The Outokumpu's Kemi chromite Mine is located near town of Kemi close to the border of Finland and Sweden. The mine consists of 4 open pits that have been mined out and 3 underground mining production areas. Ore domain is a layered intrusion open to depth and dipping 70" to North-West. The thickness of the chromite layer is 40m on an average. The chromite layer has been broken to several separate ore bodies during the tilting.
Current mining operations in the underground mine are located above mining level 500 in Elijiirvi and Viia ore domains and in Surmaoja domain above level 550. The mining is performed using sub level sloping method with stope & mining level height of 25 m. The mining advances upwards level by level and approaches the previously mined open pit bottoms. A crown pillar is planned between open pits and underground mine with approximate thickness of 75 m. Ore production is performed in several levels simultaneously; hence multiple locations are available for production that reduces risk of production cut offs.
Current ore reserves are estimated to last, with current production rate and hoisting, until 2020 without any potential resources & reserves included. After that reserves below 500 m will be utilized.
The preliminary plans deepen the mine, may consist the mining levels between 500 – 1600 in the Elijiirvi, Viia and Surmaoja mining domains. To understand the behaviour and functionality of the possible deeper extension of the Kemi Mine, simulations are used to estimate the stability of the extension. The simulation results are compared to the current mining environment and studies above level 500 in order to evaluate the conditions in the deeper mining environment. An extensive stress measurement program has been initiated and will be in role in the future mine design procedure. The stress measurements will be part of the initial data for simulations concerning new mine layout, stope sizes, mining level heights and sequencing.
In this study a sketch of the deep mine extension is studied in terms of rock mechanical stability. The stability is still defined in light of current information available from the current mine studies hence the new stress measurement will give important update to the data. Numerous studies have been previously performed concerning deformations in current mine, rock stress in the mine and multiple forecasts of coming events in the mine stability. The study reveals go/no go options for two new main level scenarios and their stability compared. Vertical pillars are defined and their advantages to the whole mine stability is determined.
The results indicate that too deep initiation level for similar mining method, as currently is used, is risky and hence cause the sterilization of the upper ore body. Therefore a less economically risky option is to initiate mining upwards form depth range of 900–1100. The vertical pillars were noted to improve mine stability significantly. The vertical pillars are recommended although the economical down side related to the ore write offs in pillars.