The Mineralogy of Gold and Silver and Importance on Ore Processing Joe Zhou Joe Zhou Mineralogy Ltd, Canada [email protected] 1st International Metallurgical Conference Peru October 28, 2012 Lima, Peru About the Presentation This presentation is prepared for the short course of ADVANCES IN GOLD MINERALOGY AND MINERAL PROCESSING organized for the First International Metallurgical Conference Peru 2012. All rights are reserved by the author of this presentation. This presentation may not be reproduced in whole or in part, stored in a retrieval system or transmitted in any form or by any means, without the prior written permission of the author. JZMI Providing world class solutions to the minerals industry 1 Topics Introduction: Why mineralogy? Mineralogy: Objectives & Roles Major gold and silver ores and minerals Min factors affecting gold/silver metallurgy Methodology & techniques Case studies Summary 1 Providing world class solutions to the minerals industry JZMI Introduction – Why Mineralogy? Simplified met testing procedure for gold process development: Grinding Gravity Tail Gravity GRG Conc Flot’n Tail Flotation Flot’n Conc Grain Size <500µm <200µm <50-100µm <50µm <20µm Equipment Sluices Jigs Spirals Shaking tables Centrifugal concentrators Oxidative Pretreatment Regrind CN Tail Leaching Concentrat’n & Purificat’n JZMI Providing world class solutions to the minerals industry 2 2 Introduction – Why Mineralogy? Is bioleaching required for this ore? 2 1 3 4 Providing world class solutions to the minerals industry JZMI 3 Mineralogy: Objectives & Roles Prediction - Response of a new ore to various processes and most likely processing options - Estimated recovery of valuable minerals & grade of concentrate - Potential mineralogical factors affecting ore processing & metal extraction Trouble-shooting - Deportment of valuable minerals and deleterious elements in concentrate & tailings - Cause for valuable losses & opportunity for recovery improvement - Cause for high reagent consumption and opportunity for reagent consumption optimization JZMI Providing world class solutions to the minerals industry 4 3 Mineralogy: Objectives & Roles Prediction More free-milling More refractory Liberated, coarse-grained Locked, medium-grained 1 Locked, fine-grained Locked, submicroscopic 3 2 4 Au Gravity, Flotation, Cyanidation Fine grinding Cyanidation ± Flotation & Preoxidation Flotation, Fine grinding Preoxidation & Cyanidation Pre-oxidation & Cyanidation ± Flotation Providing world class solutions to the minerals industry JZMI 5 Mineralogy: Objectives & Roles Prediction Size Distribution of Liberated Gold Cyanide recoverable gold Flotation recoverable gold Gravity recoverable gold Distribution (%) 30 25 20 15 10 5 0 0-10 10-20 20-40 40-60 60-80 80-100 100-120 Grain Size (µm) JZMI Providing world class solutions to the minerals industry 6 4 Mineralogy: Objectives & Roles Trouble shooting Simplified process flowsheet for a Au-Ag ore: Grinding Flot’n Tail Flotation Flot’n Conc Regrind (P80=33µm) Gravity Tail Gravity Concent’n Gravity Conc Cyanidation CN Tail Providing world class solutions to the minerals industry JZMI 7 Mineralogy: Objectives & Roles Trouble shooting Questions: JZMI • Gold & silver speciation? • Submicroscopic gold? Where & how much? • Gold & silver liberation/association • Gold & silver size distribution? • What caused gold & silver losses, and how to improve the recoveries? Providing world class solutions to the minerals industry 8 5 Mineralogy: Objectives & Roles Trouble shooting ▼60-75% of lost gold 1 ▼12-22% of lost gold 2 Py ▼13-18% of lost gold 3 -Quartz JZMI 9 Providing world class solutions to the minerals industry Mineralogy: Objectives & Roles Trouble shooting Freibergite (~18% Ag) A Freibergite (21% Ag), stephanite (67%Ag) & Gn in Py B JZMI Providing world class solutions to the minerals industry 10 