The areal distribution of Green Tuff district is re-examined, forcusing mainly on the tectonic characters of eastern Hokkaido. Miocene volcanism in eastern Hokkaido began with hornblende-bearing andesite at 14 Ma. The intrusions of ilmenite-series granitoids are slightly earlier than it. Volcanism at 14 Ma, associated with ilmenite-series granitoids, prevails through the outer zone of Southwest Japan. It is proposed that the Miocene igneous belt in eastern Hokkaido extends down to the outer zone of Southwest Japan. Igneous rocks, such as 14 Ma-andesitic basalt at Toyokoro, SE Hokkaido, and 22 Madacitic volcanic conglomerate in Holes 438 and 439, DSDP, and as a heat source for Jyouban hot spring, located off the NE Japan coast, occur between both Miocene igneous belts. On the contrary the Miocene NE volcanic belt, typical of Green Tuff belt, passes through the Oshima Peninsula and attains to the Sea of Japan. There was the zonal arrangement of middle Miocene to Pliocene igneous belts along the Japanese islands from the inner (back-arc) side to outer (trench) one: the arc, monogenic and forearc volcanic belts. The trench during this period was located less than about 100 km far from the forearc volcanic belt, probably through the present Abashiri City area in eastern Hokkaido.

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The Zijinshan copper-gold deposit, Fujian Province, is situated at the margins of an Early Cretaceous volcanic basin, beside a caldera made up of dacitic pyroclastic rocks and subvolcanic (dacite-porphyry) bodies. Silicification and hydrothermal alteration of quartz-dickite, quartz-alunite and quartz-sericite occur as concentric zones around the caldera covering a wider area.
The orebodies occur as filling-veins in a dense fissure zone and as a stockwork fissure system, accompanied by hydrothermal breccias. Native gold, pyrite, digenite, enargite and covellite are the main ore minerals, while gold and copper are the main economic metals. The gold veins occur within the silicified zone in the shallow portions of the deposit. On the other hand, the copper veins lie within the quartz-alunite alteration zone at the 350-900m interval, showing good primary mineralization zoning.
The fluid inclution data suggest that the hydrothermal fluids were characterized by low temperature, low salinity (0.0-5.0 wt% NaCl equivalent) and were in acidic conditions (pH=3.64-3.98). The fluid inclution filling temperatures ranged from 120°C to 140°C for the gold mineralization and from 180°C to 240°C for the copper mineralization. Many fluid inclusions showing evidences of boiling were observed in the quartz-alunite alteration zone. The salinity of these inclusions is higher and ranges from 7.5 to 21.6 wt% NaCl equivalent, while homogenization temperatures show a narrow range.
The δ¹⁸OH₂O values of the hydrothermal fluids range from -3.25 to -4.17‰(SMOW) and the δD values from -60 to -76‰, which coincide with the values to oxygen and hydrogen isotopic compositions of Mesozoic meteoric water in this region. Several evidences suggest that the Zijinshan deposit is a quartz-alunite type epithermal deposit and is the first of its kind to be discovered in the continent of China.

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中華人民共和国の山東省には,タンチェンールジアン(郊城―廬江)断層の東西に二つの異なる花崗岩―グリーンストーン地域(GGT)がある.東側GGTにはジアドン(〓東)グループとよばれるグリーンストーンベルトがあり,主として玄武岩－安山岩－石英安山岩－流紋岩よりなる四回の火山サイクルが認められる.このグループは,最下部にコマチアイトをもち,上部には変堆積岩類を含んでいる.全体は強い変形と変成作用を受けている.このグループの火山岩の地球化学的性質は,このグループが海洋性地殻の上に発達したことを示しており,O－タイプグリーンストーンベルトと呼ばれる.一方,西側GGTには,第一期と第二期のグリーンストーンベルトが認められる.第一期のグリーンストーンベルトは,トーナライトの貫入を受け,その中の捕獲岩として残っている.第二期のグリーンストーンベルトはタイシャン(泰山)グループと呼ばれ,バイモーダルの苦鉄質-珪長質火山岩を主とし,トーナライトを不整合で覆っている.このバイモーダル火山岩類は,最下部に少量の超苦鉄質岩を含むほか,大量の変堆積岩類を含んでいる.このグループは,大陸性地殻の上に発達したと考えられ,Cータイプグリーンストーンベルトと呼ばれる.

