| Ore Genesis of the Kalatongke Cu–Ni Sulfide Deposits, Western China: Constraints from Volatile Chemical and Carbon Isotopic Compositions |
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| 作者姓名： | FU Piaoer TANG Qingyan ZHANG Mingjie ZHANG Zhaowei LI Liwu and LI Wenyuan |
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| 作者单位： | 1 Key Laboratory of Western China’s Environmental Systems (MOE), School of Earth Sciences, Lanzhou
University, Lanzhou 730000, China
2 Xi'an Institute of Geology and Mineral Resources, CGS, Xi'an 710054, China
3 Key Laboratory of Petroleum Resource Research, Institute of Geology and Geophysics, CAS, Lanzhou
730000, China |
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| 摘 要： | The Kalatongke Cu–Ni sulfide deposits located in the East Junggar terrane, northern Xinjiang, western China are the largest magmatic sulfide deposits in the Central Asian Orogenic Belt (CAOB). The chemical and carbon isotopic compositions of the volatiles trapped in olivine, pyroxene and sulfide mineral separates were analyzed by vacuum stepwise-heating mass spectrometry. The results show that the released volatiles are concentrated at three temperature intervals of 200–400°C, 400–900°C and 900–1200°C. The released volatiles from silicate mineral separates at 400–900°C and 900–1200°C have similar chemical and carbon isotopic compositions, which are mainly composed of H2O (av. ~92 mol%) with minor H2, CO2, H2S and SO2, and they are likely associated with the ore-forming magmatic volatiles. Light δ13CCO2 values (from ?20.86‰ to ?12.85‰) of pyroxene indicate crustal contamination occurred prior to or synchronous with pyroxene crystallization of mantle-derived ore-forming magma. The elevated contents of H2 and H2O in the olivine and pyroxene suggest a deep mantle-originated ore-forming volatile mixed with aqueous volatiles from recycled subducted slab. High contents of CO2 in the ore-forming magma volatiles led to an increase in oxygen fugacity, and thereby reduced the solubility of sulfur in the magma, then triggered sulfur saturation followed by sulfide melt segregation; CO2 contents correlated with Cu contents in the whole rocks suggest that a supercritical state of CO2 in the ore-forming magma system under high temperature and pressure conditions might play a key role in the assemblage of huge Cu and Ni elements. The volatiles released from constituent minerals of intrusion 1# have more CO2 and SO2 oxidized gases, higher CO2/CH4 and SO2/H2S ratios and lighter δ13CCO2 than those of intrusions 2# and 3#. This combination suggests that the higher oxidation state of the volatiles in intrusion 1# than intrusions 2# and 3#, which could be one of key ore-forming factors for large amounts of ores and high contents of Cu and Ni in intrusion 1#. The volatiles released at 200–400°C are dominated by H2O with minor CO2, N2+CO and SO2, with δ13CCO2 values (?25.66‰ to ?22.98‰) within the crustal ranges, and are considered to be related to secondary tectonic– hydrothermal activities.
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| 关 键 词： | Ore genesis chemical composition carbon isotope volatile mafic–ultramafic intrusion Kalatongke Cu–Ni sulfide deposits Xinjiang |
| 收稿时间： | 2011/11/25 0:00:00 |
| 修稿时间： | 2012/2/25 0:00:00 |
Ore Genesis of the Kalatongke Cu–Ni Sulfide Deposits,Western China: Constraints from Volatile Chemical and Carbon Isotopic Compositions |
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| Authors: | FU Piaoer TANG Qingyan ZHANG Mingjie ZHANG Zhaowei LI Liwu LI Wenyuan |
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| Institution: | 1. Key Laboratory of Western China's Environmental Systems (MOE), School of Earth Sciences, Lanzhou University, Lanzhou 730000, China;2. Xi'an Institute of Geology and Mineral Resources, CGS, Xi'an 710054, China;3. Key Laboratory of Petroleum Resource Research, Institute of Geology and Geophysics, CAS, Lanzhou 730000, China |
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| Abstract: | The Kalatongke Cu–Ni sulfide deposits located in the East Junggar terrane, northern Xinjiang, western China are the largest magmatic sulfide deposits in the Central Asian Orogenic Belt (CAOB). The chemical and carbon isotopic compositions of the volatiles trapped in olivine, pyroxene and sulfide mineral separates were analyzed by vacuum stepwise‐heating mass spectrometry. The results show that the released volatiles are concentrated at three temperature intervals of 200–400°C, 400–900°C and 900–1200°C. The released volatiles from silicate mineral separates at 400–900°C and 900–1200°C have similar chemical and carbon isotopic compositions, which are mainly composed of H2O (av. ～92 mol%) with minor H2, CO2, H2S and SO2, and they are likely associated with the ore‐forming magmatic volatiles. Light δ13CCO2 values (from –20.86‰ to –12.85‰) of pyroxene indicate crustal contamination occurred prior to or synchronous with pyroxene crystallization of mantle‐derived ore‐forming magma. The elevated contents of H2 and H2O in the olivine and pyroxene suggest a deep mantle‐originated ore‐forming volatile mixed with aqueous volatiles from recycled subducted slab. High contents of CO2 in the ore‐forming magma volatiles led to an increase in oxygen fugacity, and thereby reduced the solubility of sulfur in the magma, then triggered sulfur saturation followed by sulfide melt segregation; CO2 contents correlated with Cu contents in the whole rocks suggest that a supercritical state of CO2 in the ore‐forming magma system under high temperature and pressure conditions might play a key role in the assemblage of huge Cu and Ni elements. The volatiles released from constituent minerals of intrusion 1* have more CO2 and SO2 oxidized gases, higher CO2/CH4 and SO2/H2S ratios and lighter δ13CCO2 than those of intrusions 2# and 3#. This combination suggests that the higher oxidation state of the volatiles in intrusion 1# than intrusions 2# and 3#, which could be one of key ore‐forming factors for large amounts of ores and high contents of Cu and Ni in intrusion 1#. The volatiles released at 200–400°C are dominated by H2O with minor CO2, N2+CO and SO2, with δ13CCO2, values (–25.66‰ to –22.98‰) within the crustal ranges, and are considered to be related to secondary tectonic– hydrothermal activities. |
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| Keywords: | Ore genesis chemical composition carbon isotope volatile mafic–ultramafic intrusion Kalatongke Cu–Ni sulfide deposits Xinjiang |
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