Characterization of gold grains from Bigorne deposit: search indicators to hypogene mineralization. Preliminary studies

Abstract

The Bigorne gold deposit (northern Portugal) located in the European Variscan belt is a system of gold-bearing quartz veins, which crosscut late-to post-D3 biotite granites. The mineralized structures correspond to sheet-veins system parallel to the late-Variscan strike-slip fault Penacova-Regua-Verin (NNE-SSW). In Bigorne veins, it was possible to define two types of gold occurrence: I - Native gold, as free particles; II- Au-Bi minerals in association with native-Bi and Bi-Te minerals. The gold minerals from mineralized veins and the gold grains sampled in superficial environments reveal similar chemical composition where the Au occurs in association with Ag, Cu, and Cd. This fact provides evidence of very limited transport and therefore a restricted and single local source for gold primary particles from the mineralized veins. It is very important to improve the geological and mineralogical knowledge about gold occurrences in Portugal to improve the knowledge of the Phanerozoic gold systems.