Sulfur Isotopic Variation of Yanshanian Magmatic-hydrothermal Deposits in Southern China |
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| Authors: | Ping'an WANG Shunso ISHIHARA |
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| Institution: | Geological Survey of Japan, Higashi 1–1–3, Tsukuba 305–8567, Japan [e-mail: ] |
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| Abstract: | Abstract: Sulfur isotope data (δ34S) of sulfides of more than 6700 samples from 157 ore deposits associated with Early and Late Yanshanian granitic and volcanic activities in South China are reviewed and summarized. Averaged δ34S values of individual deposits vary from ‐9. 3 to +20. 6%, and show a normal distribution pattern with the average of +2%. About 88 % of the ore deposits have values within the range, ?2.5 ? +13.6‰, of associated Yanshanian granitoids. There is a temporal‐spatial variation of δ34S values of the ore deposits. However, no clear zonal distribution parallel to geotectonic NNE lineaments was observed. Spatial distribution of ore sulfide δ34S values in most of the NE part of the whole studied area coincides with that of Yanshanian granitoids and volcanic rocks. A downward tendency of the average values in time is: +3. 0% (n=7, J1) → +1. 6% (n=29, J2) → +1. 7% (n=68, J3) → +1. 8% (n=37, K1) → ?1. 5% (n=16, K2). There is an “island” of high and variable δ34S values (0? +16.5‰) occurring within a generally low trough zone (?8 ? 0%) of N‐S about 800 km and E‐W 100 to 300 km, bounded by 110°E ? 116°E longitudes and 22°N ? 31°N latitudes. The island occurs at the junction of three tectonic units and a NE‐trending crustal matching line implying a variety of magmatism occurred at the junction. The low trough zone coincides with a low ferric/ferrous ratio zone of Early Yanshanian granitoids, indicating their genetic relationship. Different genetic types of ore deposits show different histogram patterns suggesting different relationships to magmatic rocks and host strata. Granite/greisen/pegmatite type deposits are most closely associated with granitoids, with average ore sul‐fide δ34S values for individual ore deposits ranging between ‐2. 0 and +4. 1%, and an average of +0. 5% (n = 15) close to type meteoric value of 0%. Porphyry‐type deposits have also narrow range of ?2.2 ? + 4.9‰, with an average value of +1. 1% (n = 18). Skarn‐type dominated ore deposits have a nearly normal distribution pattern with an average of +1. 6% (n = 62), ranging from ‐5. 3 to +11. 5%. Volcano‐subvolcanic ore deposits range between ‐3. 1 and +5. 9% with an average of +2. 3% (n = 19). Other types of hydrothermal ore deposits have averaged δ34S values of individual ones from ‐9. 3 to +20. 6%, with average value of +1. 3% (n=43). Vertical and horizontal zonations of δ34S values of ore deposits around their associated granitoid plutons are observed in several localities. Such zonations may be caused by interaction between magma and/or magmatic fluids and host sedimentary rocks, as well as the evolution of physico‐chemical conditions of ore‐forming fluids. Spatial distribution of ore sulfur isotope compositions is also clearly controlled by tectonics and deep faults. Ore sulfur isotope composition is sometimes strongly affected by host sedimentary rocks, especially by evaporite sulfur with much higher δ34S value and partly by biogenic sulfur with low δ34S value. The δ34S values of Yanshanian granitoids are from ‐2. 5 to +13. 6% for both rock samples and pyrite/pyrrhotite separates from granitic rocks, with similar spatial distribution pattern to those of associated ore deposits. The ore deposits associated with ilmenite‐series granitoids have δ34S values ranging between ‐7. 5 and +10. 4% with an average of +1. 0%, while the ore deposits associated with magnetite‐series granitoids ranging between ?8.0 ? +11.5‰ with an average of +1. 1%. δ34S values of ore deposits tend to converge to +3% as the Fe2O3/FeO ratio of associated granitoids increases from 0. 45 to 8. 7. |
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| Keywords: | Yanshanian granitoids ore deposits genetic types evaporite sulfate sulfur isotope |
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