GEOLOGIC MAPPING OF FRACTURE DENSITY AND MINERALIZATION IN THE SAN FRANCISCO RANGE, SOUTHWESTERN UTAH

The San Francisco Range in southwestern Utah has been mined heavily over the last several decades. Mining has been concentrated in Tertiary quartz monzonite intrusions into Paleozoic limestones. Significant resources occur along two major faults containing rich hydrothermal porphyry deposits, but the intersection of these faults has yet to be documented in detail due to poor outcrop exposure. In a partnership with a local mining company, undergraduates from Southern Utah University have begun preliminary mapping to locate and describe this fault intersection before underground exploration can begin. We used a Triton Juno GPS device to record the locations of exposed fractures, and we measured their fracture densities and orientations with a scale and Brunton compass. Results from rose diagrams, stereonets, and mapping show the existence of the intersection within the study area. Fracture density increases with proximity to the intersection, especially along one of the fracture orientations, and local mineralization along the faults is common. We recommend further exploration in the form of core drilling at the mineralized fault intersection to determine the viability of economic mining.