The last one consists of pumice to fine tuffs alternating to siltstone emplaced with dacite domes, quartz-porphyries and granitoids (D1 group) during 11-10 Ma. The lower unit of post-ore felsic volcanism (D2 group) consists of dacite lavas and pumice tuff alternating with black colored mudstone during 12.7-11Ma. Pre-ore dacite group is composed of regionally extended dacite lavas (D4) and massive pyroclastics with rhyolitic domes (D3,WR) adjacent to Kuroko deposits during 16-13.4Ma. Restructuring of detailed stratigraphy by field observations including drill cores and reconsideration of dating results with micro fossil data indicates that the felsic volcanisms are divided into three sequences.
The district is located in NE Honshu arc and economically the most significant mineral province where had been produced eleven Kuroko deposits from 1886 to 1991. The present study will show petrological and petrochemical differences between pre-ore (back-arc) to post-ore (oceanic-arc) volcanisms in the Hokuroku district. The deposits have been generated in association with felsic volcanic activities of bi-modal volcanism in back-arc rifting zone started from middle Miocene and have been overlain by progressive caldera forming felsic activities at oceanic arc setting.
More than hundred deposits are distributed within Neogene volcanic belt along present Honshu arc. The volcanic-hosted massive sulfide deposits named Kuroko deposits in Japan is one of representative VMS deposits in the world.
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