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Location: 82 Km NE from Ghanzi, Botswana
Unit 6B, Tau Mall Plot 8624GhanziBotswana
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The A4 deposit is located within the Ghanzi-Chobe belt in western Botswana. The stratigraphy in this belt comprises the basal Kgwebe volcanics which are unconformably overlain by Ghanzi Group sediments. The Ghanzi Group is a meta-sedimentary group comprising (in successively higher stratigraphic order) the Kuke, Ngwako Pan, D’Kar and Mamuno Formations.A4 occupies a similar structural and stratigraphic position to that of the T3 deposit in that it occurs within a NE-SW trending periclinal anticline (“Dome”) with a core of Ngwako Pan Formation sandstone, overlain by a succession of D’Kar Formation shale, sandstone, siltstone and carbonates. All mineralisation modelled and incorporated in the Mineral Resource estimate occurs within the D’Kar Formation.Second order (parasitic) upright to overturned folds are developed within the axial region of the periclinal anticline. The second order folds are cross-cut and displaced by moderately north-west dipping brittle-ductile, thrust-sense shear zones. These shear zones are characterised by zones of heterogeneous foliation of variable width and intensity. High strain zones have been recognised along which different sedimentary units have been juxtaposed by brittle displacement.Flat lying to shallow dipping zones of extensional fracture and veining are developed in the footwall of the main shear zone. These extensional zones are interpreted to have formed as shear related extensional structures during thrust movement. The extensional structures are preferentially developed within a sandstone dominated package but also penetrate the overlying carbonate and siltstone dominated units.Cu-Ag mineralisation that forms the focus of A4 is developed along both the shear zones and the extensional zones. Within the shear zones copper sulphides (bornite, chalcocite, chalcopyrite) are associated with quartz-carbonate veins developed sub-parallel to the shear foliation. Within the extensional zones copper sulphides are associated with either quartz-carbonate veins or as sulphide fill to in-situ fragmentation zones (breccias) within the host sediments. Cu-Ag mineralisation that forms the focus of the A4 study extends from approximately 5m – 220m below surface. Mineralisation extends for 1,200m along strike and the cumulative total true width of mineralisation ranges from 10m – 80m.Mineralisation extends over a strike length of approximately 900m and 270m down-dip and remains open at depth and along strike. Wireframes were developed using the high strain zones and extensional structures to guide interpretation of hosted mineralisation. A nominal 0.3% Cu cut-off grade was used to determine the external boundary of the mineralised zones. Immediately above the mineralised zone, soil/sand and calcrete extends to a depth ranging from 3 – 8m below surface. Saprolite (>25% oxidation) extends from 25 – 60m below surface and saprock (1 – 25% oxidation) from 55 – 85m below surface. Where oxidised, primary copper sulphides are altered to malachite, chrysocolla or covellite.
