On the Joyama Ore Deposit of the Ishizu Mine, Gumma Prefecture, Japan
1967 Volume 17 Issue 84 Pages 190-199
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1967 Volume 17 Issue 84 Pages 190-199
The Joyama ore deposit is a covered sulphur deposit which was found in 1964 by means of drilling, and it is now on its way of development.
The present paper gives an outline of the Joyama ore deposit and some discussions on the geologic features compared with those of the already well-known Komenashi ore deposit, about 900m to the sowthwest.
1) The ore bodies of the Komenashi deposit have a distinct cap rock which is called "Nakaban Lava" in the mine. On the other hand, at the Joyama deposit, the Nakaban Lava might not exist originally or might be eroded away before the mineralization.
2) The Komenashi deposit are composed of several small ore bodies, while the Joyama deposit shows a roughly bedded and gently sloped form of a large scale. Although the shape of the Joyama deposit suggests that the deposit might be developed in a open sulphur pond at the ground surface, it seems possible that the deposit is of dissemination-replacement type, according to present geologic data.
3) The Komanashi deposit is located at about 1, 600m above the sea level and the Joyama deposit at about 1, 400m to 1, 500m. These altitudes correspond to a general tendency of the locations of numerous sulphur deposits on the shape of a volcano of this region.
4) The Joyama ore deposit is associated with a considerable iron sulphide ore zone at the hangingwall, while the Komenashi deposit is not.
5) The volume of underground water. flow containing H2S gas, is larger in the Joyama ore deposit than in the Komenashi at present. Around the former ore deposit there exist many hot springs.
It appears that the above characteristics of these deposits were due mainly to the following factors, i.e. the topography of the konide-type volcano, the flow and level of the underground water.
The geologic features of the basement rocks apparently controlled the emplacement of the sulphur deposit. These features are not only characteristics of the ore deposits of the Ishizu mine but also of those in the Kusatsu-Shirane region.
