汾阳地区不同类型地下水SO4^2-、δ^34S的特征及影响因素

THE CHARACTERISTICS AND INFLUENCING FACTORS OF SO_4^(2-)AND SULFATE ISOTOPE(δ^(34)S)IN DIFFERENT TYPES OF GROUNDWATER IN FENYANG,SHANXI PROVINCE

本文对山西晋中盆地西南汾阳地区北侧裸露岩溶区的岩溶泉和浅井、南侧覆盖岩溶区的深井和第四系孔隙水井及石膏矿水的水化学成分、硫同位素组成进行了测试分析。结果显示:北侧裸露岩溶区的岩溶泉水和浅井δ^(34)S值的范围为4.53%0~6.42%0,SO_4^(2-)含量范围为0.12~0.62mmol/L,表明SO_4^(2-)主要来源于大气降水,受石膏溶解和居民活动影响小;南侧覆盖岩溶区的深井δ^(34)S值的范围为8.73‰~19.35‰,SO_4^(2-)含量范围为0.20~2.35mmol/L,SO_4^(2-)主要来源于石膏夹层的溶解和FeS_2的氧化。第四系孔隙水δ^(34)S值的范围为9.46‰~11.05‰,SO_4^(2-)含量范围为0.19~1.96mmoL/L,SO_4^(2-)主要来源于人为污染;石膏矿水δ^(34)S值为19.28‰,SO_4^(2-)含量为5.62mmol/L,SO_4^(2-)主要来源于石膏层的溶解。因此,应用SO_4^(2-)和δ^(34)S值可以很好的分析地下水中硫酸盐的来源,这为北方岩溶地下水资源的开发与保护研究提供了重要的手段。

The study area of Fenyang City,covering an area from 37°09′26″N to 37°29′02″N and 111°25′40″E to 112°00′00″E,is located in southwest Jinzhong basin,south of Luliang Mountain,Shanxi Province.The study area is divided into northern and southern karst water system by D3 fault.The north part is a bare karst area,with an elevation of 1100 ～ 1900m,in which the strata are primarily carbonate rocks （limestone and dolomite） of the Cambrian-Ordovician system.The Karst water is main supplied by precipitation and flows southward until it get blocked by Archaean metamorphic rock and formed the Mapao Spring （F10） and Xiakuo Spring （F11）.In the South,it is a covered karst region with an elevation of 1000～ 1100m,in which carbonate rocks buried 150～ 200m below the middle Pleistocene loess.The karst water is recharged by precipitation in exposed area in northeast and river seepage supply.It migrated from northeast to southwest through artificial discharge by deep well pumping with 500～800m depth.There are wells with high porosity and a depth of 130～180m in Middle Pleistocene loess layer.There is a gypsum mine in the southwest side of the Ordovician strata,with a spring 10m under the gypsum mine.We sampled and analysed the hydrochemistry and sulfate isotope in the shallow well and karst springs in northern bare karst area,deep well and quaternary pore water well in the southern covered karst region,and the gypsum mine water.A total of 16 location from two Quaternary pore water,five karst deep wells,two karst shallow wells,six karst springs,and a gypsum mine were sampled.The results showed that：（1） In the northern bare karst area,the δ^34Svalue in the shallow well and spring fell into a range of 4.53‰ ～ 6.42‰,and the value of S042＋ varied from 0.12mmol/L to 0.62mmol/L,indicating major atmospheric precipitation event and little gypsum dissolution and human activities.（2） In the southern covered karst region,the δ^34Svalue in the deep well fell into a range of 8.73‰～ 19.35‰,and the value of SO4^2＋ varied from 0.20mmol/L to 2.35mmol/L,indicating the SO4^2＋ was mainly came from dissolution of interbeded gypsum and oxidation of FeS2.（3） For the quaternary pore water,the δ^34Svalue fell into a range of 9.46‰o～ 11.05‰,and the value of SO4^2＋ varied from 0.19mmoL/L to 1.96mmol/L,indicating major anthropogenic inputs.（4） The δ^34Svalue of gypsum mine water was 19.28‰,and the value of SO24＋ was 5.62mmol/L,indicating major gypsum dissolution event.This study provides an important research method for development and protection of the karst groundwater resources in the North China.