Xiao Wenjiao

Re–Os Isotopic Age of the Hongqiling Cu-Ni Sulfide Deposit in Jilin Province,NE China and its Geological Significance

The major Hongqiling Cu-Ni sulfide deposit in central Jilin Province is located in the eastern part of the Central Asian Orogenic Belt. Rhenium and osmium isotopes in sulfide minerals from the deposit have been used to determine the timing of mineralization and the source of osmium and, by inference, the ore metals. Sulfide ore samples have osmium and rhenium concentrations of 0.28-1.07ppb and 2.39-13.17ppb, respectively. Ten sulfide analyses yield an isochron age of 223 ± 9 Ma, indicating that the Cu-Ni sulfide mineralization formed in the Early Triassic. The initial 187Os/188Os ratio is 0.295 ± 0.019 (MSWD = 1.14). This data indicates that the mineralization was derived mainly from a mantle source with some quantities of crustal components introduced into the rockforming and ore-forming systems during mineralization and magmatic emplacement. Together with the widespread occurrence of late Carboniferous-Permian mafic–ultramafic complexes and associated Permian Cu-Ni deposits in the western part of the Central Asian Orogenic Belt (Northern Xinjiang), we conclude that mantle-crustal interactions were active during the accretion-collisional processes that led to the Cu-Ni mineralization and considerable continental growth in the late Carboniferous-Permian to mid-Triassic.

The Paleoproterozoic Chibaisong Mafic-Ultramafic Intrusion and Cu-Ni Deposit, North China Craton: SHRIMP Zircon U-Pband Re-Os Geochronology and Geodynamic Implications

The Chibaisong magmatic Ni–Cu sulfide deposit (Jilin Province, NE China) is located in the Jiao-Liao-Ji Belt of the North China Craton. The ore-bearing mafic-ultramafic intrusions intrude the metamorphic rocks of the lowermost Sidaolazi Formation of the Anshan Group. SHRIMP zircon U-Pb dating gives a maximum depositional age of 2188 ± 8 Ma (95% confidence level, MSWD=3.2, n=8) for the host sedimentary rocks of the Chibaisong deposits. Rhenium and osmium isotopic analyses of Ni-and Cu-bearing sulfide minerals from the deposit have been used to determine the timing of mineralization, the source of osmium, and, by inference, the source of ore metals. Sulfide ore samples have Os and Re concentrations ranging from 19 to 490 ppb and from 0.47 to 13.97ppb, respectively. Analyses of these data yield a six-point isochron age of 1885 ± 94 Ma. An initial 187Os/188Os ratio of 0.80 ± 0.16 (mean square of weighted deviates=0.17) and δ34S values of -1.1 to +0.7‰ for the ores, as well as initial 87Sr/86Sr ratios of 0.703-0.708 for metalliferous intrusions, suggest a magmatic source for the ores, with the melts dominated by mantle contributions. The Chibaisong intrusion was previously considered to have formed under a post-orogenic extensional setting in the Early Cretaceous. However, our new Re-Os geochronological result indicates that the Chibaisong mafic-ultramafic intrusion, along with the Cu-Ni deposit, was related to a Paleoproterozoic extensional event, not resulting from an Early Cretaceous post-orogenic extension as previously considered.

Re-Os Dating of Molybdenites from the Daheishan Mo Deposit in the Eastern Central Asian Orogenic Belt, NE China, and its Geological Significance

The Daheishan Mo deposit is located in the eastern part of the Central Asian Orogenic Belt NE China. Rhenium and osmium isotopes in molybdenites from the Daheishan porphyry Mo deposit have been used to determine the age of mineralization. Molybdenite was analyzed mainly from granodiorite porphyry, which is characterized by moderate to strong silicification. Rhenium concentrations in molybdenite samples are between 17 and 30 μg/g. Analysis of seven molybdenite samples yields an isochron age of 168.0 ± 4.4 Ma (2σ). Based on the geological history and spatial temporal distribution of the granitoids, it is proposed that the Mo deposits in the eastern China were related to the subduction of the Paleo-Pacific plate during Jurassic time.