World Placer Journal - 2010 - Volume 10, pages 1-20.
Large gold dredges – impacts in USA, Canada, Russia, Mongolia and China.
Robin Grayson1 and Chimed-Erdene Baatar1
(1) Eco-Minex International
|Large bucket-line gold dredges are very destructive of wetlands - but can also create new wetland habitats displaying remarkably good naturalness.|
CLASSIC 'BEST PRACTICE':
Re-soiling dredging areas created high-grade pasture in Australia. The article shows how large bucket-line gold dredges produced gold and made good pasture in Australia 100 years ago.
A long forgotten success story!
The article illustrates the environmental impact of large bucket-line gold dredges. Many trunk valleys in NE China, Siberia and the Russian Far East are extensively damaged, and the damage is spreading. In their wake, the gold dredges leave arcs of dumped gravel (‘bananas’) stacked against one another as long ribbed mounds (‘crocodiles’).
Diagnostic of large bucket-line dredges, these bare mounds of washed gravel can be traced along thousands of kilometres of disrupted floodplains by means of zero-cost remote sensing using Google Earth.
Best Available Techniques (BAT) for mine closure is to ensure the land behind the dredge is immediately re-contoured, topsoiled, planted and given after-care. We demonstrate that BAT was achieved in Australia as early as 100 years ago, and a form of BAT is now seen in Mongolia.
Worst Available Techniques (WAT) for mine closure is abandonment with no attempt to recontour the gravel or spread topsoil. WAT also includes side-casting of overburden by draglines and dozers causing excessive footprint and severe loss of topsoil; and dredging in or near an active river channel leading to continuous discharge of suspended clay and silt for tens of kilometres downstream.
Remote sensing shows WAT to have been the norm in Canada and the USA for a century, and to still be the norm in NE China, Siberia, the Russian Far East and - until recently - Mongolia.
Remote sensing shows WAT to gradually become BAT* by a relentless process of natural seral change to scrub, forests and wetlands of high wildlife value.
The surprise result is a much higher degree of naturalness than by expensive painstaking rehabilitation.
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A RIVAL 'BEST PRACTICE':
Benign neglect of dredging areas created sites of high degree of naturalness in Alaska, California, Montana, China, Russian Far East, Siberia and Mongolia.
The article shows how abandonment and dereliction can produce, eventually, sites with a higher degree of naturalness than possible by expensive reclamation.