, Oregon: Studies n Geology,no. 13, p. 55-62.
Cheilletz, A., Clark, A. H., Farrar, E., Arroyo, G., MacArthur,J. D., andPichavant,M., 1990, Stratigraphy nd geochronologyof the Macusani gnimbrite field: Chronometerof the Mio-Plio-cene geodynamic volutionof the Andesof SE Peru [ext. abs.]:Internat. G•odynamique Andine Symposium, Colloques etS•minaires, Grenoble, May, 1990, p. 341-344.
Cheilletz, A., Clark, A. H., Farrar, E., Arroyo, G., and Pichavant,M., in press,Stratigraphy nd4øAr/3•Ar eochronologyf theMacusani gnimbrite field: Chronometer of the Miocene geo-dynamicevolution of the Andes of SE Peru: Tectonophysics.
Clark, A. H., 1982, Petrochemical onstraints n metallogeneticspecialization, entralAndes:A workinghypothesisabs.I:Geol.
Assoc.CanadaProgramwith Abstracts, . 7, p. 43.Clark, A. H., and McNutt, R. H., 1982, Interrelated arc-broad-
ening, topographicuplift and crustalcontamination f magmasin two transectsof the Mesozoic-Cenozoic entral Andes [ext.abs.]: nternat. Conf. Geochronology,Cosmochronology,so-tope Geology, 5th, Nikko, Japan,June 27-July 2, 1982, Abs.Vol., p. 55-57.
Clark, A. H., and Zentilli, M., 1972, The evolution of a metallo-
genetic province at a consumingplate margin: The Andes be-tween latitudes 26 ø and 29 ø south [ext. abs.]: Canadian nst.Mining Metallurgy Bull., v. 65, no. 719, p. 37.
Clark, A. H., Farrar, E., Haynes,S. J., Quirt, G. S., Conn, H., andZentilli, M., 1970, K-Ar chronologyof granite emplacementandassociated ineralization, opiapt5miningdistrict,Atacama,Chile [abs.]:ECON.GEOL.,v. 65, p. 736.
Clark, A. H., Farrar, E., Caelles, J. C., Haynes, S. J., Lortie,
R. B., McBride, S. L., Quirt, G. S., and Zentilli, M., 1973, Themagmatic, ectonic and metallogenetic volution of the centralAndeanmobilebelt between latitudes26 ø and 29 ø S [ext. abs.]:Internat. Union Geodesy GeophysicsConference on Geody-namics, Lima, Aug. 22-28, 1973, p. CGD-44.
Clark, A. H., Farrar, E., Caelles, J. C., Haynes, S. J., Lortie,R. B., McBride, S. L., Quirt, G. S., Robertson,R. C. R., andZentilli, M., 1976, Longitudinalvariations n the metallogenicevolutionof the centralAndes:A progress eport: Geol. Assoc.CanadaSpec.Paper 14, p. 23-58.
Clark, A. H., Kontak, D. J., and Farrar, E., 1983a, Evolution ofthe centralAndeanmagmatic rcs abs.I:Am. Geophys.UnionTrans., v. 64, p. 326.
Clark, A. H., Palma,V. V., Archibald, D. A., Farrar, E., and Arenas,M. J., 1983b, Occurrence and age of tin mineralization n theCordilleraOriental, southern eru:ECON.GEOL., . 70, p. 514-520.
Clark, A. H., Kontak, D. J., and Farrar, E., 1984, A comparativestudyof the metallogenetic nd geochronologicalelationshipsin the northern part of the central Andean tin belt, SE Peruand NW Bolivia, n Janelidze,T. V., and Tvalchralidze,A. G.,eds., Proceedings f the sixthquadremial AGOD symposiumheld in Tbilisi, USSR, September 6-12, 1982: Stuttgart, E.Schweizerbart'sche, . 267-279.
Clark, A. H., Johnson, . L., and Wasteneys,H. A., 1986, Phreaticbrecciasassociatedwith epithermal silver deposits,southernPeru: Petrology, ime-space elationships nd implications orexploration ext. abs.]:Terra Cognita, v. 6, p. 495.
Clark, A. H., Kontak, D. J., and Farrar, E., 1990a, The SanJudasTadeo W(-Mo,Au) deposit: Permian lithophile mineralizationin southeasternPeru: ECON. GEOL., v. 85, p. 1651-1668.
Clark, A. H., Tosdal, R. M., Farrar, E., and Plazolles, A., 1990b,
Geomorphological nvironmentand age of supergene nrich-ment of the Cuajone, Quellaveco, and Toquepala porphyrycopper deposits, southeasternPeru: ECON. GEOL., v. 85, p.1604-1628.
Colley, H., Treloar, P. J., and Diaz, F., 1989, Gold-silvermin-eralization in the E1 Salvador region, northern Chile: ECON.GEOL. MON. 6, p. 208-217.
Coney,P. J., andReynolds, . J., 1977, CordilleranBenioffzones:Nature, v. 270, p. 403-406.
Cordani, U. G., Kawashita,K., Siegl, G. G., and Vicente, J. C.,1985, Geocronolog•a el extremo surestedel Macizo de Are-quipa:Santiago,Univ. Chile, Dept. Geologla,Comun.,no. 35,p. 45-51.
Dallmeyer,R. D., 1975, 4øAr/3•Ar gesof biotiteandhornblendefrom a progressivelyemetamorphosed asement errane:Theirbearingon interpretationof releasespectra:Geochim.et Cos-mochim. Acta, v. 39, p. 1655-1669.
Dallmeyer, R. D., and Rivers,T., 1983, Recognitionof the extra-neous rgon omponentshroughncrementalelease øAr/•Aranalyses f biotite and hornblende across he Grenville meta-
morphicgradient n southwestern abrador:Geochim.et Cos-mochim. Acta, v. 47, p. 259-274.
Dalmayrac,B., Laubacher,G., and Marocco,R., 1980, G•ologiedes Andes P•ruviennes: Paris, Office Reserche ScientifiqueTechniqueOutre-Mer, 501 p.
De las Casas,F., and Ponzoni, E., 1969, Mapa metalogen•ticodel Per(l: Lima, Peru, Soc. Nac. Minerla Petr61eo.
de Silva, S. L., and Francis,P. W., 1990, Potentiallyactive vol-canoesof Peru--observationsusingLandsat hematicmapperand space huttle magery:Bull. Volcanol.,v. 52, p. 286-301.
Dodson,M. H., 1973, Closure emperature n coolinggeochro-nological nd petrological ystems: ontr. MineralogyPetrol-ogy, v. 40, p. 259-274.
