1975 Volume 25 Issue 130 Pages 109-122
The deposits of the Yaguki mine consist of massive or disseminated iron, copper and tungsten ores. The deposits are of typical contact metasomatic type and occur in an extensive skarn zone which is formed along the footwall side of gently folded limestone bed. The skarn zone consists mainly of garnet skarn in the lower part and of clinopyroxene skarn in the upper part. Principal ore minerals are magnetite, chalcopyrite, pyrrhotite and scheelite. Sulphide and scheelite mineralizations seem to have been introduced by hydrothermal sulutions in the last stage of contact metasomatism which is closely related to granodiorite intrusion.
In the Shin-bu tungsten deposit, the scheelite mineralized zone is divided into five subzones from bottom to top as follows based on the mineral assemblages and modes of occurrence: A. massive epidotized subzone, B. epidote-quartz network subzone, C. massive and lenticular sericite-quartz subzone, D. banded and stratiform chlorite-quartz subzone, and E. epidote network subzone. The B subzone is included in A subzone and E subzone grades to limestone. The B and C subzones are most intensely mineralized by scheelite.
The scheelite mineralization took place in two stages. In the first stage A subzone was formed in following successive mineralization; clinopyroxene in skarn zone was partly replaced by actinolite, actinolite was in turn replaced by epidote and scheelite, then scheelite, calcite and quartz were precipitated. Later remaining clinopyroxene and actinolite were replaced by chlorite. In this stage only the clinopyroxene skarn was attacked by hydrothermal solution. It is likely that the mineralization occurred homogeneously in the skarn and gradually advanced upward. The scheelite mineralization is not associated clearly with much quartz and calcite but closely related to pistacitic epidotization.
In the second stage, B, C, D, and E subzones were formed. The epidotized clino-pyroxene of A subzone seems to have become more stable in this stage. Hydrothermal solution ascending through numerous cracks in skarn reached just below the limestone bed and mineralization occurred there. Fractured part of A subzone was also replaced by clinozoicitic epidote, sericeite, chorite, quartz and calcite in the main period of the second stage. Toward the end of the second stage, even limestone was replaced by much of quartz, chlorite, and sericite. The replacement in this stage indicates typical hydrothermal characteristics and scheelite mineralization is closely associated with epidotization and sericitization.
