Regularly interstratified chlorite/smectite mineral occurs widely as a gangue mineral in epithermal gold-silver-quartz veins, associated closely with base-metal sulfides and occasionally with Mn minerals. The chlorite/smectite mineral from six gold-silver vein deposits, that is, Konomai, Todoroki, Chitose, Seigoshi, Omidani, and Kushikino was quantitatively analyzed by X-ray microanalyser. The chemical composition of the mineral reflects characteristic features of the ores. Mncontent of the mineral is relatively high and the correlation between Mg and Mn is obvious in the ores containing rhodochrosite, whereas it is very low in the ores free from Mn minerals. Moreover, the Mn/Fe ratio of the mineral varies widely corresponding to the Mn/Fe ratio of coexisting sphalerite. It is infered that the stability and the variations in chemical composition of the regularly interstratified chlorite/smectite mineral appear to be influenced by temperature and chemical composition of ore-forming fluid.

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The Toyoha mine located in the Green Tuff Region of southwestern Hokkaido is well known for the occurrence of polymetallic vein-type deposits. Miocene strata composed of lava and pyroclastic rocks host the deposits and are hydrothermally altered. The age of formation of the deposits has been estimated to be middle Miocene. However, K-Ar age determination for sixteen sericites in hydrothermally altered rocks from the Toyoha deposits balls in a range from 2.93 to 0.96 Ma which are considered to represent the duration of hydrothermal activity responsible for the formation of the Toyoha deposits. The gangue sericite of Izumo vein showed a very young age of 0.49±0.04 Ma. It has been estimated, on the basis of cross-cutting relations, that the mineralization stages of the deposits are mainly divided into two. The present results supported this observation that the Izumo vein belongs to the later stage.
Sericites from the Okuiburi mineralized zone and the Yunosawa geothermal alteration zone showed the K-Ar ages of 2.90±0.07 Ma and 2.40±0.10, 2.39±0.09 Ma, respectively. Therefore, it is likely that hydrothermal activity at the Okuiburi mineralized zone and the Yunosawa alteration zone is contemporaneous with that of the early stage of the Toyoha deposit.

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Manganese nodules from the northern Central Pacific Basin are subjected to chemical and mineralogical analyses as well as mode of occurrence. Under the ore microscope, three different reflectivity zones (high, moderate and low on arbitrary scale) are intermingled in the single ferromanganese oxide layer around the margins of older nodule fragments. The fragments consist mainly of ∂-MnO ₂ and amorphous Fe oxyhydroxides referred to as DAFO.
The characteristic reflectivity is attributed to micro-scale variations in chemical composition (Mn, Fe, Cu, Ni, Co, Ca, Mg, Ti, Si, K and Al) and mineral assemblage as detected by EPMA, SEM, and EDX. The results of EPMA and microscopic investigations suggest that the high-reflectivity zone consists of secondary todorokite replacing the original mixtures of DAFO (low-reflectivity) although primary todorokite layers have been commonly deposited from sediment interstitial waters in the younger encrustations. The moderate-reflectivity zone thus corresponds to an alteration front associated with great variation in Fe and Ti contents while the low-reflectivity zone represents the unaltered DAFO zone. These altered zones are usually in contact with surface sediments where the alteration takes place.
These data suggest that the alteration is related to micro-scale variations of physico-chemical conditions probably controlled by the diagenesis of surface siliceous sediments, bottom current fluctuations, and benthic activities in local bottom environments.

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Selected samples of Precambrian basement gneisses and Mesozoic granitic rocks from the Korean Peninsula are examined by non-destructive gamma-ray spectrometry. The Th/U ratios estimated for the gneisses from the peninsular interior appear to be significantly higher than those for the gneisses from the exterior localities, whereas such a difference is inconspicuous in the granitic rocks. This observation is consistent with the spatial distribution of Th/U values for source materials of Mesozoic ore leads estimated on the basis of a simple two-stage model comprising the second stage evolution in the Precambrian basement.

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Two bismuth minerals, gustavite and "bismuthinite", were newly found in an ore from an outcrop of the Taisei vein, Inakuraishi mine. The ore occurs in strongly altered andesite as veinlets less than 5 cm in width and was cut by a manganese oxides vein, 10 to 20 cm in width. The manganese oxides were estimated to have formed by weathering of hydrothermal manganese carbonates. Vein minerals are quartz, pyrite, and chalcopyrite with accessary amounts of gustavite, "bismuthinite", galena, acanthite, sphalerite, hematite, and marcasite. The gustavite and "bismuthinite" occur in close association with each other, but they do not coexist with galena or acanthite which contains a few wt.% Bi. The possible temperature and sulfur fugacity during deposition of the bismuth minerals are estimated to be in ranges of 254°C to 280°C and 10 ^-11.1 to 10 ^-9.3 atm., respectively. These data suggest that the bismuth minerals had formed at the stage II of the Inakuraishi mineralization.

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