Mining Geology

Some Characteristics of the Neogene Mineralization in the Sanin Green Tuff Region, Southwest Japan.

Makoto WATANABE, Akira SOEDA

1981 Volume 31 Issue 165 Pages 1-11
Published: April 10, 1981
Released on J-STAGE: June 12, 2009

DOIhttps://doi.org/10.11456/shigenchishitsu1951.31.1

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Efforts are made to draw some characteristics of the Neogene (kuroko-type and hydrothermal veintype) mineralization in the Sanin Green Tuff region compared with equivalent activity in the Inner Zone of northeast Japan. In the Sanin region, the Onnagawa Stage is likely to be the major mineralization epoch and some of the deposits seem to be related to the Funakawa Stage, whereas the mineralizations in northeast Japan are known to occur mainly in the Nishikurosawa and Onnagawa Stages. In general, the main stage of mineralization in the Sanin region is characterized by ore mineral assemblage chalcopyrite-pyrite with quartz-sericite-chlorite as gangue assemblage. While the base-metal deposits of both regions are much alike in several aspects including oreand gangue-mineralogy and fluid inclusion systematics, absence of pyrrhotite and arsenopyrite in the Sanin ores makes them sharply contrasted with the ores from northeast Japan. It seems that the Sanin ores were formed in relatively limited depositional conditions defined by pyrite-bornite-chalcopyrite univariant assemblage and less than 3 mol.%FeS in sphalerite coexisting with pyrite, while much varying physicochemical environments existed in the Neogene mineralization field of northeast Japan.

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The distribution of alteration zones in the central area of the Hokuroku district, northeast Japan

Minoru UTADA, Toshiharu TOKOYO, Hisashi AOKI

1981 Volume 31 Issue 165 Pages 13-25
Published: April 10, 1981
Released on J-STAGE: June 12, 2009

DOIhttps://doi.org/10.11456/shigenchishitsu1951.31.13

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In the central area of the Hokuroku district, the following alteration envelopes are recognizable in the Neogene sediments which comprise a large amount of acidic volcanic rocks.
(1) Hydrothermal alteration related to kuroko-type mineralization. Alteration zones are arranged from the center to the margin as follows: The chlorite-sericite zone→the mixed layered clay mineral zone→the montmorillonite zone→the analcime zone→the mordenite zone.
(2) Hydrothermal alteration related to vein-type mineralization. Alteration zones are arranged from the center to the margin as follows: The K-feldspar zone→the chlorite-sericite zone→the mixed layered clay mineral zone→the montmorillonite zone.
(3) Hydrothermal alteration and contact metamorphism(?) around quartz diorite intrusive mass. The chlorite-sericite zone alone is recognized.
(4) Burial diagenesis. The fresh glass zone and the clinoptilolite-mordenite zone are recognized.
The alteration envelopes (1) and (2) are pervasive in the whole area. The latter is often superposing upon the former and the rocks of the former often remain as relicts in the latter. A typical example of this superposition is found around Fukazawa kuroko deposit. Judging from the mode of distribution of the alteration zones, both kuroko-type and vein-type hydrothermal activities in this area seem to have occurred along the lines having NW-SE trend.

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On the characteristics of mineralization in the northern part of Sierra Madre Oriental, Mexico(Part 2, Ore deposits)

Hideo TAKEDA

1981 Volume 31 Issue 165 Pages 27-42
Published: April 10, 1981
Released on J-STAGE: June 12, 2009

DOIhttps://doi.org/10.11456/shigenchishitsu1951.31.27

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In the northern part of Sierra Madre Oriental, lead-zinc deposits occur in a thick sequence of Mesozoic calcareous sediments, which are folded and faulted by the Laramide orogeny. The ore deposits are divided into two groups, non-alteration(or partly marmorization)-type and skarn-type, depending upon the alteration status of the country rock. The former group, typified by such deposits as Plomosas and Dos Marias, consists of the manto-type orebodies in the Jurassic and Cretaceous calcareous sediments with no distinct alteration, being characterized by very simple ore metal association, Fe, Zn and Pb with low concentration of Ag. On the contrary, the latter group of deposits such as Santa Eulalia, Naica and La Encantada are composed of the chimney, manto and vein-type orebodies with skarn minerals. They have been found in the lower Cretaceous Aurora limestone with dome structure. Their ore metals are mainly Fe, Zn, Pb, Cu and As, being associated with minor amounts of Ag, W, Mo, So and Sb. Both groups of mineralization have calcite, dolomite, fluorite, gypsum, anhydrite, barite and quartz as the gangue minerals. In general, the conspicuous intrusive bodies as the possible source of the mineralization are scarecely recognized in the ore field concerned, although discontinuous exposures of dikes and sills of felsite and small stocks of diorite have been known.

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[title in Japanese]

1981 Volume 31 Issue 165 Pages 43-71
Published: April 10, 1981
Released on J-STAGE: June 12, 2009

DOIhttps://doi.org/10.11456/shigenchishitsu1951.31.43

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[title in Japanese]

1981 Volume 31 Issue 165 Pages 72
Published: April 10, 1981
Released on J-STAGE: June 12, 2009

DOIhttps://doi.org/10.11456/shigenchishitsu1951.31.72

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[title in Japanese]

1981 Volume 31 Issue 165 Pages 72a-74
Published: April 10, 1981
Released on J-STAGE: June 12, 2009

DOIhttps://doi.org/10.11456/shigenchishitsu1951.31.72a

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