Controls to high sulphidation epithermal mineralisation

Controls to high sulphidation epithermal mineralisation. The controls for high sulphidation epithermal Au deposits are strongly dependent upon the evolution of the hydrothermal fluid during ascent to higher crustal levels from the intrusion source at depth (Corbett, 2013). Consequently, there is a positive association between major structures and high sulphidation epithermal Au deposits although Corbett (2012) suggests the actual mineralisation may occur in minor subsidiary fracture systems (figure 6). In general Corbett (2013) proposes that the migration of the hydrothermal fluid that provide the overall form of high sulphidation epithermal Au deposits, is controlled by (figure 6):
  • Permeable lithologies such as fiamme tuffs (Pierina, Peru; Quimsacocha, Ecuador), basement conglomerate (Wafi, Papua New Guinea) or sandstone (La Arena, Peru), although ore shoots occur at intersections with feeder structures with permeable lithologies (La Coipa, Chile; Nena, Papua New Guinea; Sipan, Peru; Gidginbung, Australia).
  • Structures as dominantly dilatant fracture-veins, (El Indio, La Coipa, Chile; Peak Hill, Australia) or intersections of structures with breccia pipes (Lepanto, Philippines) or permeable lithologies (Nena, Papua New Guinea).
  • Breccias, as phreatomagmatic (diatreme) breccia pipes (Pascua-Lama, Chile-Argentina; Veladero, Argentina; Yanacocha, La Virgin, Peru; Lepanto, Philippines; Miwah, Indonesia) although the diatreme pipe may locally predate the high sulphidation system (Wafi, Papua New Guinea). Elsewhere, brecciated dome margins also provide permeability (Mt Kasi, Fiji; Yanacocha, Peru).
  • In many cases earlier lithological control to hydrothermal alteration might overprinted by a later structural control to mineralisation within veins and breccias (Peak Hill, Australia; Pascua-Lama, Chile-Argentina).
Refractory metallurgy of high sulphidation epithermal Au ore has restricted the mining of many deposits to oxide ores, terminating downward intersection with sulphide ore (Gidginbung, Peak Hill, Australia; Sipan Peru). The high As content of the enargite-bearing sulphide can be a metallurgical concern. However, some lower temperature, higher crustal level examples evolve in time and space to display improved metallurgy and higher Au grades (below).