Emond, A.M.
CGG
Burns, L.E.
Graham, G.R.C.
CGG Land (US) Inc.
2014
Tonsina electromagnetic and magnetic airborne geophysical survey data compilation
digital data
Geophysical Report
GPR 2015-1
Fairbanks, Alaska, United States
Alaska Division of Geological & Geophysical Surveys
http://dx.doi.org/10.14509/29169
The Tonsina electromagnetic and magnetic airborne geophysical survey data were acquired with a DIGHEMv Electromagnetic (EM) system and a CGG D1344 cesium magnetometer with a Scintrex CS3 cesium sensor. The EM and magnetic sensors were flown at a height of 30 meters (m). In addition the survey recorded data from radar and laser altimeters, GPS navigation system, 50/60 Hz monitors and video camera. Flights were performed with an AS-350-B3 Squirrel helicopter at a mean terrain clearance of 60 m along NW-SE (345 degrees) survey flight lines with a spacing of 400 m. Tie lines were flown perpendicular to the flight lines at intervals of approximately 4,800 m. These data were produced under contract between the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS), and CGG Land (U.S.) Inc. Airborne geophysical data for the area were acquired and processed by CGG in 2014 and 2015. The project was funded by the Alaska State Legislature as part of the Alaska Airborne Geophysical and Geological Mineral Inventory Program and the Alaska Strategic and Critical Minerals Assessment Capital Improvement Project.
The Tonsina electromagnetic and magnetic airborne geophysical survey data compilation is a product of the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) program and the Alaska Strategic and Critical Minerals Assessment Capital Improvement Project. The goal of the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) program is to enhance the understanding of Alaska's mineral resources and stimulate private-sector mineral development. The program seeks to delineate mineral zones on Alaska State lands that: (1) have major economic value; (2) can be developed in the short term to provide high-quality jobs for Alaskans; and (3) will provide economic diversification to help offset the loss of Prudhoe Bay oil revenue. Candidate lands for this program are identified on the basis of existing geologic knowledge, land ownership, and nominations from Alaska's geologic community. The AGGMI program and resulting new geologic knowledge are recognized worldwide and have encouraged millions of dollars of venture capital expenditures in the local economies of the surveyed mining districts. These venture capital expenditures have led to discovery and delineation of new mineral resources. The multi-year Strategic and Critical Minerals Assessment Capital Improvement Project (SCMA) was established to determine Alaska's geologic potential for rare-earth elements and other minerals that are essential for our modern, technology-based society. This program began in FY2012 with a data survey and compilation of existing information on rare-earth-element occurrences in Alaska, and expanded significantly in FY2013 to include additional critical minerals, re-analyses of existing samples, and obtaining new field and analytical data, including airborne geophysics.
> Project Name: Tonsina
> Contracting Agency: State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS)
> DGGS Section: Minerals Section
> Program: Alaska Airborne Geophysical and Geological Mineral Inventory Program and the Alaska Strategic and Critical Minerals Assessment Capital Improvement Program
> Funding Source: Alaska State Legislature
> Contractor: CGG Land (U.S.) Inc.
> Survey Flown By: CGG
> CGG Project Number: 14030
> DGGS Contract Manager: Abraham M. Emond
> Data Acquisition: Digitally acquired
> Line miles (km): 1240.76 miles (1996.76 km)
> Data Acquisition:
> Start Date (YYYY-MM-DD): 2014-07-25
> End Date (YYYY-MM-DD): 2014-08-20
> Platform: Helicopter
> Platform: Model: AS-350-B3 Squirrel
> Survey Altitude Model: Mean terrain clearance (height above ground)
> Nominal Helicopter Height: 60 meters
> Nominal Bird Height: 30 meters
> Traverse: Line Azimuth: N15 degrees W (heading of 345 degrees)
> Traverse: Line Spacing: 1/4 mile (402.3 m)
> Tie: Line Azimuth: N75 degrees E (heading of 75 degrees)
> Tie: Line Spacing: approximately 3 miles (approximately 4828 m)
> Border lines: present around all non-parallel and non-perpendicular edges
> Magnetics: Magnetometer: Scintrex CS3 cesium censor, mounted in bird
> Electromagnetics: Sensor Model: Dighem(V)
> Navigation System: Sensor: Global Positioning System
> Navigation System: Sensor: Novatel OEM5-GL2
> Navigation System: Method: Post-flight differential positioning
> Additional equipment: Radar and laser altimeters, video camera, and 50/60 Hz monitors
>
> Operating frequencies used for the Dighem (V) system.