Dostal, J., Zentilli, M., Caelles, J. C., and Clark, A. H., 1977,Geochemistry nd origin of volcanic ocksof the Andes (26-28 ø S): Contr. MineralogyPetrology,v. 63, p. 113-128.
Douglas,J. A., 1920, Geologicalsection hrough the Andes ofPeru and Bolivia: I. From the port of Mollendo to the InambariRiver: Geol. Soc.LondonJour., v. 76, p. 1-61.
Ellison, R. A., Klinck, B. A., and Hawkins, M.P., 1989, Defor-mation events n the Andean orogeniccycle in the AltiplanoandWesternCordillera,southernPeru: Jour.SouthAmericanEarth Sci., v. 2, p. 263-276.
Erickson,G. E., 1980, Metallogenesisn the Andes: UGS Internat.Symposium, eb. 3-6, 1980, M•xico D.F., Pub. 5, p. 289-311.
Erickson,G. E., Eyzaguirre,V. R., Urquidi,F., andS• as,P., 1987,Neogene-Quaternaryvolcanism nd mineralization n the cen-tral Andes, in IUGS/UNESCO Deposit Modelling ProgramWorkshop,Santiago,Chile, Nov. 9-18, 1987, workshopnote-book, p. 1-12.
Estrada,F., 1975, Geologlade Quellaveco:Geol. Soc.Peril Bol.,v. 46, p. 65-86.
Evernden,J. F., Kriz, S. J., andCherroni,M. C., 1977, Potassium-argonagesof someBolivian ocks:ECON.GEOL., . 72, p. 1042-1061.
Farrar, E., Clark, A. H., Haynes,S. J., Quirt, G. S., Conn, H., andZentilli, M., 1970, K-Ar evidence for the post-Paleozoicmi-grationofgranitic intrusion oci in the Andesof northern Chile:Earth Planet. Sci. Letters, v. 9, p. 17-28.
Farrar, E., Clark, A. H., Kontak, D. J., and Archibald, D. A., 1988,Zongo-SanGabfin one:Eocene orelandboundaryof the cen-tral Andean orogen, northwesternBolivia and southeastPeru:Geology,v. 16, p. 55-58.
Farrar, E., Clark, A. H., and Heinrich, S. M., 1990a, The age of
the Zongo pluton and the tectonothermalevolution of theZongo-San ab•mZone n the CordilleraReal,Bolivia ext.abs.]:Internat. G•odynamiqueAndine Symposium,Grenoble, May1990, Colloqueset S•minaires,p. 171-174.
Fartar, E., Yamamura,B. K., Clark, A. H., and Taipe, J., 1990b,4øAr/a9Argesof magmatismnd tungsten-polymetallicin-eralization, Palca 11, Choquene district, southeasternPeru:ECON. GEOL., v. 85, p. 1669-1676.
Fletcher, C. J. N., Hawkins,M.P., andTejada, R., 1989, Structuralcontrol and genesisof polymetallicdeposits n the Altiplanoand Western Cordillera of southernPeru: Jour.SouthAmericanEarth Sci., v. 2, p. 64-71.
Flores, G., Kihien, C., Figueroa,E., Arroyo, G., and Pizarro, B.,1983, E1 distrito uranlfero de Macusani--Departamento dePuno:Geol. Soc.Per6 Bol., v. 71, p. 143-158.
Fornari, M., and Bonnemaison, M., 1984, Mantos et amas sulfo-arseni• 5.or: la Rinconada,premier indice de min•ralisationdetype exhalatif-s•dimentairedans la Cordill're Orientale duP•rou: Chron. Recherche Miniere, no. 474, p. 33-40.
Fornari, M., and Vilca, N. C., 1977, Mineralizaci6nargentlferaasociada l volcanismocenozoicoen la faja Puquio-Cailloma:Soc. Geol. Per6 Bol., v. 60, p. 101-128.
Fornari, M., H•rail, G., and Laubacher, G., 1982, E1 oro en la
CordilleraSur-Orientaldel Per6: el placer luvio-glacial e SanAntoniode Potoy sus elaciones on a mineralizaci6n rimeriade la Rinconada:Cong. LatinoamericanoGeologia,5th, BuenosAires, Argentina, Actas, v. 4, p. 369-386.
Fornari, M., H(•rail, G., Laubacher, G., and Delaune, M., 1988,
Les gisements 'or des Andes sud-orientales u P•rou: G•o-dynamique,v. 3, p. 139-161.
France,L. J., 1985, Geochronology, tratigraphy ndpetrochem-istry of the upper Tertiary volcanic arc, southernmostPeru,central Andes:Unpub. M.Sc. thesis,Kingston,Queen's Univ.,182 p.
France,L. J., Clark, A. H., andFarrar,E., 1984, Geochronologicaland petrologicalstudiesof Tertiary igneous ocks,CordilleraOccidental, southernmostPeru: A preliminary report: Lima,Peru, Inst. GeologicoMineria Metalurgicounpub. rept., 28 p.
Francis, G. A., 1956, La geolog•ade la zona entre MacusaniyOllachea,Departamento de Puno: nst. Nac. Inv. Fomento Mi-nero [Peru] Bol. 21, p. 13-32.
Fuchs, F. C., 1898, Estudio sobre a regi6n aurlfera de SantoDomingo en la provlnciade Carabaya:Minas, nd6striasCon-strucciones Lima] Bol., v. 14 and 15,
Garcia,W., 1968, Geologlade los cuadrS.gulosde Mollendo yLa Joya (Hojas 34-r, 34-s): Servicios Geol. Minerla Peru Bol.19, 95p.
Garcia,W., andGuevara,C., 1975, Mapa geo16gicoel cuadr•tn-gulo de Huaitire (1:100,000): Lima, Peru, Inst. Geol. Minerla.
Girard, K. A., 1984, Mineralogyand paragenesis f Mina Cecilia,a Pb-Zn-Agdeposit n SEPeru:Unpub.B.Sc. hesis,Kingston,Queen's Univ., 76 p.
Goodell,P. C., and Waters, A. C., 1981, eds.,Uranium n volcanicand volcaniclasticocks:Studies n Geology,no. 13, 331 p.
Grant,J.,Halls,C., Avila,S.W., andSnelling, ., 1979, KoAr gesof igneousocks ndmineralizationn partof the Bolivianinbelt: ECON. GEOL., v. 74, p. 838-851.
Guerrero, T., 1980, Geologla del ProspectoSarita: Lima, Soc.Explor.del Sur SOCSUR), npub. ept., 16 p.
Gustafson,L. B., and Hunt, J.P., 1975, The porphyry copperdeposit t E1Salvador, hile:ECON.GEOL., . 70, p. 857-912.
