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 73 o N 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 m 3 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 -14.3 o C (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 Air Temperature ( C) -5.0-10.0-15.0-20.0-25.0-30.0 Mean Temperatures Values (1977 to 2013) 2013 Temperature Values**Arctic Bay -35.0 6 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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 80% pyrite, 18% dolomite Total Sulphur ~35% to 50% Unoxidized Test Covers 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
11 COVER DESIGN DIFFERENT TEST COVERS
COVER DESIGN CLIMATE CHANGE Geothermal modelling Mean Annual Air Temperature = -15.1 o C 1 in 100 year warm year = -13.3 o C Global Warming Estimate for the year 2100 = -10.1 o C 12
FINAL COVER DESIGN Reclamation Planning Final Cover Design for tailings 1.25 m minimum thickness 1.0 m granular shale fill 0.25 m surface armour (gravel and cobbles) Armour Shale Ice Saturation Tailings 13 RPIC, JUNE 2015, EDMONTON
REGRADING TAILINGS
SHALE PLACEMENT
ARMOUR PLACEMENT
TWO LAYER SYSTEM
West Twin Disposal Area 1998 July 20042005 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 0.0 0.2 0.4 2013 Ac#ve Layer Monitoring Surface Cell Tailings Cover Frost Gauge 1 2006-2013 2006 Data 2009 Data 2013 Data Ac#ve Layer Depth (m bgs) 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Cover Tailings 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