Preliminary Investigation of the Geologic Controls of Graphite Mineralization and Exploration Potential of the Wa-Lawra Belt: Implications for Kambale Graphite Deposit

Abstract

The Kambale graphite deposit is located within the Wa‐Lawra greenstone belt in NW Ghana. Historical records, recent exploration, unpublished material and accessible surface and subsurface exposures provide a valuable preliminary case study of the deposit. Examination of three transversal trenches and re-logging of eleven Rotary Air Blast (RAB) drill holes in the western part of the deposit reveal moderately to intensely sheared metasedimentary rocks of the lower Birimian formation such as mica schist, graphitic schist, quartzite, and a few pegmatite intrusions. Optical microscopic studies show that the deposit occasionally occurs in a complex mineral paragenesis of quartz ± calcite ± hornblende ± magnetite ± pyrrhotite ± rutile ± chalcocite ± graphite and other gangue minerals, often found around the boundaries of large magnesian ferrohornblende minerals, which tend to form quartz crystals. The Kambale deposit is characterized by numerous faults and shears, associated with brittle-ductile deformation at the NE part of the main shear with fewer faults and shears at the southern and western zones, generally trending E-W between 150˚ and 320˚, dipping in NE-SW direction at an average of 060˚. The rocks have undergone medium-high grade metamorphism under high T/medium P facies typically estimated as (∼600-750^◦C, 5.0–8.0 kbar), in amphibolite-granulite facies. The genesis of the flake graphite in Kambale is believed to be as a result of the high grade metamorphism, where deep-seated CO₂-rich fluid phase of crustal origin invaded the metamorphosed rocks. The intensity of the pore fluid pressures aided in the genesis of the graphite by hydraulic fracturing of the underlying rocks under regional syntectonic deformation.

Keywords: geologic controls, graphite, trench mapping, rotary air blast, graphitic schist, Wa-Lawra greenstone belt, Kambale, NW Ghana