The vein Maria Theresa, which is the most significant representative of manganese mineralization in the Krušné hory Mts, runs through the area below the Jelení hora Mountain (spot height 935 m) northwest of Horní Blatná. The vein with some strings penetrates fine-grained porphyric granites of the Horní Blatná Massif. The manganese ore mineralization was followed by the mining of an area more than 500 m in length and around 50 m in depth. The vein had variable thicknesses: 4-6 m at the level of the Segen Gottes Gallery, 6 m in the Concordia Gallery and 1-2 m in the Theresa Mine.
At the beginning of the 19th century, manganese ores were used for glass fining, colouring glasses violet, and as a pigment in potters’ glazes. Later their significance increased due to the development of the steel industry, and they were also employed in the fabrication of chlorine and oxygen. At the time of the greatest boom in the years 1852-1858, roughly 400 tons of these ores were mined near Horní Blatná. The economics of mining was also improved by the accompanying hematite occurrence.
However, during World War I import opportunities worsened and the ironworks began to suffer from lack of manganese ore. In addition, the mining of the Maria Theresa vein was renewed after several decades. 120 tons of ore containing 8–10 % manganese was gained from the Concordia Gallery. In the year 1917, mining moved into the gallery Segen Gottes, where roughly 50 tons of a rich ore with an average content of 25 % MnO2 was gained monthly. The last time both galleries were made accessible was during a geological survey in the years 1956-1958, however, their sunken entrances and overgrown dump piles are still apparent.
Tin was mined on the Jelení hora earlier than manganese ore, most likely ever since mediaeval times. The oldest mine cited, Altvater, is from the year 1535. The tin ore mineralization was bound to a series of steep greisen (rock composed of quartz and mica) zones, which course is apparent from the preserved lines of small depressions. On the other hand, the youngest mining activities are related to the uranium survey after World War II when a test pit was dug out by the Jáchymovské doly, roughly 300 m to the south from the entrance of Segen Gottes gallery.
The vein Marie Terezie is a historically significant mineralogical locality. It is known mainly for the occurrence of rich crystalline exemplars of grey-black manganese oxide - pyrolusite. Mineral specimens from this locality were the objects of one of the first scientific investigations of manganese minerals. The Austrian geologist and mineralogist, Wilhelm K. Haidinger, mainly dealt with them, and in fact in 1827 he described pyrolusite for the first time ever in the world. In 1824, the curator of mineralogical collections of the Patriotic Museum, Franz Xavier Maxmilian Zippe visited the mines personally, and the German mineralogist, August Breithaupt, did as well in 1843. The site is a favourite locality of collectors up to the present time.
Fig.:
1. Map
2. The dump of the galleries Theresa and Concordia
3. Upper dump of the Mine Maria Theresa
4. Pyrolusite