The Fuke Gold Mine is situated in the northern part of Yamanomachi in the northern part of Kagoshima Prefecture.
There are more than ten gold-bearing quartz veins in propylite, and these veins can be divided into the following two types ;
a) Hompi-type; represented by Hompi (main vein in the Fuke Mine) typically, strikes N 60°-80°E, dips 70°-80° NW. Dark green chlorite is found as one of gangue minerals in the upper part of each bonanza in addition to quartz and calcite.
b) No. 1 Vein-type ; represented by No. 1 Vein typically, strikes N 30°-40°W, dips 70°-80°W, bears quartz and calcite.
Besides the ore veins, there are fissures containing water. These cross the Hompi-type veins, striking N 15°E and dipping nearly vertical.
Compared with geotectonic lines of Kyushu, the strikes of Hompi-type are nearly parallel to the Usuki-Yatsushiro tectonic line. The strikes of No. 1 Vein-type are parallel to the long axis of Ariake Bay or to the tangent of the western edges of Kyushu Island. The strikes of the water veins are parallel to the Hinagu fault line or to the Hamamachi-Hitoyoshi line.
It is considered that three geotectonic lines in Kyushu intersect in the Fuke district. The ore veins are the older and the water veins are the younger.

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A geological columnar section was compiled during the geological survey and the exploration for strong coking coal in the Shikamachi area and its surroundings in the Saseho coal field in 1950-1951. The coal deposits of the field occur in a series of Palaeogene sediments 3, 000m in thickness. They are marine to fresh water in origin and are mainly an alternation of shale and sandstone with intercalated layers of tuffaceous rocks and very poor and hardly recognizable conglomerate. The columnar section was applied to the geologically unsubdivided coal field to the north and adjoining the area and covered for the most part by olivine basalt lava flows. A strong coking coal seam 0.70m in thickness with no parting was found at the depth of 14.25m. by the No.12 test boring of Hiratayama Mining Co. (Nakao No.1).This coal seam is correlative with the northern extention of so-called Sanmaimono (Fukui-ichimai) which is thick enough and of sufficiently good quality to be mined at several pits.It makes the coke suitable for metallurgical uses.
Black shale bed containing many remains of Cyclammina tani Ishizaki, a foraminifera of Eocene-Miocene age, crops out on the surface at Nakao. The thickness of the layers between the black shale bed and the coal seam is smaller than 30m. A local parallel unconformity was already detected under the black shale bed at Kase and no coal seam is visible locally by wash-out at Kanbayashi pit.
The authors believe, there is a local unconformity between the black shale bed and the coal seam, “Sanmaimono”, at Nakao, also.

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The vugs or microvugs in Ashio Mine are found in three types or modes of occurence, i.e., those in chert, in rhyolite-porphyry (or quartz-porpyry) and in vein. In chert, the writer observed eight examples of vugs, from which the following conclusions are made. Vugs in chert are arranged near the veins or pebble-dykes, which gave passage for the upward movement of the mineralizing solutions. It is demonstrated that the solutions come from these veins or pebble-dykes to vugs according to the writer's investigations of the crystal growths or the manner of growths of crystals of one kind of mineral on the crystals of another kind of mineral, after the method already suggested by Newhouse. The formation of vugs was brought about at first by the dissolving of the cryptocrystalline quartz of chert by the hydrothermal solution of an earlier stage, depositing in the next stage crystals of several kinds of minerals, sulphides and silicates. The general successions of vug minerals of Renkeiji-bonanza are as follows in descending stages ; quartz → Fe-Cu-Zn-sulphides (chalcopyrite, sphalerite, galena) → Fe-sulpharsenide (arsenopyrite) → apatite → pyrrhotíte of hexagonal plates, cubic crystals with curved plane of pyrite-marcasite → calcite. The arrangement of a series of vugs referring to the source of mineralizing solution goes sometimes upwards, in another cases, however, downwards. Sometimes, the mineral succession in a series of vugs varies rapidly from one vug to the next, from earlier minerals to the later. These facts may suggest the abrupt addition of cold ground water from above to ascending hydrothermal solutions at the point forming vugs and ore bodies. Each vug in chert is found to have been formed elongated to the direction of the flow of the hydrothermal solutions and to the bedding plane of chert, the passage of the solutions having been mainly via cracks and joints in the thiner chert beds intercalated by thin slate lamina.
The vugs in rhyolite-porphyry or quartz-porphyry at.Honzan district occur mainly in the pseudoconglomerate, named by the writer for the present, which resembles a boulder deposit and consists mainly of rounded or subangular pebbles or boulders of rhyolite-porphyry with a sericite-clay matrix. The origin of this sort of conglomerate remains yet in question, though the writer supposes that it may have been formed in the local kettle-depression in the very center of the rhyolite-porphyry mass, accompanying the fault movement. The faults became the passages of mineralizing solutions, causing natural stoping and the depression. The mineral assemblage in vugs in rhyolite-porphyry resembles those in chert, differing only in the richness of sericite and chlorite. This was caused probably by the chemical or mineralogical differences of the country rocks, for the material of the gangue minerals seems to have been derived in most cases from the leaching of the rock-forming minerals themselves.
From the study of vugs in Ashio Mine, the writer was strongly interested in the effect of groundwater on the hydrothermal solutions, the directions of the movement of solution, some upwards and others downwards from the source, suggesting circulation or convection of hydrothermal solutions. Further investigations in the future will clarify this problem.

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The contact zone bearing various kinds of skárn minerals, such as hedenbergite, grossularite, wollastonite, diopside and epidote, is located in the Palaeozic formations along the Ono-thrust fault which divides the Palaeozic formations from the middle Jurassic formations.
It is generally known that calcareous shales which belong to the Palaeozoic formations are most favourable for the formation of skarn minerals. Sulfide ore bodies are also predominate in these rocks.
The source of the ore has been supposed to be the quartz-porphyry which is distributed on the northern part of Senno-deposit but it is reasonable to consider that they were derived from the cryptobatholith underlying in the southern part of Ono-thrust fault.
The deposition of zincblende and galena took place in the pneumatolytic stage after the skarn minerals were crystalized. After deposition of the zincblende and galena hydrothermal mineralization followed depositing arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and some galena and zincblende.
In the later stage of the hydrothermal period, chalcedony, calcite and sericite were deposited with fine crystals of pyrite. The skarn minerals are restricted to the chemical compositions of country rocks and have no relation to the kinds of ore minerals.

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