El yacimiento de zeolitas de Los Murcianos (San José, Almería)

Abstract

Los Murcianos is the only zeolite mine in Spain and is located near San José, in the province of Almería (SE Spain). The mine is located on the western side of the Los Frailes volcanic complex, and the mineral deposit is emplaced in Miocene dacitic ignimbrites and tuffs. These rocks have been hydrothermally altered and replaced by zeolites and smectites. The main conduits for hydrothermal fluids were NW and N-S trending faults that bound the economic mineralization. The zeolite is a silica-rich mordenite, with a mean formula of Na1.92 K0.52 Ca1.51 Fe0.17 Mg0.15 (Al7.43 Si40.92 O96) 28 H2O, whereas that of the smectite corresponds to montmorillonite: (Si7.97Al0.03) O20 (Al2.36Fe3+ 0.18Mg1.47) (OH)4 [Na0.21K0.13Ca0.13] with variable amounts of amorphous silica. The chemical composition of the zeolites resembles that of the ignimbrite, whereas the chemistry of the smectites is very different. This suggests that zeolite formation occurred under confined, isochemical conditions. In addition, the textural study indicates that devitrification and hydration, during hydrothermal alteration, played a major role in zeolite formation. On the other hand, movement of fluids along faults would have resulted in leaching of alkaline and alkaline earth elements with the exception of Mg which was introduced to the system. We further suggest the mineral deposit formed during at least two episodes of fluid circulation.