The Copperwood Project is a copper ore mine located in the US state of Michigan within the Porcupine Mountains copper district. The project is currently in the development stage.
Highland Copper Company, a Canadian copper development company, owns 100% stake in the property.
The project has received all permits to begin construction, which is expected to begin in late 2022. As of September 2022, a federal operating permit to construct and operate a pumping station on Lake Superior is awaited.
Initially, the development of the mine is expected to entail an investment of $275m.
Copperwood is expected to achieve a production capacity of 6,600 metric tonnes per day (mtpd) and produce 30,000 tonnes of copper annually for 11 years.
Location and site details
Copperwood Project is located in Gogebic County in the Upper Peninsula of Michigan. The site is around 23km and 40km from the towns of Wakefield and Ironwood.
The property will benefit from locally available infrastructure including power lines, natural gas and rail line.
It can be accessed by the paved north-south County Road 519 which connects to the State Highway M-28 east of Wakefield town. The same road can also be used to access a Canadian National Railway Company (CN) rail line located at Thomaston around 18km from the Copperwood site.
The land surface of the property slopes northwest towards the shoreline of Lake Superior.
Overall, the Copperwood Project includes four metallic and non-metallic mineral leases encompassing a total area of 1,904 contiguous hectares. The lease agreements were executed by Copperwood Resources Inc. (CRI) with Keweenaw Minerals, Sage Minerals and A M Chesbrough.
CRI was formerly known as Orvana Resources US Corp., a wholly-owned subsidiary of Highland.
Discovery, geology and mineralisation
In 1954, a US Geological Survey map of the area was published indicating the potentiality of the property. Copperwood deposit was discovered two years later in 1956.
A drill programme delineated four separate deposits containing chalcocite-bearing sedimentary units in the lowermost Nonesuch Formation. However, the then private mineral lease holder AMAX did not proceed with the mine.
In 2008, Orvana Minerals began delineation drilling campaign and environmental baseline studies with the aim to develop the property.
According to Copperwood’s feasibility study in 2018, the project is situated on the flank of 2,200km long Mesoproterozoic mid-continent rift system of North America in the Nonesuch Formation.
The mineralisation, interpreted as a sediment-hosted stratiform copper deposit, comprises fine-grained chalcocite as the only ore mineral containing 79.8% copper.
Mineralisation is hosted within two sedimentary sequences called Lower Copper Bearing Sequence (LCBS) and Upper Coper Bearing Sequence (UCBS) at Nonesuch Formation base.
The LCBS is composed of the Domino, Gray Laminated, and Red Massive units, while the UCBS consists of the Upper Transition, Brown Massive, Thinly, and Upper Zone of Values units.
The two sequences were delineated by drilling an area of around 5,600m east-west and 1,700m north-south.
The Copperwood feasibility study reported mineral reserves (proven and probable) of 25.4 million tonnes (Mt) at an average grade of 1.43% Copper (Cu) and 3.83 g/t Silver (Ag). The final proven and probable mineral reserve estimate is based on the assumption of a 3% ore loss.
Inferred resources at the project are 34.4 Mt in LCBS unit, and 15.5 Mt in UCBS unit.
Mining and Ore Processing
The feasibility study has proposed a mechanised underground mining for the project as the deposit is situated relatively sub-horizontal with a thickness ranging from 1.6m to 3.7m. This will involve using a conventional drill and blast room-and-pillar mining technique to extract the ore.
The mine will be accessed through a covered box-cut forming a portal at the mine entrance from the surface.
Copperwood will be divided into eastern and the western sectors.
Mining activities will commence on the western part, which contains higher grades and a thicker mineralised zone.
The western part will feature six extraction panels, while the eastern part will have four.
The mining will usually follow the dip of the orebody, and at an angle to the dip direction when the dip is too steep to follow.
The operations will commence with drilling of the working face with two-boom hydraulic-electric jumbo drills.
It will use 10-tonne load-haul-dump (LHD) units for loading muck and transporting it to the conveyor loading point.
The process plant for Copperwood Project is designed to produce 6,600 mtpd of copper concentrate.
Other key project infrastructure
The project will have multiple infrastructure components that will support mining activities.
This includes grid power connection requiring 25mi of 115kV line between Norrie substation in Ironwood and main substation in Copperwood site, site electrical distribution and communication infrastructure.
It will also include one stockpile pad at surface, water in-take in Lake Superior with 500 USPGM capacity, sewage treatment, fuel storage (10,000lt), explosive depot, truck shop, ware house and related offices, metallurgical lab, mill offices, mine dry for 375 workers, administration and assay labs, tailings disposal facility and effluent water treatment plant among others, and event pond ditches.
The project will receive power via a 25mile long 115kV power line that will connect Norrie substation and Copperwood main substation. A 13.8kV distribution network will be developed to power all the areas of the project.
G Mining Services prepared the 2018 feasibility study report of the Copperwood project. Several other entities such as SGS Canada, Lycopodium Limited, Golder Associates, and Foth Infrastructure & Environment also contributed to the study.
Lycopodium Minerals Canada of Toronto conducted the design of the processing facility for the project.
Golder Associates designed the tailings dam and water management systems of the project. The company also provided technical support in mine geotechnics.
On 19 October 2022, Highland Copper Company selected G Mining Services for a preliminary Economic Assessment to develop Copperwood and White Pine North projects in Michigan.