Location: Central Ashanti region of Ghana in West Africa.
ReservesProven: 18.4Mt graded at 1.4g/t Au; Probable: 37.2 Mt graded at 1.1g/t Au.
Geology: TypeIntensely folded and faulted birimian flysch-type metasediments of the Paleoproterozoic age.
Mineralization Type: Narrow quartz veins within granite structures.
Production Scheduled: 2011
Estimated Mine Life: 10.2 years
The Central Ashanti gold mine is located approximately 57km south-west of Obuasi town and 195km north-west of Ghana’s capital Accra. Formerly known as Ayanfuri gold project, the mine has produced in excess of 300,000oz of gold between 1994 and 2001. It is owned by Central Ashanti Gold Limited, a wholly owned subsidiary of Perseus, which owns 650km² of tenements on the Ashanti gold belt.
The project is currently in the planning stage with a detailed feasibility study completed in July 2009. Production is scheduled to begin in 2011. The life of the mine is estimated to be approximately ten years.
Gold Mine Reserves
The mine contains an estimated 18.4Mt of proven reserves graded at 1.4g/t Au and 37.2 Mt of probable reserves graded at 1.1g/t Au. Measured and indicated resources total 29.9Mt graded at 2.1g/t Au. Inferred resources have been estimated to be 62.1Mt at 2.2g/t.
Gold Mine Geology
The deposit is hosted within the Man Shield of the Precambrian aged West African Craton. The deposit flanks the western end of the Ashanti greenstone belt along the Obuasi-Akropong gold corridor.
Intensely folded and faulted birimian flysch-type metasediments of the Paleoproterozoic age overlie the entire project area.
These sediments are metamorphosed to upper greenschist faces and include dacitic volcaniclastics, greywackes and argillaceous (phyllitic) sediments.
The sediments are intruded along multiple regional bodies by a number of small basin-type or Cape Coast-type granite structures.
The intrusions vary in size and shape from 200m to 400m long and 40 to 150m wide egg-shaped plugs, to longer and narrower sills and dykes that measure more than 2,000m in length and between 50m and 100m in width.
Regionally, the deposit hosts minor amounts of cherty and manganiferous exhalative sediments. Graphitic schists coincide with the main shear (thrust) zones. Parallel to partially parallel cleavage and bedding follow the regional trend of the 50° striking, steep to near vertical, southeast and north-west dipping Akropong structures.
Gold mineralisation at the mine is found primarily within granite structures. Two or three generations of several, narrow quartz veins host the mineralisation. The quartz veins are associated with nearly 3% pyrite, minor arsenopyrite and lesser amounts of sphalerite, chalcopyrite, galena and rutile.
Gold observed at or near the margins of the veins, occurs as fine grains along the boundaries of sulphide grain or in sulphide fractures. Coarse visible gold is hosted within the quartz. Mineralisation also occurs in shear zones that host the classic Ashanti-style sediments.
mining and processing
The deposit will be mined using hydraulic excavators ranging in size between 120 and 200t, with a backhoe configuration. Depending on the swell, flitches averaging 2 x 2.5m will be used.
Ore and waste will be excavated and loaded within the marked boundaries, thereby ensuring maximum ore recovery with minimum contamination.
Due to the intact strength of the rocks, fresh rocks will be blasted heavily. Control blasting techniques including pre-splitting, buffer rows and trimming will be used to minimise the impact of blasting on the slopes.
Mining will be carried out to support a mill feed rate of 5.5Mtpa of high grade primary ore. Processing will be carried out in a 5.5Mtpa gold processing plant that will include a primary jaw crusher , single stage SAG mill, gravity circuit, flotation circuit, regrind ball mill , concentrate CIL circuit and elution circuit.
A mining operations contract is yet to be awarded. The scope of the contract will include site preparation, construction and maintenance of haul-road, loading and transportation of ore to the ROM pad and hauling of waste material to the waste dump.
Perseus will undertake the technical services of the project including planning the mining activities, scheduling of production, grade controlling and ore blending.