EconomicGeology Vol. 85, 1990, pp. 1584-1603 IsotopicComposition of Lead in Ore Deposits of the Cordillera Oriental, Southeastern Peru DANIEL J. KONTAK, Department of Mines and Energy, P.O. Box 1087, Halifax, Nova Scotia, Canada B3J 2X1 GEORGE L. CUMMING, DR•,G•N KRSTIC, Department of Physics, University of Alberta,Edmonton, Alberta,Canada T6G 2J1 ALAN H. CLARK, AND ED FARRAR Departmentof Geological Sciences, Queen's University, Kingston, Ontario, CanadaK7L 3N6 Abstract Twenty-five new lead isotope data are provided for 23 sulfide and 2 oxideminerals from 20 oredeposits embracing thewidevariety of metallic mineralization present in the Cordillera de Carabaya, southeastern Peru,segment of the central Andean InnerArc domain. The deposits are subdivided into the following groups: (1) Cu _+ W _+ Mo _+ Sn veinshosted by Permian and Triassic, metaluminous to peraluminous granitoid plutons; (2) Pb-Zn-Ag-Cu veins spatially relatedto small, Upper Cretaceous stocks of granodioritic composition; (3) majorSn-Cu-Pb- Zn-Aglodes associated with strongly peraluminous cordierite-biotite monzogranite stocks of mid-Tertiary age;(4) Sn, W, Cu, Pb, Zn, Ag, andSb veins ofundetermined but probably mid- Tertiaryage; and (5) Fe ___ Mn _+ Bamanto deposits of poorly constrained age. Collectively,the isotopic data indicatea dominantly crustal lead component in all suites, withanalyses plotting wellabove the2ø6Pb/2ø4pb-2ø7pb/2ø4pb orogen growth curve ofZartman andDoe (1981); for several mineralized centers (Permo-Triassic anda probable mid-Tertiary Sbdeposit), the data overlap the upper crust curve. Although leadisotope data for Cretaceous andmid-Tertiary (group 3) ores exhibit tightclustering in all Pb-Pb plots, the data for Permo- Triassic ores displaya large spread and representthe most radiogenic compositions, with 2ø6Pb/2ø4pb values ranging from18.819 to 25.18.Isotopic analyses of acid leaches of sulfide ores from two mineralized centers ofPermo-Triassic age define regression lines in eø•Pb/eø4pb- eø7pb/eø4pb space and,in at least onecase, indicate the presence of a 1,700-Maradiogenic lead component. Data for group 4 mineralization, of probable mid-Tertiaryage, plot near group 3 datain all Pb-Pb diagrams, providing some corrobofating evidence for their inferred mid-Tertiaryage;the only exception is the Sb mineralization, whichis relativelyenriched in both 2ø7pband •øspb. The isotopic compositions cannot be accommodated by a single reservoir modelbecause (1) the implied age difference (ca. 100-125 Ma) betweengroups 2 and 3 in Pb-Pbplotsis greater thanthat for the host granites (ca.55 Ma); and (2) group1 mineralization, the oldest analyzed, contains the most radiogenic lead.Multiple source regions or complex mixing models are thereforepredicated for the regionasa whole. A comparison of the southeastern Peru ore lead datawith those available for the metallo- genically similar northwestern Bolivian Sn-W-Ag province reveals broadly similar results for Tertiary $n polymetallic ores but radically different compositions for (Permo-)Triassic min- eralization. Thus,different source regions or processes are indicated for at least the older mineralization. In addition, whereas the Mesozoic andCenozoic Bolivian ore leadcompositions could be accommodated by a common evolving source reservoir(s) (Tilton et al., 1981),the Peruvian data cannot. The lead isotope compositions reported here overlap extensively with much of the Pb isotope data available forcentral Andean Main Arcmineralization, although ourresults lie toward the more radiogenic ends ofdefined fields. We therefore conclude that amodel involving mixing ofleads from a single source (mantle?) with various crustal reservoirs can account for the observed data spread in Pb-Pb plots. Thisis consistent with the petrochemistry of the Inner Arc granitoid igneous suites which indicates involvement ofmantle-derived components in theanatectic granitoid rocks viamagma mixing processes. An important implication ofthis study is thatmultiple reservoirs have been involved in the metallogenic evolution of the Central Andean tin belt, a conclusion arrived at earlier frompetrologic studies of the associated igneous suites. 1584