Planning and rock mechanical evaluation of variants for the continuation of the underground mine in Kleinfeistritz

The underground mining of leucophyllite at the Kleinfeistritz mine was started in 1917. In 2007 a new mining area was opened due to the depletion of the old site at the opposite bank of the Feistritzbach creek in the Kothgraben valley. After roughly 20 years of mining, the federally approved spatial extensions of the mine workings are reached and a new mine plan has to be proposed to the federal mining authority of Austria. The mine is now owned by Imerys Talc Austria GmbH, the successor of many companies owning the Kleinfeistritz mine in the last 109 years. Imerys Talc Austria GmbH offered the Montanuniversität Leoben in this planning phase, a possibility to write a masterthesis. The goal of this thesis is to produce a feasable mine plan for the next development phase, focussing on mine design, based on 3D CAD models of the mine to extend the LoM for 15 more years with a yearly production rate of 15 000 t raw material from the mine. The starting point of this task was the existing underground workings and its infrastructure (ventilation system, water management system and surface buildings and facilities). At the start three alternatives were determined based on an existing blockmodel. Variant 1 was planned to develop the mine upwards into the deposit, basically on top of the existing mine workings; variant 2 was planned to utilize an old plan to extend the mine downwards into the deposit, basically under the existing mine workings and variant 3 was planned to protrude through a geological fault further into the deposit layer, at more or less the same altitude of the existing workings. To determine the best variant, these variants were rated at four key performance indicators and compared to each other. These key points are: haulage distance, CAPEX for full de- velopment, difficulty of development and potential further uses if the development workings for future mining development. Variant 3 was almost immediately rejected for high CAPEX. Variants 1 and 2 were investigated further, by simulations for rockmass load conditions and ventilation system behaviour. As the overburden is not very high, the rockmass load conditions were not identified as critical, but in the ventilation system simulations notable discoveries were made. It was discovered that the existing fan is capable of supplying the desired airflow quantity if the duct system is changed to a bigger diameter in critical sections of the system, it was also discovered that, with the right set of ventilation control doors and hatches, a natural ventilation airflow can be utilized to ventilate the mine without a fan. These findings and an approximate CAPEX calculation showed that variant 2 is the best choice for further development under the given circumstances and will lead to a LoM until the late 2030 at the given production rate.