Bunker Hill is a historical lead, silver, and zinc deposit in the US state of Idaho. The project is 100% owned by Silver Valley Metals Corporation (SVMC), a wholly owned subsidiary of Bunker Hill Mining Corporation (BHMC).
The present ownership aims to redevelop the Bunker Hill Mine and restart mining operations as part of its plan to consolidate a portfolio of mining assets in North America with a focus on silver.
In October 2022, BHMC filed an independent preliminary feasibility study (PFS) for the Bunker Hill Mine.
According to the PFS, the mine will require around $55m initially to restart operations. Based on current probable reserves, the project will generate around $25m of annual average free cash flow over an initial five-year mine life.
It is expected to produce 3 million ounces of silver, more than 316 million pounds of zinc and 146 million pounds of lead at an all-in sustaining cost (AISC) of $0.77 per payable pound of zinc (net of by products).
Location and Site details
The property is located in Shoshone County, Idaho. Some portions of the mine are located within Kellogg and Wardner cities.
The Kellogg tunnel is the main access to the property and is located at an approximate elevation of 2,366ft.
Overall, the project has four surface parcels, 34 platted parcels with surface rights and 108 mineral parcels without surface right claims across an area of 5,802 acres.
Discovery and Ownership history
The Bunker Hill outcrop was discovered in 1885; and the Bunker Hill and Sullivan Mining and Concentrating Company was incorporated in 1887. The mining operations focused on the upper levels.
In 1956, the corporate name was shortened to the Bunker Hill Company and continued operations until 1968 when it became a wholly owned subsidiary of Gulf Resources and Chemical Corporation.
The mine was closed in 1981 due to fall in metal prices and the company was sold to the Bunker Limited Partnership in 1982.
The mine again operated between 1988 to 1991 after which Bunker Limited Partnership went bankrupt. The mineral rights were then transferred to Robert Hooper, owner of Placer Mining Co. of Bellevue, Washington.
In 2017, Bunker Hill Mining signed a definitive agreement with Placer Mining Corp. (PMC) on a lease with a purchase option of the mine.
BHMC acquired the Bunker Hill Mine in January 2022.
The mine produced 35.78 tonnes grading 8.76% lead, 3.67% zinc and 4.52 oz/tonne silver from 1885 through to 1981.
Geology and Mineralisation
The Bunker Hill Property is situated within the Northern Idaho Panhandle region, which is underlain by the Middle Proterozoic-aged Belt-Purcell Supergroup of fine grained, dominantly siliciclastic sedimentary rocks stretching from western Montana (locally named the Belt Supergroup) to southern British Columbia (locally named the Purcell Supergroup).
Mineralisation occurs primarily in the Upper Revett formation of the Ravalli Group, a part of the Belt Supergroup of Middle Proterozoic-aged, fine-grained sediments.
This mineralization has four categories- Bluebird Veins, Stringer/Disseminated Zones, Galena-Quartz Veins, and Hybrid Zones.
Mineral Resource Estimate
According to the PFS report, Total Measured and Indicated (M&I) Resource of Bunker Hill Property is 7.03 million tonnes at a zinc equivalent (ZnEq) grade of 8.28%. This equates to 1.1 billion ZnEq pounds.
Mining and ore processing
Several mining and development methods were employed at the Bunker Hill mine over the years.
The current economically viable methods are cut-and-fill (CF), Long-hole stoping with fill (LHOS), and room-and-pillar mining with fill.
A crush-grind-flotation-concentration mill from the nearby Pend Oreille (PO) mine is expected to be redeveloped to support operations.
The process will comprise a primary and secondary ore crushing circuit, a primary grinding circuit followed by two separate flotation circuits to recover lead, zinc, silver and gold.
The products will be recovered into two separate concentrate products- a lead, silver, gold concentrate and a zinc concentrate.
It is expected to process approximately 648,000 short tonnes of ore annually.
Majority of mine infrastructure is still in place but tailing impoundment, smelter, and mill have been removed and the sites were reclaimed.
Other infrastructure such as offices, change house, car and maintenance shops are usable.
The Avista Kellogg substation situated adjacent to the Bunker Hill main offices supplies power to the mine.
There are two existing distribution lines- one feeds the surface mine facilities and the underground loads from the Kellogg side, while the other supplies electricity to the Wardner mine yard and facilities.
The current three-phase 2.5kV mine distribution system on the Kellogg side will be upgraded to three-phase 13.2kV.
Other works include upgrading overhead powerlines leading to the Wardner side of the mine, new underground power feeds on the Wardner side on 5-level and dropped down to the 9-level for distribution to the mine, replacement of existing u/g substations and switchgear among others.
MineTech USA developed the mine infrastructure and operations, CAPEX, and OPEX portions of the PFS of the Bunker Hill mine. It was also associated with portions of the mine plan and operating schedules.
Patterson and Cooke North America was in charge of the tailing backfill components, while Barr Engineering designed the process design and milling.
Yakum Consulting was selected for metallurgy and processing of the PFS.
On 3 November 2022, BHMC appointed Rivers Edge Environmental Services for critical site demolition activities.
MineWater secured a new water management consulting services in October 2022. The company has also completed a pilot water treatment study through 2021 and 2022.
On 5 October 2022, Strike Group was selected as the Procurement and Construction Management (PCM) contractor for the mine restart activities.
In February 2022, BHMC signed a Contract Services Agreement with Coeur d’Alene Mine Contracting for underground mining and development requirements through 31 December 2023.
In November 2021, Golder Associates was selected for detailed geotechnical assessments of key areas of the mine.
Resource Development was hired for metallurgical test work.
BHMC also entered into a partnership with Ensero Solutions to start Waste-to-Energy power plant feasibility study to evaluate the use of municipal solid waste to produce electrical power for the mine.
The Future Forest Company was engaged in a scoping study for the pyrolysis plant which may be located near Waste-to-Energy Facility.
In April 2021, Cutfield Freeman & Co. was selected as the financial advisor for providing independent advice on all aspects of mine restart finance.