U-Pb zircon ages from bedrock samples collected in the Tanacross and Nabesna quadrangles, eastern Alaska

This Alaska Division of Geological & Geophysical Surveys (DGGS) Preliminary Interpretive Report presents uranium-lead (U-Pb) ages of zircons from 37 igneous and metamorphic samples collected during the 2019 field season in support of a 4,800-sq-km (1,860-sq-mi) bedrock geologic map of eastern Interior Alaska surrounding 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 U.S. Geological Survey (USGS) staff identified this area as having underexplored 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. The goal of this U-Pb isotopic study is to better understand the Devonian through Paleogene magmatic and tectonic events, which have been linked to most of the known mineralization in the Yukon-Tanana Uplands. The Mount Fairplay and Ladue River areas are characterized by amphibolite- to greenschist-facies metamorphic rocks-the Lake George assemblage, Ladue River unit, and the Klondike assemblage-which have Mississippian-Devonian and Permian protolith ages. Voluminous volcanic and plutonic rocks of varying composition and texture from the mid-Cretaceous (ca. 100-115 Ma), Late Cretaceous (ca. 65-71 Ma), and Paleogene (ca. 57-58 Ma) magmatic episodes were observed to be emplaced in both the Lake George and Ladue River metamorphic units. Alaska DGGS and the USGS staff have identified both generations of Cretaceous magmatism as having potential to host deposits of the critical minerals mentioned above. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30732.