Abstract

Investigation of the Arkansas bauxite deposits by the U. S. Geological Survey during the years 1942 to 1945 has brought out the fact that secondary kaolinization or silication of the bauxite is much more common than has been generally recognized. On the other hand no direct evidence was found of the development of bauxite from kaolin. These facts have led us to reconsider the genetic relations of bauxite and kaolin.We do not mean to deny that there has been direct kaolinization of the nepheline syenite; but in view of the above observations and of the character of the kaolin derived from bauxite, we believe that the relations of bauxite and kaolin in the Arkansas deposits are more readily explained on the assumption that the bauxite is derived directly from the nepheline syenite, rather than from kaolinized nepheline syenite. The silica causing its subsequent kaolinization may be derived from overlying sediments or from remnants of unbauxitized nepheline syenite within or adjacent to it.Our conclusions about the relations of the kaolinized and bauxitized nepheline syenite are based entirely on rock weathered in place.

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