Geology, mineralogy, and cassiterite geochronology of the Ayawilca Zn-Pb-Ag-In-Sn-Cu deposit, Pasco, Peru

The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery central Andes and one of largest undeveloped In resources globally. As 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, 84 In, additional 45.0 inferred 5.6% 0.23% 17 67 a separate Sn-Cu-Ag 14.5 0.63% Sn, 0.21% Cu, 18 Ag. Newly obtained U–Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 23.05 2.06 Ma) assign to Miocene polymetallic belt Peru. mineralization occurs as up 70-m-thick mantos hosted carbonate rocks Late Triassic Early Jurassic Pucará Group, subordinately, steeply dipping veins Group overlying Cretaceous sandstones-siltstones Goyllarisquizga Group. Relicts distal retrograde magnesian skarn (stage pre-A) were identified deepest mantos. volumetrically important at comprises low-sulfidation assemblage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, traces stannite herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 10 mol% FeS, which is compatible observed transition low- subsequent intermediate-sulfidation stage (B) marked crystallization abundant pyrite marcasite. Finally, during later (C) (up 11 FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, sericite deposited. This paragenetic evolution shows striking similarities that Cerro de Pasco Cordilleran-type deposit, even if C did not reach high-sulfidation conditions. occurrence early suggests manto bodies formed between skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define T-fS2 evolutionary path close pyrrhotite-pyrite boundary. Buffering hydrothermal fluids underlying Devonian carbonaceous phyllites Excelsior imposed highly reduced conditions (logfO2 < − 30 atm). low fO2 favored efficient Sn mobility stages pre-A A, contrast other known ore deposits minerals minor. Subsequent cooling, sealing vein walls, decreasing buffering potential host promoted shift (stages B C) states. analyses reveal contents 1.7 wt%), 1908 ppm), chalcopyrite 1185 ppm). highest content was found precipitated along stannite, thus pointing early, prospective this high-tech metal similar mineral systems. Indium likely incorporated into crystal lattice via Cu+ + In3+ ↔ 2 Zn2+ (Sn, Ge)4+ (Ga, In)3+ (Cu Ag)+ 4 coupled substitutions. incorporation mechanisms lattices remain unclear.