U-Pb geochronology of igneous and detrital zircon samples from the Tok River area, eastern Alaska Range, and Talkeetna Mountains, Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
U-Pb geochronology of igneous and detrital zircon samples from the Tok River area, eastern Alaska Range, and Talkeetna Mountains, Alaska
Abstract:
This Alaska Division of Geological & Geophysical Surveys (DGGS) Raw Data File presents U-Pb zircon geochronology results from igneous, meta-igneous, and metasedimentary rocks collected during the Tok River and Wrangellia geologic mapping projects in the eastern Alaska Range and the northwestern Talkeetna Mountains. The purpose of these analyses is to better constrain the age of select geologic units encountered during the mapping projects. The samples were submitted to the U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center (GGGSC)-Plasma Lab in Denver, CO where U-Pb geochronology analyses were performed by Christopher Holm-Denoma in 2016-2017. All files are available from the DGGS website: <http://doi.org/10.14509/30439>.
Supplemental_Information: 
geochron-data: Spreadsheets with geochronology lab results, preferred age summary table, and applicable data dictionary.
  1. How should this data set be cited?

    Holm-Denoma, C.S., Sicard, K.R., and Twelker, Evan, 2020, U-Pb geochronology of igneous and detrital zircon samples from the Tok River area, eastern Alaska Range, and Talkeetna Mountains, Alaska: Raw Data File RDF 2020-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 20 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -147.594741
    East_Bounding_Coordinate: -153.27545
    North_Bounding_Coordinate: 63.336804
    South_Bounding_Coordinate: 62.862113

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 2015
    Ending_Date: 2020
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: report and digital data

  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 0.0001. Longitudes are given to the nearest 0.0001. Latitude and longitude values are specified in decimal degrees.

      The horizontal datum used is World Geodetic System of 1984.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563000025.

  7. How does the data set describe geographic features?

    rdf2020_003_geochron_data.xlsx,rdf2020_003_geochron_summary.xlsx
    Spreadsheets with geochronology lab results, preferred age summary table, and applicable data dictionary. (Source: U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center (GGGSC)-Plasma Lab in Denver, CO where U-Pb geochronology analyses were performed by Christopher Holm-Denoma in 2016-2017)

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?

    Acquisition of these data was funded through Cooperative Agreement Number 16CMFUSAGEOCHRN between the U.S. Geological Survey (USGS) and the Alaska Department of Natural Resources, Division of Geological & Geophysical Surveys. This project was jointly funded by the State of Alaska's Strategic and Critical Minerals Assessment project (part of DGGS's Airborne Geophysical/Geological Mineral Inventory program [AGGMI]), a USGS Mineral Resources Assessment Grant G16AS00003, and the USGS National Cooperative Geologic Mapping Program, STATEMAP component, under 2016 award number G16AC00182. 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. We acknowledge Heidi Lingenfelter and Joe Bovee representing Ahtna, Inc., James Mery of Doyon Limited, and Mentasta Village, for providing access to private lands in the map area. Staff at the U.S. Bureau of Land Management (BLM) Glennallen Field Office and of BLM's eastern Field Office (Fairbanks) assisted us with permitting on BLM-managed lands. Field mapping and sample collection were conducted by Lawrence Freeman, Robert Gillis, Lauren Lande, Travis Naibert, Rainer Newberry, David Reioux, Karri Sicard, Evan Twelker, Melanie Werdon, Amanda Willingham, and Alicja Wypych. Much appreciated field mapping, regional geologic context, and sample-collection assistance came from Samuel Dashevsky and James V. Jones. Sarah Bala and Thomas Strong assisted with sample preparation and processing.

  3. To whom should users address questions about the data?

    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK 99709-3707
    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

Why was the data set created?

The Tok River geologic mapping project comprised the Tanacross A-5 and A-6 quadrangles. DGGS conducted fieldwork for this project during the 2015 and 2016 field seasons, and the map was published in 2017. The 2013-2015 DGGS Wrangellia project investigated the geology and mineral potential of the Wrangellia terrane in the Talkeetna Mountains and eastern Alaska Range, where recent exploration activity has targeted nickel, copper, and platinum-group-element mineralization hosted by Late Triassic mafic-ultramafic complexes, metasediment-hosted copper, porphyry copper-gold-molybdenum porphyry, and orogenic gold systems.

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: 2015 (process 1 of 3)
    Sample selection - Fresh, unweathered samples from surface bedrock outcrops were collected by DGGS field geologists; samples of representative rock types and important intrusive bodies were prioritized for analysis.

