Spangenberg Et Al-1999

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Economic eologyVol.94, 1999, p. 1067-1092

An Evaluationf the norganicndOrganicGeochemistryf theSanVicenteMississippialley-Typeinc-Lead istrict,CentralPeru:Implicationsor OreFluidComposition,ixingProcesses,ndSulfate eductionJORGE. SPANGENBERG,

Institut eMindralogiet Pdtrographie,niversitdeLausanne,FSH-2,CH-1015 ausanne,witzerlandLLUiS FONTnOTE,

DdpartementeMingralogie,niversitde Genve, 3,ruedesMaralchers,H-1211GenOve, SwitzerlandAND STEPHEN A. MACKO

Departmentf Environmentalciences,niversityf Virginia, harlottesville,irginia 2903Abstract

Mississippialley-typeinc-lead epositsndoreoccurrencesn the SanVicente elt arehostedn dolo-stonesf heeastern pperTriassico Lower urassicucar5 asin, entral eru.Combinednorganicndor-ganic eochemicalata rom22 sites,ncludinghemainSanVicente eposit, inor reoccurrences,ndbar-ren ocalities,rovide etter nderstandingf fluidpathwaysndcomposition,reprecipitationechanisms,Eh-pHchangesuringmineralization,nd elationshipsetweenrganic atter ndore ormation.re-stagedark eplacementolomitendwhite parryolomitereFe and are arth lementREE)depleted,ndMnenriched,omparedo thehost olomite.n themaindeposit,heydisplayignificantegative e andproba-blyEu anomalies.ixing f an ncomingot,slightlyxidizing,cidic rine H2CO3 einghedominantis-solvedarbonpecies),robablyoorn REEandFe,with ocalntraformational,lkaline,educingatersx-plainsheoverall arbon ndoxygensotopeariationnd hedistributionsf REE andother race lementsin thedifferent ydrothermalarbonateenerations.he ncomingre luid lowedhroughmajor quifers,probablyasal asin etrital nits,with imitednteractionith hecarbonateost ocks. hehydrothermalcarbonateshow strongegionalhemicalomogeneity,ndicatingccessf heore luids y nterconnectedchannelwaysear heoreoccurrences.egative e anomaliesn themaindeposit,hatareabsent t the dis-trictscale,ndicateocal re-fluidhemicalifferences.xidationfbothmigratednd ndigenousydrocar-bons y he ncomingluidprovidedhe ocal educingonditionsecessaryor sulfateeductiono H2S,py-robitumenrecipitation,nd eductionf Eu3+ o Eu2+. e-Mncovariations,ombinedith heREE contentsof hehydrothermalarbonates,reconsistentith hemineralizingystemhiftingrom educing/rock-dom-inatedooxidizing/fluid-dominatedonditionsollowingredeposition.ulfatend ulfide ulfursotopesup-portsulfide riginromevaporite-derivedulfate y thermochemicalrganiceduction;urther videncen-cludeshepresencef aC-depletedalciteements--12%o 1C) ssulfateseudomorphs,lementalulfur,altered rganic attern thehost olomite,nd sotopicallyeavier,ate,solid itumen. ignificantlterationof the ndigenousndextrinsicydrocarbons,ithabsent acterialmembraneiomarkershopanes)s ob-served.he ight a4S fsulfidesromsmallmines ndoccurrencesomparedo hemaindepositeflect ocalcontributionf sotopicallyightsulfur, videncef ocaldifferencesn theore-fluid hemistry.

IntroductionMULTIPLEluidmixing nd luid-rocknteractionuringor-mation f Mississippialley-typeepositsnduces omposi-tional hangesn the fluidandhost arbonates.he elemen-tal and sotopicompositionf the hydrothermalarbonatesandassociatedrganic attermay ecordhenature ndex-tentof thesenteractions.n particular,ariationsn Mg, Sr,Na, Fe, Mn, and rare earth elements n carbonates ssociatedwithbasemetal eposits ay rovidealuablenformationnthe lowdirectionfdolomitizingndmineralizingluids,heextent of fluid-rock nteraction, nd oxidation otentialchangese.g.,M/511erndMorteani, 983;Vietset al., 1983;Graf, 1984,1988;Buelter nd Guillemette,988;Gregg,1988;Shulda,988;Gregg ndShelton,989;Meyers, 989;Farr, 1992).

Correspondinguthor: mail, [email protected]

Thiscommunicationummarizesnextensiveeochemicalinvestigationf the host ocks f the SanVicenteMississippiValley-typeistrict ostedn the UpperTriassico LowerJurassicucari asin, entral eru, ndpresentsewdataoncarbonateraceelementsndsulfursotopes.ecent xten-sionof mining ctivitiesowardshe northof the mainde-posit, swellas he ongoingntense xplorationn thewholedistrict, asopened p newareasor mappingndgeochem-icalsampling.urface utcropsndundergroundrillcoresat the SanVicentemaindeposit, inororeoccurrences,ndbarrenocalities eresystematicallyampledo characterizethe host-rockeochemistrynd ts spatial elationshipoknown rebodies.hegeochemicalpproachncludestudies13 12 18 16 87 6of carbonate race elements, C/ C, O/ O, and Sr/sSrdata, luid nclusiontudies, ndorganic eochemicalndisotopic13C/12C,SN/14N)nvestigationsf the associatedorganicmatter (Spangenberg,995; Moritz et aI., 1996;

0361-0128/99/3001/1067-266.00 1067


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1068 SPANGENBERG ET AL.

Spangenbergt al., 1995, 1996;Spangenbergnd Macko,1998). The two aims of this contributionare: to discuss on-straints etby the carbonates'EE and raceelement Fe,Mn, Sr,Na, Ba,Zn) compositionn hesourcendcomposi-tionof theoresolutionsnd heprocessesontrollingulfideprecipitation;nd o reevaluateublishedsotopicnvestiga-tionsof the carbonatesndassociatedrganicmatterusingthe newdata.Given hepoor nowledgeoncerninghebe-havior f REE and raceelementsn complex ydrothermalsystemse.g.,M611er,983;BauandM611er,991), he ob-served REE distributions in San Vicente carbonates wereevaluated singquantitative odeling f the 13C/2CndlsO/160 ovariationsn the hydrothermalarbonatesSpan-genbergt al., 1996), ndusing n organic eochemicalndisotopictudy f the hydrocarbonstaininghe SanVicenterocks Spangenbergnd Macko,1998).New isotopic atafromSanVicente istrict ulfidesre presented.he com-bined inorganic, rganic, nd isotopic eochemicalatarecord he fluid/fluidand fluid/rockmixingprocessesn-volved uring ulfide recipitationt SanVicente, ndgiveinsightsnto the compositionf the ore fluid(s), he fluidpathways,nd hesulfur ourcesnd eduction echanisms.

Geologic ettingLocation ndstratigraphicetting

TheSanVicenteMississippialley-typen-Pbdistricts o-cated 300 km east of Lima in central Peru, at an altitude be-tween ,000and2,500m, in theCejade Selva--the asternflankof theAndes overed y tropicalain orest. he accu-mulated roductionnd eservesreabout 0 millionmetrictons Mt) of oregrading 0 wt percent incand0.8 wt per-cent lead (Fontbot et al., 1995).The UpperTriassico LowerJurassicucar5 asin,whichhostshe SanVicente eposit ndotherunminedMississippiValley-typeccurrencesFig. 1), is a carbonatelatform tthewesternmargin f the Brazilian hield. he basin evel-opedat the startof the Andean yclewith a marine rans-gressionverclastic edimentsndvolcanicndvolcaniclas-tic rocks f the LatePermiano EarlyTriassic itu Group.Recent edimentological,arbonate7Sr/S6Sr,3C/inC,sO/lO,andmetallogenetictudies f the Pucart asin rediscussedin Fontbot6 (1990), Rosas 1994), and Moritz et al. (1996).Thegeologyf theSanVicentemaindeposit asdescribedby Schulz 1971),Levin (1975),Fontbot6 nd Gorzawski(1990), ndFontbot6 t al.(1995). n theSanVicenteminingarea, heNorian o Hettangianarbonateequencef hePu-car5Groupsabout ,300m thick, nd scharacterizedy a-ciesdevelopedn locallysolated asins n a shallow-marineshelf Fig. 2). Pseudomorphsf evaporiticulfates ccur nsome orizons.hreedolomiticnits,heSan udas olomite,the San Vicente Dolomite, and the Alfonso Dolomite, hostthe orebodies. Most of the economic mineralization is withinthe San VicenteDolomite.The bituminous ilty UncushLimestones a black imestoneich n organicmatter totalorganic arbon, OC, rangesrom0.1 to 4.5wt %, Spangen-bergandMacko, 998)andvery inecrystallineyrite totalsulfur p to 1.2wt %),withshalyo silty ntercalations.hisunit (Fig. 2) overlieshe majorore-bearing olomitic nit(SanVicente olomite) ndprovidesstratigraphiceference

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Legend 3 kmUnitsostncush Uncushimestonelucararoup[UnitsrencushUpperTriassi..-Lower uurassc)Undifferentiated[l RedSandstonendMituGroup[ San amnranite(UpperPermian LowerTriassic) Tarmaranodiorite(UpperPermian LowerTriassic) Groupopacabanaimestone(LowerPermian) Lower aleozoicocks PrecambrianchistsMajorectonicineament'Thrustault

Closed mine OStudied occurrences

Y+++++++

San Vicente mine

-11o15 '

Fzc.1. Geologicalapof SanVicente eltshowinghestudiedocalities(barren ndmineralizedreas). P = Quebrada ifi6n;RO = Rondayacu;S= Yanachurour;SI = Sillapata;T = Utcuyacu;U= Quebrada tcuyacu;AY= Aynamayo;H = Chilpes; C -- Afioramientoampana;S = UncushSur;UN = Uncush;J= San udas;V= SanVicentemine;SO= QuebradaSolitaria; I = Vilcapoma;R = Arcopunco;A = Machuyacu;S = Que-brada eca; A= Palmapata;J= Puntayacuunior; C = Quebradaascas;SP = Sur Pichita;P1 = Pichita.horizonFig.1). Detailed edimentologicaltudiesf thePu-car5 basin in the San Vicente district (Fontbot and Gorza-wski,1990;Rosas,994;Hasler, 998) ndicatemportanta-cies hangesn themining rea.Subtidalhallow-wateracieswith rare restricted shelf intercalations characterize the ore-bearing olomitic nits.Mineralization

Theoreoccurs ainly s ens-shapedodiesmantos)om-monly onformableithbedding n the deposit cale, p to


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INORGANIC & ORGANIC GEOCHEMISTRYOF SANVICENTE, PERU 1069UNIT DESCRIPTION

Medium o very coarselycrystalline olomitewithabundant WSD.Bituminous,aminated,blacklimestonewith shaly o siltyintercalations.

