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Linsu L¨¹, School of Earth Science and Resources, China University of Geosciences;The Geological Museum of China (China)
Jingwen Mao, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
Zuoheng Zhang, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
Andao Du, National Research Center of Geoanalysis (China)
Wenjun Qu, National Research Center of Geoanalysis (China)
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Hongqiling is a large Cu-Ni sulfide deposit in the Jilin-Helongjiang Fold Belt of the Paleozoic Xing'an-Mongolian Orogenic Belt. The Hongqiling magmatic Cu-Ni sulfide deposit is located in south-central Jilin Province of northeastern (NE) China. Thirty-three mafic-ultramafic intrusions have been identified in the Hongqiling ore district hosted by the Early-Middle Paleozoic Hulan Group, extending in NW-SE direction with occurring in group and distributing in zoning (L et al., 2007). Five intrusions contain economic Cu-Ni mineralization, especially No.1 and No.7 in the southern part of the complex. The No.1 intrusion is the largest ore body in the area whereas the No.7 intrusion contains the most significant Cu-Ni mineralization.
The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. The rock-forming ages are SHRIMP zircon U-Pb dating of 216±5 Ma for leucogabbro (Wu et al., 2004) and 40Ar-39Ar plateau dating of 225.50±0.85 Ma and isochron dating of 226.97±2.42 Ma for biotite of feldspar-bearing cortlandtite form No.1 ore-bearing intrusion associated with Cu-Ni sulfide deposits (Xi et al., 2005).
In the present study, we use Re-Os dating of Cu-Ni bearing sulfide ores from the Hongqiling intrusion to further constrain the timing of mineralization. Samples include 6 pyrrhotites from the massive ores of No.7 in the Hongqiling mine. The pyrrhotites yield an isochron age of 208±21 Ma with an initial 187Os/188Os of 0.315±0.050 (MSWD = 2.4). This age which is the ore-forming age of Hongqiling mine is roughly coeval with the rock-forming ages of the Hongqiling complex dated at 216-225 Ma (Wu et al., 2004; Xi et al., 2005). The initial 187Os/188Os ratio of 0.315±0.050 for the Hongqiling Cu-Ni sulfide ores is higher than that of 0.10889±0.00035 for uncontaminated Archean komatiite-related Cu-Ni sulfide ores (Brookes et al., 1999), and even higher than that of 0.1326±0.0025 for the Noril'sk-Talnakh Cu-Ni sulfide ores, Russia (Stein et al., 1998). The higher initial radiogenic ratio indicates that the Hongqiling complex experienced extensive crustal contamination and suggests slightly more extensive assimilation in a crustal magma chamber (Harris and Chaumba, 2001).
Acknowledgements:
The Project of National Natural Science Foundation of China (40402012) and Project of China Geological Great Survey (1212010634001) supported this work.
References
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Wu, F.Y., et al., 2004. J. Asian Earth Sci. 23, 781-797.
Xi, A.H., et al., 2005. Mineral Deposits 24(5), 521-526 (in Chinese).
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