Inquiry under s46 into amending the conditions of Ministerial Statement 85.
Worsley Alumina Pty Ltd submitted a Notice of Intent for the mining and processing of supergene and basement ores at the Boddington Gold Mine in July 1989. Following assessment of the Notice of Intent by the Environmental Protection Authority, the Minister for the Environment issued a statement "that the proposal may be implemented" on 22 November 1989 (Ministerial Statement 85).
Further metallurgical testwork carried out by the proponent on the processing of the ores has resulted in modifications to the Notice of Intent and hence has changed the proposal as covered by Condition 1 of the Ministerial approval. The original proposal described using a floatation circuit to process the copper-rich supergene and basement ores rather than the existing carbon in leach process, as the copper could interfere with the carbon in leach circuit used to process the oxide ore. Disposal of the ores treated in the floatation circuit were to be directly disposed of in a separate segment of the existing residue disposal area to prevent contamination of the carbon in leach process water by the floatation reagents.
The modifications to the Notice of Intent are as follows:
- Metallurgical testwork has shown that cyanide leaching of the tailings from the supergene floatation circuit is necessary to maximise gold recovery. It is therefore proposed to expand the pre-leach circuit to include a carbon absorption circuit which will provide additional processing of the supergene and copper-rich basement ores.
- The inclusion of a separate carbon absorption circuit for the supergene floatation taiiings, that will scavenge the floatation reagents, means that the separate residue disposal area is not required. Therefore, the supergene and basement residues will be disposed of in the existing residue disposal area.