Exhibit 99.2

NI 43-101 Preliminary Economic Assessment

Mechanized Mining of the West Reef Resource,

Prestea Underground Mine, Prestea, Ghana

May 3, 2012

Golden Star Resources Ltd.

10901 W. Toller Drive, Suite 300

Littleton, CO 80127-6312 USA

Table of Contents

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List of Tables

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List of Figures

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List of Appendices

Appendix A

Certificate of Authors

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Summary (Item 1)

Golden Star Resources Ltd (“GSR”) is a Canadian Federally-incorporated, international gold mining and exploration company producing gold in Ghana, West Africa. GSR also conducts gold exploration in other countries in West Africa and in South America.

The Prestea Underground Mine is an inactive underground gold mine located 15km south of the Bogoso mine and adjacent to the town of Prestea. The property consists of two usable access shafts and extensive underground workings and support facilities. Access to the mine site is via a paved road from Tarkwa.

The Prestea Underground Mine was mined from the 1870’s until 2002 when mining ceased following an extended period of low gold prices in the late 1990s and early 2000s. The Prestea Underground Mine has 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 1,450 meters and extending along a strike length of 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.

GSBPL now holds a 90% ownership in the Prestea Underground Mine with the Government of Ghana holding a 10% ownership interest in the Prestea Underground Mine as well as its 10% holding in GSBPL, resulting in an 81% beneficial ownership by Golden Star.

The West Reef mineral resource consists of a steeply dipping, narrow vein structure between 17L and 24L, accessible through the Prestea Central Shaft.

PEA Highlights:

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Geology

The Prestea concession lies on the western margin of the Ashanti greenstone belt, which is located in the West-African craton. The greenstone belt is composed primarily of paleoproterozoic metavolcanic and metasedimentary rocks that are divided into the Birimian Supergroup and the Tarkwa Group. Both units are intruded by abundant granitoids and host numerous hydrothermal gold deposits such as the Obuasi and Prestea mines and paleoplacer deposits such as the Tarkwa and Teberebie Mines.

The Prestea deposit can be classified as an orogenic mesothermal gold deposit where two main types of gold mineralization have been identified. The most common type of mineralization is fault-fill quartz veins along fault zones and second order structures, while the second type of mineralization is associated with brecciated zones hosted in iron-rich volcanic lenses.

Mineral Resource and Reserve

The West Reef resource estimate was conducted by SRK Consulting using a drillhole database provided by Golden Star Resources. The database contained a total of 128 underground drillholes which targeted the West Reef.

The block model was prepared by Dr. John Arthur, C.Geol., and an independent Qualified Person as defined by NI43-101.

The classified Mineral Resource Statement for the global resources contained in the West Reef Structure is presented in Table 1. Mineral resources are not mineral reserves and do not have demonstrated economic viability.

Table 1. Mineral Resource Statement for the West Reef Structure, From SRK Consulting, November, 2008. Resource Models*

There are no current Proven or Probable Minerals Reserves hosted with the West Reef structure or at the Prestea Underground project.

Underground Mining

There is an extensive infrastructure of vertical shafts, inclined shafts, horizontal development, raises and stoping developed along the 9km of strike length of the various orebodies from Prestea in the north to Tuapim in the south. Figure 1 shows a long section view of this development and Figure 15.2 indicates the extent of historical stoping operations on the Main Reef, West Reef and Footwall Reef throughout the area.

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Figure 1: Prestea mining area including stoping

For the purposes of this PEA, only the West Reef resource between 17L and 24L has been evaluated for potential mineability. The access and material movement infrastructure has been designed to reach 30L in order to facilitate future exploration programs.

Both indicated and inferred resources are incorporated in the design, schedule and economic evaluation.

The West Reef resource averages 1.5m true width and ranges from 0.5m to 3.5m wide.

It is proposed that material mined at Prestea Underground Mine will be transported by road to Golden Star Resources Bogoso Mine and processed in the current operating Oxide Plant.

A cut-off grade of 3.1g/t has been used to define the West Reef potentially mineable resource. This cut-off grade is calculated using a gold price of $1,250/oz, mining cost of $90/t, processing cost of $15/t and an administration cost of $7/t.

In July 2007, SRK Consulting (UK) Ltd prepared a geotechnical assessment for the West Reef that proposed mechanized mining could be undertaken using longhole methods with a maximum stope size of 20m on strike x 20m high x 3.5m vein width including dilution. SRK estimated that for this stope size, 1m of dilution would be generated on both the hangingwall and the footwall.

The AVOCA mining method has been applied to the West Reef resource with a stoping production rate of 1,000tpd of mineable resource.

Access to the West Reef resource will be via a new Main Access Decline driven from surface above the resource and via the currently operating Prestea Central Shaft. The Prestea Central Shaft requires significant rehabilitation work to operate at full capacity.

A new raisebored hoisting shaft will be developed from surface to 30L in the vicinity of the Main Access Decline to provide material hoisting to surface.

The AVOCA mining method requires a waste backfill supply. Once stoping operations commence, all the waste generated underground will be used for backfill. In addition, a wastepass will be developed in proximity to the Main Access Decline, to supply waste material to the stopes from surface. In order to limit contamination of the blasted mineralized material with the waste backfill, a “skin” of cemented waste will be applied at the end of the backfilling cycle.

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The production schedule includes a four-year pre-development period during which the Central Shaft will be rehabilitated, the Main Access Decline developed, the hoisting shaft developed and the waste and mineralized development carried out. In steady-state production, the stoping will produce approximately 1,000tpd of mineralized material which will be hoisted to surface in the new shaft.

Processing

West Reef material will be trucked to GSR’s Bogoso Oxide Plant in ‘on-road’ haul trucks. For the most part, this will be on a dedicated, private haul road, minimizing interaction with public traffic.

