Technical Report on the Cadia Valley Operations Property — 2011

This technical report details the processing facilities and planned expansions for the Cadia Valley Operations, including the Cadia and Ridgeway concentrators, as of December 31, 2011.

Report context

This technical report is dated December 31, 2011, and covers the Cadia Valley Operations property owned by Newcrest Mining Limited. The report describes the existing Cadia Concentrator, commissioned in 1998, and the Ridgeway Concentrator, commissioned in 2002. Metallurgical test work and engineering studies have been carried out to assess the design changes required to process ore from the Cadia East project through the Cadia Concentrator. The Ridgeway Concentrator was upgraded in 2008–2009 to maintain plant throughput with harder Ridgeway Deeps ore.

Processing route

Cadia Concentrator – Existing Operations

Ore currently being treated in the Cadia Concentrator is mostly sourced from the Cadia Hill open pit. Cadia Hill mineralization consists of chalcopyrite and native gold with lesser bornite within or disseminated near quartz veins. The flowsheet for the installed plant included semi-autogenous grinding of primary crushed ore, flash flotation and gravity gold recovery, and then conventional flotation involving roughing, scavenging, cleaner and re-cleaner, cleaner scavenging, and concentrate regrind.

The key unit operations in the processing plant are:

• Primary crushing in a 60 inch x 113 inch gyratory crusher.
• Crushed ore storage to a live capacity of 40,000 t and subsequent reclaim facilities.
• Primary open circuit milling in a single 40 foot SAG mill fitted with a 20 MW motor. Oversize pebbles from the SAG mill are crushed in two recycle cone crushers.
• Secondary milling in three ball mills, with the two original mills fitted with 10 MW motors, and a more recently installed third mill with a 16 MW motor. The mills are in closed circuit with cyclone classification for a target grind size of P 80 of 150–190 μm.
• Flash flotation and gravity processing of flash flotation concentrate to produce a gravity gold concentrate for smelting.
• Rougher and scavenger flotation of the slurry from the milling circuit with rougher and scavenger concentrates reporting to cleaner flotation circuits.
• Thickening of rougher/scavenger tailings before pumping to a tailings storage facility.
• Cleaner and scavenger/cleaner flotation with regrind of scavenger/cleaner concentrate in a vertical tower mill.
• Re-cleaning of both cleaner and reground scavenger/cleaner concentrates, and subsequent thickening of final gold-rich copper concentrate.
• Suitable reagent handling and storage facilities for the reagents used in the processing, consisting of collectors, frother, lime, and flocculant.

Raw water is pumped from nearby dams to a raw water tank and then pumped to the raw water distribution main. Raw water, concentrate thickener overflow, concentrate filtration water, and treated effluent water from towns of Orange and Blayney make up process water requirements for the plant.

Final copper concentrate slurry with a grade of 19–22% copper is pumped to the town of Blayney where it is filtered, and then railed to Port Kembla for subsequent shipment to smelters. Approximately 15% of gold in the ore feed to the concentrator is recovered as a gravity concentrate and smelted on site to produce gold bars (doré) for export from the site. The remaining gold reports to copper concentrate.

Staged Expansion of Cadia Concentrator for Cadia East Ore

A staged expansion of the Cadia Concentrator is underway to treat Cadia East ore at a nominal rate of 20 Mtpa. Ore feed to the concentrator will comprise decreasing quantities of fresh ore from the Cadia Hill pit and from stockpiles, as production from Cadia East ramps up. The staged expansion approach reduces the intensity of construction activities, and provides some immediate recovery benefits by early installation of fine grinding equipment.

Stage 1 expansion has been completed. The additional ball mill capacity and associated expanded flash flotation capacity is currently providing a finer primary grind size. Stage 1 included a ball mill 26’x42’ with 16 MW drive, a 52 m3 flash flotation cell, and a tailings thickener 40 m diameter.

In Stage 2, the two existing pebble crushers will be converted to secondary crushers by changing the crushers’ bowl assembly and liner designs. The change is required to maintain plant throughput as the more competent Cadia East ore is incorporated into the plant feed. A new screening circuit and associated conveyors will be installed, and the existing quicklime silo and the SAG ball loading facility relocated. Stage 2 includes two double deck banana screens, with completion expected December 2011.

Stage 3 is aimed at removing constraints in the existing flotation circuit resulting from the higher Cadia East copper head grade and slower flotation kinetics. The flotation circuit will be expanded by progressive installation of a new circuit consisting of rougher flotation, concentrate regrind, cleaner and cleaner/scavenger flotation, re-cleaner flotation, and concentrate storage. Additional concentrate regrind capacity will also be integrated into the existing flotation circuit. It is proposed that increased concentrate pumping capacity and increased filtration capacity will also be installed during Stage 3. Stage 3 includes five 300 m3 rougher flotation cells and one VTM 1250 regrind mill, with completion expected February 2012. Additional pumping capacity and filter plate area are also included, with filter complete and pumping due December 2011.

