A Case Study of Integrating Geophysical, Geochemical, and Field Data to Map Shallow Faulting and help Evaluate the Earthquake Potential Near the San Francisco Mountains, Beaver County, Utah

摘要

The area west of the San Francisco Mountains, located approximately 20 miles northwest of Milford, Beaver County, Utah, is underlain by Paleozoic limestones, shales, and sandstones, as well as Cenozoic volcanic rocks, which were intruded by an Oligocene quartz monzonite. It is very difficult the evaluate the subsurface geology in this area because of an extensive alluvial cover. Locations of suspected subsurface faults are unknown due to a thick, gently sloping erosional surface west of the base of Frisco Peak that was probably produced in the past by water running through this arid region. The research area is bounded by the San Francisco Mountains to the east, Wah Wah Valley to the west, highway 21 to the south, and the northern end of the San Francisco Mountains to the north. A variety of geophysical data acquired in the study area were processed, integrated, and interpreted for subsurface structures. By integrating these geophysical data with field and geochemical data taken from a distribution of rock samples in the study area, a large fault has been interpreted to lie beneath the pediment surface west of Frisco Peak. This fault, along with other interpreted associated concealed faults, help to estimate the earthquake potential of the area, groundwater flow patterns, and the extent of possible ore deposits. Rock samples taken from the pediment gravels show the presence of copper ore, and the geophysical data indicate there may be economically recoverable ore deposits concealed beneath the study area. Mineral enrichment probably occurred when fluids from the quartz monzonite intrusion west of the San Francisco Mountains moved along subsurface faults and fissures and reacted with the adjacent sedimentary and volcanic rocks to form porphyry ore deposits. The combination of geophysical, geochemical, and field data provides a cost-effective way to map the subsurface geology and assess earthquake, groundwater, and ore body potential.