豊羽鉱床における後期鉱化作用の特性と裂罅系
1992 年 42 巻 232 号 p. 85-100
詳細
1992 年 42 巻 232 号 p. 85-100
The Toyoha mine is one of the largest Ag-Pb-Zn-Cu vein deposits in Japan. Two stages of mineralization, the earlier and the later, are found in the deposits. Polymetallic and polyascendant mineralization of the later stage occurs mainly in the southwestern to southeastern parts of the mining area (Soya, Iwami, Izumo and Shinano veins).
Two substages (the first and the second) are distinguished in the later stage mineralization based on the detailed study of paragenetic sequence in ore. The former is exclusively emplaced in the E-W fracture system, while the latter mainly in the NW-SE one. Distinct ore zonations are recognized in each fracture system controlling the later stage mineralization. The zoning centers, indicating main path of ore fluids, are located at the eastern lower parts of Izumo vein for the former and the still eastern part of them for the latter, respectively. Junction of both fracture systems might have offered the largest bonanza at the Izumo and the Shinano veins in superimposed mineralizations.
A great geothermal activity is still continued at the southeastern part of the mining area, nearby the large Shinano vein. Proposed structural model for the active geothermal system deduced the success of the mining operation of the vein. A sericite alteration cap overlying the upwelling zone of the active system might have controlled the top of ore veins.
It is anticipated the discovery of new ore veins in the southeastern part and the potentiality of further ore reserves in the peripheral zone based on the characteristics of the later stage mineralization at the deposits.
