El prospecto Cerro León, Macizo del Deseado, Patagonia, Argentina: Un depósito de Ag-Sn.

CRESPI, ANA; JOVIC, SEBASTIÁN; GUIDO, DIEGO; PROENZA, JOAQUIN; MELGAREJO, JOAN; SCHALAMUK, ISIDORO

Macla

Sociedad Española de Mineralogía

Lugar: Madrid; Año: 2006 p. 143 - 145

1885-7264

The Deseado Massif (DM) is characterized by the presence of LS epithermal deposits with Au-Ag quartz veins. The veins show a geochemical signature with anomalies in precious metals (Au-Ag) and occasional anomalous contents of As, Sb, Hg, Mo, Pb, Zn, Mn and minor Cu. Metalliferous minerals are scarce, representing commonly less than 1% in volume and they are pyrite, native gold, electrum, argentite, native silver, Ag-sulfosalts, hematite, sphalerite, galena and chalcopyrite. There are also some Pb, Fe, Mn and Ag secondary minerals. Cerro León deposit is located in the center of the DM, 40km northwest from Cerro Vanguardia and is characterized by 31 oxided quartz veins. The veins are poorly exposed in surface and are characterized by the presence of grey quartz with cavities filled with limonite and minor sulphides, quartz-limonite veinlets, ferruginous silica breccias and Fe-Mn oxide breccias.Some parts of the veins are represented by a high concentration of limonite, an important pyritization, red clays, oxidation and alteration zones, forming a Fe-rich gossan. This oxidation is representing the sulphide-rich mineralization detected by drill holes at depth with values higher than 20% in volume and up to 90 % in some veins and with a mineralogical complexity. The geochemical signature of this veins is Sn, Cd and In, together with anomalies of Zn, Ag and Au, and also high contents of Cu, Mn, Pb, W and Bi. These characteristics are not typical from the LS deposits and represent a variation compared with the typical DM LS mineralization.A detailed mineralogical study from the two main veins of the area is being developed in order to recognize the complex mineralogy determinate in the drill cores polish sections. Preliminary electronic microscopy and microprobe studies were made in the Departamento de Mineralogía y Cristalografía, Universidad de Barcelona, España. Marta vein has characteristics of a typical LS quartz vein and shows a mineralogy represented by quartz, eugenite, naumannita, greenockite, ferrokesterite, pyrite, arsenopyrite, sphalerite, galena, cassiterite, wolframite, Ag-sulphosalts, Mn oxides, iodargirite, and tocornalite. Ivonne vein is characterized by a 2m thick massive sulfide vein composed by quartz, argentite, ferrokesterite, pyrite, arsenopyrite, sphalerite, galena, chalcopyrite, cassiterite, tetrahedrite, bournonite, freibergite,  argentotennantite, aramayoite, owyheeite giesenite, ourayite, izoklakeite group, greenockite, hübnerite, ferberite, Pb-Bi-Ag-sulphosalts, enargite, stolzita/raspita, alumisilicats and phosphates. These complex sulfide rich mineralogy assemblages, and some minerals determinated in these veins, are new for the DM mineralization and represent a variation in the LS metalogenic province. This change could be related with higher temperature deposit or a variation into the epithermal deposits.