6 Mineralogy: Objectives & Roles Geomet modeling (Ref: R. Baumgartner et al, 2011: Building a Geometallurgical Model for Early-Stage Project Development – A Case Study from the Canahuire Epithermal Au-Cu-Ag Deposit, Southern Peru) JZMI Providing world class solutions to the minerals industry 11 JZMI 1. Placers 2. Quartz vein-lode ores 3. Oxidized ores 4. Silver-rich ores 5. Copper sulphide ores 6. Iron oxide copper-gold ores 7. Iron sulphide ores 8. Arsenic sulphide ores 9. Antimony sulphide ores 10.Bismuth sulphide ores 11.Telluride ores 12.Carbonaceous sulphide ores More free-milling More refractory Major Gold Ore Types Providing world class solutions to the minerals industry 12 7 Gold Mineralogy Minerals & Carriers ature & Carriers of Gold Gold Mineralogy JZMI Microscopic Gold (Visible Gold) Submicroscopic Gold (Invisible Gold) Surface-bound Gold (Adsorbed Gold) Gold Alloy Solid Solution Gold & Colloidal Gold Metallic Gold & Gold Complex ative gold (Au) Electrum (Au, Ag) Kustelite (Ag, Au) Auricupride (Cu3Au) Tetraauricupride (CuAu) Gold Tellurides Calaverite (AuTe2) Gold Antimonide Auristibite (AuSb2) Gold Bismuthide Maldonite (Au2Bi) Arsenopyrite (FeAsS) Pyrite (FeS2) Marcasite (FeS2) FeOx (Fe3O4 - Fe2O3) Loellingite (FeAs2) Chacopyrite (CuFeS2) Realgar (AsS) Enargite (Cu3AsS4) Acanthite (Ag2S) Clay minerals FeOx (Fe3O4 - Fe2O3) Stained quartz Carbonaceous matter (C-matter) Graphite Arsenopyrite (FeAsS) Pyrite (FeS2) Clay minerals Wood chips Activated carbon 13 Providing world class solutions to the minerals industry Gold Mineralogy Microscopic gold A B JZMI Providing world class solutions to the minerals industry 14 8 Gold Mineralogy Submicroscopic gold Major carriers: Arsenopyrite & Pyrite 1 2 Coarse Apy (17.6 ppm Au) JZMI < 3 Porous Apy (173.1 ppm Au) < Fine Apy (545 ppm Au) Providing world class solutions to the minerals industry 15 Gold Mineralogy Surface gold Carbonaceous matter – Main preg-robber JZMI Providing world class solutions to the minerals industry 16 9 Gold Mineralogy Major factors affecting gold extraction 1. 2. 3. 4. 5. 6. Liberation/locking Association Grain size Surface chemistry Coating & rimming Cyanicides & oxygen consumers 7. Preg-robbing (c-matter & more) 8. Refractoriness (submicroscopic gold & silver) 9. Slow-dissolving gold & silver minerals 10. Other deleterious minerals/toxic elements (As, Hg, asbestos) 11. Gangue mineralogy (clays & acid-forming minerals) JZMI Providing world class solutions to the minerals industry 17 Gold Mineralogy Major factors affecting gold extraction Liberation & Association 1 JZMI Providing world class solutions to the minerals industry 18 10 Gold Mineralogy Major factors affecting gold extraction Liberation & Association 1 JZMI Providing world class solutions to the minerals industry 19 Gold Mineralogy Major factors affecting gold extraction Liberation & Association 1 JZMI Providing world class solutions to the minerals industry 20 11 Gold Mineralogy Major factors affecting gold extraction Liberation & Association 1 JZMI Providing world class solutions to the minerals industry 21 Gold Mineralogy Major factors affecting gold extraction Liberation & Association 1 JZMI Providing world class solutions to the minerals industry 22 12 Gold Mineralogy Major factors affecting gold extraction Grain size – too big or too small • 44µm gold grain will take about 13 hours to dissolve under normal cyanide leach conditions • 150µm grains will take 48 hours or more (Fleming, 1992) JZMI Providing world class solutions to the minerals industry 23 Gold Mineralogy Major factors affecting gold extraction Grain size – too big or too small Gravity? Flotation? Cyanidation? Other options? JZMI Providing world class solutions to the minerals industry 24 13 Gold Mineralogy Major factors affecting gold extraction Coating & rimming - affect flotation kinetics or retard gold