Twelker, EvanBenowitz, J.A.Naibert, T.J.2020report and digital dataRaw Data FileRDF 2020-11Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys10 p.https://doi.org/10.14509/30530During 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.The goal of DGGS's work in the Richardson mining district 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.>data: Identification numbers, coordinates, sample descriptions, and summary ages of each sample; power output levels and resultant measurements from each sample run; and an index of the the contents, format, and structure of a data.20172020ground conditioncompleteNone planned-146.359570-146.16010564.52615564.301195ISO 19115 Topic CategorygeoscientificInformationAlaska Division of Geological & Geophysical Surveys40Ar/39ArAge DatesAnalysesAnalyses and SamplingAnalytical Lab ResultsAnalytical ResultsAr-ArBedrockBedrock GeologyChloriteCrystalsDisseminatedEpidoteExhumationExplorationFeldsparFluoriteGeochronologyGeologicGeologyGraniteGranodioriteHornblendeIsotopesK-FeldsparLab MethodsMethodsMicaMineralogyMineralsMiningMuscovitePetrographyPlagioclasePlutonicPorphyryPotassiumPyriteQuartzResourcesRhyoliteRocksSample LocationSericiteSkarnAlaska Division of Geological & Geophysical SurveysBanner CreekBuckeye CreekDemocrat ProspectFairbanks Mining DistrictRichardson Mining DistrictTwentyfive Mile CreekWalker, J.D., Geissman, J.W., Bowring, S.A, and Babcock, L.E., comp., 2012, Geologic Time Scale v. 4.0: Geological Society of AmericaCretaceousThis report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.Alaska Division of Geological & Geophysical SurveysMetadata Managermailing and physical

