OREAS 295

OREAS 295 has been prepared from underground sample material from the Ventersdorp Contact Reef (VCR). The material was provided by AngloGold Ashanti from the Mponeng Mine which is located 80 km west of Johannesburg in the West Wits mining district. The VCR is the youngest of the Witwatersrand palaeoplacers and comprises a gold bearing quartz pebble conglomerate preserved on a terraced unconformity surface and buried by the 2.7 Ga Ventersdorp Lava. The VCR and the footwall Witwatersrand sediments were modified (cooked) post burial by lower greenschist level hydrothermal metamorphism. This overprinting event remobilised some of the gold and pyrite within the conglomerate matrix; and deposited minor authigenic pyrrhotite, chalcopyrite, sphalerite and galena. These Reef samples were taken underground for grade control purposes and assayed. The pulp reject material was then sorted into different grade bins for the purposes of CRM manufacture. Barren quartz and granodiorite have been added to the pulps to achieve targeted CRM grades.

Thirty-four commercial analytical laboratories participated in the program to certify:

  • Gold by fire assay;
  • Major and trace elements by borate fusion with XRF;
  • Uranium by fusion with ICP-MS;
  • Full ICP-OES and ICP-MS elemental suites by borate and peroxide fusion;
  • Full ICP-OES and ICP-MS elemental suites by 4-acid digestion;
  • Specific gravity by gas and liquid pycnometry;
  • Total Sulphur by infrared combustion furnace.
Analyte Certified Value 1SD 95% Confidence Limits Low 95% Confidence Limits High Method
Au, Gold (ppm) 0.313 0.011 0.310 0.316 Pb Fire Assay
Al2O3, Aluminium(III) oxide (wt.%) 3.90 0.046 3.88 3.92 Borate Fusion XRF
BaO, Barium oxide (ppm) 296 53 260 332 Borate Fusion XRF
CaO, Calcium oxide (wt.%) 0.710 0.010 0.705 0.715 Borate Fusion XRF
Fe2O3, Iron(III) oxide (wt.%) 1.55 0.021 1.54 1.56 Borate Fusion XRF
K2O, Potassium oxide (wt.%) 0.886 0.008 0.882 0.890 Borate Fusion XRF
MgO, Magnesium oxide (wt.%) 0.365 0.010 0.360 0.370 Borate Fusion XRF
MnO, Manganese oxide (wt.%) 0.017 0.004 0.015 0.018 Borate Fusion XRF
Na2O, Sodium oxide (wt.%) 0.663 0.016 0.654 0.671 Borate Fusion XRF
P2O5, Phosphorus(V) oxide (wt.%) 0.050 0.004 0.049 0.052 Borate Fusion XRF
S, Sulphur (wt.%) 0.096 0.005 0.093 0.099 Borate Fusion XRF
SiO2, Silicon dioxide (wt.%) 91.07 0.487 90.86 91.29 Borate Fusion XRF
TiO2, Titanium dioxide (wt.%) 0.190 0.007 0.187 0.193 Borate Fusion XRF
U3O8, Uranium(V,VI) oxide (ppm) < 10.0 IND IND IND Borate Fusion XRF
Zn, Zinc (ppm) 24.8 5.5 20.4 29.1 Borate Fusion XRF
Zr, Zirconium (ppm) 77 21 61 94 Borate Fusion XRF
U, Uranium (ppm) 6.06 0.276 5.73 6.39 Borate / Peroxide Fusion ICP
LOI1000, Loss On Ignition @1000 °C (wt.%) 0.305 0.101 0.247 0.363 Thermogravimetry
Ag, Silver (ppm) 0.084 0.016 0.075 0.093 4-Acid Digestion
Al, Aluminium (wt.%) 2.05 0.065 2.02 2.07 4-Acid Digestion
As, Arsenic (ppm) 6.55 0.641 6.14 6.97 4-Acid Digestion
Ba, Barium (ppm) 274 15 268 279 4-Acid Digestion
Be, Beryllium (ppm) 0.72 0.051 0.70 0.74 4-Acid Digestion
