文档介绍：AIG Journal – Applied geoscientific practice and research in Australia
EPITHERMAL GOLD FOR EXPLORATIONISTS
Greg Corbett
Consultant Geologist
ABSTRACT
Epithermal gold (± Cu & Ag) deposits form at shallower crustal levels than porphyry Cu-Au systems,
and are primarily distinguished as low and high sulphidation using criteria of varying gangue and ore
mineralogy, deposited by the interaction of different ore fluids with host rocks and groundwaters. Low
sulphidation deposits are in turn further divided according to mineralogy related to the depth and
environment of formation, while high sulphidation systems vary with depth and permeability control,
and are distinguished from several styles of barren acid alteration.
Low sulphidation epithermal Au + Cu + Ag deposits develop from dilute near neutral pH fluids and are
divided into two groups: those which display mineralogies derived dominantly from magmatic source
rocks (arc low sulphidation), and others with mineralogies dominated from circulating geothermal fluid
sources (rift low sulphidation). The former are classed with decreasing crustal level as: quartz-
sulphide gold + copper, passing to polymetallic gold-silver veins, carbonate-base metal gold and
shallowest epithermal quartz gold-silver. These ore types are zoned in time and space with shallower
styles overprinting the deeper, and metal contents which vary as high Cu at depth, to Ag and Au
dominant in elevated crustal settings. Low sulphidation adularia-sericite epithermal gold-silver
prise the rift low sulphidation style. These are dominated by gangue mineralogies
deposited from meteoric water rich circulating geothermal fluids, typically formed in rift settings.
Sediment hosted replacement gold deposits are interpreted to develop from low sulphidation fluids in
reactive carbonate bearing rocks.
High sulphidation Au + Cu ore systems develop from the reaction with host rocks of hot acidic
magmatic fluids to produ