鄂尔多斯盆地洛河组地下水地球化学模拟——以陕西省长武-彬县地区为例

Geochemical modeling of Luohe water-bearing layers in Ordos Basin-in Changwu-Bin county area

文中以揭示鄂尔多斯盆地长武-彬县地区白垩系洛河组地下水水化学场的形成机理为主要研究目的。在了解鄂尔多斯盆地的地形、地势、地貌、新构造运动、岩石类型、岩性构造和其他特征的基础上,运用化学热力学原理、质量作用定律和质量守恒定律,应用水文地球综合分析方法和地下水地球化学模拟技术,对白垩系洛河组地下水进行了水-岩作用的地球化学模拟。应用Phreeqc软件定量分析研究了该区地下水的演化过程、形成机理,总结了矿物或次生矿物的溶解沉淀规律以及水溶液中化学成分的变化,主要结论为:1)在水流模拟路径上主要发生了方解石与伊利石的沉淀和白云石、石膏、岩盐、斜长石、钾长石和钾云母的溶解,以及Ca-Na2间的阳离子交换作用;2)在水D20点南附近可能是洛河含水岩组地下水的排泄基点。结果表明水-岩作用模拟结果有助于揭示研究区地下水化学环境的演化机制。

The purpose of the paper is to study the evolution mechanism of geochemical field in groundwater of Luohe water-bearing layers in Changwu -Bin county in south Ordos Cretaceous Basin. Based on the comprehensions of Ordos Basin＇topography, landform, physiognomy, geotectonic cycle, rock - type, lithology and other characters, the chemical thermo -dynamics, mass action and mass conservation equations were used to simulate the water- rock reaction of groundwater in Ordos Cretaceous Basin by applying of hydrogeochemical integrated method and modeling technique. Phreeqc softwares were used to analyze quantitatively the evolution process, forming mechanism of the local groundwater. The law of mineral dissolution/precipitation and aqueous composition variety were summarized. The main conclusions were ： 1 ） the reactions of the main phases are the precipitation of the calcite and illite, the dissolution of the dolomite, gypsum, halite, plagioclase, k - feldspar, k - mica, and the cation exchange of Ca - Na; 2） The neighborhood in water D20 is the discharge base set of the groundwater of Luohe water - bearing layers. The results of water - rock interaction modeling are conductive to reveal the evolution mechanism of the groundwater chemical environment in the study area.