Peculiaridades de las mineralizaciones de la mina San Juan (Los Jarales, Carratraca) en el contexto de los depósitos de Cr-Ni de los macizos ultramáficos Bético-Rifeños

Resumo

The San Juan Mine is enclosed in highly tectonized and serpentinized peridotites which show mineralogical features corresponding to the Ariegite subfacies of the spinel-lherzolite facies. The main mineral association include chromite, Ni- arsenides, cordierite and minor pyroxene, and displays the following mineralogical and textural features : a) there is clinopyroxene instead of orthopyroxene; b) high arsenide/chromite ratio with a high relative proportion of maucherite; c) highest Au and Platinum-Group elements contents; d) cordierite is plastically deformed and it is associated with plagioclase and phlogopite which show granoblastic and poikylitic textures with inclusions of cordierite and/or chromite; e) the chromite occurs as poligonal aggregates (sometimes made up of corroded grains) or as isolated skeletal crystals; the latter show a higher Cr content and a positive correlation between their Cr/ R3+ and the Na content of the coexisting plagioclase. Note that these features are partly different from the other Cr-Ni mineralizations in the Serrania de Ronda. The deformational mechanism mixed the former chromite-Ni arsenide ores with the residual liquids leading to a plagioclase crystallization either on the previous mineral assemblage or as late discordant veins fillings. These aluminous liquids partly disolved the cromite crystals and the new Cr-bearing liquid gave rise to a later crystallization of the skeletal chromites coeval with plagioclase.