Affiliation:
1. Key Laboratory for Mechanics, Anhui Polytechnic University, Wuhu 241000, China
2. Engineering Research Center of Anhui Green Building and Digital Construction, Anhui Polytechnic University, Wuhu 241000, China
3. School of Earth Sciences, Hebei GEO University, Shijiazhuang 050031, China
4. No. 8 Institute of Geology and Mineral Resources Exploration of Shandong Province, Rizhao 276826, China
Abstract
Alunite is used as a representative mineral for indicating deposits in lithocaps, and lithocaps are generally related to the porphyry–(high-sulfidation) epithermal mineralization system. The study of alunite is of theoretical and exploration significance for prospecting potential underlying porphyry and epithermal deposits. Studies on alunite geochemistry have made breakthroughs, but there is little research on alunite mineralogy, for example, using scanning electron microscopy (SEM) images, differential thermal analysis (DTA), and Fourier-transform infrared spectroscopy (FT-IR). This study mainly focuses on alunite micromorphological characteristics, weight loss changes with temperature, and ionic group structure, aiming to identify the relationship between these features and indications for prospecting. The Fanshan lithocap is located in the northwest part of the Luzong basin, Anhui province of China, and it can potentially be used for exploring porphyry and epithermal deposits. Fanshan alunite is formed in two stages with three types of alunite. IA alunite is formed in the early hydrothermal stage and replaces felsic minerals in the Zhuanqiao Formation, IB alunite is formed in the later hydrothermal stage and fills in open spaces with bladed particles, and II alunite is the product of pyrite oxidation and reaction with other minerals in the supergene stage. Alunite electron microprobe data and energy-dispersive spectroscopy data further confirm temperature decreases with hydrothermal evolution, and the presence of a high-sulfidation epithermal system in the Luzong basin. Aside from the forming environment, SWIR, and geochemistry of alunite, there are other indication indexes; for example, the larger peak values at 3480 cm−1 and smaller peak values at 1080 cm−1 in FT-IR spectra and the deeper exothermic valleys at 750 °C and steeper weight loss slopes in the DTA curve suggest a favorable formation environment for alunite and provide valuable indications for deposit exploration and assessments of mineralization potential.
Funder
National Natural Science Foundation of China
Anhui Polytechnic University Talen Introduction Research Fund Project
Reference63 articles.
1. Porphyry copper systems;Sillitoe;Econ. Geol.,2010
2. Tschirhart, V., and Thomas, M.D. (2017, January 27). Porphyry indicator minerals (PIMS) and porphyry vectoring and fertility tools (PVFTS)-indicators of mineralization styles and recorders of hypogene geochemical dispersion halos. Proceedings of the Exploration 17: Sixth Decennial International Conference on Mineral Exploration, Toronto, ON, Canada.
3. Exploration tools for linked porphyry and epithermal deposits: Example from the Mankayan intrusion-centered Cu-Au district, Luzon, Philippines;Chang;Econ. Geol.,2011
4. Formation of the Fanshan lithocap and implications for exploration in the Luzong basin, Anhui Province, China;Li;Ore Geol. Rev.,2020
5. The stable isotope geochemistry of acid sulfate alteration;Rye;Econ. Geol.,1992