Los depósitos de talco y clorita magnesiana de la Sierra de las Estancias (Cordillera Bética, Almería, España)

Abstract

The talc and magnesium chlorite deposits of Sierra de Las Estancias occur in metapelites and marbles belonging to the Triassic cover of the Granja Unit (Alpujarride Complex). Metamorphism of this Unit reaches medium grade. The mineralizations are composed of talcites, talc chloritites and chloritites. The talc has a chemical composition very close to the ideal formula Mg₃Si₄0₁₀(OH)₂]. The chlorite correspond to clinochloro and is characterized by an extremely high Mg/(Mg + Fe) ratio ( > 0.98). Two main groups of mineralizations are established: strata-bound and vein deposits. The first one is located in the transition zone between metapelites (bottom) and marbles (top) and in the lower part of the marble member. From botton to top, the mineralizations show a gradual mineralogical and chemical variation, the latter characterized by a progressive increase in Mg and in the Mg/(Mg + Fe) ratio, and by a decrease in K₂0 content and in the Al/Mg ratio. Most of the strata-bound mineralizations were formed during the Alpine metamorphism by the transformation of sediments very rich in magnesium (probably evaporite mudstones). A small part of this type of mineralizations and those of vein character originate by remobilization of the strata-bound deposits.