Kemi Mine, Keminmaa, Lapland, Finlandi

Regional Level Types
Kemi Mine	Mine (Active)
Keminmaa	Municipality
Lapland	Region
Finland	Country

Chromium (chromite) mine. The chromite deposit was discovered in 1959/1960.

Mine Information: Open pit production started in 1968, concluding with a 1.5 km-long x 500 m-wide x 220 m-depth pit completed in 2005.

Efforts underground started in 1999 with an 8 m-wide x 5.5 m-high main decline access at 15% grade is on the footwall side of the orebody, about 100 m below the pit rim. It terminates at a depth of 600 m at the base of the hoisting shaft, connecting with several intermediate sublevels. A 14,000 cu m workshop at the 350 m level and a 23,000 cu m main workshop at the 500 m level service the facilities along with pumping stations and a gyratory crusher.

The current mining method is bench cut and fill, a type of sub-level stoping with downhole production drilling. Drifts for the primary stopes are developed laterally from the footwall through the ore zone. Primary stopes are 25 m-high, 15 m-wide and between 30 and 40 m-long. Secondary stopes are identical, but 5 m wider. Cemented fill and fly ash is placed in the primary stopes, while the secondary stopes are backfilled with mine waste rock. The primary stopes are extracted one or two levels above the secondary stopes. Mining sublevels with 5 m x 5 m cross sections are established at 25 m vertical intervals.

Geology: A 2.4 billion year-old mafic-ultramafic layered intrusion, extending 15km northeast of Kemi hosts eleven chromite orebodies within a 4.5 km-long zone varying from 5-105 m in width and an average thickness of 40 m. The chromite-rich horizon appears 50-200 m above the bottom of the intrusion and has an average dip of 70 degrees northwest. Reserves total 57.3Mt [2007], grading 25-26% Cr2O3 between the 500 m level and the bottom of the open pit. The ore body continues at depth, probably to 1,000 m.

The main immediate host rock is weak talc-carbonate in which the hanging wall contact is clearly defined. At the footwall, the chromite and host rock is inter-layered, and must be mined selectively. However, there is strong granite some 80 m below the footwall.

In 2022 a number of large, distinctive pyrite crystals were collected from the dump (article, spirirferminerals.com). The crystals apparently originated from an isolated occurrence at an unknown location in the mine.

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References