Main ore-bearingunit. Fine toverycoarsecrystalline olomite.AbundantWSD and evaporitepseudomorphs. ubtidalooliticbarrier acieswith agoonandsupratidal ntercalations.

Dolomite ayers n partdedolomitized and karstified.Shaly intercalations.

Fine to very coarse crystallinedolomite. Abundant WSD andevaporitepseudomorphs.Subtidal oolitic barrier facies withlagoonand supratidalintercalations.

Limestone with dolomite.Up to 35% detrital material,mainly at the basis which isenriched in clastic material.Facies:mainlyof open sea shelfwith few intercalations ofshallower facies

Red Clasticacies onsistingf redSandstone silt ndsandstoneithmassive

I 2 3 4 5 6 7 8 9 10 11

FIG.2. Stratigraphicolumn f hePucara roupn theSan icentemin-ing area afterRosas, 994).1: red sandstone;= marly imestone; =marly olomite;: limestone;: dolomite;: dolomite ithwhite parrydolomite;: partly edolomitizedolomite;= bituminousiltyimestone;9: subvolcanicocks; 0: gypsumenses;1: ore.1.3km ong, 00 o 300m wide,andseveral etershick. hesulfidemineralsargelyeplace olomitized,ubtidal,oliticgrainstonesnterlayeredithdolomitized,rganic-richud-stoneswith cryptalgalaminationsnd evaporitic ulfatepseudomorphs.re occursszebraore,replacements,ndoccasionallyscementsn brecciasr veinletsFig.3A, B;Fontbotd nd Gorzawski,990;Spangenbergt al., 1995,1996). hemain remineralsresphaleritendgalena, ithtracepyriteandmarcasite.Theore-bearingolutionsrebelievedo have ained eatandmetals ymigrationhrough,nd eachingf, heunder-lying etritalocks ndPermo-Triassicntrusions.hese olu-tionsmayhave een hanneledpwardsynortheast-south-west- to north-south-trendingaultsystemsndbasementhighsn thevicinityf heorebodiesSpangenberg,995; .g.,LowerPaleozoichyllites nd quartzitesearMonobamba,Fig.1).Hostandganguearbonates

Differentgenerationsf syn-andpostore ydrothermalcarbonatesre distinguishedn the ore-bearingolostones

(Fig. 4). They nclude arkreplacementolomite-I, hitesparry olomite-II,atevoid-fillingolomite-IIId r calcite-IIIc, andcalcite r dolomiteeplacingvaporiticulfate. hefollowingescriptionndclassificationf thecarbonateen-erationsresummarizedromSpangenberg1995).The darkreplacementolomite-Is a fine- to medium-crystallineolomite, ithTOC rangingrom0.02 o 1.49wtpercentSpangenbergndMacko, 998).Thisdolomite asbeen ydrothermallylteredovaryingegrees,ndhas eenclassifieds vt: ine- overy inegrained15-60/am, ig.3C,D); If: fine-grained40-100 am, Fig. 3E, F); and Im:medium-grained100-400/am, ig. 3G, H). The very inegrained olomitesnonluminescent,ndicatinghighFe/Mnratio Fig.3D), and epresentshe bestavailablepproxima-tion o hepreore ost olostoneFig.4). In dolomiteswandIf, it is possibleo recognizeelics f primaryextures,spe-cially hostsf former oliths, hereashe primaryexturepreservations poorer n the red-luminescentarkreplace-mentdolomite-Im.he changesn cathodoluminescencen-tensity uggesthat hehost olomite asdepletedn Fe andenrichedn Mn during lteration.In advancedmetasomatic lteration, he white dolomite e-placinghedarkhost olomite-Ixhibitsncreasedrain ize,anda coarse ubhedralhitesparry olomite0.4-2.5mm)whichwasprecipitatedrom he hydrothermalluid n theavailableorosity.hisaltered ark eplacementolomite-Imis ntergrownith hefirstgenerationf fine-crystallinen-hedral phaleritendoccasionallyithpyrite ndmicrocrys-tallinequartz Fig.4).Whitesparry olomite-IIs the most xtensiveydrother-maldolomite ement ndoccurshroughouthe entireSanVicente elt. The whitesparry olomite-IIs a subhedral,whiteor grayishdue o sulfide nd organicmatter nclu-sions), parrydolomite ccurring s open-spaceilling nsmall pots,n millimeter-o centimeter-thickands eplac-ing he dark eplacementolomite-I,ndasbreccia ement(Fig.3A,B).Typically,hite parry olomite-II ostdatesul-fideprecipitationnd illsopen paces.n exceptionherewhitesparry olomite-IIs argelyackings theSanVicenteTechomanto,ocatedn the upperandnorthernmargin fthemainoredeposit. lternatingepetitionf dark eplace-mentdolomite-I ndwhitesparry olomite-IIbandsgivesrise to the characteristic ebra extureof the ore rock, a com-mon eature f Mississippialley-typeepositse.g.,BealesandHardy,1980;Fontboth, 993).Fluid nclusiontudies nthewhitesparry olomite-IIndicate recipitationromhot(115-162C)aline9.5-26wt % NaC1 quiv)luids Moritzet al., 1996).The late void-fillingarbonateccurs ithinwhitesparry olomite-II scoarse-r verycoarserainedn-terstitial pen-spaceillings,mainly sanhedral ilky-whitedolomitelate oid-fillingolomite-IIId) r calcitelate oid-filling alcite-IIIc). nother arbonatehase ccursssulfatepseudomorphsn thedark eplacementolomite-I. hemainmineralseplacingvaporiticulfategypsumr anhydrite)arecalcite, herty uartz, ndsubordinateolomite.Organicmatter n the SanVicente eposit

In SanVicente, s n almost ll Mississippialley-typee-posits,he ore s associatedn time andspacewith organicmatter e.g.,MacqueenndPowell, 983;Anderson,991;


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1070 SPANGENBERGET AL.


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DRD I IIvf If Irn I WSD-II I LFD-IIIDolomite -- .I II I LFC-IIICalcite I I

Carbonate EPC I Ireplacing -- -- - I Isulfate I II IQuartz ,- I II Ipyrite I I

sll I sl II I sl IIISphalerite I iI I

Galena I -- -- -- I-- '- 'I I

Native sulfur -- -- -- I II IKerogen Free HC BitumenOrganicatter I I

FIG.4. Parageneticequencef thehydrothermalangue ineralsndore n the SanVicente istrict. bbreviations:RD = dark eplacementdolomiteDRD-I,4. ery fine grained; RD-If: fine-grained;RD-Im:medium-grained);SD= white parryolomite-II;FD = latevoid-fillingdolomite-IIId;FC= late oid-fillingalcite-Illc;l , sl I, and l II= spha-leritegenerations;PD = dolomiteeplacingvaporiticulfate;PC = cal-cite eplacingvaporiticulfate; C = hydrocarbons.o 5

i i

cm.

andore ormationSpangenbergndMacko, 998).sotopicdata aiscand SlSN)romkerogensndassociatedxtracts,combined ithorganicmoleculararametersnd he SlaCvaluesof the individualn-alkanes, ndicate that the rocks nthemineralizedreas ere tainedya mixturef ndigenoushydrocarbons--27%o)withextrinsic,aC-depleted,icro-bially erivedydrocarbons--40%o). hese xtrinsicydro-carbons ereprobablyntroducedo themineralizationiteby theore luidor, essikely, y ater luids singhesamepermeabilityetworkSpangenbergndMacko, 998).The pyrobitumen5]aC aluesSpangenbergt al., 1996;SpangenbergndMacko, 998) rom hesmaller ississippiValley-typeepositsndoccurrences-26.9to -29.4%0) reapproximatelyper mil lower han he pyrobitumensromthe maindeposit -23.0 to -28.2%0,median= -25.2%0).There re wopossiblexplanationsor he sotopiciffer-ences etweenhe pyrobitumensn the maindeposit ndthosen thesmaller ississippialley-typeeposits,utnodiscriminatingvidence.ither acies ifferencesn themainore-bearingorizonsaused ifferentmixing atioswhichwere eflectedn thecompositionf themigratingydrocar-bons, r morentense ater-washingnd hydrothermal)l-terationemovedsotopicallyight ompoundsrom hepyro-bitumens t the San Vicentemain deposit. he firstexplanations compatibleith hesedimentologicalontrolon hemain rehorizonst heSanVicente eposit, hereasthesecondxplanationuggestsocal ifferencesn theore-fluidchemistry.

FIG.5. A. Bitumennfillinghegrain oundariesf sphaleriten the ullyhydrothermallyltered ark eplacementolomitesampleSV-915, antoAyala,evel 570, rosscut00).200-tzmcale ar.B. Solid ydrothermali-tumen ccurs svoid illing ndappearso be youngerhancalcitemantoAyala,evel1750, rosscut240E).

Samples ndAnalyticalMethodsSampling

Carbonateost ocksweresampled t district nd minescalesn mineralizedndbarren reas long 32-km,north-southraverseenteredn the maindepositFig. 1). Addi-tionalsampling etails re given n Spangenberg1995).Nineteen istrict-scaleamplingocalitiesncludeminedoreoccurrences,urfaceutcrops,nddiamond-drillxplorationholes. orty-twoamples, ainly f theore-bearingolomiteunits (Alfonso Dolomite, San Vicente Dolomite, and SanJudas olomite), ereanalyzedor major,minor, nd raceelements.orty-one amplesrom13 ore occurrencesereanalyzedor REE. Forty-threeamplesrom he SanVicenteminewereanalyzedormajor,minor, nd race lements,nd27 for REE.Sample reparation

Thinsectionsfrepresentativeamplesnsuredhecorrectclassificationf thecarbonateenerations,n particulararkreplacementolomite-Ix,ark eplacementolomite-It,nddark replacementolomite-IraFig. 3C-H). Selectedhinsectionsereexaminednder athodoluminescence,sing


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INORGANIC& ORGANICGEOCHEMISTRY F SANVICENTE,PERU 1073Technosyn200MKII instrument,peratedt 16kV anda60 mA guncurrent.Weatheredurfacesf therock amplesere emovedysawingbout -cm-thicklabs.hese labs ere oughlyol-ished,washedwith distilledwater, rinsed n acetone,anddried.The different arbonateenerationsereseparatedusing diamond-drillablepress, ndgroundn an agatemortaro


