NEXGEN ENERGY LTD. TECHNICAL REPORT ON THE ROOK I PROPERTY, SASKATCHEWAN, CANADA NI 43-101 Report Qualified Persons: Mark B. Mathisen, C.P.G. David A. Ross, M.Sc., P.Geo. March 31, 2017 RPA 55 University Ave. Suite 501 I Toronto, ON, Canada M5J 2H7 I T + 1 (416) 947 0907 www.rpacan.com Report Control Form Document Title Technical Report on the Rook I Property, Saskatchewan, Canada Client Name & Address NexGen Energy Ltd. Suite 3150, 1021 West Hastings Street, Vancouver, BC, V6E 0C3 Document Reference Project #2733 Status & FINAL Issue No. Version Issue Date March 31, 2017 Lead Author Mark Mathisen (Signed) David Ross (Signed) Peer Reviewer William E. Roscoe (Signed) Project Manager Approval David Ross (Signed) Project Director Approval William E. Roscoe (Signed) Report Distribution Name No. of Copies Client RPA Filing 1 (project box) Roscoe Postle Associates Inc. 55 University Avenue, Suite 501 Toronto, ON M5J 2H7 Canada Tel: +1 416 947 0907 Fax: +1 416 947 0395 [email protected] www.rpacan.com TABLE OF CONTENTS PAGE 1 SUMMARY ........................................................................................................................ 1-1 Executive Summary ......................................................................................................... 1-1 Technical Summary ......................................................................................................... 1-4 2 INTRODUCTION ............................................................................................................... 2-1 Sources of Information .................................................................................................... 2-1 Effective Date .................................................................................................................. 2-1 List of abbreviations ......................................................................................................... 2-2 3 RELIANCE ON OTHER EXPERTS ................................................................................... 3-1 4 PROPERTY DESCRIPTION AND LOCATION ................................................................. 4-1 Land Tenure .................................................................................................................... 4-1 Mineral Rights .................................................................................................................. 4-3 Royalties and Other Encumbrances ................................................................................ 4-4 Permitting ........................................................................................................................ 4-4 5 ACCESSIBILITY, CLIMATE, LOCAL RESOURCES, INFRASTRUCTURE AND PHYSIOGRAPHY ................................................................................................................. 5-1 Accessibility ..................................................................................................................... 5-1 Climate ............................................................................................................................ 5-1 Local Resources .............................................................................................................. 5-2 Infrastructure ................................................................................................................... 5-2 Physiography ................................................................................................................... 5-2 6 HISTORY ........................................................................................................................... 6-1 Prior Ownership ............................................................................................................... 6-1 Exploration and Development History ............................................................................. 6-1 Historical Resource Estimates ......................................................................................... 6-3 Past Production ............................................................................................................... 6-3 7 GEOLOGICAL SETTING AND MINERALIZATION ........................................................... 7-1 Regional Geology ............................................................................................................ 7-1 Local and Property Geology ............................................................................................ 7-3 Mineralization .................................................................................................................. 7-5 8 DEPOSIT TYPES .............................................................................................................. 8-1 9 EXPLORATION ................................................................................................................. 9-1 Ground Geophysical Surveys .......................................................................................... 9-1 Airborne Geophysical Surveys ........................................................................................ 9-2 Geochemical Surveys ...................................................................................................... 9-3 Geological Surveys .......................................................................................................... 9-3 10 DRILLING ...................................................................................................................... 10-1 NexGen Energy Ltd. – Rook I Property, Project #2733 Technical Report NI 43-101 – March 31, 2017 Page i www.rpacan.com Drill Hole Surveying ..................................................................................................... 10-10 Drill Core Handling and Logging Procedures .............................................................. 10-10 11 SAMPLE PREPARATION, ANALYSES AND SECURITY ............................................ 11-1 Sample Preparation ....................................................................................................... 11-1 Analyses ........................................................................................................................ 11-1 Quality Assurance and Quality Control .......................................................................... 11-3 Security .......................................................................................................................... 11-9 12 DATA VERIFICATION ................................................................................................... 12-1 Site Visit and Core Review ............................................................................................ 12-1 Database Validation ...................................................................................................... 12-2 Independent Verification of Assay Table ....................................................................... 12-2 13 MINERAL PROCESSING AND METALLURGICAL TESTING ..................................... 13-1 14 MINERAL RESOURCE ESTIMATE .............................................................................. 14-1 Resource Database ....................................................................................................... 14-2 Geological Interpretation and 3D Solids ........................................................................ 14-2 Statistical Analysis ......................................................................................................... 14-6 Density ......................................................................................................................... 14-18 Block Model ................................................................................................................. 14-20 Interpolation Parameters ............................................................................................. 14-22 Block Model Validation ................................................................................................ 14-26 Cut-off Grade ............................................................................................................... 14-32 Classification ............................................................................................................... 14-35 Mineral Resource Reporting ........................................................................................ 14-37 15 MINERAL RESERVE ESTIMATE ................................................................................. 15-1 16 MINING METHODS ....................................................................................................... 16-1 17 RECOVERY METHODS ............................................................................................... 17-1 18 PROJECT INFRASTRUCTURE .................................................................................... 18-1 19 MARKET STUDIES AND CONTRACTS ....................................................................... 19-1 20 ENVIRONMENTAL STUDIES, PERMITTING, AND SOCIAL OR COMMUNITY IMPACT ............................................................................................................................................ 20-1 21 CAPITAL AND OPERATING COSTS ........................................................................... 21-1 22 ECONOMIC ANALYSIS ................................................................................................ 22-1 23 ADJACENT PROPERTIES