Halls, C., and Schneider,A., 1988, Comentarios obre a g•nesisde los yacimientosdel Cintur6n Estanifero Boliviano: Rev.Geologia Chile, v. 15, p. 41-56.
Handschumacher,D. W., 1976, Post-Eoceneplate tectonics ofthe easternPacific:Am. Geophys.Union Geophys.Mon. Ser.,v. 19, p. 177-202.
Hannington,M.P., 1983, Mineralogy nd paragenesisf VetaNazareth, SE Peru: Unpub. B.Sc. thesis, Kingston, Queen'sUniv., 87 p.
Harrison, . M., andMcDougall,., 1982,The hermal ignificanceof potassiumeldspar -Ar ages nferred rom4øAr/agArgespectrum esults:Geochim. t Cosmochim. cta,v. 46, p. 1811-1820.
Harmon, R. S., Barreiro, B. A., Moorbath, S., Hoefs, J., Francis,P. W., Thorpe, R. S., D•ruelle, B., McHugh, J., and Viglino,J.A., 1984,RegionalO-Sr-,andPb-isotopeelationshipsn lateCenozoic calc-alkaline lavas of the Andean cordillera: Geol.
Soc. London Jour., v. 141, p. 803-822.Haynes,S. J., 1975, Granitoidpetrochemistry, etallogeny, nd
lithosphere late tectonics,Atacama rovince,Chile: Unpub.Ph.D. thesis, Kingston, Queen's Univ., 330 p.
Heald, P., Hayba, D. O., and Foley, N. K., 1987, Comparativeanatomyof volcanic-hostedpithermaldeposits: cid-sulfateand adularia-sericite ypes: ECON. GEOL., v. 82, p. 1-26.
Heinrich, S. M., 1988, Geologyand geochronologyf the ZongoRiver Valley, CordilleraOriental, NW Bolivia:Unpub.M.Sc.thesis,Kingston,Queen's Univ., 185 p.
Heinrich, S. M., Farrar, E., Clark, A. H., Archibald, D. A., andParrish,R. R., 1988, Age, uplift and thermalevolutionof theZongopluton [abs.]:Am. Geophys.UnionTrans.,v. 69, no. 16,p. 487.
Hildreth, W., and Moorbath, S., 1988, Crustal contributions oarcmagmatismn the Andes f centralChile:Contr.MineralogyPetrology,v. 96, p. 455-489.
Huene, R. van, and Lallemand, S., 1990, Tectonic erosionalongthe Japanand Peru convergentmargins:Geol. Soc. AmericaBull., v. 102, p. 704-720.
Injoque, J., Atkin, B., Harvey, P., and Snelling,N. L., 1988,,Mi-neraloglay geocronologla el skarngeothermalde hierro deMarcona: Soc. Geol. Per6 Bol., v. 78, p. 65-80.
Isacks,B. L., 1988, Uplift of the central Andean plateau andbending of the Bolivian orocline: Jour. Geophys.Research,v.93, no. B4, p. 3211-3231.
Ishihara,S., 1977, The magnetite-seriesnd lmenite-series ra-nitic rocks:Mining Geology,v. 27, p. 293-305.
Jain, H., 1965, Geolog•a el Cuadr•tngulo e Tarata (Hoja 35-v):Lima, Comisi6nCarta Geol. Nac., Bol. 11, 91 p.
James,D. E., 1971a, Plate ectonicsmodel or the evolutionofthe central Andes: Geol. Soc. America Bull., v. 82, p. 3325-3346.
-- 1971b, Andean crustaland upper mantle structure:Jour.Geophys.Research,v. 84, p. 3246-3271.
James,D. E., Brooks,C., and Cuyabamba, ., 1974, Strontiumisotopic omposition nd K, Rb, Sr geochemistry f Mesozoicvolcanic ocksof the CentralAndes:Carnegie nst. WashingtonYear Book, v. 73, p. 970-983.
Jenks,W., 1946,Preliminary oteongeologictudies f hePacificslope n southernPeru: Am. Jour. Sci., v. 244, p. 367-372.
Johnson, . L., 1986, The Cacachara pithermalsilverdeposit,Puno Department, southernmost eru: Unpub. M.Sc. thesis,Kingston, Queen's Univ., 171 p.
Jordan,T. E., Isacks,B. L., Allmendinger,R. W., Brewer, J. A.,Ramos,V. A., andAndo, C. J., 1983, Andean ectonics elatedto geometry f subductedazcaPlate:Geol.Soc.America ull.,v. 94, p. 341-361.
Kaneoka, ., and Guevara, C., 1984, K-Ar age determinationsofthe late Tertiary and Quaternary Andeanvolcanic ocks,south-ern Peru: Geochem. Jour., v. 18, p. 233-240.
Karup-Moller, S., 1974, Mineralogy of two copper-antimony-sul-phide-oxideoccurrencesrom the Ilimaussaq lkaline ntrusionin southGreenland:Neues Jahrb. Mineralogie, Abh., v. 122,p. 291-315.
Keppie, J. D., Boyle, R. W., and Haynes, S. J., eds., 1986, Tur-
bidite-hostedgold deposits:Geol. Assoc.CanadaSpec.Paper32, 186 p.
Kiilsgaard,J., and Bellido, E., 1959, Plan regional para el Desar-rollo del Stir del Perfl. Los Recursos Minerales, vol. II: Infotree
PS/A/S: Lima, Peru, Servicio Coop. Interamericano, 150 p.Klinck, B. A., Ellison,R. A., and Hawkins, M.P., compilers,1986,
The geology of the Cordillera Occidental and Altiplano westof Lake Titicaca,southernPeru:Lima, Peru, BritishGeol. SurveyInst. Geo16gicoMinero Metalfirgico, 353 p.
Kono, M., Fukao, Y., and Yamamoto,A., 1989, Mountainbuildingin the Central Andes: Jour. Geophys. Research, v. 94, no. B4,p. 3891-3905.
Kontak, D. J., 1985, The magmaticand metallogeneticevolutionof a craton-orogennterface: he Cordillerade Carabaya,CentralAndes,SE Peru: Unpub. Ph.D. thesis,Kingston,Queen'sUniv.,714p.
Kontak,D. J., and Clark, A. H., 1988, Explorationcriteria for tinand ungstenmineralization n the Cordillera Oriental of south-easternPeru: Canadian nst. Mining Metallurgy Spec.Vol. 39,p. 157-169.
