68e35d29-083d-4b95-831d-c5e31d85cf48_source eng; USA utf8 dataset Simone Montayne Alaska Division of Geological & Geophysical Surveys Metadata Manager (907)451-5020 (907)451-5050 3354 College Road Fairbanks AK 99709-3707 USA dggspubs@alaska.gov 8 am to 4:30 pm, Monday through Friday, except State holidays pointOfContact 2020-09-11 ISO 19115 Geographic Information - Metadata ISO 19115:2003/Cor.1:2006(E) 40Ar/39Ar data from the Richardson mining district, Big Delta Quadrangle, Alaska 2020-01-01 publication Alaska Division of Geological & Geophysical Surveys Fairbanks Alaska, United States publisher Twelker, Evan originator Benowitz, J.A. originator Naibert, T.J. originator https://doi.org/10.14509/30530 REPORT AND DIGITAL DATA Raw Data File RDF 2020-11 10 p. 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. 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. We 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. completed Alaska Division of Geological & Geophysical Surveys Metadata Manager (907)451-5020 (907)451-5050 3354 College Road Fairbanks AK 99709-3707 USA dggspubs@alaska.gov 8 am to 4:30 pm, Monday through Friday, except State holidays pointOfContact notPlanned 40Ar/39Ar Age Dates Analyses Analyses and Sampling Analytical Lab Results Analytical Results Ar-Ar Bedrock Bedrock Geology Chlorite Crystals Disseminated Epidote Exhumation Exploration Feldspar Fluorite Geochronology Geologic Geology Granite Granodiorite Hornblende Isotopes K-Feldspar Lab Methods Methods Mica Mineralogy Minerals Mining Muscovite Petrography Plagioclase Plutonic Porphyry Potassium Pyrite Quartz Resources Rhyolite Rocks Sample Location Sericite Skarn theme Alaska Division of Geological & Geophysical Surveys Banner Creek Buckeye Creek Democrat Prospect Fairbanks Mining District Richardson Mining District Twentyfive Mile Creek place Alaska Division of Geological & Geophysical Surveys Cretaceous temporal Walker, J.D., Geissman, J.W., Bowring, S.A, and Babcock, L.E., comp., 2012, Geologic Time Scale v. 4.0: Geological Society of America The 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. otherRestrictions Use Constraints: 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. otherRestrictions Access Constraints: This 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). Data tables related to geology and gold mineralization in the Richardson district, east-central Alaska 2007-01-01 publication Alaska Division of Geological & Geophysical Surveys Fairbanks Alaska, United States publisher Graham, G.E. originator Jozwik, Diana originator https://doi.org/10.14509/15819 Raw Data File RDF 2007-2 32 p crossReference 40Ar/39Ar data from the Tanacross D-1 and D-2, Big Delta B-4 and B-5, and Mount Hayes A-6 quadrangles, Alaska 2018-01-01 publication Alaska Division of Geological & Geophysical Surveys Fairbanks Alaska, United States publisher Naibert, T.J. originator Benowitz, J.A. originator Wypych, Alicja originator Sicard, K.R. originator Twelker, Evan originator https://doi.org/10.14509/30112 Raw Data File RDF 2018-3 15 p crossReference Geologic mapping in the Richardson-Uncle Sam area, interior Alaska (presentation): Alaska Miners Association Annual Convention, Anchorage, Alaska, November 7-12, 2017 2017-01-01 publication Alaska Division of Geological & Geophysical Surveys Fairbanks Alaska, United States publisher Twelker, Evan originator Werdon, M.B. originator Sicard, K.R. originator Wypych, Alicja originator Naibert, T.J. originator Athey, J.E. originator Willingham, A.L. originator Lockett, A.C. originator https://doi.org/10.14509/29811 Poster and Presentation Twelker, Evan and others, 2017 37 p crossReference Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska 2018-01-01 publication Alaska Division of Geological & Geophysical Surveys Fairbanks Alaska, United States publisher Twelker, Evan originator Wypych, Alicja originator Sicard, K.R. originator Naibert, T.J. originator Montayne, Simone originator Newberry, R.J. originator Wyatt, W.C. originator https://doi.org/10.14509/30119 Raw Data File RDF 2018-6 4 p crossReference Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska 2017-01-01 publication Alaska Division of Geological & Geophysical Surveys Fairbanks Alaska, United States publisher Twelker, Evan originator Wypych, Alicja originator Sicard, K.R. originator Naibert, T.J. originator Werdon, M.B. originator Athey, J.E. originator Willingham, A.L. originator Lockett, A.C. originator https://doi.org/10.14509/29779 Raw Data File RDF 2017-11 4 p crossReference vector eng; USA geoscientificInformation -146.359570 -146.160105 64.301195 64.526155 2017-01-01 2020-01-01 >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. true ASCII tabular files unknown Alaska Division of Geological & Geophysical Surveys Metadata Manager (907)451-5020 (907)451-5050 3354 College Road Fairbanks AK 99709-3707 USA dggspubs@alaska.gov 8 am to 4:30 pm, Monday through Friday, except State holidays distributor Contact DGGS for current pricing Free download https://doi.org/10.14509/30530 ASCII tabular files CSDGM IMPORT ERROR: No digtinfo/formcont information dataset Horizontal Positional Accuracy Report Sample location coordinates (in WGS84 datum) were obtained using GPS-enabled field tablets, with a typical reported accuracy of about 10 meters. This data release is complete. This data release is complete. not applicable This lineage was generated by the FGDC CSDGM to 19139 transformation 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. 2018-01-01T00:00:00 Sample 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. 2018-01-01T00:00:00 Geochronology 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. 2018-01-01T00:00:00 otherRestrictions Metadata Use Constraints: If 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. unknown This metadata was automatically generated from the FGDC Content Standard for Digital Geospatial Metadata standard (version FGDC-STD-001-1998) using the 2019-08-12T11:11:00 version of the FGDC CSDGM to ISO 19139 transform. Simone Montayne Alaska Division of Geological & Geophysical Surveys Metadata Manager (907)451-5020 (907)451-5050 3354 College Road Fairbanks AK 99709-3707 USA dggspubs@alaska.gov 8 am to 4:30 pm, Monday through Friday, except State holidays pointOfContact