As the world stands together to combat novel coronavirus 2019 (COVID-19), gold is continuing to support our communities and our economy.
As the resources industry works closely with Government and enforces required restrictions and health precautions, gold companies have made significant changes to their operations. With exports keeping our economy afloat while providing jobs in a time where many other sectors are forced to suspend operations, the industry is also ensuring our hospitals and health centres keep running and donations from gold companies can ensure that aid relief such as critical health services can continue to support society's most vulnerable.
Australia's gold industry is made up of a wide variety of businesses, big and small, and is working together to keep its workforce and wider public safe during this challenging time. This includes operating sites with crucial workers, adopting strict hygiene measures, and maintaining spatial distancing at all times.
Keeping Australia's gold industry running ensures the precious metal not only supports our economy during these times of hardship, but is available for essential uses in our everyday lives.
Gold is already saving lives: helping to treat cancer, providing a protective coating around pacemakers for patients with allergies to system components, as a critical component in medical diagnostic test kits, and may one day be part of a vaccine against COVID-19.
From ore to doré
Underground workers in high visibility clothing and hard hats is generally what springs to mind when we think about gold and gold mining. Yet mining is just one stage in the process of transforming this precious metal from its raw state to the glittering end product that is so valuable to our community right now.
Experience gold’s journey with us from dirt to market.
Exploration
Long before gold can be extracted from the ground, significant amounts of exploration and development take place to determine, as accurately as possible, the size of the deposit. In addition, mining companies provide expertise towards determining how to extract and process the ore in the most efficient, safe and responsible way possible.
Gold is a relatively scarce metal, but it can occur in many different types of rock and diverse geological environments. Early discoveries of gold relied on the luck of someone spotting a yellow glint in a stream or in a crack between rocks.
Today, the search for gold is much more systematic and precise, with geologists understanding more about how gold has formed. However, exploration is still a challenging and complex process. It requires considerable time, financial resources and expertise across many disciplines which can include geography, geology, chemistry and geophysics.
The process begins by reviewing historical data including mapping, sampling or drilling records. Public data also available such as broad scale geophysical data-sets from geological surveys, or Geoscience Australia, can help to define an initial target. Once a broad area is established the next steps involve geological mapping, sampling (soil, water, vegetation) and creating more detailed geophysical surveys.
This often leads to smaller, more exact targets which can then undergo the first stage of drilling. Once the geology of the site has been defined, the ore body can be modelled, and its feasibility assessed for mining to begin.
Update: Exploration is the lifeblood of the gold industry, with many small exploration companies requiring cost relief in order to survive this period, and exploration activities across the industry are expected to reduce or stop.
Mining
Development of a gold mine is the second stage of the process, which involves the planning and construction of the site and its associated infrastructure. Mining companies must also obtain appropriate permits and licences before they can start construction and adhere to the relevant legislation or guidelines within their State or Territory. Once a gold mine has been established, the company can begin extracting the ore. How it does this depends on the type of gold deposit.
Two commonly found gold mineralisation styles include lode (concentrations of gold found in veins of solid rock) and alluvial or placer (gold discovered on or close to the surface, often as accumulations in the sediments of a stream bed).
When the gold-bearing rock is located near the earth's surface, a mining company will use open pit techniques to extract it. The company begins by drilling a pattern of holes, which are then filled with explosives. After detonating the explosives to break up the ground, large chunks of earth can be loaded into colossal haul pack trucks.
Update: While tourism is currently halted to keep people safe from COVID-19, you can experience gold from the comfort of your home with the free Heart of Gold Australia app (available for iOS and Android). Be sure to add golden experiences to your travel bucket list when life returns to normal: visit the Super Pit lookout to witness a blast, take the journey yourself from mine to mint on Go West's Day Tour, or check to see if a gold mine in your area offers site tours!
Open pit gold mines are often made of multiple tiers that look like stairs, which take miners progressively deeper into the earth. When standing at the edge of an open pit gold mine, you can sometimes look down to see green and brown veins, indicating copper deposits, streaking the multi-tiered landscape.
If a lode deposit is farther beneath the earth's surface, underground mining methods are necessary, whereby miners drill a shaft into the ground to access the lode. They then dig long vertical tunnels, known as stopes, which extend from the top of the ore block to the bottom. After they drill and load explosives into the ore block, the miners detonate explosives which cause broken ore to fall to the bottom of the stope. Haul trucks are then loaded with the ore and take it up to the surface.
In gold-bearing countryside, prospectors typically look for gold where coarse sands and gravel have accumulated and where ‘black sands’ have concentrated and settled with the gold. Magnetite is the most common mineral in black sands, but other heavy minerals such as cassiterite, monazite, ilmenite, chromite, platinum-group metals, and some gemstones may also be present.
Gold is extremely resistant to weathering and when freed from enclosing rocks, is carried downstream as metallic particles consisting of ‘dust’, flakes, grains or nuggets. These gold particles in stream deposits are often concentrated on or near bedrock, due to moving downstream during high-water periods after the entire bed load of sand, gravel and boulders has been agitated. Prospectors can find these fine gold particles that collect in depressions or pockets in the sand and gravel where the water current is gentler.
Alluvial gold is mined differently to lode deposits. Miners scoop up sand, gravel and rock, then mix it with generous amounts of water. Because of its greater density, gold sinks faster than other materials and collects at the bottom. Placer mining can be undertaken in a variety of forms, including gold panning, ‘sluice-boxing’, hydraulic mining and dredging. All these techniques use gravity and water to separate the dense gold from the lighter sand and gravel.
