World Placer Journal - 2001 - Volume 2, pages 50-64. | |
Hydraulic riffles offer promise of increasing placer gold recovery from sluice-boxes worldwide....  NEW ZEALAND HYDRAULIC SLUICE  NEW ZEALAND AND SOVIET MARRIAGE... Novel set-up of the gold washing plant! In the background, a traditional Russian-style water cannon (just visible to the top right), blasts water into placer dumped into the metal 'bath'. The operator stops the system occasionally to manhandle large stones out of the way (right), whereas "normal" oversize is simply blasted out to the left from time-to-time. In the foreground a 25m³/hour PAuSE hydraulic riffled sluice from New Zealand replaces the customary Russian-style sluices, in order to maximise gold recovery. | ABSTRACT Two high % gold recovery systems were introduced to the Bugant Goldfield in northern Mongolia: a 25m³/hour New Zealand-built PAuSE Hydraulic Sluice, gravity-fed by slurry from a static screen (40-50mm holes) blasted by a Russian-style water cannon ('monitor'); and an IHC 2-Cell Sawtooth Trapezoidal Jig Plant fed by slurry via a Warman pump from an IHC Conical Screen ('scrubber') with 35mm x 12mm slots. Difficulties were encountered: a) the high water table restricted operations, and a pontoon system is now being considered; b) the oversize was substantial with rounded slabs that damaged the screen, necessitating modifications; c) the high clay content affected washing and a clay washer is now being considered; d) the IHC Conical Screen operated at only 10-15m³/hour, instead of 60-80m³/hour, to minimise damage from large slabs, to allow clay to clear from the grizzly, and to break-up the clay; e) a change of mine ownership delayed mining until early July; f) mining ceased on 2nd October due to the hired trucks being taken to the 'Millennium Road Project'; g) frequent breakdowns of earth-moving equipment (trucks, bulldozers and excavators) occurred; h) the PAuSE NZ Hydraulic Riffled Sluice received enough pay-gravel to operate for only 720 hours (90 days x 8 hours) during the season, 24% of the target 3,100 hours; and i) the IHC jig stood idle for long periods due to a shortage of trucked feed. The advantage of using high % gold recovery systems was lost, even though they easily outperformed Russian sluices. The Russian-style method of mining by bulldozing destroyed 50% more trees than necessary, buried topsoil and sterilised gold reserves. Panning of 13 samples of overburden revealed good to rich grades (0.5-5.0 grams/m³), indicating systematic underestimation of gold by earlier Soviet drilling. |
