Hanawa Mine is located on the eastern margin of the Hokuroku green tuff region of northeastern Japan. Geology in the area is composed of pre-Tertiary rocks inferred to be Permian, and acidic to basic volcanic and pyroclastic rocks of Miocene. Geologic structure in this area is characterized by tectonic lines with NNE-SSW trend, which are shown by faults and alignment of intrusive rocks, and the basin structure with E-W axis, which has been called "Sotoyama local basin". Ore deposits at Hanawa Mine are well known for the Kuroko-type deposits, consisting of the Motoyama, the Aketooshi and the Onnataira deposits. These ore deposits are distributed along NNE-SSW tectonic lines in the western margin of Sotoyama local basin, in three stratigraphical horizons of Shimokobesawa formation correlated with the Nishikurosawa stage of Middle Miocene. The Aketooshi deposits are divided into several unit ore bodies on the basis of the modes of occurrence and the mineral assemblage.
In each of these units, a vertical zonal arrangement is observed, nameley stockwork or disseminated siliceous ore, massive ore, stratiform brecciated ore and laminated ore in ascending order. These ore bodies are dominant ly black ore as a whole, with a small quantity of yellow ore, and some of them are accompanied with gypsum. The known ore bodies occur in some troughs at surface of the foot-wall rhyolite lava domes. Thus, it is inferred that primary mineralization and deposition of the black ore in the Aketooshi deposit were performed along the troughs. The thickest parts of basalt lava (sheet) and fine tuff in the hanging-wall are closely related to the trough of the foot-wall. The dispersion of some trace elements in the foot-wall rhyolite is seen in the same direction as the trough. The above phenomena suggest that the tectonic movement with NNE-SSW trend in this area controled the volcanism and the mineralization. As the results of the application of these geological and mineralogical investigation to the circumference of the known ore bodies in the Aketooshi area, a new high-grade ore body has been found.

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In the Shakanai mine, ore deposits that have been discovered to date enumerate 11 in number. The mine runs at 26, 000 tons of crude ore production per month. Of the ore deposits mentioned above, No. 11 ore deposit, discovered in the latest, has been exploited since 1974 and is now conducing to the 1/4 production of total crude ore produced in the mine. The No. 11 ore deposit is divided into South ore deposit and North ore deposit, and is composed of high grade black ore and disseminated ore. The south ore deposit is considered to be main ore deposit of the two and mode of its occurrence has been revealed as follows.
1) Ore deposit is composed of black ore and siliceous disseminated ore and lie in two definite stratigraphic horizons.
2) Ore deposit lies only in B bed of Shakanai upper member which extends to NNW-SSE direction elliptically in the area of 400m×250m.
3) B bed consists of dacitic tuffs, breccia bed, basaltic tuffs and mudstone. The breccia bed is most important host rock, and basaltic tuff and mudstone constitute the hanging-wall having tendency to increase the thickness of bed on the center portion of ore deposits and to decrease it on the outside.
4) Observing ore shoot in each unit ore body, it is inferred that deposition of ore was performed along the small scale troughs on the foot-wall.
In addition to these occurrences, such rare minerals as stromeyerite, renierite and unidentified mineral of Cu-Pb-Ag-S system were observed in small amount by EPMA.

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Many previous articles about the theories and experiments related to induced polarization phenomena indicate that the I.P. is quite a complicated matter affected by various physical and chemical factors of sulfide minerals and groundwater at the contact. It was rather difficult to understand completely the I.P. phenomena at the Kuroko ore field only from these references. The investigation of I.P. characteristics for specimens of sulfide ores and country rocks with sulfide mineralization from Kuroko ore fields have been carried out. The relation between laboratory results and field I.P. response has been discussed quantitatively.
We started the experiments from observation of interface impedance for several combinations of ore types and varieties of solution. Then tank model experiments, theoretical analyses of the results and I.P. logging tests at the field have been followed up. The interface impedance observed about conductive massive sulfide ore samples shows a narrow range of "characteristic value (W)" of Warburg impedance, which is around 5 kilio-ohm-cm ² /√sec. Neither the variation of sulfide minerals nor the, concentration of relevant ions in the solution seems to affect practically the magnitude of I.P. response of an ore body. The mathematical expression (3) was introduced for the peak value of I.P. anomaly of a spherical massive ore body model placed in a uniform current field of pulse type, and its validity was proved by the tank model experiments.
It was observed that the total impedance of massive sulfide specimen increased when the amount of internal interfaces was increased artificially. The state of ore body with many internal interfaces is supposed to be common in nature and it will be called "mosaic massive". A single massive ore body would exist only ideally. While the expression (3) with (4) implies that a large scale single ore body requires long current pulse width more than hundreds seconds for a sufficient I.P. response, the mosaic massive is expected to respond well to the pulse width of less than ten seconds on account of increased impedance. A difinite I.P. response of massive and compact pyritic ore body in a part of the Etsuri deposits was observed by I.P. logging using conventional type of I.P. equipment and large electrodes spacings.
Analysis of decay voltage curves for specimens of both veined rock and massive black ore with abundant insulating minerals (e.g. barite rich black ore) gave the same range of the "I.P. decay factor (α)" as the mosaic massive. Impregnation of small particles (less than 1 mm) of sulfide minerals in country rocks is anticipated from the expression (5) to give little effect on the results of I.P. survey at the Kuroko field. The mineralized dacite body underneath massive sulfide ore body at Etsuri showed high I.P. effect on I.P. log measured with 2 sec. of pulse width. This is interpreted as the result of veined rock effect rather than that of impregnation. An I.P. anomalous body of extensive size has revealed by the compilation of I.P. logging results for 21 drillholes around Etsuri ore deposits.

