Active potash mine and main processing facility of the Verbundbergwerk Werra at Heringen, operating from the Schacht Grimberg (Schacht Wintershall) since 1903, continuously producing potash and magnesium salts as the principal site of the K+S Werk Werra.
The Schacht Wintershall, officially the Schacht Grimberg, is the founding shaft of the Kaliwerk Wintershall at Heringen (Werra) and the production and processing centre of the Werk Werra component of the K+S Verbundbergwerk Werra. The Bohrgesellschaft Wintershall was founded in 1893 in Kamen, Westphalia; exploratory boreholes in the Heringen area proved successful, and on 23 April 1900 the first spit was turned for the sinking of the Schacht Grimberg, named after the company founder Heinrich Grimberg. After two years of sinking, the upper potash seam was reached at 424 metres in September 1902 and the final shaft depth was achieved in December 1902 at approximately 530 metres.
Production began in 1903; a Chlorkalium- und Sulfatfabrik entered service on 1 January 1905. By 1930 Wintershall had grown into the dominant potash concern in Germany at the Werra, controlling all Werra field operators except the Kaliwerk Hattorf. A severe Gebirgsschlag (rock burst) struck the mine on 22 February 1954.
In 1976 the mine began electrostatic raw-salt separation (ESTA), the second site in the Neuhof-Ellers group to do so. An underground connection between Wintershall and the Hattorf workings was established in 1979. The Verbundbergwerk Werra was formally constituted in 1997.
The Schacht Grimberg remains the active central hoisting shaft of the Kaliwerk Wintershall today, with the processing plant, spoil heap, and central workshop all located on the Heringen site.
The foundations of the Kaliwerk Wintershall lie in the discovery of potash salts in the Werra valley in 1893, when on 5 October of that year a four-metre borehole core from the Saline Kaiseroda field demonstrated the presence of workable Kali deposits. The response from the financial community was rapid: the Gesellschaft Wintershall was founded in Bochum on 13 February 1894 specifically to drill for potash in the Heringen area. An early attempt at the Schacht Salzungen in Leimbach, completed in 1899, produced a shaft that had to be abandoned in 1901 due to heavy carbon dioxide emissions; a company was subsequently formed to exploit the carbon dioxide at that site. The Schacht Salzungen was therefore the first attempt and a failed one.
The productive Schacht Grimberg was begun on 23 April 1900 at Widdershausen, near the present Kaliwerk Wintershall site. The Plattendolomit was first reached on 9 December 1901 and was driven through by hand, with large water inrushes to be managed, by 12 February 1902 — the first time this geological horizon had been penetrated manually in the Werra-Fulda Kalirevier. In September 1902 the upper potash seam was found at 424 metres, and the final depth of the shaft was achieved in December 1902 at approximately 530 metres. The Fördergerüst was erected in June 1903 and the railway connection to the national network was completed on 2 March 1904. On 1 January 1905 the Chlorkaliumfabrik and the Sulfatfabrik both entered service. Production of potash salts commenced in 1903. The Gewerkschaft Wintershall was the operating entity at this stage.
The first Spatenstich for the Schacht Heringen — the second shaft required by the Zweischachtverordnung and also a Quotenschacht to expand the Wintershall group's Kali-Syndikat allocation — was made on 1 June 1907. The underground breakthrough between Schacht Wintershall (Grimberg) and Schacht Heringen was achieved on 1 April 1912.
Through a series of financially deft acquisitions from the mid-1910s through the 1920s, the Gewerkschaft Wintershall assembled a dominant position in the Werra Kalirevier, gaining controlling interests in the Gewerkschaften Sachsen-Weimar, Kaiseroda, Heiligenroda, and other neighbouring operators. The Wintershall AG was formally constituted in 1929. By 1930, every Werra field operator except the Kaliwerk Hattorf belonged to the Wintershall group. During the National Socialist period, the commercial attention of the Wintershall AG's leadership shifted increasingly toward petroleum exploration and production; the potash works continued to rely on forced labour to maintain production.
On 2 July 1955 a major industrial accident occurred at the Kaliwerk Wintershall: during the unloading of chlorine from a railway tanker wagon, the filling line broke under pressure because the locomotive moved too early. A large chlorine gas cloud at a pressure of 8 bar was released at ground level and drifted eastward; several settlements including Widdershausen had to be evacuated and 62 people were treated in hospital.
In 1962 production of high-purity salts commenced at the Wintershall works. In 1970 the Wintershall AG's potash operations were separated from its petroleum interests and merged with the Salzdetfurth AG to form the Kali und Salz GmbH, a BASF subsidiary. In 1976 the electrostatic raw-salt separation (ESTA) process was taken into operation at the Wintershall works. In 1979 an underground connection was established between the Wintershall and Hattorf workings, creating a combined field of approximately 150 square kilometres. Central workshops for the future Verbundbergwerk Werra were established at the Heringen site in 1993. In 1997 the Verbundbergwerk Werra was constituted, bringing together the Wintershall and Hattorf sites in Hessen with the Unterbreizbach and Merkers sites in Thüringen. In 2005 the Sylvinit project began bringing additional raw salt from Unterbreizbach to the Wintershall surface through the underground connection. The Schacht Grimberg (Schacht Wintershall) remains the active central hoisting shaft of the Kaliwerk Wintershall and the processing and logistics hub of the Verbundbergwerk Werra.