Gold Mining


US Land and Minerals

Placer mining




Metal detecting

With a metal detector, a person may walk around an area and systematically scan below the surface. The sensor can give a positive reading for a quantity of gold to a depth of as much as a meter below the surface. As the device is easy to operate and highly mobile, this method of prospecting is very popular among gold miners.









Hard rock mining

Hard rock gold mining is done when the gold is encased in rock, rather than found as particles in loose sediment. Hard rock mining produces most of the world's gold. Sometimes open-pit mining is used, such as at the Ft. Knox Mine in central Alaska. Barrick Gold Corporation has one of the largest open-pit gold mines in North America, located on its Goldstrike mine property in northeastern Nevada. Other gold mines use underground mining, where the ore is extracted through tunnels or shafts. South Africa has the world's deepest hard-rock mine, which mines gold from as deep as 3900 meters under the ground.

Byproduct gold mining


Gold ore processing

In placer mines, the gold is recovered by gravity separation. For hardrock mining, other methods are usually used.

Cyanide process

Cyanide extraction of gold may be used in areas where fine-gold bearing rocks are found. Sodium cyanide solution is mixed with finely-ground rock that is proven to contain gold and/or silver, and is then separated from the ground rock as gold cyanide and/or silver cyanide solution. Zinc is added to the solution, precipitating out residual zinc, as well as the desirable silver and gold metals. The zinc is removed with sulfuric acid, leaving a silver and/or gold sludge that is generally smelted into an ingot then shipped to a metals refinery for final processing into 99.9999% pure metals.

Advancements in the 1970s have seen activated carbon used in extracting gold from the leach solution. The gold is absorbed into the porous matrix of the carbon. Activated carbon has so much internal surface area, that fifteen grams (half an ounce) has the equivalent surface area of the Melbourne Cricket Ground (18,100 square meters). The gold can be removed from the carbon by using a strong solution of caustic soda and cyanide. This is known as elution. Gold is then plated out onto steel wool through electrowinning. Gold specific resins can also be used in place of activated carbon, or where selective separation of gold from copper or other dissolved metals is required.

The cyanide technique is very simple and straightforward to apply and a popular method for low-grade gold and silver ore processing. Like most industrial chemical processes, there are potential environmental hazards presented with this extraction method in addition to the high toxicity presented by the cyanide itself. This was seen in the environmental disaster in Central-Eastern Europe in year 2000, when during the night of 30 January, a waste pond dam breakage at the Sasar gold mine reprocessing facility near Baia Mare in northern Romania released approximately 100,000 m³ of wastewater contaminated with heavy metal sludge and up to 120 tons of cyanide into the Tisza River.


A cradle was rocked back and forth while water was poured over it. The sand and gravel was washed through the screen of the cradle, leaving the gold behind.