Electrical resistivities of rock samples (gneiss, greywacke and argillite), obtained from the western part of the La Ronge Domain of the TransHudson Orogen (Northern Saskatchewan) were studied to determine the source of elevated electrical conductivities observed deep in the subsurface of the region.
Analyses show that the resistivities of these rocks cover a wide range of values (0.3 20,000 ohm.m). While the larger values are typical for these types of rocks, the smaller ones are likely due to layers (thicknesses of about 15 mm) of sulphide concentrations. These layers are also a source of significant electrical resistivity anisotropy. These rocks are folded, with sulphide layers accumulated near the hinge of the fold forming a source of high electrical conductivity along its axis. In single specimens, an anisotropy in electrical conductivity of over two orders of magnitude is observable between the three axes of measurement. Generally, the resistivities are 38 ohm.m in the direction of the fold axis, and 2,00020,000 ohm.m for samples from the hostgneissic rock, which gives a bulk anisotropy of 200:1 to 7,000:1 for the metasedimentary unit.
Figure 7: Electrical model for the metasedimentary rocks in the western
La Ronge, showing folded layers containing highly concentrated sulphides near
the hinge of the fold. This suggests resitivities of 3 - 8 ohm.m in the
direction of the fold axis, and 2,000 - 20,000 ohm.m in the other two
directions, for an anisotropy of 200:1 to 700:1.
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