OREAS 294 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.
| CRM Code |
Principle Certified Values |
State |
Matrix |
Mineralization |
| OREAS 294 |
Au 0.207ppm |
Al2O3 3.91% |
BaO 291ppm |
primary |
quartz |
modified paleoplacer |