    Date: 2016 (process 2 of 3)
    Sample preparation - Zircon was concentrated using standard processing methods as described in Strong and Driscoll (2016), which included crushing, grinding, and sieving. The 500µm-44µm (standard U.S. mesh sizes 35-325) sieve fraction was then processed using a Wilfley table and a Frantz magnetic barrier laboratory separator; the non-magnetic fraction was further processed using heavy liquid (Methylene Iodide; density= 3.32 g/cm3). The concentrated non-magnetic, heavy mineral (>3.32 g/cm3 density) fraction was either hand-picked (for igneous grain mounting) or poured (for detrital zircon samples) onto two-sided tape and mounted in epoxy. Zircon in epoxy was ground to approximately half-width of the grains to expose internal portions of the grains. The zircon grains were imaged using transmitted and reflected light as well as scanning electron microscope-cathodoluminescence imaging to reveal inclusions, cracks, and growth zoning.

    Date: 2017 (process 3 of 3)
    Data analysis - Zircon U-Pb analyses were conducted at the U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center (GGGSC)-Plasma Lab in Denver, Colorado. C.S Holm-Denoma analyzed zircon crystals with Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) using a Nu Instruments AttoM high-resolution, sector-field ICP-MS. Zircon were ablated with a Photon Machines Excite 193 nm ArF excimer laser in spot mode (150-200 total bursts) with a repetition rate of 5 Hz, laser energy of approximately 3 mJ, and an energy density of approximately 4.11 J/cm3. The rate of helium gas flow to the HelEx cell of the laser was 0.6 L/minute and make-up Argon gas (approximately 0.2 L/minute) was added to the sample stream prior to its introduction into the plasma. As suggested by Hu and others (2008), nitrogen with flow rate of 5.5 mL/minute was added to the sample stream, which allowed for significant reduction in ThO+/Th+ ( less than 0.5 percent) and improved the ionization of refractory Thorium. The laser spot sizes for zircon were approximately 25 μm in diameter. With the magnet parked at a constant mass, the flat tops of the isotope peaks were measured at the following masses by rapidly deflecting the ion beam: 202Hg, 204(Hg+Pb), 206Pb, 207Pb, 208Pb, 232Th, 235U, and 238U with a 30-second on-peak background measured before each 30-second analysis. Raw data were reduced off-line using the Iolite 2.5 program (Paton and others, 2011) to subtract on-peak background signals, correct for U-Pb downhole fractionation, and normalize the instrumental mass bias using external mineral standard reference materials, the ages of which have previously been determined by Isotopic Dilution-Thermal Ionization Mass Spectrometry (ID-TIMS). Ages are corrected by standard-sample bracketing with the primary zircon standard Temora2 (417 Ma; Black and others, 2004), secondary standard Plešovice (337 Ma; Slama and others, 2008), and in-house standard WRP-63-08 (1707 Ma; Wayne Premo, personal commun., 2016). Reduced data were compiled and interpreted using Isoplot 4.15 (Excel version of the procedure explained in version 3.75 manual; Ludwig, 2012).

