Name: Greens Creek mine.

Location: The project is located on Admiralty Island, in south-east Alaska, in the US.

Mine Owner/s: Hecla Mining Company.

Brief Description: The Greens Creek mine is a producing 2 300 t/d underground mining operation and is one of the biggest and lowest-cost primary silver mines in the world.

The property includes 17 patented lode claims and one patented mill site claim, in addition to property leased from the US Forest Service. Greens Creek also has title to mineral rights on an estimated 3 050 ha of federal land adjacent to the properties.

Brief History: The Greens Creek deposit was discovered by the Pan Sound Joint Venture (JV) in 1973. The original JV partners included Noranda Exploration, Marietta Resources International, Exhalas Resources Corporation, and Texas Gas Exploration. In 1978, following the involvement of the Bristol Bay Native Corporation, the Pan Sound JV was terminated and replaced by the Greens Creek JV in which Bristol Bay Resources held an interest on behalf of the Native Corporation. Over subsequent years, the structure of the JV in the Greens Creek JV changed. By 2008, the partners comprised Hecla, Kennecott Greens Creek Mining Company and Kennecott Juneau Mining Company, which Hecla bought out the same year.

Primary Metals/Minerals: Silver.

Secondary Metals/Minerals: Zinc, gold and lead.

Geology/Mineralisation: The Greens Creek deposit is a polymetallic, stratiform, massive sulphide deposit. The host rock comprises mostly of marine sedimentary, and mafic to ultramafic volcanic and plutonic rocks, which have been subjected to multiple periods of deformation. These deformational episodes have imposed multiple folding of the orebodies to create a complex geometry.

Mineralisation occurs discontinuously along the contact between a structural hanging wall of quartz mica carbonate phyllites, and a structural footwall of graphitic and calcareous argillite.

Reserves: Total proven and probable reserves as at December 31, 2019, were estimated at 10.72-million tons grading 12.2 oz/t silver, 0.09 oz/t gold, 2.8% lead and 7.3% zinc.

Resources: Total measured and indicated resources as at December 31, 2019, were estimated at 8.65-million tons grading 11.7 oz/t silver, 0.10 oz/t gold, 2.8% lead and 8.1% zinc. Inferred resources were estimated at 1.85-million tons grading 13.7 oz/t silver, 0.09 oz/t gold, 3.1% lead and 7.4% zinc.

Mining Method: Greens Creek is an underground mine, using primarily cut-and-fill and longhole stoping mining methods.

Major Infrastructure and Equipment: The Greens Creek mining operation includes a significant amount of existing infrastructure primarily at two locations – the 920/860 mine area and the Hawk inlet camp, which are connected by a 14 km road.

Key existing infrastructure in the 920/860 mine area includes underground mine portals, administration and support buildings, mill building and associated processing facilities, a mobile equipment repair shop, warehouse facilities, water collection and treatment facilities, and development waste rock storage.

Key existing infrastructure in the Hawk inlet area includes personnel housing and dining buildings, concentrate storage and shipping facilities, materials receiving dock and warehouse, dry stack tailings disposal facility, water collection and treatment facilities, and fully permitted discharge facilities for treated water.

Infrastructure in other areas includes a high-voltage electrical intertie to the Juneau power grid through an undersea cable, a crew ferry terminal and more than 22 km of mine roads.

The current dry stack tailings disposal facility has sufficient capacity to accommodate tailings to the end of the current mine life in 2030. Early-stage engineering studies are under way to determine modifications to the plan of operations to accommodate additional material beyond the current Greens Creek mineral reserve life.

Prospects: Hecla is exploring several areas on the 57 km2 land package, which could potentially lead to additional reserves and resources, further extending the mine life or even leading to the discovery of another deposit like Greens Creek. There are more than 48 km of mine horizon where mineralisation has been identified and projected along surface on the property.

Contact Details:
Hecla Mining
Tel +1208 769 4100
Email hmc-info@hecla-mining.com
Website https://www.hecla-mining.com