Isotope geochemistry and geochronology of the Niujuan silver deposit,northern North China Craton: Implications for magmatism and metallogeny in an extensional tectonic setting |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. School of Earth Science and Resources, China University of Geosciences, Xueyuan Road, Haidian District, Beijing 100083, China;3. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia;1. MLR Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Centre for Exploration Targeting, ARC Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;3. Mineral Branch of Hunan Institute of Geological Survey, Changsha, China;1. Department of Geological Sciences, Jadavpur University, Kolkata 700032, India;2. School of Geosciences, University of the Witwatersrand, Johannesburg 2001, South Africa;1. Department of Geological Sciences, Jadavpur University, Kolkata 700032, India;2. School of Petroleum Technology, Pandit Deendayal Petroleum University, Gandhinagar 382007, India;1. Department of Mineralogy-Petrology-Economic Geology, School of Geology, Faculty of Sciences, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece;2. School of Earth Science and Geological Engineering, Sun Yat-sen University, 510 275 Guangzhou, PR China;3. Department of Earth Sciences, Università degli Studi di Milano, Via Botticelli 23, Milano, Italy;4. Institute of Geology and Mineral Exploration, 501 00 Kozani, Greece;5. Department of Metallurgy and Materials Technology, School of Mining and Metallurgical Engineering, National Technical University of Athens, 157 80 Athens, Greece;6. Center for Electron Nanoscopy, Technical University of Denmark, Kongens Lyngby, Denmark;7. Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, 15784 Athens, Greece |
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| Abstract: | The Niujuan breccia-type silver deposit forms part of the North Hebei metallogenic belt along the northern margin of the North China Craton. The Hercynian Baiyingou coarse-grained granite and the Yanshanian Er’daogou fine-grained granite are the major Mesozoic intrusions exposed in this region. Here we investigate the salient characteristics of the mineralization and evaluate its genesis through zircon U-Pb and fluorite Sm-Nd age data, and Pb, S, O, H, He and Ar isotope data. The orebodies of the Niujuan silver deposit are hosted in breccias, which contain angular fragments of the Baiyingou and Er’daogou granitoids. The δ34S values of pyrite from the silver mineralized veins range from 2.4‰ to 5.3‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of the sulfide minerals show ranges of 16.837–16.932, 15.420–15.501 and 37.599–37.950, respectively. The 3He/4He and 40Ar/36Ar ratios of the fluids trapped in pyrite are 0.921–4.81Ra and 299.34–303.84, respectively. The δ18O and δ18Dw values of the ore-forming fluids range from 0.6‰ to ?4.15‰ and from ?119.4‰ to ?98.7‰, respectively. Our isotopic data suggest that the ore-forming fluids were originally derived from the subvolcanic plutons and evolved into a mixture of magmatic and meteoric water during the main hydrothermal stage. The ore-forming materials were primarily derived from the lower crust with limited incorporation of mantle materials. The emplacement time of the Er’daogou granite is constrained by LA-ICP-MS zircon U-Pb geochronology at 145.5 ± 2.1 Ma. Five fluorite samples from the last hydrothermal stage yielded a Sm-Nd isochron age of 139.2 ± 3.8 Ma, indicating the upper age limit for the silver mineralization. These ages correlate with the formation of the Niujuan deposit in an extensional setting associated with the closure of the Mongol-Okhotsk Ocean and the subduction of the Paleo-Pacific oceanic plate beneath the North China Craton. |
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| Keywords: | Zircon U-Pb geochronology Stable isotopes Fluorite Sm–Nd geochronology Niujuan silver deposit Northern North China Craton |
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