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He‐Ar‐S‐Pb Isotopic Compositions of Pyrite: Constraints on the Source of Ore‐forming Materials of the Chengchao Skarn Iron Deposit, SE Hubei Province, Eastern China
Author(s) -
LI Wei,
XIE Guiqing,
ZHU Qiaoqiao
Publication year - 2016
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12816
Subject(s) - pyrite , skarn , anhydrite , geology , geochemistry , mineralization (soil science) , meteoric water , magmatic water , mineralogy , magnetite , sedimentary rock , hydrothermal circulation , fluid inclusions , gypsum , paleontology , seismology , soil science , soil water
The Chengchao iron deposit, the largest high‐grade skarn iron deposit in southeastern Hubei Province, contains considerable amounts of magnetite and by‐product anhydrite. To obtain better understanding of the ore‐formation process, this study carried out He‐Ar‐S‐Pb multi‐isotopic analyses on the pyrites formed during two stages of mineralization. The results indicate that the δ 34 S values (ranging from 14.0‰ to 17.6‰) of pyrites formed from the two stages have no obvious differences, suggesting that they were not derived from a single magmatic sulfur source. The δ 34 S values of anhydrite mostly range from 21.9‰ to 28.4‰, similar to that of the Middle Triassic sedimentary anhydrite in the Middle‐Lower Yangtze River metallogenic belt (MLYRB). The Pb isotopic compositions of the pyrites of both stages are homogeneous, with values of 208 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 206 Pb/ 204 Pb being 38.006–38.257, 15.523–15.556, and 17.806–18.052, respectively, indicating a mixed crust‐mantle source. The He‐Ar results exhibit different compositions of the two stages: the 3 He/ 4 He (R/Ra) and 40 Ar/ 36 Ar values for the early‐stage pyrite are 0.46–0.63 and 311–322, respectively, whereas the values for late‐stage pyrite are 0.23–0.34 and 305–361, respectively. Both stages of pyrites indicate the multiple sources of the ore‐forming fluids, with decreasing amount of magmatic water and increasing amount of modified meteoric water(MASW) during fluid evolution. The Triassic evaporites played an important role in the mineralization process.