The Mineralogy of Gold and Silver and Importance (Joe Zhou)

The Mineralogy of Gold and Silver and Importance
on Ore Processing
Joe Zhou
Joe Zhou Mineralogy Ltd, Canada
joe.zhou.mineralogy@gmail.com
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.
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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
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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
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Introduction – Why Mineralogy?
Is bioleaching required for this ore?
2
1
3
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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
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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
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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)
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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
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Mineralogy: Objectives & Roles
Trouble shooting
Questions:
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•
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?
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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
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Mineralogy: Objectives & Roles
Trouble shooting
Freibergite (~18% Ag)
A
Freibergite (21% Ag), stephanite
(67%Ag) & Gn in Py
B
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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)
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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
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Gold Mineralogy
Minerals & Carriers
ature
& Carriers
of Gold
Gold
Mineralogy
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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
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Gold Mineralogy
Microscopic gold
A
B
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Gold Mineralogy
Submicroscopic gold
Major carriers: Arsenopyrite & Pyrite
1
2
Coarse Apy (17.6 ppm Au)
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<
3
Porous Apy (173.1 ppm Au)
<
Fine Apy (545 ppm Au)
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Gold Mineralogy
Surface gold
Carbonaceous matter – Main preg-robber
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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)
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Gold Mineralogy
Major factors affecting gold extraction
Liberation & Association
1
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Gold Mineralogy
Major factors affecting gold extraction
Liberation & Association
1
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Gold Mineralogy
Major factors affecting gold extraction
Liberation & Association
1
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Gold Mineralogy
Major factors affecting gold extraction
Liberation & Association
1
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Gold Mineralogy
Major factors affecting gold extraction
Liberation & Association
1
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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)
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Gold Mineralogy
Major factors affecting gold extraction
Grain size – too big or too small
Gravity?
Flotation?
Cyanidation?
Other options?
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Gold Mineralogy
Major factors affecting gold extraction
Coating & rimming
- affect flotation kinetics or retard gold dissolution in cyanidation
2
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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
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Gold Mineralogy
Major factors affecting gold extraction
Cyanicides and oxygen consumers
- consume excessive cyanide & oxygen
2
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Gold Mineralogy
Major factors affecting gold extraction
Preg-robbing – Adsorb gold cyanide complex from pregnant
solution
Surface gold on TCM (167ppm)
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Gold Mineralogy
Major factors affecting gold extraction
Submicroscopic gold
- pre-oxidation required prior to cyanidation
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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.
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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
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Silver Mineralogy
Forms & Carriers
Silver minerals:
• 200+ silver-bearing minerals
• 60+ minerals containing appreciable amount of Ag
• ~20 minerals are of economic significance
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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
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Silver Mineralogy
Forms & Carriers
Pyrargyrite Ag3SbS3
A
Stephanite Ag5SbS4
B
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Silver – Extractive Metallurgy
1. Base metals (Pb-Zn-Ag ores): Flotation+Smelting
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Silver – Extractive Metallurgy
2a. Precious metals (Ag &Ag-Au ores): Heap+Tank
ZHOU, J., MERMILLOD-BLONDIN, R. and COUSIN, World Gold Conference 2009
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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)
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Silver Mineralogy
Major factors affecting silver extraction
Liberation & Association:
A
B
Sph
Ba
Py
Gn
Sph
50µm
50µm
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Silver Mineralogy
Major factors affecting silver extraction
What caused Au and Ag losses?
A
B
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Silver Mineralogy
Major factors affecting silver extraction
Submicroscopic silver:
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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
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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
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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
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Low (ppm)
Low (ppm)
Low
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Optical Microscopy
What can it do?
One of the most important mineralogy tools:
A
B
Apy
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SEM-based Techniques
What does it offer?
Good for speciation & composition of rare minerals:
Py
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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)
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Microscopy & SEM-based Techniques
What do they offer?
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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
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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)
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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
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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
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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)
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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.
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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)
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Selection and Application of Min Techniques
What’s right & what’s not?
1
2
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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?
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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.
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Case 1: on-refractory Sulfide Gold Ore
Gold in Head & Tails:
A
B
Au
100µm
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Case 1: on-refractory Sulfide Gold Ore
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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.
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Case 1: on-refractory Sulfide Gold Ore
Process optimization:
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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.
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Case 2: Carbonaceous Sulfide Gold Ore
Gold deportment:
A
B
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Case 2: Carbonaceous Sulfide Gold Ore
Gold deportment:
Surface gold on TCM (167ppm)
Colloidal gold in TCM (8.3ppm)
Grain surface
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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:
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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).
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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
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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.
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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)
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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
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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.
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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
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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
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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
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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.
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Case 3: Ag-Pb-Zn Ore
Liberated galena & dyscrasite:
2
Dy
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Case 3: Ag-Pb-Zn Ore
Silver minerals associated with gangue:
3
4
Apy
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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.
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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
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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
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Acknowledgement
Thank you for your attention!
Questions?
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