Kontak, D. J., Clark, A. H., and Farrar, E., 1984, The magmaticevolution of the Cordillera Oriental, southeasternPeru, in Har-
mon, R. S., and Barreiro, B. A., eds., Andean magmatism:Chemical and isotopicconstraints:Nantwich, ShivaPub. Ltd.,p. 203-219.
Kontak, D. J., Clark, A. H., Farrat, E., and Strong, D. J., 1985,The rift-associatedPermo-Triassicmagmatismof the EasternCordillera: A precursor to the Andean orogeny, in Pitcher,W. S., Atherton, M.P., Cobbing, E. J., and Beckinsale,R. D.,eds.,Magmatism t a plate edge:The PeruvianAndes:Glasgow,Blackie, p. 36-44.
Kontak, D. J., Clark, A. H., Farrar, E., Pearce, T. H., Strong,
D. F., and Baadsgaard,H., 1986, Petrogenesisof a Neogeneshoshonite suite, Cerro Moromoroni, Puno, SE Peru: Canadian
Mineralogist, v. 24, p. 117-135.
Kontak, D. J., Clark, A. H., Fartar, E., Archibald, D. A., andBaadsgaard,H., 1987, Geochronological data for Tertiarygranitesof the southeastPeru segmentof the central Andeantin belt: ECON. GEOL., v. 82, p. 1611--1618.
Kontak, D. J., Cumming, G. L., Krstic, D., Clark, A. H., and Farrar,E., 1990a, Isotopic compositionof lead in ore depositsof theCordillera Oriental, southeasternPeru: ECON. GEOL.,v. 85, p.1584-1603.
Kontak, D. J., Smith, P. K., Kerrich, R., and Williams, P. F., 1990b,Integrated model for Meguma Group lode gold deposits,NovaScotia,Canada:Geology, v. 18, p. 238-242.
Kontak, D. J., Clark, A. H., Farrar, E., Archibald, D. A., and
Baadsgaard,H., 1990c, Late Paleozoic-early Mesozoic mag-matism n the Cordillerade Carabaya,Puno,southeastern eru:Geochronology nd petrochemistry: our.SouthAmericanEarthSci., v. 3, p. 213-230.
Kontak,D. J., Farrar, E., Clark, A. H., andArchibald,D. A., 1990d,Eocene tectonothermal rejuvenation of an upper Paleozoic-lower Mesozoic terrain in the Cordillera de Carabaya, Puno,SE Peru, revealedby K-Ar and 4øAr/39Arating:Jour.SouthAmerican Earth Sci., v. 3, p. 231-246.
Kussmaul,S., Jordan,L., and Plaskonka,E., 1975, Isotopic agesof Tertiary volcanic ocksof SW Bolivia:Geol. Jahrb.,sec.B,v. 14, p. 111-120.
Lancelot,J. R., Laubacher,G., Marocco,R., andRenaud,V., 1978,
U/Pb radiochronology f two graniticplutons rom the easterncordillera (Peru). Extent of Permianmagmaticactivity and con-sequences:Geol. Rundschau,v. 67, p. 236-243.
Laubacher,G., 1978a, G•ologie de la Cordill're Orientale et del'Altiplano au nord et au nord-ouestdu Lac Titicaca (P•rou):ORSTOM, Trav. Doc., v. 95, 217 p.
-- 1978b, Estudio geo16gico e la regi6n norte del Lago Ti-ticaca: nst. GeologicoMinerla [Peru] Bol. 5, 120 p.
Laubacher, G., S•brier, M., Fornari, M., and Carlier, G., 1988,Oligocene and Miocene continental sedimentation, ectonics,and S-type magmatismn the southeastern ndesof Peru (Cru-cero basin): Geodynamic mplications:Jour. South AmericanEarth Sci., v. 1, p. 225-238.
Laughlin, A. W., Damon, P. E., and Watson, B. N., 1968, Potas-sium-argon ates rom ToquepalaandMichiquillay,Peru:ECON.GEOL., v. 63, p. 166--168.
Lavenu, A., 1986, Etude tectonique et n(•otectoniquede l'Alti-plano et de la Cordill're Orientale desAndesBolivi•nnes:Un-pub. th•se, Doct. Sci., France, Univ. Paris-Sud,420 p.
Lavenu, A., Bonhomme,M. G., Vatin-Perignon, N., and De Pach-tere, P., 1989, Neogene magmatism n the Bolivian Andesbe-tween 16 ø and 18 ø S: Stratigraphy and K/Ar geochronology:Jour. South AmericanEarth Sci., v. 2, p. 35-47.
Lef&vre, C., 1973, Les caract;•resmagmatiquesdu volcanisme
Plio-Quaternaire des Andesdans e sud du P(•rou:Contr. Min-eralogy Petrology, v. 41, p. 259-272.
Lehmann, B., 1978, A Precambriancore sample from the Alti-plano, Bolivia: Geol. Rundschau, . 67, p. 270-278.
Lindgren, W., 1933, Mineral deposits, 4th ed., New York,McGraw-Hill Book Co., 930 p.
Lo, C.-H., and Onstott,T. C., 1989, a9Ar ecoil effects n chlo-ritized biotite: Geochim. et Cosmochim.Acta, v. 53, p. 2697-2711.
Longstaffe,F. J., Clark, A. H., McNutt, R. H., and Zentilli, M.,1983, Oxygen sotopecompositions f central Andeanplutonicand volcanic rocks, latitudes 260-29 ø S: Earth Planet. Sci. Let-
ters, v. 64, p. 9-18.
Lyon-Caen, H., Molnar, P., and Suarez, G., 1985, Gravity anom-alies and flexure of the Brazilian Shield beneath the Bolivian
Andes:Earth Planet. Sci. Letters, v. 75, p. 81-92.
Maksaev,V., and Zentilli, M., 1988, Marco metalog(•nicoegionalde losmegadep6sitose tipo p6rfidocuprifirodel Norte Grandede Chile: Cong. Geol. Chileno Primeras ornadas eofisica, th,Santiago,Chile, Aug. 8-12, 1988, Actas,v. 1, p. B181-212.
Maksaev,V., Zentilli, M., and Reynolds,P. H., 1988a, Geochro-nolog•a øAr-a9Are dep6sitos e tipo p6rfidocuprlferodelNorte Grande de Chile: Cong. Geol. Chileno PrimerasJornadasGeoflsica, 5th, Santiago,Chile, Aug. 8-12, 1988, Actas, v. 1,p. B109-B134.
Maksaev,V., Boric, R., Zentilli, M., and Reynolds,P. H., 1988b,Significado etalog(•nicoe dataciones-Ar,4øAr-a9Artrazasde fisi6n de zonas mineralizadas en el Norte Grande de Chile:
Cong. Geol. Chileno Primeras ornadas eo•sica, 5th, Santiago,Chile, Aug. 8-12, 1988, Actas,v. 1, p. B65-B86.
