Early hydrothermal alteration stages at the giant San Rafael tin deposit, Peru
Résumé
At the giant tin deposit of San Rafael, Peru, the early hydrothermal stages, preceding the economic tin mineralization, include successively: 1) potassic alteration represented by hydrothermal K-feldspar altering magmatic plagioclase; 2) sericite replacing magmatic plagioclase in the ground mass and hydrothermal K-feldspar, with greisen formation in the apical part of the intrusion; 3) widespread albitic alteration, both disseminated and as intense replacement along fractures, overprinting and obliterating the previous stages; 4) quartz-tourmaline veins rimmed by albitic alteration halos. In this contribution, the greisen-style alteration and sodic alteration, are studied in depth. Trace element analysis of hydrothermal albite reveals a marked enrichment in incompatible elements (B, Rb, Cs) compared to magmatic plagioclase, suggesting albitization was triggered by magmatic fluids exsolved from an evolved silicate melt.