This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) Wrangellia Mineral Assessment project, part of a multi-year effort focusing on improving the publicly available geoscientific information for the western Wrangellia terrane. The samples described in this report were selected and analyzed to improve our understanding of the geology and structural history of the Wrangellia Mineral Assessment project area. A metagabbro rock sample returned a Late Triassic crystallization age consistent with regional ages for Nikolai Greenstone-related magmatism; however, the two amphibole separates ages do not overlap, and have larger errors than expected due to alteration. An Early Cretaceous age obtained on a syenogranite pluton could correspond to similar ages of an Early Cretaceous porphyry event within the Grubstake Cu-Au porphyry system, Slana Region. Finally, we obtained Oligocene ages for a dacitic dike and a schist; the schist age constrains the timing of displacement on a thrust fault in the 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 analyses were performed on igneous rocks from the Ray Mountains area of west-central Alaska. The plutonic samples have ages from about 89 Ma to 109 Ma, while the volcanic samples show ranges from about 30 Ma to 64 Ma. The three volcanic samples fall into two age groups: the younger sample, a basalt, has an age of about 30 Ma, while the two older, rhyolitic samples fall between 58 Ma and 64 Ma. 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 for download on the DGGS website at no charge.

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.

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.

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 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.

Mineral-resources geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) carried out a helicopter-supported geological and geochemical resource assessment project in the Gulkana, Healy, Mount Hayes, and Talkeetna Mountains quadrangles from July 29 through August 16, 2013. The objectives of this assessment were to improve the publicly-available geological, geophysical, and geochemical data in the area of known occurrences in the Mount Hayes Quadrangle, and to extend this coverage and any gained insight westward into the less-explored extension of the Wrangellia terrane. This program of stream-sediment, pan-concentrate, and rock sampling was conducted as part of the State's Strategic Minerals Assessment project, an initiative designed to evaluate Alaska's potential for rare-earth elements, PGEs, and other similarly supply-challenged resources. Highlights of this project include identification, sampling, and characterization of previously unmapped mafic to ultramafic intrusions and Nikolai Greenstone, modern geochemical characterizations of Ni-Cu-Co-PGE, skarn, vein, and basalt-hosted Cu mineralization, and documentation of regional-scale patterns in PGE enrichment across western Wrangellia. The analytical data tables associated with this report are being released in digital format as comma-delimited text (CSV) files.

The State of Alaska's Strategic and Critical Minerals (SCM) Assessment project, a State-funded Capital Improvement Project (CIP), is designed to evaluate Alaska's statewide potential for SCM resources. The SCM Assessment is being implemented by the Alaska Division of Geological & Geophysical Surveys (DGGS), and involves obtaining new airborne-geophysical, geological, and geochemical data. For the geochemical part of the SCM Assessment, thousands of historical geochemical samples from DGGS, U.S. Geological Survey (USGS), and U.S. Bureau of Mines archives are being reanalyzed by DGGS using modern, quantitative, geochemical-analytical methods. The objective is to update the statewide geochemical database to more clearly identify areas in Alaska with SCM potential. For this report, DGGS funded reanalysis of 1,682 historical USGS sediment samples from the statewide Alaska Geochemical Database Version 2.0 (AGDB2; Granitto and others, 2013). Samples were chosen from an area covering the western half of the Wrangellia Terrane in the Anchorage, Gulkana, Healy, Mt. Hayes, Nabesna, and Talkeetna Mountains quadrangles of south-central Alaska. USGS was responsible for sample retrieval from the Denver warehouse through the final quality assurance/quality control (QA/QC) of the geochemical analyses obtained through the USGS contract lab. The new geochemical data are published in this report as a coauthored DGGS report, and will be incorporated into the statewide geochemical databases of both agencies.

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.

This dataset accompanies planned publication '40Ar/39Ar geochronology of hydrothermal activity related to orogenic gold mineralization in the Klamath Mountains, California, U.S.A.'. The Ar/Ar data are for samples that record the mineralization of the area. The geochronology provides time constraints for the mineralization studied in the manuscript. Samples were collected from the Klamath Mountains by Ryan Taylor (U.S. Geological Survey, Geophysics, and Geochemistry Science Center), who sent them to the USGS Denver Argon Geochronology Laboratory for Ar/Ar analysis.