Sometimes saccharoidal or lamellar quartz is contained in gold-bearing quartz veins. Such brittle quartz-aggregates from Konomai Mine are called “bosa” quartz.
“Bosa” quartz is easily broken and is barren. Its silica content is very high (about 98 percent). It is one of the bands of vein structure, and is classed into angular, lamellar, saccharoidal, and platy“bosa” quartz.
“Bosa” quartz does not exhibit an intergrowth with calcite. Adjoining quartz, kaolin and marcasite are recognized. If the calcite of quartz-calcite aggregates is dissolved, porous quartz aggregates……“bosa” quartz……will be formed. The ratio of the volume of quartz to calcite and the shape of the calcite strongly affect the type of “bosa” quartz.
The dissolution may be caused by a primary acidic condition and it may occur in the original quartz-calcite aggregates. Therefore, most of the “bosa” quartz is not formed in the crushed or oxydized zone of veins.

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There are two known modes of occurrence of hematite and magnetite at the Chichibu Mine, Saitama Prefecture.
One type of hematite occurs as the earliest ore mineral. This type of hematite has been largely transformed into magnetite, especially at the time of formation of earlier pyrite. The other type of hematite is only found within the zone of oxidation product of granular magnetite.
As for magnetite, one type occurs as granular aggregates or well-shaped crystals. Most of them may be of primary origin and may have crystallized out as magnetite during the earliest stage of metallization, but some of them are closely related with the formation of platy magnetite. The other type shows a platy form and may largely be the reduction (hypogene secondary) product of primary hematite.

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The sulphur and iron-sulphide ore deposits of exhalative replacement type at the Zao mine, Yamagata Prefecture, occur in andesitic lava flows and pyroclastic rocks of the Zao volcano. The important structural components distinguished in this mining area are fractured zones striking nearly N 10°W, in which sulphur deposits, solfataras and hot springs are found. These fractured zones were the main channel ways for the mineralizing solutions and gases.
Localization of high-grade sulphur ore bodies appears to have been controlled by the intersection of fractures with favorable beds such as tuff and tuff-breccia beds.

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The Okuki mine is located in the western part of Ehime-ken. The ore deposits are cupriferous pyritic deposits (Kieslager). The rocks in the vicinity of the mine are green rocks usually called "Mikabu series". In the present paper, stratigraphy, geological structure of green rocks, and structural features of the ore deposits are described.

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The Matsuo sulphur deposit is found in two-pyroxene andesitic lava and pyrocrastic rocks which have been wholly altered by ascending vapour and hydrothermal solution. These rocks are largely replaced by sulphur and iron-sulphide. The ore deposit, therefore, can be classified into two parts, namely iron-sulpbide and native sulphur ore bodies, by their chief mineral constituent.
The iron-sulphide ore is a mixture of pyrite and marcasite, the latter as suggested by ALLEN's and CRENSHAW's artificial experiments, is assumed to have been crystallized under condition of weak sulphuric acidity and at relatively low temperature.
On the other hand, the iron-sulphide ore rich in marcasite is chiefly found at levels higher than pyrite rich ore. So, it is supposed that as hydrothermal solution rises upward, the temperature of the solution drops gradually while acidity.rises progressively.

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1. This paper deals mainly with the structural development of the Ishikari coal field situated in the central part of Hokkaidô. It is the second most important field, annually producing more than 10 million tons of high grade coal. It is about 80 km long and 10 to 20 km wide, and is known for its complex geologic structure, formed mainly by compression in an E-W direction.
2. The field is divided into the northern and the southern districts. The former, consisting of the Ishikari group (Eocene-Oligocene), reaches a thickness of 3, 000 m, and is characterized by rather gentle folds and a number of diagonal NW faults. The latter, on the other hand, consists of the thin (less than 500 m) Ishikari group and the thick Poronai shale (Aquitanian, 1, 000 m thick), and has a number of overturned folds, thrusts and several klippes.
3. For convenience in description and interpretation of tectogenesis, during the Tertiary age, the author divided the field into 20 structural units, although their boundaries often are not clear. Studies of the units and their relationship led to the conclusion that the tectogenesis of the field is controlled by rotational stress or a combination of two stresses, two : phases of tectonic movement, compensation of stress by horizontal displacement along main fault lines, and influence of early (embryonic) structures on later ones of the second phase of movement.
4. However, the most important factor influencing the different structural pattern between the northern and the southern districts is the difference of lithologic facies, i.e. formations in the north are 70% sandstone in contrast to the southern formations, which are 90% shale. The difference of competency of formations has resulted in a mozaic northern and a super-folded southern structure.
5. The tectogenesis of the Ishikari field began with the deposition of the molasse-type Kawabata formation. The first phase of tectogenesis was probably caused by a rotational stress of N 50°W which formed an embryonic structure consisting of gentle parallel folds and NW-SE weak lines. The second phase which includes the acme of tectogenesis, was from early to later Pliocene. Compressive forces are assumed to have worked from E-S, and the competency of formations played an important role during this phase.
6. In the northern district, NW faults were formed along weak lines of the first phase. The relatively horizontal movement along these faults compensated for lateral compression so that folding movement was not remarkably accelerated as the southern district where plastic strata are dominant. Such a compensation of stress by horizontal movement is also seen at Pombetsu fault where the southern end of the northern block slid clockwise and westward for several km. This is the only interpretation which can explain the present distribution of strata, the disagreement of strikes in this part with the general N-S direction, and the low fuel ratio of coal in the Bibai and Poronai areas.

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