Few attention has been paid to the sulfatization of the wall rock alteration by gypsum and barite along epithermal base-metal veins. In some of lead-zinc-bearing rhodochrosite veins, however, gypsum and barite are not rare in association with sericite-quartz aggregates and more intimately with kaolinite. Typical examples are observed on the hydrothermal zones of Senzai vein, Oe mine and Shinsei vein, Inakuraishi mine. Since gypsum is replaced by sulfide minerals and rhodochrosite, gypsum-bearing hydrotermal alteration together with kaolinization may have occurred in a sericite-quartz zone prior to the carbonatization and deposition of ore minerals.

View full abstract

In 1957 and 1958, the writers have investigated the geology of the Fukinodai district, Uryu-gun, Hokkaido and discovered lignite seams which have never been officially reported. According to their investigation, the general geologic succession in the area is summarized as follows in descending order:
The Older agglomerate is mainly developed in the eastern and western parts of the mapped area; while the Chikubetsu formation, covered by the Older agglomerate with clino-unconformity, is exposed locally in the west. In the western half of the central area, the Epishuomapp-gawa formation, which is partly covered by the Younger agglomerate, shows a synclinorium with an axis of approximately N-S direction. On the contrary, in the eastern half, the Karuushinai-gawa formation which dips slightly is distributed broadly except for the fenster-shaped outcrops of the Epishuomapp-gawa formation.
Of these formations, the Epishuomapp-gawa formation is the most important lignite measure, and contains numerous lignite seams which vary locally in their thickness and number. That is, about 20 seams are more than 1m in thickness, while a few are about 10m in thickness.
The lower part of the Epishuomapp-gawa formation interfingers contemporaneously with a part of the Older agglomerate, whereas its upper part interfingers with a part of the Younger agglomerate, of which geologic age is the upper Miocene. The Epishuomapp-gawa formation is exposed in the area covering 7km from north to south and 2.5km from east to west. It is very likely that the formation is also distributed with the similar dimensions in the adjacent area beneath the Karuushinai-gawa formation.
These lignite seams have never been mined before because of their poor quality and accessibility.

View full abstract

Drilling cores from eight sites in Odate Basin were studied petrolographically in order to clarify the relationship between alteration of the wall rocks and formation of the ore deposits. The altered zones can be divided by authigenic minerals. It was found, however, that peculiar alteration zones exist in this area together with those common in Miocene pyroclastic rocks in the Northeast Japan. The succession of the common zones are;
I. (Clinoptilolite)-mordenite zone
II. Analcime zone
III. Quartz-albite-chlorite-sericite-gypsum zone
These are found in (KA-3).
On the other hand, the analcime zone (II') and the quartz-albite-chlorite zone (III') are intercalated in the middle of zone I (OH-7, etc., ). In adjacent areas of the "Kuroko" ore deposits, the zone (III) is found sometimes in the stratigraphically upper zone. It is conjectured that these phenomena are resulted from the long-time action of hydrothermal solution after the syngenetic mineralization.
Such areas as the zone (III) developes in the upper zone are important as an indicator of the "Kuroko" ore deposits.

View full abstract