Evolution of Mine Drainage Chemistry Red Dog Mine, Alaska

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1 Evolution of Mine Drainage Chemistry Red Dog Mine, Alaska Stephen Day, SRK Consulting, Walter Kuit and Michel Filion, Teck Cominco Ltd 10th ANNUAL BRITISH COLUMBIA ML/ARD WORKSHOP December 2003

2 Outline ÂMine background ÂGeological overview of Red Dog ÂStatic geochemistry ÂKinetic geochemistry ÂWaste rock seepage chemistry ÂMechanisms controlling seepage chemistry

3 Red Dog Mine  Located in NW Alaska 55 miles from Chukchi Sea  Largest zinc deposit in the world.  Started production in  Open pit mine  Conventional sulphide flotation

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5 Black Shale-Hosted Pb-Zn Deposit ÂGeology Friable rocks Generally low carbonate content. Wide range of sulphide mineral occurrences in ore and host rock

6 Natural Weathering Effects ÂDeposit discovered by oxidized cap ( gossan gossan ) ÂNatural oxidation has produced a large number of iron, zinc, lead and copper oxides and sulphates. ÂAcidic salts and natural seepage.

7 Natural Weathering Effects

8 Oxidation Salts

9 Static Geochemistry: Sulphur Speciation ÂComplex sulphur speciation Conventional static testing is meaningless. Sulphur speciation calculated from dominant forms: S(Fe Sulphide) = Total S {S(Ba Ba) ) + S(PbS PbS) + S(PbSO 4 ) + S(ZnS ZnS) ) + S(ZnSO 4 )} Acid Potential from S(Fe Sulphide) ÂDay et al (2000 Denver ICARD)

10 Static Geochemistry: Neutralization Potential ÂCarbonate content of most rock types is very low. ÂMostly calcite. ÂIron and barium carbonates occur.

11 Geochemical Database ÂWaste Rock Characterization 600 static tests Eight humidity cells (up to 4 years) Seepage monitoring for waste rock (7 years) ÂTailings Humidity cells and subaqueous columns on one sample (3 years) Seepage monitoring (5 years)

12 Acid Generation Potential NP (kg/t) Acid Consuming Black Shales Potentially Acid Generating - Delayed Black Shales Potentially Acid Generating - Immediate - Ore and Suphide Waste AP (kg/t)

13 Humidity Cell Results ph AP 114 NP 0 AP 1119 NP Cycles (weeks) AP 70 NP 144 AP 244 NP 0 AP 198 NP 0

14 Humidity Cell Results 1000 AP 70 NP 144 S/Zn (mmol/mmol) AP 244 NP 0 AP 198 NP Cycle (weeks)

15 Humidity Cell Results Sulfate (mg/l) Equivalent molar quantities Pb (mg/l)

16 Waste Rock Characteristics Major Unit Sub-Unit Overall Classification Primary Secondary Mélange (8%) Basal and Upper Non-AG, metals AG Kivalina Shale (5%) Kogruk Limestone Non-AG, metals Non-AG (0%) Ikalukrok Ore host (55%) Rapid AG Shale (6%) Rapid AG Non-AG, metals Siksikpuk (21%) Baritic Chert Delayed AG Uncertain AG Shale Rapid AG Non-AG, metals Okpikruak (4%) Non-AG

17 Waste Rock Stockpile Seepage MWD TDS, Zn (mg/l) ph Zn Fe ph Date (Julian) 2

18 Waste Rock Stockpile Seepage MWD Molar Ratios Fe/S Zn/S Zn/Fe Date (Julian)

19 Overburden Stockpile Seepage East Sump Zn (mg/l) ph Zn ph Date

20 Observations on Trends ÂHumidity Cells Initial flush of (highly acidic) salts. Conventional delay of ph depression by carbonates. Other delay effect Possible galvanic effect (ZnS( oxidizes first) Lead release increases late in test as SO 4 decreases.

21 Observations on Trends ÂWaste Rock Seepage Main waste seeps are strongly acidic. Seeps monitored for several years indicate flat or slightly decreasing trends. Dominance of zinc over iron Overburden waste pile has non-acidic seepage No trend.

22 Conclusion Evolution of Drainage Chemistry ÂImmediate to Short to Medium Term Effects (Zn, Cd,, mildly acidic to alkaline) Immediate to Short Term Leaching of natural (original) soluble salts containing mostly zinc, cadmium (± iron). Short to Medium Term Oxidation of zinc sulphides. Galvanic protection of iron sulphides. Carbonate buffering (if carbonates present). Leaching of soluble salts produced by oxidation

23 Conclusion Evolution of Drainage Chemistry ÂLonger Term Effects (acid rock drainage) Medium to Long Term Zinc sulphide oxidation continues Oxidation of iron sulphides Leaching of soluble salts produced by oxidation Long Term Leaching of lead sulphate (increase in lead)

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