The Coroccohuayco copper deposit was discovered in the Andes of southern Peru in 1975 by joint work between Minero Peru and Overseas Mineral Resources Development Co., Ltd. The deposit is embedded in concealed skarn zone replacing a limestone part of sedimentary rocks in the form of large xenolith in dioritic batholith and has not any surface showing.
The prospecting work started at 1974 after the result of cooperative mineral exploration by governments of Peru and Japan from 1971 to 1973. At the first phase of the exploration, the main target was aimed to find out a stockwork and disseminated copper deposit but it was not succeeded. However, information drillings to be carried out in the IP anomaly zone in Coroccohuayco area caught a small part of copper mineralized skarn below dioritic batholith. In the light of the fact, detailed geological survey and magnetic survey were carried out there, and the existing IP data were also re-studied in 1976. As a result of works, it was assumed that mineralized skarn has sited in the IP simulation model area. At the second phase, drillings were planned in the IP model area to find skarn type copper deposit. Drilling resulted in obtaining the concealed high grade skarn type copper deposit in the "Southern Skarn Zone" of the Coroccohuayco area. Ore reserves has been calculated to be 15.2 million tons with Cu 2.88%.
Limestones of Ferrobamba formation of middle Cretaceous in age were skarnitized in two periods of Stages-1 and-2. Stage-1 took place with the activity of late Cretaceous dioritic batholith to form silicate minerals such as diopside and garnet. Stage-2 took place with the intrusion of Palaeogene acidic porphyritic rocks in dyke and stock forms to bring hydrothermal alteration such as carbonitization. Those igneous activities are seemed to have been the same magma origin but in defferent time.
Mineralization was accompanied by skarnization of both of Stages-1 and -2. Iron mineralization of mainly magnetite followed skarn mineral formation in Stage-1. Copper mineralization took place with hydrothermal carbonitization in Stage-2. Copper ore minerals are composed mainly of chalcopyrite, bornite and chalcocite, especially the latter two minerals are abundant. On the other hand, pyrrhotite, pyrite, sphalerite being common in skarn type deposit are not recognized in the main copper mineralized zone in the Coroccohuayco. Consequently primary ore solution is seemed to have been rich in copper but poor in iron under the condition of high CO₂ partial pressure.

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The silver-lead-zinc ore deposits of the Huanzala mine, Peru, are bedded or massive orebodies replacing a limestone formation embedded in the Cretaceous sedimentary sequence. The orebodies are composed of three types of ore; pyritic ore, "Shiroji" and skarn types.
Pyrite bodies are found associated with the orebodies and control the of ore types and patterns of ore element distributions. High grade orebodies are present adjacent to the pyrite bodies and consist mainly of the pyritic ore type. Ore elements show the zonal distribution; e.g. copper content and Ag/Pb ratio decrease, and Pb/Pb+Zn ratio increase towards marginal zones of the pyrite bodies.
The mineralization is interpreted to be two stages; the pyritic ore and the skarn ore have formed mainly with silver-lead-zinc mineralization in the first stage and the "Shirozu ore" has deposited principally with copper mineraliza-tion in the second stage.
Intrusion of quartz-porphyry is considered to be related to the mineralization and faults such as the Lower fault are passages of the ore fluid.
Based on the conclusion of these studies, exceedingly positive exploration activities carried out in the El Recuerdo and the El Recuerdo-Sur section of the Huanzala mine have resulted in the highly significant discoveries of oreb'odies consisting of the.pyritic ore and the "Shiroji" ore.

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The Hishikari deposit, which is now regarded as one of the best gold mines in the world, was discovered in 1981 during a scout-drilling programme carried out by the Metal Mining Agency of Japan (MMAJ). The original aim of the programme was to explore the target located by geophysical surveys and geological interpretation.
Subsequently, 18 follow-up surface DDHs were carried out by the Sumitomo Metal Mining Co. Ltd., the property owner, and all the holes successfully intersected high grade ores.
In March 1983, the company made an official statement that the potential gold content of the deposit may reach some 120 tonnes as metal with a grade 80 g/t.
The underground development was commenced in December 1982, and the first crosscut intersected the orebody in July 1985.
The purpose of this paper is to describe geological facts so far acquired during extensive exploration and development works. The facts are summarized as follows:
(1) Most of veins show extremely high gold content between 100 m and 0 m above sea level.
(2) The ore deposit is apparently located within the area where a gravity high anomaly and a resistivity low anomaly overlap.
(3) A low resistivity anomaly down to the depth some 30 km from the surface is located by the magnetotelluric survey in a section through the deposit. The anomaly resembels to the one in a typical geothermal area.
(4) A large volume of hot spring water occurs within the vein system itself.
(5) The fissures and veins are likely to develop preferably in brittle rocks (andesite lava, shale, sandstone, etc.) and less in ductile rocks ( argillized. fault zone, clayey tuffs, etc.)

