Permeabilities of the Ore Mountains.xlsx

An outstanding legacy dataset has been compiled from underground
excavations mostly prospected and mined by the former Soviet (-German) Stock
Company Wismut describing the hydrology of faulted basement rocks in the Ore
Mountains (SE Germany). It consists of more than 5000 detailed descriptions of
groundwater inflows to about 660 km of tunnels and 57 km of drillings measured
during or shortly after excavation. Inflow measurements (recorded between 1E-8
to 4E-2 m3/s) have been converted to fracture transmissivities using
a simplified analytical solution. Discarding site specific effects, the median
log transmissivity decreases from 1E-7 to 1E-10 m2/s within the
studied depth interval of 0-2000 mbgs and the spacing of conductive fracture
increases from 0.1 to 2500 m. This general trend is overprinted at three mining
sites by a clear reversal of fracture transmissivity which correlates with contact
metamorphic aureoles around Variscan granite intrusions (327-295 Ma). We
hypothesize that this transmissivity increase is caused by processes
accompanying granite intrusion and contact metamorphism. The thickness of these
hydraulically active aureoles is greater in lower grade metamorphic schist than
in higher grade metamorphic gneisses. Rock mass equivalent continuum conductivities
have been estimated by arithmetic averaging of fracture and matrix
transmissivities over 100 m intervals and have been converted to permeabilities.
The median equivalent continuum permeability decreases with depth according to

 (k in m2 and increasing depth z in km being positive). Matrix conductivity
controls the bulk conductivity below about 1000 mbgs and is less sensitive to the
occurrence of contact metamorphic aureoles.