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Lithogenesis of Halite-Carnallite Veins in the Gorleben Previous HitSaltNext Hit Previous HitDomeNext Hit

FISCHBECK, REINHARD R., OTTO BORNEMANN, and GERHARD MINGERZAHN

Halite-carnallite veins were observed at a depth of 355 m when an exploration mine shaft was sunk in the Gorleben Previous HitsaltNext Hit Previous HitdomeNext Hit. Gorleben is located in NW Germany near the Elbe river. The Previous HitsaltNext Hit Previous HitdomeNext Hit is being considered as a site for permanent storage of radioactive waste materials. The long-term integrity of a Previous HitsaltNext Hit Previous HitdomeNext Hit can best be assessed by the study of mineral reactions and mineral substance transport which occurred primarily during the formation of the Previous HitdomeNext Hit and in the geological past. Harmful substances can be transported to the biosphere from a permanent repository in a Previous HitsaltNext Hit Previous HitdomeNext Hit by aqueous solutions only. Therefore, understanding how the halite-carnallite veins were formed in the geological past is important for the evaluation of the future integrity of the Previous HitsaltNext Hit Previous HitdomeNext Hit.

We propose a model for the formation of the halite-carnallite veins which is based on petrographic examinations and the fact that the bromine content of the chloride Previous HitsaltNext Hit minerals of the veins can be used as an indicator of their genetic origin and the rubidium content can be used as an indicator for the potassium-bearing Previous HitsaltNext Hit minerals. Halite was formed when solutions rich in MgCl[2] from within the Previous HitsaltNext Hit Previous HitdomeNext Hit mixed with NaCl solutions from the fringe of the Previous HitsaltNext Hit Previous HitdomeNext Hit or from outside. The MgCl[2] solutions are of metamorphic origin or remnant solutions from the Zechstein sea. The fractures were not completely filled by the crystallization of hypidiomorphic halite. Later, the 1 to 2 cm thick sulfate layers which permeate the wall rock acted as pathways for MgCl[2] solutions rising from the hot lower regions of the Previous HitsaltNext Hit Previous HitdomeTop. Carnallite then crystallized in the remaining voids due to the drop in temperature. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.