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The Wassa gold mine is located in the southwestern region of Ghana approximately 35 km east of Bogoso/Prestea, and is accessible by a combination of sealed and unsealed roads. The mining operations consist of a number of open pits and a traditional Carbon-In-Leach (CIL) processing plant. In 2008, Benso mining operations commenced to provide a source of high grade ore to the Wassa processing plant. In 2009, mining operations at Hwini-Butre will commence and provide even higher grade ore to the Wassa mill.
Wassa lies within the Eburnean Tectonic Province (1,800-2,166 Ma) in the West African Precambrian Shield. The paleoproterozoic 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 Birimian, and Tarkwaian sequences.
Birimian rocks are composed largely of phyllites, schists, greywackes, volcanoclastics, and metavolcanic rocks (including lavas and pyroclastic rocks). Overlying the Birimian are the continental clastics of the Tarkwaian sequence. The Tarkwaian clastics were derived from the weathering of an uplifted continental edifice partially composed of Birimian rocks and granitic intrusions.
Wassa is hosted within the same Birimian volcano-sedimentary greenstone package as Golden Star's Bogoso/Prestea mining property. Wassa is situated along the eastern limb of the Tarkwa syncline, bounded between Tarkwaian sediments in the west and Cape Coast granites to the east. The gold deposits are hosted within altered Birimian Meta-sedimentary and Meta-volcanic sequences. Birimian rock units at Wassa can be generally subdivided into three principal sequences: 1) thin interlayered mafic and felsic flows with interdigitated carbonaceous phyllites; 2) a relatively thick felsic volcanic flow; 3) interlayered greywacke with thin beds of detrital magnetite, mafic volcanic flows and diorite. The three sequences appear to be in normal stratigraphic contact, and not structurally emplaced. The original rock types are often difficult to determine due to the pervasive sericite, silica, chloritic and carbonate alteration assemblages.
The metamorphic mineral assemblages of the Wassa rocks indicate that at one period in their history they were buried and heated to upper greenschist or lower amphibolite ranges; however, the higher grade metamorphic minerals appear to have later retrograded back to greenschist facies. Higher metamorphic grades and retrograde mineral assemblages show that the geological history of the Wassa area was more complex than deposits on the western side of the Tarkwa syncline, such as Bogoso and Prestea.
The Wassa rocks have been affected by at least two phases of deformation that have produced polyphase fold patterns in the region. Discrete high strain zones locally dissect this fold system. Two gold deposits (B-Shoot and Starter) are physically linked to megascopic folding and the associated discontinuous boudinaged quartz veins, quartz stockworks, veinlet zones and continuous quartz veins. Exploitable ore bodies at the Wassa Mine are clearly related to vein densities and sulfide contents. Coincidental quartz veining and pyrite mineralization commonly contain anomalous gold tenors. On a regional scale the Wassa ore zones were probably formed under the same tectonic regime during the final phase of megascopic folding. It is also likely that mineralizing fluids that created these bodies were derived from one regional source that could be associated with the large granodiorite bodies bounding the ore zones to the east and south.
The structural history of the Wassa area is important in that the various deformational events have been responsible for the emplacement of the gold mineralization as well as the current geometry of the ore zones themselves. Individual deposit geometries are clearly structurally controlled with the orientations changing as one approaches the megascopic fold closure. B-shoot mineralization runs roughly NE - SW dipping sub-vertically overall. The Starter pit marks the location of a fold closure and mineralization changes orientation swinging approximately NW-SE dipping shallowly to the SW. Zones parallel to B-shoot are found to the east of this zone but have not been traced North to where the large fold closure has been interpreted. It is anticipated that the fold nose as at Starter pit is a focal point of mineralizing fluid and this will lead to the discovery of additional ounces at the Wassa mine.
Wassa is one of the few modern day greenfields projects in Ghana, having been discovered and developed in the late 1990's by a joint venture between Glencar Mining plc, Moydow International Mines Inc. and the Government of Ghana.
The project was developed in 1998 at a capital cost of about $43 million as a conventional open pit operation followed by heap leaching. Gold production commenced in January 1999 with a mine life of six years. However, gold recoveries from the heap leach were slower and lower than expected resulting in a negative impact on the project's production, cash costs and cash flow. Consequently in 2001, the secured lenders to the project enforced their security over the project and agreed to sell Wassa to Golden Star. We redesigned Wassa as a conventional CIL milling operation and since 2005 the mine has been a successful operation.