dissolution in cyanidation 2 JZMI Providing world class solutions to the minerals industry 25 Gold Mineralogy Major factors affecting gold extraction Slow-dissolving gold minerals - forms a passive aurostibate (AuSbO3) or bismuth hydroxide (Bi(OH)3) rims on the surface during cyanide leaching JZMI Providing world class solutions to the minerals industry 26 14 Gold Mineralogy Major factors affecting gold extraction Cyanicides and oxygen consumers - consume excessive cyanide & oxygen 2 JZMI Providing world class solutions to the minerals industry 27 Gold Mineralogy Major factors affecting gold extraction Preg-robbing – Adsorb gold cyanide complex from pregnant solution Surface gold on TCM (167ppm) JZMI Providing world class solutions to the minerals industry 28 15 Gold Mineralogy Major factors affecting gold extraction Submicroscopic gold - pre-oxidation required prior to cyanidation JZMI Providing world class solutions to the minerals industry 29 Major Silver Ore Types • Epithermal Au-Ag ore: Pascua-Lama in Chile-Argentina; Veladero in Argentina; Yanacocha in Peru; Pinos Altos in Mexico, Kupol in Russia; Hishikari in Japan; and Akoluk Turkey. • Gold-telluride ore: Cripple Creek in US; Kalgoorlie in AU. • Porphyry Cu-Au ore: Grasberg in Indonesia. • Polymetallic ore: Fresnillo and Peñasquito in Mexico; San Cristobal in Bolivia; Greens Creek and Lucky Friday in US; Brunswick and Laronde in Canada; McArthur River, Century, Lady Loretta, George Fisher, Hilton, Mt Isa and Cannington in Australia; Hindustan Zinc in India. JZMI Providing world class solutions to the minerals industry 30 16 Silver Mineralogy Forms & Carriers Forms: • Microscopic silver • Submicroscopic silver • Surface-bound silver Carriers: • Silver minerals in which silver occurs as main constituent • Other minerals in which silver occurs only in trace amount JZMI Providing world class solutions to the minerals industry 31 Silver Mineralogy Forms & Carriers Silver minerals: • 200+ silver-bearing minerals • 60+ minerals containing appreciable amount of Ag • ~20 minerals are of economic significance JZMI Providing world class solutions to the minerals industry 32 17 Silver Mineralogy Forms & Carriers Group ame Mineral ame Au-Ag Alloy Native silver, electrum, küstelite Sulphide Acanthite, japaite, stromeyerite Selenide Naumannite Antimonide Dyscrasite Telluride Stutzite, empressite, hessite, petzite, sylvanite Sulfosalt Stephanite, proustite, pyrargyrite, miargyrite, pearceite polybasite, samsonite, freibergite, unknown phases Halide Chlorargyrite, bromyrite, iodyrite JZMI 33 Providing world class solutions to the minerals industry Silver Mineralogy Forms & Carriers Pyrargyrite Ag3SbS3 A Stephanite Ag5SbS4 B JZMI Providing world class solutions to the minerals industry 34 18 Silver – Extractive Metallurgy 1. Base metals (Pb-Zn-Ag ores): Flotation+Smelting JZMI Providing world class solutions to the minerals industry 35 Silver – Extractive Metallurgy 2a. Precious metals (Ag &Ag-Au ores): Heap+Tank ZHOU, J., MERMILLOD-BLONDIN, R. and COUSIN, World Gold Conference 2009 JZMI Providing world class solutions to the minerals industry 36 19 Silver – Extractive Metallurgy 2b. Precious metals (Ag &Ag-Au ores): Tank leaching (RAJALA, J. and DESCHENES G.: Extraction of gold and silver at the Kupol Mill using CELP, World Gold Conference 2009) 37 Providing world class solutions to the minerals industry JZMI Silver Mineralogy Major factors affecting silver extraction Liberation & Association: A B Sph Ba Py Gn Sph 50µm 50µm JZMI Providing world class solutions to the minerals industry 38 20 Silver Mineralogy Major factors affecting silver extraction What caused Au and Ag losses? A B JZMI Providing world class solutions to the minerals industry 39 Silver Mineralogy Major factors affecting silver extraction Submicroscopic silver: JZMI Providing world class solutions