Geochemical Research On Ancient Salt Rock And Prospect Of Sylvite Deposit Formation In Western Tarim Basin

It is well known that the resources of potash deposit in our country are very lack and cannot be satisfied to the developing requirement. Therefore, the paper focused on an issue about the ancient sylvite deposit formation in western Tarim Basin where many scientists regarded it as a promising area to find sylvite. The paper selected the western Tarim Basin as main research field, ancient salt rock and brine as study object, geochemistry as main methods. Through systematically and comprehensively contrastive research on ancient salt rock or brine distributed in different space and time, the paper analyzed their marine or continental sedimentary fades, paleo-brine evaporation and evolution. Then based on the research results, the paper prospected the most promising tectonic area and bearing strata to find sylvite deposit. The main content of the paper is as follows:a. The paper made a summary on common geochemical methods about ancient sylvite deposit exploration and summarized their basic theories in past years of sylvite-searching works.b. The paper analyzed the profitable and unfavorable geological conditions for sylvite deposit formation from the view of tectonic geology, sedimentary facies and paleogeography, strata and original source in different tectonic unit and geological periods in western Tarim Basin.c. The paper particularly expounded on the characteristics of geochemical composition and isotopic distribution of ancient salt rock through detailed contrastive analysis on those different tectonic units and periods in western Tarim Basin.d. It is proved in the paper that the isotopic value of 8 37C1 in salt, 5 34S in gypsum and also 6 18O in crystalline water of gypsum can be utilized as effective index to find sylvite deposit through comprehensively contrasted with typical hydrochemical features of brine, BrX 1O3/C1 ratio.e. Applying the newest index of potash salt-searching, referring on the characteristics of regional tectonic, sedimentary facies and paleogeography, the paper detailedly discussed and analyzed on the marine or continental sedimentary facies and the possible concentrated stages of the ancient brine that formed present exposed evaporates distributed in different space and time in the surface in western Tarim Basin.f. The research results in the paper prospected the most promising potash deposit-searching tectonic areas and the bearing favorable strata via multi-index evaluation in western Tarim Basin.Finally, the paper concluded that there had some commonness as well as more different respective characters to the salt rock sediment in the two largest sub-basins in Tarim— Kuqa-sub basin and Shaqa-sub basin. The commonness is that there deposit wide and thick salt rock and the original source of salt formation is connected with ancient Mid Sea water invasion. Besides, the content of typical marine elements like Bromine is much lower than those marine salts and the salts are also all lumped with clay minerals in both Kuqa and Shaqa sub-basin. As for differences, Shaqa-sub basin located in the tunnel of ancient Mid Sea water invasion and was always the first place to be flooded by sea water. The exposed salt rock in the surface mostly deposited in the late Cretaceous period and the sedimentary facies were more like marine environment. Moreover, the sedimentary stage of salt rock, especially the salt deposited in the late Cretaceous strata named Tuyiluoke formation in Kashi depression deposited much later than other regions. By contrast, the Kuqa sub-basin located far away from the heading of sea water invasion and the exposed salt rock mostly deposited in the early Tertiary period. The salt rock was intensely undergone great diagenesis and metamorphism by fresh water from Tianshan Mountain. Therefore, the sedimentary facies are more like continental environment. All thegeochemical indexes showed that the sedimentary stage of the salt rock in early Tertiary strata deposited relatively earlier than that in Kashi depression.In summary, according to the final research outcome, the Kashi depression in western Shaqa sub-basin should be proved as the most favorable and promising potash deposit-searching area and the late Cretaceous strata of Tuyiluoke formation (K2O may be the aim strata to find sylvite deposit. Certainly, those spring or river water with higher background content of Bromine and Boron in Yang Xia Depression in eastern Kuqa sub-basin may also have some clues to indicate the deep sylvite bearing minerals exist. So it is worth while to carry out more detailed research in future.