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Golden Star owns the Bogoso/Prestea mine that consists of mining and exploration concessions along the Ashanti Trend. In total the Bogoso/Prestea property covers a strike length of approximately 85 km.
The remaining 10% interest in the Bogoso/Prestea property is a carried interest owned by the Government of Ghana, with dividends payable after capital costs have been recovered.
Bogoso/Prestea is located in southwest Ghana approximately 300 kilometers west of the capital, Accra, and is accessible by sealed road.
Bogoso/Prestea lies within the Eburnean Tectonic Province (1,800-2,166 Ma) in the West African Precambrian Shield. The paleo-proterozoic rocks that comprise most of the West African craton and host the major gold mineralization in Ghana are subdivided into metasedimentary and volcanic rocks of the Tarkwaian and Birimian sequences.
The Birimian is composed largely of phyllites, schists, greywackes, volcanoclastics, and metavolcanic rocks (including lavas, pyroclastics, and some finer-grained metasedimentary rocks). Unconformably overlying the Birimian are the continental clastics of the Tarkwaian sequence. These clastics were derived from the weathering of Birimian rocks and granitic intrusions found within the Birimian.
The area is dominated by a major northeast-southwest trending structural fault zone referred to as the Ashanti Trend, which hosts the Prestea, Bogoso, Obuasi and Konongo gold deposits, among others. Parallel to the Ashanti Trend is the Akropong trend, which hosts the multi-million ounce Edikan gold deposit. The Akropong Trend is about 15 km west of the Ashanti Trend in the Bogoso region, and gradually converges with it, coalescing at Obuasi and forming the basis for the world class Obuasi deposit, owned and operated by AngloGold Ashanti Ltd.
Gold operations in the Tarkwaian sequence include the Teberebie, Abosso, Tarkwa and Iduapriem mines.
In the Bogoso area, the faulted contact zone is known as the “Main Crush Zone” and passes through the central part of the Bogoso Mine for its entire 18.5-kilometer concession length. The Main Crush Zone lies within a structural corridor that varies in width from 1,000 to 2,500 meters. Some 90% of the gold mined to date at the Bogoso Mine has come from the Main Crush Zone with the larger deposits being located at bends and junctions along this major fault. Additional faults and splays in the structural corridor may also be prospective for gold. The oxide ores tend to have fine-grained free gold that has been liberated during the weathering of pre-existing sulfides. Oxidation extends from surface down to the approximate elevation of the water table averaging 40 m below surface and ranging between 10 m and 60 m below surface. Below this, a transition zone of up to 20 meters of partially oxidized material directly overlies fresh sulfide mineralization.
The Prestea concession covers a 22 km stretch of the Ashanti Trend located immediately south of the Bogoso concession. Within the concession, the “Main Crush Zone” is comprised of an anastomosing network of thrust faults with three dominant structures trending northeasterly (40-60°). The three structures are often referred to in the old nomenclature as the Prestea Main, East and West reef zones. Sulfide gold mineralization is also associated with the hangingwall and footwall of these discrete quartz vein (reef) zones. In the Northern portion of the lease the deposits tend to be similar to the Bogoso lease deposits, whilst in the south they are more discrete vein systems. Further towards the south, in the vicinity of the Bondaye-Tuapim shafts, the structures split into two distinct zones running approximately parallel. Tuapim mineralization trends roughly along the same direction as the entire belt (32 degrees) gradually turning to an approximate N-S orientation running parallel to the Tarkwaian - Birimian contact. The second zone of mineralization, the Bondaye Zone in the vicinity of the Bondaye main shaft, swings N-S paralleling this lithological boundary.
In total over 13 million ounces have been mined to date from the Bogoso and Prestea properties.
Mining has been conducted at Prestea since 1873, primarily as an underground operation, with more than nine million ounces of gold recorded by the Ghana Chamber of Mines as having being produced during its more than 135-year history. From 1873 to 1965, the current Prestea concession comprised a number of different licenses operated by independent mining companies, which, in 1965, were amalgamated by the post-independence government. Production declined due to lack of sustained investment, and the mine operated at a loss. In 1985, the Government of Ghana secured a World Bank loan to rehabilitate the mines, but after three years of continued losses, the decision was taken to privatize the mines.
