Allied Nevada released an updated scoping study in early September 2010 of potential development of sulphide resources at its Hycroft mine in northwestern Nevada. The study envisions production of about 610,000 oz/y of gold and 27 million oz/y of silver, or approximately 1.1 million oz/y of gold equivalent. Production would be from a 100,000-mt/d milling operation and a 74,000-mt/d heap leach operation. Cost of sales is expected to average about $350/oz of gold sold, after by-product silver credits. Capital cost to develop the pro-ject is estimated at $1.1 billion.
The updated Hycroft scoping study significantly expands the production profile of 275,000 oz/y of gold and 6.5 million oz/y of silver suggested in an initial April 2010 scoping study (E&MJ, May 2010, p. 6). Of the updated study, Allied Nevada President and CEO Scott Caldwell said, “We believe the option presented represents an achievable, realistic view given the significant size of the resource at Hycroft. Management expects ongoing drilling should continue to expand the resource, which could further improve the robust economics of this project. If this project is developed as outlined in the scoping study, Hycroft has the potential to be among the largest gold mining operations in the world.”
As outlined in the updated scoping study, mining at Hycroft would be from a large open-pit. The mining rate would be about 136 million st/y, including 59 million st/y of ore and 77 million st/y of waste. Lower-grade oxide mineralization would be processed as run-of-mine heap leach material, and higher-grade oxide mineralization along with sulphide mineralization would be processed at the 100,000-mt/d mill. The mill would be comprised of two or three lines, each consisting of a primary crusher, semi‐autogenous grinding mill, two ball mills and a flotation circuit. Mill construction could be implemented in stages to manage capital expenditures over the first few years of the project.
Metallurgical testing suggests a sulphide concentrate ratio of 20:1 can be achieved. Mill production would average approximately 5,000 st/d of concentrate, containing approximately 1,400 oz of gold and 78,000 oz of silver. Allied Nevada currently anticipates the concentrate would be shipped off‐site for final processing; however, options for constructing an on‐site oxidation circuit are under review.
The cost to complete a full feasibility study over the next 12 to 18 months for the proposed Hycroft expansion is estimated at $25 million, with $15 million directed toward drilling and assaying and the remainder toward metallurgical test work, environmental studies, and mine and plant engineering. The scoping study assumes receipt within three years of all required state and federal permits to construct and operate the sulphide mine and plant. Construction and commissioning of the plant is estimated to take two years.