The Prestea-Bogoso area occurs at the southern termination of the Ashanti Belt, where the gold deposits, mined or under exploration, are localised principally along two steep to subvertical major crustal structures referred to as the Ashanti trend and the Akropong trend. The principal structures are graphitic shear zones and mineralised fault filled quartz veins. The Bogoso Prestea section of the Ashanti Trend shows a range of mineralisation styles associated with graphitic shear zone, which represents the principal displacement zone of a regional-scale shear zone that defines the mineral belt. These styles include laminated quartz vein deposits containing free gold, highly deformed graphitic shear zones containing disseminations of arsenopyrite as the principal gold bearing phase (e.g. Buesichem, Chujah-Dumasi and Bogoso North) and disseminations of sulphides in mafic/intermediate volcanic rocks generally found in the footwall of the main shear zone.

The Bogoso Prestea deposits can be classified as a lode gold deposits or orogenic mesothermal gold deposits, which are the most common gold systems found within Archean and Paleoproterozoic terrains. In the West African shield, orogenic gold deposits are typically underlain by geology considered to be of Eburnean age and are generally hosted by volcanosedimentary sequences. The Ashanti belt is considered prospective for orogenic mesothermal gold deposits and hosts numerous other lode gold deposits such at the Obuasi ........

Mining activity includes both underground using mechanized shrinkage mining and longhole open-stoping, and a recent significant investment in open pit operations feeding both refractory and non-refractory processing plants.

The planned mining method is mechanized shrinkage mining. This method uses mechanical raise climber technology (Alimak) together with longholes drilled from the raise climber. The method is an advance in terms of safety and productivity from conventional hand-held shrinkage mining. Safety is greatly enhanced both in raise development and stoping operations by having miners protected from rockfalls and removed from working on the broken muck pile. The productivity (per miner) is enhanced by introducing short longholes for stope production.

A typical cycle for Alimak stoping is:
- Raise development in the centre of a stoping block;
- Raise hangingwall rock support;
- Drilling of longhole blast rings;
- Relocation of the raise climber infrastructure to the top of the stoping block, blasting of longhole rings and swell mucking; then,
- Final draw-down mucking and possible waste backfilling.

Small diesel and electric 2 m3 LHD’s will be used for rock haulage from the base of the stoping panel. Mine development will be by hand held drills with LHD mucking. Tramming of ore and waste along the two main levels (17 and 24) will be via an upgraded rail haulage system to Central Shaft.

The rib pi ........

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