Research And Logging Evaluation Of The Potassium-forming Conditions Of The Middle And Lower Triassic Salt-bearing Systems In The Xuanda Area

The potassium is an important element of the agricultural production.The annual Chinese agricultural demand for potash is about 15 million tons of potash.However,the potash resources in China are relatively poor,and due to low production of potash,unable to meet demand,and nearly half potash consumption rely on imports.China is vigorously developing exploration projects on potash resources,and it is a great significance for Chinese agriculture and food supply.Middle-Lower Triassic of Xuanda region is one of the important horizon for the prospecting on sylvite occurrence with good prospecting perspective.Results of logging data,field survey on outcrop,X-ray diffraction analyses on powdered samples,geochemical analyses have determined characteristics of typical minerals such as calcite,dolomite,anhydrite and rock salt and their relationship.Combining with the logging data,this paper summarized characteristics of hydatogenic rock and the logging curve characteristics of every formation in the workspace,and researched stratigraphic correlation from Jialingjiang layer to Leikoupo layer.Geochemical analysis of Middle-Lower Triassic salt-bearing series display Br·103/Cl.indicating significance for potassium potential.The result of isotopic analysis shown that a sulfur isotope in the anhydrite was determined and determined salting direction of water.Chemical analysis of water of the Triassic strata display that the brine water have rich in K+,Ca2+ and poor in Mg2+,SO42-characteristics,and it is classified into a type of the chloride brine.This paper analyzed Br·103/Cl,K·103/C1,hydrogen and oxygen isotope geochemical characteristics,and their implications for the brine origin.Sedimentary structure and lithological assemblage of Lower-Midle Triassic straticgraphic section in Xuanda region,shown that potash-bearing salt formatins were precipitated in from Jialingjiang layer to Leikoupo layer.The study shows that Middle-Lower Triassic strata lithology of Xuanda region consist mainly of intercalations of limestone,dolomite and anhydrite and halite.Five potash-bearing salt are determined in the section.Relics of fossils in sequence,and lithological feature characterized that Middle-Lower Triassic formation in the workspace accumulated in enviroments of shallow sea,restricted sea,shed lagoon and salt lake.Features of structurelithology,geochemistry,paleoclimate,warter chemistry,salt minerals and precipitations shown that the brine is leached brine with supplying from deep material and the evaporation of brine has reached the stage of late salt rock deposit,which show that the workspace has a certain into potassium forming environment.Based on the log interpretation method,using crossplot method and the log comprehensive identification method,this paper conducted logging interpretation and identified a polyhalite rock and potassium-rich brine in Xuanda region.T1j4-2 and T1j5-2 formation have a preferable polyhalite rock,and potassium-rich brine was ideltified in T1j1,T1j2-1 and T1j3 layers.