Identification_Information: Citation: Citation_Information: Originator: Twelker, Evan Originator: Benowitz, J.A. Originator: Naibert, T.J. Publication_Date: 2020 Title: 40Ar/39Ar data from the Richardson mining district, Big Delta Quadrangle, Alaska Geospatial_Data_Presentation_Form: report and digital data Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2020-11 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 10 p. Online_Linkage: https://doi.org/10.14509/30530 Description: Abstract: 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. Purpose: 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. Supplemental_Information: >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. Time_Period_of_Content: Time_Period_Information: Range_of_Dates/Times: Beginning_Date: 2017 Ending_Date: 2020 Currentness_Reference: ground condition Status: Progress: complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -146.359570 East_Bounding_Coordinate: -146.160105 North_Bounding_Coordinate: 64.526155 South_Bounding_Coordinate: 64.301195 Keywords: Theme: Theme_Keyword_Thesaurus: ISO 19115 Topic Category Theme_Keyword: geoscientificInformation Theme: Theme_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Theme_Keyword: 40Ar/39Ar Theme_Keyword: Age Dates Theme_Keyword: Analyses Theme_Keyword: Analyses and Sampling Theme_Keyword: Analytical Lab Results Theme_Keyword: Analytical Results Theme_Keyword: Ar-Ar Theme_Keyword: Bedrock Theme_Keyword: Bedrock Geology Theme_Keyword: Chlorite Theme_Keyword: Crystals Theme_Keyword: Disseminated Theme_Keyword: Epidote Theme_Keyword: Exhumation Theme_Keyword: Exploration Theme_Keyword: Feldspar Theme_Keyword: Fluorite Theme_Keyword: Geochronology Theme_Keyword: Geologic Theme_Keyword: Geology Theme_Keyword: Granite Theme_Keyword: Granodiorite Theme_Keyword: Hornblende Theme_Keyword: Isotopes Theme_Keyword: K-Feldspar Theme_Keyword: Lab Methods Theme_Keyword: Methods Theme_Keyword: Mica Theme_Keyword: Mineralogy Theme_Keyword: Minerals Theme_Keyword: Mining Theme_Keyword: Muscovite Theme_Keyword: Petrography Theme_Keyword: Plagioclase Theme_Keyword: Plutonic Theme_Keyword: Porphyry Theme_Keyword: Potassium Theme_Keyword: Pyrite Theme_Keyword: Quartz Theme_Keyword: Resources Theme_Keyword: Rhyolite Theme_Keyword: Rocks Theme_Keyword: Sample Location Theme_Keyword: Sericite Theme_Keyword: Skarn Place: Place_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Place_Keyword: Banner Creek Place_Keyword: Buckeye Creek Place_Keyword: Democrat Prospect Place_Keyword: Fairbanks Mining District Place_Keyword: Richardson Mining District Place_Keyword: Twentyfive Mile Creek Temporal: Temporal_Keyword_Thesaurus: 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 Temporal_Keyword: Cretaceous 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). 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. Point_of_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: Alaska Division of Geological & Geophysical Surveys Contact_Position: Metadata Manager Contact_Address: Address_Type: mailing and physical Address: 3354 College Road City: Fairbanks State_or_Province: AK Postal_Code: 99709-3707 Country: USA Contact_Voice_Telephone: (907)451-5020 Contact_Facsimile_Telephone: (907)451-5050 Contact_Electronic_Mail_Address: dggspubs@alaska.gov Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays Data_Set_Credit: 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. Cross_Reference: Citation_Information: Originator: Graham, G.E. Originator: Jozwik, Diana Publication_Date: 2007 Title: Data tables related to geology and gold mineralization in the Richardson district, east-central Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2007-2 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 32 p Online_Linkage: https://doi.org/10.14509/15819 Cross_Reference: Citation_Information: Originator: Naibert, T.J. Originator: Benowitz, J.A. Originator: Wypych, Alicja Originator: Sicard, K.R. Originator: Twelker, Evan Publication_Date: 2018 Title: 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 Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2018-3 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 15 p Online_Linkage: https://doi.org/10.14509/30112 Cross_Reference: Citation_Information: Originator: 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. Publication_Date: 2017 Title: Geologic mapping in the Richardson-Uncle Sam area, interior Alaska (presentation): Alaska Miners Association Annual Convention, Anchorage, Alaska, November 7-12, 2017 Series_Information: Series_Name: Poster and Presentation Issue_Identification: Twelker, Evan and others, 2017 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 37 p Online_Linkage: https://doi.org/10.14509/29811 Cross_Reference: Citation_Information: Originator: Twelker, Evan Originator: Wypych, Alicja Originator: Sicard, K.R. Originator: Naibert, T.J. Originator: Montayne, Simone Originator: Newberry, R.J. Originator: Wyatt, W.C. Publication_Date: 2018 Title: Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2018-6 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 4 p Online_Linkage: https://doi.org/10.14509/30119 Cross_Reference: Citation_Information: Originator: 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. Publication_Date: 2017 Title: Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2017-11 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 4 p Online_Linkage: https://doi.org/10.14509/29779 Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: This 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. Logical_Consistency_Report: not applicable Completeness_Report: This data release is complete. Positional_Accuracy: Horizontal_Positional_Accuracy: 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. Lineage: Process_Step: Process_Description: 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. Process_Date: 2018 Process_Step: Process_Description: 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. Process_Date: 2018 Process_Step: Process_Description: 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. Process_Date: 2018 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: point Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.000001 Longitude_Resolution: 0.000001 Geographic_Coordinate_Units: decimal degrees Geodetic_Model: Horizontal_Datum_Name: World Geodetic System of 1984 Ellipsoid_Name: WGS 84 Semi-major_Axis: 6378137 Denominator_of_Flattening_Ratio: 298.257223563000025 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: rdf2020-11-summary-data-locations.csv, rdf2020-11-step-heating-data.csv, rdf2020-11-data-dictionary.csv Entity_Type_Definition: 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. Entity_Type_Definition_Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and Geochronology Laboratory at the University of Alaska Fairbanks (UAF) Entity_Attribute_Layer_Name: data Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: Alaska Division of Geological & Geophysical Surveys Contact_Position: Metadata Manager Contact_Address: Address_Type: mailing and physical Address: 3354 College Road City: Fairbanks State_or_Province: AK Postal_Code: 99709-3707 Country: USA Contact_Voice_Telephone: (907)451-5020 Contact_Facsimile_Telephone: (907)451-5050 Contact_Electronic_Mail_Address: dggspubs@alaska.gov Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays Resource_Description: RDF 2020-11 Distribution_Liability: 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. Standard_Order_Process: Non-digital_Form: 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. Fees: Contact DGGS for current pricing Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: ASCII tabular files Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://doi.org/10.14509/30530 Fees: Free download Metadata_Reference_Information: Metadata_Date: 20200911 Metadata_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: Alaska Division of Geological & Geophysical Surveys Contact_Person: Simone Montayne Contact_Position: Metadata Manager Contact_Address: Address_Type: mailing and physical Address: 3354 College Road City: Fairbanks State_or_Province: AK Postal_Code: 99709-3707 Country: USA Contact_Voice_Telephone: (907)451-5020 Contact_Facsimile_Telephone: (907)451-5050 Contact_Electronic_Mail_Address: dggspubs@alaska.gov Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays Metadata_Standard_Name: FGDC Content Standard for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998 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. Metadata_Extensions: Online_Linkage: https://www.dggs.alaska.gov/metadata/dggs.ext Profile_Name: dggs metadata extensions