The concentration of gold ore, and the market value of gold determine whether a deposit is a mineable ore-body. The highest grade deposits are associated with quartz veins. Gold also occurs as disseminated particles incorporated during magmatic rock formation or during subsequent chemical alteration of the host rock. Primary gold occurrences are termed lode deposits. Mineralized rock and gold-bearing veins release gold particles during the weathering process. Because of its high specific gravity and resistance to weathering, these sedimentary gold particles are easily concentrated by streams and rivers to form placer gold deposits.
There are three types of gold mining today: underground mining of high-grade lode and placer deposits, dredging of surface placer deposits, and open-pit mining. A technique called heap leaching is commonly used to remove finely disseminated gold from low-grade ore. In this process, mounds of crushed ore are placed on an impermeable pad and sprayed with a dilute cyanide solution. The cyanide solution percolates through the ore and dissolves fine gold particles. The gold is then electrolytically recovered from solution and poured into ingots. Gold is also a byproduct of sand and gravel production and base metal (copper, lead and zinc) mining.
GOLD DEPOSITS IN CALIFORNIA
California’s most important gold deposits have been found in the Sierra Nevada, Klamath Mountains and Mojave Desert. Significant deposits have also been developed in the Peninsular and Transverse Ranges and the northern Great Valley. Unmined low-grade deposits occur statewide. In the Coast Ranges, low-grade gold deposits are associated with low-temperature mercury mineralization.
GOLD PRODUCTION IN CALIFORNIA-2001
In 2001, California ranked fourth in the United States in gold production. Approximately 449,200 troy ounces were produced worth about $122.3 million.
PROPERTIES AND USES
Gold is one of the earliest metals known and used by humans. It resists corrosion and chemical interaction. It will not disintegrate when exposed to oxygen, water, salt, or any other naturally-occurring material. Gold’s durability accounts for the almost perfect condition of coins and artifacts fashioned from it thousands of years ago.
Gold’s most important use is in computers, weaponry and aerospace. It is used where consistent, reliable performance under all conditions is essential. The electronics industry has tried to find substitute metals and alloys, but gold’s exceptional resistance to corrosion and tarnish is still unequaled.