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, both proximal and distal to the processing plant which consists of a traditional Carbon-In-Leach (CIL) system. 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 commenced 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 was 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 mine 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.
|PROVEN and PROBABLE MINERAL RESERVES||As at December 31, 2012||As at December 31, 2011|
|Property, Mineral Reserve Category||
|Proven Mineral Reserves|
|Probable Mineral Reserves|
|Total Wassa/HBB Proven and Probable||31.8||1.44||1.47||18.1||1.38||0.80|
Notes to the Mineral Reserve Statement:
Reconciliation of Mineral Reserves
|Contained Ounces (Millions)||Tonnes
(% of Opening)
(% of Opening)
|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%|
|2012 Reserves (5)||67.1||4.31||114%||104%|
Notes to the reconciliation of Mineral Reserves:
Non-Reserve – Measured and Indicated Mineral Resources
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)|
|Father Brown Underground||Measured||0.0||0.0||0.00|
Notes to the Measured & Indicated Mineral Resources:
Non-Reserves – Inferred 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.
|Father Brown Underground||1.4||5.2||0.24|
Notes to Non-Reserves—Inferred Mineral Resources:
NI43-101 Qualifying Report for the First Disclosure of a Resource Estimate on a Material Property - Wassa Mine, Southwest Ghana
Please note that Adobe Acrobat Reader is required to view the reports below.
The Hwini-Butre and Benso mines 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 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.