Manrique, J., and Plazolles, A., 1975, Geologla de Cuajone: Soc.Geol. Per(• Bol., v. 46, p. 137-150.
Marocco,R., andDel Pino,L. M., 1966, Geologfa el Cuadr/tngulode Ichufia: (Hoja 33-u): Comisi6nCarta Geol. Nac. [Perfi] Bol.14, 57 p.
Marocco, R., and Noblet, C., 1990, Sedimentation, tectonism andvolcanism elationshipsn two Andeanbasinsof southernPeru:Geol. Rundschau, . 79, p. 111-120.
M•rquez, W. G., 1978, Geologlade loscuadr•ngulosde Puquina,Omate, Huaitire, Mazo Cruz y Pizacoma, Hojas: (34-t), (24-t),(34-v), (34-x), (34-y): Inst. Geol. Minerla [Peru] Bol. 29, 63 p.
McBride, S. L., 1972, A potassium-argon ge nvestigationof ig-neous and metamorphic rocks from Catamarca and La Riojaprovinces,Argentina: Unpub. M.Sc. thesis,Kingston,Queen'sUniversity, 101 p.
-- 1977, A K-Ar study of the Cordillera Real, Bolivia, and itsregional etting:Unpub.Ph.D. hesis,Kingston, ueen'sUniv.,231 p.
McBride, S. L., Robertson,R. C. R., Clark, A. H., and Farrar, E.,1983, Magmaticand metallogenetic pisodes n the northerntin belt, CordilleraReal, Bolivia:Geol. Rundschau, . 72, p.685-713.
McBride, S. L., Clark, A. H., Farrar, E., and Archibald, D. A.,
1987, Delimitationof a crypticEocene ectono-thermal omainin the EasternCordilleraof the BolivianAndes hroughK-Ardating nd4øAr/a"rstep-heating:eol.Soc.London our.,v.144, p. 243-255.
McKee, E. H., and Noble, D.C., 982, Miocene volcanism and
deformation n the westernCordillera and high plateausofsouth-central eru: Geol. Soc.AmericaBull., v. 93, p. 657-662.
McNutt, R. H., Crockett,J. H., Clark, A. H., Caelles, . C., Farrar,E., Haynes,S. J., andZentilli, M., 1975, Initial 87Sr/86Sratiosof plutonic and volcanicrocks of the central Andes betweenlatitudes26ø and 29ø S: Earth Planet.Sci. Letters, v. 27, p.305-313.
M•gard, F., 1984, The Andeanorogenic eriod and its majorstructuresn centralandnorthernPeru:Geol.Soc.London our.,v. 141, p. 893-900.
-- 1987, Structure and evolution of the Peruvian Andes, inSchaer,J.P., and Rodgers, ., eds.,The anatomyof mountainranges: Princeton, Princeton Univ. Press, p. 179-210.
-- 1988, The evolutionof the PacificOceanmargin n SouthAmericanorth of Africa elbow (18 ø S):New York, OxfordUniv.Press,Mon. GeologyGeophys.no. 8, p. 208-225.
M•gard, F., Dalmayrac,B., Laubacher,G., Marocco,R., Martinez,C., Paredes, ., andTomasi,P., 1971, La chaTne ercynni?•nneau P•rou et en Bolivia: Premier resultats:ORSTOM Cahiers,S6r. G•ol., v. 3, p. 5-43.
M•gard, F., Noble, D.C., McKee, E. H., and Bel16n,H., 1984,Multiple pulsesof Neogenecompressive eformation n theAyacucho ntermontane basin,Andes of central Peru: Geol. Soc.America Bull., v. 95, p. 1108-1117.
Mendlvil,S., 1965, Geologla e oscuadr•tngulose Maurey An-tajave (Hojas35-x, 35-y): Peril, Com. Carta Geol. Nac. Bol. 10,99 p.
Michel, H., andSchneider,H.-J., 1978, Uranvorkommenm Zu-sammenhangmit den Tertiiiren Vulkaniten des ateinamerikan-ischenKordillerenzuges:rzmetall, . 31, p. 1-8.
Miller, J. F., andHarris, N. B. W., 1989, Evolutionof continentalcrust n the centralAndes; onstraintsromNd isotope ystem-at/cs:Geology,v. 17, p. 615-617.
Mukasa, .B., 1986,ZirconU-Pbages f super-unitsn the Coastalbatholith, eru: mplicationsor magmatic nd ectonic ro-cesses: eol. Soc.AmericaBull., v. 97, p. 241-254.
Mukasa,S. B., andHenry, D. J., 1990, The SanNicol•ts atholithof coastal eru:Early Paleozoic ontinental rc or continentalrift magmatism?:eol.Soc.London our.,v. 147, p. 27-40.
Mukasa,S. B., andTilton, S. R., 1984, Lead sotope ystematicsin batholith ocksof the WesternandCoastalCordilleras, eru,
in Harmon,R. S., andBarreiro,B. A., eds.,Andeanmagmatism:Chemicaland sotopic onstraints: antwich,U.K., ShivaPub.Ltd., p. 180-189.
Munizaga,F., Huete, C., and Herve, F., 1985, GeochronologiaK-Ary razonesniciales rS7/Sr6de a "FajaPacifica" e "De-sarrollos idrothermales:"ong.Geol.Chileno,Antofagasta,Chile, August 5-17, 1985, Actas, . 3, p. 357-379.
Naeser, C. W., McKee, E. H., Johnson,N. M., and MacFadden,B. J., 1987, Confirmationof a late Oligocene-earlyMioceneageof the DeseadeanallaBedsof Bolivia: our.Geology, .95, p. 825-828.
Narv•tez, ., 1964, Geologla e oscuadr•tngulose lo y Locumba(Hojas36-t y 36-u): Peru Com. CartaGeol. Nac., Bol. 7, 75 p.
Narv•tez,S., and Garcia, W., 1962, Mapa geo16gico el cuadr•m-gu ode Ilo (1:100,000): Peru Com. Carta Geol. Nac.
Newell, N. D., 1949, Geologyof the Lake Titicacaregion,Peruand Bolivia: Geol. Soc. America Mem. 36, 104 p.
Newell, N. D., Chronic,J., andRoberts, ., 1953, Upper Paleozoicof Peru: Geol. Soc. America Mem. 58, 276 p.
Noble, D.C., and McKee, E. H., 1977, Spatial distribution ofearthquakes nd subduction f the Nazcaplate beneathSouthAmerica: Comment: Geology, v. 5, p. 576-578.
