40Ar/39Ar geochronology data from the Tanacross and Eagle quadrangles, Alaska

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Frequently anticipated questions:


What does this data set describe?

Title:
40Ar/39Ar geochronology data from the Tanacross and Eagle quadrangles, Alaska
Abstract:
40Ar/39Ar geochronology data from the Tanacross and Eagle quadrangles, Alaska, Raw Data File 2023-23, provides 40Ar/39Ar geochronology data from igneous and metamorphic rocks in or adjacent to the DGGS Western Tanacross and Taylor Mountain geologic mapping project areas. Western Tanacross and Taylor Mountain geologic mapping projects aim to produce more accurate and integrated modern geologic maps and supporting datasets to promote mineral resource exploration in eastern Interior Alaska. The Tanacross and southern Eagle quadrangles are within the Yukon Tanana Uplands, which DGGS and USGS identified as having the potential to host deposits of multiple critical minerals, as well as gold, copper, molybdenum, lead, zinc, and silver. Most of the known mineralization in the region is related to Mesozoic-Paleogene magmatism. Igneous rocks intrude a composite metamorphic province that includes parautochthonous North America and the allochthonous Yukon Tanana Terrane, which are multiply deformed and apparently juxtaposed along low-angle faults. Samples were collected (2009, 2018, 2019, 2021) for 40Ar/39Ar geochronology to understand the crystallization ages of igneous rocks, the exhumation history of metamorphic rocks, and the timing of mineralization. The 22 40Ar/39Ar ages reported here include six mineralization/alteration ages, one volcanic crystallization age, seven metamorphic cooling ages from the Yukon-Tanana terrane (YTT), and eight metamorphic cooling ages from parautochthonous North American rocks (pNA). The analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files. These data are available from the DGGS website: http://doi.org/10.14509/31085.
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 contents, format, and structure of the data.
  1. How might this data set be cited?
    Naibert, T.J., Heizler, M.T., Newberry, R.J., Twelker, Evan, and Wypych, Alicja, 2023, 40Ar/39Ar geochronology data from the Tanacross and Eagle quadrangles, Alaska: Raw Data File RDF 2023-23, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 19 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -143.839740
    East_Bounding_Coordinate: -141.025990
    North_Bounding_Coordinate: 64.255820
    South_Bounding_Coordinate: 63.068960
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 2021
    Ending_Date: 2023
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: csv
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a point data set.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is WGS84.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    rdf2023-23-step-heating-data.csv, rdf2023-23-step-heating-data-dictionary.csv, rdf2023-23-summary-data.csv, rdf2023-23-summary-data-dictionary.csv
    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 contents, format, and structure of the data. (Source: Alaska Division of Geological & Geophysical Surveys (DGGS) and New Mexico Geochronological Research Laboratory (NMGRL))

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    U.S. Geological Survey EarthMRI funded sample collection and analyses for the Western Tanacross and Taylor Mountain projects awards G20AC00156 and G21AC10336 and State of Alaska capital project funds. Sample analyses for the compilation mapping in the eastern Yukon Tanana Upland were funded by USGS STATEMAP award G21AC10706. We are grateful to have had access to Doyon Limited lands within the study area. We thank the USGS for lending us core samples from the Fish prospect. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

