Short-Wavelength Infrared Spectral Analysis and 3D Vector Modeling for Deep Exploration in the Weilasituo Magmatic–Hydrothermal Li–Sn Polymetallic Deposit, Inner Mongolia, NE China

The Weilasituo magmatic–hydrothermal Li–Sn polymetallic deposit is located in the eastern part of the Central Asian Orogenic Belt. It is the first giant greisen lithium deposit in Inner Mongolia. It consists of deep quartz porphyry Sn orebodies (No. I), a central cryptoexplosive breccia Li–Rb orebody (No. II), and shallow hydrothermal quartz vein polymetallic orebodies (No. III). Newly obtained short-wavelength infrared (SWIR) data from six drillholes that intersected the deposit were used to characterize hydrothermal minerals and model 3D alteration zonation. Tracking the SWIR scalars (i.e., Pos2200 and IC for white mica, Pos2250 for chlorite, and Dep2080 for topaz), the metallogenic conditions were characterized and the 3D regions of distinct mineralization were modeled by SKUA-GOCAD. The results reveal that (1) the dominant alteration mineral assemblages of orebodies Nos. I, II, and III are kaolinite + topaz, phengite + topaz ± biotite, and chlorite + muscovite ± biotite, respectively; (2) phengite (AlVI-poor) and topaz preferentially occur toward the high-temperature and alkaline core part, whereas muscovite (AlVI-rich) and chlorite are present in the low-temperature and acidic edge part of the hydrothermal alteration system; (3) the proximal Li–Rb mineralization range accompanying phengite and topaz was precisely mapped by larger IC (> 2.5) and longer Pos2200 (> 2209 nm). The proximal Sn vein mineralization range closely associated with F element was traced by larger Dep2080 (> 0.2), and the proximal Mo–Cu–Pb sulfides vein range associated with the precipitation of Fe was characterized by longer Pos2250 (> 2253 nm). The above vector indicators were validated in the Weilasituo deposit’s 3D orebody models. Therefore, we propose that SWIR spectroscopy provides a potential visual vectoring tool for deep exploration and prospecting for other similar magmatic–hydrothermal deposits.