| Potash salts are an indispensable part of mineral resources. The demand of potassium fertilizer has become more and more larger owing to the development of our country’s economy and agriculture. Therefore, to find new potash resources becomes an urgent task at present. Meanwhile, the researches about hydrochemical characteristics of potassium-rich brines which are related to potash salts also appear to be extremely important. The subsurface brines in the deep-seated aquifers are special kind of groundwater which are of industrial value. It not only can be utilized for salt production, but also is rich in many kinds of scarce materials like bromine, iodine, potassium, lithium and so on. The Sichuan basin is a famous large sedimentary basin in China and it boasts abundant brine resources, in which exists a certain content of high salinity brine containing high concentration of potassium. The Zigong area of the Sichuan Basin investigated in the present study is a typical region of brine enrichment.The research areas of this study are located in the Zigong area in southwestern Sichuan Basin and cover the three structunes: Ziliujing anticline, Xinglongchang anticline and Dengjingguan anticline. They all belong to brine-bearing structure, and from which the brines are treated as research objects. This paper discusses in detail about the reservoir and distribution characteristics of the deep brines in the research areas, and analyzes the characteristics of the aquifer system from the two aspects of formation lithology and structure. The subsurface brines in the studu area are divided into two types according to the different media of brine reservoir. One medium is composed of clastic sedimentary rocks including sandstone, sandy conglomerate and conglomerate, and the subsurface brine is the yellow brine hosting in the Upper Triassic Xujiahe Group. The other medium is brine layer series which mainly contain limestone, dolomite and dolomitic limestone, and the underground brine is the black brine hosting in the carbonate rocks of the Middle and Lower Triassic Jialingjiang Leikoupo Group. The reservoir of brines was influenced by the brine-beaing structure and fault zone obviously. For instance, the enrichment of brines at the Huanggepo fault zone is obvious in the influence zone and its production accounts for 74% of the total yield of the brine-bearing structure. The F2 fault of the Dengjingguan structure controlling length reachs 12 km undertaking the function of water control, and the average porosity is 11.82%, however, in other parts the average porosity is only 4.04%, indicating that the fault throw of the F2 tomography has a closely relationship with the brine production.The present study adoptes routine components to analyze the hydrochemical characteristics of the brines. The TDS of subsurface brines in research area range from 148 to 322 g/L, among them the TDS of the Shenhai soluble salt well is 321.68 g/L, greater than the black brine and yellow brine salinity. The hydrochemical type of the brine in the research area is of Cl-Na type. The yellow brine contains more Mg, Ca, Sr, and Ba. The black brine contains more K, Li, Br, and Sr. Trace elements in the Shenhai soluble salt well and Yong 2 well have the same change trend according the order in the periodic table. The most rich element is Sr, and the least rich elements are Hf and Th. Their lanthanide content change trends are different. The most rich lanthanide element in the Shenhai soluble salt well is Eu, and the most rich lanthanide element of Yong 2 well is Tm. It is found that the generation of deep brines is related to the sedimentary water by analyzing the results of ion proportional coefficients. According to the stable isotopes of δ2H and δ18O of the brines, the comparison between the brines and evaporation seawater curves and the Br-normalized concentration ratio of certain ion, a conclusion can be drawn that the black brine is originated from the paleo-sea-water, and was finally formed through the limestone dolomitization, the sulfate reduction, anhydrite precipitation and the formative of magnesium sulfate minerals and magnesium chlorite. The yellow brine is originated from the marine source continental syngenetic sedimentary water and the mixture of it and paleometeoric water, and was formed after the processes of membrane filtration and the.albitization of plagioclase feldspar. |
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