Comparison of Recoveries by Lead Fire Assay and Nickel Sulfide Fire Assay in the Determination of Gold/ Platinum/ Palladium and Rhenium in Sulfide Ore Samples

We compared the recovery of gold, palladium and platinum by two fire assaying procedures, using nickel sulfide and lead as collectors. The presence of appreciable amounts of sulfide minerals in the sample caused interferences in both procedures. An in-house reference sample, a reference sample of high-grade sulfide ore and samples of high sulfide content from the Recsk porphyry copper ore in Hungary were analysed by both methods. The elements were determined by inductively coupled plasma-atomic emission (ICP-AES) and/or inductively coupled plasma-mass spectrometry (ICP-MS). It was found that for the sulfide ore samples, the recoveries of Au and Pd are sometimes lower by nickel sulfide fire assay than by lead fire assay. Recovery of Re by nickel sulfide fire assay was found to be low: the average recovery of five repeated analyses of the reference sample NIST SRM 330 was 9% with a relative standard deviation of 48%. Increasing the amount of S in the fusion flux gave better recovery.