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The Ore-forming Mechanism of the Jiajika Pegmatite-Type Rare Metal Deposit in Western Sichuan Province:Evidence from isotope dating

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Acta Geologica Sinica(English Edition) 2013年第1期87卷 91-101页

作者： LI Jiankang WANG Denghong CHEN Yuchuan MLR Key Laboratory of Metallogeny and Mineral Assessment Institute of Mineral ResoucesCAGS Colleage of Earth Science and Resources Chang'an University

Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma; however, these proposals are based mainly on analyses of fluid and melt inclusions. Here, we use the Jiajika pegmatite deposit, the largest spodumene deposit in Asia, as a case study to investigate ore forming processes using isotope dating. dating of a single granite sample from the Jiajika deposit using multiple methods gave a zircon U-Pb SHRIMP age of 208.4 ~ 3.9 Ma, an 4~Ar/39Ar age for muscovite of 182.9 ~ 1.7 Ma, and an 4~Ar/39Ar age for biotite of 169.9 ＋ 1.6 Ma. Based on these dating results and the 4~Ar/39Ar age of muscovite from the Jiajika pegmatite, a temperature-time cooling track for the Jiajika granite was constructed using closure temperatures of the different isotope systems. This track indicates that the granite cooled over ^-40 m. y., with segregation of the pegmatite fluid from the granitic magma at a temperature of ~700~C. This result suggests that the Jiajika pegmatite formed not by fractional crystallization, but by segregation of an immiscible liquid from the granitic magma. When compared with fractional crystallization, the relatively early timing of segregation of an immiscible liquid from a granitic magma can prevent the precipitation of ore-forming elements during crystallization, and suggests that liquid immiscibility could be an important ore-forming process for rare metal pegmatities. We also conclude that isotope dating is a method that can potentially be used to determine the dominant ore-forming processes that occurred during the formation of granite-related ore deposits, and suggest that this method can be employed to determine the formation history of the W-Sn ore deposits found elsewhere within the Nanling Metallogenic Belt.

关键词： isotope dating liquid immiscibility in granitic magmas pegmatite Jiajika rare metal deposit

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isotope dating of the Potash and Rock Salt Deposit at Bamnet Narong, NE-Thailand

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Open Journal of Geology 2016年第8期6卷 875-894页

作者： Bent T. Hansen Klaus Wemmer Monique Eckhardt Prinya Putthapiban San Assavapatchara Geoscience Center Gottingen University of Gottingen Gottingen Germany Geoscience Programme Kanchanaburi Campus Mahidol University Kanchanaburi Thailand Department of Mineral Resources Bureau of Geological Survey Bangkok Thailand

Bamnet Narong is located in northeastern Thailand (Chaiyaphum Province). It is the largest salt mine in the country and has been mined for decades. The landscape in this part of Thailand is characterised by a low plateau, which is called the Khorat Plateau. The plateau is divided into two basins by the Phu Phan Range, the Sakhon Nakhon Basin in the north and the Khorat Basin in the south. The analysed potashes and rock salts are deposited in the Maha Sarakham Formation, which represents the salt-bearing strata of the Khorat Basin. The stratigraphic age of this deposit has been debated since the late 1960’s. The assigned ages range from Mid-Cretaceous to Late Cretaceous and up to the Eocene. In this study different isotopic dating systems (Rb-Sr, Sr-Sr, K-Ar and K-Ca) were applied. The stratigraphic age for the time of deposition was confirmed to be Mid Cretaceous (Cenomanian). Furthermore, the homogeneity of the carnallites was investigated in order to trace a possible redistribution of rubidium.

关键词： isotope dating Salt Deposits Mid-Cretaceous Asian Potash Mine Thailand

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What Caused the Inconsistency between Rb-Sr and^(40)Ar-^(39)Ar Ages of Authigenic Illites?

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Journal of Earth Science 2022年第5期33卷 1145-1151页

作者： Entao Liu I.Tonguc Uysal Jian-Xin Zhao Zi'ao Zhang Xudong Lin Hubei Key Laboratory of Marine Geological Resources China University of GeosciencesWuhan 430074China Radiogenic isotope Facility School of Earth and Environmental SciencesThe University of QueenslandBrisbaneQld4072Australia Department of Geological Engineering Istanbul University-CerrahpaşaIstanbul34098Turkey

Radiogenic isotope dating of illitic clays has been widely used to reconstruct thermal and fluid flow events in siliciclastic sedimentary basins,the information of which is critical to investigate mechanisms of hydrocarbon *** study carried out Rb-Sr and^(40)Ar-^(39)Ar dating of authigenic illitic clay samples separated from the Palaeogene sandstone in the northern South China *** Rb-Sr data further confirm the previously reported three periods of fluid flow events(at 34.5±0.9,31.2±0.6,and 23.6±0.8 Ma,respectively)in the northern South China Sea,which are related to regional episodic ***,^(40)Ar-^(39)Ar ages of illite obtained in this study are significantly younger than the corresponding Rb-Sr *** significantly younger^(40)Ar-^(39)Ar ages were probably due to ^(40)Ar loss caused by later dry heating events on the Hainan Island that have not affected the Rb-Sr isotopic *** inconsistency between Rb-Sr and^(40)Ar-^(39)Ar data should be attributed to different isotopic behaviors of K-Ar and Rb-Sr isotopic systematics in *** results indicate that Rb-Sr isotopic dating method may be a preferential approach for clay dating in geological settings where exist younger dry heating events.

关键词： authigenic illite isotope dating Rb−Sr isochron ^(40)Ar-^(39)Ar dating inconsistency geochemistry

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Krypton-85 dating of shallow aquifer in Hebei Plain

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Journal of Groundwater Science and Engineering 2016年第4期4卷 328-332页

作者： ZHANG Xiang-yang CHEN Zong-yu YANG Guo-min TU Le-yi HU Shui-ming University of Science and Technology of China Hefei National Laboratory for Physical Sciences Institute of Hydrogeology and Environmental Geology CAGS

The inert gas radioactive isotope ^(85)Kr(with a half-life of 10.74 years), due to its stable physical and chemical properties, is an ideal tracer for shallow groundwater dating. In such a dating application, first the dissolved gas is extracted from groundwater in the field, then krypton is separated from the gas sample, and finally the isotopic abundance ^(85)Kr/Kr will be determined by an ATTA instrument. According to the atmospheric input curve of ^(85)Kr, the ^(85)Kr age of groundwater is determined. We conducted ^(85)Kr analysis in three wells in Zhengding County on the plains in front of the Taihang Mountains, and made a comparison with tritium(~3H) method.

关键词： Tracer analysis Krypton-85 Tritium Groundwater isotope dating

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