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. 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.
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