World Placer Journal - 2000 - Volume 1, pages 90-106.
Review of the Gold Dredges in Mongolia, with comments on environmental impacts.
Gerrit Bazuin1, Robin Grayson2,
Frank Mc.Bride3 & Iain Barclay4 (1) General Director of Ochir Leasing Co. Ltd.
(2) General Director of Eco-Minex International Co. Ltd.
(3) General Director of MACSservices Co. Ltd.
(4) former Marketing Director of Eco-Minex International Co. Ltd.
| | Bucket-line gold dredges vanished from North America but are thriving in Mongolia and Siberia... | ABSTRACT Gold dredges are novel in Mongolia, part of the ongoing placer gold boom. Four are operating, plus one ready to assemble and one more planned.
Designs are based on dredges of 50 years ago that used mercury, a discontinued technique. The designs cause coarse tailings to be discharged on top of fine tailings giving an unnatural restored profile. Retroengineering is affordable to create a more natural profile. The dredges use the ‘spud’ system for steerage rather than ‘cable and winch’ system; thus the discharged tailings tend to accumulate in mounds. Conversion would be difficult and not affordable. An alternative would be the addition of a swinging stacker to spread the discharged tailings more evenly. Three of the 4 dredges use sluices of improved type and one uses conventional jigs. Recovery of fine gold would be much higher with ‘sawtooth’ jigs, and the dredges might boost production by 1 ton of gold a year between them. This would give a fast payback, but local interest rates are a prohibitive 4-7% per month, so incentives are needed, such as a tax holiday. The dredges are assisted by land-based draglines to strip off the overburden creating severe environmental impacts, notably steep-sided high mounds of overburden. A switch to cutter-suction dredges to pump the overburden away as slurry would produce more acceptable landforms, but financial incentives are required. A constraint is the ‘swell factor’ that increases the volume of excavated material by 30-50%, so restoration to the original landform is not possible, as complete recompaction is not achievable. Rehabilitation is possible, with scope for ‘wildlife gain’ to create a wetland mosaic. DOWNLOAD ARTICLE
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|  | SIBERIAN-BUILT NEW DREDGE... producing >1 ton of gold a year. Built in Irkutsk in Siberia and using traditional Russian mineral dredge technology. The Mongolian dredge fleet is now four in number, all built in Irkutsk by IZTM. Read the paper for details. | 
| BRITISH-BUILT OLD DREDGE... awaiting assembly in northern Mongolia.
A superb piece of engineering, the authors are doubtful if the dredge can be made operational.
|  | DREDGE IMPACTS!
Retroengineering can help mitigate many of the severe impacts, and draglines are shown to be the main culprit. |
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