Active salt mine ventilation shaft at Heidwinkel near Grasleben, sunk in April 1912 as the first Heidwinkel shaft for the Gewerkschaft Braunschweig-Lüneburg, now serving as the second shaft exit and ventilation inlet for the Steinsalzwerk Braunschweig-Lün
Schacht Heidwinkel I is the older of the two shaft installations at Heidwinkel, a settlement in the Gemarkung of Grasleben, approximately two kilometres north-west of Grasleben in the Landkreis Helmstedt, Niedersachsen. It was sunk from April 1912 by the Gewerkschaft Braunschweig-Lüneburg, 2,500 metres north-east of the main Schacht Grasleben, as the second operational shaft for the Kali- und Steinsalzwerk Braunschweig-Lüneburg. The 670-metre-deep shaft, with an internal diameter of 4.75 metres, was completed in only fourteen months; cast-iron tubbing was applied to 92 metres and masonry below.
Potash production at Heidwinkel began on 1 November 1913. Raw salt was transported first by aerial ropeway and then by narrow-gauge railway to the processing plant at Schacht Grasleben. Potash extraction ended in 1922 when the K₂O content of the salts proved uneconomic at 8.9 per cent; from 1 January 1926 the mine operated exclusively as a rock-salt installation.
In 1936 the Wehrmacht took over the Heidwinkel installation for use as a Heeresmunitionsanstalt, requiring the construction of an additional independent shaft — Schacht Heidwinkel II, sunk 1937–1939. The Heidwinkel I/II installation was returned to the Gewerkschaft Braunschweig-Lüneburg in 1949 after munitions clearance; salt hoisting resumed immediately. In 1957 an underground connection of 2,500 metres was first driven between the Heidwinkel shafts and Schacht Grasleben.
Today Schacht Heidwinkel I serves as the second shaft exit for the mine and as a ventilation inlet; its Fördergerüst, Fördermaschinenhaus, and Schachthalle survive on the site.
The first shaft at Heidwinkel was sunk beginning in April 1912, when the Gewerkschaft Braunschweig-Lüneburg commenced work on a second shaft site approximately 2,500 metres north-east of the main Schacht Grasleben. The Niederbringen required only fourteen months; the shaft was 670 metres deep with a clear internal diameter of 4.75 metres, constructed with cast-iron Tübbings to 92 metres and masonry from that depth to the bottom. Potash production from the Heidwinkel installation began on 1 November 1913, making it the earlier of the two principal shaft sites in the mine. Raw salt raised at Heidwinkel was transported to the Grasleben processing factory first by a Drahtseilbahn (wire-rope aerial ropeway) and subsequently by Schmalspurbahn (narrow-gauge railway). Under the Braunschweig mining law, the two shaft installations were not legally required to be connected underground and therefore remained legally distinct Bergwerke until their first underground connection was established in 1957.
Potash production at both shaft sites ended in 1922 when extracted salt analysis showed a K₂O content of only 8.9 per cent, making potash processing uneconomic. Under the Stillegungsverordnung § 83a, both shafts were classified as Kalibergwerke on standby until 1953. From 1 January 1926, the enterprise converted entirely to rock-salt extraction and has maintained this status ever since, operating as a Steinsalzwerk.
In 1936 the Wehrmacht took over the Schacht Heidwinkel installation and placed it under military control, prohibiting its continued use for salt extraction. The intention was to use the underground workings for protected munitions storage. To allow the Heeresmunitionsanstalt to operate independently of the civil salt operation, a second shaft — Schacht Heidwinkel II — was sunk between 1937 and 1939 to 662 metres. Munitions storage operations commenced in 1938. After the US Army occupied the Heidwinkel site in April 1945 and transferred it to British military administration, displaced persons settled in the former Waldlager camp buildings from 1946, and a Catholic chapel was established there the same year. In 1949, following the completion of munitions chamber clearance and sealing, the full Schachtanlage Heidwinkel I/II was returned to the Gewerkschaft Braunschweig-Lüneburg. Salt hoisting resumed in the same year, initially at the Schacht Grasleben, and subsequently from both Heidwinkel shafts.
In July 1957 the first underground connecting roadway of 2,500 metres was driven between the Heidwinkel I/II installation and the Schacht Grasleben, for the first time making the previously independent installations into a single legally unified mine. The two former Muna levels at 570 and 645 metres in the Heidwinkel II section were retained as working levels. In the 1980s, Schacht Grasleben received a new headframe and was simplified from a Doppelförderanlage to a single hoisting arrangement; it became the central Seilfahrts-, Förder-, und ausziehender Wetterschacht (combined personnel, production, and outflow ventilation shaft). Schacht Heidwinkel I and II together serve as the second mine exit and the principal intake ventilation inlet. The Schacht Heidwinkel I site retains its original Fördergerüst, Fördermaschinenhaus, and Schachthalle. Since 2002 the Steinsalzwerk Braunschweig-Lüneburg has been operated by the European Salt Company (ESCO), a wholly owned subsidiary of K+S.