著者

正路 徹也 佐々木 望

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.28, no.152, pp.397-404, 1978-11-01 (Released:2009-06-12)

参考文献数

9

被引用文献数

1

---

The minerals of the scheelite-powellite series containing 0, 0.5, 1, 2, 4, 6, 10, 20, 40, 60, 80 and 100 mole % CaMoO4 have been synthesized. The solid solution of this series was obtained by the slow addition of a Na2WO4-Na2MoO4 solution to a large volume of boiling CaCL2 solution. The fluorescent colors of the precipitate change as follows: blue at the scheelite end, pale blue at 0.5 mole % CaMoO4, white at 1 mole %, pale yellow at 2 mole %, and yellow at 4 mole %; and increase yellow tint up to 20 mole %, but do not show any remarkable change beyond that composition. Compared with the standard color card (Fig. 4), on which the precipitates are put, the composition of scheelite containing less than 10 mole % CaMoO4 can be determined within the accuracy of 1 or 2 mole %.The X-ray powder data show that the 2θ 116 (CuKα)-2θ220 (CuKα) values decrease linearly from 5.23° to 4.83° with the increasing amounts of powellite component in this solid solution. Using this value, the composition can be estimated within the accuracy of 10 mole % CaMoO4. From the synthesis, fluorescent colors and X-ray data, it is inferred that the solid solution of the mineral series continues from the scheelite to powellite ends above a room temperature.

著者

佐藤 源郎

出版者

資源地質学会

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.7, no.25, pp.225-230, 1957-09-30 (Released:2009-06-12)

参考文献数

14

著者

古宇田 亮一 小出 仁

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.28, no.150, pp.233-244, 1978-07-25 (Released:2009-06-12)

参考文献数

37

被引用文献数

3

---

海底で再生カルデラが生じたなら,環状に分布する岩脈群,正断層系,中心隆起構造と海底地辷り堆積構造がその痕跡として残るであろう.秋田県大館東方地域では,後黒鉱期の石英安山岩群と浅熱水鉱床群が,中心の大滝石英閃緑岩体を環状に取り囲む現象が存在する.深沢鉱床などの黒鉱鉱床群も,やや東南にずれるものの,ほぼこの環状分布に沿って,いくつか地下に存在する.鉱床群は環状分布の片側に集中度が高い.いくつかの層準で発見される海底地辷り堆積構造は上下運動の痕跡と考えられ,ボーリング資料による地下構造からは,中心の大滝石英閃緑岩体付近の隆起と,周囲の環状石英安山岩群の内側に陥没構造が示唆される.このことから,8km程度の直径をもっこの環状構造は,中新世の海底にできた再生カルデラの痕跡と考えられ,鉱床生成もカルデラの形成に関連して説明することが可能である.すなわちSMITH & BAILEY (1968)説をKOIDE & BHATFCHARJI (1975)説で解釈し直せば,尖頭的岩漿溜りの上昇で地表付近に10km前後の直径をもつ火山性陥没構造(cauldron)が発生し,環状の断裂系が発達する.この断裂系に沿って鉱液が上昇し,海底下では黒鉱をつくる.続いて,環状分布内に中心隆起が生じ,環状に石英安山岩が貫入―噴出し,その後海底が浅くなるか陸化する.この時に鉱液が環状断裂系に沿って上昇し,後黒鉱期の浅熱水鉱脈鉱床をつくったと説明できる.北鹿地域には,このような環状構造(再生カルデラ)がいくつか存在し,各鉱床群は各々のカルデラに関係して生成したと推測される.

著者

坂井 定倫 大場 実

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.20, no.100, pp.149-165, 1970-05-10 (Released:2009-06-12)

参考文献数

12

---

A number of gold-silver mines on Sado Island, Onomi, Takachi, Kanoura, Kitaebisu, Sado and Tsurushi mines, belong to the type classified as epithermal fissure-filling deposits. These mines are situated on the western slope of the Osado mountain range of the Island.The Sado mine, the largest gold producer in Japan ever since its opening in ancient age, consists of very many Au-Ag quartz veins which filled fissures in the lower Miocene formations.Main vein fissures are intimately related to the movement of the second order fractures trending east-west. These fractures are formed by the NE-SW trending master fractures, with a wider mineralized zone by virtue of many branch and parallel veins.The developments of vein fissures are observed more prominently in brittle rocks such as shale and bedded fine tuff than in the massive pyroclastic rocks and lava flows.The ore shoots are formed mostly in the lower Aikawa formation surrounding the rhyolite dome which lies in the deeper part of the mine area.Recent prospecting works based on the re-analysis of structural patterns of the mineralized areas have proved the existence of promising new veins, and this will contribute to the revival of the Sado mine, which has been idle for fifteen years.

