Publication: El yacimiento de zeolitas de Los Murcianos (San José, Almería) de una estructura potencialmente favorable
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Publication Date
2008
Authors
Suárez Barrios, Mercedes
Regueiro, M.
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Sociedad Geológica de España.
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Abstract
El Yacimiento de Zeolitas de “Los Murcianos”, situado en la provincia de Almería cerca de la localidad de San José (Cabo de Gata), es el único yacimiento de zeolitas en explotación actualmente en España. Se emplaza en rocas volcánicas explosivas de tipo ignimbrita dacítica de la caldera de “Los Frailes”. La alteración hidrotermal de los materiales ignimbríticos ha originado dos tipos de materiales diferentes: zeolitas y bentonitas, estando su disposición controlada por la facturación de la zona. Las zeolitas son mordenitas muy ricas en sílice, de elevada pureza y fórmula estructural Na1.92 K0.52 Ca1.51 Fe0.17 Mg0.15 (Al7.43 Si40.92 O96) 28 H2O. Las bentonitas son montmorillonitas de fórmula (Si7.97Al0.03) O20 (Al2.36Fe3+0.18Mg1.47) (OH)4 [Na0.21K0.13Ca0.13] con cantidades variables de sílice amorfa. Existe una enorme similitud composicional entre zeolitas e ignimbritas, mientras que las bentonitas son claramente diferentes, incluso existen variaciones significativas dentro de ellas. Todos los datos permiten deducir que las génesis de ambos materiales responde a dos procesos diferentes de alteración. La formación de la zeolita no supone una variación de la composición química global de la roca, por lo que las ignimbritas debieron quedar confinadas y alterarse a mordenita mediante un proceso de alteración hidrotermal consistente en desvitrificación e hidratación de la ignimbrita, mientras que, posteriormente, tuvo lugar un proceso de alteración en un sistema abierto ocasionado por la circulación de fluidos a favor de las fracturas, los cuales lixiviaron parte de los elementos alcalinos y alcalino-térreos de las ignimbritas y aportaron otros como Mg, necesarios para la formación de las esmectitas.
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.
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.