摘要
多年来,许多中外地质学家对白云鄂博铁矿含矿围岩——白云岩进行过研究。多数认为白云岩是沉积岩;少数则认为是岩浆碳酸岩。作者自1978—1980年在矿区从事地层岩相研究工作,通过野外和室内的研究,现已查明本区白云岩实属沉积成因,并经受了多种地质作用的改造。
The dolomite has a definite stratigraphic horizon,occurring in Section H_(8) south of kuangou.The strata of both northern and southern limbs of the ore-bearing syncline in the mining district and their overlying and underlying strata represent a succession of conformable sediments,intercalated with arkose,mudstone and iron leases,in which primary textures and structures such as microwavy lamination,horizontal lamination,banbing and involute bedding may be found.In some argillaceous and silty intercalations,lenticular bedding can be observed.The crystals of the rockforming mineral dolomite(including ankerite)are not primary but metacrysts that have undergone multiple reerystallization.Under the microscope can be seen remnants of micritic dolomite,algal olite,intraclastic and epiclastic quartz,etc.The original rock association consists of micritic dolomite intercalated with oncolite dolomite and,locally,algal olite psammitic dolomite and terrestrial fragments-bearing dolomite.Fossil thallophytes are found in them.The organic carbon is contained,and in some places the content may attain the standard of oil source rocks(>0.1).Its mineral composition is complex and highly varied,its petrochemical composition is rather peculiar,characterized by the nature of deep brines of aqueo-igneous origin.In summary,the author considers that this dolomite is of sedimentary origin and may possibly be the product in the penecontemporaneous stage.Based on the analysis of the rock association,sedimentary textures and structures and paleotectonic and paleographical settings,it is concluded that this dolomite was deposited in a low-energy tidal-flat environment with turbid and shallow water media,tide-dominated hydrodynamics and weak wave action.The environment later evolved gradually into the lagoonal environment of the closed,semiclosed evaporation type on account of the subsequent strong activity of the Kuangou fracture in the northern part of the mining district.The ironbearing section was formed under reducing,alkaline geochemical conditions.The ore-forming substances iron,niobium and REE come from the terrestrial sources as well as deep brines.
作者
孟庆润
Meng Qingrun(Tianjin Geological Survey,Ministry of Metallurgical Industry)
出处
《地质论评》
1982年第5期481-489,508,共10页
Geological Review
