罗布泊盐湖区固体钾盐沉积特征、分布及成因探讨

Sedimentary characteristics,distribution and genetic mechanism of solid potash deposits in salt lake of Lop Nur

文章对罗布泊盐湖区杂卤石、光卤石、钾盐镁矾等不同类型固体钾盐矿物特征、分布及成因进行了分析总结。杂卤石主要产于罗北凹地内部沉降区,以交代成因类型为主,代表了以硫酸盐型卤水为主体的罗布泊盐湖残余卤水钾镁富集到一定程度与石膏、钙芒硝发生水-盐反应的产物。光卤石沉积主要产于断陷带(近)地表,为深部氯化物型卤水经断裂向上运移至地表、与浅部卤水掺杂经蒸发浓缩而成。钾盐镁矾主要产于南小团地区,其形成可能与凹陷基底反转、罗北凹地高浓度卤水回灌有关。罗布泊盐湖区不同类型的固体钾盐沉积是构造-物源-气候3种成钾要素在特定时间窗下耦合的产物:在干旱气候条件下,构造活动一方面导致盆地地貌分异形成更加封闭的成钾次级凹地,为钾盐沉积提供可容纳空间;另一方面活化断裂为深部流体补给盐湖提供通道,为钾盐沉积提供不同类型的物质来源,改变盐湖卤水化学组成最终形成不同类型钾盐矿物。

The sedimentary characteristics,spatial-temporal distribution and genetic formation of various solid potash deposits,mainly including polyhalite,carnallite and kainite in Lop Nur were summarized in this study.Polyhalite sediments mainly formed in subsidence area of Luobei Sag and are characterized by replacement origin.They represent products of water-salt interaction of the potassium-and magnesium-rich residual brine with the existed calcium sulfate like gypsum and glauberite in sulfate-type lake.Sediments of carnallite mainly occur on the surface or near surface of fault zones in Lop Nur that fed by the deep CaCl-type brine through faults.The kainite sediments mainly distributed in Nanxiaotuan area and sourced from recharges of evaporated brine in Luobei Sag due to basement inversion.The formation of solid potassium sediments in Lop Nur rely on the coupling of tectonics,provenances and arid climate in a special time window.Under the arid climate condition,the tectonic activities lead geomorphic divides to form more closed sub-sage that provides accommodations for potash deposits.On the other hand,it reactivated fault to offer essential channels for upward migration of deep fluids that modified chemical composition of lake brine to finally form various potash sediments.