Constraints of Sr isotopic compositions of apatite and carbonates on the origin of Fe and Cu mineralizing fluids in the Lala Fe-Cu-(Mo,LREE) deposit,SW China |
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| Institution: | 1. School of Physical Sciences, The University of Adelaide, Adelaide, SA 5000, Australia;2. School of Chemical Engineering, The University of Adelaide, Adelaide, SA 5000, Australia;3. BHP Olympic Dam, Adelaide, SA 5000, Australia;1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;2. Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR, China;3. Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;4. School of Earth Sciences, China University of Geosciences, Beijing, China;5. Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, China;1. Department of chemical engineering and geosciences, Luleå University of Technology, SE-971 87 Luleå, Sweden;2. Swedish Museum of Natural History, Department of Geosciences, , Box 50007, SE-104 05 Stockholm, Sweden;3. Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden;1. MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Science, Beijing 100037, China;2. School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 10009, China;4. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | Numerous Fe-Cu deposits with mineralization styles similar to iron oxide-copper gold (IOCG) deposits form the Kangdian Fe-Cu metallogenic province, southwestern (SW) China. As one of the largest deposits in the region, the ~ 1.0 Ga Lala Fe-Cu deposit is hosted in a Paleoproterozoic volcanic-sedimentary succession named the Hekou Group which is alternately intruded by ~ 1.0 Ga doleritic plutons. This deposit has a paragenetic sequence evolving from Stage I of Na-alteration to Stage II of Fe mineralization, and finally to Stage III of Cu-(Mo, REE) mineralization, coeval with mafic-felsic intra-plate magmatism in the region. This study conducted in-situ Sr isotopic analyses on apatite and carbonate, aiming to resolve the long controversial issue regarding the origin of the Fe and Cu mineralizing fluids in the deposit. Apatite of Stage II has 87Sr/86Sr ratios varying from 0.71380 to 0.72733, much higher than those of synchronous igneous rocks in the region (0.7074 to 0.7091), but similar to the Paleoproterozoic host rocks (0.71368 to 0.71837 at ~ 1.0 Ga). This similarity indicates that radiogenic Sr of the Fe mineralizing fluid was dominantly sourced from the host rocks. Apatite and calcites of Stage III have 87Sr/86Sr ratios (0.75758–0.79293) much higher than apatite of Stage II and the host rocks but similar to the Archean basement rocks (as high as 0.80 at ~ 1.0 Ga) beneath the cover of the Yangtze Block, suggesting that the highly radiogenic Sr isotopic composition of the Cu mineralizing fluid was mainly inherited from the old basement rocks. In combination with previous C-O-S isotopic data indicating a magma-hydrothermal origin, it was suggested that the Fe mineralizing fluid was exsolved from a mafic magma that generated the ~ 1.0 Ga doleritic plutons, and inherited radiogenic Sr from the host rocks during fluid-rock interaction. By contrast, the Cu mineralizing fluid might have been sourced from another pulse of magmatic, Cu-Mo-REE- and CO2-rich fluid which have once interacted with Archean basement rocks prior to mineralization. The source of such a Cu-Mo-REE-rich fluid was not well constrained in current study but was inferred to be exsolved from a hidden felsic magma. We propose that intrusions of the bimodal magmas in Kangdian are responsible for regional hydrothermal circulation which led to Fe-Cu-(Mo, REE) mineralization in the Kangdian province. |
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