Ore is extracted from LKAB's surface mines by means of bench mining. The method is based on mining the ore in descending levels through drilling and blasting. As the ore is removed, production moves successively downwards.
The ore in the Svappavaara field's open-pis mines, Gruvberget and Leveäniemi, is extracted by mining the ore in descending levels. The thickness of the slabs, known as the bench height, is 15 metres, and the slabs are worked downwards.
In the first stage, the ore is extracted at one level before moving down a step (15 metres), after which the ore is removed from the underlying level. The slab is then located between the two levels. Vertical holes are drilled from the upper level, which are charged with explosive and then blasted. The ore is removed from the lower level and the process is then repeated at the next level down.
In order to expose the ore and ensure safe walls, the surrounding rock around the ore has to be removed. The surrounding rock is removed before the ore at the same level can be mined. Bench mining is an effective and well established mining method, which allows maximum extraction from the rock with a high degree of safety.
Open-pit mining takes place in several stages:
Before the ore can be mined, the land around the ore body has to be sloped so that the risk of small landslides is minimised. The incline of the slope is determined with regard to the strength characteristics of the rock mass. The incline is extremely important for the profitability of the surface mine, as too shallow an incline results in the need to remove additional surrounding rock.
Drilling is performed with a mobile drilling unit, which drills long holes down through the slabs. The execution and extent of the drilling is determined by the quality of the rock and the desired fragmentation.
After drilling, the holes are charged with around 25 tonnes of explosive, which blasts out the rock.
Loaders are used to load the ore into dump trucks, which transport the ore to an intermediate storage area and a crusher facility. The ore is then crushed and sorted, before being transported for further processing.