Présentations Colloques

Oral Presentation
8.03
Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
Achtziger-zupan Peter
Fluid Flow in the Faulted Crystalline Basement of the Ore Mountains (Germany)
Groundwater flow in fractured basement rocks on aquifer scale and processes involved in the creation of fracture network permeability are poorly understood even though they have been studied for decades. A unique hydrogeological dataset consisting of 1030 discrete inflows (corresponding to preferential groundwater pathways) to the Poehla Ore Mine (Ore Mountains) of the SDAG Wismut has been compiled and quantitatively interpreted. Transmissivities were calculated for individual inflows using analytical equations. The Variscan basement at Poehla Mine was modelled in 3-D, covering a volume of 14x4x1 km3 with 14 metamorphosed litho-stratigraphic units and 131 faults separated in 6 main strike directions. Mesoscale fractures mapped at inflows points, i.e. locally conductive fractures, show a weak correlation with fault orientation, and a large orientation scattering, which could be related to small scale mechanical heterogeneities. Inflow points were spatially correlated with major faults considering two distance criteria. The inflows are usually situated within multiple fault zones which overlap each other. The orientations of transmissive faults is highly dispersed close to the surface. The depth transition to more focused flow through NE-SW and NW-SE striking faults aligns with the elevation of the valley bottom of the Ohř+e- (Eger-) Rift which is at about 350 to 400 masl. The trace length (extent) and width of the core and damage zones of the modelled faults were compiled in order to investigate the flow distribution and permeability profiles in directions perpendicular to fault strike. It can be shown that 90% of all inflows are located in damage zones. . Cumulative flow distribution functions within damage zones are non-linear and vary between faults with different orientation. 75-95% of the flow occurs in the inner 50% of the damage zone. The flow rate distribution for all faults decreases exponentially from the fault center to the protolith and may be correlated to decreasing exponentially decreasing fracture count.
Switzerland