Igneous Rock Geochemistry

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Frequently anticipated questions:


What does this data set describe?

Title: Igneous Rock Geochemistry
Abstract:
This geodatabase contains a point data set of over 50,000 records of geochemical indices of igneous rocks in Alaska. Major and trace element data were compiled from Alaska Geochemical Database version 2 (AGDB2), Alaska Division of Geological and Geophysical Surveys (ADGGS), peer-reviewed literature, and unpublished USGS data. Data was screened to included only high-resolution analyses. This data set contains calculations of various ratios and displacements from established boundaries on x-y plots to help classify igneous rocks. The point data set is also provided as a shapefile.
Supplemental_Information:
The method for screening high-resolution analyses is as follows. All the elements used to calculate the geochemical index need to be of similarly high precision. In general, major-element data were used only for samples where all major rock forming element oxides were measured by x-ray fluorescence (XRF) methods. For trace elements such as Y and Nb, only XRF and inductively coupled plasma mass spectrometry (ICP-MS) analyses were used.
  1. How might this data set be cited?
    U.S. Geological Survey, 2016, Igneous Rock Geochemistry:.

    This is part of the following larger work.

    Susan M. Karl (ed.), James V. Jones, III (ed.), and Timothy S. Hayes (ed.), 2016, GIS-based identification of areas that have resource potential for critical minerals in six selected groups of deposit types in Alaska: U.S. Geological Survey Open-File Report 2016-1191.

    Online Links:

