The existence of authigenic and reworked clays in fault zones is well understood to control the hydrologic and mechanical properties of faults. The net effect these clays have on fluid conductivity, reservoir quality, and fluid-derived mineralization is dependent on the origin of the gouge. To address this topic, I collected samples along four high-angle normal faults exposed within a copper mine in Lisbon Valley of Southeast Utah. The GTO, Lisbon Valley, Keystone, and Centennial faults were all sampled in gouge zones ranging from ~0.1 to ~5.5 meters across. Fault displacement ranged from 5 meters to 400 meters. Complementing field work was XRD analysis of all suitable samples to determine the quantity and type of clay in each gouge. We related the hydrologic properties affected by fault gouge with shale gouge ratio (SGR) and fault permeability computer modeling. SGR quantitatively estimates clay amounts in fault gouge that allow fault zone permeability estimates to be derived. Field interpretations suggest gouge zones are dominated by either maroon or green clays with most sites having lenses of the non-dominant component. Sampled gouge zones have grain sizes ranging from clay to fine sand and are poorly to moderately consolidated. Color of gouge samples does not seem to correlate with offset of faults, however, there is a correlation between grain-size and fault offset. XRD data shows high concentrations of illite and quartz in nearly all samples, and kaolinite present in samples with green/yellow hues. Modeling results predict high seal potential from SGR and very low permeability in nearly all sample sites. Understanding the effect on hydrologic dynamics will ultimately assist the team of geologists at the Lisbon Valley Mine further understand and predict copper mineralization along fault zones in the area along with constraints on fault-seal capacity when considering in-situ recovery.
