Sublevel Stoping in Finland

Sublevel stoping has been used in Finland since the 1930's and today more than ten under- ground mines have adopted it as their main stoping method (Fig. I). Approximately 80% of the total underground tonnage is mined by sub- level stoping (Table 1) The first mines to introduce the sublevel stoping method in Finland were limestone mines. The development of sublevel stoping was very slow up to the mid 1960's when the switch to trackless mining started and the increase of mechanization lead to higher capacity and productivity. The method itself has been almost the same since the 1950's when long hole drilling was introduced. According to a future prognosis sublevel caving will give way to sub- level stoping; on the other hand, open pit mining will at the same time grow rapidly with some new mineral orebodies, which will he brought into production. Most Finnish orebodies are, however, only marginal ores and they could not support mining with more expensive methods than open pit mining or sublevel stoping. The future of sublevel stoping seems relatively bright. GEOLOGICAL AND ROCK MECHANICAL BACKGROUND The rock mechanical conditions in Finland are in general relatively good and the rocks firm. The compressive strength is normally 40 - 150 Mpa and modulus of elasticity 40 - 200 Gpa. Low values are common in altered and fractured rocks and near the ore contact Rock stress measurements have been carried out already for 20 years for mine design and monitoring purposes. The results of these measurements show that relatively high horizontal stresses seem to be common (Fig. 2).