Determination of iridium and gold in rock samples by using pre-concentration neutron activation analysis

Nickel sulfide (NiS) fire assay was used for the pre-concentration of Ir and Au in rock samples. The beads obtained after fire assay were irradiated directly with neutrons to determine Ir and Au. To suppress the reaction of (58)Ni(n,p)(58)Co, the fire assay was carried out by using a small amount of Ni (0.0625 g) and the NiS bead samples were irradiated by neutrons with high Cd ratios. Analytical results of Ir and Au for rock samples were close to literature values, confirming that our procedure of INAA with pre-concentration can be applied to rock samples for the determination of ppb to sub-ppb level of Ir and Au.