Bonnifield mining district electromagnetic and magnetic airborne geophysical survey data compilation

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   Burns, L.E., Fugro Airborne Surveys Corp., Stevens Exploration Management Corp., Graham, G.R.C., and Emond, A.M., 2016, Bonnifield mining district electromagnetic and magnetic airborne geophysical survey data compilation: Geophysical Report GPR 2016-1, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

   Online Links:

   • https://doi.org/10.14509/29557

   Other_Citation_Details: 2 sheets
   

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -148.727441
   East_Bounding_Coordinate: -147.030498
   North_Bounding_Coordinate: 64.134665
   South_Bounding_Coordinate: 63.835939
   

3. What does it look like?
4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 2006

   Ending_Date: 2007

   Currentness_Reference:

   ground condition

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

   Geospatial_Data_Presentation_Form: digital, data
   

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?
      This is a raster data set.
   2. What coordinate system is used to represent geographic features?
      

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:

      UTM_Zone_Number: 6
      Transverse_Mercator:

      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -147
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0
      

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest .00000001
      Ordinates (y-coordinates) are specified to the nearest .00000001
      Planar coordinates are specified in Meters
      The horizontal datum used is NAD27.
      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?

   ascii_data

   ASCII format line data, other ASCII data (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

   databases_geosoft

   Geosoft format database of line data, other Geosoft format databases (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

   documents

   Project and field reports, survey background information, gridded data explanations, other supporting documentation (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp. and Alaska Division of Geological & Geophysical Surveys (DGGS))

   grids_ermapper

   Geographically registered gridded data, ER Mapper ERS format (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp. and Alaska Division of Geological & Geophysical Surveys (DGGS))

   grids_geosoft

   Geosoft-format binary grids, these grids can be viewed in ESRI ArcMap using a free plugin from Geosoft or using the free viewer available from Geosoft (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp. and Alaska Division of Geological & Geophysical Surveys (DGGS))

   images_registered

   GeoTiff format images of all gridded data (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

   kmz

   Keyhole markup language (kml) kmz archive files of project data. Viewable in Google Earth and other compatible programs (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

   maps_pdf_format

   Printable maps in pdf format (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

   maps_prn_format

   Printable maps in HPGL2 printer file format with extension .prn (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

   profiles_stacked

   Distance-based profiles of the digitally recorded geophysical data are generated and plotted at an appropriate scale. The profiles display electromagnetic anomalies with their respective interpretive symbols (Source: Fugro Airborne Surveys Corp. and Stevens Exploration Management Corp.)

   vector_data

   Line path, data contours, and survey boundary in ESRI shapefile (SHP) format, ESRI Geodatabase format, and/or AutoCAD dxf format (Source: Alaska Division of Geological & Geophysical Surveys (DGGS))

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • Burns, L.E.
   • Fugro Airborne Surveys Corp.
   • Stevens Exploration Management Corp.
   • Graham, G.R.C.
   • Emond, A.M.
2. Who also contributed to the data set?

   Funding was provided by the Alaska State Legislature.

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?

The Bonnifield survey covers part of the Bonnifiel mining district. These data were collected to assist and promote mineral exploration and to aid geologic mapping of 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: 2007 (process 1 of 12)

   Data collection, processing, and delivery - The 2006-2007 airborne geophysical data were acquired with a DIGHEM(V) Electromagnetic (EM) system and a Fugro D1344 cesium magnetometer with a Scintrex CS3 censor. The EM and magnetic sensors were flown at a height of 100 feet. In addition, the survey recorded data from a radar altimeter, GPS navigation system, 50/60 Hz monitors, and video camera. Flights were performed with an AS350B-3 Squirrel helicopter at a mean terrain clearance of 200 feet along N-S survey flight lines with one-quarter mile line spacing. Tie lines were flown perpendicular to the flight lines at intervals of approximately 3 miles. A Novatel OEM4 Global Positioning System was used for navigation and flight path recovery. The helicopter position was derived every 0.5 seconds using post-flight differential positioning to a relative accuracy of better than 5 m. Flight path positions were projected onto the Clarke 1866 (UTM zone 6) spheroid, 1927 North American datum using a central meridian (CM) of 147 degrees, a north constant of 0 and an east constant of 500,000.