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TABLE. Geochemicalompositionf heAcidSolubleractionromCarbonatesf heSan icente istrictincludingheSan icente ainDeposit)CaCO3 MgCO3 Fe Mn Na Sr Zn4 BaSample Loc) Lith. Carb. (mole%) (mole%) (4ug/g) (;ug/g) (4ug/g) (4ug/g) (;ug/g) (4ug/g)

FSV-984 QP SVD WSD 56.53 42.88 476 2,358 436 93 12FSV-985 QP SVD WSD 57.40 42.00 1,284 1,674 551 74 3FSV-952 RO SVD WSD 56.30 43.43 262 982 303 113 41 5FSV-953 RO SVD WSD 56.48 43.04 185 2,022 399 72 24 6FSV-953B RO SVD WSD 56.43 43.08 628 1,617 375 88 37 6FSV-1001 YS SVD WSD 55.90 43.81 534 850 358 66 13 6FSV-1003 YS SVD WSD 55.70 43.97 326 1,275 283 92 60 5FSV-956 UT SVD WSD 56.16 43.58 375 806 384 51 9 5FSV-957 UT SVD WSD 56.43 43.34 555 535 327 60 8 6FSV-652 QU SVD WSD 55.74 43.85 621 1,247 330 107 26 7FSV-653C QU SVD WSD 56.62 42.76 1,801 962 397 37 9,343 2FSV-1057 QU UL 98.78 0.78 690 820 104 254 68 28FSV-1059 QU UL 98.58 1.10 728 262 169 625 5 49FSV-988 AY SJD DRD (I,) 56.10 43.36 1,657 982 415 68 19FSV-989 AY SJD DRD (I,) 55.56 43.66 2,523 1,213 402 97 90 7FSV-988 AY SJD WSD 56.34 42.95 2,251 1,195 378 60 22FSV-989 AY SJD WSD 55.62 44.02 398 1,299 364 67 44 6FSV-992 AY SVD DRD (It) 56.35 43.22 988 1,013 323 59 3,581 71FSV-990 AY SVD WSD 55.44 44.13 608 1,409 349 136 48 19FSV-992 AY SVD WSD 55.77 43.73 808 1,558 517 102 164 12FSV-754 CH SJD DRD (I,) 56.55 42.80 2,103 1,001 274 39 12 4FSV-753 CH SJD WSD 56.38 43.14 1,327 970 312 76 13 19FSV-754 CH SJD WSD 56.26 42.67 3,367 1,768 377 44 12 3FSV-754 CH SJD LFC 99.15 0.67 57 720 481 599 13 7FSV-982 CH SVD DRD (Im) 56.02 43.18 2,676 1,230 418 57 19FSV-755 CH SVD DRD (I,) 56.24 43.19 366 2,291 360 46 7 2FSV-759 CH SVD DRD (It) 56.47 42.79 2,558 1,016 392 50 4FSV-755 CH SVD WSD 56.33 43.31 234 1,501 542 66 4FSV-759 CH SVD WSD 56.26 43.00 2,452 1,134 289 49 7 2FSV-761 CH SVD WSD 56.39 43.24 310 1,412 537 56 6 3FSV-982 CH SVD LFC 99.64 0.25 51 445 171 507 11FSV-981 AC AD DRD (It) 55.99 42.99 3,899 1,017 340 35 1,476FSV-979 AC AD WSD 56.20 43.06 2,532 1,081 322 163 145FSV-981 AC AD WSD 55.92 43.09 3,738 1,070 422 34 1,779FSV-976 US AD WSD 55.95 43.81 64 1,095 378 49FSV-978 US AD LFC 99.18 0.70 48 480 129 249FSV-971 US SJD WSD 56.11 43.68 205 799 476 48FSV-972 US SJD WSD 56.39 43.36 435 767 456 49FSV-654 SV AD WSD 54.97 44.65 576 1,189 483 57 80 4FSV-665 SV AD WSD 56.91 43.09 2,391 1,082 282 70 137 3FSV-665 SV AD LFC 99.41 0.48 50 422 127 473 3 1FSV-801 SV AD DRD (Ivf) 60.20 39.48 746 605 581 67 263 2FSV-806 SV AD WSD 57.05 42.60 429 1,158 205 62 7 1FSV-807 SV AD WSD 56.88 42.58 1,204 1,233 390 46 1,362 1FSV-807 SV AD LFC 89.68 10.14 323 522 184 320 16FSV-811 SV AD DRD (Ivf) 59.03 40.42 1,609 566 160 56 22 2FSV-811 SV AD DRD (If) 57.67 41.79 1,797 682 286 44 760 1FSV-816 SV AD WSD 58.20 41.56 302 757 373 51 12 1FSV-830 SV AD WSD 58.06 41.32 643 2,125 349 47 12 2FSV-015 SV UL 95.48 3.94 1,448 300 161 1,406 17 71FSV-017 SV UL 98.91 0.61 1,436 379 212 793 i 32FSV-1101 SV UL 97.08 2.43 1,104 168 88 566 2 21FSV-1102 SV UL 97.17 0.87 1,446 154 146 393 5 6FSV-1103 SV UL 93.28 6.04 1,484 414 151 1,036 4 114FSV-659 SV SVD WSD 56.76 41.77 4,749 1,991 480 73 2,919 3FSV-038 SV SVD DRD (If) 56.45 42.68 2,778 1,278 391 53 890 3FSV-657B SV SVD WSD 56.72 42.56 301 3,022 455 83 8 9FSV-020 SV SVD DRD (Ivf) 57.23 42.08 1,652 1,259 318 73 134 2FSV-022 SV SVD WSD 57.61 41.18 3,551 2,031 446 92 3,842 4FSV-029 SV SVD EPC 65.83 33.90 261 995 213 213 3,656 7FSV-213-2 SV SVD WSD 56.26 42.39 4,770 1,486 448 42 149 2FSV-913 SV SVD WSD 54.92 43.81 3,358 2,207 314 56 22 2FSV-914 SV SVD WSD 55.15 44.42 696 1,182 364 50 11 3FSV-919 SV SVD WSD 54.61 44.95 536 1,349 366 61 129 3FSV-919 SV SVD LFD 55.65 43.94 30 1,684 272 153 40 3FSV-921 SV SVD WSD 55.86 43.66 1,075 1,127 422 68 10,646 3FSV-004 SV SVD WSD 54.67 44.67 1,432 1,514 299 45 32 2FSV-902 SV SVD LFC 99.18 0.76 12 277 171 305 2 2


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INORGANIC & ORGANICGEOCHEMISTRYOF SANVICENTE,PERU 1075T^mv. . (Cont.)

CaCOa MgCO3 Fe Mn Na Sr Zn BaSample Loc. Lith. Carb. (mole%) (mole%) (/ag/g) (/ag/g) (ug/g) qug/g) (/ag/g) (ug/g)FSV-904 SV SVD EPC 99.31 0.64 75 126 391 391 14 3FSV-905 SV SVD DRD (If) 55.15 44.14 2,147 1,035 300 54 4 1FSV-909 SV SVD WSD 55.00 44.57 1,309 569 456 35 17 1FSV-423 SV SVD DRD (I,) 55.88 43.53 2,021 849 331 47 1FSV-673 SV SVD WSD 54.27 45.33 1,296 527 330 89 4 4FSV-673 SV SVD WSD 54.32 44.93 1,495 1,794 377 53 5,097 3FSV-674 SV SVD WSD 54.48 43.81 5,226 2,273 303 69 4,979 2F SV-675 SV SVD LFC 5 64.89 34.73 140 1,504 221 190 26 4FSV-851 SV SVD LFC 96.94 2.93 110 458 297 503 71 3FSV-853 SV SVD DRD (If) 57.40 42.37 392 653 463 151 16 4FSV-854 SV SVD LFC 88.90 10.96 119 471 308 347 774 2FSV-856 SV SVD LFC 98.31 1.61 94 269 930 930 13 94FSV-857 SV SVD LFC 99.79 0.12 104 285 141 1,080 33FSV-862 SV SVD WSD 57.10 42.54 503 1,017 271 136 5,104 4FSV-713 SV SJD DRD (If) 57.14 42.37 1,338 880 372 47 5 4FSV-714 SV SJD WSD 56.14 43.19 1,478 1,618 417 53 4 2FSV-714 SV SJD LFD 56.77 42.78 275 1,757 516 54 7 4FSV-718 SV SJD WSD 55.99 43.54 931 1,206 379 41 1,207 4FSV-718 SV SJD DRD (Im) 55.69 43.40 2,760 1,383 355 58 998 4FSV-719 SV SJD WSD 56.13 43.38 920 1,375 346 74 6 4FSV-779 AR SVD DRD (Im) 56.90 42.92 230 620 651 62 3FSV-776 AR SVD WSD 57.31 41.95 2,700 821 339 52 6 4FSV-779 AR SVD WSD 56.50 43.22 384 909 511 69 5 2Fsv-780 AR SVD WSD 56.43 43.11 1,012 1,115 270 54 14 5FSV-959 MA SVD WSD 56.80 42.97 149 909 660 100 4 5FSV-960 MA SVD WSD 57.52 42.26 287 722 531 58 4FSV-964 PA SVD DRD (I) 56.30 43.46 533 653 494 35 4,039 3FSV-964 PA SVD WSD 56.71 42.95 328 1,266 521 41 5,772 4FSV-965 PA SVD WSD 56.53 43.22 405 763 458 37 251 1FSV-967 PJ SVD WSD 56.75 42.82 279 1,677 479 46 i 3FSV-969 PJ SVD WSD 56.39 42.59 3,506 1,249 436 36 3FSV-983 SP SVD WSD 56.42 43.34 418 769 579 53 7

Locality:eeFigure1 for abbreviations,V = SanVicentemaindeposit2Lithologies:D = Alfonso olomite; L = BituminousiltyUncush imestone;VD= SanVicente olomite; JD= San udas olomiteaDRD = dark eplacementolomiteI4:very inegrained;f: fine-grained;m:medium-grained);SD= white parry olomiteII); LFD = late oid-filling olomiteIIId); LFC = latevoid-fillingalciteIIIc); EPC = calciteeplacingvaporiticulfate4 blank = not detected5XRD resultsndicate mixture f 75 percent olomitend 5 percent alcite

sparry olomite-II) upportshecathodoluminescencebser-vations. alcite seudomorphsisplaylightly igherNa andBacompared ith he atevoid-fillingalcite-IIIc. hismayindicate supply f bothcationsrom hereplacedulfate.The distributionf Fe, Mn, Na, Sr, Zn, and Ba in hy-drothermal dolomites at the district scale is summarized inTable2 andFigure . The followinganbe recognized:1)Mn and Fe are enriched in localities between San VicenteandQuebrada tcuyacu;2) the highestMn (up to 2,360/a,g/g) ndSr (up o 110/g/g)concentrationsccurn locali-tiessouth f Chilpes, ndcorrelate ithmajor ectonicinea-ments e.g.,Yanachurour,Rondayacu)ndbasementighs(e.g.,Quebrada ifi6n); nd 3) Machuyacus characterizedby anomalousr (up o 100/a,g/g)ndNa (up o 660/g/g)concentrations,ndby low Mn and Fe (820/a,g/g nd220Rare earth elements

Theresults f thecomparativetudy etweenheanalysesof the acid-solubleraction nd he whole-rockamplesregivenn Table3. The REE results representedn twosec-tions:SanVicentemaindeposit ndSanVicente istrict.

