Metallogenic epochs in the Inner Zone of southwest Japan
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- 作者：Watanabe ; Makoto ; Nishido ; Hirotsugu ; Hoshino ; Kenichi ; Hayasaka ; Yasutaka ; Imoto ; Nobuhiro
- 关键词：metallogenic epochs ; radiometric age ; microfossil age ; Inner Zone of Southwest Japan
- 刊名：Ore Geology Reviews
- 出版年：1998
- 出版时间：June, 1998
- 年：1998
- 卷：12
- 期：4
- 页码：267-288
- 全文大小：1.09 M
文摘
The principal metallogenic epochs in the Inner Zone of southwestern Japan are classified by considering mainly radiometric and microfossil age data, as follows—(1) Early Cambrian Epoch: Characterized by podiform-type chromite deposits hosted in ophiolite complexes; these are the earliest-formed mineral deposits in the Japanese Islands, and probably formed in the shallow mantle of island-arc settings; (2) Carboniferous to Permian Epoch: Characterized by Besshi-type base metal sulfide deposits mainly associated with submarine lavas and tuffs of basaltic composition including their metamorphosed equivalents, and by bedded cupriferous pyrite deposits associated with submarine acidic tuffs. Both types of deposits would have been formed in a back-arc basin environment, geochemically influenced by an island-arc; (3) Middle Triassic to Jurassic Epoch: Characterized by most of the bedded manganese deposits associated with bedded cherts, including their metamorphosed equivalents, which would have formed by hot spring activity in an ocean basin environment with a limited current circulation. The manganese deposits and their host rocks are the result of seafloor accretion; (4) Late Cretaceous to Paleogene Epoch: Characterized by extensive continental-arc magmatism (volcanic and plutonic), resulting in formation of various mineral deposit types, related mainly to ilmenite series (Late Cretaceous) or magnetite series (Paleogene) granitic rocks. Related to the former are polymetallic skarns and veins containing Cu, Sn and W; also related to this metallogenic activity are stratabound hydrothermal clay deposits of kaolin, pyrophyllite, and sericite associated with pre-ilmenite series granitoids subaerial felsic pyroclastic rocks. Molybdenite-bearing veins and replacement-type sericite deposits are characteristics of the magnetite series terranes, with local skarns and vein occurrences. As with ilmenite — series granitoids occurring in southwestern Japan, eastward younging is also recognized in these mineral deposits, regardless of ore type; (5) Neogene Epoch: Characterized by intense submarine volcanism of acidic composition and associated Kuroko deposits in the Green Tuff region, a major tectonic division and a major metallogenic province of the Neogene Tertiary of Japan. These mineral deposits would be related to Japan Sea opening. In the ‘Non-Green Tuff region,' important mineralization events are represented by sedimentary uranium deposits, and veins characterized by Au, Sb or Hg occurrences; (6) Plio-Pleistocene Epoch: Characterized by epithermal Au–Ag and Au–Ag–Cu veins associated with subaerial andesitic to dacitic volcanic rocks of Plio-Pleistocene age. Volcanism of this and following epochs is characteristic of an island-arc setting; and (7) Quaternary Epoch: Characterized by volcanic sulfur deposits and minor iron sand deposits.