-- 1982, Nevado Portuguezavolcaniccenter, central Peru: APliocene central volcano-collapse aldera complex with asso-ciated silvermineralization:ECON.GEOL.,v. 77, p. 1893-1900.
Noble, D.C., McKee, E. H., Farrar, E., and Petersen, U., 1974,Episodic Cenozoic volcanismand tectonism n the Andes ofPeru: Earth Planet Sci. Letters, v. 21, p. 213-220.
Noble, D.C., McKee, E. H., and M•gard, F., 1979, Early Tertiary"Incaic" tectonism,uplift, andvolcanic ctivity,Andesof centralPeru: Geol. Soc. America Bull., v. 90, p. 903-907.
Noble, D.C., Vogel, T. A., Petersen, P.S., Landis, G. P., Grant,N. K., Jesck, D. A., and McKee, E. H., 1984a, Rare-elementenriched, S-type ash-flow uffs containingphenocrysts f mus-covite, andalusiteand sillimanite,southeastern eru: Geology,v. 12, p. 35-39.
Noble, D.C., McKee, E. H., Eyzaguirre, V. R., and Marocco,R.,
1984b, Age and regional tectonic and metallogenetic mplica-tionsof igneous ctivityandmineralization n the Andahuaylas-Yauri belt of southernPeru: ECON.GEOL.,v. 79, p. 172-176.
Palma, V. V., 1981, The San Rafael tin-copper deposit, SE Peru:Unpub. M.Sc. thesis,Kingston,Queen'sUniv., 235 p.
Palmer, A. R. (compiler), 1983, The decadeof North Americangeology1983 geologic ime scale:Geology,v. 11, p. 503-504.
Parada, M. A., Rivano, S., Sepulveda, P., Herv•, M., Herve, F.,Puig, A., Munizaga,F., Brook, M., Pankhurst,R., and Snelling,N., 1988, Mesozoicand Cenozoicplutonic development n theAndesof centralChile (30ø30'-32ø30' S): Jour. SouthAmericanEarth Sci., v. 1, p. 249-260.
Pardo-Casas, F., and Molnar, P., 1987, Relative motion of theNazca (Farallon) and South American plates sinceLate Creta-ceous time: Tectonics, v. 6, p. 233-248.
Petersen, G., 1954, Informe preliminar sobre a geologlade la
Faja Costaneradel Departamento de Ica: Empresa PetroleraFiscal Per6, Bol. T•cnico, no. I, p. 33-59.
-- 1960, Sobre Condoriquifia y otros dep6sitosde estafio enel Peril: Soc. Nac. Miner{a Petr61eo [Peru] Bol., v. 72, ser. 2,p. 36-44.
Petersen, G., and Vidal, C., 1983, Tr•s •pocas metalogen•ticasevidenciadas en el cenozoico del Per6: Soc. Geol. Per6 Bol.,
no. 71, p. 107-112.Petersen,U., 1965, Regionalgeologyand major ore depositsof
central Peru: ECON.GEOL.,v. 30, p. 407-476.1972, Geochemical and tectonic implications of South
Americanmetallogenic rovinces:Acad. Sci. [New York] Annal.v. 196, p. 1-38.
Pichavant, M., Valencia Herrera, J., Boulmier, S., Briqueu, L.,Joron, J. L., Juteau, M., Maria, L., Michard, A., and Sheppard,S. M. F., 1987, The Macusaniglasses, E Peru: Evidence of
chemical ractionationn peraluminousmagmas: eochem.Soc.Spec. Pub. 1, p. 359-373.
Pichavant, M., Kontak, D. J., Valencia Herrera, J., and Clark,A. H., 1988a, The Miocene-Pliocene Macusani Volcanics, SE
Peru: . Mineralogyand magmatic volutionof a two-micaalu-minosilicate-bearing gnimbrite suite: Contr. Mineralogy Pe-trology, v. 100, p. 300-324.
Pichavant, M., Kontak, D. J., Briqueu, L., Valencia Herrera, J.,and Clark, A. H., 1988b, The Miocene-Pliocene Macusani Vol-
canics,SE Peru: I. Geochemistry nd origin of a felsicperalu-minousmagma:Contr. Mineralogy Petrology, v. 100, p. 325-338.
low-anglesubduction eneath he Andes:Geol. Soc.America,Bull., v. 92, p. 448-456.
Pitcher, W. S., 1983, Granite type and tectonic environment, nHsii, K. J., ed., Mountainbuildingprocesses:ondon,AcademicPress, p. 19-40.
-- 1985, A multiple and compositebatholith, in Pitcher,W. S., Atherton, M. P., Cobbing,E. J., and Beckinsale,R. D.,
eds.,Magmatism t a plateedge:The PeruvianAndes:Glasgow,Blackie, p. 93-101.
Pitcher, W. S., Atherton, M.P., Cobbing,E J., and Beckinsale,R. D., eds., 1985, Magmatism t a plate edge: The PeruvianAndes:Glasgow,Blackie, 328 p.
Ponzoni, E., 1980, Metalogeniadel Per6: IUGS Internat. Sym-posium,Feb. 3-6, 1980, M•xico, D. F., Pub. 5, p. 101-140.
Portugal,J. A., 1974, Mesozoic nd Cenozoicstratigraphy ndtectoniceventsof the Puno-Santa ucia area, departmentofPuno, Peru: Am. Assoc.PetroleumGeologists ull., v. 58, p.982-999.
Puig, A., Diaz, S., and Cuitifio, L., 1987, Hydrothermalsystemsrelatedwith a Paleocene auldron omplexn the centralAndes,Chile:E1Guanaco, achinal e a SierraandE1Soldadominingdistricts,Antofagastaegion labs.l, n IUGS/UNESCO DepositModelling ProgramWorkshop,Nov. 9-18, 1987, Santiago,
Chile, p. 27-28.Purser,W. F. C., 1971, Metal-mining n Peru, pastand present:
New York, Praeger Pub., 339 p.Quirt, G. S., 1972, A potassium-argoneochronologicalnvesti-
gationof the Andeanmobilebelt of north-centralChile: Unpub.Ph.D. thesis,Kingston,Queen'sUniv., 240 p.
Quirt, G. S., Clark, A. H., Farrat, E., and SillRoe, R. H., 1971,Potassium-argongesof porphyry copperdepositsn northernand central Chile labs.l:ECON.GEOL.,v. 66, p. 980.
Ramos,V. A., 1988, Late Proterozoic-early Paleozoic of SouthAmerica--a collisional istory:Episodes, . 11, p. 168-174.
