Augusta Resource Corp. has released the results of an updated feasibility study for its Rosemont copper project near Tucson, Arizona. The study conforms to the preferred alternative development plan identified by U.S. federal agencies during the National Environmental Policy Act (NEPA) review process and eliminates the heap leaching of oxide minerals and associated plant facilities, such as an SX/EW plant, that were contained in earlier feasibility studies.

                The Rosemont deposit is a large-tonnage, skarn-hosted, porphyry-intruded, copper-molybdenum deposit located in close proximity to the surface and amenable to open-pit mining methods. Sulphide ore feed to the concentrator is planned to start at 27 million st/y, ramping up to 33 million st/y, at an average strip ratio of 1.9:1.

                Concentrator throughput for the first four years of production will average 75,000 st/d, ramping up to 90,000 st/d for the second half of the mine life. Process equipment will be added and optimized within the concentrator to sustain average production of copper in concentrates at approximately 243 million lb/y over the life of the mine. Average annual production for the first three years of operation is estimated at 255 million lb.

                Development time for the Rosemont project is estimated at 22 months, followed by 21 years of mining production. Total initial capital cost for construction, commissioning, and mine pre-development is estimated at $1.226 billion, an overall increase of 32% from the cost estimate in a 2009 feasibility study. The increase reflects additional equipment and escalation in costs of equipment, materials, and labor. Augusta has already spent approximately $90 million on purchases of long-lead equipment and $23 million on EPCM costs, for a total of $113 million, which is included in the capital cost estimate.

                The proposed Rosemont pit operations will be conducted from 50-ft-high benches, using large-scale equipment, including 12.25-in.-dia rotary blasthole drills, 65-yd3 electric mining shovels, 36-yd3 front-end loaders, 35-yd3 hydraulic excavators, 260-st off-highway haul trucks, 580- to 850-hp crawler dozers, 500-hp rubber-tired dozers, 297-hp motor graders, and 30,000-gal off-highway water trucks.

                The sulphide ore will be processed by crushing, grinding, and flotation to produce separate copper and molybdenum concentrates. Copper recoveries are estimated at 87%. Molybdenum and silver recoveries are estimated at 58% and 76%, respectively.

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