沖縄本島中部に分布する第四紀炭酸塩岩の生成・続成・風化過程における重金属元素の地球化学的挙動

抄録

The heavy metal contents of Quaternary "pure" limestones with little or no accessory minerals occurring in Okinawa Island are fairly small, being roughly estimated as Mn : n ppm, Zn : ca. 1 ppm, Ni, Cu : O.n ppm, Pb : <O.n ppm, and Cd : ca. 0.1ppm, respectively. Positive correlations observed between the concentrations of some trace metals and that of Fe strongly suggest that these metals have behaved together with Fe during the formation, diagenesis, and weathering processes of "impure" carbonate rocks having a large amount of the acid-insoluble residue. The main factor governing the incorporation of these metals into carbonate rocks from sea water may probably be the adsorption mechanism by colloidal hydrous Fe (III) oxides. These metals might have been successively migrated to pyrite from the hydrous Fe(III) oxides during pyritization occurred in reducing environments, and then finally incorporated into Fe(III) oxides such as goethite, which was presumably formed from pyrite by weathering under subaerial oxidizing conditions. No positive relationship was observed between the Cd and Fe contents, indicating that Cd may differ in its behavior from the above metal ions. Similary, Mn content is not proportional to that of Fe. A significant amount of the element, however, may be found in the 1M HCl-soluble fraction, that is, the lattice of carbonate minerals.