The Ryushoden mine is located at about 6 km southwest of the Monbetsu City in Hokkaido. The studied area is the northwestern margin of the sedimentary basin of the Konomai formation of Miocene in age, which belongs to the so-called green-tuff region in the northeast Hokkaido. The results of the investigation on the mercury deposits of Ryushoden mine are described as follows :
(1) The Ryushoden formation that bears the mercury deposits is correlated to the middle to upper facies of the Konomai formation.
(2) The mercury deposits are mostly of disseminated cinnabar type in the sandstone and conglomerate members of the Ryushoden formation. Some are found as networks or veinlets along the shear zone with NE trend.
(3) The deposits are spotted continuously along the shear zone with N-S trend which was due to the upwarping of the basement rocks.
(4) The scale and quality of the deposits are controlled by shapes of the black siliceous rocks and positions of the green tuffaceous sandstone which constitutes the hanging-wall of the mercury deposits.
(5) The mineral assemblages indicate that the ore solution was initially weakly alkaline and then became weakly acidic, and the crystallization of cinnabar might have taken place at the weakly acidic stage. The cinnabar was dispersed in the present host rocks primarily by vaporization at this stage.
(6) The associated alteration is represented by silicification, carbonatization, argillization (illite-montmorillonite→kaolinite) and dissemination of iron sulphides.
(7) The exploration criteria being valid at present are i) to trace the shear zone of N-S trend which is the most important structural feature of the area, ii) to find the black siliceous rocks which might be an ore-bringer, and also iii) to seak for a permeable bed of the dark grey sandstone capped by the unpermeable green tuffaceous sandstone.

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Recent geological studies on the representative Kuroko deposits at Matsumine, Hanaoka Mine, have revealed many interesting features, which uphold the submarine exhalative sedimentary theory for their origin. The process of the ore deposition inferred from those features can roughly be summarized as follows :
Taking general view of the mode of submarine acid (dacitic in chemical composition) volcanism prior to the mineralization, there seems to be two eruptive cycles in the Hanaoka District. The mineralization followed to the dacite lava doming which demonstrates the final stage of the second cycle. This lava dome is thought to have never come out on the sea bottom. The pressure that raised lava dome up would have been released at the level of tuffs and tuff breccias which were still highly saturated with sea water and unconsolidated.
The mineralization started with the exhalation of silica-rich hydrothermal solution and chemical properties of the solution was gradually changed from Ca-rich to metallicion-rich one. The exhalation was led through the marginal contact zones of lava domes. or the cracks through them.
Judging from the existene of relict breccias in zones of silicified rocks and gypsum beds, silica and gypsum are thought to have been precipitated in a closed system in the tuffs and tuff breccias, while most of the sulfide minerals deposited in open space at sea bottom or at shallow part of the sediments.
The mineralization was multi-centered as shown by the distribution of lava domes, strongly silicified parts of tuff brecciss or lava domes, anhydrite-prominent zones in gypsum beds, and veins of sulfide minerals. Productivities and durabilities of the mineralization centers were slightly different each other. The more productive and active one went over two or three repetition with tendency of decreasing activity and branching of the center to the later stage. On the other hand, physicochemical properties of the ore-forming hydrothermal solution may have gradually changed through those repetition mainly by cummulative mixing of sea water into the solution not only at the deeper area but even at the sea bottom itself. The commonly observed stratified zoning of the ores, such as barite ore, barite-Pb-Zn-Cu-Ag-bearing polymetallic sulfide ore, cupriferous pyrite ore, pyrite ore and gypsum ore, in descending order, may depend on those changes.
In proportion as the minerals were precipitated and accumulated onto the unconsolidated and mobile (or semi-liquid) beds (argillized tuffs or gypsum), some surface parts of the ores were deformed and caused the slumping or turbulent flow on account of heterogeneity and gravitational unbalance between the ores and surrounding materials, forming characteristic sedimentary features such as transposition-structure, banded structure, graded bedding, rhythmic alternation of ore beds and tuffs, groove structure, imbricate structure, slump folding and nodular ores with concentric mineral zoning. Rather round shaped-small scale ore bodies may have been formed by auto-gravitational grooving into argillized tuffs. Many kinds of these . structures and some microscopical textures of the ore indicate also that the deformation took place while the ores were in plastic condition.
As the subsidiary cause of the above mentioned "penecontemporaneous plastic (or rheomorphic) deformation", movement of the lava domes adjacent to the ore field must be taken into consideration.

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The present author has proposed once a term of pyroclastic knoll in order to emphasize its significances in volcano-sedimentology and economic geology (TAGUCHI, 1961). In this paper the term is newly proposed as volcanic knoll and its significances are discussed in more detail and also some considerations are given to the important problems, which are still neglected in recent studies on sedimentary features of water-laid volcanic deposits by many Japanese workers, of the processes such as the sedimentational relationship between the normal regional sedimentation and the submarine pyroclastic cone, and the local variations in sedimentation caused by the rapid introduction of pyroclastic cone.
Volcanic knoll is defined simply as a hill which was caused by the subaqueous volcanism on the bottom of the water, usually bottom of the sea water, during the general span of time when sediments were being deposited in a region. Particular significances of the volcanic knoll in petroleum geology and the so-called "Kuroko" ore deposits of Japan are summarized as below.
Volcanic knoll will be regarded as a variety of synchronous bottom highs, which have been recognized to present favorable conditions to the formation of petroleum and gas pools by SCHOLTEN (1959). Particularly volcanic knoll is significant for petroleum deposits to offer superior reservoir conditions, petroleum-source sediments which are commonly formed in the vicinity of volcanic knoll and favorable heat energy to transform the organic matter into petroleum after the deposition.
It has been recognized already that the various sedimentary structures found in the submarine volcanic deposits, which correspond to the author's volcanic knoll are useful to elucidate the genesis of "Kuroko" ore deposits in Japan. The author presents, moreover, as important aspects of volcanic knoll the chemical reaction between the sea water or the unconsolidated muddy sediments under the reducing condition formed by the emergence of volcanic knoll and the volcanic-producing materials or the hydrothermal solution, performed in the vicinity of the volcanic knoll.

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Hydrothermal syntheses of alkali feldspars were carried out at temperatures of 200°C, 300°C and 400°C, and at a pressure of about 1, 000 bars, using the glass of alkali feldspar composition. From the glass of K-feldspar composition, K-feldspar was formed at all the temperatures. From the glass of Na-feldspar composition, Na-feldspar was formed at 400°C, but analcime+α-cristobalite were formed at 300°C, and analcime+species P were formed at 200°C. The synthesized K-feldspar is an analogue of sanidine from the view-point of the structural state, and seems to be a kind of "adularia", because it contains a little amount of Na-feldspar molecule (5 mole % at most).

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