   Date: 2007 (process 2 of 12)

   Total magnetic field - The total magnetic field data were acquired with a sampling interval of 0.1 seconds, and were (1) corrected for measured system lag, (2) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data (saved as tfmag in bonnifield_linedata.xyz), (3) adjusted for regional variations (or IGRF gradient, 2005, updated to November 2006) using altimeter adjusted IGRF, (4) leveled to the tie line data (saved as magigrf in bonnifield_linedata.xyz), and (5) interpolated onto a regular 80m grid using a modified Akima (1970) technique. The new magnetic data and the Liberty Bell magnetic data were then gridded together to create the merged magnetic grid. The total magnetic field data were subjected to a processing algorithm that enhances the response of magnetic bodies in the upper 500 m and attenuates the response of deeper bodies. The resulting calculated first vertical derivative(vertical gradient grid(*cvg.grd)) provides better definition and resolution of near-surface magnetic units. It also identifies weak magnetic features that may not be evident on the total field data.

   Date: 2007 (process 3 of 12)

   Inphase and quadrature components - The DIGHEM V EM system measured inphase and quadrature components at five frequencies. Two vertical coaxial-coil pairs operated at 1114 (1000) and 5523 (5500) Hz while three horizontal coplanar-coil pairs operated at 916 (900), 7026 (7200), and 55,840 (56,000) Hz. The EM data were sampled at 0.1 second intervals. The EM system responds to bedrock conductors, conductive overburden, and cultural sources. The EM inphase and quadrature data were drift corrected using base level data collected at high altitude (areas of no signal). Along-line filters are applied to the data to remove spheric spikes. The data were inspected for variations in phase, and a phase correction +was applied to the data if necessary. Apparent resistivities were then calculated from the inphase and quadrature data for all frequencies based on a pseudo-layer half-space model. Manual leveling of the inphase and quadrature of each coil pair, based on the resistivity data and comparisons to the data from the other frequencies, was performed. Automated micro-leveling is carried out in areas of low signal. The new resistivity data and the Liberty Bell resistivity data were used to create the merged resistivity grids. The EM data were interpolated onto a regular 80m grid using a modified Akima (1970) technique. The resulting grids were subjected to a 3x3 hanning filter before contouring and map production.

   Date: 2007 (process 4 of 12)

   Digital terrain model - To produce the digital terrain model, the GPS-Z data were differentially corrected and transformed into the local datum. The ALTBIRD data were filtered using a 13, 13 filter. Both the Z-COR (differentially corrected GPS-Z) was checked for spikes, which were removed manually. The corrected altimeter was then subtracted from the Z-COR data to produce profiles of the height above mean sea level along the survey lines. The data were manually leveled to remove any errors between lines. After all leveling, the data were DC shifted to match the local maps, in this case, NAD27. The final Z value is recalculated as final Z = DTM + altbird.

   Date: 2007 (process 5 of 12)

   Plot files - The included plot files of the maps were produced by Fugro Airborne Surveys. The HPGL2 files were created with HP Designjet 5000 printer driver v5.32 and will not work with all plotters, but do plot on the DGGS HP Design Jet 5000. The postscript files were produced by Hewlett Packard Designjet 5000 Postcript 3 printer driver v4.293. These postscript files should work with all HP plotters that can read Postscript 3. The HPGL2 files have brighter colors and sharper topography than the postscript files. The Adobe Acrobat format files were created with Adobe Acrobat Distiller v7.0 (PDF 1.3) from the postscript files.

   Date: 2007 (process 6 of 12)

   EM anomalies - Discrete anomalous EM responses (EM anomalies) were computer picked from the electromagnetic data set and classified by type and grade. Line and polygon features of the electromagnetic and magnetic data were identified by contractor staff. EM anomalies are presented on map and profile data and are available in ASCII file format. These features are named and stored in geographically registered formats.

