Alunite spectral features and mineral chemistry of the Zijinshan-Dafanshan lithocap in SE China: Implications for mineral exploration

• Published in: Acta geochimica Vol. 42; no. 4; pp. 585 - 602
• Main Authors: Sun, Yandong, Xie, Guiqing, Chen, Jing
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01.08.2023; Springer Nature B.V; MNR Key Laboratory for Exploration Theory & Technology of Critical Mineral Resources,China University of Geosciences,Beijing 100083,China%Centre for Ore Deposit and Earth Sciences(CODES),University of Tasmania,Hobart,TAS,Australia; School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China; Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China%Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China
• Subjects: Ablation; Absorption; Alunite; Analytical methods; Copper; Deposits; Earth and Environmental Science; Earth Sciences; Geochemistry; Gold; Inductively coupled plasma mass spectrometry; Infrared spectroscopy; Laser ablation; Mass spectrometry; Mass spectroscopy; Mineral assemblages; Mineral exploration; Mineralization; Minerals; Original Article; Rock; Rocks; Volcanic belts; Wavelength; China; SWIR; Lithocap; Zijinshan Cu-Au epithermal deposit; Geochemical indicators; Dafanshan alunite deposit
• ISSN: 2096-0956; 2365-7499
• DOI: 10.1007/s11631-023-00616-8

Lithocaps are composed of silicic and advanced argillic altered rocks, and represent an important target for porphyry-epithermal Cu-Au exploration. Previous studies showed that integrating alunite spectral and composition with lithocap whole-rock geochemistry can effectively aid exploration for concealed Cu-Au mineralization. The Zijinshan Cu-Au and Dafanshan alunite deposits are located in the Coastal Volcanic Belt in SE China, where alunite is an indicator of hypogene mineralization and alteration. Detailed mineralogical studies of alunite from these two deposits were performed with short-wavelength infrared spectroscopy (SWIR), whole-rock geochemistry and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). For Zijinshan, wavelength variation of the SWIR alunite absorption peak at 1480 nm is proportional to the whole-rock Na/(Na + K) molar ratio of alunite-bearing samples. Different percentage of alunite and mineral assemblages in the lithocap samples would both affect the wavelength of the SWIR alunite absorption peak at 1480 nm. We suggest that the alunite Ba-Bi contents and the whole-rock Nb/La value (of alunite-bearing rocks) are reliable vectoring tools for detecting magmatic-hydrothermal mineralization center in the district. Comparing the alunite SWIR spectral and mineral geochemical features and whole-rock geochemistry of alunite-bearing rocks between the Zijinshan and Dafanshan deposits, Au–Ag mineralization may be concealed at depth in northwestern Dafanshan.