Los depósitos de Mn-Al-Fe de la cueva de Lazalday (Zarate, Alava): composición química y mineralogía

Abstract

Lazalday Cave is a 4 km long karstic cave where Mn deposits occur as black thin coatings covering walls and cementing conglomerates, inside calcite speleothems, and also in the floor of many passages alternating with Al-Si white gels. Fe-rich deposits are found forming black stalactites and microgours. Asbolane, allophane, hydrated halloysite, goethite, ferrihydrite and X-ray amorphous phases compose respectively the Mn-Al and Fe deposits. High metal contents of 21.5% MnO, 5.1% Zn, 2.5% Ni, 0.9% Co, and 0.2% Cu were recorded in Mn-rich levels. Allophane and Fe deposits also trap heavy metals, but in lower proportions. The presence of abundant gypsum, hydrated halloysite and jarosite point out an acidic alteration from pyrite-bearing rocks. Potential metal source rocks are discussed