A new gold cyanidation assay technique has been proven for a range of
ores, where it has demonstrated benefits of being: Accurate (reduces the typical range of assay scatter almost
three-fold, and avoids common fire assay interferences). Fast (under one hour, providing a quantum shift in space
requirement and equipment utilisation each bottle roll can
provide over 15 determinations per day). Simple (suitable for field application, no high skill or experience
requirements). Profitable (reduced drilling, drilling time, ore misclassification
and/or double handling after mining). Cheap (far lower cost than Fire or Aqua Regia Assays, ie
LeachWELLTM costs around 10 for a 20 g sample at 50 per cent
solids, proportionately greater for larger samples eg $1 for 200 g
samples which address most nugget effect problems). Relevant (distinguishes economic. ie cyanide-extractable gold, the
only unequivocal value to use for true resource definition, mine
planning and grade control). Robust (rough bucket chemistry of samplers does not seriously
affect results). A new development is the provision of LeachWELLTM CAS, a
solution, which also contains optimum cyanide and stabiliser
concentrations; and offers greater: Safety (the dilute cyanide solutions are stabilised to avoid
generating toxic HCN vapours; and present no cyanide dust or
flying chips to deal with). Ease (a single squirt dispenses precise quantities of the entire
reagent suite, avoiding multiple weighings). Reduction in total reagent costs. An inter-laboratory comparison on nine ore types, using two assay
techniques (Fire Assay and Aqua Regia) involving 45 laboratories, has
demonstrated that LeachWELLTM 60X assays for the samples tested,
were equally or more reliable than typical Fire or Aqua Regia Assays. There is particularly great benefit in applying LeachWELLTM 60X
assays to richer ores in comparison to Aqua Regia assays, which appear to
be prone to very significant underassaying depending on individual
analyst skills, and which often suffer greater nugget effects. The major impacts for heap leaching are that: Using the LeachWELLTM assay technique for grade control, ore of
marginal grade is not accidentally discarded to waste or visa versa
due to the scatter of assay data inherent in typical small charge
(25 g) fire assays. LeachWELLTM assays very importantly report only that gold
which will be recoverable in the heap, viz that which is liberated
- an important factor where the coarse crush often leaves ten per
cent of gold unliberated. These impacts are of particular importance for many ores (ie most of
those recovered from open pit operations and at the margins of rich ore
subject to slurry processing) subjected to heap leaching as the oxide zones
often present major problems of nugget effects as well as mineralisation
that cannot be accurately assigned through interpretation of clear
structural controls.