to the minerals industry 40 21 Methodology - General Procedure Chemical analysis Crushed Ores or Met Products Modal mineralogy Gold Deportment Yes Is microscopic gold present? Speciation & Composition No Mineral type & morphology of sub-gold carrier Liberation & Association Quantification of sub-gold Grain size distribution of gold & host Concentration & liberation of subgold carrier Estimation of gold recoveries by G, F & CN Distribution of sub-gold • Gold mineralogical balance • Evaluation of min factors affecting gold recovery • Recommendations for process selection optimization Providing world class solutions to the orminerals industry JZMI 41 Commonly Used Techniques Category Technique Qualitative/Semi-Quant OM Semi-Quant Technique Optical Microscopy ADIS Automated Digital Image System XRD X-ray Diffracton SEM Scanning Electron Microscopy MLA Mineral Liberation Analyser Mineral ID & qualitative/semi-quant elemental analysis of individual particles High (%) High (%) High (%) Low (%) Quantitative mineral analysis of bulk Quantitative Evaluation of Materials samples and individual particles by Scanning Electron Microscopy EPMA Electron Probe Microanalysis PIXE Proton-induced X-ray Emission Low (ppm) D-SIMS Dynamic Secondary Ion Mass Spectrometry Low (ppm-ppb) Quantitative Laser Ablation Microprobe LAM-ICP-MS Inductively Coupled Plasma Mass Spectrometry JZMI Mineral ID & qualitative/semi-quant mineral analysis of bulk samples MDL High (%) QEMSCAN Quantitative Surface Analysis Application Mineral ID & qualitative/semi-quant mineral analysis of bulk samples Synchrotron Synchrotron Radiation Light Source TOF-LIMS Time of Flight Laser Ion Mass Spectrometry TOF-SIMS Time of Flight Secondary Ion Mass Spectrometry XPS X-ray Photon Spectrometry Low (%) Low (ppm) Quantitaive elemental analysis of individual particles Low (ppm-ppb) Low (ppm-ppb) Surface analysis of bulk material & individual particle Surface analysis of bulk material Providing world class solutions to the minerals industry Low (ppm) Low (ppm) Low 42 22 Optical Microscopy What can it do? One of the most important mineralogy tools: A B Apy JZMI Providing world class solutions to the minerals industry 43 SEM-based Techniques What does it offer? Good for speciation & composition of rare minerals: Py JZMI Providing world class solutions to the minerals industry 44 23 Microscopy & SEM-based Techniques What do they offer? Size Distribution of Gold Minerals (by surface area) 30.0% Liberated Locked 25.0% 20.0% 15.0% 10.0% 5.0% 0.0% <10 10-20 20-40 40-60 60-80 80-100 100-150 150-200 200-250 Size Range (µm) JZMI Providing world class solutions to the minerals industry 45 Microscopy & SEM-based Techniques What do they offer? JZMI Providing world class solutions to the minerals industry 46 24 D-Secondary Ion Mass Spectrometry What does it offer? Quantification of submicroscopic gold: Submicroscopic Gold Concentration (ppm) Sample ID Coarse Apy Porous Apy Fine Apy Coarse Py Porous Py CIL-1 302.19 294.64 301.88 2.83 1.75 CIL-2 247.27 405.70 533.74 5.07 4.04 1 2 3 0.51 ppm Au 5.6 ppm Au 72.4 ppm Au JZMI Providing world class solutions to the minerals industry 47 TOF-Laser Ion Mass Spectrometry What does it offer? Activators & depressants of gold flotation: 16 Cl Ag, Cl (arb. units) 14 12 10 8 Ag 6 4 2 0 C1 C2 C3 C4 Concentrate C5 C6 C7 o. (Ref: S. Chryssoulis & S. Dimov: Applied Surface Science 231-232 (2004), p. 265-268) JZMI Providing world class solutions to the minerals industry 48 25 TOF-Laser Ion Mass Spectrometry What does it offer? Activators & depressants of Au-bearing sulfide flotation: Jinya pyrite Effect of Cu and FeOx on flotation O+OH in Surface Layer (% counts/total counts) FeOx in Surface Layer (% counts/total counts) 100.0 Jinya pyrite Effect of AsS & oxidation on flotation rejected slow fast 10.0 0.1 1.0 10.0 Cu in Surface Layer (% counts/total