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Intertek Minerals
Precious Metals AnalysisIntertek’s leading expertise and wide
range of services,with state-of-the-art facilities, staffed with
local experts,are critical to the minerals and mining
industries.
Intertek understands the process and in-depth analytical
requirements involved in supporting precious metals
mineralexploration, including resource estimation and the
issuesfacing explorers when analysing for precious metals.
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A diverse range of precious metals techniques are available for
applications ranging fromgrassroots exploration, where sub ppb
sensitivities are required, to accurate resourceestimation and
grade control. For gold determination lead collection fire assay
remainsthe classic method, however, aqua regia digestion,
accelerated cyanide leach and BLEGare other options that are
available for specific purposes. Platinum and palladium canalso be
detected using some of these methods. The full suite of platinum
group elements
can only be determined by nickel sulphide collection fire
assay.
Lead Collection Fire Assay
Lead collection fire assay remains the method of choice for
quantitative golddetermination and this technique is also effective
for platinum and palladium. Thesamples are mixed with a flux
containing lead oxide (litharge). The lead oxide is reducedby an
organic material to metallic lead which quantitatively collects the
gold and PGEs.The lead is removed from the previous metals by
oxidation and absorption in a processcalled cupellation. The fire
assay flux mixture has been carefully formulated to
optimiseprecious metal recovery in diverse mineralogical matrices.
Difficult sample matricesmay necessitate a reduction in the charge
weight and modification of the flux mixture.Samples submitted for
the trace determination of gold, platinum or palladium are fusedin
new pots using dedicated equipment.
Nickel Sulphide Collection Fire AssayThe nickel sulphide
collection fire assay process has been designed to
quantitativelyrecover all of the platinum group elements. The
samples are mixed and fused with aflux containing nickel oxide and
sulphur. The nickel oxide is reduced to nickel sulphidewhich
quantitatively collects the gold and PGEs. The Au and PGE sulphides
are separatedfrom the nickel sulphide, dissolved and determined by
ICP-MS. Special precautions aretaken to retain osmium. Some
reduction in charge weight may be necessary for difficultsample
matrices. All nickel sulphide collections are done using new
pots.
Screen Fire Assay
Screen fire assay is used to quantify the gold content of
samples where conventional50gram assays are subject to an
unacceptable sampling error resulting from coarse gold.
The process involves screening a nominal 1kg sample and firing
the entire coarsefraction, including the screen cloth. Duplicate
assays are carried out on the undersizefraction which is more
reproducible due to the smaller gold particle sizes. The totalgold
(or platinum and palladium) content is calculated as a weighted
mean of themeasured grades of the two screen fractions. This is
reported alongside the individualfraction results.
Aqua Regia Digestion
Aqua regia is a useful screening tool for grassroots exploration
and is a cost effectiveway to analyse for gold and other elements.
Lower detection limits are achieved utilisingGraphite Furnace
AAS.
Many minerals will digest effectively in aqua regia, however,
silicates and refractory
minerals will remain largely undigested. Aqua regia digestions
are suitable forexploration purposes only and are not recommended
for resource analyses.
Cyanide Leaches
Cyanide solutions are used to leach gold from large samples
providing a useful methodfor both grassroots exploration and
resource work. BLEG (Bulk Leach Extractable Gold)is usually
performed on screened stream sediment samples, providing detection
of lowlevel anomalies for regional exploration. High grade leaches
utilise the LeachWELLTMaccelerant to extract the cyanide
extractable gold. This is an indication of what would berecovered
in routine metallurgical processes.
Contact DetailsJohn FlynnDirector, Business Development
15 Davison Street, Maddington, Western Australia, 6109Telephone:
+61 8 9251 8100Email: [email protected]