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As at December 31, 2008 |
As at December 31, 2007 |
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Bogoso/Prestea |
Tonnes (millions) |
Gold Grade (g/t) |
Ounces (millions) |
Tonnes (millions) |
Gold Grade (g/t) |
Ounces (millions) |
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Proven Mineral Reserves |
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|
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Non refractory |
0.4 |
1.01 |
0.01 |
0.7 |
0.99 |
0.02 |
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Probable Mineral Reserves |
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Non refractory |
11.3 |
2.47 |
0.90 |
16.9 |
1.82 |
0.99 |
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Total Wassa Proven & Probable |
11.7 |
2.42 |
0.91 |
17.6 |
1.79 |
1.01 |
The stated 2007 Mineral Reserve for Wassa includes the Hwini-Butre and Benso properties.
The stated Mineral Reserves have been prepared in accordance with Canada’s National Instrument 43-101 Standards of Disclosure for Mineral Projects. Mineral Reserves are equivalent to Proven and Probable Reserves as defined by the United States Securities and Exchange Commission Industry Guide 7.
The 2008 and 2007 Mineral Reserves have been prepared under the supervision of Mr. Peter Bourke, P.Eng., Vice President Technical Services for the Company. Mr. Bourke is a “Qualified Person” as defined by Canada’s National Instrument 43-101.
The Mineral Reserves at December 31, 2008 were estimated using a gold price of $700 per ounce, which is approximately equal to the three year average price. At December 31, 2007 Mineral Reserves were estimated using a gold price of $560 per ounce.
The term “non-refractory” refers to the metallurgical characteristics of the ore and is defined in the Glossary of Terms of the 2007 Form 10-K.
Optimized pit parameters are based on historical and projected operating costs at Wassa and Hwini-Butre and Benso. Metallurgical recoveries are based on historical performance or estimated from testwork and typically range between 80% to 95% for non-refractory ores. Pit designs are based on geotechnical criteria established by external consultants. Mining dilution and mining recovery vary by deposit and have been applied in estimating the Mineral Reserves. A government royalty of 3% is allowed.
Mineral Reserves are expressed on a 100% basis. Golden Star’s share of the Mineral Reserves is subject to the Government of Ghana’s 10% carried interest which entitles them to a 10% dividend once our capital costs have been recovered.
Numbers may not add due to rounding.
Cautionary Note to U.S. Investors - The United States Securities and Exchange Commission permits U.S. mining companies, in their filings with the SEC, to disclose only those mineral deposits that a company can economically and legally extract or produce. We use certain terms on this website, such as "measured," "indicated," and "inferred" "resources," that the SEC guidelines strictly prohibit U.S. registered companies from including in their filings with the SEC. U.S. investors are urged to consider closely the disclosure in our latest Form 10K, which may be secured from us, or from the SEC’s website at www.sec.gov/edgar.shtml.
Wassa Measured and Indicated Resources as of December 31 2008 are:
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Measured |
Indicated |
Measured & Indicated |
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Tonnes (millions) |
Gold Grade (g/t) |
Tonnes (millions) |
Gold Grade (g/t) |
Tonnes (millions) |
Gold Grade (g/t) |
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Wassa |
- |
- |
3.9 |
0.89 |
3.9 |
0.89 |
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Benso |
- |
- |
0.8 |
2.24 |
0.8 |
2.24 |
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Hwini-Butre |
- |
- |
1.0 |
3.43 |
1.0 |
3.43 |
Our Measured and Indicated Mineral Resources reported below are exclusive of the Proven and Probable Mineral Reserves as shown above and have been estimated in compliance with definitions set out in NI 43-101.
The Mineral Resources were estimated in accordance with the definitions and requirements of Canada’s National Instrument 43-101. The Mineral Resources are equivalent to Mineralized Material as defined by the United States Securities and Exchange Commission Industry Guide 7.
