This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the eastern Moran area. Field samples were collected by the DGGS Mineral Resources section during detailed geologic mapping campaigns in 2011. The data provided in this report add significant detail to the thermal history of the Moran area. These new data indicate that the minimum age of prograde metamorphism of Ruby terrane rocks ranges from 148.5 +/- 1.7 to 140.4 +/- 1.7 Ma, and retrograde greenschist metamorphism is 122.6 +/- 2.3 Ma. The retrograde metamorphism is roughly coeval with the age of fabric development parallel to the Kaltag fault (128.3 +/- 1.7) and Tozitna thrust/detachment fault (123.2 +/- 1.5 Ma). The new data also indicate that the Melozitna pluton is composite, with a biotite cooling age of 116.5 +/- 1.3 from coarse-grained granite, while cooling ages for dikes cutting the granite range from 110.1 +/- 1.3 to 102.8 +/- 1.2 Ma. The age of mineralized veins in the area are variable and include 119.0 +/- 1.3 Ma galena veins in the Tozimoran drainage and an interpreted age of 66.5 +/- 2.6 for an auriferous vein from the Monday Creek area, which is synchronous with ages of biotite samples from granite and schist from the Ruby Mining district. The complete report and digital data are available through the DGGS website: http://doi.org/10.14509/30117.

During the 2017 and 2018 field seasons, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling in the Richardson mining district southeast of Fairbanks, including parts of the Big Delta B-4, B-5, B-6, and C-6 quadrangles. The project area has produced approximately 122,000 ounces of gold, mostly from placer mines, and it includes the Uncle Sam, Montecristo, Richardson, Tower, and Hilltop lode gold exploration properties. The goal of DGGS's work in this area is to conduct a mineral-resource assessment and to build an improved understanding of the area's geology and controls on gold mineralization to facilitate industry exploration targeting. The four 40Ar/39Ar ages reported here are all from samples at or near mid-Cretaceous intrusion-related gold prospects. Skarn hornblende from the Banner Creek area (18RN069) yielded an age of 104.0 +/- 1.6 Ma, which places its formation relatively early in the magmatic history of the district. Fine-grained, holocrystalline granodiorite in the immediate vicinity of the Democrat prospect yielded a biotite cooling age of 96.9 +/- 2.0 Ma (18RN568), slightly older than the white mica age reported for the nearby mineralized rhyolite dike (89.4 +/- 0.7 M). White mica from a sericite-pyrite altered, quartz-feldspar porphyry dike in the Rosa Pass area yielded an age of 87.0 +/- 1.5 Ma (17MBW526). Sericite-altered intrusive rock from drill core at the Lone Tree prospect yielded an age of 93.2 +/- 1.2 Ma (18ET057), somewhat younger than the 40Ar/39Ar age determined for presumably magmatic white mica from a dike at the nearby Naosi prospect on the Montecristo property (100.0 +/- 0.7 Ma). The complete report and digital data are available through the DGGS website: http://doi.org/10.14509/30530.

This DGGS report presents 40Ar/39Ar age dating results from selected mafic to intermediate intrusions encountered during a geological and geochemical resource assessment project in the Gulkana, Healy, Mount Hayes, and Talkeetna Mountains quadrangles. Three intrusions returned mid-Cretaceous crystallization ages, while one olivine gabbro returned a Late Triassic crystallization age. Two altered or metamorphosed samples yielded Late Jurassic and Early Cretaceous ages. Analyses were performed by the University of Alaska Fairbanks Geochronology Laboratory, and results were reported by Paul Layer and Jeff Benowitz. Products included in this data release are: a summary of sample collection method; the laboratory report, analytical data tables and associated metadata; and plots of the 40Ar/39Ar age spectra, Ca/K ratios, and Cl/K ratios. All components of this data release are available on the DGGS website doi:10.14509/29119 at no charge.

U-Pb analyses were performed on igneous rocks from the Ray Mountains area of west-central Alaska. These new age analyses will allow us to better evaluate the geochronology of the granitic rocks that are the apparent source of the alluvial REE and tin resources. The plutonic samples have ages ranging from 98.0 +/- 0.9 Ma to 111.6 +/- 1.0 Ma. The sample location coordinates and analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files.

This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) Talkeetna Mountains C-4 Quadrangle and Adjoining Areas geologic mapping project. Hornblende-bearing gabbro returned a Late Triassic crystallization age consistent with regional results for Nikolai Greenstone-related magmatism. We determined Early Jurassic metamorphic ages for hornblende and sericite from two samples of upper greenschist to amphibolite grade metavolcanic rocks. Our results indicate that a granodiorite pluton intruding Wrangellia in the study area has a Middle Jurassic age consistent with the Talkeetna Arc, indicating that the Wrangellia and Peninsular terranes were joined at that time. Cretaceous plutons and porphyry intrusions in the map area can be divided into two types: reduced granitic to felsic porphyry intrusions with latest Cretaceous ages, and an earlier, oxidized type with early Late Cretaceous ages. This observation corresponds to similar patterns in magmatism in the western Alaska Range, and may indicate geological potential for similar style intrusive-related gold, copper, and molybdenum mineralization in the study area. Finally, we obtained Eocene ages for andesite and rhyolite; these ages constrain the timing of displacement on some of the faults in the map area. Analyses were performed by the University of Alaska Fairbanks (UAF) Geochronology Laboratory, and the results were reported by Jeff Benowitz and Paul Layer. Products included in this data release are a summary of sample collection methods, the laboratory report, analytical data tables and associated metadata, and the plots of the 40Ar/39Ar age spectra, Ca/K, and Cl/K ratios.