Mineralized material will be stockpiled on the existing Bogoso ROM stockpile and fed to the Oxide Plant crusher by loader. As Prestea Underground Mine feed will displace currently fed open pit ore, no additional processing plant infrastructure will be required as a result of this project.

Tailings

Processing tails will be deposited on the currently operated TSF2 tailings storage facility and/or later approved facilities. TSF2 is a conventional tailings storage facility.

Environmental and Community Considerations

The Prestea community is supportive of the effort to reopen the underground operation; this support will pave the way for easier permitting with the Environmental Protection Agency, which is considering community input to project development as a key factor.

Due to the limited footprint associated with the development, environmental considerations are deemed manageable and environmental approval for an operating permit should be granted within the normal timelines. The main environmental consideration will be the ongoing management of the discharge water, for which options to address other local (non Golden Star) water pollution problems as part of an overall management plan are being developed.

Infrastructure

The Prestea concession is situated directly southwest of, and contiguous with the Bogoso concession. The underground mine property is adjacent to the town of Prestea, which is situated approximately 20 km south of the town of Bogoso, the capital of the newly created Prestea Huni Valley District of the Western Region. Bogoso is 35 km from Tarkwa, an important mining center for the region, and a further 85 km from the port city of Takoradi on the Gulf of Guinea. Accra, the capital of Ghana, is located approximately 370 km by road east/southeast of Prestea.

Electrical power for Prestea Underground Mine is supplied from the National Grid (GRIDCo) via the Prestea substation. In the event of power outage from the national grid, two emergency power units, one at Central Shaft and the other at Bondaye Main shaft are available to supply limited power to essential units of the mine.

Potable water supplied for use on the mine is pumped from the mine pump station which consists of two bore-holes, one of a depth of 46 meters and the other of 20 meters deep.

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The mine dewatering is carried out through the two main shafts – Prestea Central Shaft and Bondaye Main Shaft. Currently a combined average daily pumping rate of 5 Ml per day is achieved.

Waste rock hauled up the Main Access Decline and hoisted through Central Shaft highway trucks to be dumped on the Beta Boundary South Waste Dump approximately 4km to the south of Central Shaft.

Capital Costs

Table 2 presents the capital cost items for the West Reef mining.

The capital costs presented are to a PEA level of accuracy and are expected to be within ±40%. Given the preliminary nature of the study all costs have a contingency of 25% applied. All costs are in Q1 2012 US dollars.

Table 2: Capital cost summary (US$000s)

Operating Costs

PEA level operating costs were estimated as follows:

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Table 3 summarizes the operating costs incorporated in the economic analysis.

Table 3: Operating cost summary

Indicative Economic Results

Project net present value at a discount rate of 5% is $107 million with an internal rate of return of 21%. The payback period is 6.3 years from the time of initial investment. Total operating cost is estimated to be $620 per ounce produced.

The project is most sensitive to changes in gold price followed next by operating cost and then capital cost.

Conclusion

The Prestea Mine has a long history of underground stoping production and the West Reef area has good potential as a consistent, 1,000tpd production area to supply high-grade material to the Bogoso Oxide Plant.

Recommendations

The findings of this PEA provide compelling arguments to move the study to the FS design stage. The following are the recommendations for advancing the project in the individual areas:

Resource

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Underground Mining

Process and Tailings

Infrastructure

Environment and Infrastructure

Preliminary Budget

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1 Introduction (Item 2)

1.1 Golden Star Resources

Golden Star Resources Ltd (“GSR”) is a Canadian Federally-incorporated, international gold mining and exploration company producing gold in Ghana, West Africa. GSR also conducts gold exploration in other countries in West Africa and in South America. GSR was established under the Canada Business Corporations Act on May 15, 1992 as a result of amalgamation of South American Goldfields Inc., a corporation incorporated under the federal laws of Canada, and Golden Star Resources Ltd., a corporation originally incorporated under the provisions of the Alberta Business Corporations Act on March 7, 1984 as Southern Star Resources Ltd. GSR’s principal office is located at 10901 West Toller Drive, Suite 300, Littleton, Colorado 80127, with registered and records offices located at 333 Bay Street, Bay Adelaide Center, Box 20, Toronto, Ontario M5H 2T6.

GSR owns controlling interests in two gold properties in southwest Ghana:

GSR also holds interests in several gold exploration projects in Ghana and elsewhere in West Africa including Sierra Leone, Niger and Côte d’Ivoire, and in South America exploration properties are held and managed in Brazil.

The Prestea Underground Mine is an inactive underground gold mine located 15km south of the Bogoso mine and adjacent to the town of Prestea. The property consists of two usable access shafts and extensive underground workings and support facilities. Access to the mine site is via a paved road from Tarkwa.

The Prestea Underground Mine was mined from the 1870’s until 2002 when mining ceased following an extended period of low gold prices in the late 1990s and early 2000s. The Prestea Underground Mine has produced approximately nine million ounces of gold, the second highest

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production of any mine in Ghana. The underground workings are extensive, reaching depths of approximately 1,450 meters and extending along a strike length of 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.

GSBPL now holds a 90% ownership in the Prestea Underground Mine with the Government of Ghana holding a 10% ownership interest in the Prestea Underground Mine as well as its 10% holding in GSBPL, resulting in an 81% beneficial ownership by Golden Star.

GSR continues to dewater the Prestea Underground Mine, and is currently refurbishing the Central Shaft and assessing services on 12, 17 and 24 levels.

1.2 Terms of Reference and Purpose of the Report

This PEA is intended for the use of GSR to further the evaluation of the Prestea Underground Mine by estimating resources in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) classification system. A mining method and access development strategy is proposed, in addition to infrastructure and processing options. The capital and operating costs and production parameters have been used to generate indicative economics.

