40Ar/39Ar geochronology data from the Ladue River-Mount Fairbanks area, eastern Alaska

40Ar/39Ar geochronology data from the Ladue River-Mount Fairbanks area, eastern Alaska, Raw Data File 2024-32, provides 40Ar/39Ar geochronology results from rock samples collected in the Tanacross Quadrangle of eastern Alaska within the Ladue River drainage and the upper Dennison Fork of the Fortymile River drainage around Mount Fairplay. During the 2019 field season, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling in the Tanacross Quadrangle of eastern Alaska within the Ladue River drainage and the upper Dennison Fork of the Fortymile River drainage around Mount Fairplay. The area lies northeast of the Alaska Highway between Tok, Alaska, and the Canadian border. A recent geologic map of the area lies within the Yukon-Tanana Uplands, which DGGS and U.S. Geological Survey (USGS) identified as having the potential to host deposits of multiple critical minerals, as well as gold, copper, molybdenum, lead, zinc, and silver. Most known mineralization in the region is related to Cretaceous-Paleogene magmatism. These igneous rocks intrude metamorphic rocks of the North American continental margin and the structurally overlying allochthonous Yukon-Tanana Terrane, both of which are multiply deformed and juxtaposed along low-angle faults. Samples were collected for 40Ar/39Ar geochronology to further understand the crystallization ages of igneous rocks and the exhumation history of metamorphic rocks. This report's 18 40Ar/39Ar samples include one volcanic crystallization age, two pluton-alteration ages, and 15 metamorphic cooling ages. Differences in metamorphic cooling ages have been used to distinguish the allochthonous Yukon-Tanana Terrane from parautochthonous North America. The 15 metamorphic samples with cooling ages reported here were collected to aid in DGGS field mapping near this major terrane boundary. Allochthonous samples include eight samples from the Ladue River assemblage with muscovite cooling ages between ca. 105 and 235 Ma; a sample from the Klondike assemblage with a muscovite cooling age of ca. 147 Ma; a sample from the Fortymile River assemblage with a muscovite cooling age of ca. 186 Ma. Parautochthonous North America samples include a sample from the Jarvis assemblage with a muscovite cooling age of ca. 149 Ma and four samples from the Lake George assemblage with muscovite cooling ages of ca. 100 and 105 Ma and hornblende cooling ages of ca. 127 and 255 Ma. These data and report are available from the DGGS website: http://doi.org/10.14509/31454.

Tags: 40ar/39ar, age dates, alteration products, amphibolite, analyses, analyses and sampling, analytical lab results, analytical results, ar-ar, bedrock, bedrock geology, big creek, dggs, exploration, fortymile river assemblage, gardiner creek, geochronology, geologic, geology, granite, granodiorite, greenschist, hornblende, igneous, igneous rocks, isotopes, jarvis belt, klondike assemblage, lab methods, ladue river, ladue river assemblage, lake george assemblage, mcarthur creek, metamorphic, metamorphic rocks, metamorphism, methods, mineral resources, mineralogy, minerals, muscovite, orthogneiss, plagioclase, resources, rocks, sample location, schist, separation, sericite, trachyandesite
Organization: State of Alaska