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Studies of mineral assemblages, homogenization temperatures and salinities of fluid inclusions, and hydrogen and oxygen isotopic ratios for the pyrophyllite mineralization of the Nishiyama-higashi deposit, Southwestern Japan, were combined to determine the environment of formation and the origin of the hydrothermal solution responsible for this miner-alization.
Six mineralogic zones were formed in the deposit by a hydrothermal solution passing through an E-W fissure in Cretaceous dacitic volcanic rocks. The constituent minerals of the zones are: Weakly altered zone: quartz ≥ plagioclase, K-feldspar, chlorite, muscovite and pyrite; Zone I: quartz and muscovite ≥ pyrophyllite and hematite; Zone IIa: pyrophyllite and quartz ≥ hematite; Zone IIb: pyrophyllite, kaolinite and quartz ≥ dickite and hematite; Zone III: alunite and quartz ≥ pyrophyllite and kaolinite ≥ muscovite, diaspore and corundum; Zone IV: pyrophyllite, kaolinite and quartz ≥ diaspore; Zone V: corundum, diaspore, quartz, pyrophyllite and kaolinite. The paragenetic sequence of the formation of the deposit from early to late stage is: formation of corundum-diaspore (around 370°C)→formation of diaspore-pyrophyllite (325-280°C)→formation of pyrophyllite-hematite (335-260°C)→formation of kaolinite-dickite-alunite-quartz-hematite (about 190°C). The formation of kaolinite-dickite-alunite-quartz-hematite is associated with boiling of the hydrothermal solution at around 190°C. The salinities of the hydrothermal solution associated with the formation of the Nishiyama-higashi deposit range mainly from 0.0 to 1.1 wt% NaCl equivalent. Si0₂ concentration of the hydrothermal solution was less than 10^-2.3 moles/kg H₂O for the formation of corundum-diaspore, 10^-2.04-10^-1.96 moles/kg H₂O for the formation of diaspore-pyro-phyllite, 10^-2.08 -10^-1.90moles/kg H₂O for the formation of pyrophyllite-hematite, and less than 10^-2.08 moles/kg H₂O for the formation of kaolinite-dickite-alunite-quartz-hematite. The pHs of the hydrothermal solution forming the Weakly al-tered zone, Zone IIb and Zone III were 4.6 - 6.8, 1.6 - 4.5 and 1.6, respectively. The hydrothermal solution forming Zones IIb and III was very acidic. The range of total sulfur concentration of the hydrothermal solution was 10^-2 - 10^-5moles/kg H₂O and the major sulfur species in the solution was HSO₄.
On the basis of the data on hydrogen and oxygen isotopic ratios of pyrophyllite, dickite and quartz, the hydrogen and oxygen isotopic ratios of the hydrothermal solution responsible for the formation of pyrophyllite-hematite are -60‰ and 0‰, respectively. On the other hand, the hydrogen and oxygen isotopic ratios of the hydrothermal solution responsible for the formation of kaolinite-dickite-alunite-quartz-hematite range from -70 to -50‰ and from -7 to -4‰, respectively. The hydrothermal solution for the Nishiyama-higashi pyrophyllite deposit originated from meteoric water in a volcanic environ-ment. As hydrothermal activity progressed, the water/rock ratio and the ratio of meteoric water in the hydrothermal solution increased. The hydrothermal system of the Nishiyama-higashi pyrophyllite deposit was a paleogeothermal system in Creta-ceous time.

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近年,角閃石中のAl含有量を用いた地質圧力計と角閃石一斜長石の化学平衡に基づいた地質温度計が提案されてきた.韓国の花崗岩類は主としてジュラ紀と白亜紀ものである.今回はジュラ紀と白亜紀の花崗岩類の計10試料について角閃石と斜長石をエネルギー分散型蛍光X線分析装置(EDS)によって定量した.JOHNSON and RUTHERFORD(1989)の圧力計を用いてジュラ紀と白亜紀花崗岩類について,各々2.5～6.3kbarと2～4.2kbarの値が得られた.また,角閃石一斜長石の温度計(BLUNDY and HOLLAND,1990)を用いて,各々700～790℃と670～770℃の値が得られた.従って,現在の侵食レベルでみるとジュラ紀の花崗岩類は白亜紀の花崗岩類に比べてより深い部分が露出しているものと老えられる.

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Some sea-floor hydrothermal ore deposits have been identified on the mid-oceanic ridge and in the back-arc basin. This time at the top of a seamount on the volcanic front in Izu-Ogasawara Arc we have discovered the modem occurrence of hydrothermal activity. The active hydrothermal field with the occurrences of sulfide mineralization has been discovered by the JAMSTEC 'Sinkai 2000' in the caldera at the top of Suiyo Seamount in Sitiyo Seamounts.
The volcanic rocks sampled at the top and the foot of the caldera wall are the calc-alkaline rock series dacites, and the low potassium andesites. This is in contrast to the tholeiitic basalts from some seamounts around Suiyo Seamount.
The sulfides of the vent chimneys from this hydrothermal field is characterized by the enrichment in Cu. The Cu contents of many ores exceed 10wt%, suggesting that the temperature of these hydrothermal fluids is enough high to dissolve copper in them. The highest Au content of sulfide samples is 71 ppm, whose average of 12 samples is 25 ppm. The highest Ag content is 337.1 ppm, whose average of 12 sumples is 176 ppm. The average Au/Ag ratio is 0.142. This ratio is very high, compared with the sulfides from some sea-floor hydrothermal ore deposits.
The high Au content of hydrothermal ore deposits at the Suiyo Seamount is worthy to note because the geological setting resembles that of the hydrothermal system at Osore-zan that was discovered in recent year in the most northern part of Japan.

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