The Nebazawa deposits are epithermal, gold and silver-bearing quartz vein type deposits. They occur in E-W trending southward dipping steep fractures in the welded tuff member called Katashinagawa rhyoritic rocks of Paleogene age.
The study of the geology and ore deposits of the mine has disclosed following facts and suggestions which could be useful guides for current and future exploration of the mine.
1) Three stages of mineralization were identified, they are, from older to younger, base metalliferous mineralization (Stage I), auriferous mineralization (Stage II, Ag/Au≥10) and argentiferous mineralization (Stage III, Ag/Au≥100). The latter two mineralizations are important in economic sense.
2) The assay contour is fully affected by low angle east dipping faults called No. 1, No. 2 and No. 3 fault which intersect the veins diagonally. High grade part of the vein is along the hangingwall side of the fault and barren part along the footwall side. This suggests possible important role of these faults as controlling factor of convection system of ground water at the time of ore deposition.
3) Vein fractures are interpreted as high angle reverse type faults initiated by the differential block movement between relatively subsided northern block and southern relatively upheaved block. This block movement seems to be triggered by or related to the formation of N-S trending cauldron subsidence of Miocenc Kinugawa rhyolitic rocks to the east.
