Examination of the Correlation Between Shortwave Infrared Spectra of Muscovite and Mineral Geochemistry in the Pegmatite-Type Lithium Deposit in Lijiagou, Western Sichuan
HAN Jing-rui1, RAN Feng-qin1*, PENG Bo1, CHEN Ran3, TANG Bo2, FENG Da-bo1, YANG Yang1, ZHAO Yuan1, GU Chun-jin2, CHEN Hao4, ZHAO Heng-bing5
1. College of Earth and Planetary Sciences, Chengdu University of Technology, Chengdu 610059, China
2. Sichuan Institute of Comprehensive Geological Survey, Chengdu 610081, China
3. Department of Natural Resources of Sichuan Province, Chengdu 610072, China
4. The 5th Geological Brigade of Sichuan, Chengdu 610036, China
5. Sichuan Dexin Mining Resources Co., Ltd, Aba Tibetan and Qiang Autonomous Prefecture 624199, China
Abstract：The Liajiagou deposit, a massive granite pegmatite-type lithium deposit, is located in the western part of Sichuan Province. Currently, the shortwave infrared spectroscopic properties of muscovite in the Liajiagou deposit remain unknown, and a deeper understanding of the correlation between its chemical composition and spectral characteristics is required.This study examines multiple generations and types of muscovite in the pegmatite of the Li Jiagou ore deposit. Microstructural observations, shortwave infrared (SWIR) spectroscopy, and electron probe microanalysis (EPMA) were performed. The muscovite in the pegmatite was classified into three generations: ① Primary muscovite (MS), formed during the magmatic stage, is characterized by high concentrations of aluminum (Al) and potassium (K). The absorption peak of muscovite at 2200 nm (Pos2200) displays a limited variation range, ranging from 2201 to 2202.8 nm. The absorption depth at this peak (2200 Dep) often remains below 0.25. Additionally, the illite crystallinity index (IC value) typically falls within a narrow range of 1 to 1.5. ② During the magma-hydrothermal transition stage, transition muscovite (TM) becomes enriched in Li elements as a result of the exsolution of volatile-rich fluids. The Li2O content in TM varies between 2.53% and 6.22%. Additionally, Pos2200 demonstrates a concentration peak centered at 2200-2201 nm. Most 2200 Dep values are below 0.5, whereas IC values remain consistently high, often exceeding 4. ③ Hydrothermal muscovite (HM), predominantly formed via fluid metasomatism, exhibits the shortest Pos2200 values, with 2200 Dep readings mostly below 0.4 and IC values ranging from 2 to 4. The Al-OH absorption peak of muscovite in the Lijiagou pegmatite indicates variations in the elemental composition, including Si, Al, Fe, Li, and other constituents.During the transition from the muscovite (MS) stage to the topaz-muscovite (TM) stage, changes in elemental composition and substitution mechanisms primarily influence the shift in the characteristic absorption peak wavelength of muscovite. In contrast, during the hydrothermal (HM) stage, temperature becomes the primary determinant. Comprehensive research highlights the potential of the characteristic absorption wavelength (2200-2201 nm) of the muscovite Al-OH peak, coupled with an illite crystallinity value greater than 4, as effective indicators for mineral exploration in the Lijiagou pegmatite.
