40Ar/39Ar data from the northern Fairbanks mining district, Circle Quadrangle, Alaska

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Frequently anticipated questions:


What does this data set describe?

Title:
40Ar/39Ar data from the northern Fairbanks mining district, Circle Quadrangle, Alaska
Abstract:
40Ar/39Ar data from the northern Fairbanks mining district, Circle Quadrangle, Alaska, Raw Data File 2025-1, presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) geologic mapping project in the northern Fairbanks mining district, covering parts of the Circle A-4, A-5, B-4, and B-5 quadrangles, Alaska. Field samples were collected by the DGGS Mineral Resources Section during a detailed geologic mapping campaign in June 2007. In addition to analytical data compiled in the geologic map for this area, other DGGS publications supporting geologic mapping in the northern Fairbanks mining district include geophysical data, geochemical data, and a planned U-Pb detrital zircon age report. The northern Fairbanks mining district map area lies within the Yukon-Tanana Upland in rocks that we interpret to correlate with the Cambrian to Late Proterozoic Fairbanks schist and the Wickersham Grit unit. These rocks are intruded by several phases of plutonism, of which two occur in the map area: Tertiary and Cretaceous plugs, dikes, and sills with characteristic geochemical signatures. The Cretaceous intrusions are regionally associated with placer- and lode-gold mines and occurrences. The age data in this report constrain the crystallization ages of igneous rocks, the potential timing of mineralization, and the cooling histories of metamorphic rocks in the map area. These data and report are available from the DGGS website: http://doi.org/10.14509/31472.
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?
    Layer, P.W., Drake, Jeffrey, Athey, J.E., and Naibert, T.J., 2025, 40Ar/39Ar data from the northern Fairbanks mining district, Circle Quadrangle, Alaska: Raw Data File RDF 2025-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 8 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -146.450877
    East_Bounding_Coordinate: -146.142762
    North_Bounding_Coordinate: 65.398043
    South_Bounding_Coordinate: 65.226045
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 2007
    Ending_Date: 2025
    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 0.0000001. Longitudes are given to the nearest 0.0000001. 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?
    rdf2025-1_ar_ar_step-heating-data.csv, rdf2025-1_ar_ar_summary-data-locations.csv, rdf2025-1_ar_ar_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: DGGS, UAF)

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?
    The Northern Fairbanks Mining District project is part of the State of Alaska's Airborne Geophysical/Geological Mineral Inventory (AGGMI) program, a special multi-year investment by the state to expand Alaska's geologic and mineral resources knowledge base, catalyze future private-sector mineral exploration and development, and guide state planning. AGGMI was funded by the Alaska State Legislature. Fieldwork for the project was also partially funded by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number 07HQAG0076. Additional funding was provided by the State of Alaska General Fund. 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?

This work furthers our understanding of potential mineral resources in the Circle A-4, A-5, B-4, and B-5 quadrangles of the northern Fairbanks mining district map area, which lies within Alaska's Yukon-Tanana Upland.

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: 2007 (process 1 of 3)
    Sample collection - Samples from surface outcrops were collected by DGGS field geologists and were selected for dating based on the priority of information needed, presence of sufficiently large crystals appropriate for dating, and minimal weathering. Sample location coordinates were obtained using recreational-grade GPS units, with a typical reported accuracy of about 10 meters. Coordinates are reported using the WGS84 datum. Hand samples and (or) thin sections were examined to select unaltered mineral phases before sample preparation.
    Date: 2008 (process 2 of 3)
    Sample preparation - Five rock samples were submitted to the Geochronology Laboratory at the University of Alaska Fairbanks (UAF) for 40Ar/39Ar analysis. The samples were crushed, sieved to either 100-250 or 250-500 micron size fractions, and handpicked for biotite, hornblende, and sericite mineral phases. The monitor mineral MMhb-1 (Samson and Alexander, 1987) with an age of 513.9 Ma (Lanphere and Dalrymple, 2000) was used to monitor neutron flux and calculate the irradiation parameter J. The samples and standards were wrapped in aluminum foil and 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.
    Date: 2008 (process 3 of 3)
    Analytical methods - 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 Layer (2000). Argon purification was achieved using a liquid nitrogen cold trap and a SAES Zr-Al getter at 400 degrees 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). System blanks generally were 2x10-16 mol 40Ar and 2x10-18 mol 36Ar, which are 10 to 50 times smaller than fraction volumes. Mass discrimination was monitored by running both calibrated air shots and a zero-age glass sample. These measurements were made on a weekly to monthly basis to check for changes in mass discrimination, with no significant variation observed during these intervals.
  3. What similar or related data should the user be aware of?
    Athey, J.E., Freeman, L.K., Newberry, R.J., Werdon, M.B., Szumigala, D.J., and Lessard, R.R., 2022, Bedrock geologic map of the northern Fairbanks mining district, Circle Quadrangle, Alaska: Preliminary Interpretive Report PIR 2022-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 24 p., 1 sheet, scale 1:50,000
    Athey, J.E., Freeman, L.K., Werdon, M.B., Szumigala, D.J., Lessard, R.R., Newberry, R.J., Hansen, S.E., and Jing, Liping, 2008, Major-oxide, minor-oxide, and trace-element geochemical data from rocks and stream sediments collected in the northern Fairbanks mining district, Circle Quadrangle, Alaska in 2007: Raw Data File RDF 2008-1 v. 1.0.1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 41 p
    Burns, L.E., Graham, G.R.C., Barefoot, J.D., Surveys, Fugro Airborne, and Stevens Exploration Management Corp., 2019, Northeast Fairbanks electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2018-11, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 12 p
    Newberry, R.J., Bundtzen, T.K., Clautice, K.H., Combellick, R.A., Douglas, Tom, Laird, G.M., Liss, S.A., Pinney, D.S., Reifenstuhl, R.R., and Solie, D.N., 1996, Preliminary geologic map of the Fairbanks mining district, Alaska: Public Data File PDF 96-16, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 17 p., 2 sheets, scale 1:63,360

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

  1. How well have the observations been checked?
    The accompanying report and data tables provide a discussion of processing methods. The tables contain measured values, calculated values, testing parameters, and statistical errors reported by the laboratory. Summary values are also included where applicable. Analytical results may include laboratory interpretations when an interpretive review is necessary for generating usable output. While the reports and data have been evaluated by project staff for general readability and logical consistency, the laboratory data may not have undergone technical peer review.
  2. How accurate are the geographic locations?
    Sample location coordinates were obtained using recreational-grade GPS units, with a typical reported accuracy of about 10 meters. Coordinates are reported using the WGS84 datum. Hand samples and (or) thin sections were examined to select unaltered mineral phases before sample preparation.
  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 2025-1
  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: 24-Feb-2025
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 Mon Feb 24 21:35:25 2025