counts) fast JZMI slow rejected 10.0 rejected 1.0 slow 0.1 fast 0.01 0.001 0.1 1.0 10.0 100.0 AsS in Surface Layer (% counts/total counts) fast slow rejected Providing world class solutions to the minerals industry 49 TOF-Secondary Ion Mass Spectrometry What does it offer? Gold distribution on TCM (Au=105 ppm): Optical image and TOF-SIMS elemental maps (Ref: Dimov et al., Proc of 48th Metallurgist - Mineralogy, Sudbury, Aug 23-26, 2009) JZMI Providing world class solutions to the minerals industry 50 26 Selection and Application of Min Techniques Each technique is designed for certain purposes, and has its advantages & limitations. Instrument can make mistakes and provide incorrect or incomplete results. Mineralogy techniques must be selected wisely & employed properly. A comprehensive approach is recommended. The quality of mineralogical data is not only determined by the techniques, but also determined by the project manager & instrument operator. People and experience are most important. JZMI 51 Providing world class solutions to the minerals industry Selection and Application of Min Techniques Energite – Tennantite story Mineral Cu As S Enargite 48.42 19.02 32.56 Tennantite 51.57 20.26 28.17 23 Cp Tnt Sp Apy Enargite (Cu3AsS4) Tennantite (Cu12As4S13) JZMI Providing world class solutions to the minerals industry 52 27 Selection and Application of Min Techniques What’s right & what’s not? 1 2 Providing world class solutions to the minerals industry JZMI 53 Case 1: on-refractory Sulfide Gold Ore About the ore: • 1.9 – 7.7 g/t Au • 4 – 6% sulfides (pyrite & marcasite) • 85% passing 75µm • 80-84% Au recoveries Questions: • Submicroscopic gold? • Preg-robbing by pyrite & chalcopyrite? • What caused gold losses, and how to improve the gold recovery? JZMI Providing world class solutions to the minerals industry 54 28 Case 1: on-refractory Sulfide Gold Ore Gold deportment: • Gold occurred as both microscopic gold & submicroscopic gold (90-95% MG & 5-10% SMG). • Microscopic gold occurred as liberated particles (approx. 50%) and locked inclusions. • Attached & locked gold accounted for 50% (including 45% in pyrite/marcasite and 5% in NOP). • Gold grains range from less than 1µm to 350µm. Coarse gold grains were well liberated and are recoverable by gravity and/or cyanidation. • Liberated gold accounted for 30% in CN tail. JZMI 55 Providing world class solutions to the minerals industry Case 1: on-refractory Sulfide Gold Ore Gold in Head & Tails: A B Au 100µm JZMI Providing world class solutions to the minerals industry 56 29 Case 1: on-refractory Sulfide Gold Ore JZMI Providing world class solutions to the minerals industry 57 Case 1: on-refractory Sulfide Gold Ore Conclusions/recommendations: • Locking of gold in pyrite and incomplete dissolution of liberated gold were two major reasons for gold losses. • To recover the gold locked in pyrite (and other minerals), the ore needs to be ground finer. • To completely dissolve the residual liberated gold, extended leaching time and/or higher cyanide concentration is required. • Gravity concentration is recommended to recover coarse gold and reduce the cyanide consumption. JZMI Providing world class solutions to the minerals industry 58 30 Case 1: on-refractory Sulfide Gold Ore Process optimization: JZMI • 50,000 tonne campaign through the plant • 90.1% from a 2.61g/t feed grade, a vast improvement on previous campaigns of 81-84% recoveries • Finer grind and higher cyanide in both mill circuit and tanks together with oxygen addition • 71% GRG value. To add a gravity circuit. 