SanVicentemaindepositThe REE resultsrom he SanVicente eposit regivennTables 4 and 5. The distribution of the REE contents in thedifferent arbonateenerationss llustratedn Figure .ThebituminousiltyUncush imestonehowshehighestREE concentrationREE about 2/g/g). n the hydrother-maldolomites,he REE contents


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percentliesminimum

0.76

-0.720.68

O outlier0.80

DRD-Ivfn=4

oo

DRD-If DRD-Im WSD-II LFD-IIIn=8 n=8 n=58 n=2FIc. 6. Rangesndmediansf the MgCOa/CaCOaolar atioof thehydrothermalolomitesn SanVicente olostones.eeFigure forabbrevi-

ations.

calciteeplacingvaporiticulfate as REE between.12and6.50/xg/g.TheY concentrationsisplayimilarrendso those f thetotal REE contents Table4). In the UncushLimestone, heY concentrationangesrom20.4 o 22/xg/g,anddecreasesin the ore-stageolomites.he late void-fillingpostore)dolomite-IIId hows igherY concentrationsIIId: 0.7-1.2/xg/g). he atevoid-fillingalcite-IIIcIIIc: 0.7-24/xg/g)ndthe calcite eplacingvaporiticulfate2-5/xg/g)areY-en-richedcomparedo the hydrothermalore and postore)dolomites.The chondrite-normalizedEE patterns f the differentcarbonateenerationsre llustratedn Figure10.The REEpatternsf calciterom heUncush imestoneluster ithina narrowange ndparallelheshale istributionFig.10A).TheREE patternsf thevery inegrained, ark eplacementdolomite resimilaro the Uncush imestone.hissuggeststhat he hostdark eplacementolomite-IvfnheritedREEfrom a rock with REE similar to those in the Uncush Lime-stone. hemost ignificanteature ftheREE distributionnthedark eplacementolomiteubgenerationssa systematicdepletionf all heREE,particularlye,withadvancingy-drothermallterationFig.10A,Table ). Moreover,heper-vasivelyecrystallizedark eplacementolomite-Iraisplaysa slightlylattened atternn the Nd-Dy egion omparedotheunaltered olomite ark eplacementolomite-Ivf.The whitesparry olomite-IIs relativelyepletedn themiddleREE, anddisplaysEE patternsimilaro the darkreplacementolomite-ImFig. 10B).The late void-fillingdolomite-IIId xhibitswo ypes f REE patternsFig.10B).The atevoid-fillingolomite-IIIdn unmineralizedydraulicbreccia ementsFSV-919, SV-714) asessentiallyimilarREE patternsomparedo thewhitesparry olomite. ow-ever, hedolomitenfillingsn dissolutionrecciasithspha-lerite FSV-695,SV-1092)how flatter eavy EE (HREE)distributionithout negativee anomaly.urthermore,he

La/Yb atioof hehydrothermalolomitesTable ) decreasesin theorder: ark eplacementolomite-If,ark eplacementdolomite-Ira,hitesparry olomite-II, nd ate void-fillingdolomite-IIId. These indicate a trend towards more fraction-atedprecipitatesithadvancingineralization.The REE abundancesndpatterns f the atevoid-fillingcalcite-IIIc ary xtensivelyn slope,romstronglyegativeoweakly ositiveFig.10C).Threesamplesf thetranslucentcalcite nfilling oids n the dark replacementolomite-I(samplesSV-856, SV-857, nd FSV-665n Fig. 10C andTable5) haveREE patternsoughly imilaro those f thewhitesparry olomite-II. woofthese amplesFSV-665 ndFSV-857) recalcitentergrownithsphalerite-IIIement-ingdissolutionreccias.heyaredepletedn Ce (Ce/Ce*=0.35 and0.43,where Ce*= [(2LacN+ NdcN)/3],CN = chon-drite normalized)and their Eu content s lower than the de-tectionimit (Table ). Sample SV-856s depletedn lightREE (LREE) (La/Sm= 0.68,Ce/Ce* = 0.97)but hasa sig-nificant ositive u anomalyEu/Eu* = 2.14,whereEu* =[(SmcN GdcN)/2]).

Calcite roma largevein n a hydraulicrecciasamplesFSV-902n Fig. 10C andTable5) shows pronouncedn-richment in REE, with REE concentrations to 10 timesgreaterhan hondrite.n contrasto theother ydrothermalcarbonates,heREE patterns f these alcitesrecharacter-izedbya steepncreasen theLREE.Calcite t heveinmar-gin sampleSV-902m),nly fewmillimeterswayrom hecontactwith the dark replacementolomite-I, as a flatHREE pattern,n contrasto calcite rom he veincenter(FSV-902c) hich s stronglynrichedn the middleREE(MREE). In this attersample,MREE andHREE enrich-ments remore ronouncedhan hosen LREE,resultingnanoverall oncave-upEEpattern.n addition,hecalcite tthe vein center exhibitsa Tb maximum,and the calciteat themargin hows Tb minimum. sdiscussedyM611er1983),a Tb maximumn Ca mineralsndicatesn acidic arent o-lution, and a Tb minimum indicates an alkaline solution.Thus, he Tb enrichment ndicateshat the calciteat the cen-ter wascrystallizedroma moreacidicluid.The calcitese-placingvaporiticulfate avehe lattest EEpatternsFig.10C); heyareslightly e-enrichedCe/Ce*= 1.30)andEu-depletedEu/Eu*= 0.76).The REE patterns ormalizedo the averageostdolo-stone reshownn Figure 0D.Thisnormalizationrocedureeliminates the REE distribution characteristics inheritedfrom the hostrock.Thus, deviationsn the REE distributionsin thehydrothermalarbonateseflect ubsequentlterationprocesses,ncludinghe ore-formingvents. ll the hy-drothermalarbonatesremarkedlyepletedn LREE com-pared o HREE.Thewhite parry olomite-II nd atevoid-filling olomite-IIIdhow ronouncedegativeeanomalies.This may represent recipitationonditionsas discussedlater)anddoesnot necessarilymplya LREE-depletedn-comingre luid.Furthermore,heextensiveepletionf heore-stageolomitesomparedo thehostdolomitendicatesthatno extensiveEE exchangeccurred etweenhe orefluid and the REE-rich Uncush Limestone. This is consistentwith hestablesotopevidence hich uggestshatUncushLimestoneid notprovide re-formingomponentsr actasa fluidpathwaySpangenberg,995).


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INORGANIC ORGANIC EOCHEMISTRYF SANVICENTE, ERU 1077

ADRD-Ivf

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450 500

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Ba ( zg/g) Zn (p.g/g)I I I I I75 100 0 750 1500 2250FIG. . Rangesndmediansf heminor nd race lementsn thehydrothermalarbonatesf San icenteistrict..Iron.B. Manganese.. Strontium.. Sodium.. Barium.. Zinc.See igure forabbreviations.L = bituminousiltyUncushLimestone, = 7; DRD-If, n -- 4; DRD-Ir, n = 8; DRD-Im, n -- 8; WSD, n = 58; LFD, n -- 2; LFC, n = 11; EPC,n--3.

San Vicente districtThe REE concentrations and the chondrite-normalizedREE ratios or the carbonateamplesrom he SanVicentedistrict regivenn Tables and7. Thechondrite-normalizedREE diagramsre shownn Figure11. The hydrothermal

dolomitesreextremelyoor n mostREE, andseveralal-uesare below he analyticaletectionimit. Nevertheless,certainrends represent.TheREEpatternsf heUncush imestonen thedistrict-scale amplesave hapesimilaro thesamplesf thesamestratigraphicnit n theSanVicentemining rea Fig.11A).


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1078 SPANGENBERGET AL.TABLV.. MinorandTrace lement angesndMedian aluesn theHydrothermalolomitesf heSanVicente istrict

Locality Fe Mn Na Sr Zn Ba(n) qug/g) qug/g) qug/g) qug/g) qug/g) qug/g)QP 475-1283 1674-2358 436-551 74-93 3-9 -(2) (879) (2016) (493) (84) (7)RO 185-628 982-2022 302-398 72-113 24-41 5-6(3) (262) (1617) (375) (87) (37) (6)YS 326-534 850-1275 283-357 66-91 13-60 4-6(2) (430) (1062) (320) (79) (36) (5)UT 375-555 535-805 327-384 50-60 8-9 5-6(2) (465) (670) (356) (55) (8) (6)QU 620-1801 961-1247 320-397 37-107 25 2-7(2) (1104) (1105) (364) (72) (4)AY 398-2522 982-1557 322-516 19-164 19-164 6-70(7) (988) (1213) (378) (68) (46) (12)CH 234-3367 970-2291 274-542 39-76 6-18 2-19(9) (2103) (1230) (377) (50) (12) (4)AC 2532-3899 1017-1080 322-421 34-163 144-1779(3) (3758) (1069) (340) (34) (1476)US 65-435 766-1095 378-476 48-49(3) (205) (799) (455) (49)San Vicente 30-5226 527-3022 205-483 35-153 4-2919 1-9(28) (1325) (1313) (369) (56) (352) (3)AR 230-2700 619-1115 270-650 52-69 5-14 2-5(4) (698) (865) (425) (58) (6) (3)MA 149-87 722-909 531-660 58-100 4 4-5(2) (218) (816) (596) (79) (5)PA 327-533 635-1266 457-520 35-41 250 1-4(3) (405) (763) (494) (37) (3)PJ 279-3506 1249-1677 436-479 36-46 3(2) (1892) (1463) (458) (41)SP 418 768 579 53 7(1)

Themedianaluesregivenn parentheses;= number f analyzedamples Hydrothermalolomitesaltered ark eplacementolomiteIm:medium-grained),hite patryolomiteII), and ate oid-fillingolomiteIIId)2 Locality:eeFigure for abbreviations

