Genesis of the Saishitang skarn type copper deposit, West Qinling, Qinghai Province: evidence from fluid inclusions and stable isotopes

Lu, Yingchuan, Liu, Jiajun, Zhang, Dong, Carranza, Emmanuel John M., Zhai, Degao, Ge, Liangsheng, Sun, Hao, Wang, Bin, Chen, Yongfu, and Liu, Peng (2016) Genesis of the Saishitang skarn type copper deposit, West Qinling, Qinghai Province: evidence from fluid inclusions and stable isotopes. Ore Geology Reviews, 75. pp. 268-283.

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The Saishitang skarn type copper deposit, located in the southeast part of the Dulan–Ela Mountain Triassic volcanic–magmatic arc and forearc accretionary wedge, belongs to the Tongyugou–Saishitang tin–copper polymetallic ore field in West Qinling, Qinghai province. Based on the contact/crosscutting relationships, mineral associations and mineralization characteristics, hydrothermal fluid evolution can be divided into three stages: skarn (I), quartz sulfide (II) and polymetallic sulfide-bearing quartz–calcite vein (III). The quartz sulfide stage (II) can be further divided into a massive sulfide stage (II-1) and a layered sulfide stage (II-2). This paper presents detailed analysis of fluid inclusions, H–O, S and Pb isotope compositions of rock samples from each of the above three stages as well as analysis of fluid inclusions from quartz diorite. The homogenization temperature, salinity, density and pressure of fluid inclusions in quartz diorite and typical transparent minerals showed a tendency of gradual decline in these evolutionary stages. The ore-forming fluid can be classified as a Na+–Ca2 +–SO42 − Cl− system with a minor proportion of a Na+–Ca2 +–NO3− SO42 − system, which likely resulted from mixing of magmatic and formation water. The H–O isotope composition indicates that the proportion of formation water increased during the ore-forming process, and meteoric water was mixed in the late quartz–calcite vein stage. The δ34S (CDT) values (− 6.45–5.57‰) and Pb isotope compositions show that the ore-forming materials were mainly derived from magmatic fluid. Ore-forming fluid was boiling during the main ore-forming stage (II-1) due to pressure decrease. Consequently, the physical and chemical conditions (i.e., pH, Eh, fO2, fS2) changed, and metallic elements (including Cu) in the fluid could no longer exist in the form of complexes and precipitated from the fluid. According to the integrated analysis of ore features, mineral associations, alteration characteristics, ore-forming environment and fluid evolutionary process, it is concluded that the Saishitang deposit is a typical skarn deposit.

Item ID: 43172
Item Type: Article (Research - C1)
ISSN: 1872-7360
Keywords: fluid inclusion; stable isotope; West Qinling; Saishitang copper deposit
Funders: Geological Survey Project of China, Geological Survey Projects of China Geological Survey, National Natural Science Foundation of China (NNSFC)
Projects and Grants: Grant No. 1212011220924, Grant No. 1212011220899, NNSFC Grant No. 41030423
Date Deposited: 16 Mar 2016 02:46
FoR Codes: 37 EARTH SCIENCES > 3703 Geochemistry > 370303 Isotope geochemistry @ 30%
37 EARTH SCIENCES > 3705 Geology > 370508 Resource geoscience @ 20%
37 EARTH SCIENCES > 3703 Geochemistry > 370399 Geochemistry not elsewhere classified @ 50%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8401 Mineral Exploration > 840199 Mineral Exploration not elsewhere classified @ 40%
97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 60%
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