Abstract
The comprehensive geological, hydrogeological and hydrogeochemical model of the Liulin karstic spring area in the eastern limb of the Ordos syncline was established by a combination of chemical thermodynamics, chemical kinetics and hydrogeology. The study area was divided into four zones based on the saturation indices of calcite, dolomite and gypsum, which were computed by the groundwater-chemical simulation software PHREEQC (a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations), with consideration of the geological and hydrogeological conditions and hydro-geochemical reactions. The weight and volume modulus of carbonate rocks and sulphate rocks in each zone were calculated by the method of correlation analysis to evaluate the dissolution law of karst groundwater. The results showed that in the zone I (saturation index of calcite βc ≤ 1) the dissolution of calcite was the major geochemical reaction, the weight modulus of calcite was higher than that of dolomite and gypsum, and the pore space generated by the dissolution of calcite was one order of magnitude larger than that of dolomite and gypsum. In zone II (saturation index of calcite βc > 1 to saturation index of dolomite βd ≤ 1) the corrosion moduli were all smaller than that in zone I, the solubility of dolomite and gypsum increased, and calcite reached saturation. The space occupied by the calcite sediment was less than that dissolved by dolomite and gypsum. In zone III (saturation index of dolomite βd > 1 to saturation index of gypsum βg ≤ 1), calcite and dolomite had reached saturation, accompanied by dedolomitization, and the amount of gypsum dissolution increased obviously. The conclusions indicate that the hydrogeochemical environment plays an important role in mineral dissolution.
Highlights
Carbonate rocks are widely distributed in China, and its acreage accounts for about a third of the land area
It is necessary to mention that three zones (I, II and III) are analyzed since the mineral dissolution of carbonate rocks and sulphate rocks mainly occurs in these three zones, and all of the ions in zone IV are in the supersaturated state without dissolution, which means that corrosion modulus cannot be calculated
The total weight modulus reduced from 85.418 g/m3 to 5.928 g/m3, and to −23.482 g/m3, and the total volume modulus reduced from 3.213 × 10−5 to 3.105 × 10−6, increased to 5.61 × 10−6, which manifests that the quantities of precipitation of carbonate rocks minerals was greater than that of sulphate rocks, but a tiny amount of new pore space would still be produced by the interaction between the groundwater and karst aquifer
Summary
Carbonate rocks are widely distributed in China, and its acreage accounts for about a third of the land area. Scholars at home and abroad usually relate to qualitative and quantitative analysis of karstification and karst dissolution when they analyze the hydrogeology, engineering geology, and mineral geology problems in karst spring area [3] It is necessary for analysis of karst hydrogeology characteristics to make a quantitative analysis and calculation of karst dissolution. The dissolution law of underground karst water in the Liulin spring area are calculated and analyzed by Cao’s theory and method in this paper. It will provide some basis for the formation and evolution of karst groundwater characteristics.
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