The Ezuri kuroko deposits were discovered near Odate city, northern Honshu, as the result of systematic exploration activities from 1975 to 1977. This report summarizes the processes to the discovery of the deposits.
In the Hokuroku district (ca. 1, 500 km²), northeastern part of Akita Prefecture, large kuroko deposits have been known to concentrate along the eastern and western margins of the Hokuroku basin. Most of the exploration activities in 1960's were, therefore, focused on the peripheries of the basin, and several new kuroko deposits were found successfully. However, the discovery of the Fukazawa deposits in the central area of the basin in 1969 indicated the possibility of finding new deposits in the vast interior of the Hokuroku basin.
An extensive examination of the mode of volcanism and hydrothermal alteration of the dacite lavas below kuroko deposits in the Fukazawa mining area in 1974 and 1975 revealed the following points:
(1) The underlying, pre-mineralization, Neogene dacite lavas distributed widely in the Hokuroku district are discriminated into four types, D ₁ lava dome, D ₂ lava flow, D ₃ lava dome and D₄ lava dome on the basis of their mode of occurrence and eruption stage.
(2) Mineralization of the Fukazawa deposits is closely related to the latest D₄ lava dome activity.
(3) K₂O and MgO contents in the D₄ dacite increase toward the ore deposits, while Na₂O and CaO show the opposite trend.
(4) Distinct alteration haloes are observed in the country rock dacite around the orebodies with respect to the chemistry and magnetic susceptibility.
Based on the data obtained in the Fukazawa area, the Ezuri area (7 km west of the Fukazawa area) was selected as a promising target and the exploration work commenced in 1975. Firstly, a systematic drilling program was carried out at 400 m interval to investigate the geologic structure. The program disclosed the relatively wide distribution of thick D₄ dacite lava domes at the horizon about 200 m below sea level. The drill cores were then examined geochemically, particularly for the contents of alkali-and alkaline-earth metals in the dacites. Presence of the alteration haloes similar to those of the Fukazawa deposits was indicated in the central and southern parts of the explored area. Intensive drilling operations were thus concentrated in these alteration zones and the Iwagami and Ezuri kuroko orebodies were successfully discovered in November, 1975 and July, 1976, respectively.
The confirmed ore reserve is approximately 3 million tons, averaging 1.3 g/t Au, 180 g/t Ag, 0.89 % Cu, 3.3% Pb, and 10.1% Zn. The mine has been in operation since October, 1979.

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Re-examination of the volcanostratigraphy of the Fukazawa-Ezuri area, central Hokuroku basin, has clarified the paleo-volcanic structures related to the formation of the kuroko and vein-type deposits. Circular distribution of post-kuroko volcanics (intrusives and lava flows) representing eruptive centers and a crystalline stock within the circle seem to be suggestive of a latent "resurgent cauldron" in this area, as predicted by KounA and KOIDE (1978). However, any evidence of subsidence and up-doming implied by their model has not been recognized in this investigation.
It is suggested that block movement of the basement rocks is more important in having formed structural shear zones that have acted as a leading pass of acid magma, kuroko solution and post-kuroko basalt flows. Spatially, the Fukazawa orebodies have close relationship to pre-mineralization rhyolite lava domes and phreatic explosion breccias at the near surface of these domes.
Vein-type deposits were formed in a stage later than the kuroko deposits, probably during the early Funakawa stage (about 9 m.y. B.P.). Most of them are distributed along the margin of the crystalline stock and some in a local crater cauldron in the Takarakura area. Reconstructed paleo-volcanic structure of this area suggests that the vein-type deposits were formed at depth of 300 to 600 meters under very shallow submarine or terrestrial environment.

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The Kamaishi mine is one of the major producers of copper and iron ores in the present Japan. The ore deposits are of skarn type, formed in a contact zone of Paleozoic sediments of mainly limestone and Cretaceous granitic stock occurring in mid-eastern Kitakami mountains, Iwate Prefecture. Among many orebodies of the mine the Shinyama ore deposit is one of the largest and most representative. In this deposit the iron (magnetite) ore with garnet skarn occurs close to the igneous boundary, while the copper ore with clinopyroxene skarn is farther from the boundary toward the limestone. The present paper discusses the Cu-Fe-S mineralization in the Shinyama ore deposit.
On the basis of microscopic textural observation, sulfides of this deposit can be divided into three categories; host, exsolution, and alteration phases, although the amount of the last twos is not to be compared with the host sulfide phase. Chalcopyrite, cubanite, pyrrhotite and pyrite are the major host sulfides in the deposit. A close paragenetic relationship is observed between chalcopyrite, cubanite and pyrrhotite. Ni-and Co-bearing minerals such as pentlandite, mackinawite, siegenite and argentian pentlandite commonly occur as minute exsolution bodies in the host sulfides.
Of the major constituent sulfides, pyrrhotite is mostly abundant. The three phases of this mineral, that is, monoclinic pyrrhotite, hexagonal pyrrhotite and troilite are identified. Troilite is observed only as the exsolution product in the host hexagonal pyrrhotite. There is a distinct zonation in the distribution of monoclinic and hexagonal pyrrhotites and other major sulfide species in the deposit. Four successive zones, (1) monoclinic pyrrhotite-chalcopyrite-pyrite, (2) monoclinic pyrrhotite-hexagonal pyrrhotite-chalcopyrite, (3) hexagonal pyrrhotite-chalcopyrite, (4) hexagonal pyrrhotite-chalcopyrite-cubanite, and hexagonal pyrrhotite-cubanite, are distributed outwardly from the zone of garnet skarn to the limestone.
Combining the observed data and the available knowledge on the stability of ore and skarn minerals, it is inferred that the oxygen and sulfur fugacities of the mineralization had been higher toward the garnet skarn zone and that the maximum range of the temperature of formation of the sulfide orebody is 300-150°C.

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Paleozoic and Mesozoic-Cenozoic granitoids of the Chilean Andes were studied magnetically in the area between Latitude 22-35°S. The Paleozoic granitoids are found to be composed of the ilmenite-series and weakly magnetic magnetite-series, whereas all the Mesozoic-Cenozoic ones appear to be the magnetite-series. Lack of significant sulfide deposits in the Paleozoic terrains may have been resulted from the reducing nature of the granitic magmatism.
Within the magnetite-series terrains of Mesozoic-Cenozoic age, magnetic susceptibility of the granitoids seems to increase continentward. Granitoids related to porphyry copper deposits in the Andean Cordillera have higher magnetic susceptibility than those occurring in the Coast Range which could be genetically associated with manto-type deposits. The different styles of mineralization may possibly be in consequence of the different oxidation status of the granitic magmatism.

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