The report includes the mining of indicated mineral resources and inferred mineral resources that are considered too speculative, geologically, to have economic considerations applied to them. Therefore, this material cannot be classified as Mineral Reserves and the term “potentially mineable resource” is used in lieu of “reserves”.

This Preliminary Economic Assessment has been prepared in accordance with the guidelines provided by the National Instrument 43-101 (NI 43-101) Standards of Disclosure for Mineral Projects.

The metric (SI System) units of measure are used in this report unless otherwise noted to describe quantities in this report.

1.3 Sources of Information

In compiling this report, GSR has utilized data from the following sources:

1.4 Site Inspections

S. Mitchel Wasel is the QP responsible for Sections 5, 6, 7, 8, 9, 10 and 12 of this report. Mr. Wasel is based in Takoradi, Ghana and is employed by GSR as Vice President of Exploration. He has visited the site on numerous occasions over the past 10 years, the last time on May 2, 2012.

Martin Raffield is QP responsible for sections 1 through 4, 11 and 13 through 25 of this report. He is based at the corporate office in Denver Colorado and employed by GSR as Senior Vice President, Technical Services. Dr. Raffield has visited the site several times over the past year since he joined Golden Star and last visited the site on January 12, 2012.

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2 Property Description and Location (Item 4)

2.1 Property Location

The Prestea concession is located in the western region of Ghana approximately 200 kilometers from the capital Accra and 50 kilometers from the coast of the Gulf of Guinea. The map in Figure 2.1 shows the location of the Prestea area along with road infrastructure, major urban centers and surface hydrology.

Source: United Nations undated

Figure 2-1: Map of Ghana

The map in Figure 2.2 illustrates the outline of the Prestea mining lease along with geographic latitude and longitude of each points of the mining lease.

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Figure 2-2: Prestea mining lease

2.2 Mineral Titles and Agreements.

The Prestea concession is a mining lease that was issued to Prestea Gold Resources (PGR) on June 29, 2001 by the Government of Ghana with land registry number 2799/2001. The agreement granted PGR the exclusive right to operate underground mining within the Prestea Concession below a depth of 150 m below sea level for a period of 30 years effective from the date of Mining Lease. The strike of the underground lease extends from the Ankobra shaft in the north to the Tuapim shaft to the south and covers an approximate area of 11.27 km², which represents only a portion of the entire 116 km² Prestea Mining Lease. A joint operating agreement was signed in January 2002 between Bogoso Gold Limited, a subsidiary of Golden Star Resources incorporated under the laws of Ghana, and Prestea Gold Resources. An amount of USD 2,100,000 was paid to Prestea Gold Resources as a first option payment. This agreement granted Bogoso Gold Limited the right to develop and operate the Prestea underground mine while also setting out the protocols and procedures to be observed by Bogoso Gold Limited and Prestea Gold Resources in the day-to-day operations of the surface and underground mining operations.

A second agreement entitled Memorandum of Agreement was signed on March 14, 2002 between Prestea Gold Resources Limited, Bogoso Gold Limited, Prestea Goldfields Limited, the State Gold Mining Company Limited, the Ghana Mineworkers Union of Ghana and the Republic of Ghana. This agreement was formed to create a joint venture agreement between all parties who had an interest in the Prestea Underground Mine at the time and to consolidate the management of the underground mine. The agreement also defined the conditions for the Prestea

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Underground Mine to be put under care and maintenance, which include mine dewatering and shaft maintenance along with number of employees required. The Prestea Underground Mine has remained under care and maintenance since the signature of the agreement.

2.3 Royalties and Encumbrances

Royalties associated with the Prestea Mining lease are defined under Section 21 of the mining lease that was issued to Prestea Gold Resources on June 29, 2001. The agreement stipulates that the company shall pay royalty on a quarterly basis to the government as prescribed by the legislation. Royalties are based on production and are to be paid through the Commissioner of Internal Revenue within thirty days from the end of the quarter.

On September 7, 2010, a letter with reference number C.108 was issued to Golden Star Resources by the Internal Revenue Service of Ghana stipulating that Royalties were to be raised from 3% to 5% with retroactive effect from March 19, 2010. This 5% royalty is the only royalty associated with the Prestea mining lease.

The only other financial obligation related to the Prestea mining lease is a rent for land usage, which is defined under Section 20 of the mining lease that was issued to Prestea Gold Resources on June 29, 2001. The rent is paid bi-annually before the first day of January and on or before the first day of July; the amount is fixed at $0.50 per square kilometer.

2.4 Environmental Liabilities

The existing environmental liabilities associated with the Prestea underground operation were included in an indemnity granted to the joint venture. All the existing surface and underground liabilities associated with the Prestea underground mine, are, therefore, not of material consequence to the development project. It is expected that some of the liabilities will be transferred to the development company once operations commence. However, when compared to the existing asset retirement obligations in place for GSBPL, these liabilities are considered immaterial.

2.5 Operating Permits Required

To develop the Prestea Underground, an environmental approval for the project is required. The permitting process is as follows:

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3 Accessibility, Climate, Local Resources and Infrastructure (Item 5)

3.1 Infrastructure and Physiography

Local population centers are located at Bogoso Town in the north of the Bogoso Concession, and Prestea Town in the center of the Prestea Concession. Bogoso is located on the main road from Tarkwa to Kumasi. There is a tarred road between Bogoso and Prestea. The Prestea Town is located adjacent to the Plant North Deposit and the backfilled workings and offices are within the outskirts of the town. The Main Shaft complex at Prestea is also located within the Town limits.

