内蒙老石旦矿区高岭土矿床的成因分析

THE ORIGIN ANALYSIS OF KAOLIN DEPOSIT IN LAOSHIDAN MINING AREA,INNER MONGOLIA

老石旦矿区的高岭土(木节土)呈灰白、灰紫及灰黑色,质地松软,可塑性高,是一种良好的耐火材料和陶瓷原料。对其成因过去有两种看法:(1)原生沉积的;(2)由煤层风化淋滤形成的。作者认为是煤层风化残积形成的。即煤层经地壳运动抬升到地表以后,受到强烈的风化淋滤作用,使有机组分分解,流失和逸散,铝硅矿物相对富集,在表生条件下形成木节土。

Laoshidan mining area is located in the southern part of Wuhai, the Inner Mongolia Autonomous Region. There are abundant clay resource besides coal, in which the soft clay (kibusni clay) is a good kind of refractory and porcelain material with high refractoriness and plasticity.There are 5 layers of kibushi clay, occurring in Carboniferous-Permian coal-bearing strata in the form of a long belt at the outcrop and its near part.The kibushi clay is in correspondence with coalseam in position, that is, tney existed between the same roof and bottom, and transited to coal bed along the tendency. The extension of transition belt is very limited, generally about 3 to 10 meters, which varied with the tnickness of coal bed. Kibushi caly occurred in this area can be divided into three kinds according to its colour: white kibushi, porple kibushi and black kibushi. They also appeared in this order from surface to lower part. The former two are compacted mass with laminated structure, in which kaolinite and diaspore are its main and minor minerals respectively. The later is loose and earthy without lamination, in which there are a little hyllosite and hydrargillite besides kaolinite, The kibusni clav is mainly composed of SiO_2, Al_2O_3 and LOI, and the main impurities are Fe_2O_3 and CaO. By systematical studying it was deemed that the kibushi clay in this area was formed from coal bed weathering and residualling in situ.The main evidences are as follows: 1. All of 5 layers of kibushi clay appeared in the same area with similar occurrence and extension,showing that they were formed at the same time and under the same condition. Only weathering may meet the conditions. 2. The rigid-clay partings in kibushi clay is continuous with tonstein in coalbed, which has the same texture, structure and mineral composition, showing that the mother rock of kibushi clay was formed in the same environment with coalseam. To be more exact, the mother rock of kibushi clay is coal bed. 3. There are typical minerals of weathered and leached clay deposits in kibushi clay hyllosite and alumite, and there is limonite in the transition zone from clay to coal bed. So, we can get the conclusion that kibushi clay in this area is formed from coalbed weathering residual. That is, when it was lifted up to the surface by structural movement, the organic materials in coal began to decompose and bleed by weathering agency, which made the aluminosilicate minerals enriched in situ and formed kibushi clay under hypergene condition.