Stage 3b includes one VTM 1250 regrind mill, three 30 m3 cleaner and cleaner scavenger flotation cells, and one 8 m3 re-cleaner cell, with completion expected in 2014.

In Stage 4, the installation of a high pressure grinding rolls (HPGR) unit is necessitated by the increased proportion of Cadia East underground ore in the plant feed blend. The additional comminution step will allow target throughputs to be maintained despite an increase in ore hardness. Stage 4 includes one HPGR 2.4 m diameter x 1.6 m, 5.8 MW, with completion expected March 2012.

The modifications will allow the plant to achieve the design throughput of 20 Mtpa of Cadia East ore at recoveries in accordance with recovery models determined in test work.

Ridgeway Concentrator

Ore from the Ridgeway mine is processed in the Ridgeway Concentrator. The initial processing flowsheet for treating the ore from the Ridgeway SLC operations was very similar to that of the Cadia Concentrator. In mid-2008, the facilities were expanded to suit the harder Ridgeway Deeps ore. The expansion included installation of a secondary crushing circuit, and additional concentrate regrind capacity with the installation of a 0.93 MW vertical mill. A 2.24 MW vertical mill was installed in March 2011.

The Ridgeway Concentrator includes the following processes:

• Primary crushing in a gyratory crusher.
• Crushed ore storage and subsequent apron feeder reclaim facilities.
• Secondary crushing in a MP800 cone crusher and associated screens.
• Primary open circuit milling in a single SAG mill fitted with a 6.5 MW motor.
• Secondary milling in a 6.5 MW ball mill, in parallel with a Vertimill VTM 1250, both in closed circuit with classifying cyclones. A further stage of tertiary milling has recently been introduced using a Vertimill VTM 3000 to achieve a product size of P 80 = 90 μm as feed to flotation.
• Gravity concentration of ground slurry in a centrifugal concentrator to produce a gravity gold concentrate for further upgrade and smelting.
• Flash flotation in the milling circuit to recover an additional concentrate suitable for further gravity gold recovery, with the remaining copper concentrate reporting to the flotation cleaning circuit.
• Rougher and scavenger flotation in tank flotation cells. Rougher and scavenger concentrates report to cleaning flotation via a regrind circuit using a Vertimill VTM 1250.
• Thickening of rougher/scavenger tailings before pumping to the tailings storage facility.
• Cleaner and scavenger cleaner.
• Re-cleaning flotation and subsequent thickening of final gold/copper concentrate.
• The final copper concentrate slurry with a grade of around 20–25% copper is pumped to the town of Blayney where it is filtered and exported using the same filtration facilities as used by the Cadia Concentrator.

Approximately 15% of the gold in feed ore is recovered as gravity concentrate and then smelted on site to produce gold doré for sale. Additional flotation capacity is being installed in the FY2012, and comminution studies are being undertaken, with an eventual target plant capacity of 8 Mtpa.

Blayney Dewatering Facility

The Blayney Dewatering Facility is located approximately 25 km to the east of the Cadia Valley at the town of Blayney. The gold/copper concentrate slurry is pumped via a buried concentrate pipeline to the Blayney Dewatering Facility, where it is dewatered using a vertical plate pressure filter press and stockpiled within the facility.

A front-end loader is used to load the dewatered concentrate from the stockpiles into containers for rail transport. A forklift transfers the filled containers from the load-out area to hardstand areas, and then onto rail wagons for transport by rail to Port Kembla. Approximately three trains per week are currently used for concentrate transport. Water recovered from the Blayney dewatering facility is returned to the CVO processing complex for re-use.

Key reported parameters

Technical qualifications

The report includes the following specific limitations: The Cadia Concentrator currently treats approximately 17 Mtpa of ore at an average grade of approximately 0.2% copper and 0.7 g/t gold. The Ridgeway Concentrator currently treats approximately 5.6 Mtpa of ore at an average grade of approximately 0.5% copper and 1.2 g/t gold. Plant performance data for the Cadia Concentrator is presented for FY 2009, FY 2010, and FY 2011 as recent plant performance of Cadia Hill open pit ore. Ridgeway Concentrator performance data covers the last three years with ore feed from Ridgeway Deeps block cave commencing in the second half of 2009. The staged expansion for Cadia East ore is described as proposed design, with completion dates and equipment specifications as planned. The report notes that the modifications will allow the plant to achieve the design throughput of 20 Mtpa of Cadia East ore at recoveries in accordance with recovery models determined in test work.

Source: Technical Report on the Cadia Valley Operations Property, December 31, 2011, Section 17 Recovery Methods.