Pelagic surface sediments and their coarse fraction from the Central Pacific Basin were under extraction by hydroxylamine hydrochloride and acetic acid. Both the parts extracted and residual were analyzed for Fe, Mn, Co, Ni, Cu and Zn, and mineral composition of the residual parts were studied by means of X-ray diffraction.
The most refractory element among the six is Fe, while Mn is the most soluble. It is noteworthy that about a half amount of Cu stay in the residual part while only about 20% of Ni does.
The chemical composition of the extracted part from the coarse fraction of sediment are grouped into two trends in Mn/Fe-Cu/Ni diagram. One of the trends is characterized by a reverse correlation between Mn/Fe and Cu/Ni ratios and represents the expected characteristics of residual matter after preferential removing of Mn versus Fe, and Ni versus Cu from metal oxide and/or oxyhydroxide during early diagenesis. Another trend is characterized by rather positive correlation between Mn/Fe and Cu/Ni ratios, representing primary precipitates from sea water, secondary reprecipitates through early diagenesis, and/or mixture of them just like nodule composing minerals.
It is clarified that Fe, Cu and Zn in the residual part is dominantly localized in smectite and that a part of the smectite is captured or cemented in recrystallized radiolarian tests. Whereas dominant amount of Mn, Co and Ni all in the residual phase may be localized in ferro-manganese oxide and/or oxyhydroxide captured or cemented in recrystallized radiolarian tests. We infer authigenic origin of the smectite, though the mineral species is not disignated. In the area studied, biogenic silica, iron and aluminum of various origins may form smectite with together, uptaking more than a half of total Cu and Zn during early diagenesis.

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Host rocks of kuroko deposits in the northern and eastern parts of Odate city, Hokuroku district have been investigated with respect to their sulfur isotopic composition and the distribution of iron minerals. Some 40 samples were selected from the drill cores obtained by the Metal Mining Agency to cover a range of a few hundred meters each above and below the kuroko ore horizon in the stratigraphic column. Although the host rocks contain, in part, sulfate minerals such as gypsum and anhydrite, most of the sulfur in the examined specimens is found to be in pyrite.
δ³⁴S (CDT) values of the host rocks and the ores are in a wide range of -35 to +20‰. Based on the rock type, the morphology of pyrite and the relationship of host rocks to mineralized zone, these values can be classified into three principal groups as follows:
(i) δ³⁴S=-30±5‰, framboidal pyrite in mudstone;
(ii)δ³⁴S=-5-+20‰, euhedral pyrite in dacite lava and its pyroclastics referred to as the "green tuff"; and
(iii)δ³⁴S=+3-+10‰, pyrite in mineralized zone (+3-+5‰ in massive ores and +6-+10‰ in footwall rocks with disseminated pyrite).
Intermediate values between (i) and (iii), and between (i) and (ii) are observed in footwall mudstones with disseminated pyrite, and in green tuffs having both euhedral and framboidal pyrites, respectively.
Origin of sulfur in both mudstone (i) and green tuff (ii) may have been in seawater of the Miocene age. The sulfide sulfur of mudstone (i) was produced by bacterial reduction, whereas that of green tuff (ii) was probably the pro-duct of inorganic reduction involving Fe2+ and/or C in the host rocks, partly assisted by bacterial reduction. Contribution of "igneous sulfur" to the group (ii) sulfur may also be warranted, though its direct recognition would be difficult to achieve.
The sulfur in mineralized zones (iii) can be easily distinguished by its concentrated δ34S values from the sulfur in the surrounding green tuff rocks. This characteristic value is known to occur in the whole Hokuroku district and other "green tuff mineralization" areas in the Japanese Islands as well. The fact suggests that the ore sulfur concerned must have been derived from a certain large-scale reservoir by a common process.
In spite of ubiquitous "green tuff alteration", magnetite persists as the most common iron mineral in the kuroko country rocks. However, in the ore horizon as well as the mineralized footwall pyrite becomes the principal iron mineral. Variation in the relative abundance of the two minerals expressed in Py/(Py+Mt) ratio in mode ("P ratio") correlates well with the mineralization halo. Distribution of the P ratio in the host rocks would therefore be a useful pros-pecting guide to kuroko ores in the green tuff region.

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The "relict" framboidal pyrite in the Ezuri kuroko ores, which is considered as the most primitive phase in the mineralization (KOMURO, 1984), is remarkably enriched in light sulfur isotope (δ³⁴S CDT=ca.-20‰) as compared with other sulfides fixed and recrystallized during later stages (δ³⁴S CDT=-0.3-+7.9‰). The framboidal pyrite is thought to be the product of biologically mediated sulfur from the Miocene sea under euxinic environment.

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Twenty-four granitoids from three magnetite-series granitic terranes and three ilmenite-series granitic terranes were analyzed for gold by the neutron activation method. The gold values of the magnetite-series granitoids range from 0.4 to 7.1 ppb and the average is 4.3 ppb, while those of the ilmenite-series granitoids vary from 0.4 to 4.8 ppb and the average is 2.5 ppb. The higher values of the magnetite-series granitoids than the ilmenite-series ones may be attributed to the presence of rock-forming magnetite in the former series. The gold values appear to increase with the in-creasing of silica contents within the range of 61-76%. Magnetite-series granitic terranes are considered to be more favarable basement than ilmenite-series ones for Neogene gold mineralization of the Green Tuff region.

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