Redwood,S. D., and Macintyre,R. M., 1989, K-Ar datingof Mio-cene magmatism nd related epithermalmineralizationof thenortheasternAltiplanoof Bolivia:ECON.GEOL.,v. 84, p. 618-630.
Richard,K., andCourtright,H. W., 1958, Geologyof Toquepala,
Peru: Mining Eng., v. 10, p. 262-266.Rivera-Cabello,S., 1988, Exploraci6ndel depositode plata-oro
"La Coipa", regi6n de Atacama:Cong. Geol. ChilenoPrimerasJournadasGeof•sica,5th, Santiago,Chile, Aug. 8-12, 1988,Actas, v. 1, p. B135-150.
Robertson, . C. R., 1978, Investigacionesobre os yacimientosmetaliferosdel Departamentode Puno,Peru: Lima, Per6, Inst.Cient. T•c. Minero, unpub. rept., 56 p.
Ruiz, C., Corval•n, J., Klohn, C., Klohn, E., and Levi, B., 1965,Geologlay yacimientosmetalfferos e Chile: Santiago,Chile,Inst. Investig. Geol., 360 p.
Ruiz, C., Aguilar, A., Egert, E., Espinoza,W., Peebles,F., Que-zada, R., and Serrano, M., 1971, Yacimientos chilenos estrati-
formesde sulfurosde cobre: Santiago,Chile, Rev. Minerales,v. 26, p. 3-13.
S•nchez, A. W., 1983a, Edades K-Ar en rocas ntrusivas del area
de Ilo, Dpto. de Moquegua:Geol. Soc. Per6 Bol., no. 71, p.183-192.
-- 1983b, NuevosdatosK-Ar en algunas ocasdel Per6: Soc.Geol. Per6 Bol., no. 71, p. 193-202.
Sandeman, H. A., Clark, A. H., and Farrar, E., 1990, Geochro-
nological ndpetrologicalnvestigationsf Oligocene-Miocenevolcanic ndhypabyssalocks, icotani ndQuenamarimesetas,Cordillera Oriental, southeastern eru: Summaryof progress:Lima, Peru, Inst. PeruanoEnergiaNucleSr,unpub.rept., 7 p.
topic evolutionof the Los FrailesKaridariregion,Bolivia:Rev.GeologicaChile, no. 30, p. 27-33.
Schneider,A., and Halls, C., 1985, Cronologlade los procesoseruptivosy de mineralizaci6nen el campo volc•nico de LosFrailesKarikari. Cordillera Oriental, Bolivia:Univ. Chile, Dept.Geologla,Comun. no. 35, p. 217-224.
S•brier, M., Fornari, M., Vatin-Perignon,N., Vivier, G., and Ca-
brera, J., 1983, Nuevasedades adiom•tricasdel volcanismoCenozoicodel Sur del Per6: Implicancias n la tectorog•nesisandina abs.l: Soc. Geol. Per6 Cong. PeruanoGeologla,5thLima, July 4-7, 1983, Libro de Res6menes, . GR-16.
S•brier, M., Lavenu, A., Fornari, M., and Soulas, .-P., 1988, Tec-tonicsand uplift in centralAndes Peru, Boliviaand northernChile) from Eocene to present: G•odynamique, v. 3, p. 85-106.
Shackleton, R. M., Ries, A. C., Coward, M.P., and Cobbold,
P. R., 1979, Structure,metamorphism nd geochronology fthe Arequipa massifof coastalPeru: Geol. Soc.LondonJour.,v. 136, p. 195-214.
Sillitoe, R. H., 1972a, Relation of metal provinces in westernAmerica to subduction of oceanic lithosphere: Geol. Soc.America Bull., v. 83, p. 813-818.
-- 1972b, A plate tectonicmodel for the origin of porphyry
copper deposits:ECON.GEOL.,v. 67, p. 184-197.-- 1974, Tectonicsegmentation f the Andes: mplications or
magmatism nd metallogeny:Nature, v. 250, p. 542-545.-- 1976, Andeanmineralization: model or the metallogeny
of convergentplate margins:Geol. Assoc.CanadaSpec.Paper14, p. 59-100.
. 1981, Regionalaspects f the Andeanporphyrycopperbeltin Chile and Argentina: nst. Mining Metallurgy Trans., v. 90,sec. B, p. B15-B36.
1984, Tectonicsegmentation f the Andes: mplications ormagmatism nd metallogeny:Nature, v. 250, p. 542-545.
-- 1985, Ore-related breccias n volcanoplutonicarcs:ECON.GEOL., v. 80, p. 1467-1514.
-- 1988, Epochsof intrusion-related copper mineralization nthe Andes:Jour. SouthAmericanEarth Sci., v. 1, p. 89-107.
Soler, P., and Bonhomme,M. G., 1988a, Oligocene magmatic
activity and associatedmineralization n the polymetallic beltof centralPeru: ECON.GEOL.,v. 83, p. 657-663.
• 1988b, New K-Ar agedeterminations f intrusive ocks romthe Cordillera Occidental and Altiplano of central Peru: Iden-tification of magmatic pulsesand episodesof mineralization:Jour. SouthAmericanEarth Sci., v. 1, p. 169-178.
Soler, P., Grandin, G., and Fornari, M., 1986, Essaide synth•sesur a m•tallog•nie du P•rou: Gf•odynamique, . 1, p. 33-68.
S•rensen,H., 1974, Alkali syenites, eldspathoidal yenitesandrelated lavas, n S•rensen, H., ed., The alkaline rocks: London,
J. Wiley and Sons,p. 22-52.Steiger,R. H., and JSger,E., 1977, Subcommissionn geochro-
nology:convention n the useof decayconstantsn geo- andcosmochronology: arth Planet. Sci. Letters, v. 36, p. 359-362.
Steinmann,G., 1929, Geologieyon Peru: Heidelberg, Carl Win-
ters Univ., 448 p.Stevenson,F. B., 1972, Summary report: Geology and mineral-
Stewart, J. W., Evernden, J. F., and Snelling, N.J., 1974, Agedeterminations from Andean Peru: A reconaissance urvey:Geol. Soc. America Bull., v. 85, p. 1107-1116.
Streckeisen,A., 1960, On the structureand origin of the nephe-line-syenitecomplexof Ditro (Transylvania,Roumania): nter-nat. Geol. Cong., 21st, Copenhagen,1960, v. 13, p. 228-238.
Swanson,K. E., Noble, D.C., McKee, E. H., Sempere,T., Mar-tinez, C., and Cirbian. M., 1987, Major revisions n the age ofrock units and tectonic events n the northern Altiplano basin
of Bolivia [abs.]:Geol. Soc.America Abstractswith Programs,v. 19, p. 456.
