2.1 Alternatives to the Proposal
As the proposal is to expand and upgrade an existing mine there were no requirements for the proponent to consider or address alternatives to the proposal except to consider alternatives to components of the proposal.
2.2 The Mine
The proposal aims to optimise the gold available in the four existing pits by combining and deepening the pits to a maximum depth of 155 metres, and expanding the combined pit surface area from 34 hectares to about 46 hectares. The existing waste rock dumps will be combined and increased in surface area from about 30 hectares to about 50 hectares and increased in height by about 20 metres to 45 metres. Mining operations will continue as before, and be carried out by mining and earth moving contractors using hydraulic excavators and 85 tonne dump trucks. Production of ore will be expanded to around 2-3,000,000 tonnes per year over a 4-5 year period. Figure 2 shows the mine layout.
Processing of the ore will change from heap leach to a Resin in Leach (RIL) process, a new technology to Australia. Feasibility and design studies are underway for two other RIL plants in Australia. The change in process means that a ball mill will be required to treat the ore. Cyanide is still used but resin beads rather than carbon is used to adsorb the gold cyanide complex (ion exchange). The resin is required because of the carbonaceous material that occurs naturally in the Rustler's Roost primary ore. Kerosene is also required in the process to deactivate the carbonaceous material which would otherwise adsorb the gold cyanide complex. Dosage rates up to 1500 grams/tonne of ore are expected which at the maximum production rate of 3,000,000 tonnes of ore per year means up to 4,500 tonnes of kerosene will be used annually. To keep operating costs low it is in the interest of the proponent to ensure that a minimum of kerosene is used.
Because of the change in process, tailings will be produced which means a tailings dam will be required for tailings disposal. The new tailings dam will cover an area of about 62 hectares. Current land requirements at the mine are 104 hectares whilst the proposed expansion and upgrade will increase this requirement to 181 hectares. The water usage at the mine will increase considerably because of the new process. Water will be supplied from local bores, pit dewatering and surface water catchment. This water will be stored in Annie Dam, an existing dam adjacent to the mine that was previously used for pastoral purposes. Process water will be recycled within the plant or directed to the tailings dam for storage and subsequent reuse in the plant.
In addition the heap leach pads will be decommissioned and the mine infrastructure and workforce will expand. The mine and all its facilities are located within Minerals Lease North (MLN) 1083.
2.3 Major Issues
The major environmental issues associated with the proposed expansion and upgrading of the Rustler's Roost Gold Mine are:
- new technology, Resin in Leach;
- tailings dam;
- waste rock management; and
- water management including acid rock drainage.