High oxidation magmatic evolution in the Naruo porphyry Cu deposit,Tibet, China |
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| Institution: | 1. Chengdu University of Technology, Chengdu 610059, China;2. Chengdu Center, China Geological Survey, Chengdu 610081, China;3. Land and Resources Department of Tibet Province, Lasa, Tibet 850000, China;4. Geological Team 5 of the Tibet Bureau of Geology and Mineral Exploration and Development, Golmud, Qinghai 816000, China;1. The College of Earth Sciences, Jilin University, Changchun 130061, PR China;2. No. 5 Geological Party, Tibet Bureau of Geology and Exploration, Golmud 816000, PR China;3. School of Earth Science and Resources, China University of Geosciences, Beijing 10083, PR China;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;3. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China;4. John de Laeter Center for Isotope Research, TIGeR, Applied Geology, Curtin University, Perth, WA 6945, Australia;5. University of Chinese Academy of Sciences, Beijing 100049, China;1. College of Earth Sciences, Jilin University, Changchun 130061, China;2. Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources of China, Changchun 130061, China;1. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. State Key Laboratory of Geological Processes and Mineral Resources, and Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;1. College of Earth Science, Jilin University, Changchun 130061, PR China;2. Lab of Continental Collision and Plateau Uplift, Qinghai–Tibet Plateau Institute of the Chinese Academy of Sciences, Beijing 100101, PR China |
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| Abstract: | The Naruo porphyry Cu deposit is the third largest deposit discovered in the Duolong metallogenic district. Previous research has focused mainly on the geochemistry of the ore-bearing granodiorite porphyry; the metallogenesis remains poorly understood. In the present work, on the basis of outcrops and drilling core geological mapping, phases of early mineralization diorite, two inter-mineralization granodiorite porphyries, and late-mineralization granodiorite porphyry have been distinguished. Furthermore, the alteration zones were outlined, and the vein sequence was identified. The diorite and three porphyry phases were subjected to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (La–ICP–MS) zircon U–Pb dating and in situ Hf isotope analyses as well as bulk major element, trace element, and Sr–Nd isotopic analyses. Molybdenite Re–Os dating was also conducted.The zircon U–Pb dating results show that the diorite and porphyry intrusions were emplaced at about 120 Ma, and the molybdenite Re–Os isochron age is 118.8 ± 1.9 Ma; this indicates that the Naruo porphyry Cu deposit was formed during a continuous magmatic–hydrothermal process. All of the diorite and granodiorite porphyry samples showed arc magmatic characteristics. Moreover, the moderate (87Sr/86Sr)i ratios and low εNd(t) and εHf(t) values of the diorite and porphyry intrusions suggest the source region of the juvenile lower crust. The lower (87Sr/86Sr)i and (143Nd/144Nd)i ratios and higher εNd(t) values and incompatible element concentrations than those in the granodiorite porphyry samples indicate a two-stage magmatic generation process for the intrusions. The early mineralization diorite has a high Cu concentration, implying that the source is enriched in Cu. However, the slightly lower Cu content of the late-mineralization granodiorite porphyry samples might imply Cu release from magmas and deposition within the metallogenic stage. The multiple stages of intrusions and subsequent volcanism within the Duolong metallogenic district, together with high Sr/Y features, indicate persistent magmatism during the metallogenic epoch, which is necessary for maintaining the activity of magmatic–hydrothermal and mineralization processes. Thus, the high Cu content in the source region, mantle-derived melt upwelling, and multiple stages of persistent magmatism were favorable for the formation of the Naruo porphyry Cu deposit.The high Fe2O3/FeO ratios of the diorite and granodiorite porphyry intrusions show very high oxidation features, which is coincident with estimated magmatic oxidation state calculated by the zircon trace element compositions. The high oxidation facilitates sulfur and chalcophile metals to be scavenged into the magmatic–hydrothermal systems, which is crucial for the metallogenesis of the Naruo porphyry Cu deposit. |
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