Summary:
The property hosts a typical Upper Archean to lower Proterozoic style of metallogeny, characteristic of greenstone-hosted lode gold mineralisation, where deposits are often referred to as orogenic, and characterised by the presence of gold-quartz veins and disseminated mineralisation. Gold mineralisation is hosted in moderate to steeply dipping quartz-dominated shear zones with associated extensional vein systems. This model is consistent with Archean orogenic gold deposits described by Hagemann and Cassidy (2000), Richards and Tosdal (2001), Goldfarb et al. (2001) and Roberts et al. (1989).
New Liberty
Within the ultramafic unit, silicification is found proximal to the mineralisation, within the immediate hangingwall and rarely in the footwall gneisses. Other alteration styles associated with the mineralisation include the presence of phlogopite as well as chlorite within the mineralised zone, and an associated sulphidic bleaching of the rocks linked with the destruction of magnetite.
These features point to a pathway for the mineralising fluids which was active over a long period of time. The deposit shows the classic signs of sulphidation, with iron sulphides (mainly pyrrhotite) replacing the magnetite and it has a low sulphide content with sulphides forming between 0.1% and 1% of the mineralised zones.
Multi element analyses of cores have highlighted a clear association between gold and arsenic, sulphur, nickel and tungsten in the mineralised zones. Enhanced values of magnesium, sodium, potassium, rubidium and barium occur along the margins of the mineralisation. It is hypothesised that the gold-bearing metamorphic fluid may include a granitic component in its evolution.
Vast majority of the mineralisation at the Project is hosted within the altered parts of the sheared ultramafic rocks. Pyrrhotite, gersdorffite and arsenopyrite are the main sulphides with occasional pyrite and rare chalcopyrite or pentlandite. Metallurgical tests of the mineralised sections carried out by Lakefield Research Limited (Lakefield, 1999b) indicated that the gold is free in form. Gold mineralisation occurs in zones of variable thickness, with average widths of 10 m, and is nearly continuous along 2 km of strike.
Ndablama
Gold mineralisation is associated with hydrothermal alteration and disseminated sulphides and is related to shear deformation which follows the granite-metavolcanic contact zone.
Alteration is consistently defined by silicification, magnetite destruction, phlogopite and chlorite, with phlogopite dominating the relationship. Magnetite destruction within the ultramafics has been identified as having a direct relationship with gold mineralisation.
The mineralisation is located within a sheared package of ultramafic and mafic rocks intercalated within a gneiss sequence overlying/adjacent to a granite batholith. The mineralization consists of three bodies; the central zone 430 m long has been drilled to vertical depth of 290 m, southern- eastern zone which has 300 m strike length has been tested to 120 m depth, and the last zone, along north to south direction, which has about 1300 m strike length has been drilled to 360 m vertical depth. All have shallow westerly-dip (25° on average) and strike north-south. The dip of the orebody decreases with depth. Mineralisation continues to the north but at a lower grade.
Sheared amphibolite schists with biotite/phlogopite and ultramafic tremolite chlorite schists host the gold mineralisation at Ndablama, with occasional magnetite-poor ultramafics and intrusive granites also containing mineralisation. Petrography carried out during 2014 shows that the gold is associated with disseminated pyrite and pyrrhotite and trace chalcopyrite (Thatcher, 2014).
Gold often occurs at sheared contact zones between ultramafic and mafic rocks that have been intruded by granite dykes and breccias. The breccia often marks the end of the gold mineralisaOon. Spatially, gold mineralisation remains open in all directions.