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 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.

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 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. Uranium-lead (U-Pb) zircon geochronology results presented in this report show that similarly textured quartz-feldspar porphyry intrusions in the project area were generated by both Paleocene (56.8 +/- 0.9 Ma; 18WCW149) and middle Cretaceous (92.0 +/- 0.7 Ma; 18AW002, known as the Democrat Dike) magmatic episodes. The ages of medium-grained plutonic rocks at Birch Lake (92.4 +/- 0.6 Ma; 18ET587) and Gold Run (93.7 +/- 0.7 Ma; 18ET580) lie within error of the age of the hypabyssal Democrat Dike, indicating that the present-day depth of exposure juxtaposes rocks that were buried at widely different crustal depths during the middle Cretaceous. Phaneritic granodiorite near the Democrat prospect yielded a zircon age of 110.7 +/- 1.3 Ma (18RN565), extending the magmatic history of the prospect into the Early Cretaceous. Amphibolite-facies augen orthogneiss yielded a Late Devonian zircon age of 364.5 +/- 6.0 Ma (18ET040), consistent with similar rocks in the Lake George assemblage. Detrital zircons analyzed from siliciclastic schist along the Richardson Highway (18AW021) contain prominent age populations at 1.8 and 2.6 Ga, consistent with a Laurentian cratonic source and consistent with other results from parautochthonous North America. Pelitic schist from the Hilltop prospect (18TJN372) yielded a relatively small number (n=32) of zircon grains that define small age populations between ca. 1.7 and 1.5 Ga. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30555.

Twenty-two igneous and metamorphic rock samples were collected in a 20-km-long swath centered on the Alaska Highway between Tetlin Junction, Alaska, and the Canada border. Igneous and metamorphic rock samples were submitted to the Apatite to Zircon, Inc. laboratory (A2Z), where zircon U-Pb age analysis, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), was performed by Paul O'Sullivan. The 15 felsic plutonic rock samples and one gabbro sample yield Cretaceous zircon U-Pb weighted-mean ages ranging from 95.7 Ma to 106.2 Ma. Zircons from a metadiorite yield a Triassic weighted-mean age of about 241.9 Ma. Metamorphic zircons from two samples with felsic igneous protoliths yield Mississippian weighted-mean ages of 351.7 Ma and 354.6 Ma. Detrital zircons from two metaconglomerates yield individual grain ages from 100 Ma to 1,811 Ma, but are predominantly between 300 Ma and 345 Ma. Detrital zircons from a quartzite yield peaks at about 2,648 Ma, 1,946 Ma, and 1,807 Ma. Samples were analyzed for a variety of suites of major and trace elements depending on the sample type. The analytical data tables associated with this report are being released in digital format.

This data release includes raw detrital zircon U-Pb data for Paleoproterozoic metasedimentary rocks of the Gunnison block, central Colorado, USA. Detrital zircon U-Pb data for five samples of metasedimentary rock (totaling 1459 zircon U-Pb dates) were acquired via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at the University of Arizona LaserChron Center. The data provide constraints on the sediment provenance, maximum depositional age, and timing of metamorphism of these metasedimentary rocks, providing insights on the crustal and tectonic evolution of the Gunnison block and Yavapai Province.

This data release includes raw detrital zircon U-Pb data for Paleoproterozoic metasedimentary rocks of the Gunnison block, central Colorado, USA. Detrital zircon U-Pb data for five samples of metasedimentary rock (totaling 1459 zircon U-Pb dates) were acquired via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at the University of Arizona LaserChron Center. The data provide constraints on the sediment provenance, maximum depositional age, and timing of metamorphism of these metasedimentary rocks, providing insights on the crustal and tectonic evolution of the Gunnison block and Yavapai Province.

