柴达木盆地一里坪盐湖成盐卤水成分变化及其意义——来自LA-ICP-MS分析石盐流体包裹体组成的证据

The variations of brine composition and its significance in the Yiliping area of the Qaidam basin——evidence from fluid inclusions in halite analysed by LA-ICP-MS

一里坪盐湖是柴达木盆地一个以富锂卤水为主的干盐湖,蕴藏有丰富的卤水钾锂资源,目前对成矿过程中卤水的成分及其演变规律方面的研究较少。论文选取一里坪盐湖中部钻孔HC2105岩芯的石盐为主要对象,利用激光剥蚀-电感耦合等离子质谱法开展了单个石盐原生流体包裹体成分分析,探讨恢复了一里坪盐湖地区晚更新世以来成盐期的古卤水成分。结果表明,一里坪盐湖下层石盐古卤水Li、B、K等离子浓度均高于上层石盐,这说明晚更新世成矿条件更好。古卤水中Li、B、K和Mg等离子具有正相关性,再结合对Ca离子浓度变化的研究,说明一里坪盐湖的主要物质来源为那棱郭勒河,深部卤水对其物质来源贡献较小;石盐流体包裹体中各离子浓度的演变规律与钻孔沉积韵律以及古气候变化三者基本可以拟合,从而证实盐湖卤水成分变化受到古气候变化的影响,干冷期可能更有利于富锂卤水矿的形成。

Yiliping is a dry salt flat in the Qaidam Basin,which is characterized by lithium-rich brine deposits.Relatively little attention has been paid to the past composition and evolution of the brine during the mineralization process.In this paper,the samples of salt rocks were collected from the central drilling core of Yiliping.In order to obtain the composition of ancient brine during the salinization period since the Pleistocene,the chemical compositions of primaryfluid inclusions in halites were analyzed using laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).The results show that the concentrations of Li,B,and K in the lower part of the section are higher than those in lower part of the section,indicating favorable conditions for the formation of Li-enriched brine in the lower part this section compared with the upper part.The Li,B,K and Mg concentrations of ancient brines are positively correlated.Combined with the variation of Ca concentration,it is shown that the main material source for forming the Yiliping Salt Lake is derived from the Nalingol River,and the contribution of deep fluids is insignificant.The evolution of each ion concentration in the halite fluid inclusions is consistent with the sedimentary rhythm and the paleoclimate changes,thus confirming that the composition of the salt lake brine is affected by paleoclimate i.e.,a dry and cold climate is more favorable for the formation of lithium-rich brine.