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 Endorsed by QP’s Contributors Martin P. Raffield, Ph.D., P.Eng. Yan Bourassa, M.Sc., P.Geo. S. Mitchel Wasel, BSc AusIMM (CP) Mark Thorpe, Ph.D. William F. Tanaka John Miller Jerry Agala Samuel Agyemang Daniel Elvera 2128108.1 Golden Star Resources Ltd. i Mechanized Mining of the West Reef Resource, Prestea Underground Mine NI 43-101 Preliminary Economic Assessment Table of Contents 1 Introduction (Item 2) .............................................................................................................. 1-1 1.1 Golden Star Resources ............................................................................................... 1-1 1.2 Terms of Reference and Purpose of the Report ......................................................... 1-2 1.3 Sources of Information .............................................................................................. 1-2 1.4 Site Inspections .......................................................................................................... 1-2 2 Property Description and Location (Item 4) .......................................................................... 2-1 2.1 Property Location....................................................................................................... 2-1 2.2 Mineral Titles and Agreements. ................................................................................. 2-2 2.3 Royalties and Encumbrances ..................................................................................... 2-3 2.4 Environmental Liabilities........................................................................................... 2-3 2.5 Operating Permits Required ....................................................................................... 2-3 3 Accessibility, Climate, Local Resources and Infrastructure (Item 5) .................................. 3-4 3.1 Infrastructure and Physiography ................................................................................ 3-4 3.2 Topography, Elevation and Vegetation ..................................................................... 3-4 3.3 Climate and Length of Operating Season .................................................................. 3-4 3.4 Access to Property ..................................................................................................... 3-4 3.5 Surface Rights ............................................................................................................ 3-4 3.6 Local Resources and Infrastructure ........................................................................... 3-5 4 History (Item 6)...................................................................................................................... 4-6 4.1 Prior Ownership ......................................................................................................... 4-6 4.2 Past Exploration and Development ............................................................................ 4-6 4.3 Historic Mineral Resource and Reserve Estimates .................................................... 4-7 4.4 Historic Production .................................................................................................... 4-7 5 Geologic Setting and Mineralization (Item 7) ....................................................................... 5-9 5.1 Regional Geology ...................................................................................................... 5-9 5.2 Property Geology ..................................................................................................... 5-14 6 Deposit Type (Item 8) .......................................................................................................... 6-19 7 Exploration (Item 9) ............................................................................................................. 7-20 8 Drilling (Item 10) ................................................................................................................... 8-1 9 Sample Preparation, Analyses and Security (Item 11) .......................................................... 9-1 10 Data Verification (Item 12) .................................................................................................. 10-1 10.1 Duplicates (2004 - 2006) ......................................................................................... 10-1 10.2 Duplicates (2006 - 2008) ......................................................................................... 10-1 10.3 Screen Fire Assay checks (2004 -2006) ................................................................... 10-2 10.4 Screen Fire Assay checks (2007) ............................................................................. 10-3 10.5 Blanks ...................................................................................................................... 10-4 10.6 Gannet standards (2006) .......................................................................................... 10-5 10.7 Gannet standards (2007 - 2008) ............................................................................... 10-5 10.8 Conclusions .............................................................................................................. 10-8 11 Mineral Processing and Metallurgical Testing (Item 13) .................................................... 11-1 11.1 Samples .................................................................................................................... 11-1 11.2 Testwork .................................................................................................................. 11-1 May 3, 2012 Golden Star Resources Ltd. ii Mechanized Mining of the West Reef Resource, Prestea Underground Mine NI 43-101 Preliminary Economic Assessment 11.3 Results ...................................................................................................................... 11-2 12 Mineral Resources (Item 14) ............................................................................................... 12-1 12.1 Data sources ............................................................................................................. 12-1 12.2 Data cutting/filtering ................................................................................................ 12-1 12.3 Basic statistical tests ................................................................................................ 12-1 12.4 3D Variographic analysis ......................................................................................... 12-3 12.5 Block Model Grade Interpolation ............................................................................ 12-7 12.6 Resource Classification ............................................................................................ 12-7 12.7 Mineral Resource Statement .................................................................................... 12-9 13 Mineral Reserve Estimation (Item 15) ............................................................................... 13-11 14 Mining Methods (Item 16) ................................................................................................. 14-12 14.1 Introduction ............................................................................................................ 14-12 14.2 Selection of Mining Method .................................................................................. 14-15 14.2.1 Cut-off Grade Calculation ....................................................................... 14-15 14.2.2 Geotechnical Design ................................................................................ 14-15 14.2.3 AVOCA Mining Method ......................................................................... 14-19 14.3 Stope Design .......................................................................................................... 14-21 14.4 Development Design .............................................................................................. 14-22 14.4.1 Main Access Ramp .................................................................................. 14-23 14.4.2 Central Shaft Upgrade ............................................................................. 14-24 14.4.3 New Hoisting Shaft ................................................................................. 14-24 14.4.4 Backfill Supply Development ................................................................. 14-25 14.4.5 Stope Development ................................................................................. 14-25 14.5 Potentially Mineable Resources ............................................................................. 14-26 14.6 Mining Operations ................................................................................................. 14-26 14.6.1 Development ............................................................................................ 14-26 14.6.2 Drilling and Blasting ............................................................................... 14-26 14.6.3 Mucking and Hauling .............................................................................. 14-26 14.6.4 Backfill .................................................................................................... 14-26 14.6.5 Mining Equipment Fleet