40Ar/39Ar data from the eastern Moran area, Tanana B-6 and C-6 quadrangles, and the Ruby mining district, Ruby B-5 and B-6 quadrangles, Alaska

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Frequently anticipated questions:

What does this data set describe?

Title:
40Ar/39Ar data from the eastern Moran area, Tanana B-6 and C-6 quadrangles, and the Ruby mining district, Ruby B-5 and B-6 quadrangles, Alaska
Abstract:
This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the eastern Moran area. Field samples were collected by the DGGS Mineral Resources section during detailed geologic mapping campaigns in 2011. The data provided in this report add significant detail to the thermal history of the Moran area. These new data indicate that the minimum age of prograde metamorphism of Ruby terrane rocks ranges from 148.5 +/- 1.7 to 140.4 +/- 1.7 Ma, and retrograde greenschist metamorphism is 122.6 +/- 2.3 Ma. The retrograde metamorphism is roughly coeval with the age of fabric development parallel to the Kaltag fault (128.3 +/- 1.7) and Tozitna thrust/detachment fault (123.2 +/- 1.5 Ma). The new data also indicate that the Melozitna pluton is composite, with a biotite cooling age of 116.5 +/- 1.3 from coarse-grained granite, while cooling ages for dikes cutting the granite range from 110.1 +/- 1.3 to 102.8 +/- 1.2 Ma. The age of mineralized veins in the area are variable and include 119.0 +/- 1.3 Ma galena veins in the Tozimoran drainage and an interpreted age of 66.5 +/- 2.6 for an auriferous vein from the Monday Creek area, which is synchronous with ages of biotite samples from granite and schist from the Ruby Mining district. The complete report and digital data are available through the DGGS website: <http://doi.org/10.14509/30117>.
Supplemental_Information: 
summary-data-locations:    Identification numbers, coordinates, sample descriptions, and summary ages of each sample	
step-heating-data:    Power output levels and resultant measurements from each sample run
  1. How should this data set be cited?

    Benowitz, J.A., Layer, P.W., Freeman, L.K., Griesel, G.A., Elliott, B.A., Szumigala, D.J., Wypych, Alicja, and Montayne, Simone, 2018, 40Ar/39Ar data from the eastern Moran area, Tanana B-6 and C-6 quadrangles, and the Ruby mining district, Ruby B-5 and B-6 quadrangles, Alaska: Raw Data File RDF 2018-5, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 28 p.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -155.790105
    East_Bounding_Coordinate: -152.604273
    North_Bounding_Coordinate: 65.467821
    South_Bounding_Coordinate: 64.463951

  3. What does it look like?

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

    Beginning_Date: 2011
    Ending_Date: 2018
    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 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in decimal degrees.

      The horizontal datum used is North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.40000000037.
      The flattening of the ellipsoid used is 1/294.978698199999997.

  7. How does the data set describe geographic features?

    rdf2018-5-summary-data-locations.csv
    Identification numbers, coordinates, sample descriptions, and summary ages of each sample (Source: Alaska Division of Geological & Geophysical Surveys)

    SAMPLE
    The label assigned in the field to identify the sample. (Source: Alaska Division of Geological & Geophysical Surveys)

    Generic example of a sample identifier: YYAAA9999X: YY=last two digits of the year the sample was collected, AAA=geologist's initials (one to three characters), 9999=unique station number, X= optional alpha character which indicates that multiple samples were collected at a given location or that multiple observations were recorded in the project database.

    LAB_SAMPLE_NUMBER
    The label used by the lab to identify the sample. (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    The lab sample number is typically identical to the field sample number. However, in some cases, the sample number provided by the lab does differ from the number assigned in the field. We provide both numbers to document instances in which the sample numbers in the lab files differ from the field sample number.

    COLLECTOR
    The geologist who collected the sample. (Source: Alaska Division of Geological & Geophysical Surveys)

    The samples presented in this report were collected by the authors or other DGGS staff.

