Handbook of Gold Exploration and Evaluation

Eoin Macdonald

• Publisher: Woodhead Publishing
• Year: 2007
• ISBN:
  9781845692544
• Topic: Technology & Engineering
• Subtopic: Mining Engineering
• Index: Technology & Engineering

Designed for geologists and engineers engaged specifically in the search for gold deposits of all types and as a reference for academics in higher schools of learning, Handbook of gold exploration and evaluation provides principles and detailed explanations that underpin the correct interpretation of day-to-day experience in the field. Problems are addressed with regard to the analysis, interpretation and understanding of the general framework within which both primary and secondary gold resources are explored, developed and exploited.Handbook of gold exploration and evaluation covers a comprehensive range of topics including the nature and history of gold, geology of gold ore deposits, gold deposition in the weathering environment, sedimentation and detrital gold, gold exploration, lateritic and placer gold sampling, mine planning and practise for shallow deposits, metallurgical processes and design, and evaluation, risk and feasibility.

• Covers the nature and history of gold
• Addresses problems with regard to the framework in which gold resources are explored, developed and exploited
• Discusses topics including the geology of gold ore deposits, metallurgical processes and design, evaluation, risk and feasibility

1

Nature and history of gold

Gold (Au) is a transition metal between Ag and Rg in the chemical series of the Periodic Table. Its atomic number is 79, and atomic mass 196.96655 (2) g/mol, and has only one stable isotope number 197. The gold isotype ¹⁹⁸Au (half-life 2.7 days) is used in some cancer treatments. The metal has been known and prized as an object of beauty and for its unique properties of chemical stability, electrical conductivity, malleability and ductility (trivalent and univalent) since mankind’s earliest awakenings. As a standard of value against which to appraise the costs of labour, goods, currency and national economy, it has been the standard of many currencies since the world’s first coinage in Lydia between 643 and 630BC. The name for gold is derived from the historic English word ‘geolo’, for yellow and the chemical symbol for gold Au, from the Latin name for gold ‘aurum’ (glowing dawn).

1.1 Gold mineralogy

Natural resources of elemental gold are mainly contained in the mineral gold (plus 85%Au) and in seawater. The oceans contain a major resource of gold in solution but individual estimates are variable, depending upon the location of samples, which appear to range in gold content from as low as 0.1 to as high as 2.0 ppb by weight. Emery and Schlee (1963) note gold grades in the top 10 m of sediments in the Atlantis 2 Deep between 5 and 10 ppm. However, attempts to recover gold from seawater on a commercial scale have so far failed, mainly because of the large quantities of water involved; ion exchange appears to offer the present best avenue for research. Salt, bromine and magnesia are recovered from seawater on a large scale hence the oceans must be regarded as a potential gold source of major proportions. Element associations are broadly classified on the basis of their affinities for metals, sulphides, silicates or gas phases, and are referred to in Table 1.1 as siderophile, chalcophile, lithophile and atmophile respectively (from Goldschmidt, 1922). Basically a siderophile element, gold has some characteristics that relate it to chalcophile group elements. The general ubiquity of gold is demonstrated in Table 1.2, which shows common element associations in a range of ore deposit types.

Table 1.1

Goldschmidt’s geochemical classification of the elements

Siderophile	Chalcophile	Lithophile	Atmophile
Fe Co Ni	Cu Ag (au)*	Li Na K Rb Cs	H N (C) (O)
Ru Rh Pb	Zn Cd Hg	Be Mg Ca Sr Ba	(F) (Cl) (Br) (l)
Re Os lr Pt Au	Ga ln Tl	B Al Sc Y Rare earths	Inert gases
Mo Ge Sn C P	(Ge) (Sn) Pb	(C) Si Ti Zr Hf Th
(Pb) (As) (W)	As Sb Bi	(P) V Nb Ta
	S Se Te	O Cr WU
	(Fe) (Mo) (Re)	(Fe) Mn
		F Cl Br I
		(H) (Tl) (Ga) (Ge) (N)

^* Parentheses around a symbol indicate that the element belongs primarily in another group, but has some characteristics that relate it to this group.

Table 1.2

Common element associations in some different deposit types (McQueen, 1997)