3.2 Topography, Elevation and Vegetation

The topography of the area within which the GSBPL assets are located is characterized by a series of northeast-southwest trending sub-parallel ridges. The mineralization tends to occur on the western slopes of the ridges with the intervening valleys occupied by farming communities and seasonal streams. There are two rainy seasons between April-June and September-November. The average annual rainfall in the immediate project area is 2,030 mm. The heavy rains during the rainy season do not adversely affect the operation, although care needs to be taken on haul roads during heavy rain. The climate is tropical with average temperatures ranging from between 21°C and 32°C.

3.3 Climate and Length of Operating Season

As the Project is an underground mine, the climate has very little implication for the operations. In the tropical environment, work on the surface can continue year round with short breaks during storm events. However, most storms are short-lived and may be experienced through most of the year. The rainy season may affect the underground dewatering efforts.

3.4 Access to Property

Access to the property is by tarred road and it is, therefore, easily accessible from Accra (6 to 7 hours), Tarkwa (1 to 2 hours) and the major port at Takoradi (3 to 4 hours). There are airports at Kumasi and Takoradi, which provide daily services to the International Airport at Accra. Kumasi is situated some 4 hours drive from the Project. Road surfaces in the area vary from poor (on the section between Bogoso and Tarkwa) to good (Accra to Takoradi). There have been government plans to re-surface the road between Bogoso and Tarkwa for several years. The road, however, remains in poor condition but is passable throughout the year.

3.5 Surface Rights

Prestea Gold Resources (PGR) was granted the PGR Mining Lease by the Government on 29, June 2001 conferring on PGR the exclusive right to conduct underground gold mining operations with the Prestea Concession Areas below a depth of 150 m below sea level for a period of 30 years effective from the date of the PGR Mining Lease. The area of the underground lease mirrors that of the surface mining lease at a total of 129 km².

Bogoso Gold Limited (BGL) was granted the BGL Mining Lease by the Government on 29, June, 2001 conferring on the company the exclusive right to conduct surface gold mining

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operations over the Prestea Concession Area for a period of 30 years effect from the date of the BGL Mining Lease. Golden Star Resources subsequently renamed BGL to GSBPL. Therefore, the surface rights to the area remain within GSR. The mining lease is registered under 2799/2001 in the Ghana lands registry.

3.6 Local Resources and Infrastructure

The Project is in an area where mining has occurred more or less continuously since the late 1800s. The Project is the expansion of an existing underground mining operation. Therefore, the required services, infrastructure and community support are already in place. The following are relevant to the assessment of resources and infrastructure:

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4 History (Item 6)

4.1 Prior Ownership

Recorded production for the Prestea mine began in 1912 under the British company Ariston Mining, which operated the mine until the 1950’s and was responsible for the majority of the underground development including shaft sinking, ventilation and level development. The mine was nationalized in the late 1950’s, following the independence of Ghana, when all mining operations in the region were consolidated under the management of Prestea Gold limited, a subsidiary of the State Gold Mining Corporation.

In the early 1990’s, the government of Ghana reopened the mining industry to foreign companies and a joint venture agreement was formed between Barnex JCI Ltd., Prestea Gold Ltd., the State Gold Mining Corporation and the government of Ghana. Barnex JCI Ltd. withdrew from the joint venture in 1998 due to low gold price and aging infrastructure. A consortium supported by the Ghana Mine Workers Union was then founded to operate the mine under the name Prestea Gold Resources Limited. The mine operated for 3 years until a permanent closure in early 2002 due to depressed gold prices and financial difficulties, the mine has remained under care and maintenance since the 2002 closure.

4.2 Past Exploration and Development

Ariston Mining established most of the current infrastructure and underground development prior to nationalization in the late 1950’s. The Prestea Underground Mine workings extends over a distance of 9 km along strike and down to a maximum depth of about 1,400 meters. The two primary shafts of the Prestea Mine are the Central Shaft and Bondaye Shaft.

Central Shaft is the primary access to underground mining levels, extending to a depth of 1,238m below surface to 30 Level. Numerous levels were developed off the shaft to provide access to the Main Reef stoping areas. Traditional narrow vein mining methods were employed, primarily shrinkage stoping and captive cut-and-fill. Ore and waste was trammed to Central Shaft to loading pockets located below 20L, 25L, and 30L, which served to load the ore into skips for conveyance to the surface bins. The total capacity of the system at its peak may have been around 1,300-1,600t/day.

Bondaye Shaft extends to a depth of 1,103m, unlike Central Shaft, there is no dedicated rock handling system at Bondaye, ore cars were loaded into the cages and raised to surface.

In addition to Central and Bondaye shafts, there are several internal shafts. The No. 4 and No. 6 shafts are located to the south of Central Shaft. No. 4 shaft extends from level 23 to level 35 and was used as the primary access to level 35, the lowest developed level in the mine. No 6 shaft extends from level 24 to level 31.

During the Ariston Mining period, exploration consisted mainly in driving crosscuts from the main footwall drive across the fault structure and collecting channel samples across the fault-filled veins. The first drilling campaign was conducted in 1938, a total of 17 holes were drilled that year and consisted of short holes at Alpha shaft which were targeting a subsidiary footwall structure. Exploration drilling ramped up in the 1960’s after the nationalization of the mine, over 350 holes were drilled during that decade mostly targeting subsidiary structures of the Main Reef.

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Exploration drilling targeting the West Reef structure essentially started in the 1970’s and continued until the closure of the mine in 2002. Over the life of the mine between 1938 and 2002, a total of 966 underground holes were drilled at Prestea.

4.3 Historic Mineral Resource and Reserve Estimates

Previous operators of Prestea (Barnex JCI Ltd.) have historically classified a certain amount of material as a Mineral Resource. This historical resource was reviewed by SRK, which reported this data in a 2003 report to GSR. The historical resource consists of simple volumetric estimates based on vertical longitudinal projection block grades and thickness and this material had been included in the latest Mineral Resource statement. The historical resource is classified as Inferred material under the category ‘JCI Blocks’, but is not included as a mining target in this PEA.

