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POLYMETALLIC Ag-Te-BEARING PARAGENESIS of the CERRO

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POLYMETALLIC Ag-Te-BEARING PARAGENESIS of the CERRO 667 The CanndianM ineralo gi st Vol. 32,pp. 667-679(1994) POLYMETALLICAg-Te-BEARING PARAGENESIS OFTHE CERRO NEGRO DISTRICT. FAMATINARANGE, LA RIOJA.ARGENTINA ISIDOROB. SCHALAMUK aNpM. AMELIA V. LOGAN* CONICET(Consejo Nacianal de InvestiqacionesCienttficas y Tdmicas),Instituto de RecursosMinerales, UniversidadNacionnl de La Plata, calle 47 N" 522, 1940In Plata, Argentina ABSTRACT Mineralization in the FamatinaRange, La Rioj4 Argentina is related to silicic to intermediatemagmatism of l,ower to Middle Plioceneage. This metallogenicsubprovince includes 1) silver-bearingdeposits with a very rich and complex Ag-Pb-Zn (Cu-Ni-Co-Te-Sb) paragenesis,2) Cu-Au districts, and 3) Cu-Mo districts. Detailed microscopic and geochemicalstudies of the Peregrinadeposit, of the first group, revealedthe occurrenceof tellurides suchas altaite and native tellurium. The paragenesisconsists of gold silver-bearingminerals (acanthite,argyrodite, miargyrite, pyrargyrite, proustite, stephanite,freibergite), Co-Ni minerals (nickel-skutterudite,nickeline, rammelsbergite,safflorite), base-metalsulfides (sphalerite,chalcopyrite, pyrite, galena) and gangueminerals (siderite, quartz, barite and calcite). Textural and structural evidenceindicates that mineralizationtook place during three stagesfrom solutionsunder epithermalconditions. During the first stage,base-metal sulfides were depositedin a gangueof siderite.During the secondstage, gold was depositedat tle beginning,followed by the main depositionof silver antimonidesand arsenides,and Ni-Co-bearing mineralsin a gangue of quartz and ferroan rhodochrosite.Studies of fluid inclusionsin sphaleriteindicate a temperatureof formation ranging from 265" to 190"C and fluids with a salinity of 4.2 to 6.2 eq.VoNaCl. The third stageis characterizedby the depositionof scarce base-metalsulfides and Ni-Co-bearing minerals,and the main depositionof acanthite,silver, altaite,tellurium and marcasitein a gangueof calciteand quartz. Keywords: silver, proustite,acanthite, freibergite, altaite, tellurium, Cerro Negro district, Peregrina,Famatina Range, Argentina. Soruuann La mindralisationdans la chainede Famatina,h La Rioja, en Argentine,est 1i6€A un magmatismefelsique i intermddiaire d'6ge pliocbne inf6rieur i inoyen. Cette province mdtallogdniquecomprend 1) des gisementsd'argent avec une paragenbse complexeet trbs riche en Ag-Pb-Zn-(Cu-Ni-Co-Te-Sb), 2) des districts enrichisen Cu-Au, et 3) d'autresenrichis en Cu-Mo. Nos 6tudespdtrographiques et g6ochimiquesddtailldes du gisementde Peregdn4 qui fait partie du premier groupe, r6vdlent la pr6sencede tellurures, dont altarle, et tellure natif, La paragenbsecontient de 1'or, des mindraux argentifbres (acanthite,argyrodite, miargyrite, pyrargyrite, proustite, st6phanite,freibergite), des min6raux i Ca-Ni (nickel-skutterudite, nickeline, rammelsbergite,safflodte), des sulfuresde m6tauxde base(sphal6rite, chalcopgite, pyrite, galbne)et des min6raux de gangue(sid6rite, quartz, baryte et calcite).D'aprbs l'6vidence texturaleet structurale,la min6ralisationaurait eu lieu en trois