3.2 On-Land Coring: New Developments Warren Dickinson, Pat Cooper, Bain Webster

Core drilling of permafrosted sediments is common and well understood in most Arctic environments, but in the cold, dry page break Antarctic environment it is at its infancy. Coring the Sirius deposits at Table Mountain was largely an on-site experiment because such permafrosted sediments do not exist in NZ or on Ross Island.

All drilling equipment had to be hand portable, and available in the field camp. Off the shelf HQ and NQ diameter core barrels and drill rods were used with a flushing medium of compressed air. The purpose-built, portable compressor could produce 50 cubic feet of air per minute at 30 psi which was pumped down the hole via an air swivel. The drill rods were rotated by a Sthil 056 motor mounted on frame with a torque bar which was pinned to the ground. Bit weight was controlled by the weight of the operator and any additional weight from the helpers. Pulling and lifting of the drill assembly was controlled by a hand winch via a single running block attached to a tripod.

Initial drilling showed that experimentation and modification of bit types was necessary to properly core the variety of lithologies contained in the Sirius. The flushing and cooling of the drill bit with compressed air was found to be critical. At all times the drill bit must be kept at sub zero temperatures to prevent melting of core and nearly instantaneous freeze in of the bit should rotation stop unexpectedly. Cooling of the bit depends on the temperature and volume of air entering the hole as well as the kerf and diameter of the bit. For a given air supply, a thin kerf and small diameter bit runs cooler than a thick kerf and large diameter bit. Diamond bits must be used to core hard and firmly cemented dolerite clasts, but tungsten bits must be used to core ice lenses and soft friable sands. Core recovery of conglomerates in ice-free horizons, which usually occur from the surface to 50 cm deep, was not possible. Loose clasts which are jarred from this horizon and fall into the hole must be either pulverized by further drilling or scooped out of the hole if core is to be recovered.

Considering the budget restraints and limited helicopter support the drilling project was extremely successful. With moderate adjustment and modification the existing equipment could be refined into a highly reliable and portable Antarctic drilling unit.