Large Diameter Drilling (Bauer BG 36 Drill)
Working with Bauer Maschinen GmbH, Nuna developed new equipment and techniques to drill large diameter holes in 2 stages.
Nuna owned and operated 2 Bauer BG 36 large diameter drill (LDD) rig systems capable of drilling 1,200 mm diameter (4 ft) diameter holes to a depth of 350 m (1,150 ft). These diesel-powered electric/hydraulic units utilize Caterpillar-powered crawler tractors similar to excavators with retractable masts.
After a unit is walked to a large diameter drill hole location, overburden to a maximum depth of 85 m is augered using a Kelly system with a selection of excavation tools. A Bauer-supplied oscillator is used to set and recover double-walled casing to as much as 40 m depth. Beyond that depth, or in harder formations, the system is reconfigured to use reverse circulation drilling. In reverse circulation (RC) mode, 6 m (19 ft) long sections of 9-5/8 inch double-walled drill pipe are added to the drill string utilizing a manipulator which enables an operator to handle pipe while safely removed from the suspended load. Compressed air is piped down the hole between the inner and outer pipe walls. Air valves which form part of the drill string allow high-pressure air to enter the inner pipe at a distance above the hole bottom and to escape to surface; the vacuum created suctions slurry from the hole bottom. Holes are drilled in flooded conditions utilizing drilling "muds" to stabilize open holes below the casing.
A variety of drill bits are employed to suit conditions which range from soft soils to rock with high compressive strengths. Drill data is electronically recorded for later analysis.
Sampling for diamonds in kimberlite is accomplished through the use of a desanding unit which separates drilling fluids from the sample, washes the sample and recovers materials greater than a specified size. The samples are bagged and transported to a designated area.
Nuna key projects
Bulk Sample 184 Holes (38,915.9 m) (127,688 ft)
Shore Gold Inc., Star Diamond Project
Prince Albert, Saskatchewan, Canada
Shore Gold's Star Diamond Project lies some 60 km east of Prince Albert, Saskatchewan. This area, known as Fort á la Corne, hosts one of the most extensive kimberlite fields in the world. The kimberlite is overlain by as much as 120 m of overburden consisting of sand, mudstone, boulders and glacial till.
Faced with a requirement to collect bulk samples over an extensive area, Shore Gold selected Nuna to conduct a large diameter drill program with an initial target of 72 holes. Holes would be 1,200 mm in diameter (~ 4 ft) with depths ranging to over 300 m (984 ft).
Working with Bauer Maschinen GmbH, Nuna developed new equipment and techniques to drill holes in 2 stages. The process utilized 2 sets of fully equipped mobile BG 36 drill rigs, bentonite and polymer solutions and Nuna-supplied primary support equipment (Caterpillar D-8 dozer, Cat 980 loader, and IT-62 and IT-28 tool carriers).
Holes were “Kelly drilled” through the first 85 m (278 ft) of overburden and then rigs were switched to reverse circulation drilling where geologists were provided with sampling intervals. Rigs were walked between holes and skid-mounted equipment was repositioned with support equipment. Operations continued year-round on a 24 hour basis.
BG 36 large diameter drill (LDD) rig capable of drilling 1,200 mm diameter (4 ft) diameter holes to a depth of 350 m (1,150 ft)