Iron ore mine

    Iron oxide mining started in the Dunderland valley more than 100 years ago. Until 1999 iron ore was only mined by open pit methods. Today Rana Gruber operates the Kvannevann underground mine as well as satellite deposits which are mined by open-pit methods.

    Open stope mining method has been used in the underground mine until 2012.

    Vertical projections showing the ore body occurrence in the Ørtfjell area. Showing the old open pit, the access ramp to the underground mine and mined are in blue.

    Sublevel open stope mining has been used over a total length of 1,200 m of the Kvannevann ore body. The main and first production level was established at 250 m above sea level. A total of 16 stopes on average 60 m long, 30 m wide and 100 m high were aligned along the ore body. These were separated by a number of 30 m thick vertical pillars. The crown pillar is on average 30 m thick and separates the bottom of the open pit and underground operation.

    Production drilling is carried out from production drifts at level 320 m. A standard 360 degrees fan is drilled every 3 m with hole lengths chosen to encompass the iron ore. Additional production drilling is done from level 250 m upwards to create a funnel shaped design for the lower part of the stope.

    Since 2007 parts of the crown pillar within the center part of the mine have been blasted for stability field test reasons and to increase the mine production.

    The extractable ore in the Kvannevann Mine is estimated at 44.8 million tons based on sublevel caving between level 219 m to 123 m above sea level. The average iron content is estimated at 33.5%, including a magnetite content estimated at 3.5%. The waste rock composed of intrusions in the ore and form the side walls has been estimated to contain 11% Fe mainly bound to silicates and not as iron oxides

    The method is now in transition to sub-level caving. One major step in this transition was the “Giant blast” which took place in October 2010, where approximately 2 million tons of rocks were freed by using 219 tons of explosives.

    The construction of the new mine level led to the establishment of a new infrastructure around the Ørtfjell iron ore deposits.

    The ore in the underground mine is transported by trucks and crushed at the new underground crushing station. Conveyor belts transports the ore to the central underground storage silo. Ore from the open pit operations is taken the main crusher and blended with the underground ore in the silo. The crushed ore from the silo is filled in railway wagons. This filling takes place underground due to the special climate conditions of the area. The ore is then transported by rail to the dressing plant at Gullsmedvik.