>
> 24-July through 17-August, 2014 (flts 3002:3039)
>
> Cx1000 1117.0 Hz coil separation = 7.96 meters
> Cp900 927.9 Hz coil separation = 7.98 meters
> Cx5500 5923 Hz coil separation = 7.92 meters
> Cp7200 7281 Hz coil separation = 7.98 meters
> Cp56k 55380 Hz coil separation = 6.31 meters
>
>
> Frequencies adjusted 18-August, 2014 (flts 3042:3049)
>
> Cx1000 1115.2 Hz coil separation = 7.96 meters
> Cp900 909.6 Hz coil separation = 7.98 meters
> Cx5500 5928 Hz coil separation = 7.92 meters
> Cp7200 7293 Hz coil separation = 7.98 meters
> Cp56k 55410 Hz coil separation = 6.31 meters
>
2014
ground condition
as needed
-145.4467763
-144.7425039
61.7144202
61.4790324
ISO 19115 Topic Category
geoscientificInformation
Alaska Division of Geological & Geophysical Surveys
Aeromagnetic
Aeromagnetic Data
Aeromagnetic Map
Airborne Geophysical Survey
Analytic Signal
Apparent Resistivity Contours
Apparent Resistivity Data
Apparent Resistivity Map
Apparent Resistivity Survey
Electromagnetic Anomalies
Electromagnetic Data
Electromagnetic Survey
First Vertical Derivative
Geophysical Map
Geophysical Survey
Geophysics
Geophysics Search Tag
Gridded Data
HEM Survey
HFEM Survey
Magnetic Contours
Magnetic Data
Magnetic Survey
Magnetics
Raster Image
Resistivity
Strategic Minerals
Alaska Division of Geological & Geophysical Surveys
Alaska, State of
Nelchina Mining District
Valdez Quadrangle
Alaska Division of Geological & Geophysical Surveys
Border Ranges Fault
Chugach Terrane
Peninsula Terrane
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).
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.
Alaska Division of Geological & Geophysical Surveys
GIS Manager
mailing and physical
3354 College Road
Fairbanks
AK
99709-3707
USA
(907)451-5020
dggsgis@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays
Funding for this survey was provided by the Alaska Division of Geological & Geophysical Surveys' (DGGS) Airborne Geophysical/Geological Mineral Inventory (AGGMI) and Strategic and Critical Minerals Assessment Capital Improvement programs and managed by State of Alaska, Department of Natural Resources (DNR), Division of Geological & Geophysical Surveys (DGGS). The survey data was collected and processed by CGG.
> Electromagnetic system contract specification:
>
> 900 Hz coplanar apparent resistivity cutoff 1325 Ohm-m
> 1000 Hz coaxial apparent resistivity cutoff 1501 Ohm-m
> 5500 Hz coaxial apparent resistivity cutoff 8001 Ohm-m
> 7200 Hz coplanar apparent resistivity cutoff 10750 Ohm-m
> 56000 Hz coplanar apparent resistivity cutoff 60000 Ohm-m
>
> Frequency; Coil Orientation; Peak-to-Peak Noise Envelope (ppm)
> 900 Hz horizontal coplanar 10
> 1000 Hz vertical coaxial 10
> 5500 Hz vertical coaxial 10
> 7200 Hz horizontal coplanar 20
> 56,000 Hz horizontal coplanar 40
>
> Magnetic data contract specification:
> The in-flight noise envelope will not exceed 0.1 nT in straight and level flight. In rugged areas, the noise level will not exceed 0.5 nT.
>
Data originate from one company using the same contract specifications for all data. The originating data were collected using the NAD27 UTM Zone 6N coordinate system. The originating coordinate system was retained for all publication products except the KMZ files, which utilize WGS84 geographic coordinates.