    LONGITUDE
    Longitude, NAD27 (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:-155.790105
    Maximum:-152.604273
    Units:decimal degrees

    LATITUDE
    Latitude, NAD27 (Source: Alaska Division of Geological & Geophysical Surveys)

    Range of values
    Minimum:64.463951
    Maximum:65.467821
    Units:decimal degrees

    DATED_MATERIAL
    Indicates the type of material that was used for analysis (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    The type of material that was selected for dating varied according to mineral composition and grainsize of the submitted rock sample. This field specifies whether the age was derived from a mineral separate (generally 1 to 10 individual crystals dated together as a single run), a single crystal, or the whole rock.

    MINERAL
    Indicates the mineral that was used for analysis (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    The minerals selected for dating would typically be grains of biotite, hornblende, or muscovite.

    DESCRIPTION
    Description of the sample (Source: Alaska Division of Geological & Geophysical Surveys)

    A brief sample or station description.

    MAP_UNIT
    The interpreted map unit of the sample. (Source: Alaska Division of Geological & Geophysical Surveys)

    Map unit designations are based on geologic mapping and petrographic observations.

    MAP_UNIT_REFERENCE
    Bibliographic reference to the map unit nomenclature. (Source: Alaska Division of Geological & Geophysical Surveys)

    Map unit designations are based on concurrent geologic mapping or previously published reports. A comprehensive reference list is provided in the accompanying report.

    INTEGRATED_AGE_MA
    Integrated age and age error in million years (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    The values are a concatenation of the integrated age determination and the calculated error associated with the integrated age determination

    PLATEAU_AGE_MA
    Plateau age and age error in million years (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the PLATEAU_AGE_MA value was not calculated by the lab

    The values are a concatenation of the plateau age determination and the calculated error associated with the plateau age determination

    PLATEAU_PERCENT_39AR
    Value in percent of the 39 Ar used in that portion of the spectrum to determine the plateau age (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:49.1
    Maximum:99.3
    Units:percent

    PLATEAU_MSWD
    The mean square weighted deviation of the plateau age calculation (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the value was not calculated by the lab

    PLATEAU_REMARKS
    Comments and additional values that pertain to the plateau age determination method or interpretation. (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the PLATEAU_REMARKS value was not provided by the lab

    Free text

    W_M_AGE_MA
    Weighted average age and age error in million years (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the W_M_AGE_MA value was not calculated by the lab

    The values are a concatenation of the weighted average age determination and the calculated error associated with the weighted mean average age determination

    W_M_AGE_PCT_39AR
    Value in percent of the 39 Ar used in that portion of the spectrum to determine the weighted mean age (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:56.6
    Maximum:56.6
    Units:percent

    W_M_AGE_MSWD
    The mean square weighted deviation of the weighted mean age calculation (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the value was not calculated by the lab

    W_M_AGE_REMARKS
    Comments and additional values that pertain to the weighted mean age determination method or interpretation. (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the W_M_AGE_REMARKS value was not provided by the lab

    Free text

    ISOCHRON_AGE
    Isochron age and age error in million years (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the ISOCHRON_AGE value was not provided by the lab

    The values are a concatenation of the isochron age determination and the calculated error associated with the isochron age determination

    ISOCHRON_MSWD
    The mean square weighted deviation of the isochron age calculation (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the value was not calculated by the lab

    Range of values
    Minimum:0.13
    Maximum:1.59

    ISOCHRON_REMARKS
    Comments and additional values that pertain to the isochron age determination method or interpretation (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the ISOCHRON_REMARKS value was not provided by the lab

    Free text

    AGE_TYPE_PREFERRED
    Indicates the age type of the preferred age. (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    A discussion of the preferred age for each analysis is provided in the accompanying lab report. The possible values are: plateau, isochron, weighted average, or integrated.