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FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysWe thank Frazer Tabeart (PolarX Ltd.), Phil St. George and Jack Cote (Millrock Resources Inc.), Mike Stoltz, and Lynn Armstrong for access to the Lone Tree (LT) and Wolf (WFL) drill core on the Uncle Sam property. Rainer Newberry assisted with skarn petrography. The DGGS Richardson geologic mapping project was funded by the State of Alaska.Graham, G.E.Jozwik, Diana2007Raw Data FileRDF 2007-2Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys32 phttps://doi.org/10.14509/15819Naibert, T.J.Benowitz, J.A.Wypych, AlicjaSicard, K.R.Twelker, Evan2018Raw Data FileRDF 2018-3Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys15 phttps://doi.org/10.14509/30112Twelker, EvanWerdon, M.B.Sicard, K.R.Wypych, AlicjaNaibert, T.J.Athey, J.E.Willingham, A.L.Lockett, A.C.2017Poster and PresentationTwelker, Evan and others, 2017Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys37 phttps://doi.org/10.14509/29811Twelker, EvanWypych, AlicjaSicard, K.R.Naibert, T.J.Montayne, SimoneNewberry, R.J.Wyatt, W.C.2018Raw Data FileRDF 2018-6Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys4 phttps://doi.org/10.14509/30119Twelker, EvanWypych, AlicjaSicard, K.R.Naibert, T.J.Werdon, M.B.Athey, J.E.Willingham, A.L.Lockett, A.C.2017Raw Data FileRDF 2017-11Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys4 phttps://doi.org/10.14509/29779This data set is being released into the DGGS Raw Data File series. The information has been examined by several geologists familiar with the study area, but the data and accompanying report have not been formally reviewed for technical content or for conformity to the editorial standards of DGGS. Questions about the analytical values or procedures can be best answered by the originating lab.not applicableThis data release is complete.Sample location coordinates (in WGS84 datum) were obtained using GPS-enabled field tablets, with a typical reported accuracy of about 10 meters.Fieldwork - Fresh, unweathered samples from surface outcrops or drill core were collected by DGGS field geologists and were selected for dating based on the presence of sufficiently large crystals appropriate for dating. Except where noted, sample location coordinates (in WGS84 datum) were obtained using GPS-enabled field tablets, with a typical reported accuracy of +/- 10 meters. Samples were examined under a binocular microscope and in thin section to select unaltered mineral phases before sample preparation.2018Sample preparation - Four rock samples were submitted to the Geochronology Laboratory at the University of Alaska Fairbanks (UAF) for 40Ar/39Ar analysis. The samples were crushed, sieved, washed, and hand-picked for muscovite, sericite, biotite, and hornblende mineral phases. The monitor mineral MMhb-1 (Samson and Alexander, 1987) with an age of 523.5 Ma (Renne and others, 1994) was used to monitor neutron flux (and calculate the irradiation parameter, J). The samples and standards were wrapped in aluminum foil, loaded into aluminum cans of 2.5-cm diameter and 6-cm height. The samples were irradiated in position 5c of the uranium-enriched research reactor at McMaster University in Hamilton, Ontario, Canada for 20 megawatt-hours.2018Geochronology analysis - Upon their return from the reactor, the samples and monitors were loaded into 2-mm-diameter holes in a copper tray, which was then loaded in an ultra-high-vacuum extraction line. The monitors were fused, and samples heated, using a 6-watt argon-ion laser following the technique described in York and others (1981), Layer and others (1987), and Benowitz and others (2014). Argon purification was achieved using a liquid nitrogen cold trap and a SAES Zr-Al getter at 400°C. The samples were analyzed in a VG-3600 mass spectrometer at the Geophysical Institute, University of Alaska Fairbanks. The argon isotopes measured were corrected for system blank and mass discrimination, as well as calcium, potassium, and chlorine interference reactions following procedures outlined in McDougall and Harrison (1999). Typical full-system 8-minute laser blank values (in moles) were generally 2 x 10^-16 mol 40Ar, 3 x 10^-18 mol 39Ar, 9 x 10^-18 mol 38Ar, and 2 x- 10^-18 mol 36Ar, which are 10-50 times smaller than the sample/standard volume fractions. Correction factors for nucleogenic interferences during irradiation were determined from irradiated CaF2 and K2SO4 as follows: (39Ar/37Ar)Ca = 7.06 x 10^-4, (36Ar/37Ar)Ca = 2.79 x- 10^-4 and (40Ar/39Ar)K = 0.0297. Mass discrimination was monitored by running calibrated air shots. The mass discrimination during these experiments was 1.3 percent per mass unit. During sample analysis, calibration measurements were made on a weekly to monthly basis to check for changes in mass discrimination with no significant variation observed during these intervals. Note: Complete list of references can be found in the accompanying report.2018point0.0000010.000001decimal degreesWorld Geodetic System of 1984WGS 846378137298.257223563000025rdf2020-11-summary-data-locations.csv, rdf2020-11-step-heating-data.csv, rdf2020-11-data-dictionary.csvIdentification numbers, coordinates, sample descriptions, and summary ages of each sample; power output levels and resultant measurements from each sample run; and an index of the the contents, format, and structure of a data.Alaska Division of Geological & Geophysical Surveys (DGGS) and Geochronology Laboratory at the University of Alaska Fairbanks (UAF)dataAlaska Division of Geological & Geophysical SurveysMetadata Managermailing and physical

3354 College Road

FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysRDF 2020-11The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media by mail, phone, fax, or email from the DGGS Fairbanks office. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for the exact shipping amount.Contact DGGS for current pricingASCII tabular fileshttps://doi.org/10.14509/30530Free download20200911Alaska Division of Geological & Geophysical SurveysSimone MontayneMetadata Managermailing and physical

3354 College Road

FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysFGDC Content Standard for Digital Geospatial MetadataFGDC-STD-001-1998If the user has modified the data in any way they are obligated to describe the types of modifications they have performed in the supporting metadata file. User specifically agrees not to imply that changes they made were approved by the Alaska Department of Natural Resources or Division of Geological & Geophysical Surveys.https://www.dggs.alaska.gov/metadata/dggs.extdggs metadata extensions