著者

山本 栄一 日隈 四郎 家坂 貞男 有松 憲生 二司 哲夫

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.17, no.84, pp.200-213, 1967-08-20 (Released:2009-06-12)

参考文献数

15

---

The Hashima coal mine of the Mitsubishi Mining Co. is located at the semi-artificial tiny Hashima Island, well known as "Warship Island", about 20 km to the south-west of the Nagasaki Harbour.The mine was put into operation in 1887 and has yielded highest class coking coal ever since. Nevertheless, the mining condition was becoming unfavorable in recent years and new coal fields have been actively searched in this area.Since 1953, many geologists and their assistants collected large number of rock samples from the sea-bottom by means of the specially designed dredger backet. They dived with aqualung to observe directly the outcrops at the sea bottom, and examined heavy mineral frequencies of the rock samples collected. Intensive geophysical prospecting, such as marine seismic prospecting by reflection method with floating cables and pressure sensitive geophones, and sonic prospecting was also introduced, in 1957.Thus, the detailed geological maps could be constructed, and the underground geological structure in this off-shore area was revealed. Several coal seams in the Mitsuse area could be traced at the sea bottom exactly, and the coal reserves were clarified.The Mitsuse area has been mined, since Oct. 1965, 14 months after the previous working area was closed owing to a mining accident. The Mitsuse area produces monthly more than 30, 000 tons of high class coking coal at present.In the Hashima area, there is a large reverse fault, named the Hashima-oki fault. Since the depth of the coal seams beyond this fault is rather shallow and there is a large quantity of coal reserves, this huge area is much promising as the next working area.

著者

内尾 高保

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.36, no.195, pp.37-39, 1986-02-28 (Released:2009-06-12)

参考文献数

6

著者

成田 英吉

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.9, no.35, pp.167-178, 1959-06-30 (Released:2009-12-14)

参考文献数

15

---

The Kamioka Mine, working the largest lead-zinc deposits in Japan, lies in the eastern corner of the Hida gneiss complex. Around the mine, lenticular crystalline limestone beds are often intercalated among biotite-hornblende gneiss which is generally disposed in a NE direction and has NE fold axes which pitch 45°SW.The ore deposits are closely related to the crystalline limestone beds by pyrometasomatic replacement which attacked some minor folding crests to form typical skarn ores of the so-called "Mokuji ore body". The "Shiroji ore body" is a peculiar type of deposit intimately related to the skarn Mokuji ore body. It carries the distinct features of a hydrothermal deposit and is localized in narrow spaces controlled by fissure intersections which are quite different from those of the Mokuji ore body.The Shiroji ore body includes sphalerite, galena, chalcopyrite, pyrite, hematite, arsenopyrite, and silver minerals as ore, and quartz, chlorite, sericite, and carbonate as gangue. The ore is enclosed in a zone of silicification consisting of quartz-(adularia)-sericite-carbonate. All surrounding rocks have been strongly altered by silicification, sericitization, chloritization, feldspathization and argillization.The fracture system controlling the Shiroji ore body is disposed regularly in three directions, namely, NE, NS and EW. The intersections of the fractures trend NE and pitch 45°SW, and offer excellent room for ore deposition.Based on the field occurrence, the mineral assemblages and the nature of the wall rock alteration, the writer concludes that Shiroji ore bodies were produced under hydrothermal(mesothermal) conditions which followed deposition of the pyrometasomatic Mokuji ore bodies.

著者

吉村 豊文

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.11, no.45-46, pp.22-27, 1961-03-25 (Released:2009-06-12)

参考文献数

2

---

A small displacement, about two meters or less, of a manganese ore deposit is called "Hitokase Danso", meaning "one-frame fault". The movement on the fault had evidently occurred before the manganese deposit was formed, and most of the shear zones have been mineralized by various manganese ores. The manganese ore deposit itself, therefore, has not been displaced by the fault movement, although slickensides on such later formed manganese minerals indicate the renewed movement of minor scale along the one-frame fault.

