Characteristics of chlorine isotope distribution and analysis on sylvinite deposit formation based on ancient salt rock

During formation of the Tarim Basin, there repetitively happened seawater invasion for it was ever connected with wide Paleo-mediterranean Sea. At the same time, for the application of tectonic and paleoenvironmental condition, the basin deposits many sequences of thick strata of evaporites, especially in its two largest subbasins of Kuqa in the north and Shaqa in the southwest. Therefore, the western Tarim Basin has been considered to be a favorable location to prospect ancient sylvinite deposit. But it is unfortunate that the Br×103/Cl ratio, as a common geochemical index to uncover clues of sylvinite deposit, is almost invalid to indicate the stage of ancient brine condensation for very low content of bromine in salt rock samples (less than 10-6 commonly) in the western Tarim Basin evaporites. Fortunately, we noticed recently that the values of chlorine isotope (δ37Cl value) for salt rock samples follow some clear laws from place to place, which in the Shaqa subbasin, all δ37Cl values of salt rock samples behaved negatively and on the contrary, they all surprisingly showed positive values in the Kuqa subbasin. Based on conclusions of previous research and referring to the ratios of Br×103/Cl for salt rock or brine samples, we proved that the chlorine isotope (δ37Cl) could be used as an effective index to find ancient sylvinite deposit in those evaporites rock basin with low content of Br element background, such as the Tarim Basin. Thus according to the new index of chlorine isotope, we conclude that the concentration of ancient brines formed ancient salt rocks is much more concentrated in the Shaqa subbasin than that in the Kuqa subbasin. Particularly, the δ37Cl value of salt rock in Kashi depression of the western Shaqa subbasin is greatly negative (<-1.00‰), which may predicate that the ancient brine has been concentrated to the terminal stage of salt deposit or even the later stage of sylvinite deposit. Then it is possible to find sylvinite-bearing deposits around the western region (periphery of Kashi depression) of the Shaqa subbasin if we carry out more careful exploration in later works.

作 者： TAN Hongbing MA Haizhou XIAO Yingkai WEI Haizhen ZHANG Xiying   作者單位： TAN Hongbing,WEI Haizhen(Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China;Graduate School of the Chinese Academy of Sciences, Beijing 100039, China)

MA Haizhou,XIAO Yingkai,ZHANG Xiying(Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China) 

刊 名： 中國科學D輯（英文版）  SCI 英文刊名： SCIENCE IN CHINA (EARTH SCIENCES)  年，卷(期)： 2005 48(11)  分類號： P59  關鍵詞： the Tarim Basin   chlorine isotope   ancient salt rock   ancient sylvinite deposit   deposit stage  

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