We worked with Hudbay to complete two concurrent Pre-Feasibility Studies (PFS) for the design and construction of a copper/molybdenum processing plant at their Copper World project in southeast Arizona. The winning approach was to construct a less expensive Albion Process™ plant entirely within the confines of the company’s private land, saving significant capital costs. By keeping the project on their private land, this enabled the project to move forward.
The Challenge
The Copper World Project is a greenfield open pit mine and processing plant being developed on a large-scale copper/molybdenum/silver skarn deposit southeast of Tucson, Arizona. Working with Hudbay since the value engineering was undertaken in 2015, we were challenged to design and engineer a processing plant that would process an eventual 60,000 t/d of ore to produce commercial grade concentrates of copper and molybdenum. The designs had to meet stringent environmental and permitting requirements while producing the best business case for the company. Earlier studies had not yet resolved what processing methodology should be explored at the PFS stage.
The Better Way
A standard approach at the PFS stage is to use trade-off studies to determine a preferred processing method and complete the business case accordingly. With no decision on a processing methodology and significant metallurgical work still underway, we pursued two business cases simultaneously through the duration of the PFS, to better position Hudbay for upcoming deadlines in the event of either approach being chosen.
Our engineers reduced the ore processing options down to either Pressure Oxidation (POX) or the Albion Process™ – a combination of ultra-fine grinding and oxidative leaching at atmospheric pressure developed by Glencore. Engineers looked at different facility designs and throughputs, as well as options to process the ore at the mine or offsite. Heap leach column tests uncovered issues with degradation of leach, and higher than ideal acid consumption, so both methods had to be modified several times to incorporate these new results.
After both business cases were fully explored, the decision was made to move forward with the Albion Process. This method eliminates the costs of a pressurized autoclave, instead producing a copper bearing liquor that is processed in electrowinning to produce a copper cathode. The process is also more scalable. While current testing is for 50% capacity, the operation can be scaled without significant capital costs by simply adding additional oxidation tanks.
A final challenge was to design the plant layout to ease both environmental and permitting restrictions. We reworked the layout to keep the entire project on land that was privately owned by Hudbay, eliminating the time-consuming need for state or federal permits. This design also saved about $20 million in earthworks because of its smaller physical footprint.
The Outcome
Our concurrent “double PFS” allowed Hudbay to accurately assess two viable business cases in the development of the Copper World mine and processing plant. The chosen final design was reworked to fit within the tight physical borders of privately-owned company land, saving both permitting time and the considerable extra earthworks a larger footprint design would have required. The Rosemont project is now progressing to Feasibility Study stage, with new optimizations looking at expanding throughput to a full capacity of 60,000 t/d.