Tosdal,R. M., 1978, The timing of the geomorphic nd tectonicevolutionof the southernmost eruvianAndes:Unpub. M.Sc.thesis, Kingston, Ontario, Queen's Univ., 136 p.
Tosdal,R. M., Farrar, E., andClark, A. H., 1981, K-Ar chronologyof late Cenozoic volcanism n the Cordillera Occidental, south-
ernmost Peru: Jour. VolcanologyGeotherm. Research,v. 10,p. 157-173.Tosdal,R. M., Clark, A. H., and Farrar, E., 1984, Cenozoicpoly-
phase andscape nd the tectonicevolutionof the CordilleraOccidental, southernmostPeru: Geol. Soc. America Bull., v.
95, p. 1318-1332.Tourigny,G., Brown,A. C., Hubert, C., and Crepeau,R., 1989,
Synvolcanicndsyntectonicoldmineralization t the Bousquetmine, Abitibi greenstonebelt, Quebec:ECON.GEOL.,v. 84, p.1875-1890.
Turner, G., 1968, The distribution of potassium nd argon inchondrites, n Ahrens, L. H., ed., Origin and distributionofelements:Oxford, Pergamon,p. 387-398.
Uyeda, S., and Kanamori, H., 1979, Back-arcopening and themode of subduction: our. Geophys.Research,v. 84, p. 1049-1061.
Valencia, J., and Arroyo, G., 1985, Consideraciones eoqulmicasde los indiciosuranlferosde Macusani,Puno (Per6): Uraniumdeposits n volcanic rocks, nternat. Atomic Energy AgencySymposium, 1 Paso,Texas,April 2-5, 1985, Proc., p. 275-288.
Vargas,A., 1975, Geologla ainera del departamentode Tacna:Soc. Geol. Per6 Bol., v. 46, p. 187-204.
Vernon, R. H., Etheridge, M. A., and Wall, V. J., 1988, Shapeand microstructure of microgranitoid enclaves: ndicators ofmagmamingling nd low:Lithos,v. 22, p. 1-11.
Vicente, J. C., 1981, Elementosde la estratigraflamesozoica ud-peruana, n Volkheimer,W., andMusacchio, . A., eds.,Cuencassedimentarias el Jurftsico Crefftcicode America del Sur:Comit• Sud. AmericanoJurftscioCretftcio, v. 1, p. 319-351.
Vidal, C. E., 1985, Metallogenesisassociatedwith the Coastalbatholith of Peru: A review, in Pitcher, W. S., Atherton, M. P.,
Cobbing, E. J., and Beckinsale,R. D., eds., Magmatism at aplate edge: The Peruvian Andes: Glasgow,Blackie, p. 243-249.
-- 1987, Kuroko-typedepositsn the Middle Cretaceousmar-ginalbasinof central Peru: ECON.GEOL.,v. 82, p. 1409-1430.
Wasteneys,H. A., 1990, Epithermal silver mineralizationasso-ciatedwith a mid-Tertiary diatreme:SantaBS,bara, SantaLuciadistrict, Puno, Peru: Unpub. Ph.D. thesis,Kingston,Queen'sUniv., 367 p.
Wasteneys, . A., and Clark, A. H., 1986, Geologicalmapof thearea surrounding he Santa Bftrbarasilver camp (1:50,000):Lima, Peru, Minsur, S.A. unpub. rept.
-- 1990, Mineralogical oning n an epithermalsilvervein sys-tem, SantaB•bara mine, SantaLucia district, southeastern eru[abs.]:Geol. Assoc.CanadaMineralog.Assoc.CanadaProgramwith Abstracts,v. 15, p. 137.
Wasteneys,H. A., Clark, A. H., Arenas,M. J., and Valdlvia,R.,1990, Conicalepithermalsilverveinssurrounding diatreme,Santa B•rbara mine, Santa Lucia district, southeastern Peru
[abs.]:Geol. Assoc.Canada-Mineralog.Assoc.CanadaProgramwith Abstracts,v. 15, p. 137-138.
Willig, C. D., and Delgado,J., 1985, SouthAmericaasa sourceof tungsten:nternat.Tungsten ymposium,rd, Madrid, 1985,Proc. p. 58-85.
Wilson,J. J., andGarcia,W., 1962, Geologla e loscuadrftngulosde Pachlay Palca (Hojas 36-v y 36-x): Peru Corn. Carta Geol.Nac., v. II, no. 4, 82 p.
Yamamura,B. K., 1990, The Palca 11 tungstendepositand as-sociated raniticrocks,Choquenedistrict,Puno, southeasternPeru: Unpub. M.Sc. thesis,Kingston,Queen'sUniv., 312 p.
York, D., and Lopez Martinez, M., 1986, The two-facedmica:Geophys.ResearchLetters, v. 13, p. 973-975.
Zambrano,R., Lavi, P., and Eyzaguirre,R., 1965, Programadeinventarioy evaluaci6nde los recursos aturalesdu departa-mentodu Puno--Capitulo 3: GeologlaRecursosMineros,v. 2,42 p.
Zentilli, M., 1974, Geologicalevolutionand metallogenic ela-tionshipsn the Andesof northernChilebetween26ø and 29øsouth:Unpub. Ph.D. thesis,Kingston,Queen's Univ., 446 p.
Zentilli, M., Doe, B. R., Hedge, C. E., Alvarez, O., Tidy, E., andDaroca,J. A., 1988a, s6topos e plomoen yacimientos e tipop6rfidocuprlferocomparadoson otrosdep6sitosmetallferosen losAndesdel norte de Chile y Argentina:Cong.Geol. Chi-leno, 5th, Santiago,Aug. 8-12, 1988, Actas, v. 1, p. 331-370.
Zimmerman,J.-L., and Kihien, A., 1983, D•termination par la
m•thode K/Ar de l'Sge des intrusionset des min•ralisationsassoci•es ans e porphyrecuprif•re de Quellaveco sudouestdu P•rou): Mineralium Deposita,v. 18, p. 207-213.
Zweng, P. L., 1984, Evolution of the Toquepala porphyryCu(-Mo) deposit,Peru: Unpub. M.Sc. thesis,Kingston,Queen'sUniv., 131 p.
Zweng,P. L., andClark,A. H., 1984, mpactof major ourmalinebreccia formation on the evolution of the Toquepala Cu(-Mo)porphyry,Peru [abs.]:Geol.Soc.AmericaAbstracts ith Pro-grams, v. 16, p. 706.
