老挝甘蒙省钾镁盐矿床中微量硼矿物的鉴定和准确定名

Identification and precise naming of trace boron minerals in the potassium-magnesium salt deposit of Khammouan Province,Laos

以老挝甘蒙省钾镁盐矿床ZK318钻孔的含矿段(下盐层)为研究对象,对其开展了微量硼矿物的鉴定研究工作,以完善矿床的矿物组合类型。全岩样品的XRD初步结果给出,在顶部钾盐岩层中含有少量方硼石。为了进一步全面鉴定硼矿物的种类,对全岩样品溶解后得到的不溶物多晶集合体进行XRD分析,结果表明,不溶物中的硼矿物主要为方硼石(55%),其次为三斜晶系3A型氯硼钙石(15%)。3A型氯硼钙石在全岩样品中的含量不足1%,属微量矿物,因低于XRD的检出限,故在全岩样品的XRD图谱中无该矿物的衍射峰出现。此外,对三斜晶系3A型氯硼钙石的中文准确命名进行了讨论,指出中文定名应与国际惯例一致,即废除副水氯硼钙石(parahilgardite)一词,定名为3A型氯硼钙石(hilgardite-3A)以体现结构的微细差别,同时达到中文命名规范统一的目的。因此,该矿床中的硼矿物为少量方硼石和微量3A型氯硼钙石。

The potassium-magnesium salt deposit of Khammouan Province in Laos is located in the eastern part of Khorat Basin. The main salt minerals of the deposit are halite, sylvite, carnallite and anhydrite, and the boron minerals in the deposit are of small or even trace amounts. The identification of trace boron minerals in the lower salt layer of ZK318 borehole in the deposit was studied in order to complete the mineral assemblage type. Chemical analyses show that the content of boron is related to the type of salt minerals, and that according to the distribution characteristics of boron, the lower salt layer can be divided into five layers in upward succession, i. e., halite layer^sylvite layer ---~carnallite layer ---~thin halite layer -＋upper sylvite layer. According to the linear relationship between the content of boron and the salinity of brine, earnallite, as the last evaporative product of halide brine, should have the highest content of boron theoretically. However, the boron value of the upper sylvite layer is up to 890.78 ~ 10 6 which is higher than that of the earnallite layer, indicating that boron in the upper sylvite layer came not only from sea water but also from deep hydrothermal solution and that there exist small amounts of boron minerals in this layer. Preliminary XRD analytical results of bulk rock samples show that there is a small amount of boracite in the upper sylvite layer. In order to identify the type of boron minerals ac- curately, the authors conducted XRD analysis of insoluble substances collected through the soluble experiment of bulk rock samples. The result shows that the boron minerals in insoluble substances are mainly boracite （55 % ）, and subordinately anorthic hilgardite-3A （15%）. Hilgardite-3A belongs to trace mineral because its content is less than the detection limit of XRD （1% ） so that there is no diffractive peaks in the XRD pattern of bulk rock samples. In addition, the Chinese name of anorthic hilgardite-3A is discussed in this paper. It is point- ed out that the precise Chinese naming should follow the international conventions. Therefore, the name parahil- gardite is cancelled and replaced by the name hilgardite-3A so as to reflect the slight difference between the min- eral structures, i.e. the difference between this mineral and another anorthic polymorph 1A. This modification is consistent with the Chinese naming norms. Therefore, small amounts of boracite and trace hilgardite-3A （anorthic） exist in the potassium-magnesium salt deposit of Khammouan Province, Laos.