The permeability of the Gorleben-Bank (z3OSM), a strongly deformed veinbearing anhydrite rock layer, was measured in situ in three boreholes of the former Gorleben exploration mine, Germany. The corresponding drill cores were investigated for their microstructures and their mineralogical properties. The veins cutting through anhydrite rock consist of halite, kieserite, carnallite, sylvite and small amounts of polyhalite. Subgrains with a size of 100 ±40 µm are omnipresent in halite of the veins

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... and of the surrounding salt rocks. The corresponding paleodifferential stresses (2.0 +1.0/-0.5 MPa) are consistent with published values. The hydraulic borehole tests were carried out using nitrogen gas and in form of pulse tests. The permeability obtained for the Gorleben-Bank is generally <10 -20 m 2 , independent of the amount, size, orientation and mineralogical composition of healed fractures. Similar values for permeability were obtained from adjacent salt rocks. The results of the present study suggest that pervasive pathways for brines are lacking in the anhydrite rocks as most of the open fractures are healed.