NANISIVIK MINE Closure Design and Performance Monitoring Jim Cassie, M.Sc., P.Eng. Principal Geotechnical Engineer BGC Engineering Inc. 2015 RPIC FEDERAL CONTAMINATED SITES REGIONAL WORKSHOP OUTLINE • SITE / PROJECT OVERVIEW • CLIMATE / CONSTRAINTS • CLOSURE MEASURES • Tailings cover • Channels • Mine openings • Borrow areas • MONITORING • Methods • Results 2 RPIC, JUNE 2015, EDMONTON SITE / LOCATION • 73oN Latitude • 700 km north of Arctic Circle • Remote • Underground lead / zinc mine • Opened in October 1976 • Nyrstar purchased in 2011 3 RPIC, JUNE 2015, EDMONTON 4 RPIC, JUNE 2015, EDMONTON MINE HISTORY • Mine closed in 2002 • Produced ~ 10,000,000 m3 of tailings • Mine Closure Plan Finalized in 2002 and 2003 and approved in 2004. • Reclamation Construction 2004 through 2008. • Performance Monitoring 2005 through 2014 (through 2019) 5 RPIC, JUNE 2015, EDMONTON COLD CLIMATE Mean Annual Air Temperature: -15.2°C (2000) or -14.3oC (2012). Average Precipitation: 240 mm/yr. Average Evaporation: 200 mm/yr. Permafrost > 450 m depth 10.0 Mean Monthly Air Temperatures 5.0 0.0 C) ° -5.0 -10.0 -15.0 -20.0 Air Temperature ( Temperature Air -25.0 Mean Temperatures Values (1977 to 2013) -30.0 2013 Temperature Values**Arctic Bay -35.0 6 Jul Oct Apr Jan Jun Mar Feb Dec Aug Sep Nov May SITE CONSTRAINTS • Very remote site – by sealift from QC in the summer. • Summer / winter jet service • No surface mining / civil equipment at site • Very limited “summer” construction season. • Limited selection of natural materials • Revegetation not necessary 7 RPIC, JUNE 2015, EDMONTON CLOSURE ELEMENTS • Embankments, containment structures and diversion channels – 4 dykes, two tank farms, one spillway and two outlet channels • Thermal covers – tailings, waste rock, landfill, ponds (11 elements in total) • Mine openings, crown pillars and raises (11 elements) • Borrow areas (6 for shale and 4 for armour rock) 8 RPIC, JUNE 2015, EDMONTON TAILINGS COVERS • 45 ha tailings disposal area. • Tailings partially frozen (talik in middle) • Tailings characterization Test Covers • 80% pyrite, • 18% dolomite • Total Sulphur ~35% to 50% • Unoxidized 9 RPIC, JUNE 2015, EDMONTON TAILINGS RECLAMATION OBJECTIVES Ø Isolate the potentially acid generating tailings from the atmosphere to minimize the risk of acid mine drainage; Ø Minimize the risk of physical movement of the tailings to the environment; and Ø Provide a safe and useable surface environment that corresponds to the natural surroundings. – Construction of Permafrost Aggradation Covers o Promote development of permafrost in tailings and confine seasonal thaw to cover materials. 10 RPIC, JUNE 2105, EDMONTON COVER DESIGN –DIFFERENT TEST COVERS 11 COVER DESIGN – CLIMATE CHANGE Geothermal modelling • Mean Annual Air Temperature = -15.1oC • 1 in 100 year warm year = -13.3oC • Global Warming Estimate for the year 2100 = -10.1oC 12 FINAL COVER DESIGN • Reclamation Planning – Final Cover Design for tailings Armour • 1.25 m minimum thickness – 1.0 m granular shale fill – 0.25 m surface armour Shale (gravel and cobbles) Ice Saturation Tailings 13 RPIC, JUNE 2015, EDMONTON REGRADING TAILINGS SHALE PLACEMENT ARMOUR PLACEMENT TWO LAYER SYSTEM WestWest Twin Twin DisposalDisposal Area Area 1998July2004 2005 WEST TWIN DISPOSAL AREA COMPLETED COVER AUGUST 2006 CHANNELS • One new channel as spillway around West Twin Dyke • Designed for PMF • 550 m long by 6 m wide • Poor quality rock / armoured • Snow / ice blockage creates water flows higher than expected • Two other channels – 1 with minor erosion concerns 19 RPIC, JUNE 2015, EDMONTON MINE OPENINGS • 9 audits / portals and 4 raises • Different sizes and geometries, some with ice plugs • Physical barrier only • Backfilled with shale rockfill close to the crown • Sloped out at 3:1 to 4:1 and then covers placed • Raises were backfilled under mounds of fill 20 RPIC, JUNE 2015, EDMONTON SHALE QUARRIES SHALE QUARRY OUTLINE • SITE / PROJECT OVERVIEW • CLIMATE / CONSTRAINTS • CLOSURE MEASURES • Tailings cover • Channels • Mine openings • Borrow areas • MONITORING • Methods • Results 24 RPIC, JUNE 2015, EDMONTON PERFORMANCE MONITORING METHODS • Post-closure monitoring review undertaken for new Water Licence • Thermistors, frost gauges and piezometers monitored from July 1 to Sept 1 • Visual inspection by professional geotechnical engineer • Climate data review • Water quality samples and testing RPIC, JUNE 2015, EDMONTON MONITORING SCHEDULE RPIC, JUNE 2015, EDMONTON RPIC, JUNE 2015, EDMONTON 2014 ACTIVE LAYER MONITORING RPIC, JUNE 2015, EDMONTON ACTIVE LAYER MONITORING OVER TIME 2013 Ac#ve Layer Monitoring 2006 Data 2009 Data Surface Cell Tailings Cover 2013 Data 0.0 Frost Gauge 1 2006-2013 0.2 0.4 0.6 0.8 1.0 1.2 Cover 1.4 Tailings 1.6 Ac#ve Layer Depth (m bgs) 1.8 2.0 01-May 01-Jun 02-Jul 02-Aug 02-Sep 03-Oct 03-Nov 04-Dec Date (dd-mmm) RPIC, JUNE 2015, EDMONTON INTERIOR WATER QUALITY - Zn RPIC, JUNE 2015, EDMONTON Test Pit Excavated in 2007 Ice Saturation at Base of Cover TAILINGS FREEZEBACK RPIC, JUNE 2015, EDMONTON TAILINGS PORE PRESSURES (TALIK) TEMPERATURE PORE PRESSURES RPIC, JUNE 2015, EDMONTON FINAL WATER QUALITY AT OUTLET - Zn RPIC, JUNE 2015, EDMONTON Project Summary • When you have cold, make permafrost • Mine closure plan to address many elements and aspects • Closure plan and permitting benefitted from planning and site studies undertaken during operations • Used site specific environmental conditions and accounted for global warming effects • Experience northern site engineers required for field design, QA and QC • Remoteness of site and harsh environment provided constraints on construction activities, but successfully managed with experienced personnel • Monitor performance and adjust as necessary • Mine is successfully closed and has achieved stable conditions ACKNOWLEDGEMENTS / CONTACT • Nystar • Geoff Claypool • Questions? Contact Jim Cassie Principal Geotechnical Engineer BGC Engineering Inc. +1 (587) 894-2664 RPIC, JUNE 2015, EDMONTON .