Cadia Hill is one of the largest open pit gold-copper mines in Australia. The Cadia Hill ore body, discovered in 1992, is a large, low grade ore body which lends itself to economies of scale through the use of bulk mining and treatment techniques. Construction commenced in October 1996 and the project was completed on time and on budget prior to the start of operations in August 1998.
The mineralization at Cadia Hill lies within a northwest trending corridor that is approximately two kilometres wide and six kilometres long. The geology is characterized by a late Ordovician monzonite which intrudes a sequence of Ordovician volcanics and sediments. The gold-copper mineralization is hosted by sheeted quartz veins in Upper Ordovician basaltic to andesitic volcanics and monzonitic intrusives with the monzonite phase of the intrusive complex being the principal host.
The open pit has been designed in four stages with progressive cut-backs to expose the lower benches. The pit is currently approximately 650 metres below the original surface and will ultimately extend to approximately 870 metres below the surface. Open pit mining uses conventional truck and hydraulic excavator operations with an owner operated fleet.
Total material movement will decline over the coming years, due to the reduction in required waste removal as the pit becomes deeper.
Ore from Cadia Hill is processed through a plant comprising a crushing, grinding and flotation circuit to produce a gold rich copper concentrate. The two stage grinding circuit uses a single 20 MW semi-autogenous grinding (SAG) mill followed by two 9 MW ball mills in parallel. Finely ground ore is then treated by a conventional flotation process to recover the copper sulphides and gold into copper concentrate containing elevated gold levels.
A gravity circuit incorporated in the grinding circuit recovers approximately 20% of the total gold. This gravity gold is smelted on-site to produce gold bars (doré). The remainder of the recovered gold is contained within the gold-copper concentrate.
A notable aspect of the Cadia Hill concentrator design is the use of high capacity equipment in a single processing line to minimize capital and operating costs.
The gold-copper concentrates from both Cadia Hill and the adjacent Ridgeway treatment plants are combined and pumped as slurry to a filtration plant in the nearby town of Blayney. The concentrate is then de-watered before being transported by rail to Port Kembla for shipment to smelters in the East Asia region, primarily Japan and South Korea.
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