NI 43-101 compliant reserves have not been reported historically for the Prestea Underground Mine.

4.4 Historic Production

Mining in the Prestea area dates back several centuries. The first direct involvement by Europeans in the area occurred in the 1880’s with the establishment of the Gio Apanto Gold Mining Company and the Essaman Gold Mining Company.

These companies changed to the Apanto Mines and Prestea Mines Limited in 1900. Both companies merged to become Ariston Gold Mines in 1927. Companies associated with Ariston carried out exploration and some mining to the north east of Prestea at Quaw Badoo and Brumasi. The company also prospected concessions immediately to the south west of Prestea at Anfargah.

Prospecting and some mining had been carried out independently on the adjacent Ekotokroo, Bondaye and Tuappim concessions located to the south of Anfargah. These concessions were acquired by Ghana Main Reef Limited in 1933 and operated continually until 1961.

Ghana State Mining Corporation was set up with effect from March 1961 under an instrument of incorporation signed by the President. From April 1963 the various Ghanaian gold operations, were regrouped and renamed Tarkwa Goldfields, the Ariston and Ghana Main Reef concessions which were combined to form PGL, Dunkwa Goldfields and Bibiani Goldfields. The State Gold Mining Corporation [SGMC] was established under the State Gold Mining Corporation Instrument 1965.

Both the Ariston Mines and Ghana Main Reef companies were purchased by the Government of Ghana and merged to form PGL. The Buesichem concession to the north east and along strike from Brumasi was subsequently added to the Prestea concessions. The Buesichem concession contained a small historical open pit, one of several operated by Marlu Gold Mining Areas until 1955.

Accurate production figures for the area are not available, particularly for the early years. Total production from the Ariston Mines and PGL was in the order of 16.8 million t of ore for the recovery of 5.95 million ozs of gold. The average ore grade is estimated to have been 11 g/t. In addition the Brumasi Mine is reported to have produced 307,000 t yielding 230,000 ozs of gold for an average grade of 23.3 g/t. Prior to the amalgamation with Prestea, Ghana Main Reef produced about 2 million t of ore for approximately 1.0 million ozs at an estimated ore grade of 15 g/t. Total production from the area, excluding the Buesichem open cut is estimated to be in

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excess of 19 million t and 7.18 million ozs of gold. This estimate is slightly lower than the Ghana Chamber of Mines which has recorded approximately nine million ounces of gold produced from the Prestea area since 1877.

Production from Prestea peaked at 446,372 t in 1964 when 166,973 ozs of gold were obtained at an average grade of 11.6 g/t.

Recovered grade peaked much earlier in the life of mine with a grade of 20.4 g/t in 1927. Production endured a serious decline throughout the mid to late 1970’s due to a lower amount of stopes being developed and lack of underground development to access new ground. The mine closed down in 2002 and has remained under care and maintenance since.

Figure 4-1: Historic Prestea Underground Mine Production

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5 Geologic Setting and Mineralization (Item 7)

5.1 Regional Geology

The content of this section describing the regional geological setting has been summarized from Perrouty et al 2012.

The Ashanti greenstone belt in the Western Region of Ghana is composed primarily of paleoproterozoic metavolcanic and metasedimentary rocks that are divided into the Birimian Supergroup (Sefwi and Kumasi Groups) and the Tarkwa Group. Both units are intruded by abundant granitoids (Fig. 5.1) and host numerous hydrothermal gold deposits such as the Obuasi and Prestea mines and paleoplacer deposits such as the Tarkwa and Teberebie Mines.

Figure 5-1: The West African Craton (Perrouty et al, 2012)

Allibone et al. (2002a) separated the Paleoproterozoic Eburnean orogeny into two distinct phases known as Eburnean I and II. The Eburnean I event predates the deposition of Tarkwaian sediments and is associated with a major period of magmatism and metamorphism in the Sefwi Group basement. The Eburnean II event is associated with significant post-Tarkwaian deformation that affected both the Birimian Supergroup and overlying Tarkwaian sediments. The Eburnean II event is associated with major NW-SE shortening that developed major thrust faults, including the Ashanti Fault, along with isoclinal folds in Birimian metasediments and regional

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scale open folds in the Tarkwaian sediments. These features are overprinted by phases of sinistral and dextral deformational events that reactivated the existing thrust faults and resulted in shear zones with strong shear fabrics.

The Birimian series was first described by Kitson (1918) based on outcrops located in the Birim River (around 80 km east of the Ashanti Belt). Since this early interpretation, the Birimian stratigraphic column has been revised significantly. Before the application of geochronology, the Birimian super group was divided in an Upper Birimian group composed mainly of metavolcanics and a Lower Birimian group corresponding to metasedimentary basins. Subsequent authors have proposed synchronous deposition of Birimian metavolcanics. Most recently, Sm/Nd and U/Pb analyses have reversed the earlier stratigraphic interpretation with the younger metasediments overlying the older metavolcanics. Proposed ages for the metavolcanics vary between 2162 ± 6 Ma and 2266 ± 2 Ma. Detrital zircons in the metasediments indicate the initiation of their deposition between 2142 ± 24 Ma 2154 ± 2 Ma. The Kumasi Group was intruded by the late sedimentary Suhuma granodiorite at 2136 ± 19 Ma (U/Pb on zircon, Adadey et al., 2009).

