1. INTRODUCTION Since 1958, magnesite has been extracted and processed into refractories at Hochfilzen in the Austrian Alps. Building on historic open‑pit operations, early underground trials at the Bürgl deposit, and a recent core‑drilling program that updated the geological model, the reactivation of underground mining is being advanced by Montanuniversität Leoben and RHI Magnesita. The deposit comprises four major magnesite lenses and is characterized by complex geometry, steep topography, and a weak porphyroid layer acting as a large fault zone, all within a sensitive alpine environment shaped by tourism and seasonal constraints. 2. HOCHFILZEN MINING SITE – BACKGROUND AND SITE CHARACTERISTICS 2.1 Mining Operation in Hochfilzen Hochfilzen village is located in Tyrol province, 360 km west of Vienna. Magnesite (MgCO3) outcrops were discovered in 1925 by local prospectors. It was soon evident that magnesite is occurring at two mountain ridges (Weissenstein and Bürgl) that are separated by a steep valley. Both sites are roughly 5 km southwest of the Hochfilzen village. Exploration, mainly in form of adits and surface mapping took some time, and several attempts were made to use this type of magnesite for refractories. In the mid 1950ies a breakthrough in carbonate flotation was achieved allowing the treatment of the fine intergrowth of magnesite and dolomite. Hochfilzen plant was constructed in just three years starting in 1957. Initially it consisted of magnesite flotation, briquetting and sintering in a rotary kiln, over the years the plant was significantly enlarged and advanced. Mine development at Bürgl site started in 1958, a combined open pit and underground operation was intended. The plant and the mine site were linked by a material ropeway for ore transport. Perilously exploration was neglected; so, while the underground development work continued it was detected that the size of the deposit was just a fraction of that described by external consultants. In adaptation to the new situation the extraction by two different underground mining methods (open stoping and block caving) was initiated, but soon abandoned; total ore production from underground remained negligible. As the reserves of the open pit had diminished it was decided to develop Weissenstein open pit in 1971, to connect it with a second material ropeway and abandon Bürgl site except for ore transport. Ever since Weissenstein open pit has provided raw material for plant Hochfilzen. As no further push back is possible at Weissenstein because of steep terrain and location of the dumps, exploration core drilling was carried out at Bürgl site from 2015 to 2018 to maintain future magnesite supply. Exploration targets were under the abandoned Bürgl open pit and in areas not developed by the former underground mine. As these efforts were highly successful and enough resources delineated underground mine planning was started.
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