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The Yatani deposits are epithermal vein type deposits situated in acidic tuff member of Yatani formation of Miocene age. The recent study of geology and ore deposits in the mine revealed following facts and suggestions on exploration in the future.
1. The post-ore movement of faults is controlled by simple rule, namely, left lateral movement for NW-SE trending faults and right lateral movement for NE-SW trending ones, which are interpreted as the movement of conjugate set of faults.
2. Shear and tension fractures of veins were formed under E-W trending compressional force, with maximum stress axis pitching 40° to the west in the northern part of No.2 Fault and horizontal in the southern part of No.2 Fault.
3. Veins show remarkable vertical monoascendent zoning of Pb and Zn mostly in the vertical direction with Pb zone in higher level and Zn zone in lower level. Horizontal and vertical zoning is also suggested to exist between Pb-Zn and Au-Ag zones.
4. Zoning pattern and distribution of high grade portion of vein are fully controlled by No.2 Fault and No.3 Fault which played important roles as principal channel ways of ascending ore solution.

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The Iwato gold mine, located in the Makurazaki City, is known for its peculiar massive gold mineralization called the Nansatsu-type. Ore deposit of the mine consists of gold ore shoots in a gold and silver-bearing silicified mass occurring in the Nansatsu group consisting of andesitic volcanics probably of Miocene age.
The exploration and development of the mine have long been made exclusively around the high-grade outcrops, as the ore shoots as well as silicified mass have been believed to have been emplaced near the surface in a stratiform or lenticular form. Recent exploration and re-examination on the geological and geophysical data at hand, however, have revealed some interesting facts on the localization of ore deposits:
1) The gold deposits of the Nansatsu-type are emplaced only within the Nansatsu group and generally in its upper formation.
2) The gold-bearing silicified mass at Iwato occupies the center of alteration zones which show a distinct zoning from center outward, namely highly silicified zone (silicified mass of 94-95% SiO₂)-moderately silicified zone-argillized zone-propylitized zone-unaltered rock.
3) The silicified mass extends laterally about 1, 200m in the direction of E-W and abruptly expands in the upper part of the Nansatsu group (occurring in levels higher than 120m to 150m above sea level at Iwato), thus making "mushroom" form in its N-S profile.
4) Almost whole of the silicified mass contains ore to sub-ore grade gold, but the ore shoots with workable grade of over 4g/t Au are located usually in the inner part of the body, showing a mushroom shape, too.
5) The favorite host for silicification and gold mineralization is the pyroclastics such as tuff and breccia intercalated in the pyroxene andesite, thus the silicified mass often developing laterally in such layers.
The above findings of the factors controlling ore localization have led to increase exploration targets and have resulted in gain of ore reserves more than those exploited.

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The ore deposits at the Kamaishi mine can be divided into iron, iron-copper and copper ore bodies. The authors studied the occurrence and distribution of sulfide minerals in the iron and iron-copper ore bodies, especially in the iron ore bodies located at the deeper parts of the Shinyama ore deposits (6D and EN-1 to 4), and in an iron-copper ore body called 7D. The results are summarized as follows:
1. In most of the studied iron and iron-copper ore bodies, there is no correlation between the Fe and Cu contents. There are two types of relations between the Cu and S contents. In one type, the S content varies with a constant, low content of Cu. In the other type, both the Cu and S contents change at variable ratios. The former is dominant in the iron ore bodies and the latter in the iron-copper ore bodies.
In the case of the copper ore bodies, the Cu content changes in direct proportion to the S content. From the ratio of Cu and S, the ratio of chalcopyrite to pyrrhotite, the dominant sulfide minerals in the copper ore bodies, are calculated to be 2:1.
2. Predominant iron sulfide minerals in the iron ore bodies are monoclinic pyrrhotite and pyrite, both of which appear to have been changed from hexagonal pyrrhotite. This observation, together with the fact that the copper content in the iron ore bodies is always low regardless of the sulfur content, suggests that the iron ore bodies were affected by low temperature hydrothermal solution carrying abundant sulfur but very little copper.
3. In general, the area of sulfide mineralization associated with magnetite mineralization coincides roughly with the area of iron ore bodies. Sulfide minerals are relatively abundant at the top and the bottom of the ore bodies, chalcopyrite being the dominant sulfide at the top and pyrrhotite at the bottom. The midde part of the ore bodies is poor in sulfides, forming high grade magnetite ore.
4. Sulfide minerals are concentrated mainly in the clinopyroxene skarn zone developed near limestone, and in the iron ore bodies. One of the most important factors for the deposition of Cu minerals is the distance from limestone.

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