Bi, Bismuth (ppm) 0.27 0.03 0.25 0.28 4-Acid Digestion
Ca, Calcium (wt.%) 0.514 0.017 0.506 0.521 4-Acid Digestion
Cd, Cadmium (ppm) 0.072 0.008 0.069 0.075 4-Acid Digestion
Ce, Cerium (ppm) 23.2 1.59 22.5 23.8 4-Acid Digestion
Co, Cobalt (ppm) 5.68 0.554 5.43 5.93 4-Acid Digestion
Cr, Chromium (ppm) 51 11 46 56 4-Acid Digestion
Cs, Caesium (ppm) 2.86 0.106 2.82 2.90 4-Acid Digestion
Cu, Copper (ppm) 15.1 1.20 14.6 15.5 4-Acid Digestion
Dy, Dysprosium (ppm) 1.20 0.102 1.13 1.27 4-Acid Digestion
Er, Erbium (ppm) 0.51 0.08 0.45 0.56 4-Acid Digestion
Eu, Europium (ppm) 0.41 0.024 0.40 0.43 4-Acid Digestion
Fe, Iron (wt.%) 1.08 0.035 1.07 1.10 4-Acid Digestion
Ga, Gallium (ppm) 5.40 0.325 5.25 5.55 4-Acid Digestion
Gd, Gadolinium (ppm) 1.78 0.19 1.66 1.89 4-Acid Digestion
Hf, Hafnium (ppm) 0.76 0.11 0.71 0.81 4-Acid Digestion
Ho, Holmium (ppm) 0.20 0.018 0.19 0.22 4-Acid Digestion
In, Indium (ppm) 0.019 0.004 0.017 0.021 4-Acid Digestion
K, Potassium (wt.%) 0.739 0.023 0.729 0.748 4-Acid Digestion
La, Lanthanum (ppm) 11.2 0.68 10.9 11.5 4-Acid Digestion
Li, Lithium (ppm) 25.7 0.96 25.3 26.2 4-Acid Digestion
Lu, Lutetium (ppm) 0.061 0.005 0.058 0.064 4-Acid Digestion
Mg, Magnesium (wt.%) 0.220 0.010 0.216 0.224 4-Acid Digestion
Mn, Manganese (wt.%) 0.011 0.000 0.011 0.012 4-Acid Digestion
Mo, Molybdenum (ppm) 2.15 0.111 2.11 2.19 4-Acid Digestion
Na, Sodium (wt.%) 0.494 0.024 0.484 0.504 4-Acid Digestion
Nb, Niobium (ppm) 3.55 0.180 3.47 3.63 4-Acid Digestion
Nd, Neodymium (ppm) 10.5 0.65 10.1 10.8 4-Acid Digestion
Ni, Nickel (ppm) 22.5 1.41 22.0 23.1 4-Acid Digestion
P, Phosphorus (wt.%) 0.021 0.001 0.021 0.022 4-Acid Digestion
Pb, Lead (ppm) 14.2 0.87 13.8 14.6 4-Acid Digestion
Pr, Praseodymium (ppm) 2.69 0.127 2.61 2.77 4-Acid Digestion
Rb, Rubidium (ppm) 44.0 1.52 43.3 44.7 4-Acid Digestion
S, Sulphur (wt.%) 0.099 0.008 0.095 0.103 4-Acid Digestion
Sb, Antimony (ppm) 0.29 0.023 0.28 0.30 4-Acid Digestion
Sc, Scandium (ppm) 2.59 0.26 2.45 2.74 4-Acid Digestion
Sm, Samarium (ppm) 2.11 0.136 2.06 2.16 4-Acid Digestion
Sn, Tin (ppm) 1.43 0.134 1.36 1.49 4-Acid Digestion
Sr, Strontium (ppm) 40.3 1.88 39.5 41.1 4-Acid Digestion
Ta, Tantalum (ppm) 0.36 0.030 0.34 0.38 4-Acid Digestion
Tb, Terbium (ppm) 0.25 0.022 0.23 0.27 4-Acid Digestion
Te, Tellurium (ppm) < 0.050 IND IND IND 4-Acid Digestion
Th, Thorium (ppm) 4.81 0.241 4.73 4.88 4-Acid Digestion
Ti, Titanium (wt.%) 0.109 0.005 0.107 0.111 4-Acid Digestion
Tl, Thallium (ppm) 0.25 0.014 0.24 0.26 4-Acid Digestion
U, Uranium (ppm) 5.98 0.362 5.83 6.13 4-Acid Digestion
V, Vanadium (ppm) 18.9 0.92 18.5 19.2 4-Acid Digestion
W, Tungsten (ppm) 2.17 0.31 2.06 2.28 4-Acid Digestion
Y, Yttrium (ppm) 4.88 0.193 4.79 4.96 4-Acid Digestion
Yb, Ytterbium (ppm) 0.45 0.05 0.42 0.48 4-Acid Digestion
Zn, Zinc (ppm) 23.6 1.79 22.8 24.4 4-Acid Digestion
Zr, Zirconium (ppm) 24.2 4.3 22.4 26.0 4-Acid Digestion
S, Sulphur (wt.%) 0.091 0.011 0.087 0.096 Infrared Combustion
SG, Specific Gravity (Unity) 2.67 0.067 2.63 2.70 Gas / Liquid Pycnometry
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