GREENOCKITE AND ASSOCIATED SULFIDE MINERALIZATION FROM THE CALEDONIA GROUP MINES, BLANCA CREEK, LA HUERTA RANGE, SAN JUAN PROVINCE, ARGENTINA

Abstract

We document various textural occurrences of greenockite associated with several ore minerals in varying parageneses: pyrite + sphalerite + galena + chalcopyrite ± arsenopyrite ± pyrrhotite ± bornite ± tennantite ± tetrahedrite ± covellite ± chalcocite ± aikinite ± wittichenite ± matildite ± berryite ± miharaite ± geocronite ± hematite ± magnetite from mineralized samples of the Caledonia Group mines, Marayes mining district, La Huerta Range, San Juan province, Argentina, based on reflected light and scanning electron microscope investigations. The mineralization is hosted mainly in metacarbonate outcrops in contact with the granulite basement and associated intermediate to mafic meta-intrusive rocks. We recognize three types of greenockite on the basis of textural and chemical criteria. Type-1 greenockite contains less than 1 mol.% ZnS, but its Fe content varies from 0.2 up to 4.5 mol.% FeS. Type 2 is Zn-rich, with 10–25 mol.% ZnS component and <0.1 to 3 mol.% FeS component, and type 3 has a Zn content of 5–7 mol.% ZnS component and FeS <0.1 mol.%. The presence of complex Ag–Cu–Bi–Pb sulfides point to a late-stage, low-temperature overprint of the primary sulfide parageneses, accompanied by the formation of hypogene greenockite, at least partly at the expense of sphalerite. The near-end-member composition of greenockite and late-stage sphalerite also indicates a low temperature of formation.