青海大浪滩凹地梁中矿区软钾镁矾沉积元素和相化学分析

Element and Phase Chemistry of Picromerite Deposits from Dalangtan Liangzhong Depression in the Western Qaidam Basin

中文关键词:  大浪滩凹地  软钾镁矾  元素和相化学

英文关键词:Dalangtan salt lake  Picromerite  Element and phase chemistry

中文摘要:

      青海大浪滩凹地梁中矿区是典型的固、液矿共存的钾镁盐矿床。地质勘查显示,梁中矿区埋深8~10m以下沉积有层状的含钾硫酸盐固体钾矿(主要是软钾镁矾,并伴生有钾石盐和光卤石)。在兴元钾肥厂已开挖的矿层断面,选择7.3 m的沉积剖面,采集并分析了73件盐样和7件晶间卤水样离子含量,结合2件样品的软钾镁矾稳定锶同位素比值、矿物组合分布和25℃时Na⁺, K⁺, Mg²⁺//Cl-, SO2-₄–H₂O五元体系介稳相图,探讨了研究区软钾镁矾沉积的化学元素组成特征和化学演化过程。结果表明,1)5.3~2.6 m沉积了钾盐矿物,K⁺含量主要在10%~18%之间变化；2)全新世温度的升高和外来水体的混入,使软钾镁矾沉积时矿物析盐序列呈现逆向析盐过程；3)对比软钾镁矾和研究区盐湖卤水、油田卤水的⁸⁷Sr/⁸⁶Sr值,推断大浪滩凹地软钾镁矾的沉积可能与其南侧断裂—小梁山构造气田水渗入有关。

英文摘要:

      :The 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 authors collected 73 salt samples from a profile (XY-1) contained potassium salt in the Xingyuan Salt Works, and analyzed chemical composition of 73 salt samples and 7 brine samples, stable stronium isotopic composition of two picromerite samples in this study. Combining with mineral assemblages of XY-1 and Na⁺, K⁺, Mg²⁺//Cl-, SO2-₄–H₂O five system interface steady phase diagram at 25℃, the authors discussed elemental compositions characteristics and chemical evolution of picromerite deposits from Dalangtan Liangzhong depression in the western Qaidam Basin. The results indicate that:(1) the potassium minerals at 5.3-2.6 m from XY-1 were deposited, which reached 10%-18% of K⁺; (2)the temperature rose during Holocene and mixing of extraneous water resulted in reverse salting process at 5.3-2.0 m; (3)by comparing ⁸⁷Sr/⁸⁶Sr value of picromerite with those of oilfield and salt lake brines, the authors deduced that the picromerite deposits might be associated with the supply of oilfield water from southern fault of Xiaoliangshan.