Preliminary simulation analysis of fracture systems in the Sado gold mine area, Niigata Prefecture, Japan.

概要

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A system of fractures of EW direction which were filled with gold-bearing quartz veins occur in the Aikawa and Nyukawa Formations distributed in the Sado mine area. The purpose of this study is to analyze the fracture system using three dimensional elastic-plastic finite element method. This computer simulation analysis was done by Virtual Basement Displacement method (VBD method) developed by one of us (K.K.). The results of this study are as follows; (1) Half-dome-shape uplifting of the basement at the central part of the arbitarily set-up tectonic system can produce observed vein pattern. State of dislocation of the veneer rocks is in harmony with that of the basement, but there is a tendency of decreasing dislocation toward upper level. (2) The concentration of strain within the lower layer occurs near the central part of the mine. Shapes of isopleth of strain are elliptic and elongated to EW direction. (3) Typical fracture systems in the central part of the mine area is a pair of conjugate faults of EW direction which are low-angle normal fault and high-angle reverse fault. The fracture systems are more distinct in the lower layer. The concentration of strain and fracture systems shown by the simulation analysis fit well with the distribution and vertical variation of the observed fractures and vein systems of the mine area. Therefore this method is thought to be useful for exploration.
資源地質学会の論文