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Iron isotope fractionation during magmatic-hydrothermal evolution: A case study from the Duolong porphyry Cu-Au deposit, Tibet
Li, JX (Li, Jin-Xiang)1,2; Qin, KZ (Qin, Ke-Zhang)2,3; Li, GM (Li, Guang-Ming)2,3; Evans, NJ (Evans, Noreen J.)4; Huang, F (Huang, Fang)5; Zhao, JX (Zhao, Jun-Xing)3
Source PublicationGEOCHIMICA ET COSMOCHIMICA ACTA
2018-12-01
Volume238Issue:0Pages:1-15
DOI10.1016/j.gca.2018.07.008
Abstract

Ore-forming fluids ultimately precipitate Fe-bearing sulfides and oxides in hydrothermal ore deposits and the Fe isotopic composition of these minerals can trace magmatic-hydrothermal evolution. Here, we report on the Fe isotopic compositions of a suite of hydrothermal minerals (magnetite, pyrite, and chalcopyrite) and granodiorite porphyry from the giant Duolong porphyry Cu-Au deposit (Bolong and Duobuza section), central Tibet. Most magnetite grains with potassic alteration show only minor delta Fe-57 variation (0.38 +/- 0.07 parts per thousand to 0.52 +/- 0.04 parts per thousand in Bolong and 0.68 +/- 0.02 parts per thousand to 0.77 +/- 0.08 parts per thousand in Duobuza), consistent with the equilibrium fluid delta Fe-57 (similar to-0.3 parts per thousand and similar to-0.1 parts per thousand, respectively) at similar to 550-480 degrees C. The equilibrium fluids have lighter Fe isotope signatures than the Duolong granodiorite porphyry (delta Fe-57 = 0.03 +/- 0.06 parts per thousand to 0.07 +/- 0.02 parts per thousand), corroborating the hypothesis that exsolved fluids should have a lighter Fe isotopic composition relative to parental magmas. Chalcopyrite from the mineralized Bolong and Duobuza porphyries have relatively consistent delta Fe-57 values of -0.60 +/- 0.07 parts per thousand to -0.42 +/- 0.07 parts per thousand and -0.40 +/- 0.08 parts per thousand to -0.30 +/- 0.05 parts per thousand, respectively, with equilibrium fluids at similar to 450-350 degrees C having lighter delta Fe-57 values of similar to-0.7 parts per thousand and similar to-0.6 parts per thousand. The trend of decreasing delta Fe-57 values in evolved fluids likely reflects Rayleigh fractionation of magnetite enriched in heavy Fe isotopes. This supposition is supported by the lighter delta Fe-57 value (0.25 +/- 0.07 parts per thousand) recorded in magnetite that equilibrated with a lighter delta Fe-57 fluid (similar to-0.5 parts per thousand) at similar to 470 degrees C. Compared to chalcopyrite, pyrite from the Bolong and Duobuza sections have heavier delta Fe-57 values of 0.35 +/- 0.06 parts per thousand to 0.71 +/- 0.06 parts per thousand and 0.53 +/- 0.06 parts per thousand to 0.71 +/- 0.07 parts per thousand, respectively. The pyrite values correlate variably with the Fe isotopic composition of ore-forming fluids (delta Fe-57 -0.6 parts per thousand to -0.7 parts per thousand), likely due to variations in the degree of Fe isotope exchange between pyrite and fluid. Moreover, combined with previously published Fe isotopic compositions of hydrothermal minerals from oxidized and reduced ore deposits, the results show that chalcopyrite in oxidized hydrothermal deposits always has a lighter Fe isotopic composition than chalcopyrite from reduced hydrothermal deposits. This is likely controlled by melt composition and precipitation of magnetite/pyrrhotite-bearing mineral assemblages. Therefore, the Fe isotopic composition of chalcopyrite could be a useful diagnostic tool for distinguishing oxidized from reduced fluids in hydrothermal systems. (C) 2018 Elsevier Ltd. All rights reserved.

Subject Area地质学
WOS IDWOS:000441893500001
Language英语
Indexed BySCIE
KeywordFe-isotope Copper-deposit U-pb Qiangtang Terrane High-temperature El-salvador Re-os Gold Mineralization Geochronology
WOS Research AreaGeochemistry & Geophysics
WOS SubjectGeochemistry & Geophysics
Cooperation Status国际
ISSN0016-7037
Department大陆碰撞与高原隆升重点实验室
PublisherPERGAMON-ELSEVIER SCIENCE LTD
Citation statistics
Cited Times:1[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://ir.itpcas.ac.cn/handle/131C11/8539
Collection图书馆
Corresponding AuthorLi, JX (Li, Jin-Xiang)
Affiliation1.Chinese Acad Sci, Inst Tibetan Plateau Res, Key Lab Continental Collis & Plateau Uplift, Beijing 100101, Peoples R China;
2.CAS Ctr Excellence Tibetan Plateau Earth Sci, Beijing 100101, Peoples R China;
3.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Mineral Resources, Beijing 100029, Peoples R China;
4.Curtin Univ, John de Laeter Ctr, TIGeR, Appl Geol, Perth, WA 6945, Australia;
5.Univ Sci & Technol China, Sch Earth & Space Sci, CAS Key Lab Crust Mantle Mat & Environm, Hefei 230026, Peoples R China.
Recommended Citation
GB/T 7714
Li, JX ,Qin, KZ ,Li, GM ,et al. Iron isotope fractionation during magmatic-hydrothermal evolution: A case study from the Duolong porphyry Cu-Au deposit, Tibet[J]. GEOCHIMICA ET COSMOCHIMICA ACTA,2018,238(0):1-15.
APA Li, JX ,Qin, KZ ,Li, GM ,Evans, NJ ,Huang, F ,&Zhao, JX .(2018).Iron isotope fractionation during magmatic-hydrothermal evolution: A case study from the Duolong porphyry Cu-Au deposit, Tibet.GEOCHIMICA ET COSMOCHIMICA ACTA,238(0),1-15.
MLA Li, JX ,et al."Iron isotope fractionation during magmatic-hydrothermal evolution: A case study from the Duolong porphyry Cu-Au deposit, Tibet".GEOCHIMICA ET COSMOCHIMICA ACTA 238.0(2018):1-15.
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