Metals and Mining

gold surface mine

Gold Mining and Production
Gold is mined by the poorest people with simple tools and by wealthy corporations with sophisticated chemistry. Gold is not at all common in the earth's crust - even several of the so-called rare earth elements are more abundant. Nevertheless, it can be mined efficiently for two reasons. First, gold is dense and tends to concentrate. Second, gold is somewhat inert and is usually found in free form. The gold that is bound in minerals still calls for the sophisticated chemistry.

Placer gold mining is taking gold from loose material. (See Mining Claims.) Although this can be a large industrial operation, it usually isn't. Lode mining involves blasting, drilling, and crushing gold ore in hard rock. If the gold is chemically free, it is then separated by sluices, floation, or some other gravity method. Very fine gold, or even microscopic gold particles, must be isolated by a process such as cyanide leaching. Sodium or potassium cyanide will dissolve the particles into solution, where they can be recovered by electroplating.

In the past, cyanide compounds have caused a great deal of misery in gold mining. Modern methods isolate and recover the toxic chemical as well as prevent the formation of poisonous hydrogen cyanide. Regulators pay particular attention to gold leaching operations.

Gold may also be found alloyed with silver or copper. (In the case of copper, gold is really the by-product of copper mining.) The metals can be separated with sulfuric or nitric acid that famously do not dissolve gold. Many other methods of processing gold have been developed over the centuries for particular types of ore.

U.S. Gold Mining Overview

The USA is the world's third largest gold producer, after China and Australia. The country produced 227 t in 2013, representing a dramatic drop from 2000's total of 355 t. Gold was produced at about 50 major lode mines, a few large placer mines (all in Alaska), and numerous smaller placer mines (mostly in Alaska and in the Western States). In addition, a small amount of domestic gold was recovered as a byproduct of processing base metals, chiefly copper. Thirty mines yielded more than 99% of the gold produced in the United States.

Domestic output in 2013 was estimated to be less than in any of the previous 3 years, perhaps a lagging economic indicator.

The Carlin Trend in Nevada has been responsible for most of the USA's gold production and is responsible for forming a stable mining platform for several global major gold producers such as Newmont, Placer Dome and Barrick. Gold mineralization in the Carlin Trend is characterized by a large low-grade sedimentary carbonate hosted gold resource.

The USA is the lowest cost gold producer (cash costs of $185/oz) in the world, followed by Canada, Australia and South Africa. The largest US gold mine is the Goldstrike in north-eastern Nevada, operated by the world's largest gold miner, Barrick Gold. The Goldstrike complex produced 1.7 million ounces of gold in 2008 and 200,000 ounces of silver. However, poor gold price and rising costs have placed several of Nevada's flagship mines under pressure, resulting in job losses and mine suspensions.

gold mining transport

Newmont Mining remains the USA's largest gold producer, with 3 Moz being produced from its Carlin mine near Elko, Nevada in 2000. Newmont was responsible for the discovery of the Carlin Trend in 1961, and now operates 14 open pit and four underground mines in Nevada, employing a total of 3000 people. Production from the Nevada mines has exceeded 1.5 Moz per year for the past seven years. Due to the varied oxide and carbon/sulphide refractory ores that are found intermixed throughout the mine, Newmont has had to employ several methods of gold extraction. Newmont, the world's second-largest gold miner, also has properties in Peru, Australia, and elsewhere.

Barrick Gold owns and operates several operations in Nevada, California, and South Dakota. The most promising may be tbe Cortez mines in Nevada, which produces at least half a million ounces per year. Barrick also owns Bald Mountain, Marigold (jointly with Goldcorp), and Round Mountain (jointly with Kinross), in addition to its operations in Australia, Tanzania, and elsewhere.

In Alaska, Kinross Gold operates the Fort Knox mine through a subsidiary. NovaGold Resources and Barrick are making good progress on the development of the Donlin Creek Gold Deposit that has a potential gold resource of at least 29 Moz gold, making it one of North America's largest unexploited gold deposits. Donlin Creek is located more than 500km west of Anchorage in southwest Alaska. The challenge here is isolating the gold from an unusual pyrite rock.

In California, New Gold operates the Mesquite Mine, producing about 100,000 ounces per year. Many gold mines have opened and closed in California since the 1849 gold rush. Most are now simply historical landmarks.

AngloGold Ashanti also has operations in the USA. Here AngloGold operates the Cripple Creek and Victor gold mines producing 200,000 ounces per year. AngloGold has much larger operations in South Africa and elsewhere.


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