罗布泊断陷带内形成富钾卤水机理研究

Formation mechanism of potash-bearing brine in fault belts of Lop Nur Lake,Xinjiang

罗布泊干盐湖位于新疆塔里木盆地东部。1995年以来,在罗布泊发现了超大型规模钾盐矿床,钾盐资源主要赋存于罗北凹地等盐系地层中。近年来调查发现,在罗布泊分布有地堑式张性断陷带,不仅控制成钾凹地的形成,其本身也储集卤水,蕴藏有一定规模的卤水钾盐资源。地球物理(EH-4)测量显示,断陷带深达1000m处有卤水存在的信息;断陷带内钻孔卤水化学分析结果揭示,下部卤水比重高于上部,卤水中氯化钾含量也呈"下高上低"的态势,这与盐湖蒸发析盐序列不一致或正相反。文章认为,卤水垂向对流是导致卤水化学特征垂向分异的机理,即,在罗布泊盐湖演化过程中,断陷带内出现较小规模的洼地或盐湖,湖表水蒸发浓缩形成卤水,上部卤水比重不断增加,并沿张性断裂逐渐向下部或深部流动、渗透,形成了卤水的对流;由于罗布泊地堑式断陷带长达30～50km,向下延长深度可达1000m,这些都说明罗布泊断陷带内可以形成和储集一定规模的富钾卤水,它们应该成为今后罗布泊盐湖钾盐资源扩大找矿的新空间。

Located in the east of Tarim Basin,Lop Nur Lake is one of the biggest playas in the world. Since 1995,large-size potash deposits have been found in the playa,and these potash resources are mainly preserved in the intercrystalline pores of glauberite layers. Recent investigations show that there are graben-type faults in Lop Nur Lake,which not only controlled the formation of the potash-forming subbasins or hollows but also preserved brine and accumulated certain amounts of potash reserves. Geophysical survey （EH-4） reveals that there probably exists brine down to 1 000 m of the fault belts. And the brine from drill holes is characterized chemically by the phenomenon that salinity and potassium content of the brine are higher in the lower strata than in the upper strata. The authors hold that this vertical chemical differentiation of brine might have been caused by the brine convection. As the graben-type faults in Lop Nur Lake are 30～50 km in length and 1 000 m in depth,it is most probable that potash deposits with some reserves are preserved in them. Therefore,these fault belts should be regarded as new space in exploring potash deposits within Lop Nur Lake in future.