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Tonnes (millions) |
Gold Grade (g/t) |
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Benso |
0.4 |
4.04 |
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Hwini-Butre |
0.5 |
4.53 |
| Chichiwelli Manso | 1.0 | 2.12 |
| Cautionary Note to US Investors concerning estimates of Inferred Mineral Resources | ||
This section uses the term “Inferred Mineral Resources”. We advise US investors that while this term is recognized and required by Canadian regulations, the US Securities and Exchange Commission does not recognize it. “Inferred Mineral Resources” have a great amount of uncertainty as to their existence, and great uncertainty as to their economic and legal feasibility. It cannot be assumed that all or any part of an Inferred Mineral Resource will ever be upgraded to a higher category. In accordance with Canadian rules, estimates of Inferred Mineral Resources cannot form the basis of feasibility or other economic studies. US investors are cautioned not to assume that part or all of the Inferred Mineral Resource exists, or is economically or legally mineable..
Inferred Mineral Resources have been estimated in compliance with definitions defined by NI 43-101 regulations.
The Inferred Mineral Resources, were estimated using an optimized pit shell at a gold price of $800 per ounce from which the Mineral Reserves have been subtracted. Other than gold price, the same optimized pit shell parameters and modifying factors used to determine the Mineral Reserves were used to determine the Mineral Resources.
The Inferred Mineral Resources are not included in and are in addition to the Mineral Reserves described above.
The Qualified Person for the estimation of the Inferred Mineral Resources is S. Mitchel Wasel, Golden Star Resources Vice President of Exploration.
Numbers may not add to the total due to rounding.
Inferred Mineral Resources are shown on a 100% basis. The Inferred Mineral Resources shown are subject to the Government of Ghana’s 10% carried interest which entitles it to a 10% dividend once our capital costs have been recovered, in the case of Bogoso/Prestea and Wassa. The mineral resources at Prestea Underground, are subject to the Government of Ghana’s 19% minority interest, with Golden Star currently having an 81% beneficial interest.
NI43-101 Qualifying Report for the First Disclosure of a Resource Estimate on a Material Property - Wassa Mine, Southwest Ghana
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The Hwini-Butre and Benso deposits are located in the Western Region of Ghana, south of Golden Star’s Wassa mine.
The feasibility study for the development of Hwini-Butre and Benso was completed in May 2007 and project development commenced immediately following receipt of environmental approvals in October 2007. The feasibility study work is summarized in our National Instrument 43-101, of the Canadian Securities Administration, Technical Report.
The underlying concept for the feasibility study and development of the Hwini-Butre and Benso projects is to provide a source of high grade mill feed to the Wassa CIL processing plant. Construction for the haul road commenced in October 2007 and pre-stripping and ore mining at Benso commenced in the third quarter of 2008. The higher grade deposits on the Hwini-Butre concession, south of Benso, are scheduled to be mined following the completion of the 30 kilometer haul road extension in 2009.
Metallurgical test work has indicated that the Hwini-Butre and Benso ore is harder than the Wassa ore which should result in higher milling costs and a slightly reduced throughput. The Wassa processing plant will be slightly modified to increase total residence time and achieve design metallurgical recoveries.
The HBB concessions lie along the southeastern flank of the Birimian-aged (lower Proterozoic) Ashanti Belt, along the same structure as Wassa. The southwestern part of the Hwini-Butre concession covers Mpohor Complex, a syn-volcanic mafic intrusive that is bound to the east and north by the Butre volcanic sequence. The Mpohor Complex is a polyphase intrusion with compositions ranging from gabbroic to granophyric, with intermediate phases such as diorite and granodiorite. The Butre volcanic sequence, which also underlies the South Benso concession further north, mostly comprises volcanic flows with minor meta-sediment horizons. The main regional structural orientation trends northeasterly but extensive north to northwest trending cross-cutting fracture systems are also well developed. The latter host much of the mineralization in the district, with vein systems at Dabokrom, Father Brown, Adoikrom, the Subriso zones and Amantin located within or marginal to the Mpohor Complex.
Mineralization on the Hwini-Butre concession is typically associated with shallow east-dipping narrow quartz veins and their associated sericitic alteration halos, with coarse free gold associated with sulfides and as specks within the quartz veins and altered host rocks. In contrast, mineralization at Subriso West and Central Subriso forms a series of relatively steep dipping, north-trending zones characterized by strong shearing and pervasive silica replacement with local silica flooding and only minor thin quartz veining.
See Wassa for Mineral Reserves and Mineral Resources
