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Fire Assaying Today (cont'd)
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- The amount of gold and silver individually can be
determined by removing the silver by "parting"
with nitric acid, in which the silver dissolves but the
gold does not. After the nitric acid solution that
contains the silver is carefully poured away from the
gold bead, the remaining gold is fused (annealed) by
heating, then cooled and reweighed. This yields the
amount of gold in the sample, and by difference the
amount of silver in the sample. (Other analytical
techniques for the final determination of this
concentrate of gold and silver and the platinum-group
elements can be used, too.)
- This small bar of gold was refined by the fire assay
method.
Detailed descriptions of present day methods of fire assaying
can be found in Hafferty, J., L. B. Riley, and W. D. Goss, A
Manual on fire assaying and Determiniation of the Noble Metals in
Geological Materials, U.S. Geological Survey Bulletin 1445,
Washington DC, 1977; and Bugbee, E. E., A Textbook of Fire
Assaying, John Wiley and Sons, Inc., New York, 1940.
Not all assayers use well established techniques, such as fire
assaying, and some assayers have been known to be crooks (see
section on Mining Scams ).
