Mineralogía y Microtermometría de la Veta Buena Vista, Distrito Minero Andacollo, Neuquén, Argentina

Abstract

The Andacollo Mining District is located on the west margin of the Cordillera del Viento, in the Neuquén province. The Buena Vista vein (Fig. 1a) is a mineralized structure emplaced in the Arroyo del Torreón Formation and located on Las Minas hill. It has NESO (N30 °E- N45 °E) direction and an average width of 3.5 meters. Five pulses were recognized. The first one (Fig. 1b, d) is composed by quartz (quartz I) in mosaic; the second (Fig. 1b) is formed by quartz veins with primary growth textures (quartz II) and the third one (Fig. 1c, d) is constituted by veins of anhedral quartz (quartz III). The fourth pulse (Fig. 1d) represents the formation of hydrothermal breccias from the previous pulses. The cement of the breccias is formed by microcrystalline quartz (quartz IV) pyrite, galena, sphalerite, chalcopyrite, marcasite, argentite and electrum (Fig. 1e, f, g). The fifth pulse is formed by calcite veins which cut the previous pulses. The mineralogical and microthermometric studies were made systematically in different positions within the Buena Vista vein with the objective of comparing the abundance of minerals and the characteristics of the hydrothermal fluids at different depths. From the surface to the deeper vein levels, silver content decrease, while sulfides and electrum increase. The fluids of the third pulse (Fig. 1c, d), prior to the mineralization episode, had minimum temperatures between 210 and 278ºC and an average salinity of 1,37% wt. NaCl eq and show dilution and cooling processes.