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Geological Journal of China Universities ›› 2023, Vol. 29 ›› Issue (2): 174-185.DOI: 10.16108/j.issn1006-7493.2021047

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Characteristics of Mineralizing Fluids Forming the Debao Skarn-type Deposit in Guangxi Province

WANG Chenguang1,2,ZHANG Dehui1,LIU Xiangchong2,3*,XIAO Changhao2,3   

  1. 1. School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China;
    2. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;
    3. Key Laboratory of Paleomagnetism and Tectonic Reconstruction, Ministry of Natural Resources, Beijing 100081, China
  • Online:2023-04-20 Published:2023-04-20

Abstract: The Debao skarn-type copper-tin deposit in the Youjiang Basin is the largest copper deposit in Guangxi province. Little is known about the geochemical characteristics of ore-forming fluids and the occurrence state of tin beyond its chronology and mineralogy. We constrain the characteristics and parameters of mineralizing fluids using microprobe analysis, fluid inclusion petrography and microthermometry, and geochemical modeling. Different from typical skarn-type copper deposits, the garnet in Debao belongs to the end-member of pyrope and grossular and contains a small amount of andradite. Tin occurs mainly in chalcopyrite and pyrite, and its abundance can reach up to 0.11%. The homogenization temperatures of fluid inclusions in garnet are 182- 249 ℃ with an average of 219 ℃ , and those of fluid inclusions in calcite ranges from 109 ℃ to 215 ℃ with an average of 157 ℃ . Therefore, the mineralizing fluids in the early stage of the Debao deposit were interpreted to be of low temperature and mediumlow salinity, while those in the late quartz-carbonate stage are characterized by low temperature and low salinity. Temperature decrease favors precipitation of chalcopyrite. The oxygen fugacity and sulfur fugacity of the Debao deposit constrained from equilibrium phase diagrams of Cu-S-O and Fe-S-O systems under mineralization temperatures are log fS2 >-20, and -44<log fO2 <-25, respectively. The oxygen fugacity levels of the Debao deposits were higher than those of typical tin deposits and the high log fO2 fluid environment prevents tin transport in fluids. This is probably one of reasons why cassiterite is rare in the Debao deposit.

Key words: Debao copper deposit, fluid inclusion, metal sulfides, geochemical modeling

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