Ishizu S-mine is one of the impregnated deposits of Numajiri-type it is composed of many cre bodies which lie almost all in the pyroclasic rocks and in some parts of andesite lava-flows. The genesis. of this deposit may be infefed as follows;
(1) The scending hydrothermal acidic solution spreaded into the pyroclastic rocks
(2) Plagioclase decomposed into kaolin and alunite by the action of hydrothermal solution,
(3) Greater parts of alunite desolved into solution, then the coutry rocks became more porous
(4) When external pressure decreases, the hydrothermal solution vaporized to solfataric gas, and the sulphur sublimated into cavities of rocks.
(5) External pressure then increases, the solfataric gas liquidized to solution.
(6) These mineralizat on took place many tiines, then the ores of high-grades were formed.
(7) H
2S disolved into solution, combined with iron that derived from country rocks and iron sulphides yielded
(8) Silica-sol precipitated into gel and remaining parts, of the country rocks were replaced by opal.
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