Former potash mine at Menzengraben, Thuringia, whose shafts remain in active use by K+S as material and ventilation shafts within the Verbundwerk Werra.
Schacht Menzengraben I, known as Großherzog von Sachsen II, was the first of two shafts sunk at Menzengraben from 1911 in the northern fields of Stadtlengsfeld, approximately 2.5 kilometres from the primary Dietlas shaft of the Gewerkschaft Großherzog von Sachsen. Sinking of Schacht II began in spring 1911 and the shaft was completed in 1916; a companion shaft, Schacht III, was begun in the same year and reached the potash seam in 1924. The lower potash bed lay at approximately 525 metres depth and averaged 11 metres in thickness.
A large chemical processing plant serving both shafts came into operation in early 1923. After Schacht Dietlas closed in 1926, crude salt from Menzengraben was diverted to the Heiligenroda factory at Dorndorf. The Wintershall AG operated the site before the Second World War and used the carnallite for magnesium production.
In 1946 the site passed to the Soviet SAG Kali and later to the East German state. Two serious carbon dioxide outbursts, in 1953 and 1958, killed nine people in total and led to the progressive cessation of potash extraction by 1966. Schacht II has since been retained by K+S as a material and manriding shaft serving the wider Verbundwerk Werra network.
The Menzengraben shaft complex came into being as an expansion of the Gewerkschaft Großherzog von Sachsen during the years before the First World War. In spring 1911, twelve hectares of land were acquired in the southern field of the concession and construction of a double-shaft installation began. Schacht II, which carried the designation Großherzog von Sachsen II, had its sinking begin in 1911; the shaft was completed and in production by 1916.
A headframe, winding engine building, pithead baths, electric winding machine house, steam turbine house, and fan house were erected at Schacht II. The companion shaft, Schacht III (Großherzog von Sachsen III), had its sinking also begun in 1911; however, it advanced more slowly and the potash seam was not intersected until 17 April 1924, at a depth of 524 metres. Schacht III was connected underground with Schacht II.
The lower potash bed at the Menzengraben site lay at approximately 525 metres and displayed an average thickness of 11 metres; the carnallite encountered was notable for its purity and white colouration. The upper seam was not deemed workable. A large chemical processing plant at the Menzengraben shafts, built from around 1921, came into operation at the beginning of 1923.
It was designed initially to process 10,000 quintals of crude salt per day. In 1922 the Großherzog von Sachsen Aktiengesellschaft carried out a field exchange with the Gewerkschaften Heiligenroda and Kaiseroda to rationalise the concession boundaries. After the closure of Schacht Dietlas in June 1926 due to technical problems, the production from Menzengraben was rerouted to the Heiligenroda factory at Dorndorf.
The Wintershall AG operated the site. During the Second World War, carnallite from Menzengraben was transported to the Heringen plant of Wintershall, where an electrolysis process converted it into magnesium for use in aluminium alloys for the aviation industry. Workers were also trained at the Menzengraben winding engines by outside firms preparing to take over other facilities.
After the Second World War the site fell within the Soviet occupation zone. In 1946 the Wintershall AG was expropriated and the works transferred to the Sowjetische Aktiengesellschaft (SAG) Kali. Operations resumed in 1946 and a new rail connection was re-established on the former alignment.
The site was returned to the DDR in 1952 and incorporated into the VEB structure in subsequent years. On 7 July 1953 a major carbon dioxide outburst in the shaft killed three people above ground: two men and a woman. Between 1,100 and 3,900 tonnes of carbon dioxide were released over more than twenty minutes, forming a dense ground-level cloud that spread through the Felda valley and reached the nearby settlements of Stadtlengsfeld and Dietlas.
This event remains the only recorded mining accident in which people above ground were killed by carbon dioxide. In April 1958 a second outburst occurred when a prospecting borehole at 71.5 metres depth struck a gas pocket. The gas spread explosively through the underground workings, killing six miners.
In reaction to the 1958 disaster, potash extraction was progressively wound down, and mining ceased entirely by 1966. Following connection of the Menzengraben underground workings to the Merkers mine field during the DDR period, the surface structures above ground were demolished, with the exception of a few buildings adapted to other uses. Schacht II has since remained in use, currently serving as a material and manriding shaft for the transportation of large vehicle parts and aggregate to the Merkers and Unterbreizbach underground operations.
Schacht III retains pipework serving the underground operations.