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 GQ - 10 microns ( u m) + – Pyrite - FeS 2 – Arsenopyrite - FeAsS GQ - 1-2 microns ( u m) Carbonates – Calcite - CaCO 3 – Dolomite - CaMg(CO 3 ) 2 – Siderite - FeCO 3 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 FeS 2 + 7 O 2 + 2 H 2 O 2 FeSO 4 + 4 H + + 2 SO 4 2- Leads to Acid Rock Drainage
ANP Acid Neutralization Potential - ANP – Equal to 3.67 * % CC Sample Equation: 2- – CaCO 3 + 2 H + + SO 4 CaSO 4 + H 2 O + CO 2
NCV Net Carbonate Value - NCV – Equal to ANP + AGP – NCV = 3.67 * % CC - 1.37 * % SS
EQUATIONS Cyanide Hydrolyses at pH < 10 – CN - + H 2 O HCN + OH - Cyanide Reaction with Sulfides – 2 FeS + 12 CN - + 5 O 2 + 2 H 2 O 4- + 2 SO 4 2- + 4 OH - 2 Fe(CN) 6 Lime Hydrolyses – CaO + H 2 O Ca(OH) 2
LIME USE MODEL Net Reaction – 4 FeS 2 + 8 CaO + 15 O 2 + 6 H 2 O 4 Fe(OH) 3 + 8 CaSO 4 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 Column Model: CaO (lbs/ton) = 5.066 - 2.6874 * NCV 25 20 Lime lbs/ton 15 10 y = -2.6874x + 5.066 R 2 = 0.5904 5 Column Tests Linear (Column Tests) 0 -5 -4 -3 -2 -1 0 1 2 3 NCV
CYANIDE USE MODEL Cyanide Addition to Oxide CN Extractions vs. NCV Column Model: NaCN (lbs/ton) = 0.505 - 0.1534 * NCV 1.8 Column Tests 1.6 Linear (Column Tests) 1.4 NaCN lbs/ton 1.2 1 0.8 0.6 y = -0.1534x + 0.505 R 2 = 0.477 0.4 0.2 0 -5 -4 -3 -2 -1 0 1 2 3 NCV
GOLD EXTRACTION AND NCV Percentage of Total Gold Extraction as a function of NCV Percent of Total Gold Extracted 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 Column Tests 0.2 0.1 0 -5 -4 -3 -2 -1 0 1 2 3 4 NCV
BLAST HOLE INFORMATION Gold Quarry Blast Hole Information Class LGL Low Recovery General Leach Drill Hole # 13645 99 016 Series # 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]
GOLD QUARRY PIT - POLYGON Gold Quarry Pit Newmont Mining Co. December 2,1999 Bench: 4550 SS%: 1.06 Poly Num: C245 OC%: 0.04 Mat'l Class: LGL CC%: 0.02 Tons: 10,397 NCV: -1.37 AuFA: 0.04 Lime #/ton: 10.5 AuAA: 0.02 AA/FA Ratio: 43% Spacing: 18' Drill Depth: 30' Hole Dia: 7.9"
LIME USE MODEL Net Reaction – 4 FeS 2 + 8 CaO + 15 O 2 + 6 H 2 O 4 Fe(OH) 3 + 8 CaSO 4 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 * CC 1.01 + 45.7 * SRO 1.09 CC = % Carbonate Carbon SRO = % S as SO 4 (Sulfate Sulfur)
Lime Model for ARD Stockpiles NA Stockpiles [Lab Lime vs Stk Lime Model-1] 50 Lab Lime #/ton 40 30 20 R 2 = 0.7075 10 0 0 10 20 30 40 Stk Lime Model-1 #/ton
NAL Gold Production NAL Gold Production - 3Q 2001 800 Au oz/ton Solution 700 600 500 400 300 6/18 7/8 7/28 8/17 9/6 9/26 10/16 Shifts
NAL Solution Grade NAL Preg Grade - 3Q 2001 INPreg 0.018 0.017 Au oz/ton Solution 0.016 0.015 0.014 0.013 0.012 0.011 0.01 6/18 7/8 7/28 8/17 9/6 9/26 10/16 Shifts
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
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