In 1994, JCI Limited won the privatization bid for participation in the Prestea mining operation. JCI made improvements to the productivities and efficiencies of the underground operation and carried out exploration programs and feasibility studies on the near surface resources amenable to open pit mining. However, owing to the declining gold price and continued financial losses, JCI closed down the Prestea underground mine in September 1998 and commenced a process to sell their rights in the project. The closure of the underground mine was opposed by the Prestea workforce who consequently formed Prestea Gold Resources (“PGR”"), which was granted a permit by the Government of Ghana to run the mine in December 1998.
In June 2001, the Government of Ghana granted two separate leases for the Prestea concession. One lease, over the surface rights down to a depth of 200m below general ground elevation (an elevation of approximately 150m below sea level) was granted to Golden Star Bogoso/Prestea Limited (“GSBPL”), and the second, for the underground mine below this level, was granted to PGR. In March 2002, GSBPL reached an agreement with PGR to form a joint venture, to be managed by GSBPL for the assessment and future operations of the Prestea underground mine.
Gold was first commercially mined at Bogoso in the early 20th century. In 1935, high-grade oxide ore was mined from a series of open pits and from limited underground operation on the concession. Until its closure in 1955, this operation produced over 900,000 ounces of gold at an average recovered grade of 3.73 g/t.
Billiton International Metals BV took control of the Bogoso concession in the late 1980’s, and completed the construction of mining and processing facilities in 1991. The plant was designed to process oxide ores by using conventional CIL technology at a design capacity of 1.36 million tonnes per year and to process sulfide ores by using flotation, fluid bed roasting and CIL technology at a design capacity of 0.9 million tonnes per year. Billiton encountered serious operational and mechanical difficulties with the fluid bed roaster and closed the flotation circuit and roaster in early 1994.
Following closure of the roaster, Billiton, by then owned by Gencor, focused the Bogoso operations on oxide ore until it sold its interest in the mine to the mine’s project lenders, who subsequently sold the majority interest in the mine to Golden Star in 1999.
|
PROVEN and PROBABLE MINERAL RESERVES |
As at December 31, 2012 |
As at December 31, 2011 |
||||
|---|---|---|---|---|---|---|
|
Bogoso/Prestea |
Tonnes (millions) |
Gold Grade (g/t) |
Ounces (millions |
Tonnes (millions) |
Gold Grade (g/t) |
Ounces (millions) |
|
Proven Mineral Reserves |
|
|
|
|
|
|
|
Non refractory |
1.3 |
1.82 |
0.08 |
1.3 |
1.64 |
0.07 |
|
Refractory |
7.8 |
2.52 |
0.64 |
8.3 |
2.72 |
0.73 |
|
Total Proven |
9.2 |
2.42 |
0.71 |
9.6 |
2.57 |
0.80 |
|
Probable Mineral Reserves |
|
|
|
|
|
|
|
Non refractory |
4.8 |
2.35 |
0.36 |
6.9 |
2.31 |
0.51 |
|
Refractory |
21.2 |
2.58 |
1.76 |
24.2 |
2.60 |
2.02 |
|
Total Probable |
26.0 |
2.54 |
2.12 |
31.1 |
2.54 |
2.54 |
|
Total Proven and Probable |
|
|
|
|
|
|
|
Non refractory |
6.2 |
2.23 |
0.44 |
8.2 |
2.21 |
0.58 |
|
Refractory |
29.0 |
2.57 |
2.39 |
32.6 |
2.63 |
2.75 |
|
Total Bogoso/Prestea Proven and Probable |
35.2 |
2.51 |
2.84 |
40.8 |
2.55 |
3.34 |
Notes to the Mineral Reserve Statement:
Reconciliation of Mineral Reserves
| Tonnes (Millions) |
Contained Ounces (Millions) |
Tonnes (% of Opening) |
Ounces (% of Opening) |
|
|---|---|---|---|---|
| 2011 Reserves | 58.8 | 4.14 | 100% | 100% |
| Gold Price (1 & 6) | 3.5 | 0.75 | 6% | 18% |
| Exploration Changes (2 & 7) | 23.6 | 1.03 | 40% | 25% |
| Mine Depletion (3) | -6.6 | -0.49 | -11% | -12% |
| Engineering (4) | -12.3 | -1.11 | -21% | -27% |
| 2012 Reserves (5) | 67.1 | 4.31 | 114% | 104% |
Notes to the reconciliation of Mineral Reserves:
