Abstract

ECHAVARRIA, Leandro E.. Hydrothermal fluids ofthe El Dorado-Monserrat epithermal mineralization, Macizo del Deseado. Rev. Asoc. Geol. Argent. [online]. 2004, vol.59, n.1, pp.70-82. ISSN 0004-4822.

El Dorado-Monserrat is a low-sulphide epithermal deposit located in the Macizo del Deseado, Santa Cruz province, Argentina. Au and Ag vein mineralisation is genetically linked to the Chon Aike Formation of Late to Middle Jurassic age and is hosted by volcanic rocks of the Middle Jurassic Bajo Pobre Formation. The mineralization is present in veins carrying quartz, adularia, pyrite, hematite, magnetite and barite. Precious metals are contained in electrum, which presents a strong Au to Ag zonation. From fluid-inclusion homogenisation temperatures, mineral precipitation is estimated at between 280° C and 180° C from low-salinity fluids mainly of meteoric origin. Au and Ag transportation mechanism include solution as bisulphide (HS)2 complexes. Mineralogical and textural evidence, including the early generation of bladed calcite, later replaced by quartz, and the precipitation of rhombic adularia, suggest that the mineral precipitation, including that of Au and Ag, is due to boiling. Paragenetic and thermochemical studies established the initial conditions of the hydrothermal fluids at between fO2 -33,5 and -34 and pH 5,2 to 6.

Keywords : Macizo del Deseado; Epithermal ore deposits; Hydrothermal fluids; Gold; Silver.

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