The Tochibora ore deposit of the Kamioka mine is mainly composed of skarn-type lead and zinc orebodies formed by the replacement of tightly folded limestone. Two main types of ore deposits are distinguished. One is what is called "Mokuji", representing pyrometasomatic deposits associated with skarn minerals, and the other is "Shiroji" being mesothermal replacement deposits. The shape and extent of orebodies are controlled by original shape of limestone, complicatedly folded in general. This fact serves as one of the major keys to exploration.
As a result of the recent survey carried out in the lower part of the Tochibora ore deposit, the geological structure and the characteristics of the mineralization have been ascertained as follows.
1) In the lower part of the Tochibora ore deposit, two folding structures called "Inishi No. 3 syncline" and "Inishi No. 10 syncline" can be clearly recognized, as is the case in the upper and middle parts.
2) At -300 m level, the plunge of these synclinal axes is 15°-20 °SW, changing smoothly from 40°-45° SW, which is generally observed in the upper and middle parts.
3) It is evident that the axis of the Inishi No. 10 syncline is reversely plunging to NE at -370 m level after the above-stated smooth change, to form a basin structure.
4) Inishi No. 3 syncline is not clearly recognized between -300 m level and -370 m level.
5) The horizon composing the main series of the Tochibora ore deposit in the lower part is a chain of orebodies of No. 1B-No. 4B-No. 4A-No. 3B-SNo. 1-No. 6B-No. 8C(5)-No. 9-No. 10.
6) Main mineralized zone is situated between the barren skarn (Mokuji) zone and the unmineralized limestone zone.
7) In terms of the Ag: Pb: Zn ratio (so-called π-ratio) of the individual orebodies constituting the Tochibora ore deposit, zonal distribution is clearly recognized; i.e., from west to east, No. 1 type zone (π-Pb<25) No. 2 type zone (5<π-Pb<40)→No. 3 type zone (15<π-Pb<60)→No. 4 type zone (45<π-Pb).
8) The zonal distribution of ore types is also recognized, corresponding with the above zoning of π-ratio; i.e., Cu-bearing Mokuji ore→Pb-Zn Mokuji ore (size of orebodies is small to moderate)→Pb-Zn Mokuji ore (size large)→high-grade Shiroji ore.
Exploration based on the above-mentioned knowledge has been successfully carried out in the lower part of the Tochibora ore deposit, and led to the discovery of new orebodies and of the continuation of known orebodies.

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Pyrometasomatic lead and zinc deposits in the Nakatatsu mine are localized in skarn masses consisting of clinopyroxene (hedenbergite) and garnet. The data obtained through recent exploration works and the various data accumultated for several decades were critically studied for elucidating the geological and mineralogical features controlling the localization of ores. The results are as follows: (1) Ore/skarn ratio is much higher in the clinopyroxene skarn zone than in the garnet skarn zone. (2) The clinopyroxene skarn zone with high ore/skarn ratio is located in the hanging wall side of the Nakayama skarn zone below -200 m Level. (3) ρPb, which is defined here as 10Pb%÷(10Pb%+Zn%)×100, is distributed in each orebody in a zonal fashion with higher value at the central part of the orebody and lower at the margin. (4) The areas of the ρPb ranging from 20 to 40 are favourable sites for high grade and large scale orebodies in this mine. (5) Orebodies are often associated with the folded structure in the clinopyroxene skarn zone surrounding non-skarnized limestones.
These indicators were employed as guides in prospecting works and two high-grade orebodies were found below the -200m level down to the present lowest level (-360m) of the mine.

