南九州北薩地域における金銀鉱脈鉱床の生成とその造構史的背景(その2)

スケールモデル実験による検討

抄録

The Hokusatsu district of southern Kyushu is known for its gold mineralization. Vein-type fracture systems similar to those in this district have been produced in scale-model experiments in which a diapir-like mass is pushed upward through an overlying brittle layer consisting of a sand-powdery cement mixture. Progressive development of the experimental fractures, combined with predicted behavior of natural fluid phases during gold-silver mineralization, lead to following hypothetical scenario for the mineralization.
Two collapse basins was formed in the northwestern and southeastern parts of the Hokusatsu district in the early Pleistocene. The middle part of these two collapse basins was subjected to tentional stress resulting in fracture systems trending NE-SW which is paralleled by the fringe of these collapse basins. These surface fractures were penetrated by meteoric water.
Above the magma diapir, a second system of fractures developed due to shouldering aside of the overlying crust. Mineralized hydrothermal solutions penetrated upward into these deeper fractures. Eventually, with continued rising of the magma diapir, the fracture systems (surface and deep) became connected, and the vein deposits were precipitated as the hydrothermal solutions were cooled by mixing with meteoric water.