Summary:
Gold deposits at Sissingué are orogenic, greenstone hosted.
The Sissingué Gold Mine main pit mineralisation is structurally controlled and mainly hosted within a granitic stock associated with a network of quartz-carbonate veins and veinlets with associated pyrite and arsenopyrite dissemination. Gold-bearing veins have a dominant NNW to NS trend and are steeply dipping. Disseminated mineralisation is also located in the alternation envelops of the mineralised quartz veins.
Additional mineralisation is seen within interconnecting mineralised felsic dyke complexes that propagate from the main granite stock. These mineralised felsic dyke complexes, also trending NNW, host the mineralisation for the additional pits in the area, namely Binkadi, Bagoé, Western Arm and Boribana.
The Sissingué Deposit occurs in a strongly deformed Birimian greenstone belt intruded by quartz-feldspar felsic dykes and granitoid bodies. Gold mineralisation at Sissingué is associated with the felsic dykes and small granitoid (tonalite) bodies that cross-cut sedimentary rocks. Subsequent hydrothermal activities and metasomatism of the granitoids has led to a sericite-carbonate alteration within the intrusive and the more permeable horizons (sandstones and conglomerates) of the sedimentary rocks, and a low to moderate grade disseminated gold mineralisation. Late-stage high grade Au-As-quartz-carbonate veins exploited the altered and brittle portions of the intrusive and sediments with common occurrences of visible gold.
The gold Mineralisation was domained by its host lithology for modelling (granite, felsic dykes and sediments). Within the dyke domains, mineralised sediments in the alteration halo of the dykes were included to maintain a minimum width of the wireframes and to maintain continuity along strike. Where geological contacts were not clearly controlling the distribution of mineralisation, a grade cut-off of 0.3 g/t Au was used to construct Mineral Resource boundaries and to provide overall geometry to mineralised zones. A minimum of 2 m width was used for the wireframes and samples of grades below the nominal cut-off of 0.3 g/t Au were included where the wireframe would otherwise be less than 2 m wide. Analysis of the global grade distribution shows that there is a natural change in grade population at around 0.3 g/t Au.
Sissingué – Airport West
The deposits occur in a strongly deformed Birimian greenstone belt intruded by quartz-feldspar felsic dykes and granitoid bodies.
Gold mineralisation is associated with the felsic dykes and small granitoid (tonalite) bodies that cross-cut sedimentary rocks.
Subsequent hydrothermal activities and metasomatism of the granitoids has led to a sericitecarbonate alteration within the intrusive and the more permeable horizons (sandstones and conglomerates) of the sedimentary rocks, and a low to moderate grade disseminated gold mineralisation.
Late-stage high grade Au-As-quartz-carbonate veins exploited the altered and brittle portions of the intrusive and sediments with common occurrences of visible gold.
Dimensions
The mineralisation trends extend over 2,500 metres strike and dip steeply to the west or east with horizontal widths varying between 5 to 30 metres for the dyke associated domains and up to 180 metres in width for the granite domains. Domains are interpreted to a maximum vertical depth of 300 metres.
Satellite deposits follow similar trends however with more restricted strike and depth extents.
Airport West: The mineralisation trend extends over 350 metres strike and dips sub-vertically with horizontal widths varying between 3 to 10 metres. Domains are interpreted to a maximum vertical depth of 150 metres.
Fimbiasso East and West
The Fimbiasso gold deposits are located within a north-westerly striking splay of the SyamaBoundiali Greenstone Belt. At Fimbiasso, Birimian aged rocks comprise a sequence of metasedimentary rocks and subordinate mafic volcanics that have been intruded by a nearly circular granitoid body approximately 4 km in diameter. The sequence has also been intruded by numerous felsic dykes of various compositions.
Gold mineralisation is associated with deformation zones developed at and adjacent to the margins of the granitoid intrusion. Gold is associated with disseminated pyrite and lesser pyrrhotite hosted by both mafic and felsic lithologies where they feature chlorite-sericite-calcite alteration. Vein-hosted mineralisation is rare.
Dimensions
Fimbiasso East mineralisation trends mine grid north, extend over 520 metres and dip steeply to the east with horizontal width varying between 15 to 90 metres. Domains are interpreted to a maximum vertical depth of 180 metres.
Fimbiasso West mineralisation is interpreted to extend around 1,500 m in strike, up to 50 m thickness (comprising several lodes each up to 20 m in thickness) and to a depth of 250 m. The currently defined mineralisation is open at depth.
Bagoé
The Bagoé Gold Project is located in the West African Craton and covers Palaeoproterozoic (Birimian) rocks of the southern extension of the Syama Greenstone Belt and the western margin of the Senoufo Greenstone Belt. Gold deposits at Bagoé are of the orogenic, greenstone-hosted type and probably lie within the Senoufo belt.
Antoinette gold deposit is hosted by a fine-grained, siliceous and, in places, carbonaceous metasediment unit within a sequence of felsic volcaniclastic rocks and porphyritic dioritic dykes.
Juliette gold deposit is located 3.5 km SW of Antoinette and is hosted by the extension of the Antoinette sequence/structure.
Veronique gold deposit is located 16 km SSE of Antoinette and generally comprises a single NWstriking quartz vein hosted by an extensive granodiorite stock. Alteration selvages extend 2 m to 3 m either side of the vein.
Dimensions
Antoinette mineralisation is subvertical, extends over about 800 m strike, with individual lenses generally about 10 m wide; in places lenses combine resulting in widths of up to 25 m. Weathering extends to 50 to 60 m below surface.
Juliette mineralisation is subvertical, extends over about 470 m strike and generally comprises a single lens 4-10 m wide. Weathering extends to 30 to 40m below surface.
Veronique mineralisation extends over 800 m strike and generally comprises a single NW-striking quartz vein 1-2 m thick that dips at 45 degrees to the SW. Mineralised alteration selvages, extending 2 m to 3 m either side of the vein in places, results in up to 10 m true thickness of mineralisation. Weathering extends to 50 to 60 m below surface.