The Toyoha ore deposits, which consist of more than fifty veins, are known as polymetallic vein-type deposits. The principal ore minerals are galena, sphalerite and pyrite with small amount of silver minerals, chalcopyrite, tetrahedrite, arsenopyrite, marcasite, pyrrhotite, magnetite, hematite etc. Tin, tungsten, indium, cobalt and bismuth as well as gold and silver occur as minor elements in the ore.
The authors recently proposed a poly-ascendant mineralization model, that is, such variety of ore minerals and elements was caused by the superimposed mineralization of at least seven stages (YOSHIE, et al., 1986) . In this paper, we have reviewed the poly-ascendant mineralization model with the latest knowledge and minor modification.
That model gives an effective guide for exploration. Since 1986, extensive and systematic underground diamond drillings have been carried out for the targets extracted from the model and have successfully resulted in a discovery of the giant new vein, "Sinano vein", which extends 600 meters long, with 30 meters maximum width, estimated more than three million tons of ore reserves at 250 g/t silver, 2% lead, 13% zinc and with considerable amount of copper, tin and indium.

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リビア南西部ムルズク盆地の西縁に分布する,三畳紀のザルザイティン層中には無数の砂岩型ウラン鉱床の鉱徴が見られる.同層中には5回の堆積サイクルがあり,粗粒から細粒のいずれも陸成の堆積物がみられる.ウランの鉱徴はその中の有機物に富む粗粒砂岩中にみられ,古流系のチャンネル堆積物中に限られている.
ウラン鉱物としてはβ－ウラノフェン,カルノータイト,テュヤムナイトが重要で,4価のウラン鉱物は見つかっていない,鉱化に伴いパナジン,モリブデン,セレン,鉄,およびイオウの濃集がみられる.これらの元素およびウランはホッガー花崗岩マッシフより,地下水により溶出沈澱してできたものと考えられる.

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ボリビアの東アンデスに分布する中生代～新生代花こう岩類を,モード組成,化学組成,帯磁率について検討した.その結果,ラパスから北部に分布する中生代花こう岩類はチタン鉄鉱系に属する.中部および南部に分布する新生代花こう岩類の大部分はチタン鉄鉱系であるが,部分的には磁鉄鉱系のものも存在する.これらの中生代～新生代花こう岩類の大部分は,化学組成的にはI-タイプに属する.
中生代花こう岩類は一般的に新生代のものよりSiO₂に富み,低いK₂O/Na₂O比によって特徴づけられる.しかし,両者はK₂Oを除いて,SiO₂含有量に対して同様の組成変化を示す.これらの両者を日本の花こう岩類の平均組成と比較すると,東アンデスのものは高いK₂Oを示し,低いAL₂O₃, MgO, CaO,全鉄を示す.
ボリビアの東アンデスには多くの熱水性鉱脈鉱床が存在しているが,それらの成因は中生代～新生代の花こう岩類と密接に関係している.すなわち,中生代花こう岩類に伴って,中熱水あるいは深熱水性スズおよびタングステン鉱床が生成され,新生代の酸性マグマの活動によって,浅所高温型多金属鉱床が生成された.

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Izu-Oshima Volcano erupted in 1986 after dormant 12 years. The first phase of eruption started on Nov. 15 at the crater A on the summit of Miharayama cone by splendid' fire fountaining which attained 540 m high. Lava extruded with high rate, filled up the summit crater and flowed down to the caldera floor on Nov. 19. The second phase of eruption started on Nov. 21 with opening of fissure vents B trending NNW on the caldera floor. Eruption column rose up to a height of 16, 000 m. Strong seismic activity began two hours before opening of the vent and continued during the eruption. One and a half hour later another fissure vent C opened on the upper slope outside the caldera rim. Eleven craterlets were opened and a lava flow LC had almost reached to Motomachi, the largest town in the island. Until next morning most vents ceased their activity. Main part of the B fissue was covered with a large spatter rampart from which two lava flows LB I and LB III spread out on the caldera floor. Another small lava flow LB II flowed out from unsolidified interior of the spatter rampart on Nov. 23. Thick deposit of air-fall scoria was distributed mainly eastward.
A small eruption occurred on Dec. 18, lasted about two hours, and ejected bombs from A crater.
The activity of 1986 erupted about 6×10⁷ tons or more of magma. This quantity is nearly comparable to that of 1950-1951 activity and a tenth of 1777-1792 activity. The rocks erupted from A crater are basalt, very common in this volcano. The rocks from B and C vents are more differentiated basaltic andesite or andesite which has not commonly found in this volcano. Volcanic tremor, once stopped after the eruption of Dec. 18, recurred on Jan. 1, 1987. Activity of tremor and earthquake gradually increased and since Aug., 1987 remarkably. It culminated to the small eruptions of Nov. 16 and 18, 1987. The pit crater on the summit of Miharayama was reproduced at the Nov. 18 eruption.
No marked activity has occurred after the eruption of Nov., 1987. Activities as volcanic tremor, earthquake and gas emission, however, has continued since then. Prudent watching and monitoring of the activity and the study of the eruption mechanism are needed.

