罗布泊“大耳朵”湖区钾元素地球化学与富集机理

Geochemical characteristics and enrichment mechanism of potassium in Lop Nur "Great Ear" playa

对罗布泊"大耳朵"干盐湖盐壳的沉积过程、钾元素空间分布特征及地下卤水化学性质进行了实地调查研究。"大耳朵"湖区地下卤水盐度为341g/L左右,ρ(K+)变化于7.0～12.4g/L,平均值9.61g/L,高浓度富钾卤水通过毛细管上升和地表析盐,导致钾盐矿物在地表析出,地表盐壳的w(K+)变化于0～4.7g/kg,平均含量2.05g/kg,钾盐矿物主要包括光卤石、杂卤石和软钾镁钒。研究表明盐壳盐类矿物在干盐湖地表的聚集及地球化学分布特征与地下卤水的化学性质有着密切关系,盐壳沉积后期风蚀、雨淋、季节性的地表径流都会影响和重塑盐壳地球化学组成特征,钾盐矿物可作为盐壳增长发育的指示矿物。

Based on field investigation of the sedimentary process of evaporite crusts,spatial distribution characteristics of potassium and groundwater chemistry in the ＂Great Ear＂ playa of the Lop Nur basin,this study reports the spatial distribution and enrichment pattern of potassium and potash minerals in the surface salt crusts. The present-day concentrated groundwater brines have salinities of～341 g/L and K＋ concentrations ranging from 7.0～12.4 g/L with the average being ～9.61 g/L. The investigation results show that the upward capillary flux from the concentrated K＋-bearing brines results in the formation of such potash deposits on the ground surface as carnallite,polyhalite and picromerite. Potassium content in the surface crusts was measured to range from 0～4.7 g/kg,with an average of 2.05 g/kg. There is a close correlation between accumulation of evaporite minerals,geochemical distribution characteristics of surface salt crusts and chemical composition of groundwater brines. In addition,this paper deals with the process of geochemical differentiation during the later stage of efflorescent salt crusts deposition,in which the geochemical composition was also affected and modified by aeolian erosion,rainfall infiltration and seasonal surface runoff. Potash minerals could be the indicator of salt crust growth.