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OPEN PIT & STOCKPILE ORE CONTROL FOR CYANIDE HEAP LEACHING to PREVENT A SOUR PAD Presented by Thom Seal, Ph.D., PE. Co-Authors: C. L. Bolin SME Salt Lake City March 1, 2000 Knight Piesold ARD Conference Elko, NV. March 15, 2012

SLIDE 1

OPEN PIT & STOCKPILE ORE CONTROL FOR CYANIDE HEAP LEACHING to PREVENT A SOUR PAD

Presented by Thom Seal, Ph.D., PE. Co-Authors: C. L. Bolin SME – Salt Lake City March 1, 2000 Knight Piesold – ARD Conference – Elko, NV. March 15, 2012

SLIDE 2

ORE CONTROL

 Cyanide Leachable - Mill & Heap Leach  Refractory

– Mill {Roaster - Autoclave - Flotation} Grade – Leach {Biooxidation - ATS} Grade

 Waste

– General (Non Acid Generating) – Acid Generating (PAG)

SLIDE 3

METALLURGICAL CHARACTERISTICS

 Cyanide Gold Extraction

– CN Shake Test - AA for [Au] = AUCN – Fire Assay – AA/FA - Theoretical CN Gold Extraction

 Preg. Rob

– Spike w/Au CN Shake Test – Determine [Au] Absorbed by Ore – PRV = (AUCN + 0.1) - AUPR

 Fuel Value = 1.3 (OrgC) + SS - Target 2.5

SLIDE 4

MINERAL CHARACTERISTICS

 Sulfides

– Pyrite - FeS2

GQ - 10 microns (um) +

– Arsenopyrite - FeAsS GQ - 1-2 microns (um)

 Carbonates

– Calcite - CaCO3 – Dolomite - CaMg(CO3)2 – Siderite - FeCO3

 Carbonaceous Material

SLIDE 5

ANALYTICAL

 LECO Total Sulfur & Carbon  Sulfur as a Percent

– % Sulfate Sulfur = SRO – % Sulfide Sulfur - Roast {% SS} = STOT -

SRO

 Carbon as a Percent

– % Organic Carbon = CAI = OrgC – % Carbonate Carbon - Leach HCl {% CC} – % CC = CTOT - CAI

SLIDE 6

AGP

 Acid Generating Potential - AGP

– Equal to - 1.37 * % SS

 Sample Equation:

– 2 FeS2 + 7 O2 + 2 H2O 

2 FeSO4 + 4 H+ + 2 SO4

 Leads to Acid Rock Drainage

SLIDE 7

ANP

 Acid Neutralization Potential - ANP

– Equal to 3.67 * % CC

 Sample Equation:

– CaCO3 + 2 H+

+ SO4 2- 

CaSO4 + H2O + CO2

SLIDE 8

NCV

 Net Carbonate Value - NCV

– Equal to ANP + AGP – NCV = 3.67 * % CC - 1.37 * % SS

SLIDE 9

EQUATIONS

 Cyanide Hydrolyses at pH < 10

– CN- + H2O  HCN + OH-

 Cyanide Reaction with Sulfides

– 2 FeS + 12 CN- + 5 O2 + 2 H2O 

2 Fe(CN)6

4- + 2 SO4 2- + 4 OH-

 Lime Hydrolyses

– CaO + H2O  Ca(OH)2

SLIDE 10

LIME USE MODEL

 Net Reaction

– 4 FeS2 + 8 CaO + 15 O2 + 6 H2O 

4 Fe(OH)3 + 8 CaSO4

 Regression Model

– Lime (pounds/ton) = 5.066 - 2.6874 * NCV – Multiply by Safety Factor: Using S.F. = 2 for

NA Stockpiles

SLIDE 11

LIME USE AND COLUMN TESTS

Lime Addition to Oxide CN Extractions vs. NCV

y = -2.6874x + 5.066 R2 = 0.5904 5 10 15 20 25

1 2 3

NCV Lime lbs/ton

Column Tests Linear (Column Tests)

