Ashanti Gold Belt, Ghana
The flagship operation of Signature Metals Limited is 70%-owned Owere Mines, which holds 100% of the Konongo Project. Its concessions cover 192 square kilometres within Ghana’s renowned Ashanti Gold Belt, with a gold resource of nearly 1.5 million ounces. The area has a rich gold mining history. Since the early 1900s, Konongo has produced over 1.6 million ounces of gold from high-grade ore at 11.8 grams per tonne, mostly mined from underground.
LionGold acquired a 76% interest in then ASX-listed Signature Metals in April 2012 following a successful off-market scrip takeover bid for the company. The Group’s shareholding has been subsequently raised to 77% following the completion of an exercise to consolidate odd-lot holdings.
The Konongo and adjoining Kurofa concessions cover 192 square kilometres and are along the strike of the prolific gold-producing Ashanti Sheer Zone. A processing plant is located northwest of the capital city of Accra, about 50 kilometres from the country’s second largest city, Kumasi, which supports mining activities in the area. Facilities here include a 250 tonne per hour crushing plant, a ball mill, a 200,000 tonne per year Carbon in Pulp/Carbon in Leach (CIP/CIL) plant, a trommel with Knelson concentrator and an RG200 APT gravity plant. Management works closely with the 18 surrounding agrarian communities which reside on the concession land to mitigate impact of the mining operations on farming activities and to coordinate additional social welfare efforts.
Under the directive of a new management team, Signature announced in the March 2013 quarter a change in operational focus in the interest of optimising capital expenditure and to fast-track an assessment of the more extensive high-grade refractory sulphide gold ore underground. Trial mining was ceased as this had yielded only 8,600 ounces of gold bullion from March to December 2012. Site activities reverted to an aggressive exploration programme which is continuing into FY2014. A technical life-of mine study to assess the commercial viability of a larger scale underground mining operation is now underway, and a metallurgical assessment is also being carried out on the deeper segments of the ore body.
The two-pronged exploration programme is examining near-surface oxide ore potential, close to the existing infrastructure and current ore sources, as well as on the relatively unexplored Ashanti Shear itself, and the deeper, higher grade sulphide mineralisation at a depth between 50 and 300 metres. Trenching, multi element soil geochemical survey work and re-processing of existing geophysical data (captured in 1995) were carried out during the FY2013. In addition, approximately 964 aircore holes were drilled, for a total of 35,077 metres, and 201 reverse circulation holes were drilled for a total of 12,214 metres.
From 1903, approximately 4.4 million tonnes oxide and sulphide-ore yielding approximately 1.6 million ounces of gold at average grade of 11.8 grams per tonne. Underground ore explored but not fully mined.
Gold discovery and colonial mining. Started underground mining from four shafts, mainly in Konongo and Obenemase.
Underground developed to 844m depth with discovery of Odumase-Baobedroo, Awere and Akyenase high-grade, free-milling gold ore deposits. Produced 1.4 million ounces gold, 2.8 million tonnes ore, recovered grade 15.7 grams per tonne.
A 30 year 125 square kilometres Konongo concession was granted to the State Gold Mining Corp. In 1988, the Southern Cross Mining Limited joint venture was formed with North Queensland Company Limited to mine surface oxides. 852,000 tonnes of ore was heap leached, recovering 86,000 ounces of gold at 3.15 grams per tonne from open pits on the Obenemase A/B and Kwakawkaw deposits. Operations ceased due to poor recovery.
Obenemase Gold Mines Limited acquired 90% of the Mining Lease, with the Ghanaian government taking a 10% stake. A used CIP/CIL plant used was added to enhance recovery. Open pit oxide ore mining took place from 1995 to 1997, processing 614,000 tonnes of ore and producing 58,500 ounces of gold at a grade of 2.96 grams per tonne at the Boabedroo, Apan, Atunsu, Aserewa, Obenemase A/B deposits.
Ghana Gold Mines (GGM) acquired 90% of Obenemase Gold Mines, and 19.9% of GGM acquired by Resolute Mining Limited. A pre-feasibility study was conducted on the Obenemase A/B deposit and the 95-year-old exploration and development database was validated.
Resolute Mining increased its stake in the project to 81%, with the balance held by the Ghanaian government (10%) and the Apollo Group (9%). The mine was placed under care and maintenance in 2002, due to financial difficulties, and reverted to the Government. Talos Ghana acquired 90% the Mining Lease from the Government in 2004 and formed the Owere Mines Limited joint venture with African Gold Plc (Mwana).
Signature Metals purchased Mwana’s 70% stake in Owere.
West Africa has the geologic potential to become among the leading gold producing regions globally. Numerous new gold-mining projects are being developed in Ghana, Burkina Faso, Mali, Liberia, Mauritania and Sierra Leone. Gold production in the greater region has reached 6.7 million ounces in 2010, accounting for nearly 8% of global supply.
Ghana in particular has benefited from foreign investment in the region’s gold resources, underpinned by government initiatives and under the auspices of the Minerals and Mining Act 2006. The country has a gold mining history going back over 1000 years and is currently the second largest producer of gold in Africa and the eighth largest globally.
The West African Craton has an Archean core surrounded by younger Precambrian and Phanerozoic greenstone sequences. In Ghana especially, gold (and manganese) mineralisation is concentrated in 10 to 15 kilometre structural transition zones of Palaeoproterozoic meta-sedimentary basins and Birimian meta-volcanic belts within the southerly Man Shield. The Tarkwaian Group consists of a distinctive metasedimentary sequence that occurs along the Ashanti Gold Belt which hosts significant palaeoplacer style gold deposits derived from the erosion of the primary greenstone/granite rock sequences.
Gold mineralisation within the Konongo Project can be divided into four distinct styles, two of which include:
- KONONGO: Quartz reef style, with gold/sulphide mineralisation hosted within narrow, intensely sheared quartz veined and altered transition zone sediments.
- OBENEMASE-KWAKAWKAW: disseminated sulphide/gold lodes hosted within Upper Birimian volcano-sedimentary rocks.