Reverse Circulation Rotary Drilling Sample Clauses

Reverse Circulation Rotary Drilling. The RC drilling conducted by Atna was completed by D▇▇▇▇▇ Construction & Drilling of Winnemucca, Nevada using a S▇▇▇▇▇▇ 1500 truck mounted drill, supported by a water truck, pipe truck, and service truck, and staffed by a driller, helper and sampler. RC drilling was used principally for pre-collaring core holes. The pre-collar portion consisted of drilling through non- or weakly-mineralized rock and stopping at a known depth above target mineralization. After drilling, the hole was cased using 4 5/8 inch threaded steel pipe to maintain the integrity of the hole until the core rig arrived to finish the hole to target depth. Drilling started out using a 5 5/8 inch hammer bit. The hammer bit used a pounding action along with rotation to break the rock into pieces, and air pressure to lift the cuttings up out of the hole, and into the sample splitter. When the air system was no longer powerful enough to drive the hammer in the presence of high downhole water pressure, the hammer bit was replaced with a tri-cone bit. A tri-cone uses three rotating wheels with pointed carbide buttons to grind the rock into little pieces. Air pressure is used, as with the hammer bit, to lift the ground-up cuttings to the sampling apparatus.