Precious metals in gossanous waste rocks, Angostura copper mine, Iberian Pyrite Belt, Spain

The Iberian Pyrite Belt (IPB) is one of the largest (if not the largest) of the world's massive sulphide provinces. Since the Chalcolithic era, gossans formed from the massive sulphide mineralisations have been worked for copper, silver and gold, and consequently many historic mine sites have abandoned dumps of gossanous material. The aims of this study are to determine the mineralogical hosts of precious metals (Au, Ag) and environmentally significant elements (As, Ba, Bi, Cu, Hg, Mo, Sb, Se, Pb, Zn) in gossanous waste rocks from historic dumps, using geochemical, optical, SEM-MLA and laser ablation techniques. Preliminary data demonstrate that the precious metals are contained as inclusions of Au, electrum and Ag-Hg halides that are commonly encapsulated within iron oxides and hydroxides. The encapsulated nature of the precious metal inclusions along with their small size could make mineral processing difficult and expensive. In addition, the As, Bi and Pb enrichment of iron oxides and the presence of Ag-Hg halides may require suitable and safe storage of processing wastes. The study demonstrates that a solid knowledge of the mineralogical siting of precious metals and environmentally significant elements in gossanous waste rocks is required to achieve sustainable mineral resource development.