2.2.3 Alpine environment The mining site is in extremely steep, high alpine area with harsh climatic conditions. Weissenstein open pit is only operational during snow-free periods. Accessibility and avalanche danger are limiting factors. Also, for future backfill extraction at Bürgl site this will be very true; it is thus anticipated to extract and sort the backfill during summer months. Backfill should be stored for the winter months in the abandoned Bürgl open pit connecting it with a draw point chute to the future underground mine. 2.2.4 Tourism The mining site is in an area of multiple land use by tourism and agriculture, causing further constrains for the operation. 3. ROCK ENGINEERING CONSIDERATIONS 3.1 Rock Engineering Challenges 3.1.1 Complex Geological Setting As described in the previous section, the geology of the deposit is unique. The foot wall consists of stable dolomite. Above this lies the first magnesite lens, which is separated from the magnesite above it by the porphyroid layer. The valley floor is formed of less stable black shale. This shale can be considered to have low strength. For this reason, it can be assumed that it has no regional load-bearing effect. As the distance between the future stopes and the surface is comparatively small. Similarly, to the black shale, the porphyroid is also low-strength and has a limited load bearing capacity. Additionally, the porphyroid is mylonitised in areas less than 1 m thick and has very low strength. Like the dolomite in the hanging wall, the magnesite is stable. However, the low-strength porphyroid can cause instabilities in the rock mass, which can lead to an increase in shear stresses in the mining area. Figure 1 gives a schematic overview on the geological setting in Hochfilzen. This geological setting can primarily influence the stability of stopes and pillars. For this reason, this circumstance must be taken into account when dimensioning the stopes and pillars. Porphyroid can also be problematic in terms of quality control, as the high silicate content reduces the quality of the magnesite extracted in the chambers. For this reason, attention must also be paid to minimizing dilution during mining. At the same time, the different qualities of magnesite are distributed unevenly throughout the deposit. This means that besides the rock engineering challenges, selective mining is also a major goal in Hochfilzen. Due to the rather small size of the deposit, it is of major importance, to optimize the recovery of the mine. However, mine safety should be one of the major topics. This implies that safe mining conditions are given to any time during the mining process in Hochfilzen.
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