Raman Spectra Characteristics of Alunite in the Zijinshan Gold-Copper Deposit
WANG Cui-zhi1, 2, XIONG Xin3
1. Zijin Mining College of Fuzhou University, Fuzhou 350108, China 2. Fujian Key Laboratory of Mineral Resources, Fuzhou 350108, China 3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract：The Zijinshan gold-copper deposit is the first one of high sulfidation epithermal hydrothermal deposits. The gold bodies up, and the copper bodies down. The gold bodies mainly occur above the ground water table associated with strong silicification, and the copper bodies mainly occur below the ground water table associated with alunitization. The alunite of the Zijinshan gold-copper deposit has four types of occurrence status, that is the altered rock type, the intergrowth-with-Cu-sulphide type, the vein type and the powder type. Different types of the alunite are of different Raman spectra characteristics and fluorescence scattering background. Laser Raman spectra of inclusions in the alunite show that: (1) The characteristics of the Laser Raman spectra of the alunite are of characteristic spectral bands of alunite, just fluorescent scattering weaken gradually from the altered rock type, the intergrowth-with-Cu-sulphide type to the vein type; the alunite in the Powder type has different bands of the Laser Raman spectra relative to the former three types, the intensity of each band is weaker, and it’s fluorescent scattering intensity is strongger. (2) The bands in 100～700 cm-1 of the Laser Raman spectra can be used as "fingerprint" bands indicating the condition of the cation replacement in the molecular structure of alunite. The intensities at 161 and 234 peak change obviously in the bands of the alunite in the altered rock type, which indicating a wide replacement between K and Na; the intensities at 381 and 484 peak in the bands of the alunite in the intergrowth-with-Cu-sulphide type change significantly, indicating Al can be replaced with Cu, Ga, etc.; the larger and stable intensities of the alunite in the vein type in the bands at the peaks about 161, 234, 484, 508, etc. indicate that there are less chances with the replacement between K and Na, Al and Si; fluorescence scatorescent scattering is very strong and the intensity of each band is weaker in the bands of the alunite in the powder type, which indicate that the alunite formed in the underground water condition. (3) The laser Raman spectra of the alunite can be used together with it’s infrared spectra, and provide the characteristics of complete vibration spectra of the alunite and the structure information with the mineral research. Based on the mineralography, the petrography, the ore deposit geology, the geochemistry of mineral deposits, the regional geological features, the Laser Raman spectra of the alunite (Combined with fluorescence scattering background) can further the evolution process for the Zijinshan gold-copper deposit as a typical high sulfidation epithermal hydrothermal deposit.
