| Abstract |
Numerous studies have shown the relationship between alteration mineralogy and the characteristics of a geothermal system, as well as the fluid-rock interaction processes. Various Ca-rich hydrated silicates as epidote, prehnite, zeolites, calcite and anhydrite, together with clay minerals, including diverse chlorite, illite and smectite interstratified, are the most currently developed secondary minerals observed in geothermal systems. These secondary minerals show a number of characteristics which, together with their formation and changes when exposed to different conditions, have been described as dependent on temperature, pH, fluid composition and lithology as the main factors. In this work we present the ongoing study of the alteration mineralogy associated to the geothermal system of the Irruputuncu. This is a currently active volcano with geothermal manifestations such as fumaroles near the craters and hot springs at their base. It is mainly composed by a mixture of andesitic to dacitic lavas and pyroclastic rocks, and built on top of various ignimbrites and older lava flows. Sampling from a continuous drill core gives the opportunity to explore and study how factors such as fluid composition, lithology and permeability are playing a role in the formation of different alteration minerals, and to see how they compare to known first order factors such as fluid temperature and pH. Petrography studies and X-ray diffraction data have shown the presence of calcite and anhydrite in association with mixed-layer clays, particularly illite/smectite, as the main secondary mineralogy. These results, together with a future fluid-inclusions and isotopes study, will allow us to constraint T, pH and fluid composition of the different hydrothermal event(s) developed in this geothermal volcano-related field. |