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.

Keywords

epithermal alteration / fluid evolution / mineral exploration / SWIR / Ulan Uzhur Ag deposit

RIGHTS & PERMISSIONS

2026 Geological Society of China