Trace metals in pyrite and marcasite from the Agua Rica porphyry-high sulfidation epithermal deposit, Catamarca, Argentina: Textural features and metal zoning at the porphyry to epithermal transitionReportar como inadecuado




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Resumen

Agua Rica is a world-class Cu Mo–Au deposit located in Catamarca, Argentina, in which the porphyry and highsulfidation epithermal stages are juxtaposed due to the telescoping of the mineralizing system. Pyrite is the mostabundant sulfide in the analyzed section of the deposit and shows variations in textures and tracemetal content determinedby LA–ICPMS, between the porphyry and epithermal stages. Pyrite from the porphyry stage isfine grained and depleted in most trace elements analyzed, except for traces of Co up to 276 ppm and Ni up to131 ppm. Pyrite from the epithermal stage is texturally complex, compositionally heterogeneous, and the tracemetal content varies with depth and within sub-stages of mineralization. At an intermediate depth 2625 m,epithermal pyrite from the cement of the jig-saw and clast-supported hydrothermal breccias are enriched in Cuup to 2961 ppm that correlates with the highest Cu grades in the section. This pyrite contains micro-inclusionsof sulfosalt minerals as inferred by LA–ICPMS elemental mapping and individual spot ablation profiles. They arezoned and show a Co-rich core, an intermediate zone enriched inCu, and anouter rimrich inZn.At shallower levels3000m, epithermal pyrite cements in the heterolithic hydrothermal breccia are unusually rich in trace metals thatcorrelate with the highest Pb, Zn, Au, and Ag grades. The ore-stage pyrite occurs as either successive colloform bandson earlier Co-bearing cores or as veinlets infill. The colloform pyrite bands and veinlets are As-poor b30 ppm andenriched in Pb up to 4528 ppm, Cu up to 3900 ppm, Zn up to 1078 ppm, Ag up to 136 ppm, Au up to6.7 ppm, Bi up to 1077 ppm, and Te up to 3.1 ppm. In LA–ICPMS elemental maps, arsenic concentrates in athin inner band within the thicker, trace element-rich rims. The colloform banding in pyrite is interpreted to reflectrapid crystallization during fluid boiling at a hydrothermal fluid–meteoric water interface, creating intense fluctuationsin temperature and producing undercooling in the mixed fluid. This late and shallow fluid was depleted in Asand Cu and also precipitated alunite, Fe-poor sphalerite, and marcasite enriched in trace metals. Maximum Au andAg inputs into the system occurred towards the end of the epithermal cycle and are expressed by the Au–Ag-richrims in hydrothermal pyrite. Based on Au–As data in pyrite, ore fluids forming early pyrite were undersaturatedwith respect to native Au solid solution incorporation, while later fluids precipitating colloform pyritewere supersaturatedwith respect to native Au forming Au nanoparticles. This study provides evidence that pyrite recordschemical changes at the porphyry to epithermal transition that can be used tomonitor hydrothermal fluid evolution,constrain different mineralization stages, and vector towards undiscovered ore zones.Nota general

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Autor: Franchini, Marta; - McFarlane, Christopher; - Maydagán, Laura; - Reich Morales, Martín; - Lentz, David R.; - Meinert, Lawrence;

Fuente: http://repositorio.uchile.cl/



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