PYHASALMI

The Pyhäsalmi mine is an underground copper, zinc and pyrite mine located in central Finland.

Overview

The Pyhäsalmi copper, zinc and pyrite mine is in central Finland, four kilometers southeast of the town of Pyhäjärvi, on Lake Pyhäjärvi.

Pyhäsalmi is one of the oldest and deepest underground mines in Europe. It is also one of the most efficient non-caving underground mines in the world. It was developed by Outokumpu Oyj in 1962 following accidental discovery of the deposit by a farmer. In the 1990s a 1450-metre deep automated hoisting shaft was constructed to exploit deeper ore. The shaft itself is a rare asset, providing access via hoist in less than three minutes or via driving the 11km decline in 30 minutes. It added ten years to Pyhäsalmi's life of mine. It has produced around 60 million tonnes of ore in its history.

Outokumpu started production from the new shaft in 2001, and in 2002, Inmet completed the acquisition of Pyhäsalmi and continued underground production. First Quantum acquired Pyhäsalmi in 2013 through its acquisition of Inmet.

Mining and Processing

The Pyhäsalmi deposit is a copper-zinc volcanogenic massive sulphide deposit of Proterozoic age.

Pyhäsalmi uses non-entry, bulk open-stope mining methods in a primary-secondary sequence. On average, stope size varies from 50,000 tonnes for narrow primary stopes to over 100,000 tonnes for wider secondary stopes. After single-stage primary crushing by an underground jaw crusher, ore is hoisted to a fines crushing plant, where it is ground in three stages. This is followed by conventional flotation, consisting of three sequential flotation circuits, one each for copper, zinc and pyrite.

Outlook

The life of the mine has been extended into June 2021 with an assumed lower copper cut-off grade.

Mine closure plans, including dismantling and earthworks, are being planned in accordance with legal requirements and best practice. Pyrite supply will extend until 2025, based on reclaiming pyrite from tailings.

Planning is in place for the mine facilities and associated infrastructure to be repurposed. Callio, a joint project by the town of Pyhäjärvi and the University of Oulu, will provide an umbrella organization for new businesses and activities to take advantage of Pyhäsalmi's unique deep underground infrastructure. Proposed new activities include underground physics laboratories, a secure underground data center, pumped hydroelectrical energy storage, plant and fungus growing laboratories and experimental production of insects and fish.

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