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Abstract
As in the past, gold and, to a lesser extent, silver are attracting considerable attention from the mineral industry. Expenditure on gold exploration dominates exploration budgets worldwide.
Gold is most common in the native form, but also occurs as tellurides. Although silver does occur as the native metal, it more often exists as sulfide minerals and sulfosalts, or as minor constituents of common sulfide minerals such as galena, sphalerite, and chalcopyrite.
The inertness and high specific gravity of gold account for its concentration by mechanical processes as a heavy mineral in stream and beach environments (placers). Gold and silver are both mobilized by hydrothermal fluids as sulfide or chloride complexes, and precipitated in response to changes in solubility caused by decreasing temperature, or variations in fluid composition, pH, oxygen fugacity. or sulfur fugacity.
Gold and silver occur in a diverse range of mineral deposits including recent placers and paleoplacers of gold, epithermal gold-silver vein and disseminated deposits, stratabound (iron formation-hosted) and vein gold in Archean greenstone belts, turbidite-hosted gold, skarn gold, Cordilleran vein silver deposits, veins of silver, cobalt-nickel-arsenides, and sediment-hosted copper-silver deposits.
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