Element association	Deposit type
Au-As-Sb (CO2-Si)	Mesothermal. slate-hosted quartz-gold veins (e.g. Bendigo, Central Victoria).
Au-As-W-Ag-Sb-Te- ± Cu-Pb-Mo (CO2-S)	Archaean greenstone-hosted lode gold deposits (e.g. Kalgoorlie, Eastern Goldfields WA).
Ag-Au-As-Sb-Te ± Hg-Mn (S-Si)	Epithermal gold-silver veins in volcanic host rocks (e.g. Golden Cross, NZ, Gidginburg, NSW).
Au-As-Hg-Fe ± Sb-Te TI (Si-S)	Carlin-type disseminated pyrite-arsenopyrite gold-bearing systems.
Sb-Au (Si-S)	Quartz-stibnite veins in metasediments (e.g. Costerfield, Vic., Hillgrove NSW).
Au-Fe-As-Cu ± Zn (S-Si)	Quartz-sulfide veins containing Au associated with pyrite and arsenopyrite.
Hg-Cu-Au-S ± As-Bi-Co	Associated with ultrabasic rocks.
Cu-U-Au-Ag-REE (S-F)	Hydrothermal hematitic breccia complexes (e.g. Olympic Dam, SA).
Pb-Zn-Ag ± Cd-Cu (S)	Structurally controlled lead-silver veins and hydrothermal replacement bodies (Northhampton WA).
Fe-Pb-Zn-Cu-Ag ± Hg-Sb-Au (S)	Stratabound volcanic-hosted massive sulfide deposits (e.g. Woodlawn, NSW, Roseberry, Que River, Tas.).
Fe-Pb-Zn-Ag, Mn-Ba-TI ± Cu-As-Sb (S)	Shale-hosted stratiform lead-zinc deposits (e.g. McArthur River, NT).
Fe-Pb-Zn-Ag-Cu (S) Fe-Cu-Au ± Pb-Zn (S)	Turbidite-hosted sulfide vein systems (e.g. Cobar deposits, NSW).
Fe-Cu-Au ± Ag-Bi-Mo Te (S) Fe-Mo (S)	Porphyry copper-gold and porphyry molybdenum deposits in subvolcanic acid to intermediate rocks (e.g. North Parkes, NSW, Climax, Co.).
Cu-Au-Bi(S) Fe-Cu-Pb-Zn-Ag W-Mo ± Cu-Pb-Zn-Bi-As	Proximal contact replacement skarns (e.g. Browns Creek, NSW, Mt Biggendon, Qld, Old Cadia, NSW, King Island, Tas.).
Fe-Sn ± As-Cu-Zn (O-S-F)	Replacement tin skarns in carbonate units (e.g. Mt Bischoff, Renison, Tas.).
Cu-Pb-Zn-W-S	Sulfides and scheelite occurring within sediments and volcanic rocks.
Fe-Ni-Cu-Co-PGE (S)	Nickel-copper sulfide deposits in mafic/ultramafic rocks (e.g. komatiite-hosted deposits, Kambalda WA, Sudbury, Canada).
Ni-Co ± Mn (Si-O)	Ni laterites on ultramafic rocks (e.g. Greenvale, Qld, New Caledonia).
Cr-PGE-Ni-Cu (S-O)	Chromite lenses in layered ultrabasic rocks (e.g. Merensky Reef, S. Africa).
Fe-Ti-V (O)	Magnetite bands in layered mafic bodies and anorthosites (e.g. Bushveld Complex, S. Africa).
REE-Zr (CO2-P)-Nb-Ta-Cu	Carbonatite deposits (e.g. Mt Weld, WA, Palabora, S. Africa).
Cu-U-V ± Se-As-Mo-Pb	Redox front uranium deposits in terrestrial sediments (e.g. Lake Frome deposits, S. Africa).
U-V (K)	Calcrete uranium deposits (e.g. Yeelirrie, WA).
U-Au-Cu ± Zn-Sn-Pb-Bi, Pt-Pd	Stratabound and structurally controlled uranium-gold deposits in carbonaceous sediments (e.g. Alligator River, NT).
Sn-W-As-B ± Pb-Zn-Cu (O-S)	Porphyry style tin deposits (e.g. Ardlethan, NSW).
Sn-W-Mo-Cu-Pb-Zn-Au (F-B-Si-S)	Zoned vein systems in and around granites (e.g. Zeehan, Tas., Emmaville, NSW).
Ta-Nb-Sn-Li-Be (Si)	Pegmatites and complex veins associated with granites.
AI ± Nb-Ti-Ga (O)	Bauxite deposits.

1.1.1 Elemental and native gold

The following physical properties of gold are based on normal temperature and pressure (20 °C @ 1 atm).

• Coefficient of linear thermal expansion
– 0.0000142 cm/cm/°C (0 °C)

• Conductivity
Electrical: – 0.452 × 10⁶/cmΩ
Thermal: – 3.17 W/cmK

Electronic processes create heat, and gold is essential to transfer heat easily from delicate instruments. A 35% gold alloy is used in the main engine nozzle of the space shuttle, where temperatures can reach 3300 °C. It is the most tenacious and long-performing material available for protection at these temperatures.

• Reflectivity – high-purity gold reflects up to 99% of infra-red rays. This makes it ideal for heat and radiation reflection, as in life-saving face shields for astronauts and fire fighters.

• Density – 19.32 g/cc @ 300 K

• Melting point – 1064.58 ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Foreword
• Preface
• Acknowledgements
• 1: Nature and history of gold
• 2: Geology of gold ore deposits
• 3: Gold deposition in the weathering environment
• 4: Sedimentation and detrital gold
• 5: Gold exploration
• 6: Lateritic and alluvial gold sampling
• 7: Mine planning and practice
• 8: Metallurgical process and design
• 9: Evaluation, risk and feasibility
• Appendix I: Field laboratories and techniques
• Appendix II: Variogram structural analysis
• Appendix III: Sitework testing
• Appendix IV: Gold economics
• References and further reading
• Index