History
The identification of potash in the Werra valley began with a series of exploratory boreholes commissioned by successive owners of the Saline Kaiseroda concession. Early boreholes in 1816 and 1825 at Unterrohn and Kaiseroda failed to find potash; further borings in 1876 and 1881, commissioned by the Berlin banker Leopold Hadra after he acquired the concession on 24 December 1879, encountered rock salt at 151 and 144 metres depth respectively. After Hadra's death his widow Franziska Hadra continued the exploration. In the summer of 1893 potash was identified for the first time in borehole no. 5 at Hämbach at a depth of 377 metres, and on 5 October 1893 the finding was officially certified. This date is treated as the founding event of potash mining in the Werra-Fulda-Revier.
The Gewerkschaft Kaiseroda was founded in Berlin on 27 November 1894. Teufarbeiten for Schacht Kaiseroda I began in January 1895 at the site of borehole no. 5 at Hämbach. This was the first shaft sinking in the entire Werra-Fulda-Kalirevier. The upper potash seam was reached at 318 metres depth in March 1900; a second lower layer of carnallite was intersected at 378 metres in April 1900. The teufarbeiten were completed in December 1900 at a final depth of 391 metres. The Gewerkschaft raised an infrastructure loan of 2,500,000 Mark, secured under Großherzoglicher approval of 29 November 1900, at five per cent interest, amortisable from 1906.
Rohsalzförderung from Schacht Kaiseroda I began on 30 April 1901, making it the first operating potash mine in the Werra-Fulda district. A KCl processing plant entered service in November 1901, processing approximately 270 tonnes per day of raw salt hoisted from the mine. The Rasenmühle and Auenmühle on the Werra at Tiefenort were purchased to secure hydroelectric power. A Glaubersalz factory came on stream in February 1904, a Sulfatfabrik and new administrative building and workshops in 1905, and a modern boiler and steam turbine installation in 1912.
In May 1911 the Gewerkschaft Kaiseroda began teufarbeiten for two further shafts, Kaiseroda II and III, at Merkers, 225 metres apart, as a Doppelschachtanlage. These were intended to develop a new, larger field and to provide the basis for a major modern processing plant. On 15 May 1925 the new Kaliwerk Kaiseroda II/III at Merkers, by then part of the Wintershall-Konzern, entered trial operation. At the time it was described as the largest and most modern potash processing plant in the world. The new Merkers plant was large enough to process raw salt from Schacht Kaiseroda I as well as from the adjacent Großherzog von Sachsen shafts at Dietlas; accordingly, the Kaiseroda I processing plant was closed in 1921 and the Dietlas plant in 1924.
In the late 1930s a serious accident occurred at the Schacht Merkers (Kaiseroda II) when a carbon dioxide outburst in 1938 killed eleven men. A further fourteen workers at a salt shed were killed the following day; the central memorial service took place on 2 August 1938.
During the Second World War both the Schächte I and II of Merkers and the shafts of the neighbouring Kaiseroda and Hämbach sites were worked by approximately 700 prisoners of war and forced labourers drawn from occupied territories across Europe. In the closing weeks of the war, large quantities of Reichsbank gold and currency reserves and Kunstgegenstände from Berlin museums — including the bust of Nofretete — were concealed in the Merkers workings. On 8 April 1945 they were discovered by the 3rd US Army, and on 12 April 1945 US generals Eisenhower, Bradley, and Patton descended the shaft to inspect the find, an event that brought Merkers to worldwide attention.
From July 1945 the Kaiseroda works were in the Sowjetische Besatzungszone. Rohsalzförderung resumed in November 1945 and the KCl factory was restarted in December 1945. On 1 September 1946 all potash works in the Soviet zone were incorporated into the Sowjetische Aktiengesellschaft (SAG) for potash fertilisers. On 24 June 1952 the Merkers operation was reorganised as a Volkseigener Betrieb under the designation VEB Kaliwerk Kaiseroda II/III (Merkers). On 5 July 1953 this was renamed VEB Kalikombinat Ernst Thälmann. In 1965 winding of raw salt from Schacht Kaiseroda I was permanently discontinued.
In 1990 the VEB Kombinat Kali was converted into the Mitteldeutsche Kali AG. The three thüringische Werrawerke formed the subsidiary Kali Werra AG. On 22 June 1993 the last raw salt from the Merkers site was hoisted through Schacht III (formerly Kaiseroda III). The Kalibetrieb Merkers was permanently closed on 25 June 1993. Demolition of the Merkers works began on 1 April 1994.
Today the Schacht Kaiseroda I serves as the einziehender Wetterschacht (intake ventilation shaft) for the Grubenbetrieb Merkers of the Werke Werra division of K+S Minerals and Agriculture GmbH. The Erlebnisbergwerk Merkers, operating from the Schacht Kaiseroda III headframe complex, is an active visitor mine offering underground tours to a depth of around 800 metres, with access to the historical gold room and the Kristallhöhle discovered in 1980. The site is an anchor point of the Europäische Route der Industriekultur. A spoil heap consisting of boiler ash and anhydrite is the most visible surface relic at the Kaiseroda I shaft site.