Hydrothermal Alteration at El Humazo Geothermal Area, Domuyo Volcano, Argentina

Abstract

The Domuyo volcano is located on the east side of the Andes range in Argentina, where a series of young volcanoes are arranged in NW-SE direction. The Domuyo volcano to the NW is the largest of these volcanoes, which generally decrease in size to the SE. The Domuyo Volcanic Complex consists of late Tertiary intrusives and silicic volcanic rocks. Younger volcanism of intermediate to acidic composition took place during the Quaternary, yielding lava flows of basaltic andesite, andesite, dacite and rhyolite.

Surface manifestations at the geothermal area are most prominent along W-SW slopes of the Domuyo volcano. These include hot springs and fumaroles that commonly occur where young tuff breccias and lava flows directly overlie Mesozoic formations and/or basement rocks. The El Humazo hot spring and fumaroles area is one of the largest areas with surface alteration. Gas geothermometry indicates reservoir fluid temperatures of above 200?C.

The alteration minerals at El Humazo have been studied by means of X-ray diffraction analyses, and optical and scanning electron microscopy. The alteration mineralogy is characterised by the presence of smectite, kaolinite and tridymite, with minor amounts of cristobalite and quartz. In areas surrounding the fumaroles, zeolites such as heulandite and mordenite are also present. These minerals occurred in alteration zones around the geothermal manifestations.