|Results of a recent study outline a two-phase expansion plan for Allied Nevada’s Hycroft gold mine that would require a larger loading and haulage fleet, and ultimately would boost mill capacity to 120,000 st/d.|
Allied Nevada has reported the results of a pre-feasibility study (PFS) for a proposed expansion at its Hycroft mine in northwest Nevada. The PFS assumes a two-phase construction program that would first result in mill throughput capacity of 60,000 short tons per day (st/d); a second phase would increase it to 120,000 st/d. An increase in the mine’s loading and haulage fleet would take place starting in 2017 to assure an adequate supply of ore to the expanded facilities.
As a result of successful ambient alkaline oxidation (AAO) pilot plant work, on-site oxidation of sulphide concentrate has been incorporated into the PFS, which should allow production of doré on-site, as compared to the previous plan to sell concentrate.
Full production from both expansion phases is assumed to be reached in 2018. Average annual production during the first five years of full production (2018-2022) is projected at 450,000 oz of gold and 21 million oz of silver, or approximately 800,000 gold equivalent oz/y. Average adjusted cash costs for the first five years of full production are estimated at $478/oz, with silver accounted as a byproduct.
Allied Nevada currently operates Hycroft as an open-pit, heap leach only operation. Solution from the heap leach pad is processed through a Merrill-Crowe plant, and metals are further processed in a refinery to produce doré bars.
In 2013, production totaled 191,831 oz of gold and 882,225 oz of silver. Production during 2014 is forecast to increase to between 230,000 and 250,000 oz of gold and 1.7 million and 2 million oz of silver.
Based on the results of the mill expansion PFS, Allied Nevada is moving forward with a feasibility study that is expected to be complete by the end of the third quarter of 2014. Current planning calls for start of construction of Phase 1 of the expansion during the fourth quarter of 2014, contingent on securing necessary financing. Phase 1 construction is scheduled to be complete within 24 months, which would result in commissioning in the fourth quarter of 2016. Phase 2 commissioning would follow a year later.
Phase 1 capital requirements are estimated at $900 million, with Phase 2 adding $422 million.
Phase 1 construction is expected to include one grinding line, comprised of a SAG mill, two ball mills and a regrind mill; sulphide flotation cells; tails leach tanks; oxidation tanks; an oxygen plant; starter tails capacity; and the associated infrastructure for these facilities. Rail spur and power requirements for both phases would be constructed during Phase 1. Current estimates assume that the oxygen plant will be constructed by a third-party vendor, which is accounted for in operating costs.
The mill flowsheet incorporates three processing streams. In stream one, highly oxidized transitional ore is ground and leached in the tails leach plant. In stream two, sulphidic ore is ground and floated to create a concentrate. The concentrate is oxidized through the AAO plant and leached to extract the gold and silver. In stream three, partially oxidized material is ground and floated to create a concentrate. The concentrate is oxidized and leached, while the remaining material that does not float (the flotation tails) is leached directly.
Phase 2 is designed to increase the mill capacity from 60,000 st/d to 120,000 st/d by adding a second grinding line, comprised of an additional SAG mill and two additional ball mills; additional flotation cells; and additional tanks for the AAO circuit commensurate with the increased capacity of the grinding circuit.
Mining to feed the expanded Hycroft mill initially will be conducted using the existing equipment fleet. Between 2017 and 2025, the company expects to add two additional wire rope shovels and 19 haul trucks.