OREAS 61e

OREAS 61e was prepared from coarse reject splits of gold-silver ore samples from the Cracow mine located 500km northwest of Brisbane in Queensland, Australia. Cracow is a low sulphidation epithermal deposit hosted by meta-andesitic volcanics. High grade gold mineralisation occurs within fissure quartz veins and is associated with zones of silicification, present as quartz lode breccia and as quartz vein breccia.

Twenty-six commercial analytical laboratories participated in the program to characterise Au and Ag. The following methods were employed:

  • Au by 26 labs via fire assay with AAS (21 labs) or ICP-OES (5 labs) finish;
  • Instrumental neutron activation analysis for Au on 20 x 1g subsamples to confirm homogeneity (1 lab);
  • Ag via four acid digestion with ICP-OES (17 labs), AAS (4 labs) or ICP-MS (3 labs) finish except for 2 labs that used a 3-acid digestion;
  • S was also determined via four acid digestion with ICP-OES (5 labs);
  • Ag by 24 labs via aqua regia digestion with ICP-OES (18 labs), ICP-MS (4 labs) or AAS (2 labs) finish;
  • Au by 15 labs via aqua regia digestion with ICP-MS (8 labs), AAS finish (4 labs), graphite furnace AAS (2 labs) or solvent extraction AAS (1 lab) finish.
Analyte Certified Value 1SD 95% Confidence Limits Low 95% Confidence Limits High Method
Au, Gold (ppm) 4.43 0.152 4.38 4.48 Pb Fire Assay
Ag, Silver (ppm) 5.27 0.431 5.10 5.44 4-Acid Digestion
Au, Gold (ppm) 4.51 0.264 4.39 4.63 Aqua Regia Digestion
S, Sulphur (wt.%) 0.790 0.029 0.757 0.823 4-Acid Digestion
Ag, Silver (ppm) 5.37 0.382 5.21 5.54 Aqua Regia Digestion
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Specifications