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The Nippo ore deposit, formerly called the Ohmine deposit, is a pyrometasomatic copper deposit. Recently the mining development has been carried out in the lower level of the deposit and some interesting geological phenomena different from those observed in the upper level have been encountered.
Skarns and mineralized rocks are classified into six types: banded skarn, diopside skarn, garnet skarn, hedenbergite skarn, brittle skarn (so-called "bosa" garnet skarn), and quartz vein. Of these rocks, diopside skarn, garnet skarn, hedenbergite skarn, and quartz vein are accompanied by ore minerals. Two types of zonal arrangement of skarns are observed: (1) hornfels through banded skarn, diopside skarn, garnet skarn, hedenbergite skarn to limestone, and (2) quartz diorite through garnet skarn, hedenbergite skarn to limestone. The former is seen between slate and limestone and the latter between quartz diorite and limestone. Assemblages of ore minerals are chalcopyrite-cubanite-pyrrhotite, chalcopyrite alone, chalcopyrite-bornite, chalcopyrite-pyrite, and chalco-pyrite-pyrrhotite.
The orebodies of this deposit are classified into two groups: one is associated with diopside skarn and garnet skarn, and the other with hedenbergite skarn and garnet skarn. The former type of orebodies is massive in shape and the latter is tabular and commonly accompanied by vertical quartz veins. The mineralization of these orebodies seems to be strongly controlled by the pre-ore faults.

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The Fukazawa deposits are located in the central part of the Hokuroku basin, Akita Prefecture. They are stratabound kuroko deposits occurring in volcanics of Miocene age. Kuroko ore is a main constituent of the Fukazawa deposits, and Oko, Keiko and Sekko ores, which are common in many other kuroko deposits, are seldom contained in the deposits. The stratiform orebody has a considerably greater lateral extension than thickness and occurs immediately under a thick basalt flow.
Some interesting modes of occurrence have been observed in the deposits. In the Manjakuzawa No. 2 ore-body, basalt is interstratified with kuroko ore and divided into small irregular or ellipsoidal masses like a stack of pillows at the end of the flow. This suggests that the basalt flowed into unconsolidated sediments and ores.
The upper Yellow ore (Oko) occurring within the hanging wall layered tuff and basalt in the Fukazawa deposits has been considered to be an evidence of post-kuroko mineralization. Mineralization lasted probably after main kuroko mineralization. This type of ore of the Tsunokakezawa No. 1 orebody and intensely silicified zone with chalcopyrite and pyrite in the foot wall lithic tuff may have been formed by the later mineralization.

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Recently many studies regarding alteration of acidic volcanic rocks below the black ore deposits were performed. For example, DATE and TANIMURA (1973) showed that Na₂O was subtracted from, and K₂O and MgO were added to the acidic volcanic rock during mineralization. Furthermore, ISHIKAWA et al. (1976) indicated that CaO was also subtracted from dacite.
This time, the authors restudied the chemical data of Na₂O, K₂O, CaO and MgO from dacite below the Fukazawa ore deposits that ISHIKAWA et al. (1976) used, and the followings were revealed 1) Below the black ore deposits, Na₂O-poor dacite develops in the extent of 3.0km (NW-SE direction)×1.5km(NE-SW). 2) The fbrmation of Na₂O-poor dacite depends onmineralization of black ore deposits. And in the area of Na₂O poor dacite, parts relatively rich in Na₂O formed by alteration differentiation can be seen. 3) AlteredIndex(K₂O+MgO/Na₂O+K₂O+MgO+CaO)that wasproposedbyISHIKAWA et al. (1976) relys definitely on its Na₂O content. Thus it is required to find Na₂O poor dacite for exploration of black oredeposits. 4) It is not always effective to use independendentlv subtractional trend of CaO and additional trend of K₂O and MgO in dacite as indications for exploration, but they may beuseful as an auxiliary instrument.

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The ore deposits of the Toyoha Mine, Hokkaido, are of fissure filling lead-zinc veins. The ore is mainly composed of sphalerite, galena, and pyrite with an important amount of silver minerals. The modes of occurrence and mineralogy of silver minerals in major veins are reviewed in this paper.
The veins can be classified into two groups based on their stage of mineralization, earlier and later. It is noteworthy that silver mineral assemblages are different in the veins of the two stages. Main silver minerals in the earlier group, represented by Tajima and Harima veins, are argentite, electrum and silver, while in the later one, represented by Soya and Sorachi veins, are Ag-tetrahedrite, pyrargyrite and diaphorite.

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