Lithological, fluid and structural controls of gold mineralization at Massawa, eastern Senegal

Senghor, Dioumacor (2011) Lithological, fluid and structural controls of gold mineralization at Massawa, eastern Senegal. (MSc(R) thesis), Kingston University, .


The Massawa gold project is situated on the Senegalese side of the highly prospective/productive Kedougou-Kenieba Inlier, which hosts several world-class orogenic gold deposits/districts in Western Mali (e.g. Loulo and Sadiola). Massawa is located in the Kounemba exploration permit along the eastern margin of the Palaeoproterozoic (Birimian) Mako volcano-sedimentary belt, with the Mineralisation focussed along splays off a major terrane-bounding sinistral shear known as the Main Transcurrent Zone (MTZ). The MTZ hosts other known Au deposits along strike including Sabodala to the NNW. The Massawa orebody is at least 8.5km long and has a current resource of 3.01 Moz of gold at an average grade of 3.96 g/t, with mining scheduled for 2011/2012. The Massawa structure trends NE (030[degrees]) with high grade gold zones situated along N-S trending dilational shears that are interpreted as right-hand flexures developed during dextral reactivation. Exploration is currently focussed on the northern 4.5 km section of the structure where the deposit is split into two separate mineralised zones (Central and Northern). Host rocks strike sub-parallel to the main shear direction and consist of a package of low grade regionally metamorphosed volcaniclastic sediments (tuffs and ash-tuffs), quartz-feldspar and lithic wackes, carbonaceous shales, hydrothermal breccias, and gabbro and porphyry skills. These sediments have undergone pervasive silica alteration (Central zone) followed by a sericite-ankerite-dolomite alteration event related to the Mineralisation (both zones). Two major styles of Mineralisation are recognized at Massawa from field and laboratory studies. The first stage of sulphide-Au Mineralisation is associated with disseminated arsenopyrite-pyrite, which follows shear bands in the sedimentary-igneous host rocks. The second stage consists of quartz-stibnite plus-or-minus tetrahedrite veining (confined to the Central zone) distinguished by coarse visible gold Mineralisation (100 [mu]m to a few mm). A distinctive trace assemblage is linked to stibnite formation including multiple Sb phases such as chalcostibite, zinkenite, roschinite, aurostinote, jamesonite and robinsonite. This Sb-Au Mineralisation is likely to represent a shallower (<6 km) late stage overprint according to the Groves model for orogenic gold. Shallow-level Mineralisation is also suggested by fluid inclusion studies on quarts-stibnite veins which show the predominance of low temperature (homogenisation temperatures between 115-252.8[degrees]C) H[sub]2O-NaCl fluids (<6 wt% NaCl equiv.).

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