Alteration and mineralization at the Zhibula Cu skarn deposit,Gangdese belt,Tibet |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, and Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;2. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;1. Department of Earth Sciences, Faculty of Natural Sciences, University of Tabriz, 5166616471 Tabriz, Iran;2. Department of Geology, Faculty of Science, University of Zanjan, 45371-38791 Zanjan, Iran;3. ARC Centre of Excellence in Ore Deposits (CODES), School of Physical Sciences, University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australia;1. CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 10094, China;3. SOA Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;4. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;5. Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China;6. Center of Deep Sea Research, Institute of Oceanography, Chinese Academy of Sciences, Qingdao 266071, China;7. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China;8. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;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, Beijing 100083, China;3. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;4. Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China;5. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;6. Petrochina Research Institute of Petroleum Exploration & Development, Beijing 100083, China |
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| Abstract: | The Zhibula Cu skarn deposit contains 0.32 Mt. Cu metal with an average grade of 1.64% and is located in the Gangdese porphyry copper belt in southern Tibet. The deposit is a typical metasomatic skarn that is related to the interaction of magmatic–hydrothermal fluids and calcareous host rock. Stratiform skarn orebodies occur at the contact between tuff and marble in the Lower Jurassic Yeba Formation. Alteration zones generally grade from a fresh tuff to a garnet-bearing tuff, a garnet pyroxene skarn, and finally to a wollastonite marble. Minor endoskarn alteration zonations are also observed in the causative intrusion, which grade from a fresh granodiorite to a weakly chlorite-altered granodiorite, a green diopside-bearing granodiorite, and to a dark red-brown garnet-bearing granodiorite. Prograde minerals, which were identified by electron probe microanalysis include andradite–grossularite of various colors (e.g., red, green, and yellow) and green diopside. Retrograde metamorphic minerals overprint the prograde skarn, and are mainly composed of epidote, quartz, and chlorite. The ore minerals consist of chalcopyrite and bornite, followed by magnetite, molybdenite, pyrite, pyrrhotite, galena, and sphalerite. Three types of fluid inclusions are recognized in the Zhibula deposit, including liquid-rich two-phase inclusions (type L), vapor-rich two-phase inclusions (type V), and daughter mineral-bearing three-phase inclusions (type S). As the skarn formation evolved from prograde (stage I) to early retrograde (stage II) and later retrograde (stage III), the ore-forming fluids correspondingly evolved from high temperature (405–667 °C), high salinity (up to 44.0 wt.% NaCl equiv.), and high pressure (500–600 bar) to low-moderate temperature (194–420 °C), moderate-high salinity (10.1–18.3 and 30.0–44.2 wt.% NaCl equiv.), and low-moderate pressure (250–350 bar). Isotopic data of δ34S (? 0.1‰ to ? 6.8‰, estimated δ34Sfluids = ? 0.7‰), δDH2O (? 91‰ to ? 159‰), and δ18OH2O (1.5‰ to 9.2‰) suggest that the ore-forming fluid and material came from magmatic–hydrothermal fluids that were associated with Miocene Zhibula intrusions. Fluid immiscibility likely occurred at the stage I and stage II during the formation of the skarn and mineralization. Fluid boiling occurred during the stage III, which is the most important Cu deposition mechanism for the Zhibula deposit. |
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