著者

池田 周作

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.20, no.100, pp.114-124, 1970-05-10 (Released:2009-06-12)

参考文献数

19

---

Modes of occurrences of ore shoots in each vein of the Akenobe Mine may suggest the direction of flows of ore-forming solutions, which were introduced at the north-east trending faults. A rather remarkable horizontal zonal arrangement of ores has been recognized in the mining area where the zones of Sn-W, Cu, Pb-Zn and Au-Ag ores are arranged from center succesively. In this central portion is an deep Akenobe fault with the north-south strike, which might have intimate relation with a set of the north-east trending. faults. The both sets of faults mentioned above may have been active before and after the mineralization. Recent exploration works have been conducted again in the neighbourhood of the Akenobe fault.

著者

鹿園 直建 綱川 秀夫

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.32, no.176, pp.479-482, 1982-12-15 (Released:2009-06-12)

参考文献数

24

被引用文献数

1

---

One sample of adularia from the Hosokura Pb-Zn vein-type deposits gives a K-Ar age of 5.8±0.2 Ma. This age is quite younger than that of the host rocks (Hosokura formation) of Daijima to Nishikurozawa (early to middle Miocene).Two samples of adularia from the different veins of the Sado Au-Ag mine give the K-Ar ages of 14.5±0.5 Ma. and 13.4±0.5 Ma. These ages are 25-15 m. y. younger than those of the host rocks (Odate and Aikawa formation).Summary of the ages of the vein-type deposits and those of the host rocks in the Green tuff region previously studied, including the present data on the Hosokura and Sado deposits, suggests that almost all of the vein-type mineralization in the Green tuff region of north eastern part of Japan took place after the Nishikurozawa stage (14-16 Ma.). This implies that the ages of the vein-type mineralization were later than and/or similar to that of the Kuroko mineralization.

出版者

資源地質学会

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.9, no.35, pp.199-202, 1959-06-30 (Released:2009-06-12)

著者

大町 北一郎

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.5, no.18, pp.241-247, 1955-12-30 (Released:2009-06-12)

参考文献数

18

---

The iron oxides and iron sulphides of the Kamaya mine, located about 12 km northeast of Datemonbetsu, Iburi Province, Hokkaido, are of hydrothermal origin. In this area liparitic tuff and tuff breccia sediments of the Miocene Toyoura formation have been intruded by propylite, nevaditic liparite and andesite dikes, and later covered by flows of two-pyroxene andesite lava.The iron ores are generally irregular, massive deposits within the nevaditic liparite and breccia tuff. These ore bodies consist of reddish brown iron ore and some blackish iron sulphide. Ore and associated minerals are quartz, iron ore (hematite), pyrite, marcasite, and sericite.The most characteristic feature of the iron ores is their higher iron content and lower combined-water content than so-called "limonite" in the zone of oxidation. The ore is red to reddish black, has a micaceous luster, and gives a reddish brown streak. In thin section this iron ore is opaque and ussually associated with quartz. Its X-ray powder pattern is very similar to that of artificial Fe2O3. Chemical analysis gives Fe2O3, 88.40% ; H2O (+), 0.34% ; H2O (-), 1.72%; and insoluble residue, 8.33%; total. 98.79%.

著者

小野 広一郎

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.19, no.97, pp.299-311, 1969-10-20 (Released:2009-06-12)

参考文献数

11

---

Abundant copper vein deposits of the mine occur in the Itaya formation composed of sandstone and intercalating shalebeds of the Miocene Miyai group. Principal ore mineral is chalcopyrite, and it is associated with pyrite, sphalerite, galena, quartz, calcite, chlorite, sericite, etc. Chloritization, silicification and sericitization of wall rocks are very distinct. Vein fissures of the mining district can be grouped in three sets of strike direction: N-S, E-W and NW-SE groups. Fissures of N-S and E-W group are shear fractures, while those of NW-SE group are tension cracks. The ore-bearing veins of the E-W and NW-SE groups have been mined chiefly for copper ore. Fissures of the N-S group contain a large amount of pyrite but are rather barren of chalcopyrite.Depth zone that comprises the workable extent and ore shoots of each veins is remarkably limited within the sandstone-rich members of the Itaya formation.Th0e Miyai group surrounding the main ore-bearing area has general strike of N20-4°E and dips 10-30°eastward. The main ore-bearing area is situated in a, dome within the northwestern part of a large basin of the. Miyai group. The long axis of the dome is orientated parallel to the general strike of the Miyai group. The ore-bearing area is divided into four districts by the difference of local structures: northeastern, northwestern, southeastern and southwestern districts. Structural and mineralogical features of ore-bearing fissures in each district reflect the difference of geologic structure. A notable difference is that the fissures in the northeastern district run at nearly right angles to the strike of the strata, while those in the southwestern district are parallel to them.Four stages of mineralization can be recognized: the first stage (Cu-Py), the second (Pb-Zn), the third (Au-Ag) and the fourth (calcite).Distribution of the metals deposited in the area are expressed as assay grade multiplied by the width of veins, and iso-metal quantity contours are illustrated on the maps. It seems possible that mineralization centers of each four stages overlap one after another in the southwestern district, while no evidence of coincidence is observed in the northeastern district. Fissures of the N-S group can be regarded as the channelways of mineralizing solutions.Cu and Pb-Zn zones can be depicted successively outwards from centers where two sets of fissures of the N-S group and the E-W or NW-SE group cross each other. These features might be useful for further exploration.

