Open Pit:
Conventional open cut bench mining methods are used at the Macraes Goldfield. Pits are excavated on level benches 2.5m high within the ore zone (approx. 2.8m high after blasting) and 4m high within the waste zone.
Hydraulic backhoe excavators in the 250t and 360t class are used for mining ore and waste. Ore is mined with different techniques depending on the style of mineralisation.
- Hanging wall lode ore is mined by first removing the hanging-wall waste with an excavator under visual control of a geological technician, then mining the exposed ore. Footwall ore is selectively removed from the underlying footwall waste if it can be visually controlled, otherwise the footwall ore is diluted with the wedge of underlying waste; and
- Stockwork ore is generally mined within the defined ore blocks. Ore blocks are defined with the guidance from a conditionally simulated grade control model.
With this mining method and equipment, the smallest selective mining unit (SMU) used when defining ore blocks is 4m by 4m by 2.5m high (approximately 100t), but blocks are generally a minimum of 500t to minimise dilution.
Mining to date at Macraes has come from thirteen pits comprising (from north to south), Coronation North, Coronation, Deepdell North, Deepdell South, Golden Point, Northwest Pit, Round Hill, Southern Pit, Innes Mills, Innes Mills West, Frasers, Golden Ridge and Golden Bar. Current operations are based in Coronation North ........
