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.

40Ar/39Ar data from plutonic, dike, and alteration samples collected during geologic mapping of the eastern part of the Bonnifield mining district geologic map area in parts of Fairbanks A-1 and Fairbanks A-2 and Healy D-1 and Healy D-2 quadrangles yield results indicating the plutons, dikes, and a gold-bearing quartz vein in the Bonnifield Map area range from 85 to 95 m.y.

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 describes the results of geologic mapping and sample analysis from the Richardson district, east-central Alaska.

The Preliminary Interpretive Report 2004-3B, "Bedrock geologic map of the Livengood SW C-3 and SE C-4 quadrangles, Tolovana mining district, Alaska," is the bedrock geologic map of an approximately 123-square-mile area in the central Livengood Quadrangle, Alaska.

This dataset contains 40Ar/39Ar isotopic data and ages for rocks from the Yukon-Tanana upland of eastern Alaska and the northern Aleutian Range of south-central Alaska. The entire sample suite was collected as part of geological mapping and supporting geochemical and geochronological analysis were conducted from 2013 to 2019 by the Mineral Resources Program of the U.S. Geological Survey (USGS). Legacy bedrock samples archived from earlier USGS field investigations were also analyzed in some cases. Hornblende, muscovite, and (or) biotite were extracted from bedrock samples of igneous and metamorphic rocks and analyzed at the University of Alaska Fairbanks Geochronology Laboratory in order to determine the 40Ar/39Ar age of each mineral phase. The data tables accompanying this data release report the resulting 40Ar/39Ar analytical data and interpreted ages for each mineral separated from a bulk rock sample.

URL: https://geoscience.data.qld.gov.au/dataset/cr041075 GSQ RECORD 1993/09: MINERAL OCCURRENCES - COEN, ROKEBY AND SILVER PLAINS 1:100 000 SHEET AREAS, CAPE YORK PENINSULA, QUEENSLAND

Bedrock geologic map of the Big Hurrah-Council-Bluff area, Southern Seward Peninsula, Alaska, Report of Investigation 2024-7, presents bedrock geologic mapping from the blueschist-facies-metamorphosed, Late Proterozoic to Devonian Nome Complex was conducted by the Alaska Division of Geological & Geophysical Surveys (DGGS) on southern Seward Peninsula, Alaska. This map, covering portions of the Solomon C-4, C-5, D-4, D-5, and the southern Bendeleben A-4 quadrangles, includes new mapping by DGGS in the summer of 2006 and incorporates previous mapping conducted by DGGS in 2003 and 2004. Surficial geologic mapping was also conducted in the area. This 595-square-mile, 1:50,000-scale, bedrock geologic map coincides with portions of the DGGS Council airborne magnetic and resistivity survey. The geophysical survey and geologic map are part of the State of Alaska's Airborne Geophysical/Geological Mineral Inventory program, focusing on enhancing public knowledge of Alaska's geology and mineral districts. More than 1 million ounces of placer gold have been extracted from the map area since the turn of the century, with most production derived from the Casadepaga and Solomon rivers and Ophir Creek. Widespread low-sulfide, gold-bearing quartz veins of Cretaceous age were the primary lode source for the placer gold. Approximately 27,000 ounces of gold were produced from low-sulfide quartz veins at the Big Hurrah lode gold mine between 1903 and 1907. Other notable lode gold prospects in the map area include Silver (Flynn), West Creek, and an unnamed prospect at the head of Albion Creek. The Bluff area along Norton Sound has both lode gold and mercury prospects. The map area contains numerous occurrences of silicified marble with anomalous geochemistry of uncertain age and genetic origin. Various lithologies of the Layered sequence subdivision of the Nome Complex, primarily the Mixed unit, have the potential to host sedimentary exhalative (SEDEX) mineralization of Late Devonian to possibly Mississippian(?) age, as found elsewhere on the Seward Peninsula. The complete report, geodatabase, and ESRI fonts and style files are available from the Alaska Division of Geological & Geophysical Surveys website: http://doi.org/10.14509/31308.