Column Model: CaO (lbs/ton) = 5.066 - 2.6874 * NCV

SLIDE 12

CYANIDE USE MODEL

Cyanide Addition to Oxide CN Extractions vs. NCV

y = -0.1534x + 0.505 R2 = 0.477 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

1 2 3

NCV NaCN lbs/ton

Column Tests Linear (Column Tests)

Column Model: NaCN (lbs/ton) = 0.505 - 0.1534 * NCV

SLIDE 13

GOLD EXTRACTION AND NCV

Percentage of Total Gold Extraction as a function of NCV

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

1 2 3 4 NCV Percent of Total Gold Extracted Column Tests

SLIDE 14

BLAST HOLE INFORMATION

Class

Low Recovery General Leach

Drill Hole #

Series #

99 016

Pattern # Au Fire Assay [AuFA] 0.031

0.010 CN Extractable Au [AuAA]

Ratio AuCN/AuFA 0.323

0.006 Preg. Rob Value [AuPR]

Total Sulfur [STOT] 1.32 0.06 Total Carbon [CTOT] Sulfate S [SRO] 0.43 0.05 Organic Carbon [OC] Sulfide S [SS] 0.89 0.02 Carbonate Carbon [CC] Fuel Value [FV] 0.96

1.17

Net Carbonate Value [NCV]

LGL 13645 Gold Quarry Blast Hole Information

SLIDE 15

GOLD QUARRY PIT - POLYGON

Gold Quarry Pit Newmont Mining Co. December 2,1999 Bench: SS%: Poly Num: C245 OC%: Mat'l Class: LGL CC%: Tons: NCV: AuFA: Lime #/ton: AuAA: AA/FA Ratio: Spacing: 18' Drill Depth: 30' Hole Dia: 7.9" 10.5 10,397 1.06 0.04 0.02

1.37

43% 0.02 4550 0.04

SLIDE 16

LIME USE MODEL

 Net Reaction

– 4 FeS2 + 8 CaO + 15 O2 + 6 H2O 

4 Fe(OH)3 + 8 CaSO4

 Regression Model – Oxide Ore

– Lime (pounds/ton) = 5.066 - 2.6874 * NCV – Multiply by Safety Factor: Using S.F. = 2 for

NA Stockpiles

SLIDE 17

LIME USE MODEL

 Regression Model – ARD Stockpile Ore

Lime (pounds/ton) = 6.68 – 7.68 * CC1.01 + 45.7 * SRO1.09 CC = % Carbonate Carbon SRO = % S as SO4 (Sulfate Sulfur)

SLIDE 18

Lime Model for ARD Stockpiles

NA Stockpiles [Lab Lime vs Stk Lime Model-1]

R2 = 0.7075 10 20 30 40 50 10 20 30 40 Stk Lime Model-1 #/ton Lab Lime #/ton

SLIDE 19

NAL Gold Production

NAL Gold Production - 3Q 2001

300 400 500 600 700 800 6/18 7/8 7/28 8/17 9/6 9/26 10/16 Shifts Au oz/ton Solution

SLIDE 20

NAL Solution Grade

NAL Preg Grade - 3Q 2001

0.01 0.011 0.012 0.013 0.014 0.015 0.016 0.017 0.018 6/18 7/8 7/28 8/17 9/6 9/26 10/16 Shifts Au oz/ton Solution INPreg

SLIDE 21

Gold Quarry Results

 2.6 million stockpile tons  2.5 million mines tons  85,000 recovered Au oz.  Net Revenue  $ 18,000,000  1996 - 1999

SLIDE 22

CONCLUSIONS

 Reagent Utilization is Ore Dependant  Run of Mine Ore to have + NCV Value  Biooxidation of Ores with NCV Values less than -

2.0

 Caustic Cost is 7.5 times higher than Lime  Cyanide Cost is 22 times higher than Lime  Ore Destination by Grade, AA/FA, Preg. Rob and