甘肃南部宕昌-武山县地下水化学特征及成因分析

HYDROCHEMICAL CHARACTERISTICS AND GENESIS OF GROUNDWATER IN TANCHANG-WUSHAN COUNTY,SOUTHERN GANSU

为识别甘肃南部宕昌-武山县不同地层条件下的地下水特征、演变规律及其形成原因,本文运用数理统计、Piper图、Gibbs图、离子比值、饱和指数等方法,对研究区地下水化学类型、分布特征及成因进行分析。结果表明:(1)碳酸盐岩地层及碳酸盐岩夹砂岩地层中各离子含量稳定,阴阳离子分别以HCO_(3)^(-)、SO_(4)^(2-)和Ca^(2+)、Mg^(2+)为主,水化学类型为HCO_(3)-Ca型水;砂岩地层中离子浓度变化大,Na^(+)、Cl^(-)浓度差异突出,水化学类型为HCO_(3)-Ca、HCO_(3)-Ca·Mg以及HCO_(3)-Na·Ca型水。(2)各地层地下水中离子均受岩石风化作用控制,在地下水径流过程中,主要发生了岩盐、石膏的溶解,方解石的沉淀,白云石和长石的溶解或沉淀,以及阳离子交换作用。其中砂岩地层中阳离子离子交换作用强于其他地层。(3)特殊地质条件下如断层泉水样点受补给来源、径流路径、地下水循环交替程度等因素影响,水化学组分异于常值。

In order to identify the hydrochemical characteristics,evolution rules and genesis of groundwater under different stratigraphic conditions in Tanchang-Wushan County,southern Gansu.This paper analysed the groundwater chemical types,distribution characteristics and causes in the study area by using mathematical statistics,Piper diagram,Gibbs plots,ion ratio,saturation index and other methods.The results showed that:(1)The content of ion in the carbonate formation and the sandstone formation interspersed with carbonate is stable,and the anions and cations are mainly HCO_(3)^(-),SO_(4)^(2-)and Ca^(2+),Mg^(2+)respectively,the water chemistry type is HCO_(3)-Ca;The ion concentration in the sandstone formation varies greatly,with prominent differences in Na^(+)and Cl^(-)concentrations,the water chemistry types are HCO_(3)-Ca,HCO_(3)-Ca·Mg and HCO_(3)-Na·Ca.(2)The ions in the groundwater of each stratum are controlled by rock weathering,and mainly the dissolution of rock salt and gypsum,the precipitation of calcite,the dissolution or precipitation of dolomite and feldspar,and cation exchange occur in the process of groundwater runoff.The cation exchange effect is stronger in sandstone strata than in other strata.(3)Under special geological conditions,such as fault spring water which are affected by the source of recharge,runoff paths and the degree of alternation in the groundwater cycle,the water chemistry components are different from the constant value.