59 Providing world class solutions to the minerals industry Case 2: Carbonaceous Sulfide Gold Ore Gold deportment: A B JZMI Providing world class solutions to the minerals industry 60 31 Case 2: Carbonaceous Sulfide Gold Ore Gold deportment: Surface gold on TCM (167ppm) Colloidal gold in TCM (8.3ppm) Grain surface JZMI Providing world class solutions to the minerals industry 61 Case 2: Carbonaceous Sulfide Gold Ore Refractory Ore Pretreatment Refractory ores require a pretreatment for acceptable gold extractions by subsequent cyanide leaching. Some of the pretreatment processes are: JZMI Providing world class solutions to the minerals industry 62 32 Case 2: Carbonaceous Sulfide Gold Ore Refractory Ore Pretreatment Refractory ores require a pretreatment for acceptable gold extractions by subsequent cyanide leaching. Some of the pretreatment processes are: o o o o o Roasting Pressure Oxidation (Acid or Alkaline) Biooxidation/bioleaching Chlorination Nitric Acid Oxidation Ammonium thiosulfate leaching Chemical Oxidation Ultrafine grinding Pre-aeration These pretreatment options are applicable to whole ore or flotation concentrates. The choice of pretreatment option depends on the economics for a particular ore type treated (sulfides, carbonates and carbonaceous matter). JZMI Providing world class solutions to the minerals industry 63 Case 2: Carbonaceous Sulfide Gold Ore Roasting is one of the pre-oxidation processes used for sulfidic and/or carbonaceous refractory gold ores, and base metal ores. The objective of roasting is to: Oxidize sulfide minerals to produce a porous calcine Burn preg-robbing organic carbon JZMI Providing world class solutions to the minerals industry 64 33 Case 2: Carbonaceous Sulfide Gold Ore Roasting is one of the pre-oxidation processes used for sulfidic and/or carbonaceous refractory gold ores, and base metal ores. The objective of roasting is to: Oxidize sulfide minerals to produce a porous calcine Burn preg-robbing organic carbon Preg-robbing carbonaceous material (organic carbon containing matter) is oxidized to carbon dioxide and the calcine is therefore rendered not preg-robbing. 2C(s) + O2 = 2CO 2CO + O2 = 2CO2 Carbonates decompose to metal oxide and carbon dioxide during roasting. CaCO3 = CaO + CO2 MgCO3 = MgO + CO2 If carbonates are present in >2% CaCO3 the evolved carbon dioxide can form an unreactive gas blanket over the roaster bed preventing oxidation. JZMI Providing world class solutions to the minerals industry 65 Case 2: Carbonaceous Sulfide Gold Ore Oxidation of Sulfide Minerals: Two-stage roasting: • Pyrite, marcasite and arsenopyrite decompose to pyrrhotite: FeS2 ⇌ FeS(s) + S(g) FeAsS(s) ⇌ FeS(s) + As(g) • Pyrrhotite is then oxidized to magnetite, and subsequently to hematite, in a second stage of roasting: 3FeS + 5O2 ⇌ Fe3O4 + 3SO2 4Fe3O4(s) + O2(g) ⇌ 6Fe2O3(s) JZMI Providing world class solutions to the minerals industry 66 34 Case 2: Carbonaceous Sulfide Gold Ore Impact of oxidation and texture of FeOx on gold extraction 1 2a 1ST Roasting 540-570ºC 540ºC 2b 3a 2nd Roasting Major Carriers of Submicroscopic Gold Disseminated fine FeOx inclusions (3b) (carrying up to 40% Au) 2. Free maghemite (4a) (15-35% Au) 3. Rimmed FeOx (5a) (5-15% Au) 4. Porous hematite (6a) (5-15% Au) 5. Fine pyrite (2b) (2-4% Au). 4a 1. 6a 3b 5a 40 µm JZMI Providing world class solutions to the minerals industry 67 Case 2: Carbonaceous Sulfide Gold Ore Pressure oxidation (or autoclaving) is another pre-oxidation process used for sulfidic refractory gold ores & base metal ores. The objective of autoclaving is to: Oxidize sulfide minerals and render the gold leachable by cyanide Carried out at either acid or alkaline media at elevated temperature and pressure (220oC & 140-180 kPa oxygen partial pressure (3300 kPa total pressure). Refractory sulfide ores and concentrates containing greater than ~4% sulfide sulfur can be treated autogeneously to liberate gold and render it amenable to cyanide leaching. Materials containing less than ~4% sulfide sulfur may require additional heat to be added in the form of steam for effective pressure oxidation. JZMI Providing world class solutions to the minerals industry 68 35 Gold: Predictive Metallurgy # Ore Type Gold Deportment Predictive Metallurgy 1 Placers Normally coarse-grained (50-100µm) and easily liberated or Gold can be recovered by direct leaching w/wo gravity has been liberated prior to processing. 