著者

大町 北一郎

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.8, no.27, pp.18-32, 1958-02-28 (Released:2009-12-14)

参考文献数

70

---

The Inaushi mine, about 10 km west of Engaru town, Kitami Province, is located in one of the epithermal deposits of Northeast Hokkaido. The sedimentary rocks in the vicinity of the mine consist mainly of black shale, sandstone and conglomerate of Mesozoic age, they are overlain unconformably by Neogene Tertiary (Miocene) sediments. The Mesozoic beds are cut by many dykes. The rocks of the dykes are predominantly quartz-porphyrite, andesite and liparite which range widely in composition.The No.3 ore deposit of the Inaushi mine is worked as a source of copper ore and occurs along a fault zone in quartz-porphyry, sandstone, black shale and conglomerate of Mesozoic (Pre-Cretaceous?) age. The deposit consists of several parallel veins, which occur at various distances from the main vein (N 50-Vein). The No.3 ore deposit seems to be associated with parallel dykes of quartz-porphyrite. The veins are characteristically of the composite "chlorite-quartz-copper-vein" type and strike N 70-80°E, and dip 80-90° south. The veins may attain widths of 0.4-0.8 meters. These deposits have been believed to be of epithermal origin. The structure of the veins is classified as follows: brecciated, banded and networked. The brecciated veins usually contain angular fragments of country rocks cemented by a matrix consisting of variable amounts of sulphide and gangue minerals. In some veins, ring ore is observed.The predominant sulphides of the ore deposit are pyrite, chalcopyrite, sphalerite and galena. Other minor minerals are hematite, bornite, chalcocite, marcasite and pyrrhotite. The gangue minerals are chlorite, quartz, calcite and adularia. From the mineralogical association of the ore, the mineralization in the deposit is divided into four stages:1) Quartz-chlorite-pyrite-stage2) Quartz-chlorite-chalcopyrite-pyrite-stage3) Chlorite-sphalerite-galena-pyrite-hematite-stage, and 4) Quartz-pyrite-stage.The ore mainly shows a brecciated and banded appearance. Most of it contains chalcopyrite and pyrite often accompanied by sphalerite and galena, with gangue minerals such as chlorite, quartz and calcite. The brecciated ore usually contains fragments of wall rocks and the banded ore consists mainly of chalcopyrite and pyrite.Paragenesis and texture of ore minerals were studied in detail. Chalcopyrite has occasionally been enclosed in the sphalerite. Also, chalcopyrite within sphalerite occurs as emulsion blebs, commonly in seriate arrangement, and shows definite preferred orientation relative with any one host grain, indicating control by the crystal structure of the sphalerite. Therefore, from the mineralogy of the vein, the No. 3 ore deposit may be classified as fissure-filling veins which belong to the "xenothermal deposits" type (shallow high-temperature condition) rather than the epithermal type deposit.The minor elements in chalcopyrite from sulphide ore of several levels in the N50-vein and also from other chlorite-quartz-copper-vein deposits were determined by spectrographic methods. The results show the presence of Bi and Sn in chalcopyrite from the Inaushi mine, Komaki mine, and Miyatamata mine. The chlorite of the gangue was determined to be aphrosiderite by means of both chemical analysis and X-ray studies.In conclusion, it seems highly probable that the No. 3 ore deposit of the Inaushi mine was formed under high temperature conditions of subvolcanic origin similar to those prevailing in the Inner Zone of Northeast Japan.

