L6 - Gold Flashcards
Why is gold considered valuable?
The human race continues to believe it is valuable for various reasons.
What events have historically influenced the price of gold in USD?
- High inflation, Iranian revolution, and war in Afghanistan.
- Reduction in central bank gold reserves.
- Financial crises.
US Federal Reserve stimulus reductions. - Hedge against global uncertainty (e.g., COVID-19).
- Chinese demand and inflation fears.
Where are the largest global gold reserves found?
25% in Australia.
23% in Russia.
10% in South Africa
Which countries lead in gold mine production?
17% in China.
14% in Australia.
14% in Russia.
5% in South Africa.
33% from others.
What are the key chemical properties of gold?
- Reacts at ambient temperatures with aqua regia, CN⁻, and S₂O₃²⁻.
- Reacts at high temperatures to form AuHS or AuCl₂ in aqueous solutions
What are the main types of gold deposits?
Magmatic-hydrothermal fluids: Epithermal, volcanogenic massive sulfides, porphyries.
Hydrothermal fluids: Orogenic deposits.
Meteoric sedimentary fluids: Alluvial placers.
What is the Barberton greenstone belt?
Located in South Africa, it is the core of an old orogenic crater.
Contains ultramafic, mafic rocks, and shallow marine deposits.
What is the setting of Barberton gold deposits?
Gold mines clustered around Barberton.
Found near major faults with pyrite-rich zones
What is the gold content in Barberton deposits?
Veins hundreds of meters long, less than 1 meter wide.
Average grade is 8 g/t, with some up to 60 g/t.
How is gold formed in Barberton deposits?
Low-salinity fluids from 10-20 km depth.
Devolatilization of water-bearing minerals during regional metamorphism.
Gold precipitates via wall rock alteration, boiling, mixing with meteoric water, or temperature drops.
What are magmatic-hydrothermal gold deposits?
Epithermal deposits: Form at shallow crustal depth from local fluid circulation.
Porphyries: Form at greater depths with magmatic-hydrothermal fluids.
What is the Witwatersrand gold deposit?
Produced 50,000 tons of gold (1886-2004).
Once held 46% of global reserves; now only 6%.
Located in a sedimentary basin near Johannesburg.
What is the depositional system of Witwatersrand gold?
Braided fluvial system with sediment transport from greenstone belts and granitic crust.
Gold concentrated in conglomerate reefs and paleo-channel deposits.
How did low atmospheric oxygen affect Witwatersrand deposits?
Formed 2.9 billion years ago under low oxygen conditions, preserving detrital pyrite and uranium
How do placer gold deposits form?
Result from density separation of heavy minerals like gold during sedimentary transport.
What are key exploration techniques for gold?
Geochemical and structural mapping.
Geophysical surveys (magnetics, resistivity, gravity, seismic).
Drilling
What are the current economic thresholds for gold mining?
Underground: 4-10 g/t
Open-pit: 1-4 g/t
How is gold beneficiated using mercury?
- Mercury amalgamation dissolves gold to form an amalgam.
- The amalgam is boiled or treated with acid to recover solid gold.
- Mercury use is toxic and has environmental risks.
How is gold produced via cyanidation?
- Gold is dissolved in a cyanide solution (e.g., KCN/NaCN).
- Gold is recovered by adding zinc or activated carbon.
- Cyanidation offers higher recovery but risks groundwater contamination.
What are other gold production methods?
Roasting: Converts sulfides to Fe-oxide, allowing gold leaching with cyanide.
Bioleaching: Oxidizes sulfides for heap leaching or directly recovers gold
What are the environmental impacts of gold mining?
Acid mine drainage from roasting.
Cyanide and mercury pollution of groundwater.
Radioactive waste from tailings.
Greenhouse gas emissions from mining operations.
What are the main types of gold deposits summarized?
Magmatic-hydrothermal: Epithermal, porphyries.
Hydrothermal: Orogenic deposits.
Sedimentary: Placers.
Why is gold processing environmentally sensitive?
Most methods produce toxic byproducts (e.g., cyanide, mercury, acid drainage).
Tailings and waste management pose long-term risks.
