Geology
The mine is located within the Obuasi concession area in southwestern Ghana along the northeasterly striking Ashanti volcanic belt. The deposit is one of the most significant Proterozoic gold belts discovered to date. The Ashanti belt predominantly comprises sedimentary and mafic volcanic rocks, and is the most prominent of the five Birimian Supergroup gold belts found in Ghana.

Deposit type
The Birimian was deformed, metamorphosed, and intruded by syn- and post-tectonic granitoids during the Eburnean tectonothermal event around two billion years ago. Folding trends are dominantly north-northeast to northeast. Elongate syn-Birimian basins developed between the ridges of the Birimian system, and these were filled with the Tarkwaian molasse sediments made up primarily of conglomerates, quartzose and arkosic sandstones and minor shale units. Major faulting has taken place along the same trends. The Lower Birimian metasediments and metavolcanics are characterised and defined by argillaceous and fine to intermediate arenaceous rocks. These rocks are represented by phyllites, metasiltstones, metagreywackes, tuffaceous sediments, ash tuffs and hornstones in order of decreasing importance. Adjacent to the shear zones, these rocks are replaced by sericitic, chloritic and carbonaceous schists, which may be graphitic in places. Multiple lodes are a common feature. Mineralised shears are found in close proximity to the contact with harder metamorphosed and me ........

Obuasi Gold Mine is located in the municipality of Obuasi, in the Ashanti region of Ghana, about 240km northwest of the capital Accra and 60km south of Kumasi.

Obuasi is an underground operation utilising both vertical shafts and declines as main access routes to the underground workings. The mine has seen extensive historical mining activities with varying applications of different mining methods to date. The current LOM design employs mostly the long-hole open stoping (LHOS) mining method for ore extraction. LHOS is a highly selective and productive method of mining that can be employed for orebodies of varying thicknesses and dips. The main distinct variations of the LHOS used at Obuasi are longitudinal retreat stoping (LRS), and transverse open stoping (TOS). The blind upper stoping is a form of LRS or TOS used for partial sill pillar recovery.

TOS is designed in areas of the orebody that are greater than 15m in thickness. Stopes are accessed by the cross-cut in the centre of the stope and than a tee along the hanging wall contact on the extraction level (lower) and on the upper level is developed to create the initial slot for stope blasting. Stope heights are on average 20m to 25m with a stope length along strike of 15m to 20m. Primary TOS stopes are the initial stopes in the mining sequence which are surrounded by fresh rock. Secondary stopes are stopes that have at least one wall of curred paste fill or hydra fill from an adjacent primary stope. ........

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