著者

小野 広一郎

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.21, no.106, pp.150-161, 1971-05-01 (Released:2009-06-12)

参考文献数

13

---

The copper deposits, consisting of chalcopyrite, pyrite, sphalerite, galena, quartz, calcite, sericite and others, in the main area of the Kishu Mine occur in the Okochi 'the Itaya and the Taketo formations of the Miocene Miyai Group. They are mainly composed of sandstone, and sandstone and shale.The Miyai Group surrounding the main ore-bearing area has a general strike of N20-40°E and a dip of 10-30°E. The main ore-bearing area is situated in a dome of a large basin of the Miyai. Group. The long axis of the dome is parallel to the general strike of the Miyai Group.Vein fissures of the main mining district are grouped in the following three sets according to the strike directions: i. e N-S, E-W and NW-SE. Intersections between two sets of fissures of the N-S group and the E-W or NW-SE group, can be regarded as the channelways of mineralizing solutions and mineralization centers. The most important intersection is situated in the vicinity of the dome where Josen No. 20 vein meets Josen 9-level North Cross-cut.Five mineralization stages can be recognized. i.e Py, Cu-Py, Pb-Zn, Au-Ag and calcite stages. There are two types of copper ores. The one is associated with chlorite formed during the Cu-Py stage and the other with sericite formed during the Pb-Zn stage. The latter's deposition centers are generally beneath the former's.Silicification, chloritization and sericitization are recongnized as wall-rock alterations.The Cl- content distribution in the deep seated ground-water in the mine well reflects in the geologic structure.Filling temperatures of the minerals mainly measured by decrepitation method are 172-318°C in chalcopyrite, and 160-330°C in pyrite.

出版者

資源地質学会

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.17, no.84, pp.239-242, 1967-08-20 (Released:2009-06-12)

著者

池田 則生 肥田 博行 野口 一明 藤原 操

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.33, no.178, pp.97-114, 1982-05-10 (Released:2009-12-14)

参考文献数

34

---

The tungsten-copper-tin deposit of the Takatori mine is of plutonic vein type and developed in alternating beds of sandstone and shale which constitute Yamizo Group of Triassic age. Detailed examination on the mode of occurrence of the deposit both in the underground and in the field has provided some important informations and suggestions for future exploration. Our observations and conclusions in this study may be sum-marized as follows:(1) Vein fractures in the deposit are classified into two groups, i.e., "Tatehi" group and "Yokohi" group. Fractures of the former in general trend NWW-SEE and steeply dip southward, while those of the latter are almost horizontal but in general gently dip northward. The two groups of fractures constitute a set of conjugate shears under the same stress field, principal stress axes of which being as follows; maximum compressional stress axis (σ1): S25°W30°, intermediate compressional stress axis (σ2): trending NWW-SEE and nearly horizontal, and minimum compressional stress axis (σ3): N30°E60° with angle of shear planes (2θ) of 80°.(2) Three mineralization stages are identified, i.e., wolframite-quartz stage, sulfide-quartz and cassiterite-quartz stage, and barren quartz stage with only pyrite, in chronological order.(3) At Nanabanhi Vein, the champion vein of the deposit, a vertical metal zoning is clearly observed, i.e., wolframite-rich zone, chalcopyrite-rich zone and cassiterite-rich zone in ascending order.(4) The localization of ore shoot appears to be structurally controled by some faults named as No.7 fault, No. 15 fault and W28 fault at-7 level, among which No.15 fault, being located in the central part of the deposit, is assumed to have acted as a channel feeder of ore fluid. All the faults were formed prior to the mineralizations and were probably in active during a certain period after the mineralizations as well.(5) It is suggested that the vein fracture systems were related in origin to the intrusion of a granitic magma. Namely, the uplifting of the southern geologic block with northwestward tilting at the stress field given by the granitic intrusion is considered to have been responsible for the reverse S-shaped regional structure of the area to have resulted the vein fracture systems observed.

