民勤盆地地下水地球化学演化模拟

根据稳定同位素分析，民勤盆地地下水在第四系总体补给环境较现代凉。在200m以下的深层地下水为晚更新世补给的古封存水，表现为还原环境。60m—120m左右的浅层水为古地下水与现代降水的混合水，但古地下水占的成分较多，部分水样为氧化环境。民勤盆地地下水地球化学特征主要形成于山区，在沿途运移过程强烈的蒸发浓缩作用占据主导地位，形成了浅层高矿化盐碱水，深层地下水活跃的阳离子交换作用形成高钠浓度水。通过利用PHREEEQC法对民勤盆地地下水化学进行质量平衡模拟，表明民勤盆地地下水水化学沿水流路径以HCO3^-、SO4^2-、Cl^-、Ca^2 、Na^ 升高为主要特征，方解石、白云石的饱和指数随水流路径有减少趋势，而石膏、芒硝和岩盐的饱和指数有增加的趋势：沿水流途径白云石、CO2、石膏、岩盐和芒硝溶解量逐渐增加是常量离子浓度升高的物质来源。

Simulation of Geochemical Evolution of Groundwater beneath the Minqin Basin,Gansu Province

According to the analyzed results of stable isotopes, the Quaternary environment of groundwater recharge was cooler than that at present. The deep groundwater beneath 200 m is the paleo-sealed water recharged in late Pleistocene Epoch under the reduction environment. The shallow groundwater in aquifer of 60m-120m is the mixed water of the paleo-groundwater and modern precipitation, the proportion of the paleo-groundwater, however, is higher than that of modern precipitation, and the oxidation environment is revealed by the analyzed results of some groundwater samples. The geochemical properties of groundwater beneath the Minqin Basin form mainly in the mountainous regions. Under the effects of the violent evaporation and concentration, the shallow salty groundwater with high-mineralization forms, and the deep groundwater has the active cation exchange and high natrium content. The mass balance of the chemical properties of groundwater is simulated by using PHREEEQC. The results show that the increase of HCO 3-, SO 4 2-, Cl-, Ca 2+ and Na+ is dominant, the saturating indexes of calcite and dolomite are reduced with the increase of the groundwater flow route, but that of gypsum, Glauber's salt and halite are increased to some extent; the solutes of dolomite, CO 2, gypsum, halite and Glauber's salt are increased with the increase of groundwater flow route, thus, the concentrations of constant ions are increased.