Application of infrared (IR) spectral for exploration indicators in the Zhouwu Fe-Cu Skarn Deposit, South China

Abstract

The Nanling Range is a globally significant W-Sn polymetallic province in South China, which is mainly associated with the Mesozoic magmatism. The recently discovered Zhouwu deposit, situated along the southern margin of this range, is classified as a stratabound skarn-type Fe-Cu system, with an inferred ore reserves of 24 million tons of Fe and 42 thousand tons of Cu. This system exhibits distinct lithological control, with mineralization and alteration predominantly concentrated in ore-rich strata within the Zhouwu deposit, with poor development of mineralogical zonation. This study systematically elucidates the alteration mineral assemblages and their spatiotemporal relationships with mineralization through detailed geological surveys, mineralogical observations, and an integration of thermal infrared (TIR) spectroscopy, short-wave infrared (SWIR) spectroscopy, and electron probe micro-analysis of pyroxene. This study reveals that the paragenesis of the Zhouwu deposit can be subdivided into distinct phases, i.e., garnet-pyroxene, iron oxide, sulfide, and carbonate stages. The spectral parameters for garnet (Pos 11,400 > 11,400 nm), chlorite (Pos 2335 < 2335 nm), and white mica (Dep 1900 < 0.36) are closely associated with Fe and Cu mineralization. Additionally, the presence of diopside combined with low Pos 9700 values (Pos 9700 < 9720 nm) can serve as a proximal indicator for iron-rich fluids, suggesting magnesium enrichment in pyroxene within the proximal zone of iron mineralization. In addition, the spectral characteristics of chlorite and white mica exhibit subtle differences between Fe and Cu deposits. These findings suggest that Fe mineralization formed under high temperature, oxidizing conditions, while Cu mineralization takes place under medium–high temperature, less oxidizing conditions. Integrating spectral parameters with ore-forming fluid evolution, three exploration target zones were identified. Overall, this research underscores the effectiveness of combining TIR and SWIR spectroscopy in skarn exploration, particularly in stratabound skarn-type Fe-Cu system such as Zhouwu.