    Other_Citation_Details:
    The larger work includes data sets for mineral resource data, geochemistry (stream sediment, rock, soil, mineral, and heavy mineral concentrate), igneous rock geochemical indices, lithology, aeroradiometric data, and hydrologic units analyzed for select deposit types.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: 173.11667
    East_Bounding_Coordinate: -130.01306
    North_Bounding_Coordinate: 70.20583
    South_Bounding_Coordinate: 51.25
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2014Currentness_Reference: compilation date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector 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?
      The map projection used is NAD 1983 Alaska Albers.
      Projection parameters:
      Standard_Parallel: 55.0
      Standard_Parallel: 65.0
      Longitude_of_Central_Meridian: -154.0
      Latitude_of_Projection_Origin: 50.0
      False_Easting: 0.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.001
      Ordinates (y-coordinates) are specified to the nearest 0.001
      Planar coordinates are specified in meters
      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is GRS_1980.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222101.
  7. How does the data set describe geographic features?
    all_igneous_ratios
    Point feature class, found in rock_igneous.gdb, contains geochemical indices of igneous rocks in Alaska. (Source: this data set)
    LAB_ID
    A character field where null values may be present. For SOURCE = 'USGS', LAB_ID is a unique identifier assigned to each submitted sample by the Sample Control Officer of the USGS analytical laboratory. For SOURCE = 'DGGS', LAB_ID is a unique identifier that is a concatenation of 'AK' and field SAMPLE_ID from the ADGGS data base. For SOURCE = 'PR_LIT', LAB_ID is either free text or null. (Source: this data set) free text
    FIELD_ID
    FIELD_ID is the field identifier assigned by the sample collector. The values in FIELD_ID are not unique and null values are present. (Source: this data set) free text
    SAMPLE_ID
    SAMPLE_ID is a numeric field and is the key field for the ADGGS data. Null values are present. (Source: this data set)
    Range of values
    Minimum:1906
    Maximum:100799
    SOURCE
    SOURCE identifies where the geochemical data was obtained. (Source: this data set)
    ValueDefinition
    DGGSData from Alaska Division of Geological and Geophysical Surveys (ADGGS) geochemical database, located http://www.dggs.alaska.gov/webgeochem.
    PR_LITData was obtained from either peer-reviewed literature or is unpublished USGS data.
    USGSData was obtained from the U.S. Geological Survey Alaska Geochemical Database, version 2.0. Data is available at http://mrdata.usgs.gov/agdb/
    LATITUDE
    Latitude coordinate of sample site reported in decimal degrees, usually with NAD27 datum and Clark 1866 spheroid. Resolution is variable. (Source: this data set)
    Range of values
    Minimum:51.25
    Maximum:70.20583
    Units:degrees
    LONGITUDE
    Longitude coordinate of sample site reported in decimal degrees, usually with NAD27 datum and Clark 1866 spheroid. Resolution is variable. (Source: this data set)
    Range of values
    Minimum:-179.11667
    Maximum:179.45
    Units:degrees
    SiO2_pct
    Silicon, as silicon dioxide, in weight percent. A null or empty cell means not analyzed. (Source: this data set)
    Range of values
    Minimum:-21.4
    Maximum:99.11111
    Units:weight percent
    ASI_calc
    Aluminum saturation index; ASI = [Al/(Ca - 1.67P + Na + K)]. The aluminum saturation index is used to subdivide granitic rocks into peraluminous, metaluminous or peralkaline. Null values are present.
    (Source: this data set)
    Range of values
    Minimum:0
    Maximum:715.97213
    ANK
    ANK = Al/[Na + K]; geochemical index for determining if granitic rock is metaluminous or peralkaline. Null values present. (Source: this data set)
    Range of values
    Minimum:0
    Maximum:715.97213
    Fe_no
    Fe_no, sometimes written Fe#, is the ratio FeO/(FeO + MgO), which is used to differentiate if a rock is ferroan or magnesian (Frost and others, 2001). Null values are present. (Source: this data set)
    Range of values
    Minimum:0
    Maximum:0.99919
    Fe_no_displ
    Displacement along the y-axis from the ferroan-magnesian boundary line on the SiO2 vs Fe_no plot. Null values are present. (Source: this data set)
    Range of values
    Minimum:-0.87373
    Maximum:0.38882
    MALI_displ
    MALI_displ is the displacement along the y-axis from the alkali-calcic and calc-alkalic boundary on the SiO2 vs MALI plot. MALI is the modified alkali-lime index; MALI = Na2O + K2O - CaO. Null values are present. (Source: this data set)
    Range of values
    Minimum:-48.78075
    Maximum:30.40781
    Ga_Al
    Trace element concentration ratio 10,000 x Ga/Al; can be used to distinguish alkaline and subalkaline igneous rocks. Null values are present. (Source: this data set)
    Range of values
    Minimum:0
    Maximum:68.32067
    Nb_Y
    Trace element concentration ratio Nb/Y; can be used to distinguish alkaline and subalkaline igneous rocks. Null values are present.
    (Source: this data set)
    Range of values
    Minimum:0
    Maximum:40
    class_Fe_no
    Classification ferroan or magnesian. Null values are present. (Source: this data set)
    ValueDefinition
    <null>Not determined
    FerroanFe_no_displ > 0. There are also samples in which Fe_no_displ is null included in Ferroan, because MgO was extremely low (extremely fractionated), that Fe_no could not be calculated. These samples are judged to be ferroan because Fe would be about 1.0.
    MagnesianFe_no_displ <= 0
    class_MALI
    Classification of alkali-calcic or calcic-alkalic based on MALI_displ. Null values present. (Source: this data set)
    ValueDefinition
    <null>insufficient data to determine
    calcicMALI_displ < -2.5
    alk-calc-2.5 < MALI_displ < 0
    calc-alk0 < MALI_displ < 1.5
    alkalicMALI_displ > 1.5
    class_ASI
    Classification metaluminous, peralkaline, or peraluminous. (Source: this data set)
    ValueDefinition
    <null>insufficient data to determine
    peraluminousANK > 1.2 and ASI >= 1.1
    metaluminousANK > 1.2 and ASI < 1.1
    peralkalineANK <= 1.2

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?
    Erin Todd and Nora Shew, USGS
  3. To whom should users address questions about the data?