2 Quartz vein-lode ores Occurs mainly as native gold, some tellurides, aurostibite Gold can be recovered by direct leaching w/wo gravity. Fine grinding is required and maldonite. Commonly occurs as liberated gold particles when gold occurs as tiny inclusions quartz. Flotation may be applicable when gold but may have some disseminated gold. is associated with sulfide minerals. 3 Oxidized ores Gold can be recovered by direct leaching w/wo gravity. The presence of clays can Gold usually occurs as either liberated grains or inclusions in have significant impact on processing. Carbonate minerals can affect pH control, Fe-oxide, and the degree of gold liberation is generally and oxide copper minerals may interfere gold leaching and recovery. Flotation increased with oxidation. may be applicable to some ores. 4 Gold is often recovered by leaching w/wo gravity. The presence of Ag-rich electrum can have important process implications due to its tarnishing. Flash Gold commonly occurs as electrum, although küstelite may Silver-rich flotation may be considered to avoid the formation of secondary rim which often be present in some ores. Native silver, acanthite and silver ores cause gold and silver losses. Finer grinding and high cyanide dosage may be tellurides may be present. required when gold is associated with slow-leaching silver minerals such as pyrargyrite (Ag3SbS3), proustite (Ag3AsS3) and stephanite (Ag5SbS4). Flotation is the principal process for pre-concentration of the gold and Cu sulphides. Leaching of tailings may be required. When gold is associated with pyrite, a pyrite concentrate can be produced by flotation. 5 6 Gold occurs as coarse liberated grains and also fine-grained In gold ores containing significant secondary copper sulphide minerals (such as Copper inclusions in pyrite and copper sulfides. Auricupride sulfide ores (Cu3Au) and tetraauricupride (CuAu) may be present in the covellite, digenite, chalcocite), gold recovery by cyanidation is usually uneconomic because the reactions of these minerals will cause excessive reagent leach cap or supergene zone of porphyry Cu-Au ores. consumption which increases the cost of production as well as decreasing gold recovery. Therefore, gold recovery via a copper flotation concentrate or chemical pretreatment to remove copper is required. Flotation is the principal process for pre-concentration of the gold and copper Iron oxide Gold is often associated with copper minerals, and to a lesser sulphides. In addition to copper minerals, gold also occurs in hematite or other copper-gold extent, with iron oxides (mainly hematite). Submicroscopic gangue as tiny inclusions and submicroscopic gold and causes gold loss. The ores gold may occur in hematite as well. presence secondary copper sulphide minerals may cause excessive reagent Providing world class solutions toofthe minerals industry (IOCG) consumption and lower gold recovery. JZMI 69 Gold: Predictive Metallurgy # 7 Ore Type Iron sulfide ores Gold Deportment Predictive Metallurgy Gold in non-refractory gold ores can be recovered by flotation w/wo Gold occurs as liberated particles, attachments to gravity, and followed by cyanidation of flotation tails. Finer grinding and and inclusions in sulfide (commonly in pyrite, and pretreatment will be required when gold occurs as fine-grained inclusions less commonly in marcasite and pyrrhotite), and in sulfide minerals. For refractory sulfide ores, pretreatment is often as submicroscopic gold in sulfide minerals. required prior to leaching. High As content in the final conc will incur significant penalties and