Quaterra Resources reports that an independent preliminary economic assessment (PEA) concluded that its MacArthur property, which forms part of its suite of assets in the Yerington copper district, Nevada, has potential for development as a large-scale, copper-oxide heap leach operation that would provide long-term cash flows for a relatively modest capital outlay. An open-pit mine would be based on an acid-soluble measured and indicated copper resource of 159 million st at 0.212% copper and an inferred resource of 243 million st at 0.201% copper. Production would total 747 million lb of copper over an 18-year mine life at an average mining rate of 15 million st/y.
The MacArthur project is located five miles north of the Yerington mine that was operated by Anaconda for 25 years until 1978, producing 1.7 billion lb of copper from 104.8 million st of oxide ore and 58.6 million st of sulphide ore. Quaterra has a 40-mi2 land position that includes the former Yerington mine site, the large Bear porphyry deposit, and other oxide and sulphide deposits, as well as MacArthur, in the Yerington district.
Initial capital expenditure to develop the MacArthur project is estimated at $232.7 million. Average life-of-mine operating costs are estimated at $1.89/lb. The project breaks even at a copper price of $2.56/lb initially and at $2.23/lb after the first three years when the capital is paid off.
The PEA envisions a mining rate of approximately 41,000 st/d. Run-of-mine ore will be delivered to the heap leach pad. The waste-to-ore stripping ratio would average 0.90:1.
The project financials were enhanced by including a sulphuric acid plant at the site compared to purchasing and transporting acid to the site. An on-site acid plant provides more long-term certainty for the highest-operating-cost item (sulphuric acid), reduces the requirement for purchased electric power, and would leverage future consolidation and development of other oxide deposits in the district.
“We see MacArthur as the first step in creating a much larger Yerington district copper project,” Quaterra President and CEO Thomas Patton said. “In fact, the many assets we have in the Yerington district provide a number of options that could both optimize and expand the MacArthur project. This project looks good now, and we expect it will get better.”
Some of the options being considered to add value to the project include: processing the Yerington site oxide residuals as part of a district-wide oxide project; additional drilling, particularly at the north end of the MacArthur site, to investigate integrating both deeper acid-soluble and primary sulphide copper into an expanded MacArthur mine plan; pit studies to raise grades, lower the strip ratio, and optimize production rates; and inclusion of other smaller oxide deposits on Quaterra’s land position in the Yerington district.
