Gold Minerals

Gold does not react at ambient temperature and pressures and consequently there are very few naturally occurring compounds of the metal. The average concentration of gold in the world is about 0.005 g/t, that is lower than other metals. The low concentration of gold in primary rocks means that upgrading by a factor of 3000-4000 is usually required during ore formation processes to achieve commercial concentrations. This may be possible natural gravity concentration processes or leaching gold with natural fluids from the host rock. Thus, by highly oxidizing, acidic and complexing (chloride) solutions, followed by redeposition in a more concentrate form. Owing to its siderophile properties (weak affinity for oxygen and sulfur, high affinity for metals) gold tends to concentrate in residual hydrothermal fluids and subsequent metallic or sulphidic phases, rather than silicates, which form at an early stage of magma cooling. Rocks that are high in clays and low in carbonates are the best sources of gold, and reprecipitation occurs when the hydrothermal solutions encounter a reducing environment, such as a region of high carbonate, carbon or reducing sulphide contain.

The predominant occurrence of gold is as native metal, often alloyed with up to 15 % silver. Other gold minerals include alloys with tellurium, selenium bismuth, mercury, copper, iron, rhodium and platinum. Therefore gold occurs in a mineral form different to most other elements.