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Tan X.,Institute of Geological Survey of Yunnan Province | Zhao B.,Institute of Geological Survey of Yunnan Province | Li X.,Institute of Geological Survey of Yunnan Province | Xu Z.,Institute of Geological Survey of Yunnan Province | Zhang Z.,Chinese Academy of Geological Sciences
Acta Geologica Sinica

The general classification of intermediate-acid intrusive rocks in the metamorphic zone of Gaoligong Mountains as one of the metamorphic terranes of Proterozoic Gaoligong Mountains is problematic regarding the intrusion stage and age, as well as the subsequent metamorphism and deformation. In this study, we investigated granitic gneiss in the metamorphic zone of Gaoligong Mountains based on the 1:50,000 regional geological survey of Qushi Street (2011-2013) and SHRIMP U-Pb zircon geochronology. Results showed that the SHRIMP U-Pb zircon dating of granitic gneiss ranged from 163.5±5.7 Ma to 74.0±2.0 Ma. Thus, the granitic gneiss was grouped into orthometamorphic rocks (metamorphic intrusions). The dating data of granite rocks associated with intense metamorphism and deformation were divided into three groups, 163.5±5.7 to 162.3±3.1 Ma, 132.2-1 01 .0 Ma and 99.4±3.5-74.0±2.0 Ma, which respectively represented three independent geologic events including an important magma intrusion with superimposed metamorphic effects in the late Middle Jurassic, regional dynamic metamorphism and superimposed reformation of fluid action in the early Cretaceous, and dynamic metamorphism dominated by ductile shear and metamorphism starting from the late Cretaceous. Source

Zheng M.-P.,Chinese Academy of Geological Sciences | Zhang Z.,Chinese Academy of Geological Sciences | Yin H.-W.,Nanjing University | Tan X.-H.,Institute of Geological Survey of Yunnan Province | And 7 more authors.
Acta Geoscientica Sinica

Through an intensive analysis of the data obtained from previous geological survey and study in southwestern Yunnan, the authors found some doubtful points. Starting with the salt-forming setting of the restricted sea formed in Neo-Tethys and the specific and complex geological and structural conditions of southwestern Yunnan and based on considerable ground geological surveys and sedimentary facies, salt structure and hydrochemical studies, the authors infer that the horsetail potash beds in the Mengyejing Formation of Mengyejing area were squeezed up and flowed in the plastic form through faults from the deep Jurassic potassic rocks onto the surface. In this study, light, portable and practical geophysical means such as the low-frequency magnetotelluric method (EH4) and high-precision method for detecting the electromagnetic spectrum (MES) were used; in addition, the previously-used gravity survey (1:100, 000) was also employed. An integrated analysis indicates that there exist several salt beds at the depth. For the purpose of verifying the above-mentioned new idea of potash search, two potash intermediately deep boreholes were drilled, and the drilling results are consistent with this idea. Of the two boreholes, one (MK-1) has been completed and encountered a 70 m thick potash-bearing halite bed in the central part of the Middle Jurassic Huakaizuo Formation, and the other (MK-2) has intersected a gypsum-bearing sequence in the upper part of the Huakaizuo Formation. Meanwhile, Sr isotope study, inclusion thermometry and analyses of the structure and sedimentary features of the salt body were carried out. In summary, the authors demonstrate the formation mechanism of the Mengyejing potash deposit and put forward a "two-storey potash-forming model", i.e., Jurassic salt body lies in the deep part and diapirism in the shallow part. Guided by this model, the authors deployed regional, high-precision gravity survey (1:50, 000), MES spectrum and shallow drilling engineering, thus expanding prospects of potash exploration in the deep and shallow parts of the Lanping-Simao salt-forming belt. Source

Zheng M.-P.,Chinese Academy of Geological Sciences | Hou X.-H.,Chinese Academy of Geological Sciences | Yu C.-Q.,Chinese Academy of Geological Sciences | Li H.-P.,Qaidam Integrated Geological Exploration Institute of Qinghai Province | And 12 more authors.
Acta Geoscientica Sinica

The salt formation theory has led to the breakthrough and important progress in potash deposit prospecting: a new type gravel brine layer rich in potassium was discovered in the early pre-Quaternary strata in Altun Mountains in the west of Qaidam Basin. This progress was made by the Salt Party of the Institute of Mineral Resources, Chinese Academy of Geological Sciences, headed by Professor ZhengMianping, academician of the Chinese Academy of Engineering, with such institutions as the Qaidam Comprehensive Exploration Institute of Geology and Mineral Resources as the co-researchers and under the joint support of geological survey projects and key projects of the National Natural Science Foundation of China. Drilling shows that it possesses the estimated resource quantity of 350 million tons and hence is likely to be the reserve base of potash salt in Qaidam Basin. Additionally, Paleogene potash-bearing ore beds with the thickness of 100 meters were found in Kuqa depression, Tarim, where there is a 41 meter-thick salt bed of potassium chloride that reaches industrial grade. Furthermore, Triassic polyhalite was found in Sichuan Basin, which is not only an important potassium source in deep brine rich in potash but also a precious slow-release potassium fertilizer. Besides, in Upper Yangtze River Basin, 13 potassium-rich brine deposits of brine-bearing structure were evaluated, and the potassium chloride resource is estimated to be 49.17 million tons. What is more, in Mengyejing of southwestern Yunnan Province, a "two-storey" potash-forming model was set up, and, in Ordovician salt basin of northern Shaanxi Province, the area of potash prospecting target area has been largely reduced, which shows the dawn of the breakthrough in marine potash prospecting. ©, 2015, Science Press. All right reserved. Source

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