    PREFERRED_AGE
    The values are a concatenation of the preferred age determination and the calculated error associated with the preferred age determination (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    The preferred age for each analysis is discussed in detail in the accompanying lab report.

    rdf2018-5-step-heating-data.csv
    Power output levels and resultant measurements from each sample run (Source: Alaska Division of Geological & Geophysical Surveys)

    SAMPLE
    Label assigned in the field to identify the sample. (Source: Alaska Division of Geological & Geophysical Surveys)

    Generic example of a sample identifier: YYAAA9999X: YY=last two digits of year, AAA=geologist's initials (one to three characters), 9999=unique station number, X= optional alpha character which indicates that multiple samples were collected at a given location or that multiple observations were recorded in the project database.

    LAB_SAMPLE_NUMBER
    Label used by the lab to identify the sample. (Source: Alaska Division of Geological & Geophysical Surveys and Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    The lab sample number is typically identical to the field sample number. However, in some cases, the sample number provided by the lab does differ from the number assigned in the field. We provide both numbers to document instances in which the sample numbers in the lab files differ from the field sample number.

    Laser_mW
    Laser output level in megawatts (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the values in the row were calculated by weighting the individual heating steps by the fraction of 39Ar released.

    Range of values
    Minimum:300
    Maximum:9000
    Units:megawatts

    Integrated
    We indicate whether the values in the row were derived from a heating step or calculated by weighting the individual heating steps by the fraction of 39Ar released. (Source: Alaska Division of Geological & Geophysical Surveys)

    ValueDefinition
    NULLThe values in the row were derived from a heating step
    Integratedthe values in this row were calculated by weighting the individual heating steps by the fraction of 39Ar released

    Cum39Ar
    Cumulative ratio of 39Argon released at this step (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    ValueDefinition
    NULLA NULL or blank values indicates that the value was not applicable or not calculated by the lab

    Range of values
    Minimum:0.0011
    Maximum:1

    Me40Ar39Ar
    Measured 40Ar/39Ar ratio for each heating step, corrected for blank and 39Ar decay (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:9.59019
    Maximum:2155.92823

    Er40Ar39Ar
    The one sigma error for each 40Ar/39Ar measurement (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.05292
    Maximum:142.8695

    Me37Ar39Ar
    The ratio of measured 37Ar to measured 39Ar for each heating interval for each sample corrected for blank and 37Ar and 39Ar decay (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:-0.22738
    Maximum:38.19865

    Er37Ar39Ar
    The one sigma error for each 37Ar/39Ar measurement (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.00006
    Maximum:1.31526

    Me36Ar39Ar
    Ratio of measured 36Ar to measured 39Ar for each step interval for each sample corrected for blank and 39Ar decay (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:-0.01753
    Maximum:7.05618

    Er36Ar39Ar
    The one sigma error for each 36Ar/39Ar measurement (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.00003
    Maximum:0.46725

    Atm40Ar
    Percent of 40Ar which is atmospheric in composition at each step level (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:-28.45257
    Maximum:98.48928

    ErAtm40Ar
    The one sigma error for the percent of 40Ar which is atmospheric in composition at each step level (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.03976
    Maximum:51.8597

    MeCaK
    Ratio of Calcium to Potassium as determined from 37Ar/39Ar (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:-0.41715
    Maximum:72.03245

    ErCaK
    The one sigma error for each Ca/K determination (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.00011
    Maximum:2.47635

    MeClK
    Ratio of Chlorine to Potassium as determined from 38Ar/39Ar (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:-0.00458
    Maximum:0.23006

    ErClK
    The one sigma error for each Cl/K determination (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.00001
    Maximum:0.01315

    Ar40Rad39ArK
    Ratio of radiogenic 40Ar to 39Ar derived from potassium (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:2.85421
    Maximum:73.04206

    Er40ArRad39ArK
    One sigma error for each 40ArRad/39ArK value (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.04818
    Maximum:38.81533

    AgeMa
    Calculated age for each temperature step for each sample (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:20.47
    Maximum:462.13
    Units:MA

    ErAgeMa
    One sigma error of the age determination of each heating step (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    Range of values
    Minimum:0.55
    Maximum:246.42
    Units:MA

    WeightedAverageOfJFromStandards
    J value, calculated from the weighted average of standards placed in various positions in the nuclear reactor (Source: Geochronology Laboratory at the University of Alaska Fairbanks (UAF))

    WeightedAverageOfJFromStandards value and error

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?

