福島縣羽山ニッケル鑛床

抄録

The Hayama Mine is situated on the Abiikuma Plateau about 15 kilometers to the southeast of Fukushima City. The district is composed mostly of hornblende biotite granodiorite. However, some hornfels and ultra-basic rocks, such as dunite and diallagite, are present in the form of a roof-pendant. The nickel-bearing minerals, such as niccolite, gersdorffite, pentlandite and nickeliferous pyrrhotite etc., occur as fine grains in the forsterite aggregates, which form a vein-like body in dunite. The forsterite rock is also cut by remarkable black veinlets, composed of the acicular or fibrous crystals of ludwigite. Ludwigite is known to be produced by the chemical reaction of boron- and iron-bearing emanations from granitic magma on some magnesium-bearing rocks such as dolomite and magnesite. Under the microscope, the nickel minerals generally appear in pure crystals, filling up the interstices between the forsterite grains. The niccolite, is rarely rimmed with gersdorffite. Ludwigite is always accompanied by magnetite and chromite which are thought to have been derived from the ultra-basic rock.
The paragenesis of nickel minerals-forsterite-ludwigite-chromite is very critical in the interpretation of the ore genesis. This deposit must be studied from two viewpoints, one from magmatic differentation and the other from contact metasomatism.