石狩炭田幌加別層中に産するリョウテッ鉱質鉄質岩に就いて(予報)

抄録

Sideritic Band (Ironstone) is located in the dark gray thin-bedded shale of the Horokabetsu Formation in the Ishikari Coal Field (Palaeogene-Tertiary in age), Hokkaido, Japan. Near the surface it is sometimes changed to limonite.
1) Occurrence : Sideritic band is pararelled to the stratification and formed as lenses, nodules, and beds ; having a thickness of 50 or 60 cm in maximum. The formation contains more than 10 seams.
2) Analysis : For example No. 2 : Total. Fe 26.26, FeO 33.23, SiO₂ 26.30, CaO 5.09, MgO 2.55, Ig. loss 26.30 wt % and Mol. %, as follows : FeCO₃=58%, CaCO₃=10%, MgCO₃=5%, Others=27%.
3) Microscopic observation : Essential mineral is siderite, and accessories are quartz, calcite, plagioclase, chlorite and pyrite, etc. In some section angular quartz is very common, plagioclase and chlorite are very rare. Carbonatization is strongly characterized.
4) Genesis : Siderite is a sedimentary origin as the products of calm sedimentation.
Iron is transported as ferric oxide hydrozol in the main. Then siderite is formed by diagenetic differentiation under moderately high Eh potential environment.