Aquila Advances Back Forty Zinc-Gold Project in Michigan
The feasibility study is based on proven and probable open-pit mineral reserves totaling 11.65 million metric tons (mt), grading 1.85 g/mt gold, 2.64% zinc, 21.7 g/mt silver, 0.28% copper, and 0.21% lead. The process plant design is based on a flexible metallurgical flowsheet designed for treatment of a variety of different ore types. Nominal throughput is planned at 4,000 mt per day (mt/d) of sulphide ore and 800 mt/d of oxide ore.
Mineralization at the Back Forty project consists of discrete zones of zincrich or copper-rich massive sulphides, with or without lead, that may contain significant amounts of gold and silver; stockwork stringer and peripheral sulphides that can be gold-, zinc- and copper-bearing, with or without lead and silver; precious-metal-only low-sulphide mineralization; and oxide-rich precious- metal-bearing gossan.
The mining operations will be based on a large open pit that will be mined in three pushback phases using blast hole drills, hydraulic excavators and 91-mt haul trucks. Support equipment will include dozers, graders, water trucks, and light vehicles for maintenance, personnel transport, and mine supervision.
Sulphide mineral reserves that will be processed through the flotation concentrator have been classified into five ore types from three zones. Project value will be maximized by campaigning the different sulphide ore types through the plant separately, with the minimum duration of any campaign being approximately one month. A total of seven different ore stockpiles will be used to facilitate campaigning and also ensure that both the sulphide and oxide process plants are fed the highest-value ore available.
The oxide process plant flowsheet includes crushing, grinding, classification, pre-leach thickening, cyanide leach, CCD washing and clarification of pregnant solution, de-aeration and Merrill Crowe zinc precipitation, mercury removal using a retort, and smelting to produce doré.
Some pre-construction activities have begun at the Back Forty project. Aquila is finalizing a project execution plan that will further define the project development strategy, including contracting philosophy, plans for basic and detailed engineering and any required permit amendments, as well as plans for building the owner’s team in preparation for the construction and operational readiness phases of the project. Construction is expected to take about 24 months.