The following table summarizes Golden Star’s estimated non-reserves – Measured and Indicated Mineral Resources as at December 31, 2012 as compared to the totals as at December 31, 2011:
| Property | Measured & Indicated | |||
|---|---|---|---|---|
| Category | Tonnes (Millions) | Gold Grade (g/t) | Ounces (Millions) | |
| Bogoso/Prestea | Measured | 2.9 | 1.9 | 0.18 |
| Indicated | 16.1 | 2.2 | 1.13 | |
| Total | 19.0 | 2.1 | 1.31 | |
| Prestea Underground | Measured | 0.0 | 0.0 | 0.00 |
| Indicated | 1.6 | 13.2 | 0.66 | |
| Total | 1.6 | 13.2 | 0.66 | |
| Wassa HBB | Measured | 0.0 | 0.0 | 0.00 |
| Indicated | 20.0 | 1.3 | 0.81 | |
| Total | 20.1 | 1.3 | 0.81 | |
| Father Brown Underground | Measured | 0.0 | 0.0 | 0.00 |
| Indicated | 1.2 | 5.8 | 0.23 | |
| Total | 1.2 | 5.8 | 0.23 | |
| Total 2012 | 41.9 | 2.2 | 3.01 | |
| Total 2011 | 41.3 | 2.2 | 2.92 | |
Notes to the Measured & Indicated Mineral Resources:
The Inferred Mineral Resources as at December 31, 2012 and December 31, 2011 have been estimated in compliance with definitions defined by NI 43-101.
| Inferred | |||
|---|---|---|---|
| Property | Tonnes (Millions) |
Gold Grade (g/t) |
Ounces (Millions) |
| Bogoso/Prestea | 3.8 | 3.1 | 0.37 |
| Prestea Underground | 5.2 | 7.4 | 1.24 |
| Wassa HBB | 13.2 | 1.7 | 0.70 |
| Father Brown Underground | 1.4 | 5.2 | 0.24 |
| Total 2012 | 23.6 | 3.4 | 2.55 |
| Total 2011 | 13.3 | 3.7 | 1.57 |
Notes to Non-Reserves-Inferred Mineral Resources Table
Bogoso/Prestea ores consist of both non-refractory and refractory material. The non-refractory ore is processed in the 1.5 million tonnes per year Bogoso Oxide Processing Plant utilizing a conventional carbon-in-leach (“CIL”) process. The refractory ore is processed in the 2.7 million tonnes per year Bogoso Sulfide Processing Plant which utilizes a sulfide concentrate flotation circuit, bio-xidation (“BIOX®”) and CIL.
Since the acquisition of Bogoso in 1999, Golden Star has adopted a forward-looking approach to investment in the area, and during the extended downturn in the gold industry, we were able to acquire significant landholdings along this southern portion of the Ashanti Trend. Having consolidated the district-scale land position, our next step was to expand our mining and processing capacity to optimize the rate of gold production to match the size of the resource.
Given that the majority of the current reserves and resources are refractory, we built a 2.7 million tonne per annum processing facility which incorporates a Gold Fields' proprietary BIOX® bio-oxidation circuit to breakdown the sulfide mineralization. The plant was put into commercial production on July 1, 2007. The expansion project, including the construction of the sulfide processing plant and the expansion of the mining fleet, cost approximately $125 mi.
Golden Star announced a new discovery at the Prestea concession, just south of the Buesichem pit on March 4, 2010.
Buesichem Significant Intersections
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Buesichem intersections drilling 10-10-2010
The Prestea Underground is an inactive gold mine located south of Bogoso and adjacent to the town of Prestea. The property consists of three surface access shafts and extensive underground workings and support facilities. Access to the mine is via a paved road from Tarkwa and Accra and is maintained by the Government of Ghana. Any potential future production from the Prestea Underground would be trucked to the Bogoso processing plants.
From the 1870s to 2002 when mining ceased following an extended period of low gold prices, the Prestea Underground operations produced approximately nine million ounces of gold, the second highest production of any mine in Ghana. The underground workings are extensive, reaching depths of approximately 1,400 meters and extending along a strike length of approximately nine kilometers. Underground workings can currently be accessed via two surface shafts, one near the town of Prestea (Central Shaft) and a second approximately four kilometers to the southwest at Bondaye.
Prestea Underground (81% interest)
