Volcanic-related hydrothermal systems in the Circum-Pacific Basin and their potential for mineralisation.

Abstract

Epithermal ore deposits hosted by volcanic rocks and formed by volcanic-related hydrothermal systems are becoming increasingly important gold producers in Circum-Pacific countries, with many recent discoveries. One such type of epithermal deposit, termed low sulfidation, is characterized by reduced sulfur. This deposit formed in an en-vironment analogous to many active geothermal systems; it is now recognized that in the low sulfidation system, gold precipitates from boiling fluids focussed into zones of high permeability. Exploring for this type of deposit can be greatly aided by detailed mapping of alteration. The other group of gold deposits reviewed here is characterized by relatively ox-idized sulfur, termed high sulfidation. They remain somewhat enigmatic because they are poorly studied exceptions be-ing Summitville, Colorado and El Indio, Chile. However, indications are that their formation is closely related to an acid magmatic fluid, with mineralization therefore more intimately associated with volcanism such as that at White Island, New Zealand than is the case for the low sulfidation type. Further exploration for this style of mineralization will be greatly assisted through integrated geologic and geochemical (particularly paragenetic) studies of this style of deposit and of active volcanic systems.