The use of nuclear tracers to evaluate the gold recovery efficiency of sauceboxes

CIM Bulletin, Vol. 87, No. 979, 1994

Randy Clarkson, NEW ERA Engineering Corporation, Whitehorse, Yukon

Sluiceboxes can provide a much higher concentration ratio than most other gravity concentrators (up to 50 000:1) at very high overall placer gold recoveries (greater than 99%). They are also very reliable, inexpensive and simple to operate. This combination is very difficult to beat and explains why the sluicebox is still the most important placer gold concentrator in Canada's Yukon Territory. A sluicebox is a rectangular flume containing riffles on matting, through which a dilute slurry of water and alluvial gravel flows. Sluiceboxes operating under ideal conditions are actually centrifugal concentrators whose riffles overturn ribbons of slurry to form vortices. At the bottom of these vortices, centrifugal and gravitational forces combine to drive placer gold particles into matting. Testing sluiceboxes with conventional sampling and evaluation techniques is very costly, time consuming and problematic. The effect of a single gold particle can cause large unpredictable errors (nugget effect) even when large sample volumes are processed with care. Nuclear tracer tests are more accurate, faster, cheaper and safer than conventional sampling. In 1989 through 1991, the recovery efficiency of several sluicing systems was determined by mixing radioactive gold particles (tracers) into the feed streams of 27 placer mines in the Yukon Territory. Four distinct sizes of nuclear tracers were used and their recovery was related to the design and operational characteristics of the individual sluiceboxes and their pay gravels. Over-all gold losses ranged between 71% and 0, or from $2.5 million to less than $1000 per 1200 hour season. One of the triple-run sluiceboxes and one of the single-run boxes lost more gold than they recovered. The sluiceboxes which were fed with pre-screened gravels (minus 25 mm) had the lowest losses of all, averaging only $47,000 per season. Three of these sluiceboxes recovered 99% of their gold. Many of the mine recovery plants tested in 1990 had already implemented recommendations from the 1989 test program including the use of unbacked Nomad matting, coarse expanded metal and 25 mm angle iron riffles. None were using doubled expanded metal riffles and few were using cocoa matting or Monsanto matting. Four operators installed screening equipment which increased their gold recovery by 10% to 20%. Another four operators modified their sluicing systems and increased their gold recovery by 3% to 44%. This paper presents a summary of the existing and potential gold recoveries, and recommends sluicebox designs and operating parameters based on the results of nuclear tracer testworkfrom 1989 through 1991, conventional sampling in 1988 and laboratory investigation in 1989-1990.
Keywords: Gold recover, Mineral processing, Nuclear tracers, Sluiceboxes.