Analysis of gold in geologic samples: Colorimetric method to be used in the field

A method is presented for the analysis of gold in geologic samples. The met hod is based on the digestion with a mixture of potassium bromide, sulfuric acid and hydrogen peroxide solution. The dissolved gold is retained in an activated polyurethane foam. The gold adsorbed is eluted with acetone and i ts concentration is determined spectrophotometrically as a complex with Mit chler's Thiokethone, at a lambda max of 550 nm. The method permits detectio n in samples near 50 ppb. The use of a column of silica gel, allows the sep aration of the gold complex from metals that could interfere with the measu rement. The method was tested several times with many soil samples previous ly analyzed by the ACME and ACTLABS laboratories of Canada, and with certif ied standards of the Canadian Certified Reference Materials Project (CCRMP) . The method precision is on average 10% and the accuracy is 5-10%. The adv antages of this method are the short time required for the analysis, its lo w cost, and the possibility to carry a kit and perform gold analysis in the field, for geochemical exploration or mineral deposit exploitation.