Epithermal gold deposits of the circum-Pacific - characteristics, genesis and exploration

A diversity of epithermal deposit styles can form in convergent margin settings around the Pacific Rim. Some of the resources can be very large (e.g. Lihir, PNG – 57 Moz Au –Newcrest Mining Ltd., 2016; Pascua-Lama, Chile and Argentina – 324.6 Mt @ 1.47 g/t Au, 64.66 g/t Ag, 0.072 % Cu for 15.38 Moz Au, 674.8 Moz Ag, 0.23 Mt Cu – Barrick, 2014), whereas others have spectacular high grades (e.g. Hishikari, Japan – produced ~193 t for 6.2 Moz of gold from 3.9 Mt of ore with an average grade of 49 g/t Au to the end of 2010; El Indio, Chile – 23.2 Mt @ 6.6 g/t Au, 50 g/t Ag, 4% Cu; http://www.portergeo.com.au/database/index.asp).

Two major classes of epithermal deposits can be recognised readily in the field based on key features such as vein and alteration mineralogy. These are commonly referred to as (1) low and/or intermediate sulfidation, and (2) high sulfidation epithermal deposits (e.g. White and Hedenquist, 1990, 1995; Hedenquist et al., 2000; Cooke and Simmons, 2000; Einaudi et al., 2003; Simmons et al., 2005). These two groupings can be further subdivided based on a variety of features, such as metal tenor, tectonic setting, deposit form, and inferred relationships to porphyry-style mineralisation. Such subdivisions are generally applied inconsistently and, in some cases, illogically.