stades,d partir de solutionssous conditions 6pitlermales. les sulires des m6tauxde basesont appamsau cours du premier stade,dans une ganguede siddrite.Au cours du second,I'or a d'abord 6t6 d6pos6,suivi par les antimoniureset les arsdniures d'argent, et par les min6rauxb Ni-Co dansune ganguede quaxtzet de rhodochrositeferrifbre. lrs inclusionsfluides dansla sphal6riteindiquent une temp6raturede formation entre 265 et 195'C, et une salinit6 enre 4.2 et 6.27ode NaCl (6.quivalent). Le troisiamestade est marqu6par la ddpositionde raressulfures de m6tauxde baseet de min6rauxtr Ni-Co, et de la plupart de l'acanthite,I'argent, l'altaite, le tellure et la marcasitedans une ganguede calcite et de quaxtz. (Traduit par la R6daction) Mots-cl6s: argent, proustite, acanthite,freibergite, altai'te, tellure, district de Cerro Negro, Peregrina,chalne de Famatina, Argentine. x Presentaddress: U.S. GeologicalSurvey, MS 959,National Center, Reston,Yigjna22092, U.S.A. 668 TIIE CANADIAN MINERALOGIST .0 67?45' NCRUCIJAOA + + % + + :.w.+ + + + t+ + +++ + ++ + ++ + i:+ + + /.+++ ' '; '-._ + * + * I%:: * J--- -\r- + + * +k * *'%."i1-, Detriticol, cover.OUATERNARY / raun @." MogoteFormsliqn TERTIARY a Oro - .u B PotquioFormotion PERMIAN (Do, Elon Ef,Nuiorco Formotion0EVONIAN O# 74 *"nroPeinodoFormotion ORooVlC,o* Ftc. 1. Geologicalsketch of the eastemside of the FamatinaRange showing the metallogenicsubprovince with Cu-Au, Cu-Mo andPb-Ag-Zn districts.Geology modified from variousregional geological studies: Bassi (1953), De AIba (1960, 1972)and Tumer (1962, 1,964, 197 1). Ag_Te MINERALZATION, ARGENTINA 669 INttooucrroN Although exploitation has been sporadic,and none of the mineshas been active in the last several Polymetallic and precious metal depositsoccur in decades.these areas are believed to still haveeconomic the FamatinaRange, province of La Rioja, Argentina potential.In the last few years,regional research as and define a polymetallic and monocyclicsub- well as detailed mapping, geophysicalstudies and province. Although the size of this metallogenic drilling of the Cu-Au and Cu-Mo mineralizations subprovinceis about200 km2,the majority of the min- have been completed (Marcos & Zarettini L981, eral concentrationsoccur in an areaof 20 km2 (Frg. l). M6ndez1981). Angelelli (1984),Schalamuk er a/. Three distinct zonesare recognized:1) the Pb-Ag-Zn (197'7),Bodenbender (1.913, 1.922) and Allchurch (Cu-Ni-Co-Te-Sb) depositsof the Caldera,Tigre and (1895) reportedinformation aboutthe Pb-Ag-Zn con- Cerro Negro districts (.a Viuda and Peregrinamines), centrationsin Famatina. which form a north-south-hendingband on tle east- em side of the FamatinaRange, 2) the Cu-Au districts ANaLvncaL Msrrrons known as La Mejicana, Los Bayos, Offir and Ampallado, located in the northwesternregion, Compositionsof altaite, tellurium, Pb(As,Sb) and the El Oro mine" in the southeasterncomer of the Te2.72-2.54,freibergite, sphaleriteand carbonateswere study areq and 3) the La EstrechuraCu-Mo district, determinedby the authorswith a CAMECA SX located in the northwesternregion. The regional 50 electron microprobe at the Comisi6n Nacional de zoning of Cu-Mo, Cu-Au and Pb-Ag-Zn Energia At6mica (CNEA) in BuenosAires. The ana- (Cu-Ni-Co-Te-Sb) assemblagesshows similarities lytical