老挝龙湖矿区ZK309孔泥岩层矿物学与地球化学特征

The Mineralogy and Geochemistry Characters of Mudstone Strata in ZK309 Hole,Longhu Diggings,Laos

老挝龙湖钾盐矿区是呵叻高原钾盐矿在老挝境内最主要的钾盐矿区之一,ZK309钻孔是龙湖矿区打穿最好、取样最完整和最典型的钻孔之一,通过对该钻孔盐岩上覆碎屑层的地层、矿物、元素的分析,得出泥岩层作为成盐沉积旋回中的一部分,其矿物元素变化和与其接触的下伏盐层的类型、特征等密切相关。同一旋回中自下而上泥岩颜色由青灰色变为红色,明显表现出沉积环境由还原性转变为氧化性。盐类矿物在垂向上表现出自下而上的淡化序列。矿物和元素在103～107 m处的突变显示盐岩沉积后期曾明显有水流体的淋滤作用,通过微量元素含量等的分析,该水流体表现为偏向淡水的淡水、海水混合水。碳酸盐矿物组合及含量显示当时可能有高Mg流体的活动。将粘土矿物组合与中国其它海相和陆相盆地粘土矿物组合相比较,得出粘土矿物组合与海相更相似,加上绿泥石含量较高,初步推测粘土矿物可能来源于海相沉积环境。

Longhu Diggings is one of the most important potash deposits in Khorat Plateau, Laos, ZK309 hole is one of the most representative holes in this area, it is a perfect penetrated drilling where we have got complete mud rock samples. In light of analysing the upper clasolite strata, minerals and elements, mudstone as one of the cycle of sedimentation of diagenesis, we concluded that minerals and elements in mudstone are bound up with the type and character of below salt stratum. The changing regularity of saline minerals in vertical direction accord with the depositional environment that change from low salinity to high salinity. The saltation of minerals and elements located in 103 - 107 metres indicates that the fluid e- luviation had taken place during the late consolidation stage of rock salt sedimentation. It is easy to concluse that the fluids were water with low salt content and mixture of little seawater and much freshwater by analysing the minerals and elements. In terms of distributions and contents of and carbonate minerals, we concluded that there were high magnesian fluids, we had the composition of clay minerals of mudstone compared with other facies and land facies basin of China, and concluded it leaning towards sea facies. Additionally, it has more chlorite, we speculated that it may be from ocean environment.