NANISIVIK MINE Closure Design and Performance Monitoring

Transcription

1 NANISIVIK MINE Closure Design and Performance Monitoring Jim Cassie, M.Sc., P.Eng. Principal Geotechnical Engineer BGC Engineering Inc RPIC FEDERAL CONTAMINATED SITES REGIONAL WORKSHOP

2 OUTLINE SITE / PROJECT OVERVIEW CLIMATE / CONSTRAINTS CLOSURE MEASURES Tailings cover Channels Mine openings Borrow areas MONITORING Methods Results 2 RPIC, JUNE 2015, EDMONTON

3 SITE / LOCATION 73 o N Latitude 700 km north of Arctic Circle Remote Underground lead / zinc mine Opened in October 1976 Nyrstar purchased in RPIC, JUNE 2015, EDMONTON

4 4 RPIC, JUNE 2015, EDMONTON

5 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 Reclamation Construction 2004 through Performance Monitoring 2005 through 2014 (through 2019) 5 RPIC, JUNE 2015, EDMONTON

6 COLD CLIMATE Mean Annual Air Temperature: C (2000) or o C (2012). Average Precipitation: 240 mm/yr. Average Evaporation: 200 mm/yr. Permafrost > 450 m depth 10.0 Mean Monthly Air Temperatures Air Temperature ( C) Mean Temperatures Values (1977 to 2013) 2013 Temperature Values**Arctic Bay Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

7 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

8 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

9 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

10 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 11 COVER DESIGN DIFFERENT TEST COVERS

12 COVER DESIGN CLIMATE CHANGE Geothermal modelling Mean Annual Air Temperature = o C 1 in 100 year warm year = o C Global Warming Estimate for the year 2100 = o C 12

13 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

14 REGRADING TAILINGS

15 SHALE PLACEMENT

16 ARMOUR PLACEMENT

17 TWO LAYER SYSTEM

18 West Twin Disposal Area 1998 July WEST TWIN DISPOSAL AREA COMPLETED COVER AUGUST 2006

19 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

20 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

21 SHALE QUARRIES

22

23 SHALE QUARRY

24 OUTLINE SITE / PROJECT OVERVIEW CLIMATE / CONSTRAINTS CLOSURE MEASURES Tailings cover Channels Mine openings Borrow areas MONITORING Methods Results 24 RPIC, JUNE 2015, EDMONTON

25 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

26 MONITORING SCHEDULE RPIC, JUNE 2015, EDMONTON

27 RPIC, JUNE 2015, EDMONTON

28 2014 ACTIVE LAYER MONITORING RPIC, JUNE 2015, EDMONTON

29 ACTIVE LAYER MONITORING OVER TIME Ac#ve Layer Monitoring Surface Cell Tailings Cover Frost Gauge Data 2009 Data 2013 Data Ac#ve Layer Depth (m bgs) Cover Tailings May 01- Jun 02- Jul 02- Aug 02- Sep 03- Oct 03- Nov 04- Dec Date (dd- mmm) RPIC, JUNE 2015, EDMONTON

30 INTERIOR WATER QUALITY - Zn RPIC, JUNE 2015, EDMONTON

31 Test Pit Excavated in 2007 Ice Saturation at Base of Cover

32 TAILINGS FREEZEBACK RPIC, JUNE 2015, EDMONTON

33 TAILINGS PORE PRESSURES (TALIK) TEMPERATURE PORE PRESSURES RPIC, JUNE 2015, EDMONTON

34 FINAL WATER QUALITY AT OUTLET - Zn RPIC, JUNE 2015, EDMONTON

35 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

36 ACKNOWLEDGEMENTS / CONTACT Nystar Geoff Claypool Questions? Contact Jim Cassie Principal Geotechnical Engineer BGC Engineering Inc. +1 (587) RPIC, JUNE 2015, EDMONTON