柴达木盆地中西部背斜构造深层卤水水化学特征与成因

Origin and Hydrochemistry of Deep Brines from Anticlinal Reservoir in the Western-Central Qaidam Basin

柴达木盆地西部背斜构造深层卤水资源勘查和评价成果显示,第三系背斜构造赋存深层卤水,具有良好的资源成矿条件,且潜力大。采集柴达木盆地中西部(一里坪拗陷和三湖拗陷)9处背斜构造深层卤水,分析了其水化学特征与成因。结果表明,深层卤水矿化度一般低于150 g/L,水化学类型均为氯化物型;K^(+)、Na^(+)、Mg^(2+)含量较低,不具找矿价值;而B_(2)O_(3)、Li^(+)含量普遍高于评价指标,Br^(-)、I^(-)含量普遍高于综合评价指标,为主要成矿元素;卤水的元素特征系数和分布规律及微量离子组成揭示,深层卤水是大气降水溶滤盆地周缘岩浆岩和火山岩及火山热泉的补给后,汇入古近纪—新近纪湖盆经蒸发浓缩封存在地层中的沉积卤水。

Resource exploration and evaluation of deep brines from Dalangtan and Lenghu anticlinal reservoirs in the western Qaidam Basin had been conducted over the past twenty years.These studies have shown that anticlinal reservoirs reserve deep brines,which have good metallogenic conditions and great potential.Eighteen deep brines from nine anticlinal reservoirs in the western-central Qaidam Basin were collected and analyzed for major and trace elemental concentrations in this study.Similarly,origin and hydrochemistry of those deep brines were discussed,combining with element characteristic coefficient,distribution pattern and trace elemental concentrations in the different reservoirs.The results indicate that the total dissolved solids(TDS)and hydrochemical types of deep brines are generally less than 150 g/L and chloride-type,respectively.The K+,Na^(+) and Mg^(2+) concentrations is low,indicating no potential of resource exploitation,while B^(2)O^(3),Li+,Br^(-) and I^(-) concentrations are higher than comprehensive evaluation index,indicating good potential of resource exploitation.Trace ionic concentrations,element characteristic coefficient and distribution pattern of deep brines reveal that these resource solutes in deep brines are originated from dissolving magmatic and volcanic rocks by meteoric waters,and then inflowing into paleomega-lake during Paleogene and Neogene,and reserved and forming formation brines through evaporation and concentration along with evolution of paleolake.