摘要
柴达木盆地是中国主要的钾盐储备地,其中察尔汗盐湖是最大的钾镁盐沉积和钾肥生产基地。东陵湖是察尔汗北缘沉积的小盐湖,其浅部石盐层中伴有光卤石沉积,氯化钾(KCl)品位为4.55%~10.26%,显示东陵湖边缘浅层沉积有低品位固体钾矿。盐湖卤水和蒸发盐的沉积必须有持续水文补给,才能保持强烈蒸发条件下盐湖卤水的水文平衡和化学蒸发盐的沉积,而盐湖“源-汇”水文补给过程是制约东陵湖钾盐沉积的重要科学问题。因此,本文以东陵湖湖表卤水、钻孔晶间卤水、承压卤水为研究对象,通过卤水水化学和H-O-Li-Sr同位素,结合盆地主要河流和尾闾盐湖水化学数据,从源-汇视角探讨了东陵湖水文补给来源,主要得出以下结论:(1)东陵湖卤水矿化度变化较大,介于80.6~547.1g/L之间,水化学类型为Ca-Cl型;湖表卤水和湖区晶间卤水钾含量(0.81g/L)较低,而湖区外凹地晶间卤水(3.13g/L)和承压卤水(1.10g/L)钾含量较高,这与东陵湖边缘浅层沉积有低品位固体钾矿有关;B-Li含量呈现相似的空间分布和正相关性,湖表卤水含量最高,其次为晶间卤水和承压卤水,总体呈现高B低Li特征;(2)东陵湖卤水与盆地Ca-Cl水具有相似的氧同位素正偏移现象和高δ^(7)Li(+28.74‰~+36.2‰)-δ11 B(+20.33‰~+29.17‰)同位素值特征,解释了东陵湖卤水及光卤石沉积与断裂带Ca-Cl水的补给控制密切相关;(3)东陵湖湖表卤水具有高Sr含量(375.38~525.82mg/L)及较高的^(87)Sr/^(86)Sr同位素比值(0.711735~0.711766)特征,位于柴北缘高B含量和高Sr同位素背景区。结合盆地南北两侧水文补给与地形地势条件(察尔汗北缘东陵湖地势高而察尔汗其他区域地势低),提出东陵湖与柴北缘水文补给有关,柴北缘地下水沿山前断裂下渗、经历深部循环沿红梁山等背斜构造断裂上涌补给至东陵湖南缘,该水文循环过程溶滤了古近纪-新近纪地层中可溶盐组份为东陵湖提供了含盐溶质。
The Qaidam Basin(QB)is a major potash reserve area in China,with the Qarhan Salt Lake(QSL)being the largest potash and magnesite sedimentation and potash fertilizer production base.Dongling Lake(DL),located on the northern edge of QSL,is a small salt lake with halite deposits accompanied by sylvite in its shallow layers,with potassium chloride(KCl)grades ranging from 4.55%to 10.26%,indicating that the marginal shallow deposits of DL contain low-grade solid potash.The deposition of brine and evaporite salts in salt lakes requires continuous hydrological replenishment to maintain the hydrological balance of brine and the deposition of chemical evaporite salts under intense evaporation conditions.The“source-sink”hydrological replenishment process of salt lakes is an important scientific issue that constrains the potash sedimentation of DL.Therefore,this paper takes the surface brine,intercrystalline brine,and confined brine of DL as the research objects,and through the hydrochemistry of brines and H-O-Li-Sr isotopes,combined with the hydrochemical data of the main rivers and terminal salt lake waters in the basin,discusses the hydrological replenishment sources of DL from a source-sink perspective,and mainly draws the following conclusions:(1)The total dissolved solids degree of DL brines varies greatly,ranging from 80.6g/L to 547.1g/L,with a hydrochemical type of Ca-Cl;the potassium content in the surface brine and intercrystalline brine of the lake area(0.81g/L)is low,while the potassium content in the intercrystalline brine of the lake area outside the depression(3.13g/L)and the confined brine(1.10g/L)is higher,which is related to the low-grade solid potash deposits in the marginal shallow deposits of DL;the B-Li content shows a similar spatial distribution and positive correlation,with the highest content in the surface brine,followed by the intercrystalline brine and confined brine,generally showing a high B and low Li characteristic;(2)The brine of DL exhibits a positive oxygen isotope shift similar to that of the Ca-Cl water in the QB,with highδ^(7)Li(+28.74‰~+36.2‰)andδ^(11) B(+20.33‰~+29.17‰)isotopic values,which explains the brine and carnallite potassium salt deposits in DL are closely related to the control of Ca-Cl water recharge in the fault zone;(3)The surface brine of DL has high Sr content(375.38~525.82mg/L)and relatively high ^(87)Sr/^(86)Sr isotopic ratios(0.711735~0.711766),located in the high B content and high Sr isotope background value area on the northern edge of QSL,combined with the hydrological replenishment and topographical conditions on both sides of the QB(the terrain of DL on the northern edge of QSL is high while the terrain of other areas of QSL is low),it is proposed that the hydrological replenishment of DL is related to the northern QB.Groundwater from the northern QB infiltrates along the mountain front fault,undergoes deep circulation,and then rises along the fault of the Hongliangshan anticline,supplying water to the southern edge of DL.This hydrological cycle has leached soluble salt components from the Paleogene to Neogene strata,providing salt-solute to DL.
作者
石海岩
樊启顺
刘万平
李庆宽
赵为永
陈天源
杨浩田
商雯君
SHI HaiYan;FAN QiShun;LIU WanPing;LI QingKuan;ZHAO WeiYong;CHEN TianYuan;YANG HaoTian;SHANG WenJun(Key Laboratory of Green and High-end Utilization of Salt Lake Resources,Qinghai Institute of Salt Lakes,Chinese Academy of Sciences,Xining 810008,China;Qinghai Provincial Key Laboratory of Geology and Environment of Salt Lakes,Xining 810008,China;University of Chinese Academy of Sciences,Beijing 101408,China;Technology Innovation Center for Exploration and Exploitation of Strategic Mineral Resources in Plateau Desert Region,Ministry of Natural Resources,Qinghai Geological Survey,Xining 810001,China;Qinghai Salt Lake Industry Corporation,Golmud 816099,China;Research Institute of Exploration and Development,Qinghai Oilfield Branch,CNPC,Dunhuang 736202,China)
出处
《岩石学报》
北大核心
2025年第3期1067-1083,共17页
Acta Petrologica Sinica
基金
第二次青藏高原综合科学考察项目(2019QZKK0805)
国家自然科学联合基金重点项目(U21A2018)联合资助.