The purpose of the Western Tanacross and Taylor Mountain projects is to produce more accurate, detailed, and modern geologic maps and supporting datasets that will promote mineral resource exploration in eastern Interior Alaska. The Tanacross and southern Eagle quadrangles are within the Yukon Tanana Uplands, which DGGS and USGS identified as having the potential to host deposits of multiple critical minerals, as well as gold, copper, molybdenum, lead, zinc, and silver.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 2021 (process 1 of 3)
    Fieldwork - DGGS field geologists collected fresh, unweathered samples from surface outcrops based on the presence of sufficiently large crystals appropriate for dating. Sample 21RN612 from the Fish prospect is from a drill core obtained by Rainer Newberry from the USGS. 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/or in thin section to select unaltered mineral phases before sample preparation.
    Date: 2022 (process 2 of 3)
    Sample preparation - Twenty-seven samples were submitted to the New Mexico Geochronological Research Laboratory (NMGRL) in Socorro, New Mexico. Twenty-two samples yielded acceptable mineral separates for 40Ar/39Ar geochronology. Muscovite, biotite, phlogopite, hornblende, and sericite were separated from rock samples using standard magnetic, heavy liquid, and handpicking procedures. The samples were loaded into machined aluminum discs and irradiated for 20 hours at the USGS reactor in Denver, Colorado (NM-327), along with the Fish Canyon Tuff sanidine standard (FC-2; assigned age - 28.201 Ma; Kuiper and others, 2008) as a neutron flux monitor.
    Date: 2022 (process 3 of 3)
    Geochronology analysis - After irradiation, the samples and monitors were analyzed by step-heating with a defocused 810 nm diode laser. The samples were step-heated using between 10 and 17 increments, and most separates yielded moderate-quality to complex age-spectra patterns. Reactive gases were removed by a 45-second reaction with a SAES GP-50 getter at 450 degrees C, and gas was also exposed to a cold finger at -140 degrees C. The samples were analyzed in a Thermo-Fisher Scientific Helix MC-plus mass spectrometer at NMGRL. Total system blanks were 3.5 x 10^-17 mol 40Ar, 8 x 10^-18 mol 39Ar, 5 x 10^-19 mol 38Ar, 3 x 10^-18 mol 37Ar, 5 x 10^-19 mol 36Ar. Isotopic ratios were corrected for blank, radioactive decay, and mass discrimination but were not corrected for interfering reactions. Note: Complete list of references can be found in the accompanying report.
  3. What similar or related data should the user be aware of?
    Gavel, M.M., Regan, S.P., Holland, Mark, Wildland, A.D., Wypych, Alicja, Naibert, T.J., and Twelker, Evan, 2023, U-Pb zircon geochronology of bedrock samples collected in the Eagle and Tanacross quadrangles, eastern Alaska: Preliminary Interpretive Report PIR 2023-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 38 p
    Solie, D.N., Werdon, M.B., Freeman, L.K., Newberry, R.J., Szumigala, D.J., Speeter, G.G., and Elliott, B.A., 2019, Bedrock-geologic map, Alaska Highway corridor, Tetlin Junction, Alaska to Canada border: Preliminary Interpretive Report PIR 2019-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p., 2 sheets, scale 1:63,360
    Twelker, Evan, Newberry, R.J., Wypych, Alicja, Naibert, T.J., Wildland, A.D., Sicard, K.R., Regan, S.P., Athey, J.E., Wyatt, W.C., and Lopez, J.A., 2021, Bedrock geologic map of the Ladue River-Mount Fairplay area, Tanacross and Nabesna quadrangles, Alaska: Report of Investigation RI 2021-5A, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: p. 1-32, 1 sheet, scale 1:100,000
    Twelker, Evan, Newberry, R.J., Wypych, Alicja, Sicard, K.R., and Naibert, T.J., 2020, Mineral occurrences in the Tok River area, eastern Alaska Range: Report of Investigation RI 2020-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 49 p
    Wypych, Alicja, Hubbard, T.D., Naibert, T.J., Athey, J.E., Newberry, R.J., Sicard, K.R., Twelker, Evan, Werdon, M.B., Willingham, A.L., Wyatt, W.C., and Lockett, A.C., 2021, Northeast Tanacross geologic map and map units and descriptions: Report of Investigation RI 2020-9B, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: p. 9-26, 1 sheet, scale 1:63,360

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    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. The originating lab can best answer questions about the analytical values or procedures.
  2. How accurate are the geographic locations?
    Sample 21RN612 from the Fish prospect is from a drill core obtained by Rainer Newberry from the USGS. Sample location coordinates for the DGGS samples (in WGS84 datum) were obtained using GPS-enabled field tablets with a typical reported accuracy of about 10 meters.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This data release is complete.
  5. How consistent are the relationships among the observations, including topology?
    Not applicable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
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.
  1. Who distributes the data set? (Distributor 1 of 1)
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? RDF 2023-23
  3. What legal disclaimers am I supposed to read?
    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.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 01-Dec-2023
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.50 on Fri Dec 01 18:52:58 2023