The Tarkwa super group was first recognized by Kitson (1928) and consists of a succession of clastic sedimentary units, which have been divided in four groups by Whitelaw (1929) and Junner (1940) (Table 5.1). The Kawere Group located at the base of the Tarkwaian super group is composed of conglomerates and sandstones with a thickness varying between 250 m and 700 m. The unit is stratigraphically overlain by the Banket Formation, which is characterized by sequences of conglomerates interbedded with cross-bedded sandstones layers, the maximum thickness of this group is 400 m. The conglomerates are principally composed of Birimian quartz pebbles (>90%) and volcanic clasts (Hirdes and Nunoo, 1994) that host the Tarkwa Placer deposits. The Banket formation is overlain by approximately 400 m of Tarkwa Phyllites. The uppermost unit of the Tarkwa super group is the Huni Sandstone, comprised of alternating beds of quartzite and phyllite intruded by minor dolerite sills that form a package up to 1300 m thick (Pigois et al., 2003). U/Pb and Pb/Pb geochronology dating of detrital zircons provide a maximum depositional age of 2132 ± 2.8 Ma for the Kawere formation and 2132.6 ± 3.4 Ma for the Banket formation (Davis et al., 1994; Hirdes and Nunoo, 1994). These ages agree with the study by Pigois et al. (2003) that yielded maximum depositional age of 2133 ± 4 Ma from 71 concordant zircons of the Banket formation. According to all concordant zircons histogram (161 grains) and their uncertainties (Fig. 5.2), a reasonable estimation for the start of the Tarkwaian sedimentation could be as young as 2107 Ma.

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Table 5.1: Tarkwaian sedimentary sequences and estimated thicknesses (Perrouty et al, 2012)

Figure 5-2: Radiometric age data histograms (Perrouty et al, 2012)

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Abundant granites and granitoids intruded the Birimian and Tarkwaian units during the Paleoproterozoic. Eburnean plutonism in southwest Ghana can be divided into two phases between 2180–2150 Ma (Eoeburnean) and 2130–2070 Ma (Eburnean) that is supported by the current database of U/Pb and Pb/Pb zircon ages. Most of the granitoids intruded during both phases correspond to typical tonalite–trondhjemite–granodiorite (TTG) suites. However, in the southern part of the Ashanti Belt, intrusions within the Mpohor complex have granodioritic, dioritic and gabbroic compositions.

Dolerite dykes oriented N-S and ENE-WSW that are generally less than 100 m in thickness are abundant across the West African craton where they cross-cut Archean and Paleoproterozoic basement. In southwestern Ghana these dykes are well defined in magnetic data where they are characterised by strong magnetic susceptibility. Dolerite dykes are observed to cross-cut undeformed K-feldspar rich granites that formed during the late Eburnean, and are overlain by Volta basin sediments with a maximum depositional age of 950 Ma (Kalsbeek et al., 2008). These relationships constrain dyke emplacement to between 2000 Ma and 950 Ma. In contrast some older dolerite/gabbro dykes and sills were deformed during the Eburnean orogeny and are dated at 2102 ± 13 Ma (U/Pb on zircon, Adadey et al., 2009).

With the exception of some late Eburnean granitoids, dolerite dykes and Phanerozoic sediments, all other lithologies have undergone metamorphism that generally does not exceed upper greenschist facies. Studies on amphibole/plagioclase assemblages suggest the peak temperature and pressure was 500–6500 ºC and 5–6 kbar (John et al., 1999), dated at 2092 ± 3 Ma (Oberthür et al., 1998).

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Source: Golden Star, 2012

Figure 5-3: GSR Prestea concession

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5.2 Property Geology

The geology of the Prestea Mine site is divided into four main litho-structural assemblages, which are fault bounded and steeply dipping to the west. This suggests that the contacts are structurally controlled and that the litho-structural assemblages are unconformable. These packages are from the eastern footwall to the western hanging wall, the Tarkwain litho-structural assemblage, the tectonic breccia assemblage, the graphitic Birimian sedimentary assemblage and the undeformed Birimian sedimentary assemblage. A simplified geology map in Figure 5.3 illustrates the relationship between the Tarkwain and Birimian litho-structural assemblages.

The Tarkwaian litho-structural assemblage to the west is mostly composed of sandstone, and locally pebbly sandstone. Bedding and sedimentary textures have been observed but very sporadically, in most cases they have been obliterated by hydrothermal alteration and deformation.

The litho-structural assemblage overlying the Tarkwaian sediments is a tectonic breccia bounded to the west by the Main Reef fault. The tectonic breccia is a polygenic assemblage, composed of various rock types such as volcanic rocks, volcanoclastics, Birimian sediments and sparse Tarkwain sediment clasts. Volcanic lenses illustrated on Figure 5.4 have been divided into two units based on their alteration pattern, weakly altered mafic volcanic rocks are characterized by a distal chlorite/calcite alteration pattern while strongly altered mafic volcanic rocks are characterized by a proximal silica/sericite/Fe-Mg carbonates alteration pattern. These strongly altered mafic volcanic lenses are generally located at proximity to the Main Reef Fault or bounded by second order footwall faults. The tectonic breccia assemblage is believed to have been the focal point of the post thrusting deformational event (syn-D2 to syn-D4), therefore, no primary textures, whether syn-volcanic nor syn-sedimentary, have been observed. Pictures D to F of Figure 5.4 illustrates well the diversity of protoliths found within the Main Reef Fault footwall, in picture F, pale green volcanic and volcanoclastic clasts have structurally been stretched and thinned along foliation within a graphitic matrix.

The graphitic Birimian sediment litho-structural assemblage is bounded to the east by the Main Reef fault and to the west by the West Reef Faults. This sedimentary package is a strained and brecciated sequence of siltstones, mudstones and wacke units. As show in pictures B and C from Figure 5.4, the unit is strongly deformed and affected by a pervasive graphite alteration. Primary textures are generally overprinted and obliterated by deformation, but bedding has locally been preserved. Although this package is strongly strained, deformational reactivation has only taken place within a discrete corridor of deformation, the reason being that movement during the second to fourth deformational event mainly affected the footwall of the Main Reef fault where reactivation developed some strong penetrative shear fabric.