Processing
Removing gold-bearing rock from the ground is just the beginning. Ore is stockpiled on the mine site while further mining takes place, before it is carted to a nearby processing plant. Some stockpiles can hold approximately 500,000 tonnes of ore at their peak!
To isolate gold, mining companies use a complex extraction process. The first step is breaking down large chunks of rock into smaller pieces. At a mill, gigantic machines called crushers reduce the ore to pieces no larger than standard road gravel. This gravel-sized material then enters rotating drums filled with steel balls. In these drums, the ore is ground down to a fine powder.
Next, mill operators will thicken the powder into a slurry using water, which gradually forms a pulp and is run through a series of leaching tanks. Once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes. Leaching dissolves the gold out of the ore using a chemical solvent. The most common solvent is cyanide, which must be combined with oxygen in a process known as carbon-in-pulp. There are very well-defined rules for the safe and responsible use of cyanide which are specified in the International Cyanide Code. As the cyanide and oxygen react chemically, gold within the pulp dissolves.
When workers introduce small carbon grains to the tank, gold adheres to the carbon. Filtering the pulp through screens separates the gold-bearing carbon. This then moves to a stripping vessel where a hot caustic solution separates the gold from the carbon. Another set of screens filters out the carbon grains, which can be recycled for future processing.
Finally, the gold-bearing solution is ready for electrowinning, a process which recovers the gold from the leaching chemicals. Operators pour the gold-bearing solution into a special container known as a cell. Positive and negative terminals in the cell deliver a strong electric current, which causes gold to collect on the negative terminals.
Smelting involves melting the negative terminals in a furnace at about 1,149 degrees Celsius (or 2,100 degrees Fahrenheit). Workers add a chemical mixture called flux to this molten material, which separates the gold from the metal used to make the terminals. Workers pour off the flux and then the gold. Moulds are used to transform the liquid gold into solid blocks called doré bars, which are relatively low-purity (typically containing between 60-90% gold) and are sent to refineries for further processing.
A polished product
Refining
Gold refineries begin the refining process with the rough doré bars that are receipted and stored. Inside a furnace room, the bars are loaded into clay-graphite crucibles and melted at 1,200 degrees Celsius (or 2,192 degrees Fahrenheit) within induction furnaces. Once molten, button-sized samples of the metal are extracted and sent to a laboratory for assay or analysis.
The two refining methods most often employed to derive pure gold are the Miller process and the Wohlwill process. In the Miller process, molten gold undergoes chlorination to remove any impurities. This chemical procedure involves the insertion into the molten metal of perforated graphite pipes through which a stream of chlorine gas is injected. The gas reacts with any iron, zinc and lead present to form a gaseous base metal chloride, which is extracted from the molten gold. Next to be removed is the liquid layer of silver or copper chloride.
The Miller chlorination process continues until all base metals have been isolated and removed from the melt, leaving gold with a minimum purity of 99.50%. This is either cast into 400 ounce London Good Delivery Bars or poured into anodes to undergo the next level of refining. This stage is the Wohlwill process, whereby multiple gold anodes are suspended from brass hooks and submerged into an electrolytic cell. The cell contains a corrosive liquid to which an electrical current is applied. Through the electrolytic process further impurities are collected and removed, leaving 99.99% pure gold. This gold is removed, washed, dried and returned to the furnace room to be transformed via a granulation process into pebble-sized fragments.
To achieve this, the gold is placed into another crucible for melting, before being poured into a second perforated vessel. Molten gold streams through the holes of this vessel into vats of water where the metal instantly solidifies into thousands of small granules.
Manufacturing
Precise amounts of these granules are used in the manufacture of gold ingots and smaller gold bars, ranging from half an ounce to one kilogram, to ensure the weight of each product is exact. After being melted and cast in moulds, which move through an inline tunnel induction furnace, the bars are cleaned and polished.
In the final step of the refining process, each bar is stamped with its weight, metal purity and a unique serial number along with a registered mark to ensure the bars are accepted and traded on international markets.
In addition to cast bars, gold is also manufactured into a wide variety of bullion and commemorative coins or medallions, trophies and awards, glittering displays of expertly crafted jewellery; or is used in a wide variety of applications across a number of industries such as dental, electronics, medical and aerospace. Gold is also used in the environment, consumed in food and is found in your blood. Find out more by playing the Discover Gold Game in the free Heart of Gold Australia app.
Exhibition
In the production of coins, gold bars are melted, rolled and re-rolled into strips of varying widths and thicknesses. From these strips, blanks are pressed, on which artists design coins for collectors of all ages and diverse interests. Their creativity is bought to life by talented staff using time-honoured skills alongside state-of-the-art robotics. The transformation of plain, flat gold disks into some of the world’s most innovative and exquisite coins involves using laser engraving machines to transfer intricate designs onto a piece of steel in reverse relief to create the die.
Each die is then meticulously refined by hand to produce a flawless finish. Two metal dies, one displaying the creative theme and the other exhibiting the Monarch’s effigy, are used to simultaneously strike both sides of a blank disk. To further enhance the appeal of select coins and medallions, artisans can apply additional treatments such as colour, gilding, antiquing or hand-set gemstones.
Following its evolution from raw material to finished product, the mined gold is now available to investors, collectors and the wider public thanks to the expertise of hundreds of Australia’s gold workers.
Self-isolation fun: Learn more glittering gold facts and experience gold from anywhere via the free Heart of Gold Australia app.