Application of short- wavelength infrared spectroscopy in porphyry- epithermal system: a case study of Tiegelongnan super- large copper (gold) deposit, Tibet
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    Abstract:

    The Tiegelongnan copper (gold) deposit is the first porphyry- high sulfide type- epithermal deposit in Tibet. Figuring out the accurate alteration zonation of the deposit is pivotal to the subsequent exploration. In this paper, we use the short wavelength infrared spectroscopy (SWIR) to extract the altered mineral information of Tiegelongnan deposit, and use X- ray diffraction (XRD) as a supplementary method for mineral identification. Combined with petrography, electron probe microanalysis (EPMA), and the spectral parameters of sericite, the alteration zonation model of Tiegelongnan ore district was constructed, and its significance for exploration was evaluated. The results show that eight typical alteration minerals (kaolinite, alunite, dickite, pyrophyllite, muscovite, gypsum, diaspore and montmorillonite) can be identified by the SWIR. Meanwhile, according to the spatial distribution of the alteration mineral assemblage, from the center of porphyry to the outside, the alteration includes potassium silicate alteration, sericite- quartz alteration and propylitization alteration, which are widely superimposed by later argillic alteration in the middle and shallow part. Sericite was widely spread in mineral area. Its main absorption valley spectral wavelength ranges from 2196. 4 nm to 2214. 8 nm (average value is 2206. 6 nm), the main absorption valley wavelengths of sericite in the deep potassium silicate alteration zone and sericite alteration zone are obviously different. The wavelength of sericite in the potassium silicate alteration zone in the deep part can be greater than 2210 nm, while sericite in sericite- quartz alteration has Pos2200 2206 to 2208 nm. The absorption peak wavelength of sericite at 1400 nm (Pos1400) and the absorption depth of sericite Al- OH (Dep2200) values of muscovite have a good positive correlation with the copper mineralization intensity, which can be used as an indicator for subsequent exploration and evaluation of porphyry epithermal deposits. We concluded that the elevated Pos2200 (<2203 nm) and SWIR- IC values (>5. 5) can indicate that the hydrothermal mineralization center of Tiegelongnan deposit is mainly located in the deep of ZK2404.

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Tang Nan, Lin Bin, Li Yubin, Wang Yiyun, Li Jiajiun.2021. Application of short- wavelength infrared spectroscopy in porphyry- epithermal system: a case study of Tiegelongnan super- large copper (gold) deposit, Tibet[J]. Acta Geologica Sinica,95(8):2613-2627

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History
  • Received:December 20,2020
  • Revised:January 22,2021
  • Adopted:January 23,2021
  • Online: May 27,2021
  • Published: