In
different parts of the world the term epithermal is commonly used for a variety
of deposit styles. Using the redox state of the ore-forming fluid (inferred from
mineralogy and alteration), the metal assemblage of deposits, and other
characteristics, at least five different styles of epithermal deposit can be
distinguished. Most of these different deposit styles appear to be related to
magmatic fluids, with differences resulting from different compositions of
source magmas. The most common style of epithermal deposit (low-sulfidation
gold-silver deposits associated with calc-alkaline volcanic rocks) remains the
most difficult to explain; the metals in these deposits may be derived by
basement leaching without magmatic input, or they may come from magmatic
volatiles, with contaminated I-type or S-type magmas as the most likely
source.