Gold occurs in nature mainly as the metal and as various alloys. It forms complete series of solid solutions with silver, copper, nickel, palladium, and platinum. In association with the platinum metals, gold occurs as free gold as well as in solid solution.
The native elements contain the most gold, followed by the sulfide minerals. Several gold tellurides are known, but no gold selenides have been reported, and only one sulfide, the telluride-sulfide mineral nagyagite, is known.
The nonmetallic minerals carry the least gold, and the light-colored minerals generally contain less gold than the dark minerals.
Some conclusions in the literature are conflicting in regard to the relation of fineness of native gold to its position laterally and vertically within a lode, the nature of the country rocks, and the location and size of nuggets in a streambed, as well as to the variation of fineness within an individual nugget.
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USGS Numbered Series
Gold in minerals and the composition of native gold