Acid Rock Drainage (ARD) to the Rock Drain and North Fork of Rose Creek, Faro Mine Complex

Transcription

1 Acid Rock Drainage (ARD) to the Rock Drain and North Fork of Rose Creek, Faro Mine Complex Paul Ferguson 1, Christoph Wels 1, Dustin Rainey 2, and Carrie Gillis 2 1 Robertson GeoConsultants Inc. Vancouver, B.C. Canada pferguson@rgc.ca 2 Assessment and Abandoned Mines, Government of Yukon Whitehorse, YT, Canada November 6 th, 2017 Tailings and Mine Waste (Banff)

2 Overview: ML/ARD Prevention and Mitigation Strategies Available methods (see GARD Guide): Minimize oxygen supply Minimize water infiltration Remove or isolate sulphide minerals Maximize available Neutralization Potential (NP) Control bacteria (biogeochemical processes) Pyrite, FeS 2 ML/ARD Prevention (Source Control) Avoidance Underwater disposal Co-disposal (tailings and waste rock) Blending (PAG and Non-PAG waste rock) Closure covers Effectiveness ML/ARD Mitigation; protective but often inefficient and costly Seepage or groundwater interception ( Collect and Treat ) Clean water diversion Natural attenuation and dilution ARD generated, now in receiving environment 2

3 Life-of-Mine (LOM) ML/ARD Prevention and Mitigation Abandoned mines 3

4 Faro Mine Complex (FMC) FMC: once one of the largest Pb and Zn producers in the world Mining ceased in 1990s (formally abandoned in 1998) 70 Mt of sulphidic tailings and 320 Mt of waste rock Closure planning ongoing ($500M+, 10 to 15 years to complete) CVD SIS (closure) ETA SIS (C&M) S-Cluster SIS (C&M) To Vangorda Plateau Jan 3 rd,

5 Key Site Features Rock Drain Rose Creek Tailings Facility (RCTF) Intermediate WRD Faro Pit NFRC 5

6 Seepage from Intermediate WRD and S-Cluster SIS Mill X23 Main WRD Intermediate WRD (Sulphide Cell) NFRC ARD-impacted groundwater Rock Drain (60 m haul road) RCTF S-Cluster SIS 6

7 Monitoring Wells and Surface Water Monitoring Stations SRK08-SPW3 NFRC at NF1 NFRC at NF2 NFRC at X2 7

8 Study Impetus, Objectives, and Approach Study Impetus: In 2013, Zn concentrations in the NFRC increased to more than 1 mg/l due to larger seepage loads from Rock Drain Site discharge limit: 0.5 mg/l Zn 100 x previously-observed Zn concentration Study Objectives: 1. Determine whether the Zn loads that bypass the S-Cluster SIS via groundwater affect Zn concentrations in the NFRC. 2. Determine whether the interception of Zn loads by the NFRD SIS and/or pumping well PW14-06 have improved Zn concentrations in the NFRC. 3. Recommend measures to further reduce Zn loads to the NFRC. Approach: Review monitoring data from 2010 to 2017 when the S-Cluster SIS, pumping well PW14-06, and the NFRD SIS were each operational 8

9 Contaminant (ARD) Flushing Events, Main WRD 2013 C V ARD not yet developed 9

10 S-Cluster SIS Performance (Shallow Aquifer) ~35 t/year Zn intercepted (some recent deterioration in performance) ~400 mg/l Zn Zn, mg/l 1 mg/l Zn From 2015 GWQ Review, RGC (2016) January 2009 (SIS operational) 10

11 Zn Concentrations in the NFRC, 2010 to 2017 Increased recharge and associated flushing from Intermediate WRD Supported by: Higher flows and [Zn] to S-Cluster SIS (SRK09-SPW3) Higher flows and [Zn] in Main WRD seepage (X23) Higher Zn in NFRC attributed to larger seepage loads from Intermediate WRD (not lateral seep movement) 11

12 Seepage Interception Systems near Rock Drain PW14-06 (since 2016) S-Cluster SIS (since 2009) NFRD SIS at NF2A (7 months in 2015 and 2016) 12

13 Seepage Interception Systems near Rock Drain Effective SIS Components: S-Cluster intercepts the majority of Zn load (protects NFRC) PW14-06 intercepts a substantial load that would likely report to S-Cluster SIS (no effect on NFRC) Ineffective SIS Component NFRD intercepts negligible load (large SW flows, 0.5 mg/l Zn) Future SIS Options 1 to 3 L/s pumped near NF1 Pond Zn load in NFRC < 1 kg/day Zn (meet CCME guideline) Upgrade S-Cluster SIS Zn load: 40 t/year 11% PW % NFRD SIS 89% S-Cluster SIS 13

14 NFRC Remediation Project (Urgent Works) o Two component: Component #1. Clean water diversion, i.e. raise and line creek Component #2. Contact water collection system (SIS) NFRC Intermediate WRD (Sulphide Cell) ARD-impacted groundwater SIS (wells) RCTF S-Cluster SIS (remains) NFRC Diversion Channel (raised and lined) RCDC (existing) 14

15 Questions or Comments? Project details and updates: Faro-related papers and presentations:

16 END

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19 ARD TO ROCK DRAIN AND NFRC Key Facts and Observations Rock Drain: 60-m high haul road built over pre-mining course of NFRC Intermediate WRD: South of Faro Pit near the NFRC Lower lift (25 to 30 m): PAG and Non-PAG waste rock Upper lift (25 to 30 m): Highly-sulphidic PAG waste rock (segregated) S-Cluster SIS (constructed in 2009): Intercepts seepage from Intermediate WRD before it reaches NFRC Several pumping wells and an interceptor trench Seepage from Intermediate WRD also reports to Rock Drain Seepage (up to 3,000 mg/l Zn) likely originates from highly-sulphidic waste rock within the Intermediate WRD Faro Winter Drilling Program (RGC) in 2014: Monitoring wells and PW14-06 North Fork Rock Drain (NFRD) SIS installed near Rock Drain in