All gold deposits (except placers) are associated with characteristic mineral alteration zones, which makes them amenable to detection by the high resolution HyMap spectrometer.
For most gold deposit styles, including epithermal, greenstone and intrusion-related deposits, gold is generally remobilised from surrounding country rock, often via large sub-surface hydrothermal convection systems.
These sub-surface hydrothermal systems are usually characterised as being of acidic pH under and moderate-high pressure and temperature. If these hydrothermal fluids are subjected to a change in either the redox, pH and/or pressure then the gold will be deposited as either free gold or in various mineral forms which may be economic.
Interestingly, all minerals form within discrete pH, pressure and temperature boundaries also. HyMap data is well suited to rapidly mapping all of the important alumino-silicate minerals, including alunite, pyrophyllite, kaolinite and sericite that are associated with various hydrothermal gold deposits.
Thus accurate and precise mapping of surface mineralogy is an indirect measure of paleo redox and temperature of mineral crystallisation, which allows geologists to vector their exploration efforts towards more favourable gold-bearing regions.