Trace Analysis of Au in Carbonaceous Gold Ores by Inductively Coupled Plasma Optical Emission Spectrometry and Mass Spectrometry

Abstract

Trace analysis for Au contents in three different gold ores was investigated from aspects of acid digestion conditions of ore samples, the analytical techniques of Au determination, and quantification methods. The results were evaluated in comparison with the reference values by the fire assay. In the standard calibration method, acid digestion of Au in highly reverse aqua regia followed by determination of Au using ICP-OES showed good agreement results with the reference values, when the standard solutions include the same Fe concentration as in unknown samples. Meanwhile, the standard addition method produced the best-fit values to the reference values when the ore samples were digested in highly reverse aqua regia and then Au concentration was determined by ICP-MS. Under the optimal condition with ICP-MS, the limit of detection and the limit of quantification were recorded 0.24 ppb and 0.80 ppb, respectively. The ICP-OES was not suitable in the standard addition method causing the overestimation of Au probably due to the multi-element interference in plasma emission. In case of the limited amounts of samples, the present finding will be practically useful.