Metales traza en pirita como indicadores de la transición del estadio porfírico al epitermal en el yacimiento Agua Rica

FRANCHINI, MARTA; LENTZ, DAVE; MAYDAGÁN, LAURA; LOU, YAN

San Juan

Congreso; XI Congreso de Mineralogía y Metalogenia; 2013

Asociación Mineralógica Argentina

Pyrite is the most abundant sulfide in the analyzed section of the deposit and shows variations in textures and trace metal contents, determined by LA-ICPMS, between the porphyry and the epithermal stages. These variations may serve as vectors in exploration. Pyrite from the porphyry stage is fine-grained and has low contents of most the trace elements analyzed, except for Co and Ni. Pyrites from the epithermal stage are texturally complex and compositionally heterogeneous. At intermediate depth, pyrites from the cement of the jig-zaw and clast-supported hydrothermal breccias are enriched in Cu (up to 2567 ppm) that correlates with the highest Cu grades in the section. Pyrites are porous, contain late inclusions of sulfosalts, and are zoned, with a Co-rich core, a mid section and a rim enriched in Cu and Zn, respectively. At higher elevations, pyrite cement of the heterolithic hydrothermal breccia is unusually rich in trace metals that correlate with the highest Pb, Zn, and invisible Au-Ag contents of the section. The ore pyrites occur as either successive colloform bands on earlier Co-Mo-bearing cores or in late veinlets. These bands are As-poor (<50 ppm) and enriched in Pb (up to 4470 ppm), Cu (up to 4160 ppm), Zn ( up to 960 ppm), Ag (up to 148 ppm), Au (up to 12.90 ppm), Bi (up to 208 ppm), and Te (up to 4 ppm). The colloform banding in pyrite is interpreted to reflect rapid crystallization during fluid boiling at a hydrothermal fluid-meteoric water interface, creating intense fluctuation of temperatura and producing undercooling in the mixed fluid. Maximum gold and silver input into the system occurred toward the end of the epithermal cycle and is expressed by the Au-Ag-rich rims to hydrothermal pyrite, marcasite and Bi-sulfosalts.