Alteración diferencial de las rocas volcánicas ácidas en el sector de Riotinto, Faja Pirítica Ibérica

Abstract

Regional hydrothermal alteration of rhyolitic rocks from the Odiel area, Iberian Pyrite belt, Spain, has been assessed through geochemical study. Disregarding volcanic facies, all rhyolites have similar immobile trace element contents. However, they show a contrasting hydrothermal alteration on currently used alteration plots: volcaniclastic rocks mainly plot as albitized rocks, whereas coherent rocks plot as weakly altered rocks. Also, a sharp contrast is shown between regional and focused, VHMS-related alteration trends. Differences in the degree of regional alteration between volcaniclastic and coherent rocks are to be related to contrasting permeability, resulting in different water-rock ratios during hydrothermal processes. Accordingly, coherent rocks are to be preferred as least-altered samples for mass balance and other geochemical purposes