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In 1981 epithermal vein type gold deposits were discovered in the Hishikari mine area after systematic exploration works performed by the Metal Mining Agency of Japan. Subsequently detailed geophysical surveys (Gravity, MT, CSAMT, Charged Potential and Spectral IP Surveys) have been carried out in the area by the Sumitomo Metal Mining Co. since 1982.
This paper reports the results, interpretations, and the evaluation of the validity of each geophysical survey giving a special attention to the interrelationship between the geophysical and the geological factors which might be responsible for the mineralization in the area.
The results of the geophysical surveys are summarized as follows:
1. The location of high gravity anomaly correlates well with known ore zone.
2. The regional resistivity distribution of the area was clarified, and the low resistivity zone detected in the vicinity of the mine site is interpreted to be a reflection of the alteration zone which occurs horizontally at the upper parts above the gold vein system.
3. A resistivity cross-section constructed along a N-S profile from the MT survey indicates the existences of the conductive rocks at shallower levels near the mine site and an extremely low regional resistivity anomaly at the deepest investigated levels of 30-40 km. 4. An IT anomaly in the low resistivity zone is a very important indicator to locate of the ore zone.
The results obtained by each geophysical technique and the comprehensive analysis on them showed that they were very effective in clarifying the geophysical environments pertinent to the ore zone and provided very useful information for the exploration in the area. The "multi" geophysical method described here might readily be applicable to any other exploration projects for similar hydrothermal deposits.

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The Nurukawa kuroko ore deposits was discovered on the west of Lake Towada on the border of Aomori and Akita Prefectures, northern Honshu, Japan, as the result of systematic exploration program from 1979 to 1984. This report is a summary of story of the discovery, the geology and the ore deposits.
In the east of this area, the old Towada Ginzan deposits which mined from late 19th century to early this century has been known, and also the Namariyama Ginzan deposits were discovered in 1968. Both deposits are of the kuroko type.
In 1982, a possible existance of the new kuroko deposits was indicated by the study of old Towada Ginzan deposits, detailed geological survey, geochemical study of the alteration of low Na₂O content in pre-mineralization acidic volcanics, and geophyisical exploration of IP method.
Based on the information obtained by these study, drillings for investigation on the geologic structure and a systematic drilling program was planned and carried out. Consequently Nurukawa No. 1 to No. 5 ore bodies were discovered by underground and surface drillings between late in 1982 and September 1984.
The geology of the area is mainly characterized by active dacite lava and dacitic pylocastics of the Miocene Tertiary, which are divided into four units named Nabekurazawa, Lower Hayasemori, Upper Hayasemori, and Tobe formations in ascending order.
The ore deposits occur at the top of the Lower Hayasemori formation and consists of five ore bodies of black ore. The ore is also divided into two types on the basis of their mode of occurtences. The one is bedded, and associated with silicious network ore, disseminated ore and gypsum ores. The other is fragmental, and associated with gypsum ores.

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Hosokura mine is located at about 80 km north of Sendai, Miyagi Prefecture. The deposit is of the metalliferous vein type formed in the Miocene strata. The fissures of the deposit are different in pattern and development between the eastern and western blocks devided by northwest-southeast trending faults. On the eastern blocks fissures were formed mainly in the dacite lavas and on the boundary between dacite lava dome and surrounding pyroclastic rocks as gravity faults caused by the upheaval of pre-Tertiary basement. On the other hand, fissures on the western blocks were formed as gravity faults caused by the gentle upheaval of pre-Tertiary basement in the northwestsoutheast tension stress field.
Oiwake and Ohtori vein swarm in the northern part of the deposit belongs to the later group, while the Motogoya and Higashi-nigo veins also in the northern part of the deposit belong to the former group.

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The Toyoha ore deposit, which consists of more than fifty veins, is known as polymetallic hydrothermal deposits. The principal ore minerals are galena, sphalerite and pyrite with small amount of silver minerals, chalcopyrite, tetrahedrite, arsenopyrite, marcasite, pyrrohtite, magnetite and hematite. Tin, tungsten, indium, cobalt as well as gold and silver occur as minor elements in the ore.
Such variety of ore minerals and elements was caused by the superimposed mineralization of several stages. It is clarified that there were at least seven mineralization stages, from the evidences of cutting relationship in the veins. Each mineralization stage is characterized, respectively, by the mineral assemblages and minor element concentrations. For example, stage I and stage IV represent main stages of deposition of silver minerals, galena and sphalerite. Tin, tungsten and indium concentrations are recognized to be closely related with occurrence of sphalerite in stage IV.
The poly-ascendent model of veins in the Toyoha mine has been proposed. The model gives an effective guide for exploration and actually, some encouraging results have been obtained.

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