Permian intrusion-relatd tourmaline breccias in Val Trompia, N.Italy

摘要

Permian quartz-tourmaline breccias, intruding pre-Alpine basement, are related to K-Al-rich granite and Sn-W-bearing hydrothermal veins. Tourmaline crystallized in at least four stages with systematic variations in tourmaline chemistry. Compositions vary from schorlite-dravite, in the main stage of tourmalinization, to povondraite in the late stage. Fe-Al_(-1) exchange and Fe~(3+) increase are related to oxidation of the magmatic-hydrothermal fluids with increasing distance from the pluton. Relative distribution of schorl-dravite-only-bearing and povondraite-bearing breccias may reflect the transition from a deeper, pluton-centred part of the hydrothermal system towards an external zone with hydrothermal vein deposits.