U-Pb zircon data and ages for bedrock samples from the Richardson mining district, Big Delta Quadrangle, Alaska

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Frequently anticipated questions:


What does this data set describe?

Title:
U-Pb zircon data and ages for bedrock samples from the Richardson mining district, Big Delta Quadrangle, Alaska
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 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. Uranium-lead (U-Pb) zircon geochronology results presented in this report show that similarly textured quartz-feldspar porphyry intrusions in the project area were generated by both Paleocene (56.8 +/- 0.9 Ma; 18WCW149) and middle Cretaceous (92.0 +/- 0.7 Ma; 18AW002, known as the Democrat Dike) magmatic episodes. The ages of medium-grained plutonic rocks at Birch Lake (92.4 +/- 0.6 Ma; 18ET587) and Gold Run (93.7 +/- 0.7 Ma; 18ET580) lie within error of the age of the hypabyssal Democrat Dike, indicating that the present-day depth of exposure juxtaposes rocks that were buried at widely different crustal depths during the middle Cretaceous. Phaneritic granodiorite near the Democrat prospect yielded a zircon age of 110.7 +/- 1.3 Ma (18RN565), extending the magmatic history of the prospect into the Early Cretaceous. Amphibolite-facies augen orthogneiss yielded a Late Devonian zircon age of 364.5 +/- 6.0 Ma (18ET040), consistent with similar rocks in the Lake George assemblage. Detrital zircons analyzed from siliciclastic schist along the Richardson Highway (18AW021) contain prominent age populations at 1.8 and 2.6 Ga, consistent with a Laurentian cratonic source and consistent with other results from parautochthonous North America. Pelitic schist from the Hilltop prospect (18TJN372) yielded a relatively small number (n=32) of zircon grains that define small age populations between ca. 1.7 and 1.5 Ga. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30555.
Supplemental_Information:
geochron-data:    Spreadsheets with geochronology lab results and a preferred age summary table.	
geochron-summary:    Identification numbers, coordinates, sample descriptions, and summary ages of each sample.
  1. How might this data set be cited?
    Twelker, Evan, and O'Sullivan, P.B., 2021, U-Pb zircon data and ages for bedrock samples from the Richardson mining district, Big Delta Quadrangle, Alaska: Raw Data File RDF 2020-14, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 17 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -146.700350
    East_Bounding_Coordinate: -146.357620
    North_Bounding_Coordinate: 64.426240
    South_Bounding_Coordinate: 64.290670
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2018
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: report, tables
  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?
    rdf2020-14-geochron-data.zip, rdf2020-14-geochron-data-dictionary.csv
    Spreadsheets with geochronology lab results and a preferred age summary table. (Source: U-Pb geochronology analyses were performed by Paul O'Sullivan of GeoSep Services)
    rdf2020-14-geochron-summary.csv, rdf2020-14-geochron-summary-dictionary.csv
    Identification numbers, coordinates, sample descriptions, and summary ages of each sample. (Source: Alaska Division of Geological & Geophysical Surveys)

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?
    We gratefully acknowledge James V. Jones III for his assistance with the age interpretations and figures. The 2018 Richardson geologic mapping project was funded by the State of Alaska.
  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?

DGGS's work in the Richardson mining district supports improved understanding of the area's geology and controls on gold mineralization. This work facilitates industry exploration targeting.

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: 2018 (process 1 of 2)
    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. Rocks were collected in summer 2018. Petrographic thin sections of each rock were examined to determine suitability for U-Pb geochronologic analysis. In some cases, samples from several closely adjacent outcrops were combined to create a composite sample of sufficient volume for analysis.
    Date: 2018 (process 2 of 2)
    Sample preparation and data analysis - Zircon grains from rock samples were analyzed to obtain U-Pb isotopic geochronologic ages using the methods described in the accompanying report.
  3. What similar or related data should the user be aware of?
    Burns, L.E., Graham, G.R.C., Barefoot, J.D., Fugro Airborne Surveys Corp., and Stevens Exploration Management Corp., 2019, East Richardson electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2018-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 12 p
    Graham, G.E., and Jozwik, Diana, 2007, Data tables related to geology and gold mineralization in the Richardson district, east-central Alaska: Raw Data File RDF 2007-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 32 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
    Twelker, Evan, Benowitz, J.A., and Naibert, T.J., 2020, 40Ar/39Ar data from the Richardson mining district, Big Delta Quadrangle, Alaska: Raw Data File RDF 2020-11, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 10 p
    Twelker, Evan, Werdon, M.B., Sicard, K.R., Wypych, Alicja, Naibert, T.J., Athey, J.E., Willingham, A.L., and Lockett, A.C., 2017, Geologic mapping in the Richardson-Uncle Sam area, interior Alaska (presentation): Alaska Miners Association Annual Convention, Anchorage, Alaska, November 7-12, 2017: Poster and Presentation Twelker, Evan and others, 2017, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 37 p
    Twelker, Evan, Wypych, Alicja, Sicard, K.R., Naibert, T.J., Montayne, Simone, Newberry, R.J., and Wyatt, W.C., 2018, Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska: Raw Data File RDF 2018-6, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 4 p
    Twelker, Evan, Wypych, Alicja, Sicard, K.R., Naibert, T.J., Werdon, M.B., Athey, J.E., Willingham, A.L., and Lockett, A.C., 2017, Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska: Raw Data File RDF 2017-11, 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?
    A summary of all interpreted U-Pb ages is included with uncertainty for all ages and isotope ratios reported at the 2 sigma level. A concordance filter was used to eliminate grains that were either heterogeneous or experienced Pb loss after formation. Filtered grains were not included in the final interpretation. 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 obtained using GPS-enabled field tablets, with a typical reported accuracy of +/- 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. 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
    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 2020-14
  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: 08-Jan-2021
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 Jan 08 00:14:14 2021