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Furutobe mine is located in the northern part of Akita Prefecture. The deposits of the mine is known as one of the typical Kuroko deposit occurring in the acidic pyroclastic rocks of Miocene age. Ore deposit of the mine is classified into siliceous ore zone of the lower part and stratiform ore zone of the upper part. Siliceous ore zone is divided into lower siliceous ore zone occurring in rhyolite and upper siliceous ore zone occurring in rhyolitic pyroclastic rocks. Stratiform ore zone consists of following three types of ores. Type A, the typical Kuroko deposit composed of powdery yellow ore, yellow ore, semi-black ore, black ore, ferruginous chert in ascending order. Type B, disseminated ore deposit which is a loose aggregate of sulphide minerals and argillized tuff and Type C, graded ore deposit composed of fragments of ores and rocks. The following processes of mineralization are suggested. Lower siliceous ore zone is fissure-filling type origin. Constituent minerals of this zone were formed from the ascending hydrothermal mineralizing solution. Upper siliceous ore zone was formed in the accumulation of explosion breccia covered by the thin layer of unconsolidated sediments near the sea bottom. Type A deposit of stratiform ore zone is sedimentary ore deposit formed on the sea bottom. Type B was formed in the unconsolidated layer of tuff by filtration and absorption of sediments and clays. On the other hand, Type C is the submarine sliding deposit transported and redeposited along the channel of footwall rocks by local submarine landsliding or slumping during and after mineralization.

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The Toyoha Mine is reputed to be one of the typical epithermal lead and zinc vein-type deposits in Hokkaido. The ore is composed mainly of sphalerite, galena and pyrite with an important amount of silver minerals and also include accessarily chalcopyrite, tetrahedrite, marcasite, pyrrhotite, magnetite, hematite etc. Any characteristic feature indicating a xenothermal condition has not been known.
Recently the tin minerals such as cassiterite and stannite were found by the present author from Izumo Vein, one of the important veins of Toyoha Mine. The tin minerals occur almost always in association with finegrained sphalerite and rarely with quartz, pyrite or coarse-grained sphalerite. Both minerals have, in general, about the same grain size as that of the associated sphalerite, but a grain of cassiterite is always an aggregate of minute crystals, 10-20μ in diameter. The formation temperatures estimated by fluid inclusion study of quartz associated with cassiterite, of coarse-grained sphalerite and of banded quartz are in the range of 241°-230°C, 218°-215°and 202°-190°C respectively. Quantitative chemical analysis of stannite by EPMA is not performed yet but Cu, Fe, Sn and S are detected in a good amount with a trace of Zn.
In Hokkaido there have been known two mines where tin minerals occurred, one Suttu Mine for stannite and cassiterite and the other Kutosan Mine for tetrahedrite containing an appreciable amount of Sn. Sn-free tetrahedrite, stannite and cassiterite in a sample from of Kutosan Mine are newly described. It is known that many base metal deposits in West Hokkaido show a zonal distribution from the inner zone of Cu, Pb and Zn to the outer one of Au and Ag. It is an interesting fact that both Toyoha Mine and Suttu Mine are located in the central part of the inner zone and show the characteristics of xenothermal ore deposits.

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Wolframite has been found from the contact-metasomatic scheelite deposits of the Kiwada, Fujigatani and Kuga mines. Wolframite in the Kiwada deposit occurs in porous, relatively low-grade ores composed mainly of quartz, albite, muscovite, chlorite and siderite, and is intimately associated with pyrite. The mineral assemblage is unique in its Ca-poor chemistry which contrasts with Ca-rich ordinary ores from the deposit. The mineral occurs as pseudomorph after scheelite (<1 mm in diameter). The pseudomorph is composed of fine-grained (0.02-0.04 mm) wolframite crystals.
Wolframite from the Fujigatani and Kuga deposits examined here are obtained from mill products. Although their modes of occurrence in field have not been clarified yet, microscopic observation indicates that these wolframites are also pseudomorphic products after scheelite. Sporadic and minor occurrence of wolframite in all of the deposits suggests that the favorable condition for wolframite in place of scheelite may have been attained only in limited portions of the deposits towards the last stage of mineralization.
Mineralogical data obtained by X-ray diffraction, wet chemical analysis and EPMA analysis are summarized in Table 1 and Fig. 4. It is likely that Fe/Mn ratio of pseudomorphic wolframite can be variable widely, though Fe-rich species seem to be most common.
Fe/Mn ratios in the specimens collected from two ore bodies of the Kiwada deposit show large difference: 0-12 mol.% MnWO₄ in the Oogiri No. 5 ore body and about 44% MnWO₄ in the Shin-ei ore body. Mn-content in coexisting chlorite is found to be correspondingly higher in the Shin-ei ore, suggesting that the mineralization environment has been more manganiferous in this ore body than the Oogiri No. 5. Wolframite from the Fujigatani and Kuga deposits seem to be generally close to the Fe end-member. However, some of the grains from the mill product of Kuga are rich in Mn up to 80% MnWO₄. The observation is in accord with the fact that common constituent minerals in the two deposits such as clinopyroxene, garnet and calcite are occasionally more manganiferous in the Kuga deposit.

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