柴达木盆地大盐滩矿区深层晶间卤水的成因

Origin of Deep Intercrystalline Brines from Dayantan Mine Area in Qaidam Basin

柴达木盆地西部昆特依盐湖大盐滩矿区地下卤水资源丰富,具有很好的开发利用前景。野外采取了大盐滩矿区不同深度(9.8～133 m)晶间卤水样品和冷湖构造油田水样品,分析了卤水的水化学组成和氢氧同位素值。结果显示,晶间卤水矿化度较高(平均为363.94 g/L)且富K^+,水化学类型为硫酸镁亚型;油田水矿化度较低(平均为39.02 g/L),富Ca^(2+)和Sr^(2+),水化学类型为氯化物型。离子含量及钠氯系数和溴氯系数分析显示,大盐滩矿区晶间卤水主要为大气降水汇聚后经蒸发作用形成,深层晶间卤水(30～133 m)具有大气降水盐岩溶滤成因及受具有深部来源性质油田水补给的特征。氢氧同位素组成分析表明,卤水均发生了明显的"氧同位素正漂移"现象,推断深层晶间卤水较高的δ^(18)O、δD值与浅层晶间卤水(9.8～11.5 m)以及大气降水溶滤盐岩沿断裂下渗补给有关。

Dayantan Mine Area,which is located in the west of Kunty playa in Qaidam basin,has rich underground brine resources and has a prospect of exploitation and utilization. 10 oilfield brine samples in Dayantan playa were taken and 10 samples of intercrystalline brine were taken from different depths(9. 8 .133 m) of the Dayantan Mine Area in this study. The chemical compositions, hydrogen and oxygen isotopic characteristics of brine were analyzed. The results show that the salinity of intercrystalline brines is high (with an average of 363. 94 g/ L ),and these brines have a high content of K + and are enriched in Mg^2+,SO4^2-. The chemical type of intercrystalline brines is magnesium sulfate subtype. According to the ion contents and water chemistry characteristic coefficient(r Na/r Cl and r Br ×10^3/r Cl), the result shows the intercrystalline brines are mainly formed by atmospheric precipitation which has been converged and evaporated,and the deep intercrystalline brines(30 - 133 m) are derived from atmospheric precipitation dissolving rock salt and supplied by oilfield brines which have properties of deep origins. The hydrogen and oxygen isotopic compositions show that there is an obvious phenomenon of “oxygen isotopic positive deviation” in deep brine,which can be inferred that it is related to the infiltration supply of the shallow brines(9. 8 - 11. 5 m)and the atmospheric precipitation dissolved rock salt along the fractures.