| Potash has extremely vital significance to the national economic construction and resources security. However, it is one of the most our country scarce resources in our country. Deepening the potash resources exploration and strengthening the study and survey in the ancient and modern salt basins are the very urgent tasks for all the geologists in China.In the period of Oligocene, Hoh Xil Basin was in the arid climate condition as same as the Qaidam Basin. There are a lot of salt rocks and evaporates deposits distribute in the stratum of Oligocene which was called Yaxicuo formation in Hoh Xil. These rocks own multi-layer and large thickness in vertical serial. In Qaidam, geologists have found a large number of salts mineral resources in Cenozoic, and the same result in Tarim basin where is in west of the Hoh Xil), meanwhile, in the south of Qiangtang-western Yunnan salt minerogenetic belt, Simao basin also be found as a solid potassium deposits area, has industrial value. Anyhow, vast Hoh Xil region has good prospect of potash resources, always be regarded as a key ones for potash search. Unfortunately, due to bad climate condition and high altitude, it is still a virgin land for potash resources evaluation.Take sedimentology and salt geochemical analysis as guiding theory, focus on Yaxicuo formation in Oligocene, select Cuorendejia(CRDJ) basin and Tuotuohe(TTH) basin in Hoh Xil region as the main research object, combine field exploration with indoor geochemical method, this paper summarizes the sedimentary characteristics and deposition model of the salt-bearing series in Cenozoic basin, in addition, by geochemical analysis, summarizes the condition of salt-forming processes, finally, evaluates the potash resource perspective. This paper is not only my master degree thesis, it also expected to give some theoretical support and new scientific basis for potash search in inland lacustrine facies evaporite basin in Qinghai-Tibet plateau.First, based on litho-facies and precipitation facies analysis of field section planes, identify sedimentary characteristics and deposition model of the salt-bearing series. The results showed that the Hoh Xil area can be at least identified two sets of salt-bearing series. Symbolize amaranth salt sediment group in the north, CRDJ basin, with yellow-green as mass-tone, sandwiched amaranth, celadon and gray, variegated salt sediment group in the south, TTH basin. Both of them are located in upper stratigraphic position in Oligocene Yaxicuo group, belong to inland lacustrine sediment, formed in ancient playa, but had different deposit modes. The former was formed in opening playa type, the latter belong to closing playa sediment. Nevertheless, both of the sedimentary environment and paleogeographic pattern are conducive to form potash mineral.Secondly, compared with the known salt occurrences and temporal and spatial distribution of the salt-bearing series, cooperated with satellite remote sensing, restoring the domain of ancient salt lake, delineating sedimentary center. The results showed that the distribution of salt occurrences and salt- bearing series are highly consistency, and perfectly identical with the remote sensing data. In Oligocene, ancient CRDJ salt lake basin center appeared in Gongmaorima mountain—Xiushui river area, could be marked at outcrops by the sectors-connecting Miocene Wudaoliang group limestone. TTH salt lake's center at the region of Tanggula mountain—Bumalangna, with it deepest place at the area of Bucha lake—Gaibaxiega lake, could be identified by large sectors-connecting plaster layer, many of them was more than 50m in thickness.At last, using brine and salt geochemical method analysis, rely on Br×103 /Cl ratio, K×103 /Cl ratio, K/Br ratio, nMg/nCl ratio, which are common characteristics coefficient in potash resources evaluation, analytical the type of brine, the potentiality of mineral-bearing and the potential of salt-bearing stratum. As the results showed that large-scale halite outcrop relatively rare, but the salt lake, surface springs(brine) was plenty, having high salinity, and all belong to the concentrated solution, containing the old information of lixiviation with salt layer or potash layer. In the brine, Br×103 /Cl ratio is high, generally greater than 0.3, the other features coefficients have the same character and change trend, illuminate that chemical analysis is authentic. According to the geochemical index, most samples reach into good level of potash potential, Hoh Xil regions is proved as favorable and promising potash deposit-searching area.Comprehensive evaluation revealed that salt-forming environment belong to inland playa deposition system in this area, sedimentary environment, paleo- geographic and climate condition conducive to potash deposit. As respectively deposit center of CRDJ and TTH basin, Ma Anshan salt lake and Bucha salt lake and their circumambience exist obviously potash-mineral abnormalities. The two ancient salt lakes have been come through the stage of exhalation sylvite. Hoh Xil regions have good prospect of potash deposit. In comparison, the CRDJ basin is better than TTH basin, provided with probability to find some concealed potash ore-bearing. |
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