Petrogenetic constraints of the W-Sn-bearing Abraveses granite (Viseu, Central Portugal)

The Abraveses massif consists of a syn- to late-D3 two-mica granite which crops out along the core of the NW-SE-trending Porto-Viseu D3 antiform. Multiple W-Sn mineralizations are spatially associated with this granitic massif. From a geochemical standpoint, the Abraveses granite is characterized by a strongly peraluminous signature (A/CNK = 1.25 - 1.51), suggesting it was produced by partial melting of a metasedimentary protolith in mid crustal levels (S-type affinity). The low CaO/Na2O ratio (0.1 - 0.2) and high Rb/Sr (12.2 - 18.5) and Rb/Ba (3.4 - 5.3) ratios indicate that the respective magma was derived from a metapelitic (plagioclase-poor) protolith. The granitic samples present low REE contents (ΣREE = 69.19 - 91.33 ppm). The respective chondrite-normalized pattern is moderately fractionated, showing a relative enrichment in LREE (LaN/YbN = 9.02 - 10.86) and a negative Eu anomaly (Eu/Eu* = 0.32 - 0.39). The LREE fractionation is higher compared to the HREE fractionation (LaN/SmN = 2.75 - 3.30; GdN/YbN = 1.82 - 2.17). The UCC-normalized spidergram shows a strong enrichment in Rb, Cs, U and Ta. A significant depletion in Ba, Sr and Ti is also observed. These geochemical features are consistent with the presence of biotite in the crustal source. The strong ore-forming potential of the Abraveses granite is confirmed by its remarkable enrichment in Sn (51 - 106 ppm), W (4 - 17.8 ppm) and ore-transporting volatiles such as F and B. Specialized peraluminous granites from northern and central Portugal typically contain Sn and W concentrations close to those obtained in our study.