山口県東部三郡変成帯中の鉱化作用の特性について

On the Characteristics of Metallization in the Sangun Metamorphic Zone at the Eastern District of Yamaguchi Prefecture

竹田 英夫

廣島大學地學研究報告

Geological report of the Hiroshima University

Geology of the district in question, situated at the eastern side of Yamaguchi Prefecture, is composed mainly of green schist and black schist of the Sangun metamorphic zone and sandstone and phyllite in the Paleozoic, associated with many intrusives of serpentinite, quartz-diorite, quartz-porphyry and porphyrite of Mesozoic.
In the district there are some ore deposits, which are divided into two types; vein type and bedded lenticular type. The deposits of the former type, namely Shibutani and Kamagahara, occur in the steep faults, and the mineral paragenesis is as follows;
Shibutani: arsenopyrite-pyrrhotite-marcasite-pyrite-magnetite-cassiterite-sphalerite-
chalcopyrite-stannite-cubanite-valleriite-galena-fluorite-sericite-chlorite-
epidote-garnet-quartz-carbonate mineral.
Kamagahara : pyrrhotite - marcasite - ilmenite- chalcopyrite-cubanite-valleriite-sphalerite-
bismuthinite-native bismuth-tetradymite-native gold-Ni-Fe-S mineral (un-
determined)-tourmaline-spinel-chlorite-epidote-ilvaite-carbonate mineral.
Under the ore microscope, the high temperature texture, such as sphalerite star in chalcopyrite and emulsions of chalcopyrite and stannite in sphalerite are often observed in the ores.
On the contrary, the deposits of the latter type, namely Kodai and Nobugahara, lie subconcordantly with the structure of country rocks, and the ore and gangue minerals are as follows;
Kodai : pyrrhotite-marcasite-pyrite-magnetite-chalcopyrite-cubanite-sphalerite-
wollastonite-chlorite-eqidote-quartz-carbonate mineral.
Nobugahara: pyrrhotite-marcasite-pyrite-chalcopyrite-sphalerite-magnetite-hematite-
sericite-quartz-tremolite-chlorite-carbonate mineral.
The high temperature texture is scarcely found in the ores in spite of presence of cubanite and skarn mineral, and "pressure shadow" of quartz around pyrite grain is observed in the disseminated ore from the eastern part of Kodai deposit.
The metallization of vein type deposits is characterized by the high temperature association of various kinds of metallic elements, and is appeared to be related with the igneous activity of granitic complex in the late Mesozoic. However, the bedded lenticular deposits preserve the different characteristics of metallization, and it seems that the metallogenetic epoch of bedded lenticular type is earlier than that of vein type on the field evidence, but the genesis of bedded lenticular type deposits is still obscure.

日本語

廣島大學理學部地學教室

[ISSN] 0073-2303

[NCID] AN00213676