> CHANNEL; Valid Data Points; Missing Data Points (dummy value = *)
> res900; 950,442; 6,944
> res7200; 950,442; 6,944
> res56k; 950,442; 6,944
> dep900; 565,245; 392,141
> dep7200; 876,697; 80,689
> dep56k; 900,248; 57,138
>
> Missing values in the calculated 'resistivity' (res56k, res7200, and res900) and 'depth' (dep56k, dep7200, and dep900) are due to calculations being meaningless, generally caused by increase in altitude. See supporting documentation for more information.
A Novatel OEM5-G2L Global Positioning System was used for navigation. The helicopter position was derived every 0.5 seconds using post-flight differential positioning to a relative accuracy of better than 5 m.
Akima, H.
1970
A new method of interpolation and smooth curve fitting based on local procedures
Journal of the Association of Computing Machinery
v. 7, no. 4
New York, NY, USA
Association for Computing Machinery
paper
1970
publication date
Akima, H., 1970
magnetic and derivative magnetic grids
Fraser, D.C.
1978
Resistivity mapping with an airborne multicoil electromagnetic system
Geophysics
v. 43
Tulsa, OK, United States
Society of Exploration Geophysicists
paper
1978
publication date
Fraser, D.C., 1978
apparent resistivity
Geophysical data - The airborne geophysical data were acquired between July 25, 2014 through August 20, 2014 with DIGHEM (V) Electromagnetic (EM) systems, Scintrex CS3 cesium magnetometer sensors. The EM and magnetic sensors were flown at a height of 30 meters (m), with the magnetic sensor installed in the EM sensor. In addition, the survey recorded data from radar and laser altimeters, GPS navigation system, 50/60 Hz monitors, thermometer, barometric pressure instrument, and video camera. Flights were performed with one Aerospatiale AS-350-B3 helicopters. All were flown at a nominal mean terrain clearance of 60 m. Survey flight lines were flown at a heading of 345 degrees (NW-SE) with one-quarter mile (402.3 m) line spacing). Tie lines were flown at a heading of 75 degrees (NE-SW), perpendicular to the flight lines, and were spaced at intervals of approximately 4,800 m. Novatel OEM4-G2L Global Positioning Systems were used for navigation and flight path recovery. The helicopter positions were derived every 0.5 seconds (2 Hz); the ground GPS base station data were collected at 1.0 second (1 Hz) intervals. The positional xy data are interpolated from 2 Hz to 10 Hz. The use of the differentially-corrected base station data results in a positional accuracy of better than five meters. Flight path positions were projected onto the Clarke 1866 (UTM zone 6N) 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.
2014
Total magnetic field data - The total magnetic field data were acquired with a sampling interval of 0.1 seconds. The raw magnetic data (channel 'mag_raw') were (1) corrected for measured system lag (resulting in channel 'mag_lag'), (2) corrected for diurnal variations by subtraction of the digitally recorded base station magnetic data (resulting in channel 'mag_diu'), (3) adjusted for regional variations (by subtracting IGRF model 2010, updated for date of flight and elevation variations), (4) levelled to the tie line data resulting in the final residual magnetic intensity, (5) manually levelled with final small microleveling (resulting in channel 'mag_rmi'), and (6) increased by a constant IGRF average value to restore the mag_rmi values to a total magnetic field channel (resulting in channel 'magigrf'). 'Mag_RMI' and 'MagIGRF' were then interpolated onto a regular 80-m grid using a modified Akima (1970) technique.