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The Nishi Ore Body was discovered approximately two hundred meters west of the Fukasawa (Fukazawa) Deposits through drilling from the surface. The subsequent underground drilling exploration revealed the following characteristics of the ore.
(1) The ore body is mainly composed of fragments of the kuroko ores and the footwall dacite which are commonly observed in the Fukasawa mine.
(2) The ore body is hosted slightly above the stratigraphical horizon of the other kuroko deposits of the mine and is intercalated with thin beds of mudstone.
(3) The distribution of the ore body overlaps the area of thickening of the mudstone and the overlying basalt lava suggesting the topographic low of the sea floor at the time of sedimentation of the ore.
(4) The ore body is divided into lower and upper ore bodies by a thin layer of mudstone. Each body consists of several layers of depositional units. The size grading structure is observed within the main part of each unit and in a finer facies at its uppermost. Furthermore, the total sequence becomes finer-grained upward showing the doubly size-graded structure.
From the above-mentioned occurrences, it is concluded that the Nishi Ore Body consists of ores transported by the high-density turbidity currents which have been subsequently generated by two phreatic eruptions which might have collapsed the primary kuroko ore deposit. The density currents are believed to have flowed down westwards judg-ing from the horizontal change in the grain size of the clastic sediments, distribution of the ore body, and the sedimentary structures observed in the drilling cores.
The basalt lava which covered the ore body also flowed down westwards stripping off the top of the Nishi Ore Body.

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A new soil-gas geochemical exploration method called "Fingerprint" was developed by KLUSMAN and VOORHEES (1983) for the direct detection of hydrocarbons. It has been proved to be very effective and technically advantageous over conventional geochemical methods to detect buried fault/fracture. In this technique, soil-gas is adsorbed on activated charcoal and is analyzed by Curie point desorption mass spectrometry. New interpretation technique has been introduced to extend applicability of the technique to geothermal exploration and various field tests have been performed since 1985. In this paper, basic ideas and the results of our interpretation technique on Fingerprint data for fault/fracture detection and geothermal reservoir definition are explained:
(1) Fault/fracture detection: "Gas feature diagram" (HIGASHIHARA et al., 1988) is a plot of cluster number on log-transformed Total Modified Ion Count (TMIC) vs High Mass Gas Ratio (HMGR) diKgram after clustering all mass spectra into several categories. This diagram is used to distinguish anomalous population which indicates existence of fault/fracture from the background population. The anomaly which is plotted in the high TMIC and high HMGR area and the background which is plotted in the low TMIC and low HMGR area are clearly divided by a nonpopulated zone. All the members of anomalous population are classified into the different cluster categories of mass spectrum pattern from those of background population.
(2) Geothermal reservoir definition: Newly developed interpretation techniques using gas feature diagram are also applied to the Okuaizu geothermal field. In a geothermal area, the catagenesis zone (VASSOYEVICH et al., 1970; where heavy hydrocarbons are inferred to be generated) is located at higher levels in the crust due to the high temperature gradient. At first, anomalous population which is due to fault/fracture should be eliminated since they do not represent an effect from geothermal reservoir. It was found that the data from the Okuaizu geothermal reservoir zone tend to fall into the high TMIC and high HMGR area compared with the other background data of the same area on the gas feature diagram.

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