著者

アルファロ フルートス

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.38, no.207, pp.15-25, 1988

---

チリ南部の太平洋沿岸域(Coast Range)南部(南緯39°~42°)の古生層中に,ソレアイト玄武岩熔岩,チャート,堆積岩に伴って銅・亜鉛を主成分とする塊状硫化物鉱床が胚胎している.黄鉄鉱,磁硫鉄鉱と共生する閃亜鉛鉱中のFeS含有量は17.0~18.2mol%であり,変成作用の圧力は約2.5kbと推定される.黄鉄鉱のイオウ同位体比は+2.5%(+0.3~+5.4%)で,日本の別子型鉱床のそれ(+2.7‰)に近い,硫化鉱中のコバルトおよび金の含有量はそれぞれ0.1~0.6%,20~700ppbであった.<BR>微量元素およびREEの分析結果より母岩はoceanicbasaltであることが判るので,この塊状硫化物鉱床は日本の別子型鉱床ないしノルウェーのカレドニアのレッケン鉱床に似ていると結論される.

著者

中野 啓二 佐藤 憲隆 山田 亨

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.31, no.166, pp.81-97, 1981-06-05 (Released:2009-06-12)

参考文献数

7

---

The Nebazawa deposits are epithermal, gold and silver-bearing quartz vein type deposits. They occur in E-W trending southward dipping steep fractures in the welded tuff member called Katashinagawa rhyoritic rocks of Paleogene age.The study of the geology and ore deposits of the mine has disclosed following facts and suggestions which could be useful guides for current and future exploration of the mine.1) Three stages of mineralization were identified, they are, from older to younger, base metalliferous mineralization (Stage I), auriferous mineralization (Stage II, Ag/Au≥10) and argentiferous mineralization (Stage III, Ag/Au≥100). The latter two mineralizations are important in economic sense.2) The assay contour is fully affected by low angle east dipping faults called No. 1, No. 2 and No. 3 fault which intersect the veins diagonally. High grade part of the vein is along the hangingwall side of the fault and barren part along the footwall side. This suggests possible important role of these faults as controlling factor of convection system of ground water at the time of ore deposition.3) Vein fractures are interpreted as high angle reverse type faults initiated by the differential block movement between relatively subsided northern block and southern relatively upheaved block. This block movement seems to be triggered by or related to the formation of N-S trending cauldron subsidence of Miocenc Kinugawa rhyolitic rocks to the east.

著者

草薙 忠明

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.5, no.16, pp.77-88, 1955-07-05 (Released:2009-06-12)

参考文献数

14

被引用文献数

1

---

The funnel or basin shaped rhyolitic complex occupies almost the whole area of the Ashio mining district, and its surface distribution makes an imperfect ellipse-like outline, reaching about 3.3km in its minor axis and about 4.4 km in major axis, and the volcanic activities of these volcanic complex are supposed to have taken place in the late Tertiary period.The rhyolitic complex is composed of rhyolite massive flow and rhyolitic pyroclastics, such as volcanic breccia, tuff, tuff breccia, lapilli tuff and also welded tuff. They are accumulated alternately, forming nearly horizontal beds. The lower part of the complex consists mainly of rhyolitic lava, intercalating some rhyolitic volcanic breccia and tuff. In the upeer parts are found alternations of tuff breccia, lappili tuff and welded tuff, the last one being most conspicuous. Thus, the volcanic complex of the Ashio mining district seems to form a stratovolcano.The basal breccia, named by the writer, occurs along the contact surface between the rhyolitic complex and the Palaeozoic sediments or sometimes the late-Mesozoic granodiorite of basement complex, and is composed mainly of angular or subangular fragments of basal rocks, such as chert, clay slate, sandstone, siliceous slate, schalstein and granodiorite. Judging from the mode of occurence, it may be concluded that the basal breccia is not of explosion, but of talus origin, formed on the steep slope of the wall of the basin.The funnel or basin shaped hollow, filled up with rhyolitic rocks, may represent a caldera, formed by the depression preceding the volcanic explosion. The central vents of this rhyolitic volcano are supposed to be situated near the pyrophyllitized and brecciated zone of Tenguzawa, and the original crater, now indistinct by erosion, might be located also at the same place.Fissure veins are formed abundantly in rhyolite flow and welded tuff, but scantly in tuff and tuff breccia. Ore shoots of veins are mostly localized in favorable beds such as rhyolite or rhyolitic welded tuff, which lies nearly horizontally, and then the shoots may have a flat elongation. The localization of ore shoots may be attributed mainly to the deflection of each vein according to the different physical characters of each bed. Bonanzas of so-called "Kajika type" are formed sometimes in tuff and tuff breccia, only when the fissure veins swarm closely, though it is not the case where an isolated vein is present.