2014
Magnetic and derivative magnetic grids - Three different algorithms were applied to the total magnetic field 80 m grid, resulting in three magnetic derivative grids. The analytic signal grid is the total amplitude of all directions of magnetic gradient calculated from the sum of the squares of the three orthogonal gradients. Mapped highs in the calculated analytic signal of the magnetic parameter locate the anomalous source body edges and corners (e.g., contacts, fault/shear zones, basement fault block boundaries or lithologic contacts, etc.). Analytic signal maxima are located directly over faults and contacts, regardless of structural dip, and independently of the direction of the induced and/or remnant body magnetizations. The calculated magnetic tilt grid is the angle between the horizontal gradient and the total vertical gradient, and is useful for identifying the depth and type of magnetic source. The tilt angle is positive over the source, crosses through zero at, or near, the edge of a vertical sided source, and is negative outside the source zone. It has the added advantage of responding equally well to shallow and deep sources and is able to resolve deeper sources that may be masked by larger responses caused by shallower sources. The first vertical derivative grid was calculated using a fast Fourier transform (FFT)-based frequency-domain filtering algorithm. The vertical gradient algorithm enhances the response of magnetic bodies in the upper 500 m and attenuates the response of deeper bodies. The resulting (calculated) vertical gradient grid provides better definition and resolution of near-surface magnetic units and helps to identify weak magnetic features that may not be evident in the total field data. All magnetic and derivative magnetic grids were then resampled from the 80-m cell size down to a 25-m cell size using a modified Akima (1970) technique to produce the maps and final grids contained in this publication. When resampling the grids to a 25-m cell size, the original grids are scanned to determine the minimum and maximum values which the new grids are then limited to, avoiding extreme extrapolation errors between lines.
Akima, H., 1970
2014
Inphase and quadrature components - The DIGHEM (V) EM systems measured inphase and quadrature components at five frequencies. Two vertical coaxial-coil pairs operated at nominal frequencies of 1000 and 5500 Hz while three horizontal coplanar-coil pairs operated at 900, 7200, and 56,000 Hz. The actual recorded frequencies and coil separations are listed by flight and date in these metadata.
2014
Apparent resistivity - 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. The apparent resistivity and depth were then calculated from the inphase and quadrature data for all coplanar frequencies. The calculation used the pseudo-layer (or buried) half-space model defined by Fraser (1978). This model consists of a resistive layer overlying a conductive half-space. The apparent depth is defined as the sensor-source distance minus the measured altitude of the sensor above the ground. The apparent depth channels estimate the depth below surface of a conductive half-space and are the apparent thickness of the overlying resistive layer. The apparent depth (or thickness) parameter will be positive when the upper layer is more resistive than the underlying material, in which case the apparent depth may be quite close to the true depth assuming it is a buried halfspace and altimeter is correct. The apparent depth will be negative when the upper layer is more conductive than the underlying material, and will be zero when a homogeneous half-space exists. The apparent depth parameter must be interpreted cautiously because it will contain any errors that might exist in the measured altitude of the EM bird (e.g., as caused by a dense tree cover). Manual levelling 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-levelling is carried out in areas of low signal. The EM data were interpolated onto a regular 80-m grid using a modified Akima (1970) technique. The resulting grids were subjected to a 3x3 Hanning filter and resampled to a 25-m cell size before contouring and map production. When re-sampling the grids to a 25-m cell size, the original grids are scanned to determine the minimum and maximum values which the new grids are then limited to, avoiding extreme extrapolation errors between lines.
Fraser, D.C., 1978
2014
Digital elevation/terrain model - The digital elevation/terrain model was produced from the differentially corrected GPS-Z data (channel 'GPSZ' in line data) and the laser altimeter data measured in the bird (channel 'ALTLAS_BIRD' included in the same files). Both the GPSZ and ALTLAS_BIRD data were checked for spikes, which were removed manually. The ALTLAS_BIRD data were despiked and then filtered using a 13 median filter, followed by a 13 Hanning filter. The corrected altimeter data were then subtracted from the GPSZ data to produce profiles of the height above mean sea level along the survey lines. The data were manually levelled to remove any errors between lines. After all levelling, the data were DC shifted to match the local maps, in this case, NAD27. The 80-m DTM grid was then resampled to a 25-m cell size to produce the DTM grid contained in this publication.
2014
Geographically registered gridded data - All grids with 25 m cell size were converted to GeoTIFFs and KMZs using CGG's specialized software.
2014
Print files - The HPGL/2 files were created with HP Designjet T1300ps HPGL driver, and plot on some plotters, but not all plotters correctly. The Adobe Acrobat format files were created with Adobe Acrobat Distiller v9.0 from Postscript files.
