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

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)

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

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

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

AGP

Acid Generating Potential - AGP– Equal to - 1.37 * % SS

Sample Equation:– 2 FeS2 + 7 O2 + 2 H2O

2 FeSO4 + 4 H+ + 2 SO42-

Leads to Acid Rock Drainage

ANP

Acid Neutralization Potential - ANP– Equal to 3.67 * % CC

Sample Equation:– CaCO3 + 2 H+

+ SO42-

CaSO4 + H2O + CO2

NCV

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

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)64- + 2 SO4

2- + 4 OH-

Lime Hydrolyses– CaO + H2O Ca(OH)2

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

LIME USE AND COLUMN TESTS

Lime Addition to Oxide CN Extractions vs. NCV

y = -2.6874x + 5.066R2 = 0.5904

0

5

10

15

20

25

-5 -4 -3 -2 -1 0 1 2 3

NCV

Lim

e lb

s/to

n

Column Tests

Linear (Column Tests)

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

CYANIDE USE MODEL

Cyanide Addition to Oxide CN Extractions vs. NCV

y = -0.1534x + 0.505R2 = 0.477

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

-5 -4 -3 -2 -1 0 1 2 3

NCV

NaC

N lb

s/to

n

Column Tests

Linear (Column Tests)

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

GOLD EXTRACTION AND NCV

Percentage of Total Gold Extraction as a function of NCV

0

0.10.2

0.3

0.40.5

0.6

0.7

0.80.9

1

-5 -4 -3 -2 -1 0 1 2 3 4

NCV

Pe

rce

nt

of

To

tal

Go

ld E

xtr

act

ed

Column Tests

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]

LGL13645

Gold Quarry Blast Hole Information

GOLD QUARRY PIT - POLYGON

Gold Quarry Pit Newmont Mining Co. December 2,1999Bench: 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"

10.510,397

1.060.040.02-1.37

43%0.02

4550

0.04

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

LIME USE MODEL

Regression Model – ARD Stockpile OreLime (pounds/ton) =

6.68 – 7.68 * CC1.01 + 45.7 * SRO1.09

CC = % Carbonate Carbon

SRO = % S as SO4 (Sulfate Sulfur)

Lime Model for ARD Stockpiles

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

R2 = 0.7075

0

10

20

30

40

50

0 10 20 30 40

Stk Lime Model-1 #/ton

Lab

Lim

e #/

ton

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 10/16Shifts

Au

oz/t

on

So

luti

on

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 10/16Shifts

Au

oz/t

on

So

luti

on INPreg

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

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

NCV Value