云南维西花岗岩地区水文地球化学特征及形成机制研究

基于矿物风化分析,以典型花岗岩地区云南维西为例,对该地区2005年8月地下水和河水水化学性质(pH、Ca2 、Mg2 、K 、Na 、Cl-、HCO3-、SO42-)进行了观测,在Piper图上分析了花岗岩地区水文地球化学特征,并利用主成分分析法探讨了其形成机制。研究认为,在野外调查基础上可将云南维西地区地下水分为6类:花岗岩孔隙水、浅部裂隙水、矿带影响的浅部裂隙水、深部构造裂隙水、花岗岩与灰岩接触带水、花岗岩与第四系堆积物接触带水。利用主成分分析法可以提取影响这6类水的3项公因子:Y1(反映钙长石、黑云母、黄铁矿风化)、Y2(反映水循环深度)、Y3(反映钠长石、钾长石溶滤作用)。地下水和河水公因子得分图分析表明:(1)全风化带孔隙水长石、黑云母溶滤作用弱,而且几乎没有黄铁矿氧化作用;(2)浅部裂隙水和花岗岩与第四系堆积物接触带水两者埋深差不多,但后者因水岩接触面积更大,长石、云母溶滤作用以及黄铁矿氧化作用更强;(3)矿带作用下,浅部裂隙地下水体现一定程度的深部构造裂隙水特征,其钠长石、钾长石风化在所有风化带中最强。因钙长石、黑云母矿物活性相对较弱,其增加幅度不如钾长石、钠长石明显;(4)深部构造裂隙水循环深度大,水岩作用充分,钙长石风化强于其他矿物,钾长石、钠长石因为影响因素多,特别是风化淋滤时间的影响,其风化增强不明显;(5)花岗岩与灰岩接触带水失去花岗岩水特征,更多地表现为灰岩水性质;(6)河水主要离子主要来源于循环较浅的裂隙水、全风化带孔隙水等,循环深度大的地下水贡献小。

Hydrogeochemical characteristics and mechanisms of granite area in Weixi, Yunnan Province

To research the hydrogeochemical characteristics and mechanisms of granite area, a typical granite area, Weixi of Yunnan are chosen as a target and some chemical indexes of springs and rivers there are discussed, which include pH,K , Na , Ca2 , Mg2 , , Cl- and , based on the analysis of mineral weathering. According to the result of field study, granite ground water in Weixi, Yunnan is divided into 6 groups: granite pore water, shallow seated fracture water, fracture water influenced by mineral zone, deep seated tectonic fracture water, water in the interface of granite and Quaternary deposit and water in the interface of granite and carbonate rock. From the major component figures that are composed of three major factors extracted by the major component method, the following six conclusions can be obtained. (1) As for granite pore water, the leaching effect is weak and there is almost no oxidation effect. (2) Leaching and oxidation effect are weaker for the shallow seated fracture water than that of the springs on the interface of granite and Quaternary deposit which are similar in depth, because the later enjoys high surface area. (3) Mineral zone can reinforce weathering so that the shallow seated fracture water shows geochemical characteristics of deep circulating water. For example, the weathering of albite and orthoclase of fracture springs influenced by mineral zone is the strongest in all kinds of water. However, as for biotite and microcline weathering, they don't increase as rapidly as albite and orthoclase because of their mineral activity. (4) The anorthite weathering of deep seated tectonic fracture springs increases rapidly as springs cycle deeper while feldspar has no obvious incremental trend because of complex controlling factors. (5) The springs on the interface of granite and carbonate rock show the characteristics of carbonate rock spring instead of granite spring. (6) The hydrogeochemical characteristics of river are mainly influenced by the pore water and the shallow fracture water that are characterized by shallow cycling, while the effect of deep cycling water is weaker.