Drilling Method With a Small Angle to Schistosity in the Besshi Mine

Abstract

In the Besshi Mine, it was recognized that a drill hole tends to assume a direction at right angles to schistosity finally. For instance, a drill hole which was started horizontally at the collar has deviated upward by 25° degrees for a length of 200 meters. Another drill hole which was started vertically downward has changed by 60° degrees at a depth of 200 meters. Recently it has been recognized that a drill hole driven at a small angle to schistosity can advance straight for a length of more than 150 meters and that the deviation of the hole depends upon the angle between the hole and the schistosity. Using these facts in prospecting, we have been able to economize both time and cost 50 to 70% as long cross-cut tunnels became unnecessary.