Maps showing distribution of thorium in heavy-mineral concentrates, Richfield 1° x 2° quadrangle, Utah
These maps are part of a folio of maps of the Richfield 1° x 2 ° quadrangle, Utah, prepared under the Conterminuous United States Mineral Assessment Program. Other publications in this folio are listed in the selected references. Located in west-central Utah, the Richfield quadrangle covers the eastern part of the Plioche-Marysvale igneous and mineral belt, which extends from the vicinity of Plioche in southeastern Nevada east-northeastward for 250 km (155 mi) into central Utah. The western two-thirds of the Richfield quadrangle is in the Basin and Range province and the eastern third is in the High Plateaus of Utah, a subprovince of the Colorado Plateau. Bedrock in the northern part of the Richfield quadrangle consists predominantly of latest Precambrian and Paleozoic sedimentary strata that were thrust eastward during the Sevier orogeny in Cretaceous time onto an autochthon of Mesozoic sedimentary rocks in the eastern part of the quadrangle. The southern part of the quadrangle is largely underlain by Oligocene and younger volcanic rocks and related intrusions. Extensional tectonism in late Cenozoic time broke the bedrock terrane into a series of north-trending fault blocks; the uplifted mountain areas were deeply eroded and the resulting debris deposited in the adjacent basins. Most of the mineral deposits in the Pioche-Marysvale mineral belt were formed during igneous activity in middle and late Cenozoic time. The regional sampling program was designed to define broad geochemical patterns and trends which can be utilized along with geologic and geophysical data to assess the mineral resource potential for this quadrangle. These maps of the Richfield 1° x 2° quadrangle show the regional distributions of copper in two fractions of heavy-mineral concentrates of drainage sediments.