The geology of the gold deposits of Prestea gold belt of Ghana

Abstract

This paper presents the geology of the gold deposits along the Prestea gold belt of Ghana to assist exploration work for new orebodies along the belt. Prestea district is the third largest gold producer in West Africa after Obuasi and Tarkwa districts (over 250 metric tonnes Au during the last century). The gold deposits are structurally controlled and occur in a deep-seated fault or fissure zone that is regarded as the ore channel. This structure, which lies at the contact between metavolcanic and metasedimentary rocks in Birimian rocks, is more open (and contains more quartz lodes) at the southern end around Prestea than at Bogoso to the north. The gold deposits consist of the Quartz Vein Type, (QVT) and the Disseminated Sulphide Type (DST). The QVT orebodies, which generally carry higher Au grades, lie within a graphitic gouge in the fissure zones whilst the DST is found mostly in sheared or crushed rocks near the fissure zones. Deposits were grouped into three in terms of geographic location and state of development; The deposits south of Prestea are the least developed but have been extensively explored by Takoradi Gold Company. Those at Prestea have been worked exclusively as underground mines on QVT orebodies by Prestea Goldfields Limited and its forerunners; Ariston and Ghana Main Reef companies until 1998 whilst the deposits north of Prestea, which were first worked as surface mines (on DST orebodies) by Marlu Mines up to 1952, were revived by Billiton Bogoso Gold in 1990. Bogoso Gold Limited, a subsidiary of Golden Star Resources, now runs the mines, which are currently working “Oxide ore” (the oxidised derivate of the DST ore) by surface operations in open cut mines at Bogoso and Prestea. Active exploration is presently underway to find extensions to the orebodies and extend the life of the mines. The summary of the special attributes of the deposits presented in this paper may be useful in re-evaluation of the orebodies.