Name: Garpenberg mine.

Location: Hedemora municipality, Sweden.

Mine Owner/s: Boliden Mineral.

Brief Description: Garpenberg is one of the world’s most modern mines and is Sweden’s oldest mining area still in operation. The mine’s productivity is also among the highest in the world.

The mine comprises several polymetallic orebodies.

The discovery of a major deposit in Lappberget at the end of the 1990s saved the mine from closure. 

An expansion project completed in 2014 increased the capacity of the mine to 2.5-million tonnes, and in 2020 minor investments in bottlenecks were made in Garpenberg to allow for a production rate of three-million tonnes a year.

Brief History: Systematic mining has been conducted at Grapenberg since the thirteenth century.

Boliden acquired the Garpenberg mine from AB Zinkgruvor in 1957.

Primary Metals/Minerals: Complex ores containing zinc, lead, silver, copper and gold. 

Secondary Metals/Minerals: None stated.

Geology/Mineralisation: The Garpenberg mine is situated in the mineralised Palaeoproterozoic igneous province of Bergslagen, in south-central Sweden, which is host to a variety of ore deposits, particularly iron-oxide and polymetallic sulphide deposits.

The Garpenberg mine encompasses several orebodies that follow a limestone-marble horizon occurring in a synform structure. The structure is compressed at the southern end and opens to the north. The horizon is strongly isoclinally folded and the tectonic structure is divided into blocks. The orebodies occur in the contact zone between the limestone and underlying siltstones. The contact zone is heavily altered to skarn and the limestone to dolomite. The structures are consistently steeply dipping.

Mineralisation is mainly of replacement style and is likely to have taken place where metal-bearing fluids penetrated up along synvolcanic, extensional faults and came in contact with reactive limestone to form large, massive sulphide bodies.

Reserves: Total proven and probable reserves as at December 31, 2020, were estimated at 89.5-million tonnes grading 0.3 g/t gold, 94 g/t silver, 0.04% copper, 2.8% zinc and 1.3% lead.

Resources: Total measured and indicated resources as at December 31, 2020, were estimated at 36.6-million tonnes grading 0.35 g/t gold, 90 g/t silver, 0.06% copper, 2.8% zinc and 1.4% lead. Inferred resources were estimated at 25.5-million tonnes grading 0.42 g/t gold, 57 g/t silver, 0.07% copper, 2.5% zinc and 1.4% lead.

Mining Method: Almost 90% of the mined ore in Garpenberg is extracted by sublevel stoping, where the ore is mined in layers between two drifts, vertically 25 m apart. Other mining methods include cut-and-fill and avoca.

Major Infrastructure and Equipment: The mine includes two underground crushing plants.

Trucks provide the means of transportation from the active mining areas to the crushers. The crushed ore is hoisted to surface in a shaft, unloaded into a bin in the headframe and then transported by conveyor belts to an intermediate ore storage facility, which can hold about a week of production.

In the concentrator, the ore is ground using autogenous grinding in the primary stage and pebble mill grinding in the second stage.

After grinding, the ore is screened, with the coarse fraction being returned to the primary mill and the fine fraction undergoing gravimetric separation (Knelson concentrator).

After gravity separation, the material is classified using hydrocyclones. The overflow constitutes the main flotation feed, while the underflow undergoes flash flotation in the grinding circuit.

Flotation is conducted in a three-stage process flotation circuit – copper/lead flotation, copper/lead separation and zinc flotation. Regrind mills are installed in the copper/lead and zinc circuits. The mineral concentrates are dewatered using thickeners and pressure filters. Zinc, lead and copper are produced in flotation as mineral concentrates.

Prospects: None stated.

Contact Details:
Boliden Garpenberg
Tel +46 225 360 00
Website https://www.boliden.com/ 

Sources:
Boliden Mineral.  https://www.boliden.com/  (accessed: July 19, 2021)