Active rock salt mine at Rheinberg-Borth, Europe's largest of its kind, with Schacht I equipped with a 1964 concrete winding tower still in continuous production for K+S Minerals and Agriculture.
The Steinsalzbergwerk Borth at Rheinberg-Borth is the largest conventionally mined rock salt operation in Europe. The salt deposit in the Niederrheinische Salzpfanne, part of the Werra-Serie of the Zechstein and some 200 metres thick at depths of 500 to nearly 1,000 metres, was discovered in 1897 during exploratory coal borings. The Deutsche Solvay-Werke established a Sodafabrik at Rheinberg in 1906, and from the same year undertook the sinking of Schacht I on the Karlstraße in Borth, a complex and slow process requiring the freezing method throughout because of the proximity of the Rhine and its water-bearing overburden.
Both Schacht I and Schacht II reached a final depth of approximately 850 metres and came into production in 1925, initially extracting coal and salt jointly before the decision in 1930 to abandon coal and focus exclusively on Steinsalz. The original headframe over Schacht I was replaced in 1964/65 by the concrete winding tower that remains in service today. Steinsalz production continues under the ownership of K+S Minerals and Agriculture GmbH, yielding approximately two million tonnes annually across a Berechtsame of 88 km².
The geological formation underlying the Niederrhein between Rheinberg and the Dutch border at Winterswijk was unknown until 1897, when the Deutschen Solvay-Werke, conducting exploratory borings for coal in the communities of Borth and Wallach north of Rheinberg, encountered the Steinsalz deposit of the Werra-Serie (Zechstein 1, z1). The Solvay company initially operated a Sodafabrik at Rheinberg drawing on salt from other sources, but the Bergbaubehörde refused permission for large-scale Aussolung, directing instead that a conventional bergmännisch operation with shafts and underground workings be established.
Schacht I was begun in 1906, the same year as the erection of the Kantine and Kesselhaus on the Borth site. The proximity of the Rhine made the Bergbaubehörde (Oberbergamt) require the Gefrierverfahren for the sinking, even though the method was at that time not yet fully established for these conditions. The long sinking period was further extended by the complications of the First World War and the Inflationszeit. An earlier attempt to sink shafts at Wallach, between Borth and the Rhine, had been abandoned after a fatal water inrush with several deaths; the Wallach site was replaced by the Borth 1/2 location at the boundary of Borth, Menzelen-Ost, Büderich, and Wallach. Both Schacht I and Schacht II reached their final depth of approximately 850 metres in 1925, passing through the Carboniferous strata and the coal seams on the way, and intercepting the 200-metre-thick Steinsalz formation of the Zechstein at depths of 718, 740, and 795 metres. The Steinsalz deposit, with a purity of 98–99 per cent, proved to be of exceptional quality for food, pharmaceutical, and industrial use.
Coal production and salt extraction began simultaneously in 1925. The decision to abandon coal was taken in 1930, partly because the mine was geographically isolated from other Ruhr collieries and could not benefit from centralised infrastructure. From 1930 onwards the Steinsalzbergwerk Borth became an exclusively salt-producing operation, using the Kammerbau method: in each extraction cycle, the salt is drilled, blasted in charges producing approximately 2,000 tonnes per shot, loaded with large wheel loaders, crushed, and transported by conveyor to the shaft. The Kammern, up to 600 metres long, 20 metres wide, and 20 metres high, are supported by salt pillars according to the Stützpfeilerprinzip.
In 1964/65 a new concrete Förderturm was erected over Schacht I to replace the original headframe, and in the same years a Saline for the production of Siedesalz was established, one of the first in Germany, with an initial capacity of 150,000 tonnes per year. The Doppelbock-Förderturm over Schacht II in Fachwerksbauweise was demolished in 2006 and replaced by a modern Vollwandstrebengerüst with greater carrying capacity and reduced to a single-trum hoisting arrangement. The 1964 concrete Förderturm over Schacht I remains in service. In 2011 Schacht I received a new winding machine. The Solvay interests managed the mine until the formation of the joint venture esco - european salt company GmbH & Co. KG with K+S in 2002 (K+S 62%, Solvay 38%), which was fully absorbed by the K+S Gruppe in 2004. The mine is now operated by K+S Minerals and Agriculture GmbH, a subsidiary of K+S AG, and on a Berechtsame of 88 km² produces up to approximately 2,000,000 tonnes of Steinsalz per year. In 2015 the rail transport of salt to the Ossenberger Rheinhafen at Rheinkilometer 806 was replaced by lorry delivery and a new harbour at Wesel.