ThreesamplesromQuebrada tcuyacuhow positivemanomaly.he REE abundancef the Uncush imestonesmarkedlyighern Vilcapomaelativeo SanVicente nd heother localities.The altered ark eplacementolomiteIf, Ira) n the dis-trict-scaleamplesonothave Ce anomaly,nlike he SanVicente amples.Thewhitesparry olomite-II amplesreextremelyow nREE (0.6-2.8 /xg/g)with REE concentrationsenerallybelowheanalyticaletectionimit Fig.11C).The ollowingfeatures,owever,anbe recognized:he REE concentra-tions ndoverall atterns f the district amplesrebroadlysimilaro themainSanVicente epositamples;heabsenceof negative e anomaliesn thewhitesparry olomite-II fthedistrict amplesCe/Ce*= 0.67-1.50)s heonlymarkeddifferenceo thewhitesparry olomite-II f theSanVicentedepositCe/Ce*= 0.25-0.53); ndone samplerom Que-brada ifi6n howssignificantREE enrichment,hichscharacteristicf latevoid-fillingolomite-IIIdn dissolutionbrecciasithsphaleriteromSanVicente.Depletionsn LREE (La-Sm) ndHREE (Sm-Yb)n car-bonatesonotshow ny lear egionalrends ithin heSanVicente elt (Table ). The greatscatter hown y the ele-mentalatios a/Sm,Sm/Yb, ndCe/Ndof thehydrothermaldolomitesdark replacement olomite-I,white sparrydolomite-II)sprobablyue o fluctuationsn thepore-fluid

chemistryseebelow).n summary,he REE patterns f theore-stageolomites,xceptinghe behavior f Ce andTm,are mostly imilarn samplest district nddeposit cales(Figs.10, 11). This supportshe stable sotope vidence(Spangenbergt al., 1994,1996;Spangenbergnd Macko,1998)of a common ydrothermalystem ontrollinghechemistryf dolomitesndassociateditumensn the egionasa whole, ven hough lterationsmore ntensen themainminearea.However,heabsencefnegative e anomaliesntheore-stageolomitest hedistrict cale omparedo hosefound t the maindepositmaybe consideredsevidenceflocaldifferencesn the ore-fluid hemistrypossibly oreoxidizing).Sulfursotopes

The sotopicompositionf theevaporiteulfate15.6and20.9%0, able , Fig. 12) allswithin heexpectedangeorMiddle TriassichroughLate Jurassic arineevaporites(Claypoolt al., 1980;Holser t al., 1988)andclearlyndi-cates marine ignatureor the sulfur. he sphaleritesl-I:8.1-12.1%o, median = 10.6%o;sl-II: 5.7-12.6%o, median =10.6%o;sl-III: 5.9-14.2%o,median = 11.2%o),galena(2.5-9.8%0,median 6.8%o), yrite 8.1-12.2%o,median10.3%o)and sulfur (7.6-9.7%0, median = 8.7%0) have uni-formly imilarsotopeatioswithin he SanVicentemainde-posit Fig.12).The 8a4S alues f sphalerites-I,II, and III


13/26

INORGANIC& ORGANICGEOCHEMISTRY F SANVICENTE,PERU 1079

/

P

/'PA/ oA

I San icente,.,Chilpes

Fe> 2000900o2000< 900

5 km

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Chilpes 1000 to 1500 YS0 < 1000

C ,-i,c/ .,/

P // //

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5 km ) QP

/P

// /PA'" hOAC /Chllffis, /

/350o460 j.o I350FIc. 8. Distributionf the minorand raceelementsn the ore-stageydrothermalolomitesdark eplacementdolomite-If,ark eplacementolomite-Im,hite parryolomite-II)f heSan icenteistrict.. ron.B. Manganese..Strontium.. Sodium.incwasnot ncludedecausehehighconcentrationsreprobablyue o contaminationuringanalysis.


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1080 SPANGENBERG T AL.

eq i


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INORGANIC& ORGANICGEOCHEMISTRYOF SANVICENTE,PERU 1081


16/26

1082 SPANGENBERG ET AL.T^BLE. REERatiosor heDifferent enerationsfCarbonatesn San icente eposit ormalizedo ChondritealuesromHanson1980)

Ce/Nd La/Yb LaJSm Sm/Yb Ce/Ce* Eu/Eu* Eu*Sample Carbonate2 (CN) (CN) (CN) (CN) (CN) (CN) (CN)FSV-015 UL 1.35 8.38 3.97 2.11 0.65 0.64 10.56FSV-1101 UL 1.46 8.76 3.43 2.55 0.78 0.57 12.85FSV-1103 UL 1.49 9.63 3.91 2.46 0.73 0.65 12.44FSV-801 DRD (I,) 1.70 19.39 4.58 4.23 0.76 0.72 1.53FSV-2508 DRD (I,) 1.19 21.52 4.94 4.35 0.47 0.69 1.21FSV-2502 DRD (If) 1.37 19.08 4.83 3.95 0.60 0.70 1.18FSV-020 DRD (Ivf) 1.28 8.35 2.88 2.90 0.81 0.65 1.49FSV-423 DRD If) 1.74 12.16 5.16 2.36 0.70 0.59FSV-853 DRD (If) 1.68 10.69 4.02 2.66 0.82 0.94FSV-905 DRD (I.) 1.70 26.21 6.88 3.81 0.53 0.34FSV-718 DRD I.) 1.21 17.91 6.58 2.72 0.23 0.25FSV-654 WSD 1.91 26.87 8.23 3.27 0.48 0.31FSV-806 WSD 1.13 12.27 7.52 1.63 0.25 0.08FSV-661 WSD 1.50 17.91 6.58 2.72 0.44 0.23FSV-919 WSD 1.20 2.72 2.78 0.98 0.58 0.45FSV-869 WSD 1.18 20.24 3.38 5.99 0.53 0.48F SV-919 LFD 0.83 1.15 1.98 0.58 0.47 0.30FSV-714 LFD 1.47 6.45 4.61 1.40 0.60 0.35FSV-695 LFD 0.73 0.46 0.60 0.76 0.95 0.34FSV- 092 LFD 1.10 0.66 1.22 0.54 1.14 0.25FSV-665 LFC 0.91 21.90 2.51 8.71 0.35 0.71FSV-857 LFC 0.82 17.91 2.74 6.53 0.43 0.52FSV-856 LFC 0.73 0.68 - 0.97 2.14 0.39FSV-902c LFC 0.52 0.72 0.39 1.85 0.49 0.81 6.53FSV-902m LFC 0.69 0.33 0.30 1.09 1.28 0.81 2.91FSV-423 EPC 0.82 0.88 0.61 1.45 1.30 0.76 1.81F SV-904 EPC 0.84 1.09 0.67 1.63 1.33 0.71 1.36

CN = chondrite normalized (Ce/Nd)cNextentfCedepletion;LaYb)cNfractionationfLBEEromheHREE;La/Sm)csfractionationf heLBEE,Sm/Yb)cfrae-tienationf the HREE; Eu/Eu)cs Eucs/[(SmcNGdcs)/2],alues 1 positivenomaly,1 negativenomaly,1 no anomaly;Ce/Ce)csCecs/[((2Lac+ Ndcs)/3] ince rwasmostlyotdetected2UL= bituminousilty ncushimestone;RD= darkeplacementolomiteIvf;eryine rained;f: ine-grained;m:medium-grained);SDwhiteparryolomiteII);LFD= ate oid-fillingolomiteIIId); FC ate oid-fillingalciteIIIc); PC calciteeplacingvaporiticulfate

I I i I i i/[ I IUncushimestoneI (a)(4) (Ivf)

(2) TH (if) Darkeplacementolomite(2) (Im)

(5) Whiteparryolomite11)(4) Lateillingolomite111d)I--II I I Lateillingalcite111c)

(2) CalciteeplacingulfatevaporiteEPC)I I I I I I/I/ I I0.0 2.5 5.0 7.5 10.0 12.5 50.0 75.0

T_,REElag/g)FIG. . Rangesndmediansf he otalare arth lementbundancef hecarbonatesrom an icenteeposit.eeFigure for abbreviations.


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INORGANIC & ORGANIC GEOCHEMISTRYOF SANVICENTE, PERU 1083

100.

10

0.1

0.01

10:

0.01

A UL FSV-015) UL (FSV-1101)_,.AS ULFSV-1103)

Dark replacementdolomite DRD) DRD-IvfFSV-801)[] DRD-Ivf FSV-2502) DRD-IvfFSV-2508)DRD-IfFSV-853)]DRD-I FSV-905) DRD-IvfFSV-020) x DRD-If FSV-423)E]DRD-I(FSV-718)La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er TmYb LuC o

Late illing calcite III) Calcite eplacingx LFC-IIIcFSV-665) LFC-IIIcFSV-902c) sulfate EPC)/ LFC-IIIcFSV-857) LFC-IIIcFSV-902m)] EPC FSV-423)v LFC-IIIcFSV-856) []EPCFSV-904)La Ce Pr Nd Sm EuGd Tb Dy Ho Er TmYb Lu

10

0.01

B DarkeplacementolomiteI f)

White sparrydolomite II)[] WSD-II (FSV-654)[] WSD-II (FSV-869)A WSD-II (FSV-661)v WSD-II (FSV-919)[] WSD-II (FSV-806)

Late filling dolomite III)o LFD-IIId FSV-714)o LFD-IIId FSV-919)+ LFD-IIId (FSV-695)x LFD-IIId (FSV-1092)

lOO

lO

o.1

O.Ol

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er TmYb Lu

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb LuFIG.10. A.-C. Chondrite-normalizedEE abundancesn carbonatesrom he SanVicente eposit;eeFigure for ab-breviations.. Uncush imestonendsubgenerationsf dark eplacementolomiteDRD) comparedo NorthAmericanshale ompositeNASC).B.Whitesparry olomite-II nd he atevoid-fillingolomite-IIId. . Latevoid-fillingalcites-IIIcandcarbonateseplacingvaporiticulfatesEPC).D. MedianREE patterns f theUncush imestone,nd hehydrother-malcarbonatesormalizedo hehost olomiteDRD-Ivf). IId A: Latevoid-fillingolomite-IIIdn unmineralizedementofhydraulicrecciasFSV-919,SV-714);IId B:Latevoid-fillingolomite-IIIdn dissolutionrecciasithsphaleriteFSV-695,FSV-1092);IIc A: Latevoid-fillingalcite-IIIcwith similarREE patterns omparedo the atevoid-filling olomite(IIId B); IIc B: Latevoid-fillingalcite-IIIcroma arge ein n thehydraulicrecciaFSV-902).

fromsample SV-663 how n sotopichiftwithparageneticsequencesl-I->sl-II:-1.0%o) and (sl-II->sl-III: -1.3%o).Fontbot ndGorzawski1990)noted similarsotopichiftfor hedifferent phaleriteenerationsn sphalerites-IndII. Thesphaleritesn thewhole ampleetshow o statisti-callysignificantifferencesithparagenesisFig. 12).Thesphalerite3.8-7.0%,, median= 4.9%,), galena -0.7-10.9%,,median 0.9%,),andpyrite 6.1%o)rom he smallmines ndprospectsredepletedn 34Sonaverageyup to4.2%,)compared ith he maindepositFig.12).Thissug-gestshat sotopicallyightsulfur, robably f magmaticri-ginorderivedromdegradationf sedimentaryyrite nd/ororgano-sulfurompoundsOhmoto,1972; OhmotoandGoldhaber,997),wasmoremportantn theprecipitationfthese sulfides.

