Short-Wave Infrared Spectral Characteristics of the Mamupu Cu-Au Skarn Deposit in Eastern Tibet: Insights Into Exploration and Evaluation

Abstract

The Mamupu deposit is recognised as the inaugural skarn-type Cu-Au deposit identified within the southern segment of the Yulong porphyry copper belt (YPCB) in Tibet, which contains 0.28 Mt Cu with an average grade of 0.85% and 19.6 t Au with an average grade of 0.60 g/t. The relationship between alteration and mineralization is of considerable significance for the exploration of deep and surrounding ore deposits. This study elucidates the alteration and mineralization characteristics of the deposit through comprehensive geological mapping of alterations, logging of drill holes and short-wave infrared (SWIR) spectroscopy. Detailed geological mapping of surface alterations indicates that intense silicification and hornfels alteration are predominantly located within the central mining area, which is proximal to the location of deep ore bodies. The spatial distribution of chlorite alteration closely aligns with the locations of the ore bodies, thereby serving as an effective indicator of ore body occurrence. Results from drill hole logging and SWIR analysis reveal that skarn alteration minerals, such as diopside, garnet, phlogopite and actinolite, are directly associated with copper-polymetallic mineralization, while chlorite alteration is consistently observed across the drill holes. In terms of SWIR spectral characteristics, the Fe-OH characteristic absorption peak (Pos2250) of chlorite associated with porphyry-type alteration diminishes from the No. VII copper-polymetallic ore body towards the periphery. This trend effectively reflects the distance from the hydrothermal mineralization centre: chlorite located near the ore body is relatively Fe-rich, whereas that situated further away is comparatively Mg-rich. Notably, the Pos2250 value of chlorite within the skarn alteration does not exhibit a distinct spatial pattern. Although the Al-OH characteristic absorption peak (Pos2200) of montmorillonite–muscovite group minerals also decreases outward from the ore body, its interpretative significance is limited in this deposit due to the inherent differential alteration zoning characteristic of skarn-type deposits. Consequently, elevated Pos2250 values of chlorite (> 2250.0 nm) within porphyry-type alteration, in conjunction with the presence of abundant skarn mineral assemblages, are identified as effective exploration indicators for the mineralization centre of the Mamupu deposit. For future exploration in the southern YPCB, we advocate for a comprehensive research approach that integrates geology, spectroscopy and genetic analysis: delineating alteration zones through geological mapping, targeting mineralization centres using spectral parameters and interpreting genetic models through comparative geological analysis. This methodology is anticipated to facilitate advancements in the exploration of deep and peripheral regions.