Sub level caving

    After more than 30 years of open pit mining, Rana Gruber AS started underground mining using the sublevel open stoping method at the Kvannevann Mine in 2000. The mining has been continuously improved and further developed to suit the difficult rock conditions in the area and to reduce operating costs. A combination of low grade iron ore (with on average 33% Fe) and significant rock mechanics challenges (large horizontal stresses) has made the mining in the Kvannevann Mine extraordinary.

    Thanks to of the last years increase of production due to the demand for iron ore, Rana Gruber AS investigated alternative methods to increase the mining capacity and resources. This resulted in a decision to change over from sublevel open stoping to sub level caving. Key arguments were: a) mineable reserves b) cost and benefits with respect to investment c) extraction values show an optimistic and satisfactory result and d) estimations and field tests indicating a satisfactory caving of the deposit. This mining method involves dividing the ore body in horizontal layers, starting with the first layer on top of the ore body and then work downwards. In sublevel caving the production is divided into four different stages of operation.

    Development drifts
    Long hole drilling
    Production, Blasting and loading
    Production loading

    Sub level caving method allows working in parallel on different sub levels in the mine. This means that continuous excavation works can be on-going at one sub level without interfering with another. Project Sublevel Caving was carried out during the years 2009 and 2011, with a budget on 450 million NOK.