Linking Low‐temperature Alteration to Mineralization in Epithermal Deposits: SWIR Spectral Analysis and 3‐D Modeling of the Ulan Uzhur Ag Polymetallic Deposit, China

Abstract Epithermal deposits are characterized by complex low‐temperature hydrothermal alterations, but the links between mineralization and superimposed alteration are obscure and require further elucidation. This study employs short‐wave infrared (SWIR) spectral scalars for alteration mineral mapping and three‐dimensional modeling of the Ulan Uzhur Ag polymetallic deposit, a newly discovered epithermal deposit in the Qimantagh. Alteration zoning transitions from illite‐muscovite‐carbonate‐pyrite in the core (Zone I), through muscovite ± illite‐kaolinite‐chlorite‐carbonate (Zone II), to muscovite‐chlorite‐biotite (Zone III) at the periphery. The Zone I with mineralization features long‐wavelength white mica (wAlOH > 2207 nm) with a high Illite Crystallinity (IC) (mean > 2.0), suggesting a relatively high‐temperature environment conducive to mineralization. Petrographic analyses with fluid inclusion and IC curve characteristics suggests that fluid boiling may be a pivotal mechanism for mineral precipitation. Furthermore, surface mapping and deep three‐dimensional modeling of spectral characteristics reveal a correlation between long‐wavelength white mica, high IC and mineralization zones. These findings indicate that SWIR spectroscopy reveal the evolution of fluids and provide valuable guidance for future exploration efforts.