The Similkameen Copper Project located near Princeton, British Columbia, is operated by the Similkameen Mining Company Limited, a wholly-owned subsidiary of Newmont Mining Company. The orebodies for this project are located on both sides of the Similkameen River for which the project is named.
The Pipeline Tunnel
To complete a tailing line routing to Smelter Lake, a tunnel with clearance dimensions 10 feet wide by 8 feet high approximately 800 feet long was driven where an area of sheer cliffs blocked access. The tunnel was driven on a downward slope of 1 percent in the direction of tailing flow so that any leakage of tailing would flow naturally into the impoundment area and eliminate this portion of the line as a possible source for escape of tailing into streams. A suitable location was found which provided an adit elevation about 100 feet below plant discharge elevation.
The tailing pipeline material chosen was 20 inch spiral-weld abrasion resistant steel with ¼ inch wall thickness in 40 foot random lengths equipped with end fittings for assembly by wedge-lock couplings. The pipe has a minimum Brinnell of 170 having an approximate analysis of 0.70 percent Mn, .015 Si, 0.50 percent C. Under normal rating, pulp velocity in the pipe is about 8.3 feet per second. Minimum downgrade slope is one percent. Maximum upgrade slope is 10 percent. Where possible the pipe is supported on timber sleepers. Where the pipe crosses roads, it is encased in reinforced concrete so that a concrete pipe remains even though the steel may wear away completely.
Despite the project location in the heart of a sportsman’s paradise teeming with fish and game, no objection was raised to the use of Smelter Lake as a tailing pond. The lake had eutrophied naturally from a collection of organic debris and silt. It was unable to support fish life despite a number of plantings. The presence of silt and organic debris was not, however, conducive to ideal foundation conditions for the dams. A foundation exploration, program disclosed that the silts and debris were impounded and not a part of the alluvial sand and gravel which had created plugs in the canyon to form the lake in the first place. Suitable locations were found on the alluvial plugs which permitted dam construction downstream of unstable material but yet upstream of tributary creeks which could wash away dam construction. Starter dams were constructed of compacted zoned fill available in the immediate vicinity to a height of 70 feet above lake level.
The starter dams were constructed with downstream drainage blankets to relieve hydraulic pressure from possible seepage through foundation material and dam structures. Slopes on the starter dams were placed at 2-½ to 1 to provide safety factor for seismic disturbance. Steeper slopes would have created higher unit pressures on the somewhat variable foundation material. The dams are scheduled for raising to an ultimate height of about 200 feet by placement of tailing sands downstream of the starter dams. Sand fill will be placed in compacted layers to produce a downstream slope of 3 to 1.
The Cycloned Sand System
In order to provide a source of relatively clean tailing sand fraction for dam raising, a cyclone station was located near the west end of Smelter Lake. The station was composed of four 30 inch cyclones pressurized from a 25 foot high drop structure. This facility will produce a coarse split, nominally 80 percent plus 200 mesh from 40 percent of whole tailing solids. The elevation of sand discharge was above ultimate pond level and sand could be transported by gravity at 60 percent solids for discharge at the west dam. The east dam was two miles from this location. It did not appear economical to carry whole tailing in a 20 inch pipeline this distance in rugged terrain along the canyon wall of the lake and to construct a duplicate cyclone station at the pipeline discharge.