The secular variation of major chemical compositions and those normative compositions suggest that (1)Kuroko deposits have been formed at the final stage of pre-ore dacite sequence associated with the most differenciated magma in the sequence and another felsic magmatism commenced immediately after Kuroko formation, and (2)Pre-ore felsic rocks would be derived from a deeper magma chamber under extentional stress field and post-ore ones had taken place as caldera-forming eruption on gradually upheaving seafloor derived from shallower magma chamber in weakly compressional field. On the other hand, post-ore felsic rocks are characterized by various amounts of quartz-plagioclase phyric texture in aphanitic groundmass. Regionally extended pre-ore dacite (D4, in other word, footwall dacite) are distinguished as plagioclase phyric dacite with lower TiO2 and CaO contents and rhyolitic members (D3 and WR, so-called white rhyolite) closely related to Kuroko formation can be distinguished by peculiar aphyric texture with higher aluminum content than that of the other dacites. 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.

Globus simulation quiz 1