Portuguese granites associated with Sn-W and Au mineralizations

Abstract

In northern and central Portugal, there are different tin-bearing granites. Most of them are of S-type, others have mixed characteristics of I-type and S-type granites and a few are of I-type. Tin-tungsten deposits are commonly associated with Hercynian tin-bearing S-type granites. Some quartz veins with wolframite are associated with an I-type granite, which has a low Sn content. In suites of tin-bearing S-type granitic rocks, Sn content increases as a function of the degree of fractional crystallization. Greisenizations of two-mica S-type granites associated with tin-tungsten mineralizations are accompanied by an increase in SiO2, H2O+, Sn, W, Nb, Ta, Rb, Zn, and Pb and decrease in MgO, Na2O, V, Sc, Zr, and Sr. The granite associated with the Jales gold deposit is of S-type and strongly differentiated like the tin-bearing S-type granites, but it has a very low Sn content. During fractional crystallization, Si, Rb, Sn, Pb, Au, As, Sb, and S increase. During increasing degree of hydrothermal alteration of this granite at the gold-quartz vein walls, there are progressive increases in K2O, H2O+, Sn, Cs, Cu, Pb, Au, Sb, As, and S.