Characterisation and evolution of Au mineralisation in the Loulo mining district, Western Mali

Loulo is a world-class orogenic gold district in SW Mali. The mininig district is comprised of two major operational mines at Yalea (6.5 Moz at 4.7 g/t) and Gara (3.7 Moz at 4.1 g/t), plus numerous satellite deposits and other prospective targets, which takes Loulo's overall resource to 14.4 Moz. Two distinct types of ore deposit are recognised. Gara-style deposits are Fe-rich and characterised by a Fe-Cu-REE-Au-Ni-W-As ± Co-Ag-Pd metal association. Yalea-style, As-rich, deposits exhibit more typical orogenic gold features with a metal signature consisting of Fe-As-Cu-W-Au-Pb-Sb-Ag. Investigations into the source and composition of the auriferous fluids indicate two styles of ore fluid were responsible for mineralisation: (1) a 'Gara-style' oxidised (FM-buffered), high temperature (>400 °C), hypersaline (35-55 wt.% NaCl equiv.), Na-Fe-Cl-B-bearing magmatic fluid; and (2) a 'Yalea-style' reduced (QFM-buffered), lower temperature (300-350 °C), low-salinity (