Cyanide Leaches

 

Commonly referred to as "BLEG" (Bulk Leach Extractable Gold), this technique is typically used on samples known to contain coarse gold. The larger sample weights will help overcome the variability produced by coarse gold, however cyanide solutions are generally not as efficient at extracting Gold as the Fire Assay or Aqua Regia techniques.
Gold assaying by cyanide leach should achieve similar extraction efficiencies as those achieved in the C.I.L. and C.I.P. processes.

The sample is tumbled for 24 hours in a 0.1% Sodium Cyanide solution maintained at a pH of 10. After settling, an aliquot of the supernatant liquor is taken and analysed for Gold by ICP-Mass Spectrometry. Brand new containers are used for every sample, thus eliminating any chance of cross contamination. A Detection limit of 0.02ppb Gold is readily achieved in the following methods. A range of other elements can also be analysed from the same solution.

Method Name	Method Code
2 gram Micro Cyanide Leach	BL005
50 gram Mini BLEG	BL003
1 kilogram BLEG	BL001
2 kilogram BLEG	BL004
5 kilogram BLEG	BL002
200 gram "Leachwell" extraction	LWB005

 

The Micro Cyanide Leach often finds use when only small sample weights are available. Mini-BLEGs are very reliable in their own right, bearing in mind the sample weight is the same as used in conventional fire assay. Mini-BLEGs are also used within the laboratory as a method of checking and providing duplicate analyses for normal BLEG samples. Cyanide extraction using "Leachwell" additives is also available.

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