However, there are also small veins containing barite and pitchblende and the nature of this deposit is under discussion. Most likely it is a combination of a sedimentary style and hydrothermal mineralisation. Construction of the mine started immediately after the discovery and two main shaft along with several ventilation shafts were sunk to depths up to 300 m. Mining started in 1967 and it developed into one of the main producers of SDAG Wismut in the 1970s, with more than 1,000 tonnes of uranium per year in this decade. The ore mined was transported by a cable way down to the Elbe river valley from where it was transported by rail to the mill at Seelingstädt. Besides conventional mining using drilling, blasting and transport of the ore to the mill, already in 1969 studies were started on unconventional production methods for low grade ore using leaching. The low permeability of the sandstone prevented usual in-situ leaching from drillings. Therefore, different methods were developed to blast the ore underground, seal the blasted blocks, and press sulphuric acid into them. Heap leaching was also carried out as well as uranium extraction from mine water before it was released into the Elbe River. In 1984 conventional ore production ceased and only unconventional methods were used from that year on. Production sunk to about 450 tonnes uranium per year, but the Königstein mining division produced at the lowest costs of all Wismut mining divisions. The uranium bearing solution from leaching was transported by rail to the Seelingstädt mill where the final concentrate was produced. Total production of uranium until 1990 was about 18,000 tonnes, with 12,250 tonnes by conventional mining and 5,750 tonnes by unconventional methods. In 1990 production ceased, as in the other mining divisions. However, the hydrogeological situation was difficult because of the high amount of uranium-bearing solution in the sandstone units hosting the mineralistion. Above that unit there are three aquifers supplying water to the cities of Pirna and Dresden. Therefore, large amounts of water had to be treated before the mine could finally be flooded. The uranium extracted in this cleaning process was sold to an American company in solution form. The total production of uranium from the mine water treatment between 1991 and 2008 can be estimated to be 1,000 t. This mining area covers parts of the cities Dresden (part Gittersee) and Freital. Mining for hard coal in the area is known to date from the 16th century. In 1949 Wismut studied radioactive anomalies in parts of the coal field and took over some mines.