青海西部尕斯库勒盐湖沉积物中铀和钍地球化学特征探讨

Geochemical characteristics of uranium and thorium in sediments from Gasikule Salt Lake in western Qinghai Province

文章以柴达木盆地西部尕斯库勒盐湖沉积物为研究对象,通过对钻孔沉积物和地表沉积物中铀和钍含量的研究,探讨了盐湖沉积物中铀和钍的地球化学特征。分析表明,钻孔沉积物中铀和钍之间存在明显的正相关关系。在横向上,随地表取样点逐渐远离湖表卤水,沉积物中铀和钍的含量先增高后又急剧降低,且受补给水铀含量影响大;在纵向上,同一个晶间卤水层或者碎屑物沉积层内铀含量垂直分异明显,铀含量随深度增加而递增。就沉积物中铀和钍的赋存形式而言,2/3的铀被黏土质点吸附,1/3的铀夹杂在盐类矿物中;而90%以上的钍被黏土质点吸附,10%以下的钍夹杂在盐类矿物中。干盐滩中毛细蒸发和淋滤等化学沉积分异作用造成盐湖沉积中心的沉积物铀含量相对较高。

In order to explore the geochemical behavior of uranium/thorium in salt lake＇ s sediments, the authors studied the concentrations of uranium and thorium in drill holes and surface sediments of the Gasikule Salt Lake located on the western margin of Qinghai Province. The results reveal that uranium concentrations exhibit a positive correlation with thorium concentrations in sediments. With the distance from the surface brine, uranium and thorium values of sediments increase and then decrease rapidly in horizon, deeply impacted by the supplemental water. Vertically, uranium concentrations in debris deposition are higher than the values of the evaporite period. Moreover, vertical differentiation of uranium concentrations is obvious in a crystal brine layer or debris layer and increases with the depth. The average uranium concentration in pure salts （halite, epsomite, gypsum） is 1.02μg/g, which is approximately one third of that of the sediments. Therefore, two thirds of uranium in sediments was absorbed by clay while one third of uranium was mixed with saline minerals. However, more than 90 percent of thorium in sediments was absorbed by clay while less than 10 percent of thorium was mingled with saline minerals. Chemical sedimentary differentiation in playa such as capillary evaporation and leaching was significant for uranium enrichment in sediments.