Silver geochemistry and isotope systematics in Ag-rich mine tailings from Namibia

Abstract

In this study, we present a detailed geochemical characterisation and stable isotope systematics of silver (Ag) in a mining waste facility at the Namib Lead & Zinc mine in Namibia (Africa). We examined a series of flotation tailings and ore minerals to address two principal questions: (1) the distribution, chemical form and leachability of Ag, and (2) the local Ag isotopic signature(s) and its variability in relation to Ag speciation in the solid phase, as well as the fate of stable Ag isotopes. Our findings reveal a significant correlation between Ag and Pb concentrations, indicating that galena is the primary Ag carrier. Most importantly, all mild extractions mobilised only a minimal amount of Ag (≤ 1 wt.% of the total amount). This suggests that most Ag is associated with geochemically stable phases, specifically sulphides, which are not subjected to leaching and/or intensive weathering. Unlike other isotope studies, the present research demonstrates a homogeneous Ag isotopic signal in the tailings and individual ore samples with an average δ109Ag value of ~ 0‰ (± 0.1, 2SD). Therefore, this study provides new knowledge and clearly supports the use of Ag isotopic data to track primary Ag sources globally, not only in Africa.