Tungsten-Molybdenum Ore Deposits and Uranium Mineral of the Komaki Mine, Shimane Prefecture

Abstract

The Komaki Mine is one of the pheumatolytic to hypothermal tungsten and molybdenum deposits which have been found to contain radioactive minerals, and is situated about 44km south of Matsue City, Shimane Prefecture.
In this mine, the ore deposits are found in marginal facies of fine-to medium-grained biotite granite. They are irregular string-or chimney-like domes of tungsten-molybdenum quartz veins. Cross sections of the chimneys are circular or elliptical in form and from one to several meters in diameter. The largest chimney is about seventy or more meters in length and has several ramifying branches at many places.
The main ore minerals are wolframite, sheelite and molybdenite, together with broggerite, magnetite, chalcopyrite, pyrrhotite and pyrite.
The "greisen" halo, extending about 0.3 meter from the chimney, has the mineral assemblage: muscovite, quartz, garnet, topaz, potash-feldspar, plagioclase, axinite, biotite, fluorite, apatite and zircon.
In the dressing mill, the tungsten ore has been separated by the Wilfley Table and (the remnants of them mined about twenty years? ago has been found to be highly radioactive.) Uraninite-mineral has been gathered from the tungsten concentrates by means of both Magnetic and Isodynamic Separaters, and the Super Panner.
The uraninite was identified by the powder methods of X-ray diffrection analysis, and its cell dimension was measured: a0=5.48₁ Å. It was also clarified that the mineral contains about fourteen percent ThO₂, by fluorescence X-ray analysis. It is therefore, thought to be bröggerite.
Bröggerite, which has an intimate paragenetic relation to the main ore minerals occurs in the marginal part of the chimney. The grain size of the mineral is up to 1mm in diameter.
Note : () ? "talings of ores mined about 20 years ago have been found to be highly radioactive"