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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 ~3He/~4He(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.
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 analysis on the pyrites formed during two stages of mineralization. Results that results in 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, 1523-15.556, and 17.806-18.052, respectively, indicating a mixed crust-mantle so Urce.The He-Ar results exhibit different compositions of the two stages: the ~ 3He / ~ 4He (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 pyrites are 0.23-0.34 and 305-361, respectively. Two 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.