ISOTOPE RATIO AND TRACE-ELEMENT IMAGING OF PYRITE GRAINS IN GOLD ORES

Secondary ion mass spectrometry techniques for imaging measurements of S-34/S-32 isotope ratios and quantitative trace element concentrations in pyrite mineral grains have been demonstrated. Test samples show that the S-34/S-32 isotope ratios are constant within Poisson error, independent of image position. Variable S-34/S-32 isotope ratios have been found within a single pyrite grain in a sample of gold ore from the Carlin mine in the Carlin District of Nevada. The locations of trace gold concentrations in this ore sample correlate with relative S-34 enrichment. Imaging has the inherent problem of spreading already limited minor isotope signals among many pixels. This problem can be overcome with improved analysis methodology including new electron multiplier circuitry to accommodate more intense secondary ion signals, stable data collection over relatively long time periods, and improved software. High mass resolution imaging and careful neutralization of ion beam induced sample charging are also required.