The Burro Canyon Formation in Lisbon Valley, UT forms excellent reservoirs and pathways for fluid storage and transport. Rock permeability is an important metric for geologists and society alike, as it controls the distribution of important resources like metals, petroleum, and water. Chief among these factors that determine permeability are the fractures within a rock. The spatial distribution of fractures is imperative in understanding how fluids flow through the Lisbon Valley District.
The Lisbon Valley District is localized on a NW-trending, doubly plunging anticline. A normal fault (GTO Fault) on the anticline’s southwest flank has a 1000 feet of vertical offset. This fault has acted as a primary pathway for hydrothermal copper-bearing fluids that produced the ore deposits. The influences on localized fracture networks in the area are still relatively understudied and have yet to be quantified. A further investigation of Average Fracture Spacing through outcrop and core analysis is necessary in determining the controls on damage zones and how that relates to permeability and fluid flow at the Lisbon Valley Mine.
A total of six cores were collected from the Lisbon Valley Mining Company and were systematically examined to determine AFS based on proximity to the fault. Parameters described in each core include: number of fractures, upper/lower terminus depth, length, aperture, dip relative to core axis, and cementation. This quantitative data was inserted into an Excel calculator using the calculation methods of Narr (1996) to obtain AFS measurements within a given core.
AFS values vary from as low as 4.48 ft near the fault, up to 22.14 ft further from the fault. The distribution of fractures theoretically should be more intense closer to the normal fault. However, the additional structures in the area could be influencing the fracture networks in a way that contradicts this.
Results from this analysis can be used to plan for in-situ recovery of copper at the Lisbon Valley Mine. The data received from the AFS calculations can be used by the geologists and engineers at the mine site to create 3D/4D models to observe spatial distribution of fractures and estimate permeability and fluid flow. Existing permeability and porosity data at the mine can also be quantitatively compared to AFS values.
