The ore deposits of the Chichibu mine occurring mostly in Paleozoic limestone and basic tuff or lava flow adjacent to the quartz-diorite mass can be classified into the following two major types on the basis of their modes of occurrence, the stages of formation, the characteristics of the ore, the nature of wall-rock alteration, the mineral paragenesis, the formation temperature and other geologic features.
i) Earlier deposits (Contact-metasomatic deposits in the strict sense) : Iron-copper-zinc-iron sulfide deposits
ii) Later deposits (Hydrothermal replacement deposits and veins) : Zinc-lead-copper-gold-silver-iron sulfide-(bismuth-antimon)-manganese deposits
The Akaiwa deposits consist of both the earlier and the later deposits, and the Wanabe deposits mainly of the earlier deposits.
The earlier deposits are further subdivided into the earlier I and II deposits.
The pyrrhotite occurs mostly in the earlier deposits as one of the most important constituent minerals of the deposits. Pyrrhotite of the earlier I deposits belongs, to the hexagonal type and that of the earlier II deposits to the monoclinic type.
The hexagonal pyrrhotite is associated with magnetite and skarn minerals, and the monoclinic one with sphalerite, quartz and carbonate minerals in the deposits.
The monoclinic pyrrhotite of this type (primary monoclinic pyrrhotite) is considered to have formed directly from the ore solution at temperatures between 240° and 290°C. The mineral have been altered to marcasite widely during the later stage mineralization.
There is another type of monoclinic pyrrhotite in the mine. The mineral of this type is believed to be a hydrothermal alteration product from hexagonal pyrrhotite at temperatures between 200° and 250°C under the sulfur rich environment during the later stage mineralization and is mixed with the latter.
The chemical composition (atomic % metal) of pyrrhotite is as follows:
Hexagonal pyrrhotite (Wanabe deposits) 47.35-47.78
Primary monoclinic pyrrhotite (Akaiwa deposits) 46.51-46.71
Mixture of hexagonal and monoclinic pyrrhotite (Akaiwa deposits) 46.82-46.99
Before attempting to use pyrrhotite as a geothermometer, much attention must be payed for the modes of occurrence and the genesis of pyrrhotite.

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This study attempts to find out some regularities or general tendencies in thickness variation of coal seams of the Noborikawa coal-bearing formation, one of the major coal-bearing formations of the Paleogene Ishikari Group in the area.
The directional properties are exposed in regional variation of coal thickness of major seams dealing with their iso-thickness maps (Fig. 4), and the tendencies are shown by the frequency of occurrence of the direction of rather stable elongation. There are two such directions of NNE-SSW and NNW-SSE, of which one appears more frequently on a seam and alternatively in successive major seams interbeded by cyclothems, and both are observed in the isopachous map of thickness and sandstone ratio of major part of the coal-bearing member and of the formation. The former is considered to be parallel to the general elongation of the sedimentation basin, and the latter to the prominent trend of the faults in this area and is considered to be caused by an embryonic factor of the movement.
The correlationship in variation of coal thickness between lower and upper seams at various points is plotted and extracted on correlation diagram of coal thickness (Fig. 7), of which regression equation (Y=ax±b) reveals a positive and negative linear correlation, and the coefficient (a) and constant (b) of the formular are adopted for drawing a transitional development curve of successive coal seams in the formation. The curve enable us to consider the coal forming condition of the basin and coinsides with the generalized geohistory of early Ishikari sedimentation. A certain correlationship among composition of sediments (sandstone ratio), coal seam (coal thickness ratio of total major seams) within the major coal-bearing member and total coal thickness of major coal seams is extracted and discussed based on the correlation diagram (Fig. 8).
The results of the studies are utilized for predicting the variation of coal thickness in virgin field on a mining geology view point, and applicable to describe a minute variation of sedimentary condition in the general history of the basin.

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CO₂-rich fluid inclusions in minerals were studied by means of the freezing method. When CO₂-rich inclusions were cooled, liquid CO₂ or CO₂ gas hydrate appeared in them, and the volume of these phases was various according to the content of carbon dioxide. As the change of the CO₂ hydrate which was formed in inclusions was comparable to the phase diagram of the H₂O-CO₂ system at low temperature, it was possible to infer the inside pressure of fluid inclusions and to calculate the approximate concentration of carbon dioxide from the data on the solubility of carbon dioxide in water and the pressure-temperature-density relation of carbon dioxide. The CO₂-rich inclusions were found in quartz from the Ohtani and Kaneuchi mines, Kyoto Pref., Takatori mine, Ibaragi Pref., and Taishu mine, Nagasaki Pref. It is interesting that these ore deposits except that of the Taishu mine belong to the hypothermal tungsten quartz veins. In any case, however, CO₂-rich inclusions were found as secondary inclusions, or as primary inclusions in rock crystals from druses. This fact will imply that CO₂ has been concentrated in the late stage of mineralization of these ore deposits.

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The Sado mine, Niigata Prefecture, is composed of epithermal gold-silver veins genetically related to the Neogene volcanism. It is a very old and one of the large gold mines in Japan. Many gold and silver minerals such as electrum, native silver, hessite, argentite, stromeyerite, stephanite, pyrargyrite, polybasite, antimonpearceite, and cerargyrite (Br-bearing) were identified in the ore by microscopic observation, X-ray powder and fluorescence methods, and qualitative analysis by E.P.M.A. These minerals constitute so-called "Gin-guro" (black ore rich in silver). Hessite, the first finding in this mine, occurs in patchy or massive "Gin-guro" surrounded by aggregate of chalcedonic or white quartz with adularia. This "Gin-guro" part consists of large amounts of hessite and polybasite with small amounts of electrum and pyrite. A bromian cerargyrite occurs along its crack or drusy part.

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