A RAPID FIELD ANALYTICAL METHOD FOR GOLD IN GEOCHEMICAL-EXPLORATION

A rapid field method for gold analysis in geochemical exploration has been developed. Cold extraction of Au, at room temperature, using a mi xture of sodium bromide, sulphuric acid, hydrogen peroxide is performe d; the technique has the advantage of avoiding the irritating odour of commonly used aqua regia digestion. Polyurethane foam is used to conc entrate gold from solution. After desorption of Au using mixed reagent s (0.5% Na2SO3-NaCl solution at pH 8), two sequential procedures, depe nding on the concentration, are followed for the determination of gold . (i) A 1 mL portion of desorbed solution is used to form Au-TMK-DBS ( Thio Micher's Ketone and dodecyl benzene sodium sulphonate) ternary co mplex. Concentrations below 20 ng/g Au are determined by visual colour comparison of the organic layer with a series of standards. (2) If th e concentration is greater than 20 ng/g Au, a complexation reaction us ing the same reagents is followed by fibre-optic colorimetry. The meth od is rapid and simple, and the tiresome operation of ashing the foam is avoided. The limit of detection is 0.5 ng/g Au and eighty determina tions can be made in one working day. The method could be used for rap id follow-up of rock sample or in situ drill core analyses. About 600 samples from 5 gold districts were tested by this method. The results are very satisfactory.