parametersare reported in footnotes to the to that shownby mineralizationin Colorado. Tables.Al1 analyseswere performedunder an acceler- The complexand interestingmineral paragenesisof ation voltage of 20 kV and a beamintensity of 20 nA, the Peregrinamine motivated this detailed mineralo- exceptfor the analysisof the Te-bearingminerals, in gical and geochemicalstudy, in which we soughtto which casethe beam intensity was 30 nA. In the identify the Te-bearingminerals. The veins in the analysesof altaite, native tellurium and freibergite, Peregrinamine that we studiedare locatedin the west- pure elementswere used as standardsfor Cu, Pb,7n, ern part of the Cerro Negro (Fig. 1). Bi, Te, Sb, Au and Ag, pyrite for S and Fe, and a syn- Some of the argentiferousdeposits were mined by thetic As-Se compoundfor As and Se. The following natives,then (1780-1810)by Spaniards(aic Jesuits), standardswere used in the analysesof sphaleriteand and also sporadicallyin the late 1800sand early carbonates:MnTiO2 for Mn, MgCO3for Mg, FeS2for 1900s.The major mining activity was concentratedin S and Fe, CaCO, for Ca, synthetic ZnS for Zn, and the Cerro Negro district, where the bonanzascould synthetic CdS for Cd. CO2 was calculatedby dif- contain 1G-12kg of silver per tonne.In the Peregrina ference.The following incorporatedprograms were mine, the ore was recoveredfrom open-castworkings used: CALIB (Calibration of standards),DECLAR and galleriesdown to 300 meters. (Declarationof analyticalconditions) and QUANTI TABLE 1. RESIJLTS OFFTECTRON-MICROPROBEAI.IALYSBS OFALTAITE ,ilt%o To q.73 39.33 39.49 39.t3 39.U 39.47 3957 40.19 Pb 58.32 58.03 58.97 59.82 57.97 58.43 5E.32 60.r0 sb 0.30 0.?5 0.36 0.30 0.33 o2l 't oz7 Au 0.r2 As 0.trt 0.08 0.06 Se 0,19 0.04 0.08 0.19 Sum 9.69 nS3 9t.t6 9,33 n2A 9E.19 9E,8 1m.81 al% Te 5Lt3 5222 sLJg 5rA, 52.n S2.m 5Ll3 51.62 Pb 6,94 47.43 47,63 4f,23 6& 47.{t {tA 4754 sb 0.40 o.49 0,41 0,47 029 056 0.36 AI 0.r0 "t: Ag - 0.13 0.(B Se 0.39 0.(B o,rE 0.40 f.i&s ur€d (aralyzitrgrystals): ToLc (IJF), PbLc gJF), Sfc (PgD, Sbtc eED, tuIr (I19, A8,c egO, SeJ(cfiJF), d AsIa (iF). 670 TTIE CANADIAN MINERALOGIST (Quantitativeanalysis). Linares 1975)is representedin the areaby the Mogote Data on trace elementsin sphaleriteand galena rhyodacite-dacitecomplex (Fig. 1). Theserocks gen- were obtained by neutron-activationanalyses by Dr. erally have a granophyrictexture madeup of large I.M. Cohenat the Comisi6nNacional de Energia phenocrystsof plagioclase, qvafiz and biotite in a At6mica, Ezeiza, Argentina. In order to avoid inter- microgranulargroundmass with tie samemineralo- ferencesproduced by some nuclides presentin the gical compositionas the phenocrysts,plus abundant matrix (6etZn znd65zn),samples were irradiatedfor a K-feldspar.At depth,the rhyodacitegrades into a gra- very short period of time to identify most of the ele- nodiorite in the areaof La Estrechuraand Ampallado ments. Irradiations were performedin the RA-3 (Marcos & Zanettini 1981).In many areas,intense atomic reactor at the Comisi6n Nacional de Energia hydrothermalalteration has been superimposedon the At6mica, Ezeiza, Argentina, with a flow of primary assemblages. l0l3 n/cm2.s,using thermal or epithermalneutrons Structurally,
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