Offshore placer drilling technology: a case study from Nome, Alaska

Abstract

A drill system configuration capable of working in the arctic offshore environment was developed to evaluate the placer gold resources contained in the glacio-fluvial sediments offshore Nome, Alaska. This system is capable of working on the shore fast ice during the winter months and is deployed on a drill ship during the summer. Transfer of the drill between its summer and winter configurations is accomplished with a minimum of modification to the design. The system is designed around the Becker drill, a percussive reverse circulation drill capable of penetrating the indurated glacial sediments present in the offshore Nome environment. This drill has operated effectively to depths in excess of 50 metres below sea level. Since early 1987, in excess of 2,000 holes have been drilled using the system. The drill system, often operating in extreme weather conditions, has averaged approximately 10 holes per day of drill production. The ore reserves defined during these drilling programmes have resulted in the recovery of greater than 70,000 fine ounces of gold to date by the mining vessel BIMA.