Deep Vector Exploration via Alteration Footprints and Thermal Infrared Scalars for the Weilasituo Magmatic–Hydrothermal Li–Sn Polymetallic Deposit, Inner Mongolia, NE China

The Weilasituo Li–Sn polymetallic deposits exhibit spatial and genetic relationships with magmatic–hydrothermal alteration, resulting in distinguishable mineral zonation patterns across the different metallic orebodies. The mineral zonation of breccia, quartz vein, and quartz porphyry orebodies are distinguished efficiently by regularly spaced samples analyzed by shortwave infrared and thermal infrared (TIR) spectroscopy techniques. The method provides semiquantitative abundance estimates of the mineralogy and allows the reliable recognition of diagnostic alteration as well as mineralization-related alteration footprints from detailed mineral and geochemical ternary diagrams. The alteration footprints are the result of a sequence formation of albite, topaz, and phengite alteration in weakly acidic and high-temperature ore-forming environments, followed by muscovite alteration, chlorite alteration, and local calcareous plagioclase alteration in acidic and low-temperature ore-forming environments. Quartz, topaz, and phengite are predominantly associated with the economic Li–Sn mineralization. Likewise, the TIR scalars W9300 of quartz-bearing samples and TIR scalars H9660/H9920 and D9800 of plagioclase-bearing samples at Weilasituo follow some specific rules concerning mineralization types: (1) for porphyry Sn ores, D9800 is > 0.13; (2) for breccia Li–Rb orebody, W9300 within 9450–9600 nm and H9660/H9920 is > 15; (3) for quartz vein Sn orebodies, H9660/H9920 within 5–15 nm and W9300 within 9050–9250 nm; (4) for quartz vein sulfide orebodies, H9660/H9920 is < 2, and its W9300 within 9250–9350 nm or 9850–9900 nm. Specifically, the combination of mineralogical alteration footprints with TIR scalars obtained from The Spectral Geologist software (TSGTM) has the potential to direct a program of vectoring exploration toward Li–Sn-polymetallic orebodies.