Bedrock geologic map of the Ladue River-Mount Fairplay area, Tanacross and Nabesna quadrangles, Alaska

The Mineral Resources section of the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted bedrock geologic mapping of a 4,800-sq-km (1,860-sq-mi) area of eastern Interior Alaska, including Mount Fairplay and the Ladue River drainage. The area lies north of the Alaska Highway and is approximately 65 km (40 mi) east of Tok, Alaska; it runs west from the Alaska-Yukon border to encompass the Taylor Highway. DGGS and the U.S. Geological Survey (USGS) staff identified this area as having the potential to host deposits of critical minerals, including rare earth elements (REE), uranium, niobium, zirconium, tin, tungsten, bismuth, and rhenium, as well as conventional mineral resources including gold, copper, molybdenum, lead, zinc, and silver. Most of the known mineralization in the area is related to Cretaceous-Paleogene magmatism, which spans a broad diversity of compositions and ranges in scale from batholiths to shallowly emplaced dikes to volcanic rocks. The igneous rocks intrude a composite metamorphic province that includes both parautochthonous North America and components of the allochthonous Yukon Tanana Terrane, now juxtaposed against one another by Jurassic-Cretaceous low-angle faults and subsequently disrupted by multiple generations of Cretaceous-Cenozoic high-angle faults. Our map interpretation relies on observations of outcrop, subcrop, and float, and we make extensive use of airborne magnetic (Emond and others, 2015) and magnetic-electromagnetic surveys for interpolation between field stations. Our mapping of high-angle faults relies on tilt-derivative processing of aeromagnetic data, low resistivity anomalies in electromagnetic surveys, photo and topographic lineaments, and lithologic discontinuities between ridges. Rock names were assigned based on field and petrographic observations, modal-mineral percentages, and interpretations of geochemical data. Age determinations and interpretation of cross-cutting relationships were facilitated by 40Ar/39Ar and Zircon U-Pb geochronologic analysis. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: http://doi.org/10.14509/30735.

Tags: albian, basalt, batholith, big creek, chicken creek, conglomerate, cretaceous, deep creek, dennison fork, devonian, dggs, eocene, exploration, fortymile mining district, gardiner creek, geologic, gneiss, granite, granodiorite, greenschist, greenstone, igneous, interpretation, jarvis belt, klondike assemblage, ladue river, lake george assemblage, logging cabin creek, mcarthur creek, metamorphic, metamorphism, mineral assessment, mineral deposit, mineral development, mineral exploration, mineral resources, minerals, miocene, mississippian, moosehorn ridge, mount fairplay, mountain, neogene, orthogneiss, paleocene, paleogene, pegmatite, permian, plutonic, plutons, polymetallic, porphyry, pumice, quartzite, resource assessment, resource information, rhyolite, rocks, sandstone, schist, scottie creek, sedimentary, serpentinite, seventymile terrane, south fork ladue river, sulfides, swamp creek, taylor highway, terranes, triassic, tuff, ultramafic, volcanic, yellow water creek, yukon-tanana terrane
Organization: State of Alaska