Characterization of heavy mineral concentrates and detrital gold particles from the Bigorne granite-hosted gold deposit in the Iberian Variscan Belt

Abstract

Abstract The Bigorne gold deposit, located in the Iberian Variscan belt, is a gold-bearing vein system, which cross-cuts Variscan granites. The hypogene mineralization corresponds to sheet-veins parallel to the late-Variscan Penacova–Régua–Verín fault. A combined study was undertaken of gold particles from hypogene mineralization and locally derived eluvial material, as well as gold from alluvial deposits in local drainages, to assess possible sources of the alluvial gold. The geochemistry and mineralogy of heavy mineral concentrates revealed a similar signature to the hosted granites and hypogene mineralization, which indicates a local source for the surficial materials, with limited contribution from surrounding rocks. Hypogene and detrital gold particles at Bigorne area are entirely primary in origin and correspond essentially to a Au–Ag alloy (<22 wt% Ag), locally with minor amounts of Cu. The compositional range of Ag and Cu is a consequence of variation in parameters formation of the deposit, such as temperature. Our study highlights the first results on gold detrital particles chemistry for granite-hosted gold deposits in the Iberian Variscan belt, and has provided a platform for further work to characterize gold from this environment, such that it may be used as a generic indicator mineral together with other resistant ore minerals.