OREAS 64

OREAS 64 was prepared from a blend of Ag–Au ore materials sourced from the Cerro Moro Mine, Santa Cruz Province, Argentina. The Cerro Moro material represents epithermal precious-metal mineralisation characterised by elevated silver and gold with minor associated base metals.

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

• Gold by Pb collection fire assay (30-40 g charge weight) with gravimetric finish
• Silver by Pb collection fire assay (10-30 g charge weight) with gravimetric finish
• Silver by 4-acid (HNO3-HF-HClO4-HCl) digestion with AAS or ICP-OES finish

To confirm homogeneity, gold by instrumental neutron activation analysis (INAA) was undertaken on 18 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.