The most western litho-structural assemblage within the Prestea Mine site is bound to the east by the West Reef fault and consists of relatively undeformed to weakly strained Birimian sediments. The assemblage is composed of a series of flyschoid sequences where the most common units found are argillites, mudstones, siltstones and wackes, which are all commonly referred to as phyllite in Ghana. Several syn-sedimentary textures have been observed such as beddings, graded beddings and cross-beddings. Chert horizons are locally intercalated within the flysch sequence, but appear to lack lateral continuity. Picture A from Figure 5.4 illustrates typical beddings of siltstones intercalated with wacke sub-units.

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Figure 5-4: Lithologies hosting the Prestea deposit

A: Undeformed Birimian sediments from Plant North pit. B: Graphitic Birimian sediments from Plant North pit. C: Brecciated graphitic Birimian sediments from hole UC1044 at a depth of 68.4 m. D: Contact between altered mafic volcanic and the footwall tectonic Breccia from level 30 at crosscut 204N. E: Hand sample from level 24 of mafic volcanic rocks. F: Footwall tectonic breccia from Plant North Pit.

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The Prestea Mine site litho-structural assemblages are affected by five distinct syn-Eburnean ductile events and at least one post-Eburnean brittle event, resulting in late reactivation of the major thrust fault systems. The Eburnean deformational events have been described and observed by several authors throughout the West African shield including Milesi, Alibone and Perrouty. The D1 deformational event at Prestea affects the older volcano-sedimentary Birimian and was generated during an extensional phase. The D2 deformational event is believed to be a thrusting event, resulting in the thrusting of the older Birimian volcano-sedimentary sequences over the younger Tarkwaian sedimentary group. At Prestea, the development of the penetrative S2 foliation as well as major thrust faults, such as the Main Reef fault and the West Reef faults are the main syn-D2 structural features. The third and fourth Eburnean phases (the D3 and D4 events) are transcurrent events, resulting in strike-slip movement along the major D2 faults, the development of regional scale fold (Figure 5.5) and of second (D3) and third penetrative foliations (D4). On the Prestea Mine site, the tectonic breccia located in the footwall of the Main Reef fault is the assemblage that was the focus of reactivation during the second and third deformational event resulting in a strong shear fabric while the Birimian hanging wall developed orthogonal steep penetrative fabrics at an angle to the main S2 foliation. The fifth and last Eburnean phase, the D5 event, is defined as a minor transcurrent event, the effects of the D5 event are noticeable in Prestea by the presence of a flat lying crenulation (S5), observable locally on the S2 foliation plane. Relationships between all the different structural features are exposed in pictures E and F of Figure 5.5.

Over five hundred structural measurements were taken during the course of an underground geological compilation which was undertaken between 2003 and 2007. All measurements have been compiled per levels, distributions of S0 beddings and S2 foliations are very similar, suggesting a transposition of beddings along S1 foliation during the D1 event. Both distributions for S0 and S2 are consistent with increasing depths, showing identical patterns regardless of levels. A total of 241 measurements were taken for S2 foliations and 90 for S0 beddings. The average orientation for S0 beddings is 172/76 and 175/80 for S2 foliations, all measurements were taken at mine grid (40 degree eastern rotation to magnetic North). The average orientation for S3 foliations is 229/55, suggesting approximately a 55 degrees rotation in azimuth and 25 degrees in dip of the main stress fields from the D2 deformational event to the D3 event. No measurements of the S4 foliations were taken during the underground compilation as this feature is more discrete than the S3 foliation. A total of 8 measurements were taken for L⁵² lineations, very little attention was paid to syn-D5 structural features during the geological compilation as mineralization controls are believed to be syn-D2 to syn-D4. Nonetheless, the lineations’ average indicates a shallowly north plunging feature (356/22). Syn-D5 structural features are not very common on the Prestea Mine site, minor reactivation of the main fault system probably accommodated most of the stress during that event.

The structural complexity of the Prestea Mine site is mainly due to reactivation of the fault system during the later events of Eburnean deformation. A more detailed look at S3 foliations recorded on level 17 from crosscut 307-308S shows that the tectonic breccia located in the footwall of the Main Reef fault has undergone intense shearing during the D3 and D4 deformational events. A comparison between the orientation of S2 foliations taken from the footwall and the hanging wall of the Main Reef fault was conducted and the average orientation for S3 foliations in the footwall of the Main Reef fault is 211/53, while the average for the hanging wall of the Main Reef fault is 252/49, suggesting syn-D3 reactivation in the footwall domain and transposition along the S2 foliation.

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Several studies along the Ashanti trend are suggesting a syn-D4 timing for gold emplacement. Earlier studies at Prestea also suggested a syn-D3 to syn-D4 gold mineralized event, but it is still unclear whether syn-D2 gold events could have taken place and have been remobilized during later hydrothermal syn-D3 to D4 pulses. Field evidence and structural relationships are suggesting that certain quartz veins along the Prestea major fault systems were in place during the earlier deformational event and deformed by subsequent events.

Two distinct styles of mineralization are found on the Prestea Mine site. The more extensive of the two mineralization styles are laminated fault fill quartz veins (reef style mineralization), bound to the Main Reef fault or to the second order faults found in the Birimian sediments hanging wall. The second mineralization style, which has never been mined in past, consists of arsenopyrite rich, brecciated and altered volcanic lenses.

