Supergene ore modifications of epithermal silver mineralization at Martha Mine, Deseado Massif, Argentina

PAEZ, G.N.; RUIZ, R.; PERMUY VIDAL, C.; LÓPEZ, L.; GUIDO, D.M.; JOVIC, S.M.

Uppsala

Congreso; 12th SGA Biennial Meeting; 2013

Society for Geology Applied to Mineral Deposits (SGA)

The Martha underground silver mine is located in the southwestern portion of the Deseado Massif, Santa Cruz province, Argentina. Martha is an intermediate sulphidation epithermal deposit with a complex mineralogy dominated by Ag-As-Sb sulphosalts and Cu-Pb-Zn sulphides. The deposit is characterized by a structurally controlled vein system characterized by a complex history of fracturing and cementation, arranged in nine paragenetic stages that can be grouped into four episodes. Metal ratio vs. depth profile show a shallow 20 m thick oxidation zone dominated by mean Ag/Au ratio of about 800:1. This upper zone is composed an association of kaolinite, plumbogummite, limonites, jarosite, cerussite, chlorargyrite/embolite, native silver, malachite and azurite. Below the oxidized zone, a 30 m thick enrichment zone can be recognized by a sharp increase in the Ag/Au ratio (up to 20,000:1). This zone is composed by a mineral assemblage dominated mainly by argentite/acanthite, pyrargirite, native silver, chalcocite, digenite, covelite, and minor bornite and spionkopite. Below the enrichment zone, the primary hypogene zone is characterized by a progressive reduction in the Ag/Au ratio to values of about 1000:1. These changes are the first mention of a supergene enrichment blanket in the Deseado Massif; this possibility must be considered during exploration, as high grade ore-shoots may be concealed below a lower grade oxidized horizon at surface.