Comparative analysis of sulfides for gold using SXRF and SIMS

Sulfides may be analyzed for gold using Secondary Ion Mass Spectrometry (SIMS) and Synchrotron X-Ray Fluorescence (SXRF); we have compared the two methods with respect to instrumental requirements, time, analysis volume, and detection limits. A limitation in this comparison is the inhomogeneous distribution of Au within arsenopyrite, as demonstrated using SIMS imaging for samples from the Sb Bento deposit, Brazil. Analysis of the same grains of arsenopyrite produces good agreement between the two techniques; discrepancies are attributable to slight shifts in analysis locations between the two techniques or the different volumes being analyzed. Whereas SIMS has imaging capability and sub-ppm detection limits, quantitation is difficult. SXRF spectra are relatively simple, and quantitative analysis is not as matrix-dependent as with SIMS. The detection level for Au in arsenopyrite by SXRF is limited by the background from AsK alpha to about 50 ppm, but will be reduced to about 15 ppm using more intense synchrotron sources.