Gold occurs primarily in its native form and secondarily as a gold solid-solution of which tellurides are an example. Gold extraction from tellurides has attracted increasing atttention over the past several decades. Gold tellurides have been commercially treated in Kalgoorlie (Western Australia), Vatukoula (Fiji), Cripple Creek (Colorado), and Kirkland Lake (Ontario).
Gold-bearing tellurides are silvery to pyrite-yellow minerals, commonly striated, unlike gold which is a deeper yellow and rarely crystalline. The first modern treatment of gold-telluride ores was performed in 1891 in the Cripple Creek goldfield near the Rocky Mountains in Colorado. Kalgoorlie, in Western Australia, had the honor of being the second major goldfield, and tellurides were successfully processed to extract gold.
This discovery led to a second gold rush to find these veins with a silvery to pyrite-like mineral, testing them with fire to determine if that mineral contained gold. Out of this rush came the mining camps of Cripple Creek and Telluride along with other mining camps in the San Juan region of Colorado. Of these, the mining camp of Cripple Creek is the most famous, producing nearly 20 million ounces of gold over a 70 year period from 1891 to 1961.
It was well known that gold was commonly associated with tellurium minerals. The co-occurrence of tellurium with noble metals such as gold and silver was attributed to the semi-metallic nature of tellurium. The composition varied significantly from different tellurium minerals. For instance, gold-telluride ores could be classified into six mineral groups: calaverite, sylvanite, montbrayite, krennerite, petzite, and muthmannite.
Calaverite was the simplest and most common association of tellurium with gold. It was also the most common gold bearing mineral apart from native gold. In a modern gold processing plant, the recovery can be up to 98% with the aid of the latest concentration and smelting techniques.
Gold-bearing tellurides are common in gold-bearing deposits throughout the world, including British Columbia. A tip on finding tellurides: The mineral commonly has a greenish halo around it when weathered, due to oxidation of the telluride.