2014
Boundary polygon - The boundary polygon was generated by loading the final line data in Geosoft Oasis montaj v8.4. No tie (control) line data were used in this process. 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 ERSI shapefile.
2015
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. More information about these products is found in the project report.
2015
Universal Transverse Mercator
6
0.999600
-147
0
500000.000000
0
coordinate pair
0.01
0.01
meters
North American Datum of 1927
Clarke 1866
6378206.4
294.9786982
ascii_data
ASCII format final line data with readme files; note: these data are provided in both UTM NAD27 and Geopgraphic WGS84 projections.
CGG
ascii_data
databases_geosoft
Geosoft format database of final line data with readme files; note: these data are provided in both UTM NAD27 and Geopgraphic WGS84 projections.
CGG
databases_geosoft
documents
Field operations report, gridded data explanations, survey background information, processor notes.
CGG
documents
grids_ermapper
Geographically registered gridded data, ErMapper ERS format.
CGG
grids_ermapper
grids_geosoft
Geosoft-format binary grids, these grids can be viewed in ESRI ArcMap using a free plugin from Geosoft.
CGG
grids_geosoft
kmz
Google Earth kmz files of of all gridded data; note: these files use the WGS84 datum.
CGG
kmz
images_registered
GeoTiff format images of all gridded data.
CGG
images_registered
maps_pdf_format
Print format maps in pdf format.
CGG
maps_pdf_format
maps_prn_format
Print format maps in HPGL/2 printer file format with extension .prn.
CGG
maps_prn_format
vector_data
Line path, data contours, and survey boundary in ESRI shape file (SHP) and Autocad (2000) DXF formats.
CGG
vector_data
video_flightpath
Downward looking video to verify position and record ground conditions. Video synchronized with data.
CGG
video_flightpath
profiles_stacked
Electromagnetic and magnetic data profiles with EM anomalies.
CGG
profiles_stacked
Alaska Division of Geological & Geophysical Surveys
mailing and physical
3354 College Road
Fairbanks
AK
99709-3707
USA
(907)451-5020
(907)451-5050
dggspubs@alaska.gov
8 am to 4:30 pm, Monday through Friday, except State holidays
Please view our website (http://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
GPR 2015-1
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.
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.
Contact DGGS for current pricing
GeoTiff, ESRI shapefile, Geosoft binary grid, Microsoft Office documents, PDF, ER Mapper ERS, ASCII text files (including CSV), Geosoft ascii grid (GXF), Geosoft database, AutoCAD DXF, Geosoft PLT, Printer file type HPP, Geosoft ASCII XYZ, and KMZ
http://dx.doi.org/10.14509/29169
Free download
Technical requirements for use of all of the data on this publication includes software with ability to use, import, or convert Geosoft float GRD, Geosoft binary GDB,, ESRI Shape files or Autocad DXF, Adobe Acrobat PDF, Google Earth files, and text files. Free downloadable interfaces to view or convert the gridded and shape files are available at the Geosoft Web site (http://www.geosoft.com; Oasis Montaj viewer). The KMZ files can be dragged and dropped into the 'My Places' folder of the free downloadable 'Google Earth' software. Freeware software 'printfile' (http://www.lerup.com/printfile) prints HPGL/2 files easily on compatible printers. The HPGL/2 files have brighter colors and sharper topography than the PDF maps and should be used for printing when possible. The PDF format maps are the only maps digitally viewable in this publication.
20151229
Alaska Division of Geological & Geophysical Surveys
Metadata Manager
mailing and physical
3354 College Road
Fairbanks
AK
99709-3707
USA
(907)451-5020
FGDC Content Standard for Digital Geospatial Metadata
FGDC-STD-001-1998
If the user has modified the data in any way they are obligated to describe the types of modifications they have performed in the supporting metadata file. User specifically agrees not to imply that changes they made were approved by the Alaska Department of Natural Resources or Division of Geological & Geophysical Surveys.
http://www.dggs.alaska.gov/metadata/dggs.ext
dggs metadata extensions