High-resolution short-wave infrared hyperspectral characterization of alteration at the Sadiola Hill gold deposit, Mali, Western Africa

Sadiola Hill is an ~8 Moz gold deposit located in western Mali within a ca. 2200-2050 Ma tectonic window known as Kédougou-Kénieba inlier (KKI), exposing the Western African craton. The deposit is hosted in a metasedimentary package made up of impure carbonate rocks, wackes, and arenites intruded by three distinct igneous phases. A N-S-trending Sadiola shear zone, related to the regional Senegal-Mali shear zone, and NNE-trending third order fault splays acted as conduits for auriferous hydrothermal fluid flow. The deposit has undergone a complex poly-phase alteration history. Alteration assemblages related to gold mineralization consist of biotite-carbonate-quartz-sulphide. Other assemblages include calc-silicates, chlorite, white mica, scapolite, and tourmaline (Hein and Tshibubudze 2007; Cameron 2010; Masurel et al. 2017). Current research is aimed at characterising alteration at the mineral-scale, as well as assessment of cooling trend(s) and alteration footprint(s) with high-resolution short-wave infrared (SWIR) hyperspectral scanning. In addition to detailed mineralogical classification, changes in fluid chemical parameters are determined with variations in white mica, namely, the position of Al-OH bond in the SWIR range and white mica crystallinity. Furthermore, hydrothermal fluid chemistry is assessed with Fe2+ content in carbonate group minerals. Protolith control on alteration expression is also investigated.