柴达木盆地西部大浪滩梁中矿区软钾镁矾沉积的矿物组合特征

Mineral Assemblage of Picromerite Deposits from Dalangtan Liangzhong Depression in the Western Qaidam Basin

中文关键词:  大浪滩盐湖  软钾镁矾  矿物组合

英文关键词:Dalangtan Salt Lake  Picromerite  Mineral assemblage

中文摘要:

      柴达木盆地西部大浪滩梁中矿区是一个以液体钾矿为主、固液并存的大型钾镁盐矿田。通过对梁中矿区大浪滩凹地钾镁盐矿点实地考察，以兴元钾肥厂开挖的固体钾盐（软钾镁矾、钾石盐和杂卤石等矿物）剖面为研究载体，采集73件固体盐样。通过XRD矿物组成分析，发现梁中凹地盐类呈石盐＋泻利盐～石盐＋泻利盐＋软钾镁矾-石盐＋泻利盐＋钾石盐一石盐＋钾石盐＋光卤石一石盐＋水氯镁石矿物组合变化。其中，在Ⅱ阶段（5．3～2．6m）沉积了层状的固体钾盐矿物（包含软钾镁矾、钾石盐和光卤石）。地层中沉积的软钾镁矾，结晶良好。通过对比分析认为，软钾镁矾的形成条件：1）外来水体的混入，溶滤了地表盐滩中可溶性钾；2）（全新世）相对较高的温度条件，芒硝等矿物的溶解，会使湖表卤水中硫酸盐含量明显增加，卤水组成点易落在25℃介稳相图的白钠镁矾相区，有利于软钾镁矾结晶析出；3）干旱的气候条件。

英文摘要:

      Dalangtan Liangzhong depression in the western Qaidam Basin consists of liquid brines enriching K ＋ and potassium salt minerals. Based on the field investigation for these salt deposits of LiangZhong depression,the anthors collected 73 salt samples from a profile （XY- 1） contained potassium salt in the XingYuan Salt Works and analyzed the mineral assemblage of these samples with X-Ray Diffraction. The results indicate that the mineral sequences of these salt deposits in XY- 1 profile are composed of halite ＋ epsomite,halite ＋ epsomite ＋ picromerite ,halite ＋ epsomite ＋ sylvinite ,halite ＋ sylvinite ＋ carnallite and halite ＋ bischofite. In the second zone （5.3 -2.6 m）, laminated potassium salts （including of picromerite, sylvinite and carnallite） were deposited and the pieromerite mineral was characteristic of better crystallization and higher grade of po- tassium salt. Comparing with other records of salt lakes in the Qaidam Basin,three conditions for the forming picromerite deposits in the Dalangtan playa can be gotten. They are （ 1 ） the supply of water might have been dissolved the potassium salt of the upper salt crust; （2） the mirabilite mineral was dissolved under higher temperature condition during Holocene, which increased the concentration of sulphate salt in the parent solutions and facilitated parent solution to fall over phase region of astrakhanite in the 25℃ medium temperature phase diagram; and （3） hyper-arid paleoclimate conditions in the Qaidam Basin.