鄂尔多斯盆地东胜砂岩型高岭土矿特征及成因机制

Genesis and Characteristics of the Dongsheng Kaolin Deposits in Ordos Basin

东胜砂岩型高岭土矿床位于鄂尔多斯盆地东北部,含矿层为延安组。经薄片鉴定、扫描电镜、X-衍射、全岩主要元素分析(XRF)以及稀土元素地球化学分析,对矿层白色砂岩与红色原岩的岩石地球化学特征进行了对比。结果表明,原岩为基质被铁质浸染的以碎屑片状高岭石和伊利石为主的红色砂岩,而矿层则为褪色的以粒度粗细不一的高岭石胶结为主的白色砂岩。矿层砂岩的分布与盆地北部油苗位置具有很好的对应关系。综合区域地质特征、岩石学、岩石化学以及天然气运散的信息,认为砂岩型高岭土矿层的形成是由于研究区以南气田中的上古生界天然气向北运移散失过程中,将红色原岩中的氧化铁胶结物还原成易于运移的Fe2+,从而使其褪色变白;同时酸性流体使长石溶蚀形成高岭石,后期的风化淋滤作用使砂岩中的高岭石含量进一步提高,进而形成目前较大规模的高岭土矿床。

Dongsheng kaolin deposits lie in Jurassic Yan＇an Formation in northeast of the Ordos Basin. Genesis of the kaolinites is disputed. Based on thin section observation, scanning electro microscope （SEM）, X--ray diffraction, major elements component （XRF） and REE analysis （ICP--MS）, the characteristics of kaolin sandstone deposits in the studied area were determined. By contrasting with country rocks, the ore-bearing sandstone is white sandstone cemented by kaolinite with coarse and fine fraction in the same sample, and the original rock is red sandstone with clastic kaolinite and illite. The distribution of the ore beds are well correspondent to the oil seepage in northern basin. Field characteristics, petrography, bulk chemistry and natural gas migration and leakage suggest that the kaolin sandstone deposits experienced chemical reduction from the Neopaleozoic gas seepage in field south of the studied area where fluids reduced some Fe3＋ of iron to Fe^2＋ within the red sandstone, and then the red beds were bleached. At the same time, acid fluid dissolved feldspar grains and transformed feldspar into kaolinite. Kaolin deposits experience later weathering and leaching and improve present scale.