华北铝土矿的物质来源及成矿模式探讨

A DISCUSSION ON MATERIAL SOURCE AND METALLOGENIC MODEL OF BAUXITE DEPOSITS IN NORTH CHINA

华北石炭纪岩溶型铝土矿的主要物质来源为下伏的晚寒武世—中奥陶世碳酸盐岩。在长期的风化过程中，碳酸盐岩中活泼元素被带走，而残余的Ａｌ、Ｔｉ、Ｆｅ等惰性元素得到富集，其依据为下伏基岩具有与铝土矿相近的Ａｌ／Ｔｉ值；两者的痕量元素分布和富集系数基本一致；重砂矿物的种类、标型特征具有明显的继承性；现代碳酸盐岩岩溶洼地上正在形成的铝土矿矿床可提供例证。华北铝土矿的成矿模式可概括为：在早古生代碳酸盐岩风化壳的物质基础上，由于中石炭世湿热气候对粘土物质的铝土化作用，生成三水型铝土矿，并在附近的泻湖和海湾环境中沉积，经多次再沉积和成岩、后生阶段形成现代的铝土矿矿床。

The material source of the Carboniferous karst type bauxite in North China mainly came from the underlying Late Cambrian—Middle Ordovician carbonate rock. During the course of weathering for a long time, the mobile elements in the carbonate rock were carried over, but the residual inert elements(Ai、Ti、Fe etc ) enriched in the rocks.The bases of this knowledge are as follows:the AL/Ti ratio was near and the distribution and enrichment coefficient of the trace elements were roughly identical between the underlying bedrock and bauxite;the type and typomorphic characteristics of the placer minerals have obviously property in the inheritance; it is even an example that the bauxite deposit is forming on the present carbonatite karst depression. The metallogenic model of North China type bauxite can be summarized as follows:the gibbsite type bauxite formed on the material source of crust of weathering in the Early Palaeozoic carbonate rock by the allitization of the clay mass in the Middle Carboniferous humid hot climate. These materials were nearby sedimentated in the lagoon and gulf environments, and then, the present bauxite deposits were formed underwent the redeposition, diagenesis and epigenesis.