Neutron Activation Analysis for Platinum Group Elements and Gold in Chromitites

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Abstract
Noble metals are inhomobeneously distributed as discrete minerals and to a limited extent in solid solution in sulfides, silicates and chromian spinel. A N1-N1 sulfide bead fire assay technique has been adapted to analyse noble metals in chromiterich rocks and chromitites. The fire assay technique concentrates the noble metals into a nickel sulfide button. Upon dissolution of the button, the Pt group elements and Au remain as a residue and are filtered off for analysis. The previous method employed a sodium borate-sodium carbonate flux which did not dissolve chromite grains. It is found that a lithium tetraborate-sodium carbonate flux attacks the chromite to form a worm-like residium of chromian sesquioxide, which allows access to inclusions and elements held in solid solution in the chromite. Losses during the fire assay have been checked by spiking the charge with noble metal radiotracers and found to be within 10 percent of the amount present. The technique has also been checked by making replicate analyses of a noble metal-bearing chromite-rich ore.