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.

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.

Raw Data File 2023-15,Zircon U-Pb results from the eastern Moran area, Tanana B-6 and Melozitna B-1 quadrangles, Alaska, Raw Data File 2023-15, U-Pb geochronologic data from 2011 DGGS field studies in the eastern Moran area. These dates were obtained as part of an integrated geological, geophysical, and geochemical mineral inventory study in the eastern Kokrines Hills near Moran Dome in the Tanana B-6 and Melozitna B-1 quadrangles. The project area is of historical and current interest for the potential development of mineral resources. The data are available from the DGGS website: http://doi.org/10.14509/31016.

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.

We report U-Pb zircon geochronology results for one metavolcanic and one metaplutonic rock sample from the Mount Hayes A-6 Quadrangle of central Alaska. These samples are representative of rock units assigned to the Clearwater terrane of Jones and others (1987), a sequence of greenschist-grade metavolcanic and metasedimentary rocks of poorly constrained age and tectonic origin. Our results indicate a crystallization age of 277.33 +/- 11.84 Ma for a felsic metavolcanic rock, and a 268.05 +/- 11.64 Ma crystallization age for a granitic metaplutonic unit intruding the former.

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 dataset contains U-Pb isotopic data and associated ages of detrital zircon from sedimentary and metasedimentary rocks collected from southwestern Alaska and from the Yukon-Tanana upland and environs of eastern interior Alaska and western Yukon, Canada. The samples were collected as part of geological mapping and research conducted from 1996 to 2021 and funded by the Mineral Resources Program of the U.S. Geological Survey. Detrital zircon grains were separated and analyzed by four different laboratories: U.S. Geological Survey laboratories in Denver, Colorado; Apatite to Zircon, Inc. (A2Z); GeoSep Services (GSS); and the University of British Columbia. All analyses were conducted between 2007 and 2021 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques.

This data set contains U-Pb isotopic data and associated ages of detrital zircon from sedimentary and metasedimentary rocks collected from southwestern Alaska and from the Yukon-Tanana upland and environs of eastern interior Alaska and western Yukon, Canada. The samples were collected as part of geological mapping and research conducted from 1996 to 2021 and funded by the Mineral Resources Program of the U.S. Geological Survey. Detrital zircon grains were separated and analyzed by four different laboratories: U.S. Geological Survey laboratories in Denver, Colorado; Apatite to Zircon, Inc. (A2Z); GeoSep Services (GSS); and the University of British Columbia. All analyses were conducted between 2007 and 2021 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques.

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.