Discussion

The ncorporationf minorand raceelementsincludingREE) ntoCa-Mg-carbonatesscontrolledy hedistributioncoefficientDTE:DTE = (CTE/CM)c/(CTE/CM)f

Where C is the concentration f the trace element (TE) orthemajor ationM, Ca + Mg n thecase f dolomites)n thecarbonate c) or in the fluid (f). The few reliable distributioncoefficientsor carbonatest diageneticemperatureshichare available for minor and trace elements (Kretz, 1982;Veizer, 1983) indicate hat the Fe, Mn, and Zn coefficients re>1 (DFe= 1.18-23.6;DMn= 6.37-38.1; Dzn= 23.8-95.2), andforMg,Sr,Na,andBa


18/26



19/26

INORGANIC & ORGANIC GEOCHEMISTRY OF SAN VICENTE, PERU

TABLE. REE Ratiosof theCarbonateamplesrom he SanVicente istrictNormalizedo Chondritealues1085

Sample Loc. Carbonate Ce/Nd La/Yb LaJSm Sm/Yb Ce/Ce2 Eu/Eu* Eu*(CN) (CN) (CN) (CN) (CN) (CN) (CN)F SV-684 QP DRD (Lf) 1.39 9.11 2.30 3.96 1.00 0.19 1.64FSV-685 QP DRD (I) 0.60 1.33 0.24 5.48 0.74 0.21 6.60FSV-984 QP WSD 1.10 1.14 0.00F SV-985 QP WSD 1.17 1.14 0.83 0.26 1.20FSV-681 SI DRD (Lf) 1.48 6.80 2.12 3.21 1.05 0.23 5.58FSV-2562 SI DRD (Lf) 3.12 4.06 1.66 2.45 1.66 0.25 0.91F SV-682 S E PC 1.93 7.70 0.86 0.27 1.05FSV-1059-1 QU UL 1.51 7.86 3.48 2.26 0.78 0.22 12.19FSV-1059-2 QU UL 1.62 9.91 3.62 2.74 0.81 0.23 3.63FSV-1058 QU UL 1.77 10.81 4.45 2.43 0.78 0.23 3.17FSV-1136 QU UL 1.58 10.00 3.06 3.27 0.90 0.19 3.56FSV-2538 CH DRD (Lf) 1.36 0.84 1.50 0.21 1.87FSV-2545 CH DRD (Lf) 2.94 0.25 3.04 0.26 1.26FSV-754 CH DRD (Lf) 1.03 2.62 0.72 0.32 0.65FSV-759 CH DRD (If) 0.73 0.00 2.20 0.25 0.45FSV-763 CH DRD (Irn) 1.84 0.50 1.25 0.12 0.75FSV-754 CH WSD 1.47 0.74 0.00F SV-759 CH WSD 1.17 1.72 0.86 0.17 0.42FSV-753 CH WSD 0.73 0.00 0.00 3.27 1.79 0.26 0.31FSV-754B CH LFD 1.33 7.68 1.85 4.15 0.98 0.20 11.39FSV-982 CH LFD 0.98 1.06 0.00FSV-978 US LFD 0.37 0.66 0.79 0.84 0.10 0.35 2.43FSV-979 AC WSD 2.94 1.50 0.00FSV-2524-1 UN UL 1.42 5.25 4.39 1.20 0.49 0.23 6.28FSV-2524-2 UN UL 1.67 6.35 5.48 1.16 0.51 0.24 7.32FSV-2550 sJ UL 1.67 11.57 2.90 3.99 0.74 0.21 4.87FSV-2555 sJ DRD (Lf) 1.65 1.30 1.25 0.20 0.94FSV-2558 sJ DRD (If) 2.94 1.03 1.39 0.16 0.49FSV-1097 V UL 0.73 3.98 1.36 2.93 0.60 0.22 35.39FSV-1098 VI DRD (Lf) 0.88 2.76 0.79 3.48 0.88 0.21 8.53FSV-778 AR DRD (If) 1.29 0.76 1.61 0.26 0.42FSV-962 MA DRD (If) 2.20 1.12 0.00FSV-959 MA DRD (Im) 4.41 0.87 2.24 0.18FSV-960 MA DRD (Im) 16.89 5.38 1.95 0.24 0.29FSV-880 QS DRD (If) 0.42 5.89 0.59 0.20 0.25FSV-689 SP DRD (Im) 1.25 2.44 0.76 0.22 0.91FSV-691 SP DRD (Im) 1.65 3.81 0.70 0.21FSV-694 SP DRD (Im) 9.55 3.96 1.12 0.22 0.36FSV-693 SP DRD (Ira) 0.37 0.87 0.65 0.18FSV-693 SP WSD 1.84 0.67FSV-694 SP WSD 2.20 0.73

CN = chondrite normalized (Ce/Nd)c = extent f Ce depletion;La/Yb)c = fractionationf LREE from heHREE; LaJSm)c= fractionationf the LREE; Sm/Yb)c= frac-rionationf the HREE; (Eu/Eu*)c = EUCN/[(SmcNGdcm)/2],alues 1 positive nomaly,1 negativenomaly,1 no anomaly;Ce/Ce*)c =CeCN/[((2LacNNdcN)/3since rwasmostlyotdetecteds Locality:eeFigure forabbreviationsaUL = bituminousiltyUncushimestone;RD = dark eplacementolomiteI. very inegrained;f: fine-grained;m:medium-grained);SD=white parryolomiteII); LFD = latevoid-fillingolomiteIIId); LFC = latevoid-fillingalciteIIIc); EPC= calciteeplacingvaporiticulfateDNa= 0.00003; Ba 0.05-0.22). he apparent istributionvaluesor the REE in foraminiferalalcite re >1, andgen-erally ecreaseexceptinge)with onic adii romDLa 125to Dyb = 73 (Palmer, 1985). Distribution of the trace ele-ments,moreover,s nfluencedy sorption n the carbonatesurface Zacharaet al., 1991), the concentration f the com-plexingigandse.g.,Cantrell ndByrne, 987;M611er,991),and he precipitationate Lorens, 981).VahrencampndSwart 1990)suggestedhat he Sr distributionoefficientndolomites dependentn hedolomite toichiometry.Mg, Fe,Mn, St,Na, andZn in thehydrothermalarbonates

The observedelativencreasef Mg in the hydrothermaldolomitesFig. 5) would equire highMg/Caratio n the

incomingluid.Possibleourcesf Mg are rom heconversionof highMg to low Mg calcite, edolomitizakionf Ca-richdolomites,ndsmeckiteo llitcconversione.g.,Richter, 974;Pingitore, 978;McHargue ndPrice,1982;Leuchs, 985).The ncomingluid ssuggestedohaveeachednderlyinge-trital rocks Fontbot6and Gorzawski, 990,Moritz et al., 1996),andsmectitereakdownould ea ocalMg source.hesmec-kite o llitc ransformation,ndother rocessesncludinglbiki-zation,lkalieldsparndmica issolution,nd nterlayer-cationexchangen clayminerals ay lsoeleaseignificantuantitiesof Fe2+ ndNa+ (e.g., rice, 982;McHargnendPoseyt al.,1987; ankowskindJacobson,989).TheFe-depletionn theore-stageydrothermalolomites(dark eplacementolomite-I ,white parry olomite-II,ate


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1086 SPANGENBERG ET AL.lOO

OlCE

180:

10

0.1

0.0110:

0.1.

0.01

AN.Bituminousiltyncushimestone

x QU UN QU , , UN QU O SJ QU Vl

'a (e Ir IdSan Vicenteepositm IuGd l:b y o Ir 'l:mb 'uB Dark replacementdolomite

x IvfQP'lvfQP IvfCH IvfSl ,I, IvfCH lvfSl O IvfCH[] Ivf Vl M Ivf SJ'a Ce 15rNd

A If Ar If QS vf P DRD_ImA Im SP' ImSP San icenteepositm Iu(d b Oy o 'lr 'l:mb 'u

c White sparrydolomite

o II QP + II CH[] II QP ,e, II AC[] II CH II SPV II CH II SP

'a Ce r IdSan Vicenteepositm u(d 'b[y o r rnb 'u

FIG. 11. Chondrite-normalizedEE abundances.. BituminousiltyUncushLimestone. . Dark replacement olomite-I.C. White sparrydolomite-IIrom heSanVicente istrict. ompare ith he ielddefined ysamplesromSanVicentemine shadedrea).SeeFigure for ocationfthesampleites.

void-fillingolomite-IIId;ig.7) suggestshatFe '+mayhavebeen emoved efore olomite recipitation.ince e, Mn,andZn haveD > 1, the fluidwouldhavebecome rogres-sively epletedn thesemetals uringprecipitationf thedolomitesnless xternallyecharged.n addition, othZnand Fe wouldhavebeen extractedrom the fluid duringsphaleriterecipitation.major ontrol nFe '*substitutionin carbonates s fluid redox conditions,as discussedater. Thenoncathodoluminescencef dolomite-IvFig. 3D) and thered uminescencef dolomite-II Fig.3H) furthermoreug-gest hat hehigh-Fe ostdolomite-Ivas ltered y a fluidwitha relativelyighMn/Feratio,and/orhatFe '+wasex-cludedromprecipitatedarbonatee.g.,due o redox ondi-tions).A large xternalMn source ould e the detrital edi-ments ndvolcaniclasticocks f theunderlying itu Group,Permo-TriassicntrusivesSanRam6n ranite ndequivalentrocks), nd he LowerPaleozoicearSanVicente. eachingof these ould ringmportantmountsf Fe, Mn, Mg,andSr intosolution. trontiumsotope tudiesndicatehat hePertoo-Triassicntrusions n the Pucar5 basin, or the clasticrocksn theMituGroup rat hebase f hePucargequence,area ikely ourcefradiogenic7SrMoritz tal.,1996). hepreferentialnrichmentf the fluid n Mn comparedo Femay eexplainedyoxidizingonditionsuringmigrationseebelow). he occurrencef massive arcasite,owpseudo-morphedypyrite, t theborder f theuppermargin f themain eposite.g., an icente echomanto) uggestshat heore luidmayhave ecome nrichedn Fe during reprecipi-tation. * is iberateduring recipitationfsulfidese.g.,Ms*+ H.S > 2H + + MS, M '+= divalentmetal).Thus he ore luidmay ave ecomenrichedn Febydissolutionf hedolomitehost ocksdark eplacementolomite-Ivt;ig.7).Fractionationf theREEduringmineralization

