JUNIOR MINING — Drilling contractor delivers kimberlite

An active player in the process of providing kimberlite core and bulk samples to mining concerns investigating kimberlite anomalies is Calgary-based S D S Drilling Ltd.

The drilling contractor is involved in diamond exploration and bulk-sampling projects in the Fort a la Corne area of Saskatchewan and the Lac de Gras area of the Northwest Territories.

To date, several reverse circulation and core programs have been completed at Fort a la Corne utilizing 634-inch dual-wall, 1058-inch dual wall and 3-inch wireline core system. These were followed by a 614-inch dual-wall program on the discovery pipe of Dia Met Minerals (TSE). S D S is completing a larger 1058-inch bulk-sampling program in the Lac de Gras area. These two kimberlite-prone areas of Canada present many difficult obstacles to overcome with respect to drilling and obtaining bulk samples. At Fort a la Corne, kimberlite pipes are covered with about 400 ft. of overburden consisting of clays, tills, boulders, sands and gravels that requires rotary mud drilling a 15-inch hole with tricone bits and setting 1234-inch casing to the kimberlite contact.

The drilling system is then changed to dual-wall, large-diameter pipe with open-centre specially designed bits using air flushing. The kimberlite is penetrated and all kimberlite material cut flows up the inner area of the dual-wall pipe into a cyclone and over a screened shale shaker into the bulk sample bags. When completed, the surface casing is pulled and the hole plugged and abandoned.

The benefit of the reverse circulation system is that as the kimberlite is drilled, it is isolated from the remainder of the formation by the outer pipe to provide an accurate non-contaminated sample. This is important for stratigraphic and geological data purposes. S D S fabricates bits based on formation hardness to maximize chip size and optimize formation recovery. The Lac de Gras area presents a completely different, and much more complex, set of circumstances. To date, most kimberlite pipes have been discovered below existing lakes varying in size and depths of up to 160 ft. of water. Bulk sampling of the area can only be done during the winter months when the access roads and lakes are frozen sufficiently to allow the movement and support of heavy equipment.

The drilling for bulk samples on a lake involves drilling a 14-inch hole through the ice and setting a 1234-inch casing and shoe to lake bottom. Water depths of up to 170 ft. have been encountered. Most lake bottoms consist of sands, gravel and boulders, in depths ranging from 20 ft. to 150 ft.

This overburden material is drilled and cased off to the kimberlite contact using downhole tools and air. The kimberlite is then sampled to depths of approximately 850 ft. using the large diameter dual-wall pipe with specially designed 1058-inch bits.

Air is used as the circulating medium to flush the kimberlite up the inner pipe of the dual-wall system into a cyclone and over a screened shale shaker into sample bags. Upon completion, all surface casing is pulled and the hole abandoned. Ice thickness and setup procedures are critical for a successful hole completion.

The bulk sample is screened, prior to collection, to eliminate water and fines. Dewatering screens are adjusted to client’s specifications regarding fine sizes. Significant amounts of formation water have also been encountered that must be controlled to prevent flooding of the working area. In practice, control of water has presented serious problems when working amid winter arctic conditions.

Drilling is performed under severe winter weather conditions where temperatures range to 50 F., frequently accompanied by strong winds with occasional whiteouts. When whiteout conditions occur, movement of equipment is impossible.

All equipment working in this environment must be extremely well winterized, and wind barriers for personnel, as well as protective clothing, are essential. Harsh conditions have presented a multitude of maintenance-related problems with respect to high-horsepower engines and gear boxes. The first opportunity for S D S to sample kimberlite came in the early 1980s, on a 2-year reverse-circulation drilling project for a Falconbridge-De Beers joint venture in the Central Kalahari Desert region of Botswana in Africa. After completing an extensive exploration program, S D S conducted a bulk sample operation on a selected target pipe.