Integrated Rock Magnetic and VNIR–SWIR Hyperspectral Characterization: A Quantitative Classification Tool for VMS Alteration Systems

Volcanogenic massive sulfide (VMS) deposits are among the world’s most important sources of copper (Cu), zinc (Zn), lead (Pb), gold (Au), and silver (Ag), metals that are critical for modern infrastructure and energy technologies. These deposits are characterized by systematic hydrothermal alteration halos that preserve mineralogical and chemical gradients generated by spatial and temporal variations in temperature, redox conditions, and hydrothermal fluid composition. Such alteration zones provide important vectors for mineralization; however, their traditional characterization is commonly qualitative, reliant on subjective geological interpretation, and difficult to collolate at scale across exploration projects. This study investigates the Rävliden deposits of the Paleoproterozoic (1.89 Ga) volcanic–sedimentary sequence of the Skellefte district, Sweden, to evaluate whether integrated rock magnetic and VNIR–SWIR hyperspectral data can be used to objectively characterize hydrothermal alteration in VMS deposits. In this study, rock magnetic measurements are cross-referenced with hyperspectral data and supported by mineral chemistry and sulfur isotope analyses to develop a quantitative and reproducible framework for fingerprinting hydrothermal alteration in both metalliferous and barren VMS systems. The approach comprises three objectives: (1) defining diagnostic magnetic and hyperspectral signatures of alteration mineral assemblages to construct a reference dataset, which is then validated using Raman spectroscopy; (2) evaluating trace-element variations in magnetite and associated sulfide minerals to assess their influence on magnetic properties across alteration zones; and (3) using sulfur isotope compositions (δ³⁴S) of sulfide minerals across alteration zones and structural domains to constrain fluid sources and reconstruct the hydrothermal fluid evolution of the system. This workflow systematically links observable physical alteration patterns to their underlying mineral-chemical controls and fluid origins, providing a robust and scalable tool for hydrothermal alteration characterization in VMS exploration.