The shiny yellow metal that is made into jewelry and attracts commodity investors is highly sought-after. But do you know how gold is mined and produced?
Mining for gold begins with finding it in the right place in the right quantities. While gold is present in the earth’s crust, the concentrations are very low, making it commercially unviable to mine and extract gold.
Gold mining companies seek geographical regions where the concentration of gold is high enough to mine and refine it into pure bullion. High concentrations can be present close to earth’s surface or deep inside the ground where gold is present along with other important metals like silver and copper. Depending on the location of the gold, mining companies employ the mining process.
Usually, these companies use geologists to study the type of rock formations to ascertain whether gold is present. To determine the exact site, core samples are extracted from the earth and studied and analyzed. If these samples contain high concentrations of gold, the mining company begins the mining process.
Mining for Gold
Gold mines can be open-pit mines or underground mines. Usually, a mining company will press the button for an open-pit mine when the gold is located relatively close to the earth’s surface. Such a mine does not have a profound effect on the environment and is also considered economically viable.
The mining company digs a massive hole in the ground. This is done using explosives and heavy machinery. The extracted ore from the open-pit mine is then taken to a processing plant where the gold is separated from other minerals and metals.
In case the gold is located deep in the ground, the mining company will press the button for an underground mine. This requires digging of shafts that then branch out into tunnels that lead to the place where gold deposits are present. Once these are built, the extraction and hauling of the ore begin.
Gold Extraction Process
After the ore has been extracted from the mine, it needs to be processed to separate the gold from the rest of the ore. Here, large chunks of ore are taken and reduced to smaller sizes, until the ore has the same consistency as the sand you find on a beach. Then cyanide is added to the mix, transforming it to a muddy and watery solution.
You may wonder why mining companies use cyanide. When a weak cyanide solution combines with air, it has the ability to dissolve gold, thereby separating it from other minerals and metals present in the ore.
The fluid is then pumped out of the mix and the remaining mixture is transferred to an agitation tank where any remaining cyanide solution continues the gold extraction process. Water and air are pumped into these agitation tanks so that the gold dissolves in the water. This causes the heavier metals to sink to the bottom of the agitation tank while the solution containing the dissolved gold remain suspended. This solution is then combined with a fluid and zinc and the gold forms a residue.
Using cyanide, mining companies can extract as much as 95 to 98 percent of the gold present in the ore. This process of extracting gold using cyanide can be made economical if the ore contains less than one gram of gold in one ton of ore.
However, if a mining company wants to reduce its cost of extraction, it will use the heap leaching method to extract gold. Here, the ore is placed in piles in a prepared area that is lined and then treated with diluted solution of cyanide. The cyanide slowly makes its way down the piled ore and the dissolved gold reaches the bottom. The gold-containing solution is collected and the gold is extracted and refined.
The heap leaching process is a long-drawn process and can extract just 65 to 85 percent of gold present in the ore.
The extracted gold is refined in a smelter using a chemical mix known as flux. This mix is created using fluoride, magnesium dioxide, sodium nitrate, borax, and silica flour. The gold and flux are combined and heated to a temperature of 1,600 deg. C. This helps to remove any impurities from the gold. The molten gold is then poured into molds that are shaped like a bar. The resultant gold bars are 80 percent pure gold.
The mining company will further refine the 80 percent pure gold so that it reaches the gold standard of purity: 99.9 percent pure.