Upper Rhine saliferous basin
UPPER RHINE SALIFEROUS BASIN (RU: Верхнерейнский соленосный бассейн) is one of the largest basins of the potassium salts within Europe; the largest part of this basin is situated on the territory of France, and the smaller part is situated within West Germany. The Alsatian deposit of the potassium salts is the major raw material base of the potassium industry within France. The depositions of the salt have been discovered during the 1904, and the development of these salts has been started during the 1910.
The saliferous depositions (Upper Eocene - Lower Miocene) are well developed throughout 200 kilometres to the north of the Mulhouse city, the maximal width is 30 kilometres, the area is approximately 5500 square kilometres. These depositions are represented by the interbedded layers of the marls, dolomites, clays, and rock salt, with the total thickness of approximately 2000 metres. The basin is situated within the limits of the southern part of the Rhine graben. There have the industrial importance the two layers of the potassium salts (Lower Oligocene), which are formed of sylvite. The lower layer (2-5.3 metres) is well developed on the area of 170 square kilometres, and contains 15-25% (18% on average) of the K2O compound; the upper layer (0.9-2.7 metres) is well developed on the area of 90 square kilometres, and contains 22-30% (24% on average) of the K2O compound. There is contained within sylvite up to 12% of the insoluble residue (anhydrite, dolomite, and clay).
The extraction of the potassium salts is concentrated within the region of the Mulhouse city, and is performed by the "Mines de Potasse d'Alsase S. A." firm. There work three underground potassium mines; the quantities of the production of the potassium salts are 12 million tonnes per year (1978). The depth of the development is from 420 to 1100 metres. The systems for the development are: room and pillar, and continuous. The first system is used at the bottom layer with the thickness of more than 1.7 metres. There is characteristic for the technology of the extraction the high degree of mechanization (the hydraulic mechanized roof support, the self-propelled railway wagons, the combined extracting machines, and so on). The ratio of the extraction of the reserves is 93-97%. The development is complicated by the release of the gases, which are caused by the presence of the bituminous depositions, by the mine bumps, unstable roof, and high temperature. By the middle of the 80-ies, there is expected the transition to the continuous system for the development. The potassium salts are mostly used for the production of fertilizers, the obtainment of which is performed using the chemical (halurgical) and flotation methods. There are produced the fertilizers with the content of 50% and 60% of the K2O compound. During the 1980, there has been produced 1.89 million tonnes of fertilizers (in terms of the K2O compound).
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