has to Gold occurs as liberated particles and inclusions, be reduced, which may result in a loss of a significant proportion of the and submicroscopic gold in arsenopyrite and gold. The association of gold with arsenic must be determined at the early oxidized products. stage of a project. Gold occurs mainly as native gold, with a minor Sb-bearing 9 to moderate amount of aurostibite (AuSb2), either sulfide ores liberated or locked in sulfides. Gold occurs mainly as native gold, with minor to Flotation w/wo gravity, followed by regrinding of concentrate and Bi-bearing moderate amounts of maldonite (Au2Bi). leaching of flotation tails. Aurosibite, maldonite and most gold tellurides 10 sulfide ores Submicroscopic gold can also be present in dissolve slowly during leaching and may cause gold loss due to incomplete sulfides. dissolution. Pretreatment may be required prior to leaching. Gold occurs as native gold and gold tellurides, 11 Telluride ores either liberated or locked in sulfides. Submicroscopic gold may be present. Leaching w/wo flotation. Gravity is rarely employed. Pretreatment is Gold occurs mainly as fine-grained gold particles Carbonaceous required prior leaching. Preg-robbibg by carbonaceous material and 12 and submicroscopic gold in sulfides, and also as sulfide ores incomplete oxidation ofAu-bearing sulfide minerals are the major causes surface gold on C-matter and iron oxide. for gold losses. 8 Arsenic sulfide ores JZMI Providing world class solutions to the minerals industry 70 36 Case 3: Ag-Pb-Zn Ore About the ore: • Grade: Ag ~400g/t; Pb 9.1%; Zn 3.3%. • Ag – freibergite, dyscrasite, pyrargyrite acanthite, native silver. • Pb – galena & Zn – sphalerite. • Ag recovery : 85-88% (60g/t in Pb Tail & 48 g/t in Zn Tail). Where is the lost silver and what it looks like? Plant Feed P80 @ 75µm Pb Circuit Pb Conc Pb Tail Zn Circuit Zn Conc Final Tail JZMI Providing world class solutions to the minerals industry 71 Case 3: Ag-Pb-Zn Ore Silver deportment: • Silver occurred mainly as freibergite, dyscrasite, pyragyrite and galena with a moderate amounts of acanthite & native silver. JZMI Providing world class solutions to the minerals industry 72 37 Case 3: Ag-Pb-Zn Ore Liberated galena & dyscrasite: 2 Dy JZMI 73 Providing world class solutions to the minerals industry Case 3: Ag-Pb-Zn Ore Silver minerals associated with gangue: 3 4 Apy JZMI Providing world class solutions to the minerals industry 74 38 Case 3: Ag-Pb-Zn Ore Silver deportment: • Silver occurred mainly as freibergite, dyscrasite, pyragyrite and galena with a moderate amounts of acanthite & native silver. • Silver in Pb Tail (60 g/t Ag): 15% of the lost silver (or 2.2% of head assay) was liberated and associated with Gn, and can be recovered in lead circuit without further grinding. • Silver in Zn Tail (48 g/t Ag): 15% - 20% of the lost silver (or 1.8% of head assay) was locked in Gn, Sph and other sulphide minerals, and is recoverable by flotation in zinc circuit. • A total of 4% silver recovery is expected by optimizing the plant operating conditions. JZMI Providing world class solutions to the minerals industry 75 Summary: Benefits of Using Mineralogy A process mineralogy study should be conducted: Prior to the start or at early stage of a project as a predictive tool Whenever it is needed as a trouble shooting tool • Exploration • Scoping study • Prefeasibility study • Feasibility study • Plant operation & process optimization JZMI Providing world class solutions to the minerals industry 76 39 Do I eed a PGeo & QP in Mineralogy? A Mineralogist with hands-on experience A licensed Professional Geoscientist (P.Geo.) A Qualified Person (QP) in Mineralogy JZMI Providing world class solutions to the minerals industry 77 Acknowledgement Thank you for your attention! Questions? JZMI Providing world class solutions to the minerals industry 78 40