The overallractionationf REE in hydrothermalarbon-ates anbe explainedsing b/Ca ersus b/La Parekh ndMi511er,977), n termsof assimilationndremobilization ur-ingmineralizationFig.13).TheYb/Ca atio srelatedo theextent of interaction ("assimilation")between the hostdolomitend he luidat ncreasingater-rockatios hile heYb/La atio epresentsheoverall EE fractionation"remo-bilization").heSanVicente ydrothermalarbonatesisplaya roughly iagonalrend n the Yb/Ca-Yb/La iagramFig.13), ndicatinghat heywereprecipitatedroma fluidwhichincreasinglyractionatedheREE duringmineralization.ThepronouncedREE depletionndscattern theREEpatternsf theore-stageolomitesIm, I) reflect ost-rockalterationy circulationf arge mountsf REE-poor olu-tions. The carbonate-fluid distribution coefficients of theREE are arge 70-120;Palmer, 985).Thus, xtremelyighwater/rockatios re equiredo alter heREE distributionncarbonatesuringdiagenesisBanner t al., 1988;McLen-nan, 1989). Graf (1984), however, ocumentedhat the al-teredhostdolomitesn theViburnum rendMississippial-ley-typeistrictresignificantlyepletedn LREEcomparedto the unaltered host dolomite, as a result of host-rock nter-actions ithLREE-depletedresolutions.Since REE are more abundant n calcite than dolomite, itis notsurprisingo seehigherMREE andHREE in the ateopen-spaceilling alciteIIIc). TherelativelyowLREE of


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INORGANICORGANICEOCHEMISTRYFSAN ICENTE,ERU 1087

SampleTABLE. SulfursotopeompositionfSulfurineralsrom epositsnd re ccurrencesn he anicenteistrictLocality(abbreviation) Lith. Manto Description/sulfurhase

334S(%, CDT)

FSV-1002 YanachuroSur (YS) SVDFSV-0995 PefiaBlanca PB) SJDFSV-0752 ChilpesCH) SJDFSV-0765 ChilpesCH) SJDFSV-0687 ChilpesCH) SVDFSV-0873 ChilpesCH) SVDFSV-2534A Uni6n Mantus (UM) RSFSV-2534B Uni6n Mantus (UM) RSFSV-0666 SanVicente (SV) ADFSV-0667 SanVicente (SV) ADFSV-0811 San Vicente (SV) ADFSV-0815 SanVicente (SV) ADFSV-0816 San Vicente (SV) ADFSV-0818 SanVicente (SV) ADFSV-0851 San Vicente (SV) SVDFSV-861 SanVicente (SV) SVDFSV-870 SanVicente (SV) SVDFSV-1092 SanVicente (SV) SVDFSV-2517 SanVicente (SV) SVDFSV-683 SanVicente (SV) SVDFSV-1090A SanVicente (SV) SVDFSV-1091 San Vicente (SV) SVDFSV-679 SanVicente (SV) SVDFSV-675 SanVicente (SV) SVDFSV-422 San Vicente (SV) SVDFSV-0794 SanVicente (SV) SVDFSV-663 SanVicente (SV) SVD

FSV-916 San Vicente (SV) SVDFSV-921 SanVicente (SV) SVDFSV-924 SanVicente (SV) SVDFSV-0074 San Vicente (SV) SVDFSV-0444 SanVicente (SV) SVDFSV-0394 SanVicente (SV) SVDFSV-031 SanVicente (SV) SVDFSV-0414 San Vicente (SV) SVD

FSV-680 ArcopuncoSR) SVDFSV-690 Pichita PI) SVD

Galena n WSD 10.9Massivealena -0.1Pyritencalcite 6.1SphaleriteI inWSD 3.8Galena n WSD II -0.7SphaleriteI inWSD 4.9Galena n WSD II 0.9SphaleriteI inWSD 7.0Galena n WSD 1.4Evaporiteulfateense 15.6Evaporiteulfateense 20.9Alfonso PyritenWSD 8.1Alfonso PyritenWSD 10.1Alfonso SphaleriteII inLFD 11.0Alfonso SphaleriteII inLFD 10.9Alfonso SphaleriteII inLFD 11.2Alfonso SphaleriteI inWSD 12.6SV echo SphaleriteI inzebra re 12.1Galena n WSD 8.1SV echo SphaleriteII inWSD 13.9SV echo Massiveyrite 12.2SphaleriteII inWSD 13.5Sulfurnquartz 9.7Massivey nWSD 10.5SV echo SphaleriteII inLFD/LFC 13.9SV echo SphaleriteinWSD 12.1SV echo SphaleriteII inLFDand yrobit. 14.2Jesus Sulfurncalcite 7.6Jesus SphaleriteI inzebrare 11.5Ayala SphaleriteinDRD Im) 10.6SphaleriteI inWSD 9.9Ayala SphaleriteinDRD Im) 8.1SphaleriteI inWSD 7.1SphaleriteII inLFD 5.9Galena 3.8Ayala SphaleriteI inWSD 5.7Galena 2.6Ayala SphaleriteI inWSD 8.0Galena 9.8Ayala SphaleriteII inLFD 7.3Galena 2.53t Sphaleritein DRD Im) 10.4Galena 9.63t SphaleriteI inWSD 10.62 SphaleriteI inWSD 12.2Galena 6.83i SphaleriteI inWSD 10.2Galena 6.7

3p SphaleriteinDRD Ira) 12.1SphaleriteI inWSD 12.2Galena 6.9Sulfur n EPC 10.3Sulfur n EPC 10.2The ocationsf he ampleitesre hownnFigure,SV= San icente ain epositLithologies:D=Alfonsoolomite;L=bituminousilty ncushimestone;VD San icenteolomite;JD SanudasolomiteAbbreviations:RDIm) medium-grainedarkeplacementolomite-Im);SD whiteparryolomiteII);LFD= ate oid-fillingolomite(IIId);LFC= ate oid-fillingalciteIIIc);EPC= calciteeplacingvaporiticulfateData romFontbot ndGorzawski1990) ncludedorcomparison


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1088 SPANGENBERG ET AL.i i i i i

Pyrite SanVicente(n=4) main depositSulfur H(n=2)Sphalerite (n=5)SphaleriteI (n=10)Sphaleritell o I --H(n=9)Galena ] -(n=8)

I I I I I I I I ISan VicenteGalena m district

Yanachuro SurSphaleriteI []Pefiaianca ChilpesSulfur O UniOn antus

O ArcopuncoPyrite PichitaEvaporite sulfate i i i i i i i i i

0.0 5.0 10.0 15.0 20.0634S %o,CDT)

FIG.12. Rangesndmediansf 1534Salues f thesulfurmineralsromSanVicente epositndoccurrencesn SanVicente istrict.

theseatecalcites ay ecordminor ractionationuring is-solutionndprecipitationf thehydrothermalarbonates.Eh-pH considerations

Thetrace lementshatoccurn aqueousolutionsn mul-tipleoxidationtates, .g.,Fe(II,III), Mn(II,IV), Ce(III,IV),andEu(II,III), arepotentialracers f Eh-pHchangesuringaliageneticrocesses.hus, he distributionf Fe, Mn, Ce,andEu in thehydrothermalarbonatesanbe consideredntermsof theredox onditionsuring reprecipitation.Cerium ndcuropium nomalies

In a sedimentarynvironment,e3+maybeoxidizedo the13.9percent maller e4+ ation, hichs argely dsorbedyhydrolizatesr suspendedatter e.g.,Piper,1974;Palmer,1985; ligandM'Rabet, 985)or retainedn solutionscar-bonate omplexese.g.,M611er,983;M611ert al., 1984).nsuch ases, recipitatedarbonates ayhavea negative eanomaly.Thenegative e anomalyn theore-stageolomitesf theSanVicente epositFig.10A,B, Table ) suggestshat heincomingre luidcontainedominantlye4+whichwasnotincorporateduring olomiteormation.his mplies rela-tively xidizingre luid.The Eu behaviorn the SanVicentedeposit arbonates(Table ) is summarizeds ollows. he bituminousiltyUn-cush imestonend hehost ark eplacementolomiteIvf)

10'61 .--.071o-91 ,I ti0-10/ ...........0.001 0.01 0.1 1Yb/La (atomic atio)

UL DRD-Ivf DRD-If13DRD-Im[] WSD-II[] LFD-IIIdO LFC-IIIc

FIG.13. Yb/Ca s.Yb/Laplot or hehydrothermalarbonatesn theSanVicente istrict,howinghe rends f REE fractionationuringmineraliza-tiondefined y Parekh ndMOller 1977).SeeFigure for abbreviations.

have negativehondrite-normalizedu anomalyEu/Eu*:0.57-0.65 or Uncush imestone,.65-0.72 or dark eplace-ment dolomite-Ivf).he Eu concentrationn the ore-stagehydrothermalolomitesdark eplacementolomite-If, arkreplacementolomite-Ira,hitesparry olomite-II,atevoid-fillingdolomite-IIId)s lower han he analyticaletectionlimit, lowerimitof detection,LD: 0.05/xg/g; hondrite-normalizedLD: 0.69).Thisdoes otnecessarilyuggestnegativeu anomalysee heEu* valuesn Table ) in thesedolomites.he ate-stage,oid-fillingalcitesaveess ega-tive 0.81)or positive2.14)Eu anomalies.hisEu enrich-ment n the late calcite-IIIcmeritsan explanation. hile2+Eu2+ 1.17A) is arger hanCa (1.00A), it has he samecharge ndsize sSr + 1.18A) that sknowno substituteorCa +.Thisargument ayexplainhe essnegativeor morepositive) u anomaliesn the atecalcitesomparedo thedolomites.hus, hangesn sizeof the Eu anomaliesn thehydrothermalarbonatesay eflect impleemobilizationfthehost-rockEE,with ittle ractionationuring issolutionandprecipitation.Fe-Mn covariation