Fault fill quartz veins have been generated over an extensive period of time through multiple fluid pulses. They are bound to major and second order faults and characterized by laminated and stylolitic smoky to translucent quartz veins. Pictures A and B from Figure 5.5 are examples of two fault filled quartz veins coming from two different faults, the Spur Reef fault from Bondaye shaft and the West Reef fault from Main shaft. Late gouge is commonly associated to the mineralized quartz veins and is also generally mineralized, although in most cases at lower grades then the associated quartz veins. Quartz veins are typically one to two meters wide, but widths up to 5 meters have been observed. Thicker fault fill quartz veins occur in dilation zones along the fault systems, it is still unclear what controls the emplacement of those dilation zones, but several mineralized quartz veins seem to have a spatial association with volcanic lenses found in the immediate footwall of the Main Reef fault.

An alteration assemblage of silica/sericite/Mg-Fe carbonates characterizes the arsenopyrite rich volcanic lenses. They are typically composed with 2-10% acicular arsenopyrite crystals and 1-5% euhedral to sub-euhedral pyrite grains. They are also characterized by presence of brecciated and stockwork-like smoky to translucent quartz veins that can account for up to 30% of the volcanic lenses’ volume. Picture C from Figure 5.5 illustrates typical mineralized volcanic lenses with narrow, buckled smoky quartz veins. Those mineralized volcanic lenses are generally located in the immediate footwall of the Main Reef fault or faulted within the Main Reef fault system. Mineralized volcanic lenses are generally narrow (10-25 meters) and stretched along a North-South trend, sub-parallel to the main foliation. On average the lenses will be 50-100 meters long and locally up to 300 meters. This style of mineralization has never been in the past the object of economic mining activity.

Several subsidiary faults are developed within the Birimian sedimentary hangingwall, these faults are generally narrower in comparison to the Main Reef fault which is located at the contact between the tectonic breccia and the Birimian sedimentary package. The West Reef fault is characterized as a hanging wall subsidiary fault, the fault is typically 1.5m to 2.0 m with fault filled quartz vein developed along a graphitic gauge rich fault. The quartz veins within the West Reef fault have laminated textures with smoky to translucent quartz.

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Figure 5-5: Mineralization styles and structural features characterizing the Prestea deposit

A: Reef style mineralization (Fault fill quartz veins) from hole UC 1044 at a depth of 130 meters. B: Reef style mineralization (Fault fill quartz veins) from the Spur Reef Fault, level 7 of the Bondaye shaft. C: Altered and brecciated mafic volcanic with hydrothermal breccia and arsenopyrite mineralization. D: Birimian sediments affected by F3 folding, both bedding (S0) and S1-S2 foliation are tightly folded. E: Structural relationship between S0, S2, S3 and S5. F: Refraction of S3 foliations across Birimian mudstone and a more competent wacke sub-unit.

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6 Deposit Type (Item 8)

The Prestea deposit can be classified as a lode gold deposit or an orogenic mesothermal gold deposit, which are the most common gold systems found within Archean and Paleoproterozoic terrains. In the West African shield, orogenic gold deposits are typically underlain by geology considered to be of Birimian age and are generally hosted by volcano-sedimentary sequences. The Ashanti belt, which hosts the Prestea deposit, is considered prospective for orogenic mesothermal gold deposits and hosts numerous other lode gold deposits such at the Obuasi mine.

B. Dubé and P. Gosselin of the Geological Survey of Canada described these deposits as greenstone-hosted quartz-carbonate vein deposits in the 2007 special publication no.5 entitled Mineral Deposits of Canada. The authors described these deposits as typically occurring in deformed greenstone belts and distributed along major compressional crustal scale fault zones commonly marking the convergent margins between major lithological boundaries. The greenstone-hosted quartz-carbonate vein deposits correspond to structurally controlled complex deposits characterized by networks of gold-bearing, laminated quartz-carbonate fault-fill veins. These veins are hosted by moderately to steeply dipping, compressional brittle-ductile shear zones and faults with locally associated shallow-dipping extensional veins and hydrothermal breccias. In these deposits, gold is mainly confined to the quartz-carbonate veins, but can also occur within iron-rich sulphidized wall rocks or within silicified and arsenopyrite-rich replacement zones.

At Prestea, gold mineralization exhibits a strong relationship with major shear zones, fault zones and second order structures. Two types of mineralization have been identified at Prestea, which are both characterised as mesothermal gold mineralization: 1) Fault-fill quartz veins along fault zones and second order structures, which typically contains non-refractory, free milling gold and 2) Disseminated mineralization associated with brecciated zones of iron-rich footwall volcanic lenses, which are characterized by finely disseminated arsenopyrite rich and silicified replacement zone. This type of mineralization is generally lower grade, refractory and locally termed “sulphide ore”.

The weathering profile at Prestea is deep and typically results in extensive surface oxidation of bedrock, to a depth of up to one hundred metres. Generally, the weathering profile typically consists of a lateritic surface, a saprolitic horizon, a transitional zone and a deeper primary sulphide zone.

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7 Exploration (Item 9)

The Prestea underground West Reef structure was the last area to be mined by PGR in 2002. The subsequent exploration of the West Reef underground structure has been planned and managed by Golden Star Resources Ltd and was initiated in 2004. The 17 level West Reef drive exposes the vein structure from 7618 N to the south to 8065 N to the north which represents a distance of approximately 450 meters. Along the West Reef drive the back has been sampled approximately every 5 meters using a 2 x 2 inch channel sample which was cut using a compressed air driven diamond blade rock saw. The channel samples were cut orthogonal to the main structure. The channel samples and the reef drive have been surveyed and tied into the mine grid at surface. A total of 81 channel samples were collected on the 17 level reef drive averaging 2.4 m width with composite grades ranging from 0.1 g/t to 127 g/t. The results are summarized in Table 7.1.

Table 7.1: Channel Sample results 17 Level West Reef Drive