古生代炭酸塩岩に見られる微量金属元素含量の特徴 –栃木県葛生地区二畳紀炭酸塩岩の重金属元素含量–

抄録

The Kuzuu carbonate rocks are divided into three major units, the Upper Limestone, Middle Dolostone, and Lower Limestone Members. Ni, Cu, Zn, and Cd contents of twenty-four limestone and twenty-six dolostone samples from these members were determined by atomic absorption spectrophotometry coupled with APDC - MIBK extraction to clarify the geochemical behavior of these metal ions during the formation and diagenesis of Permian carbonate rocks. As far as the limestones having a relatively small amount (< 1 wt. %) of impurities are concerned, both Quaternary and Permian limestones contain Ni and Cu in the same order of magnitude, but Zn and Cd tend to accumulate in the latter. The abundance of these metals in the Permian limestone is roughly eastimated as Ni and Cu; ca. 1 ppm, Zn; n ppm, and Cd; O.n ppm, respectively. The average ratios of 1 M acetic acid-soluble metal content to the total are fairly high (> 60%) as to Upper Limestone and the Middle Dolostone samples whose impurities are less than 1 wt. %. This fact suggests that a significant amount of these metals is sieved in the lattice sites of low Mg-calcite and dolomite rather than impurities. On the other hand, these metals in the Lower Limestone samples may mainly be contained in pyrite which has probably been formed under reducing envi ronments during the formation of these limestones. No significant increase can be seen in these metal contents of the Middle Dolostone samples due to dolomitizing solutions, though 1 M acetic acid-soluble Zn and Ni are slightly higher in these rocks as compared with those of the Upper Lime stone samples.