The geology of hydrothermal gold deposits in Chile

A detailed geologic study has been undertaken of the characteristics of 20 of the best known hydrothermal gold deposits in Chile. Characteristics include production and reserve data, metal grades, geotectonic setting, morphology, mineralogy, zonation, alteration assemblages and fluid-inclusion studies. Based on this geologic data base, two broad categories of gold deposits have been recognized: volcanic-hosted epithermal deposits of the adularia-sericite and acid-sulphate types and porphyry-related deposits.

Volcanic-hosted epithermal deposits of the adularia-sericite type appear to be more abundant than the acid-sulphate type. Very few examples of porphyry-related deposits have been recognized. The majority of the acid-sulphate type deposits were formed during the Oligocene-Quaternary time-span and no adularia-sericite type examples are yet known from this period. This latter epithermal type was formed exclusively during the Mesozoic and Early Tertiary.

Presently accepted ore-deposit models have been applied to the Chilean epithermal gold deposits, and an empirical model for adularia-sericite epithermal system is presented.