  3. What similar or related data should the user be aware of?

    Benowitz, J.A., Layer, P.W., Wypych, Alicja, and Twelker, Evan, 2015, 40Ar/39Ar data from the Talkeetna Mountains C-4 Quadrangle and adjoining areas, central Alaska: Raw Data File RDF 2015-10, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 19 p
    Benowitz, J.A., Layer, P.W., Wypych, Alicja, and Twelker, Evan, 2017, 40Ar/39Ar data from rocks collected in the 2015 Wrangellia mineral assessment project area, Mount Hayes A-5, Mount Hayes B-6, and Talkeetna Mountains D-2 quadrangles, Alaska: Raw Data File RDF 2017-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 9 p
    Benowitz, J.A., Layer, P.W., and Twelker, Evan, 2014, 40Ar/39Ar data from rocks collected in 2013 in the Wrangellia mineral assessment area, Gulkana, Healy, Mount Hayes, and Talkeetna Mountains quadrangles, Alaska: Raw Data File RDF 2014-18, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 10 p
    Benowitz, J.A., Sicard, K.R., Naibert, T.J., and Layer, P.W., 2017, 40Ar/39Ar data from the Tok River area, Tanacross A-5 and A-6 quadrangles and adjoining areas, eastern Alaska Range: Raw Data File RDF 2017-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 26 p
    Naibert, T.J., Benowitz, J.A., Wypych, Alicja, Sicard, K.R., and Twelker, Evan, 2018, 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: Raw Data File RDF 2018-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 15 p
    Naibert, T.J., Werdon, M.B., Lande, Lauren, and Wypych, Alicja, 2016, Trace-element geochemical data from stream sediments collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016: Raw Data File RDF 2016-10, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p
    Sicard, K.R., Naibert, T.J., Hubbard, T.D., Twelker, Evan, Wypych, Alicja, Werdon, M.B., Willingham, A.L., Gillis, R.J., Lande, L.L., and Newberry, R.J., 2017, Geologic map of the Tok River area, Tanacross A-5 and A-6 quadrangles, eastern Alaska Range, Alaska: Preliminary Interpretive Report PIR 2017-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 15 p., 1 sheet, scale 1:63,360
    Todd, Erin, Kylander-Clark, Andrew, Wypych, Alicja, Twelker, Evan, and Sicard, K.R., 2017, U-Pb and Lu-Hf isotope, age, and trace-element data from zircons at four sites in the western Alaska Range and Talkeetna Mountains, Alaska: Raw Data File RDF 2017-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 7 p
    Twelker, Evan, Bachmann, E.N., Freeman, L.K., Newberry, R.J., Reioux, D.A., Sicard, K.R., Tuzzolino, A.L., Wright, T.C., and Wypych, Alicja, 2014, Major-oxide, minor-oxide, and trace-element geochemical data from rocks and stream sediments in the Wrangellia mineral assessment area, Gulkana, Healy, Mount Hayes, and Talkeetna Mountains quadrangles, Alaska: Raw Data File RDF 2014-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 6 p
    Twelker, Evan, Freeman, L.K., Sicard, K.R., and Busk, A.C., 2016, Preliminary report on mineral occurrences in the Tok River area, Alaska: Preliminary Interpretive Report PIR 2016-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 7 p
    Twelker, Evan, Hubbard, T.D., Wypych, Alicja, Sicard, K.R., Newberry, R.J., Reioux, D.A., Freeman, L.K., and Lande, L.L., 2015, Geologic map of the Talkeetna Mountains C-4 Quadrangle and adjoining areas, central Alaska: Preliminary Interpretive Report PIR 2015-6, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 16 p., 1 sheet, scale 1:50,000
    Twelker, Evan, and O'Sullivan, P.B., 2016, U-Pb zircon age data from meta-igneous rocks in the Clearwater Mountains, Mount Hayes A-6 Quadrangle, Alaska: Raw Data File RDF 2016-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 17 p
    Wypych, Alicja, Sicard, K.R., Gillis, R.J., Lande, L.L., Naibert, T.J., Newberry, R.J., Twelker, Evan, Werdon, M.B., and Willingham, A.L., 2016, Major-oxide and trace-element geochemical data from rocks collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016: Raw Data File RDF 2016-9, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p
    Wypych, Alicja, Sicard, K.R., Twelker, Evan, Freeman, L.K., Lande, Lauren, and Reioux, D.A., 2015, Major-oxide and trace-element geochemical data from rocks collected in 2015 in the Tok area, Tanacross A-5, A-6, and parts of adjacent quadrangles, Alaska: Raw Data File RDF 2015-15 v. 1.1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p
    Wypych, Alicja, Twelker, Evan, Freeman, L.K., Lande, Lauren, Newberry, R.J., Reioux, D.A., and Sicard, K.R., 2014, Major-oxide and trace-element geochemical data from rocks collected in 2014 in the Wrangellia mineral assessment area, Talkeetna Mountains C-4, C-3, and B-4 quadrangles, Alaska: Raw Data File RDF 2014-22, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 p
    Wypych, Alicja, Twelker, Evan, Freeman, L.K., Lande, Lauren, Newberry, R.J., Reioux, D.A., and Sicard, K.R., 2015, Major-oxide and trace-element geochemical data from rocks collected in 2015 in the Wrangellia mineral assessment area, Alaska: Raw Data File RDF 2015-16, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 p

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

  1. How well have the observations been checked?

    These data are being released in the DGGS Raw Data File series. Reports in this series present raw field data and analytical results with limited or no interpretation by DGGS staff or project collaborators. Analytical results may include interpretations by laboratories when an interpretive review of the analytical findings is necessary to develop usable output. The reports and accompanying data have been evaluated by project staff for general readability and logical consistency but have not undergone technical peer review.

  2. How accurate are the geographic locations?

    Sample-location coordinates (in WGS84 datum) were collected using handheld Trimble Juno T5 GPS units, with typical reported accuracy of about 10 meters. Location coordinates for all dated samples are provided in an accompanying .csv file in decimal-degree format, WGS84 datum.

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    This data release is complete. Requests for additional information regarding the parameters and definitions of the analytical values should be directed to the originating lab.

  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 99709-3707
    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
  2. What's the catalog number I need to order this data set?

    RDF 2020-3

  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: 04-Jun-2020
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
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 2.9.21 on Thu Jun 4 18:41:49 2020