Tourmaline as a prospecting guide for the porphyry-style deposits

Tourmaline-supergroup minerals are proposed as efficient indicators of porphyry-style Cu, Au and Sn deposits and therefore are considered as useful for both the prospection and exploration of these important mineral deposits. The tourmaline-supergroup minerals from the porphyry deposits exhibit some general features: (1) sector and oscillatory chemical zoning of crystals; (2) presence in several generations; (3) Fe -> Al coupled substitution; (4) evolution from Fe-rich to Mg-rich varieties resulting from sulphide deposition at the late stage; (5) Li concentration ranging from a few to similar to 30 ppm. On the other hand, there are distinguishing features for tourmalines from different deposits: (1) total Mg content is similar to 2 apfu for tourmaline in the Cu deposits, 1-2 apfu in the Au deposits, and 0-1 apfu in Sn deposits; (2) maximum Fe-tot similar to 3 apfu (Cu, Sn) and similar to 5 apfu (Au), (3) maximum F content up to 0.1 apfu (Cu, Au) and up to 0.5 apfu (Sn); (4) Fe3+/Fe-tot similar to 0.5-0.8 (Cu, Au) and similar to 0.2 (Sn).