Most gold mining today is done in open-pit mines that are excavated using geological survey information. Before deciding where a gold mine should be constructed, geologists have to find gold deposits in the Earth. They can locate gold with satellite imagery or chemistry from the ground. Once geologists find an ore deposit, they have to map its exact dimensions to see how far the deposit extends. This is to find out whether the deposit will yield enough gold to offset the costs of building a mine. Also, the mine has to be built to the exact measurements of the deposit to get the most out of it; overbuilding would cause a waste of resources, and not building enough would leave some of the mine's potential untapped. Most gold mines in the United States are in Nevada, according to Arnold Jewelers.
Purification of Low-Grade Ore
Depending on the quality of the ore--how much gold is present--the gold can be extracted and purified by a different method. According to Responsible Gold, gold can be found in low-grade or high-grade ore. If the ore is low-grade, the mining company breaks it into smaller chunks. The miners pour a cyanide solution to dissolve the gold and collect the solution with the dissolved gold. A carbon strip collects the actual gold from the solution in further chemically treat it via electrolysis. Once the gold has been purified, it can be melted and formed into bars that contain up to 89% gold, according to Responsible Gold.
Purification of High-Grade Ore
The Earth has a crust mostly made of silicon, but other elements such as oxygen, sulfur, carbon, and calcium are found in the Earth's crust. Whenever we mine gold, the gold has to be extracted from ores of these elements. Sometimes there are gold veins with higher concentrations of gold. According to eHow, the mining company sends this high-grade ore to a refinery, where it can be ground into a fine powder. If the high-grade ore is a refractory ore, they heat it to over 1,000 degrees Fahrenheit to remove carbon and sulfide compounds. The gold can be formed into bars that are 90% pure gold, as with low-grade ore. Both types of of ore can be further refined into bars that have virtually 100% gold concentrations.
