ラテライト・ボーキサイトに関連するいくつかの地学的問題
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概要
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Many problems of laterites and bauxites as mineral resources concern basically to geology. For example, how are the characteristics of the laterite profile of the bauxite deposits, how are the features of association of the deposits with the kaolinitic sedimentary clays, and how are the diagenetic or metamorphic features of the fossil laterites or lateritic sediments. In this paper, some critical review on these problems is briefly given. Sequence of development of the laterite profile as the function of time and depth from surface, and in response to the climatic change is of critical importance.<BR>The bauxite deposits and laterites, if provided with proper depositional terranes on the front of the weathering lands, should be very often associated with sedimentary bauxitic or kaolinitic clays. Not a few examples of this sort of evidence have been reported from Eurasian and North American Continents. In Japanese Islands, also, the same evidence is, for instance, recognized either as the intimate association of the “emery” like rocks and sillimanite hornfels, or almandine hornfels and andalusite hornfels from some localities.<BR>Diagenesis-the first step of metamorphism of laterites seems to be started by the conversion of gibbsite or boehmite to diaspore, although this opinion remains probably still some argument. As a result of the reexamination of the chemical composition as well as the mode of occurrences of the “emery” deposits, chloritoid rocks and staurolite rocks, which had been discovered from many localities in Japan, it is concluded by the present author, that these rocks in Japan are the metamorphic products from the lateritic sediments of mostly upper Plaeozoic.
- 社団法人 東京地学協会の論文