This DGGS Raw Data File presents 40Ar/39Ar age dating results for selected igneous rocks encountered in the Styx River area of the western Alaska Range. Crystallization ages on biotite and hornblende from plutonic rocks range from about ~60 to ~63 Ma, while a sericite alteration age in plutonic rocks altered by a dike swarm also is around ~63 Ma. Sericite alteration associated with a copper-molybdenum porphyry ranges from ~10 to ~11 Ma. Analyses were performed by the University of Alaska Fairbanks Geochronology Laboratory, and results were reported by Paul Layer and Jeff Benowitz. This data release includes the following products: a summary of sample collection methods, the laboratory report, analytical data tables and associated metadata, and plots of the 40Ar/39Ar age spectra, Ca/K, and Cl/K ratios. All components of this data release are downloadable from the DGGS website at no charge.

40Ar/39Ar geochronology data from the Tanacross and Eagle quadrangles, Alaska, Raw Data File 2023-23, provides 40Ar/39Ar geochronology data from igneous and metamorphic rocks in or adjacent to the DGGS Western Tanacross and Taylor Mountain geologic mapping project areas. Western Tanacross and Taylor Mountain geologic mapping projects aim to produce more accurate and integrated modern geologic maps and supporting datasets to promote mineral resource exploration in eastern Interior Alaska. The Tanacross and southern Eagle quadrangles are within the Yukon Tanana Uplands, which DGGS and USGS identified as having the potential to host deposits of multiple critical minerals, as well as gold, copper, molybdenum, lead, zinc, and silver. Most of the known mineralization in the region is related to Mesozoic-Paleogene magmatism. Igneous rocks intrude a composite metamorphic province that includes parautochthonous North America and the allochthonous Yukon Tanana Terrane, which are multiply deformed and apparently juxtaposed along low-angle faults. Samples were collected (2009, 2018, 2019, 2021) for 40Ar/39Ar geochronology to understand the crystallization ages of igneous rocks, the exhumation history of metamorphic rocks, and the timing of mineralization. The 22 40Ar/39Ar ages reported here include six mineralization/alteration ages, one volcanic crystallization age, seven metamorphic cooling ages from the Yukon-Tanana terrane (YTT), and eight metamorphic cooling ages from parautochthonous North American rocks (pNA). The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files. These data are available from the DGGS website: http://doi.org/10.14509/31085.

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.

This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) geologic mapping project in the Tanacross A-5 and A-6 quadrangles and adjoining areas. Our results indicate the Hona granodiorite pluton intruded the area in the Late Cretaceous between 76 and 71 Ma. We determined Cretaceous metamorphic ages from 126 to 121 Ma for hornblende, biotite, sericite and muscovite from multiple samples of upper greenschist to amphibolite grade rocks. This is consistent with regional argon results that imply this area is in the upper plate of the Yukon Tanana Terrane (Hansen and Dusel-Bacon, 1998). Basaltic andesite dikes returned Late Cretaceous (99.0 +/- 0.5 Ma) and Tertiary (58.4 +/- 0.3 Ma) ages from biotite; these constrain late brittle faulting in the area. Finally, we obtained a Late Cretaceous age (71.5 +/- 0.5) for a basaltic andesite flow; these ages constrain the timing of displacement on some of the faults in the map area. Analyses were performed by the University of Alaska Fairbanks (UAF) Geochronology Laboratory, and results were reported by Jeff Benowitz and Paul Layer. Products included in this data release are a summary of sample collection methods, the laboratory report, analytical data tables and associated metadata, and plots of the 40Ar/39Ar age spectra and Ca/K and Cl/K ratios.

40Ar/39Ar data from the northern Fairbanks mining district, Circle Quadrangle, Alaska, Raw Data File 2025-1, presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) geologic mapping project in the northern Fairbanks mining district, covering parts of the Circle A-4, A-5, B-4, and B-5 quadrangles, Alaska. Field samples were collected by the DGGS Mineral Resources Section during a detailed geologic mapping campaign in June 2007. In addition to analytical data compiled in the geologic map for this area, other DGGS publications supporting geologic mapping in the northern Fairbanks mining district include geophysical data, geochemical data, and a planned U-Pb detrital zircon age report. The northern Fairbanks mining district map area lies within the Yukon-Tanana Upland in rocks that we interpret to correlate with the Cambrian to Late Proterozoic Fairbanks schist and the Wickersham Grit unit. These rocks are intruded by several phases of plutonism, of which two occur in the map area: Tertiary and Cretaceous plugs, dikes, and sills with characteristic geochemical signatures. The Cretaceous intrusions are regionally associated with placer- and lode-gold mines and occurrences. The age data in this report constrain the crystallization ages of igneous rocks, the potential timing of mineralization, and the cooling histories of metamorphic rocks in the map area. These data and report are available from the DGGS website: http://doi.org/10.14509/31472.