Geological and geochemical characteristics of the gold-bearing Nurukawa Kuroko deposit, Aomori Prefecture, Japan

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Other Title
  • 青森県温川含金黒鉱鉱床の地質学的·地球化学的研究
  • 青森県温川含金黒鉱鉱床の地質学的・地球化学的研究
  • アオモリケンオンガワ ガン キン クロコウ コウショウ ノ チシツガクテキ ・ チキュウ カガクテキ ケンキュウ

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Abstract

The Nurukawa Kuroko deposit is a gold-rich Kuroko deposit in Hokuroku district, Japan. The Nurukawa deposit consists of gold-bearing network siliceous orebodies (stockwork), gold-bearing bedded siliceous orebodies and bedded black orebodies in ascending order. The ores of gold-bearing network and bedded siliceous orebodies are cut by network of lead-zinc-bearing siliceous ore. The bedded black orebodies are composed of compact black ores and brecciated black ores. The mineral assemblage of ores of gold-bearing network and bedded siliceous orebodies is large amounts of chalcopyrite, pyrite and quartz with small amounts of hematite, sphalerite, galena, electrum and kaolin, while the mineral assemblage of lead-zinc-bearing siliceous ore is large amounts of sphalerite, galena and quartz with small amounts of chalcopyrite, pyrite and sericite. The mineral assemblage of bedded black ore consists of sphalerite, galena and barite with small amounts of chalcopyrite, pyrite, teterahedrite, pearceite, pyrargyrite and electrum. Some kaolin layers are intercalated in the bedded black orebodies consisting of brecciated black ores. Based on the data of mineral assemblage, chemical compositions of sphalerite and homogenization temperature, formation environment of gold-bearing siliceous ore is estimated to be relatively oxidized and acidic compared with the formation environment of bedded black orebody. Hydrogen isotopic ratios of hydrothermal solution forming gold-bearing siliceous ore (approximately -40 ‰) and bedded black ore (approximately -10 ‰) suggest that the gold-bearing siliceous ore was formed by hydrothermal solution of magmatic origin and the bedded black ore was formed by hydrothermal solution of seawater origin mixed with hydrothermal solution of magmatic origin. The presence of kaolin layers in bedded black orebodies consisting brecciated black ores suggests that acidic hydrothermal solution of magmatic origin took place during the period of formation of bedded black orebody. The Nurukawa Kuroko deposit is one of volcanogenic massive sulfide deposits that were formed by hydrothermal solution associated with magmatic hydrothermal system below seafloor.

Journal

  • Shigen-Chishitsu

    Shigen-Chishitsu 65 (3), 117-132, 2015

    The Society of Resource Geology

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