Why was the data set created?

Feature class all_igneous_ratios is used to identify permissive rock types for REE deposits and Sn-W-Mo deposits. The ratios for the aluminum saturation index, ASI, (Al/[Ca-1.67xP)+Na+K], and ANK, Al/[Na+K], allow for the differentiation between peraluminous, metaluminous, and peralkaline rocks. Trace element concentration ratios Nb/Y and Ga/Al can distinguish alkaline and subalkaline igneous rocks. Also, the modified alkali-lime index, MALI, (Na2O+K2O-CaO), and Fe_no, FeO/[FeO+MgO], can used to distinguish alkaline vs calcic, and ferroan vs magnesian rocks.

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: 2014 (process 1 of 1)
    All indices were calculated using Matlab. Indices using major elements were calculated using values normalized to anhydrous compositions, assuming that the sum of oxides equalling less than 100% were due to the presence of water or other volatile species. Thus each major element used in the index calculation was divided by the sum of major element oxides. (SumMajors = SiO2+TiO2+Al2O3+FeOt_calc+MnO+MgO_CaO+Na2O+K2O+P2O5).
    If any of these major element oxides were not measured, or if measured values were below detection limits, they were assumed to equal zero. No major element indices were calculated if SiO2 was not measured, if SiO2 was below detection limits, or if SiO2 was analyzed by a method not associated with robust analysis. Analytical methods for SiO2 considered robust within the context of this study were: AES_Fuse, CM_Fuse, EDX, WDX_Fuse, XRF (DGGS data only), and XRF_Slab (DGGS data only). Data for trace elements Y and Nb were also filtered to include only data measured by robust methods. Nb data included only measurement by AES_HF, EDX, MS_Fuse, MS_ST, and WDX_Fuse. Y data included only measurement by AES_HF, EDX, MS_Fuse, MS_Fuse_REE, NA, and WDX_Fuse. No filter was used for Ga data. Person who carried out this activity:
    Erin Todd
    U.S. Geological Survey
    Research Geologist
    4210 University Drive
    Anchorage, AK
    USA

    907-786-7441 (voice)
    etodd@usgs.gov
  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?
    The samples in this data set were collected by several agencies for various projects with differing needs. In addition, the analyses were performed over a long period of time during which analytical methods have changed. Therefore the degree of accuracy is varied and difficult to assess.
  2. How accurate are the geographic locations?
    Users must be aware that the locational accuracy is an unknown factor because of the background of each contributing dataset. Resolution is variable. Samples with obvious spurious locations (such as quadrangle corners) in the contributing source datasets were not included in this dataset.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    The original data set includes many more fields than are presented here. The fields in this subset are those that are used in the analyses for REE-Th-Y-Nb and Sn-W-Mo deposits.
  5. How consistent are the relationships among the observations, including topology?
    Analytical data included in this data set were screened for being high-resolution analyses. Elements used to calculate geochemical indices need to be of similar high precision. In general, major-element data were only used for samples where all major rock forming element oxides were measured by x-ray fluorescence (XRF) methods. For trace elements, such as Y and Nb, only XRF and inductively coupled plasma mass spectrometry (ICP-MS) analyses were used.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints: None
Use_Constraints:
None. Users are advised to read the publication text and metadata to understand the appropriate use and data limitations.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    MS902
    Box 25286
    Denver Federal Center
    Lakewood, CO
    USA

    1-888-ASK-USGS (voice)
  2. What's the catalog number I need to order this data set? USGS Open-File Report 2016-1191
  3. What legal disclaimers am I supposed to read?
    This publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 10-Dec-2015
Last Reviewed: 06-Sep-2016
Metadata author:
U.S. Geological Survey
Attn: Nora Shew
4210 University Drive
Anchorage, AK
U.S.A.

907-786-7445 (voice)
nshew@usgs.gov
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)

Generated by mp version 2.9.34 on Fri Nov 4 13:25:33 2016