    This study is part of the Alaska Airborne Geophysical/Geological Mineral Inventory Program funded by the Alaska State Legislature. The research was also supported by the U.S Geological Survey, National Cooperative Geologic Mapping Program, under STATEMAP award number G11AC20203. Access to Doyon Limited lands and to drill core from the Monday Creek prospect stored in Fairbanks, as well as permission to collect samples and publish data was kindly granted by Doyon Limited.

  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?

This work was part of an integrated geological, geophysical, and geochemical mineral inventory study in the eastern Kokrines Hills near Moran Dome in the Tanana B-6 and C-6 quadrangles. Previous geologic work in the area is at a reconnaissance scale, although two localities in the study area have undergone detailed mineral-resource evaluations (Tozimoran Creek Placer and Monday Creek). No geochronological data from the area have been published, but limited geochronology has been published from the region.

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: 2011 (process 1 of 2)
    Fieldwork - Fresh, unweathered samples from surficial outcrops were collected by DGGS field geologists; samples were selected based on their cross-cutting relationships with structural features.

    Date: 2011 (process 2 of 2)
    Sample preparation and analysis - Before processing, samples were examined under a binocular microscope, or thin sections were prepared and scrutinized to eliminate the possibility of analyzing altered mineral phases. Rock samples suitable for dating by 40Ar/39Ar geochronology analysis were submitted to the Geochronology Laboratory at the University of Alaska Fairbanks (UAF) where they were dated according to the protocols outlined in the accompanying report. Additional sample preparation details may be found in the accompanying report.

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

    Freeman, L.K., Szumigala, D.J., Blessington, M.J., and Werdon, M.B., 2012, Geochemical trace-element and rare-earth element data from stream-sediment and pan-concentrate samples collected in 2011 in the Melozitna mining district, Tanana and Melozitna quadrangles, interior Alaska: Raw Data File RDF 2012-3, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p
    Lough, T.A., Freeman, L.K., Elliott, B.A., Griesel, G.A., Newberry, R.J., and Szumigala, D.J., 2012, Geochemical, major-oxide, minor-oxide, trace-element, and carbon data from rocks collected in 2011 in the Moran area, Tanana and Melozitna quadrangles, Alaska: Raw Data File RDF 2011-4 v. 2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 176 p

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. Questions regarding the accuracy of the analytical values can be best answered by the originating lab.

  2. How accurate are the geographic locations?

    Location data for samples collected during the 2011 DGGS field campaign were derived using Garmin eTrex hand-held GPS units. Waypoints were downloaded from the eTrex units and merged with a hand-transcribed Microsoft Access field notes database on a daily basis, and locations were spot checked to ensure that the data merge was correct. Location error for this process is estimated to range between 3 and 20 m. The North American Datum of 1927 (NAD27) was used consistently for recording and reporting sample locations. Sample 11LF004A used the coordinates for the drill hole collar, which were transformed into NAD27 from World Geodetic System of 1984 coordinates provided by Doyon, Limited. The error for this sample is less than 10 m. Samples from the Ruby mining district were digitized from sample locations depicted on georeferenced images of scanned geologic map sheets (Puchner and others, 1998); these samples were collected prior to the use of GPS, and locations were hand plotted by geologists on USGS 1:63,360 topographic maps. Cumulative error for these locations could be in excess of 100 m. Sample RM 23241-R was collected from sluice box concentrates and the source is at or below the confluence of Ash and Tozimoran creeks. The location provided is for the creek confluence, and a location error of 1,000 m is assigned to this sample.

  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 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 2018-5

  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: 15-Feb-2019
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 Fri Feb 15 16:37:12 2019