This Alaska Division of Geological & Geophysical Surveys (DGGS) Preliminary Interpretive Report presents U-Pb ages of zircons from 14 sedimentary, metamorphic, and igneous samples collected during 2017 and 2018 field investigations in the northeastern Tanacross Quadrangle, Alaska. The DGGS Northeast Tanacross project is a part of multi-year effort to investigate the geology and mineral-resource potential of the Yukon-Tanana Uplands region in collaboration with the U.S. Geological Survey. The purpose of the U-Pb isotopic study is to better understand the Devonian-to-Mississippian and Mesozoic-to-Early Paleogene episodes of magmatic and tectonic events within the Yukon-Tanana Uplands and the relationship of magmatism to the metallic mineral deposits. This area is characterized by the presence of two Late Devonian to Mississippian metamorphic assemblages--Lake George and Fortymile River. Both assemblages are composed of metasedimentary and metavolcanic rocks that have been intruded by Devonian to Eocene intrusive rocks of varying composition and texture. Paleozoic intrusive rocks are deformed and metamorphosed and include prevalent Late Devonian-Early Mississippian augen orthogneiss, herein called the Divide Mountain suite, that was emplaced into and deformed together with the Lake George assemblage. The Fortymile River assemblage is primarily cross cut by Mississippian to Permian intrusive rocks that are also pervasively deformed and metamorphosed. Following Jurassic to mid-Cretaceous regional metamorphism and deformation, all metamorphic rock packages were intruded by Mid- to Late-Cretaceous volcanic and plutonic rocks, some of which have known or suspected potential for gold together with silver, zinc, copper, and lead mineralization. Products included in this data release are: A summary of sample-collection methods, the laboratory report, analytical data tables, and associated metadata. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30465.

This dataset contains U-Pb isotopic data and associated dates for sampled igneous, meta-igneous, and metamorphic rocks of interior and southwestern Alaska. Samples were collected during geologic mapping and mineral deposit research from 2019 to 2023. Mapping and research were funded by the Mineral Resources Program of the U.S. Geological Survey. Mineral separations were conducted at the U.S. Geological Survey mineral separation laboratory in Denver, Colorado and GeoSep Services in Moscow, Idaho. Laser-ablation-inductively-coupled-plasma-mass spectrometry analyses of zircon grains were performed from 2020 through 2024 at the U.S Geological Survey Microbeam Laboratory in Denver, Colorado and at the GeoAnalytical Laboratory, Washington State University, Pullman, Washington by GeoSep Services.

This report presents U-Pb detrital zircon dates from three sedimentary rock samples collected in the eastern Tanacross Quadrangle during 2019 geologic mapping by the Alaska Division of Geological & Geophysical Surveys. This geologic map is published concurrently by Twelker and others (2021). The data were collected to support the map interpretation by establishing maximum depositional ages (MDAs) for the sampled strata. Further, these results also bolster a regional detrital zircon dataset that will, collectively, further constrain the Cretaceous-Cenozoic paleogeography of the region. This work is of economic and scientific interest: placer gold in the Fortymile District originated in Jurassic orogenic veins and, in some areas, was transported and concentrated by Cretaceous-Cenozoic depositional systems prior to its deposition in modern placer deposits. This process is described for the Coal Creek and Woodchopper Creek placers between Circle and Eagle and may be relevant elsewhere in the eastern Yukon Tanana Uplands. The analytical data tables associated with this report are available in digital format. Users can access the complete report and digital data from the DGGS website: http://doi.org/10.14509/30683.

This data set contains two data sets. One data set is of U-Pb isotopic data and associated ages of detrital zircon grains from 16 sedimentary and metasedimentary rocks from the western Alaska Range, Livengood area and Seward Peninsula, Alaska. Two samples were collected from the York Mountains area of the Seward Peninsula of western Alaska. Three samples were collected from the Livengood quadrangle of central Alaska. Eleven samples were collected from the western Alaska Range of south-central Alaska. Detrital zircon grains from each of the sixteen samples were separated and analyzed by Apatite to Zircon, Inc. (A2Z) and Geosep Services (GSS) laboratories between 2011 and 2014, using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques. The second data set contains fossil identifications and age assignments from a select sedimentary rock from the western Alaska Range of south-central Alaska. Fossils were identified by visual inspection. All samples were collected as part of geological mapping research conducted between 1984 and 2014 and funded by the Mineral Resources Program of the U.S. Geological Survey.