HYDROTHERMAL MINERALIZATION OF THE JURASSIC NAVAJO SANDSTONE IN THE FOOTWALL OF THE BLUE MOUNTAIN THRUST FAULT, SOUTHWESTERN UTAH

The Wah Wah Mountain Range near Minersville, Utah, has been prospected for mining resources during the last several decades. Resources are concentrated along hydrothermally altered fractures as porphyry deposits, typically where Tertiary quartz monzonite has intruded into Paleozoic limestones. In addition to Tertiary magmatism, the Wah Wah Mountains display significant Late Cretaceous Sevier Orogeny thrusting that placed Paleozoic sedimentary rocks over Middle Cretaceous sedimentary rocks. During a structural mapping project in this region, the Navajo Sandstone in the footwall of the Blue Mountain Thrust Fault was found to have undergone hydrothermal silicification, making it appear to be a quartzite. Upon closer inspection, other hydrothermal mineralization was discovered. These discoveries changed the research focus from documenting the structural geology to documenting the unique hydrothermal alteration in the Navajo Sandstone.

This study included the following methods. The Blue Mountain area was prospected for deposits near the Sevier-age thrust faults. Jurassic Navajo Sandstone samples were collected and thin sections were made to analyze the metal content within the rock. Samples found near the eastern-most edge of the Blue Mountain Thrust Fault contain quartz, hematite, and other minor metals. Mineralization is not particularly abundant, but the vein could be richer in metal deposits with increased depths. Further analysis, such as an analysis of gravity and core data, is necessary to determine the value of the mineralization.