Geochemistry of hydrothermally altered rocks from Los Azufres geothermal field, Mexico

Abstract

Qualitative and semi-quantitative studies of element mobility at Los Azufres geothermal field, Michoacan, Mexico, were carried out, in order to get a better understanding of the hydrothermal alteration processes that affected the volcanic rocks from this area. X-ray fluorescence techniques were applied to analyse well cuttings and drill cores from wells Az-3, Az-26 and Az-52 at different depths. With these analyses a 2000-m thick volcanic sequence was recorded. Geochemically these rocks form a calc-alkaline trend from basaltic to rhyolitic composition. Comparing the chemical composition of altered samples with that of 'fresh' samples from the surface we find relatively low element mobility during alteration. Simple calculations of element loss and gain indicate a weak silicification and low mobility of alkalis.