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
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+ + SO4
2-
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 + 5.066
R2 = 0.5904
0
5
10
15
20
25
-5 -4 -3 -2 -1 0 1 2 3
NCV
Lim
e lb
s/t
on
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 + 0.505
R2 = 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
Na
CN
lb
s/t
on
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
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-5 -4 -3 -2 -1 0 1 2 3 4
NCV
Pe
rce
nt
of
To
tal
Go
ld E
xtr
acte
d
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]
LGL
13645
Gold Quarry Blast Hole Information
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
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 Ore
Lime (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 #
/to
n
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/
ton
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/
ton
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