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Item type:Publication, Geology, mineralogy, and cassiterite geochronology of the Ayawilca Zn-Pb-Ag-In-Sn-Cu deposit, Pasco, Peru(Springer Science+Business Media, 2021-09-13)The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery in the central Andes and one of the largest undeveloped In resources globally. As of 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, and 84 g/t In, an additional 45.0 Mt inferred resource grading 5.6% Zn, 0.23% Pb, 17 g/t Ag, and 67 g/t In, and a separate Sn-Cu-Ag inferred resource of 14.5 Mt grading 0.63% Sn, 0.21% Cu, and 18 g/t Ag. Newly obtained U–Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 and 23.05 ± 2.06 Ma) assign the Ayawilca deposit to the Miocene polymetallic belt of central Peru. The polymetallic mineralization occurs as up to 70-m-thick mantos hosted by carbonate rocks of the Late Triassic to Early Jurassic Pucará Group, and subordinately, as steeply dipping veins hosted by rocks of the Pucará Group and overlying Cretaceous sandstones-siltstones of the Goyllarisquizga Group. Relicts of a distal retrograde magnesian skarn and cassiterite (stage pre-A) were identified in the deepest mantos. The volumetrically most important mineralization at Ayawilca comprises a low-sulfidation assemblage (stage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, and traces of stannite and herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 to 10 mol% FeS, which is compatible with the observed transition from low- to a subsequent intermediate-sulfidation stage (B) marked by the crystallization of abundant pyrite and marcasite. Finally, during a later intermediate-sulfidation stage (C) sphalerite (up to 11 mol% FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, and sericite were deposited. This paragenetic evolution shows striking similarities with that at the Cerro de Pasco Cordilleran-type polymetallic deposit, even if at Ayawilca stage C did not reach high-sulfidation conditions. The occurrence of an early retrograde skarn assemblage suggests that the manto bodies at Ayawilca formed at the transition between distal skarn and skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define a T-fS2 evolutionary path close to the pyrrhotite-pyrite boundary. Buffering of hydrothermal fluids by underlying Devonian carbonaceous phyllites of the Excelsior Group imposed highly reduced conditions during stage A mineralization (logfO2 < − 30 atm). The low fO2 favored efficient Sn mobility during stages pre-A and A, in contrast to other known ore deposits in the polymetallic belt of central Peru, in which the occurrence of Sn minerals is minor. Subsequent cooling, progressive sealing of vein walls, and decreasing buffering potential of the host rocks promoted the shift from low- (stage A) to intermediate-sulfidation (stages B and C) states. LA-ICP-MS analyses reveal significant In contents in Fe-rich sphalerite (up to 1.7 wt%), stannite (up to 1908 ppm), and chalcopyrite (up to 1185 ppm). The highest In content was found in stage A sphalerite that precipitated along with chalcopyrite and stannite, thus pointing to the early, low-sulfidation assemblage as prospective for this high-tech metal in similar mineral systems. Indium was likely incorporated into the sphalerite crystal lattice via Cu+ + In3+ ↔ 2 Zn2+ and (Sn, Ge)4+ + (Ga, In)3+ + (Cu + Ag)+ ↔ 4 Zn2+ coupled substitutions. Indium incorporation mechanisms into the stannite and chalcopyrite crystal lattices remain unclear. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Petrology, metallogeny and U-Pb geochronology of the Paleoproterozoic mafic-ultramafic Hamutenha intrusion, Angolan Shield(Elsevier BV, 2022-10-12)The Hamutenha intrusion (Huíla province, SW Angola) is a 3-km-long elongated magmatic body defined by a set of two intrusive units. The northern unit is formed by alternating bands of dunites and olivine gabbros, while the southern unit is composed of amphibole diorites. The Hamutenha body is hosted by the Paleoproterozoic Epupa Complex in the Angolan Shield, SW margin of the Congo Craton. A mineralogical, petrological and geochemical study of the Hamutenha intrusion has been performed. The constrained compositional features of the parental melt suggest interaction of tholeiitic magmas with a significant enrichment in Fe and Ti. Although disseminated Fe–Ni–Cu-(Co) secondary sulphides are observed, both the crustal contamination parameters and generally low bulk-rock metals contents indicate that these elements were most likely previously extracted from the parental melt. U–Pb zircon dating of amphibole diorite samples from the southern unit yields a date of 1844 ± 14 Ma. These data suggest that the emplacement of these rocks was previous to the KC emplacement and it was probably related to the Paleoproterozoic Epupa Complex magmatism. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, The Morococala Volcanic Field, Bolivia: Geochemistry and geochronology in the Huanuni district(Elsevier, 2026-08-01)The Central Andes constitute a key natural laboratory for studying the tectono-magmatic response to subduction beneath thick continental crust and the formation of associated ore deposits. In the Bolivian back-arc region, world-class Sn-polymetallic deposits of the Huanuni district are spatially associated with rhyolitic dikes and voluminous peraluminous pyroclastic deposits related to the Morococala Volcanic Field. New geochronological data indicate that the peraluminous rhyolitic dikes in Huanuni were coeval and likely part of the same magmatic plumbing system at ca. 7.0-6.4 Ma, and hence are not associated with the Oligocene-Miocene Sn-polymetallic mineralization (ca. 24 Ma). Mixing models based on Nd-Sr isotopic compositions of the Morococala Volcanic Field, supported by Monte Carlo simulations, suggest crustal contributions of ∼45-70%. These are, in general, concordant with the ∼50:50 mantle-derived melts and continental crust mass balance models proposed for other ignimbrite fields of the Neogene Ignimbrite Province of the Central Andes in the back-arc region (e.g., Los Frailes Volcanic Field and the Panizos, Coranzuli, Vilama, and Ramadas fields within the Altiplano-Puna Volcanic Complex). Mineralogical and geochemical evidence suggests that the associated magmas formed under thick-crustal conditions, with garnet as a residual phase. The voluminous rhyolitic magmatism in the Morococala Volcanic Field likely resulted from hot mantle upwelling induced by slab re-steepening of the subducted slab after a flat-slab episode.