Hydrothermal systems linked to epithermal and porphyry-Cu mineralisation display mineralogical zoning that works as a proxy for fluid chemistry and temperature. In high-sulphidation systems, advanced argillic assemblages (alunite ± pyrophyllite) are commonly overprinted by sericitic alteration (white micas) as fluids evolve.

Delineating these patterns is central to exploration targeting. Airborne hyperspectral surveys have proved effective but can be limited by cost and coverage. Recently available spaceborne hyperspectral missions (PRISMA, EnMAP, EMIT) offer systematic acquisitions at a coarser spatial resolution. PRISMA and EnMAP have proven effective for hydrothermal alteration mapping, but EMIT is largely unexplored.

We assess EMIT’s ability to map hydrothermal alteration mineralogy and characterise mineral chemistry variations for fluid composition analysis in the lithocap of the Yerington mining district, Nevada. Using wavelength and decision-tree classification maps, we (i) identify an outward shift from Al-rich to Mg-Fe-rich white micas (a pH proxy), and, for the first time from space, we (ii) differentiate alunite- from pyrophyllite-rich zones, previously thought to require high-resolution airborne data. Alunite-rich zones are linked to high-temperature magmatic sulphur input, forming acidic environments, while pyrophyllite-rich zones reflect evolving fluid conditions.

Our findings confirm EMIT’s ability to characterise mineral chemistry variation as a proxy for fluid composition despite its coarser resolution when compared to PRISMA and EnMAP. This capability reinforces the role of spaceborne hyperspectral data for mineral exploration in high-sulphidation epithermal-Au and porphyry-Cu systems.