   Date: 2016 (process 7 of 12)

   Legacy data compilation - DGGS staff compiled and organized previously published data and the originating data from the contractor. Original vector data were compiled into an ESRI ArcMap File Geodatabase using ArcMap 10.3.1's CAD to Geodatabase tool in batch mode. In this publication's older products and documentation the magnetic data products have been referred to as Total Field Magnetics on the maps and the MAGIGRF channel in the line data and 'magigrf' as a filename abbreviation. The new term 'sim_magtf' has been created to rename and clarify that the data are not representative of the true total magnetic field as the IGRF values have been removed with a single average IGRF value added back to the data, resulting in the IGRF gradient being removed. The term simulated magnetic total field and the filename abbreviation 'sim_magtf' is now used to identify the final magnetic data. Also in this publications older products, the calculated first vertical derivative grids and images were labeled with cvg or named with calculated vertical gradient. This was renamed here to be consistent with the other survey projects.

   Date: 2016 (process 8 of 12)

   Data in Geosoft GDB format - These data were created by importing the final ascii data into Geosoft Oasis Montaj v8.5.1 using the created *.iO import file.

   Date: 2016 (process 9 of 12)

   Geographically registered gridded data in Geosoft GRD format - DGGS assigned missing projection info to grids as needed using Geosoft Oasis montaj v8.3. Geosoft Oaisis montaj MAGMAP extension was used to create analytic signal grid.

   Date: 2016 (process 10 of 12)

   Geographically registered gridded data in GeoTiff format - These data were created by DGGS using Geosft Oasis montaj v8.5.1. Geosoft grd files were displayed in Geosoft and exported to GeoTiff. A matching colorbar for each grid was displayed in Geosoft and export as a GeoTiff. ER Mapper ERS files were created using Geosoft Oasis montaj v8.5.1 grid copy/convert function from the Geosoft format grids.

   Date: 2016 (process 11 of 12)

   Google Earth KMZ files - Created Google Earth KMZ files from the GeoTiff format gridded data using ESRI ArcGIS 10.3.1.

   Date: 2016 (process 12 of 12)

   Boundary polygon - The boundary polygon was generated by loading the final line data in Geosoft Oasis montaj v8.5.1. The final magnetic data was gridded using the Minimum Curvature option with the following settings: grid cell size = 1/5 of line spacing, blanking distance = double the line spacing, cells to extend beyond data = 0. The polygon file was created using Grid Outline tool with edge resolution = 1. The polygon file was exported to ESRI shapefile.

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?
   Geophysical data were acquired according to the contractor, contract, and request-for-proposals specifications. For additional detail about survey parameters, see the accompanying project report available in the documents directory of this data distribution package.
2. How accurate are the geographic locations?
   Station coordinates were positioned using a real-time or post-processed corrected differential GPS.
3. How accurate are the heights or depths?
   Not applicable
4. Where are the gaps in the data? What is missing?
   This data set includes files that contain processed aeromagnetic measurements, electromagnetic measurements, altimetry measurements, and locational data for the entire survey area.
5. How consistent are the relationships among the observations, including topology?
   Data originate from one company using the same contract specifications for all data. The originating coordinate system was retained for all publication products.

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? GPR 2016-1
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?
   • Availability in non-digital form:
     DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media by mail, phone, fax, or email from the DGGS Fairbanks office. To purchase this or other printed reports and maps, contact DGGS by phone (907-451-5020), e-mail (dggspubs@alaska.gov), or fax (907-451-5050). Payment accepted: Cash, check, money order, VISA, or MasterCard. Turnaround time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for the exact shipping amount.
   • Cost to order the data: Contact DGGS for current pricing

   • Availability in digital form:

     Data format:

     Airborne magnetic and radiometric geophysical survey data compilation in format GeoTiff, ESRI shapefile, Geosoft binary grid (GRD), Microsoft Office documents, PDF (with or without georeferencing), ER Mapper ERS, ASCII text files (including CSV), Geosoft ASCII grid (GXF), Geosoft database, AutoCAD DXF, Geosoft plot file (PLT), Printer files (HPP, PRN, or other), digital images (multiple formats), georeferenced photos (multiple formats), digital video (multiple formats), Geosoft ASCII XYZ, Geosoft ASCII files (PLY, i0, EXP), and KMZ.

     Network links:

     http://dx.doi.org/10.14509/29557

   • Cost to order the data: Free download

Who wrote the metadata?

Dates:

Last modified: 18-Sep-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:

• https://dggs.alaska.gov/metadata/dggs.ext