The Fe-Mn covariationFig. 14) in the hydrothermaldolomitesisplays roughly -shapedrend,characterizedbya verticalield A-B)withMn between 00and3,000/xg/gand owFe (


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INORGANIC& ORGANICGEOCHEMISTRYOF SANVICENTE,PERU 10893500

B

2500.:::i:;::::; I /.;::;::.2000-:..11:::::: :1' / ..... [] .... ' O .....:&.::i::::::61 ======================= i;t:_':::01 .,"':::;;::..'::;::::::::J

i:''' o" "' b: ;. .... [] ......L. Or' ......... - ............1%:-J;fi.; ; ; : :. ? : : ;El;; ; ; ; ; DRD_iv..............00- ....;:;;;::;;;;;-.) DRD-If[] DRD-Im[] WSD[] LFD0 0 1000 2000 3000 4000 50'00 6000Fe (p,g/g)

Fc. 14. Mn vs.Fe plot or hehydrothermalolomitesrom he SanVi-centedistrict. here s an overall -shapedrend,with a dogleg xtension.See ext or discussion.eeFigure for abbreviations.

precipitation:hermochemicalulfateeductionsee ulfide-sulfate h-pHboundaryn Fig. 15)andpyrobitumenorma-tion SpangenbergndMacko, 998).The Mn 2+ ndFe 2+ oncentrationsn the ncomingxidiz-ing fluidwereconstantnd ow (e.g., n the range f


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dolomite, and could not further deliver reductants. Conse-quently,echarge f the fluid-rock ystem ith oxygenatedbasinal olutionsould rovide xidizingonditions.exturaland stable sotope videnceSpangenberg,995;Spangen-berget al., 1996) howhat he atevoid-fillingydrothermalcarbonatesrecipitatedroma fluid-bufferedystem,nd helow Mn andFe concentrationsn the ate nfillingdolomitessupporthehypothesisf a return o oxidizingonditionsn afluid-bufferedystem. hus, he Ce anomaliesnd he Fe-Mn covariationsf the hydrothermalarbonatesecord hechangesn Eh of the ncomingre luid.Theevolvedsotopicandelementalompositionf heepigeneticarbonatesom-pared o the host-rockointso a model hat representsnopen ystemn the mineralizedone hatshiftsrom ock- ofluid-dominated.hisdynamicluid-rocknteractionystemincludes ultiple tagesf epigeneticarbonateementationand evolvingock-fluidnterfacese.g., dark replacementdolomite-I/fluid;hitesparry olomite-II/fluid;atevoid-fill-ingdolomite-IIId/fluid;nd atevoid-fillingalcite-IIIc/fluid).Source f sulfurThe difference etweenhe sulfur sotope ompositionfthe SanVicente ulfides nd hoseof the smallMississippiValley-typeccurrencesuggestsifferent ulfur ources.ntheSanVicentemaindeposithe834Saluesndicate dom-inantlyMiddleTriassico LateJurassic arine vaporitieul-fatesoume. he negativerending 34S aluesound or thesulfidesromminoroccurrencesChilpes, efiaBlanea) ug-gest localcontributionf magmaticulfur ~0%0;Ohmoto,1972).A locallymore mportant ontributionf isotopicallylightsedimentaryulfurpyrite r organic-sulfurompounds;e.g.,Ohmoto ndGoldhaber,997) annot e excluded.It hasbeenwell documentedhat dissimilatoryacterialsulfateeductionntails large sotoperactionationup to-60%0).Accordingly,hebacteriogeniculfidesregenerallyidentifiedy a marked hift oward 4S-depletedaluesom-pared o theparent ulfate, nda large cattern their8a4Svaluese.g.,Holser t al., 1988).Thermochemicalulfatee-ductionnvolvesittle or no net isotoperactionatione.g.,Machel t al., 1995; ones t al., 1996).Fontbot6 ndGorza-wski 1990) nterpretedhehigh8a4S alues f SanVicentesphaleritendgalena sresultingrom hermochemicalul-fatereduction. ur results uggesthat he deposit ulfideswerederivedrom abiogeniceduction f MiddleTriassicthrough ateJurassic arine vaporite-derivedulfate. ur-thersupportor thisconclusions provided y depletedaCcalcite cements ~-12%o 81aC) n the San Vicente district(Spangenbergt al., 1996) and the organicgeochemicalanalysesSpangenbergndMacko, 998).The introductionof bacterial-derived-alkanesy theore luiddoes ot mplythat he ncomingluids rought acteriao the oresite.AtSanVicente,he relativelyighcontent f n-alkanesnd so-prenoids, nd absence f steranes, opanes, nd aromaticcompounds,eflectshe highbitumenmaturity ndstronglysuggesthatbiotawasnot ntroducedy he ncomingluidatthe time of ore precipitationSpangenbergnd Macko,1998).This,with he sulfursotope ataandgeochemicalv-idence discussed bove, indicates hat thermochemicalsul-fate reduction as he mainhydrogen ulfide ourceo theore fluid.

Ore-fluidlow pathandhost-rocknteractionThe traceelement istributionsn the hydrothermalar-bonatesndicatehat he ncoming ineralizingluidwasnotin chemical quilibrium ith the Pucar5Groupcarbonates.Thesame onclusionas uggestedn hebasis f stableso-tope data (Spangenberg,995;Spangenbergt al., 1996).

This mplieshat he Pucar5 arbonateost ocks ouldnothaveacted s he mainaquifer or fluid low,and hat luidshad o be isolatedrom the Pucar5 ocks long heir entireflowpath.We assumehat luid lowwas hrough quifersn-cludingdetritalunitsat the baseof the Pucar5basinanddeeper ermeableocks ssuggestedy the ocalchemicaldifferencesf the ore-fluid hemistrye.g.,Fe concentra-tions,REE data,81aC f the pyrobitumens,nd8a4S ata),withvery ittle nteractionith hePucar5 arbonates.ccessto the ore depositioniteswasby interconnectedhannels(faults, asementighs) ear heoreoccurrences,here luidcould lowupwardwithout xchangingignificantlyith hesurroundingsocks. ixing f he ncomingluid slightlycidic,oxidizing, 2CO dominant)nd ocalpore luidsn the hostrocksalkaline,educing, CO3- dominant),nd nteractionwith hehost ocks, xplainshegreat catter f the REE andother race lementsn thehydrothermalarbonates.Conclusions

Majorand race lementincluding EE) geochemistryfthe hydrothermalarbonatesf the SanVicenteMississippiValley-type istrict, ombined ith carbon nd oxygenso-topes, rganic eochemicalndorganicsotopeesults f thebitumensndassociatederogens,nd hesulfursotopical-uesof the different ulfurminerals,rovide datasetwhichcharacterizeshe fluid/fluid nd luid/rockmixing rocessesinvolveduring ulfide recipitationt SanVicente, ndgivesinsightsnto hecompositionf theore luids,he luidpath-way, nd hesoume nd eduction echanismf sulfur:1. The ncoming ineralizingluidwasslightlycidicpH~5),oxidizing,robablyue o circulationhrough nderlyingdetrital rocks.2. Theregional eochemicalomogeneityf hydrothermalcarbonates,ombinedith he ackof geochemicalquilibra-tionbetweenhe ncomingluidand he carbonateocks fthe PuearaGroup, onstrainhe regional-scaleluid low ohighpermeabilityhannelsfaults, asementighs) ear he

ore occurrences.3. The dissolutionlteration f the hostdolomite y thecorrosivencomingluidexposedndigenousydrocarbons,andprovidedhe ocal edox onditionsecessaryo reducesulfate o sulfide, nd Eu3+to Eu2+. n this early rock-buffered tage,hehostdolomite as eplaced yhydrother-maldolomitesdark eplacementolomite-Ifo whitesparrydolomite-II) ndsphalerite-I.4. Precipitationfopen-space-fillinghite parryolomite-II and sphalerite-II ccurredn acidic, educing luid-buffered onditions,s ndicatedy heMn uptake ndREE-depletion f thewhitesparry olomite-II.5. The REE enrichment,he Mn depletion, nd positiveEu anomaly f the late-stageug-fillingarbonatesndicatethat hepostore,residual"cidicluid,wasoxidizingdue oinfluxof fresh asinal aters), ndwould xtensivelynhance


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INORGANIC & ORGANICGEOCHEMISTRYOF SANVICENTE,PERU 1091the secondaryorosity y carbonate issolutionntil pH-buffering ccurred. O2degassingould ause recipitationof REE-rich late carbonates.6. The traceelement ignaturef the SanVicente arbon-atessupportshe geneticmodelproposed y quantitativemodeling f the stable sotope ovariations,hich nvolvesmixing f indigenousntraformationalluidandan ncomingslightlycidic re luid,and nteractionetweenhecorrosivefluid and the host dolostone.7. The absencef negative e anomaliesn the ore-stagedolomitest the district cale ompared ith hose ound tthemaindeposits n agreementith he83C hiftof thepy-robitumenn themining rea. heseactorsreconsideredsfurther evidence of local differences in the ore-fluid chem-istry, ossiblyf a moreoxidizing ature, ombined ith anintense ydrothermallteration f the hostdolomite t themain San Vicente mineralization site.8. The positive nduniform ulfursotope ompositionfthe sulfideminerals,ombined ith he presencef nativesulfur ssociatedith extremely3C-low alciteseplacingevaporiticulfates,ltered ative rganicmatter,sotopicallyheavier ydrothermalitumen, nd absence f hopanesnSanVicentehydrocarbons,oint o thermochemicaleduc-tion of sulfate.

AcknowledgmentsThorougheviews f the paperby A. Giz and he Eco-nomicGeologyeviewers .H. BottrellandJ. Wilkinson regreatly ppreciatednd esultedn significantmprovementsto thepaper. hisstudy as upportedy he Swiss ationalScienceFoundation (Grant No. 2000-040575.95 to L. Font-bot6andNo.2100-47023.96o Z. Sharp ndJ.Hunziker).Wearegratefulo San gnacio e Morococha.A.MiningCom-

pany nd hestaff f the Geology epartmentf SanVicentemine or theirhelp n the fieldwork.The EA-IRMS acilitiesat the Department f Environmentalciences,niversityfVirginia, eresupportedy heU.S.NSF.The authorshankJ. Buffle,J.C. Negre,andM. Martin ICP-AES aboratory),R. Martini cathodoluminescenceicroscopy)f the Univer-sity f Geneva,h.Th61inXRD-analyses)ndF. Bussyelec-tronmicroprobe)f the Universityf Lausanneor theirco-operationuringhe analyticalork.Thisstudywascarriedout n the rame f the GCP357ProjectOrganicsndmin-eraldeposits."REFERENCES

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