Ag-Pb-Bi minerals of the Pingüino In-bearing polymetallic epithermal deposit, Deseado Massif, Patagonia, Argentina

JOVIC, SEBASTIÁN; GUIDO, DIEGO; LOPEZ, LUCIANO; PERMUY VIDAL, CONRADO; RUIZ, REMIGIO; PAEZ, GERARDO; MELGAREJO, JOAN; CRESPI, ANA

Whistler

Conferencia; Whistler 2013: Geoscience for Discovery; 2013

Society of Economic Geologists

The Deseado Massif, located in the Santa Cruz province in southern Argentinean Patagonia, is an important Au-Ag producer with four mines in operation, as well as an area of intense prospecting activity. This metallogenic province is characterized by the presence of Upper Jurassic low sulfidation epithermal deposits. Pingüino represents an atypical deposit in the Deseado Massif, because of the presence of Lower Jurassic polymetallic mineralization, that is characterized by complex sulfide mineralogy and geochemical signature enriched in Zn, Ag, Pb, Au, Cu, Sn, W, Bi and In. Due to the important Indium anomalies, Pingüino was classified as an In-bearing polymetallic deposit similar to the Japan, Bolivian and German deposits (Jovic et al., 2011). The Pingüino polymetallic mineralization is characterized by the presence of massive and banded sulfide veins and vein breccias up to 13 m in width. The ore geochemistry indicates the presence of high values of Zn, Ag, Pb, Au, Cu, Sn, W and Bi in the sulfide-rich veins (Jovic et al., 2011). Three main stages were defined for the mineralization. The early stage (Ps1) presents anomalous values of Au, Cu, In, Sn, W and Bi and is characterized by a complex paragenesis, composed mainly of idiomorphic pyrite crystals, zoned arsenopyrite, hübnerite and ferrokësterite [Cu2(Fe,Zn)SnS4] replacing cassiterite, and is in turn replaced by stannite [Cu2FeSnS4]. The second stage (Ps2) is characterized by a Zn, Pb, Ag, In, Cd and Sb paragenesis, where Ps1 minerals were brecciated and replaced mainly by banded sphalerite and galena. Grains of hipidiomorphic tetrahedrite, freibergite argentotennantite and Pb-Ag sulfosalts are present in this stage. Fluid inclusion studies indicate homogenisation temperatures of 308°?327°C for Ps1 and 255°?312°C for Ps2, and low to moderate salinities (2 to 5 eq.wt.% NaCl and 4 to 9 eq.wt.% NaCl, respectively; Jovic et al. 2011). A third stage of mineralization (Ps3) was recognized only at microscopic scale, characterized by an interbedding of botryoidal bands made up by Fe-poor sphalerite and greenockite, with idiomorphic crystals of greenockite. Within the complex sulfide mineralogy and mainly associated to the end of the first mineralization stage, very fine-grained acicular and prismatic minerals was found. In order to determine this minerals and their composition optical microscopy and electron-microprobe microscopy were done. The presence Ag-Bi, Ag-Pb-Bi, Pb-Bi sulfosalts were determinate. The minerals are aramayoite [Ag3Sb2(Bi,Sb)S6], owyheeite [Ag3Pb10Sb11S28], ourayite [Ag3Pb4Bi5S13], giessenite [(Cu,Fe)2Ag26.4(Bi,Sb)19.6S57] and izoklakeite [Pb26.4(Cu,Fe)2(Sb,Bi)19.6S57]. These specimens are very rare and are typical from hydrothermal sulfide Sn-Ag and Pb-Zn ores. Generally, the presence of Bi-Ag-Pb assemblage is related with relative high temperature hydrothermal fluids; in the Pingüino deposit is associated with temperatures between 308 and 328°C and Sn, W, Cu, Au and In, in the Ps1. The presence of these minerals represents a new contribution to the characterization of a new and atypical deposit type for the Au-Ag Deseado Massif epithermal province.