The Loulo-Gounkoto complex in the Kédougou-Kéniéba Inlier hosts three multi-million ounce orogenic gold deposits, situated along the Senegal-Mali Shear Zone. This west Malian gold belt represents the largest West African orogenic gold district outside Ghana. The Gounkoto deposit is hosted to the south of the Gara and Yalea gold mines in the Kofi Series metasedimentary rocks. The ore body is structurally controlled and is characterised by sodic and phyllic alteration, As-and Fe-rich ore assemblages, with abundant magnetite, and overall enrichment in Fe-As-Cu-Au-Ag-W-Ni-Co-REE + minor Te-Pb-Se-Cd. Fluid inclusion analysis indicates that the deposit formed at P-T conditions of approximately 1.4 kbar and 340 °C and that two end member fluids were involved in mineralisation:(1) a moderate temperature (315-340 °C), low salinity (<10 wt. % NaCl equiv.), low density (≤1 gcm Gounkoto are of metamorphic origin and that the high levels of salinity in the brine are likely derived from evaporite dissolution.

Please cite this article as: Lambert-Smith, J.S., Lawrence, D.M., Müller, W., Treloar, P.J.,Palaeotectonic setting of the south-eastern Kédougou-Kéniéba Inlier, West Africa: new insights from igneous trace element geochemistry and U-Pb zircon ages, Precambrian Research (2015), http://dx.doi.org/10. 1016/j.precamres.2015.10.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

The genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilisation reactions. However, there is considerable debate as to the ultimate source of these fluids and the metals they transport. Tourmaline is a common gangue mineral in orogenic gold deposits. It is stable over a very wide P-T range, demonstrates limited volume diffusion of major and trace elements and is the main host of B in most rock types. We have used texturally resolved B-isotope analysis

Economic gold mineralization in Mali is confined to two terranes of Birimian-aged (Paleoproterozoic) rocks in the south and south-west of the country. The West Mali gold belt, along the border with Senegal, hosts two world-class orogenic gold districts (>5 Moz of Au mined or in reserve): the Loulo-Gounkoto and Sadiola-Yatela complexes. This gold province is hosted within greenschist metamorphosed siliciclastic and carbonate sedimentary rocks along the eastern side of the Kédougou-Ké-niéba inlier, with mineralization linked to higher-order shears and folds related to the Senegal-Mali Shear Zone. Gold deposits within the West Mali gold belt show many features typical of orogenic gold mineralization, such as geological setting (accretionary orogen), late-orogenic timing (strike-slip deformation; post peak metamorphism), structural paragenesis, and deposit geometry (steep, tabular ore bodies). However, alteration assemblages (tourmalinization, silica-carbonate, sericite-chlorite-biotite, calc-silicate) and ore fluid compositions (carbonic-rich and high-salinity aqueous-rich fluids) are highly variable along the belt. Fluid inclusion and stable isotope studies have shown that this variability is caused by multi-fluid sources, with magmatic, evaporitic and regional metamorphic fluids all likely contributing to gold mineralization within the region. Supergene enrichment of the orogenic gold lodes is economically important in the northern parts of the West Mali gold belt, involving karstification of mineralized limestones. In addition to orogenic gold deposits, other styles of gold mineralization have been reported within the Birimian crust of West Africa. The Morila gold deposit, in southern Mali,

The Gara, Yalea, and Gounkoto Au deposits of the &gt;17 Moz Loulo mining district, largely hosted by the Kofi series metasediments, are located several kilometers to the east of the 650-Mt Fe skarn deposits in the adjacent Falémé batholith. The Au deposits are interpreted to have formed through phase separation of an aqueous-carbonic fluid, which locally mixed with a hypersaline brine of metaevaporite origin. Recognition of an intrusive relationship between the Falémé batholith and Kofi series opens the possibility that the Fe skarns and Au deposits are part of the same mineral system. In this paper, we combine new δ13C, δ18O, and δ34S data from the Karakaene Ndi skarn, Au occurrences along the western margin of the Kofi series, and zircons within plutonic rocks of the Falémé batholith. We combine these with existing data from the Loulo Au deposits to model the contribution of magmatic volatiles to Au mineralization. C and O isotope compositions of auriferous carbonate-quartz-sulfide veins from the Loulo Au deposits have wide ranges (δ13C: –21.7 to –4.5‰ and δ18O: 11.8 to 23.2‰), whereas values from carbonate veins in Kofi series Au prospects close to the Falémé batholith and the Karakaene Ndi Fe skarn deposit have more restricted ranges (δ13C: –16.8 to –3.7‰, δ18O: 11.4 to 17.2‰, and δ13C: –3.0 ± 1‰, δ18O: 12.6 ± 1‰, respectively). Kofi series dolostones have generally higher isotopic values (δ13C: –3.1 to 1.3‰ and δ18O: 19.1 to 23.3‰). Pyrite from Kofi series Au prospects adjacent to the Falémé batholith have a wide range of δ34S values (–4.6 to 14.2‰), similar to pyrite from the Karakaene Ndi skarn (2.8 to 11.9‰), whereas δ34S values of pyrite and arsenopyrite from the Loulo deposits are consistently &gt;6‰. Comparison of the C and O isotope data with water-rock reaction models indicates the Loulo Au deposits formed primarily through unmixing of an aqueous carbonic fluid derived from the devolatilization of sedimentary rocks with an organic carbon component. Isotopic data are permissive of the hypersaline brine that enhanced this phase separation including components derived from both Kofi series evaporite horizons interlayered with the dolostones and a magmatic-hydrothermal brine. This magmatic-hydrothermal component is particularly apparent in O, C, and S isotope data from the Gara deposit and Au prospects immediately adjacent to the Falémé batholith.