OREAS 505c

OREAS 505c was prepared from a blend of copper–gold ores, barren granitic material, and minor amounts of copper and molybdenum concentrates. The principal ore component was sourced from Northparkes Mines, New South Wales, Australia, together with lesser quantities of porphyry-related materials from Australia and Papua New Guinea. Barren granite sourced from a quarry in northern Melbourne, Australia, comprises mafic S-type Late Devonian Bulla Granodiorite and was included to achieve the target copper and gold grades while maintaining matrix similarity to typical porphyry Cu–Au systems.

Twenty-five commercial analytical laboratories participated in the program to certify the elements reported below using the following methods:

• Gold by Pb collection fire assay (25-30 g charge weight) with AAS or ICP-OES finish
• Gold by aqua regia digestion (10-50g sample weight) with AAS or ICP-MS finish
• Full ICP-OES and ICP-MS elemental suites by four-acid (HNO3–HF–HClO4–HCl) digestion
• Full ICP-OES and ICP-MS elemental suites by aqua regia digestion

To confirm homogeneity, gold by instrumental neutron activation analysis (INAA) was undertaken on 20 x 85mg. This format enabled a nested ANOVA treatment of the INAA results to compare within- and between-unit variances, providing a statistical measure of batch homogeneity.