Ore fluid evolution in a volcanic-hosted epithermal ore deposit: Farallón Negro, Argentina.

MÁRQUEZ-ZAVALÍA, M.F.; HEINRICH, C.A.; MEIER, D.

Neuchatel, Switzerland

Congreso; Swiss Geoscience Meeting 2009; 2009

Swiss Geological Society

The Farallón Negro mineral deposit is located in Catamarca province, Argentina, at 27º19´S and 66º40´W. This low sulfidation epithermal gold deposit belongs to the Farallón Negro mining district, along with other epithermal and porphyry deposits in the area. This cluster of Cu-Au mineral deposits are genetically linked to a Miocene volcanic complex with a suite of rocks of high-K calk-alcaline to shoshonitic afinities known as Farallón Negro Volcanic Complex (FNVC). Alto de la Blenda, where this study is focused, is one of the two main suits of veins of the Farallón Negro mineral deposit, and the main veins there are Laboreo, Esperanza and Esperanza SE. The W part of Laboreo is hosted in andesite and the rest of that vein and the other two are hosted in monzonite. There were recognized four stages of the mineralization with seven generations of quartz. Preliminary fluid inclusion results give ranges of homogenization temperatures from 200 to 270ºC, and salinities from 3.40 to 4.70 NaCl equiv. for Esperanza vein and similar homogenization temperatures but lower salinities for Laboreo vein. Though the results are still preliminary, the research in progress shows the first saline epithermal fluids in a low-to intermediate-sulfidation epithermal system containing significantly higher metal concentrations than fluids in any active geothermal system. These very high metal concentrations (ppm-levels of Au and hundreds of ppm of Cu) in the fluid indicate that even low- to intermediate-sulfidation economic vein deposits do not form from convecting groundwater alone, but from injection of vapor-derived magmatic fluid.