SITUATION ANALYSIS OF THE SMALL-SCALE GOLD ... - WWF

6. conjunction with another excavator, or a conveyor belt, to feed ore into a grizzly
(parallel bar screens) and then into a sluice. Water is only used in the ore
processing phase, not during ore extraction. The water system is „closed,‟ that is,
the effluent is channeled into settling ponds and then re-used. The system
produces considerably less effluent than the hydraulic ore extraction methods.
This system has been tried at the Goliath Berg areas in West-Suriname.
7. Missile river dredging (MRD). River based operations that rely on suction pumps
to vacuum alluvial sediments from the beds of larger rivers. The slurry is then
channeled into a large sluice box on a dredge for primary concentration.
8. Cutter head dredging (CHD). River based operation using a rotating saw-tooth
conical device that penetrates the hard crust in the river bed to retrieve
consolidated material. The suction intake system is basically similar to the missile
dredge.
In the section on amalgamation methods of the referred WWF-Guianas Technical Paper,
Vieira notes that mercury is the preferred chemical in the recovery of gold. It is used in
the mining pit, in the sluice box and during the final clear up process. At Benzdorp the
miners report that only small amounts of mercury are poured into the channel of the
mining pit, through which the slurry is directed to the intake hose of the gravel pump
feeding the sluice box. Mercury is placed behind the riffles if the sluice box has them.
The sluice boxes observed in Benzdorp did not have Hungarian (referred to dredge or
angle iron) riffles. The nomad matting was covered only with expanded metal. During
clean-up of the sluice box small quantities of mercury were used to amalgamate the ore.
Vieira reports that “most miners only amalgamate gravity concentrates. This practice
utilizes less mercury than those mentioned earlier and hence losses to the environment
are significantly reduced. Approximately eight grams of mercury is used to recover one
kilogram of gold, since most of the course gold particles are hand sorted.” Once the ore in
the sluice box has been amalgamated, miners take to a creek or pond or use a barrel or
pail to pan the gangue. The miner is left with a ball of mercury and gold, that is squeezed
through a piece of fine cloth. Next, chemicals (bleach, soap powder and vinegar) are used
to further clean the amalgam.
In Benzdorp, it was observed that during the final wash-phase of the channel in the
mining pit, the miners were very meticulous about recovering every last gram of gold
from the basin in the mine pit channel. Very little mercury was used during final clean-up
of the sluice box. If a retort is used still more mercury is recovered. The amalgam
squeezed through the cloth recovered considerable amounts of mercury. It seems that
most of the mercury used, during final clean-up of the sluice box is recovered. This
information contrasts sharply with reports which suggest that for every kilogram of gold
three to five kilograms of mercury is used. The information from the field and from
Vieira suggests that more thorough field investigations are needed to more precisely
assess mercury use during mining and amalgamation.
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