Identification_Information: Citation: Citation_Information: Originator: Petersen, E.I. Originator: Fusso, L.A. Originator: Geotech Ltd. Originator: Aqua Geo Frameworks LLC Publication_Date: 2026 Title: Granite Mountain airborne electromagnetic survey, Kuskokwim Region, Alaska Geospatial_Data_Presentation_Form: digital, data Series_Information: Series_Name: Geophysical Report Issue_Identification: GPR 2026-4 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 8 p. Online_Linkage: https://doi.org/10.14509/31964 Description: Abstract: Granite Mountain airborne electromagnetic survey, Kuskokwim Region, Alaska, Geophysical Report 2026-4, covers a portion of the Iditarod Quadrangle across part of the Kuskokwim Mountains in western interior Alaska, southwest of McGrath. The Iditarod Quadrangle is a prime exploration target, which includes historically productive mining districts and contains geologic structures and rock units known to host gold and other metallic mineral deposits. The survey was conducted to characterize subsurface electrical resistivity variations and to support geologic mapping and mineral resource evaluation. These data provide a framework for identifying concealed lithologic contacts, structural features, and alteration zones that may indicate areas of elevated mineral potential. Time-domain electromagnetic data were acquired using the helicopter-mounted VTEM Terrain system from August 12 to September 14, 2025, by Geotech Ltd. A total of 2516 line-kilometers were flown over a single survey block measuring 916.5 square kilometers. The block was flown with northwest-southeast line orientation and a nominal spacing of 400 meters, along with northeast-southwest oriented tie lines with a nominal spacing of 4000 meters. Mean ground clearance was 47 meters, with a nominal survey speed of 87 km/hr. Geotech Ltd. provided initial resistivity models produced via simple inversion using a technique termed Resistivity Depth Imaging (RDI). These models are referred to in the provided data files as 'geotech_rdi.' Aqua Geo Frameworks then produced a spatially constrained inversion model (referred to in the data files as 'agf_sci'), which incorporates both along-track and cross-track constraints. The Aqua Geo Frameworks model is recommended for end-users as it resolves finer-scale structures, including faults. We also provide a 3D voxel dataset registered to elevation rather than raw depth for the agf_sci model. These data are provided as a Geophysical Report under an open end-user license and are available on the DGGS website https://doi.org/10.14509/31964. Purpose: The purpose of the Granite Mountain airborne electromagnetic survey is to characterize subsurface electrical resistivity across a portion of the Iditarod Quadrangle in western interior Alaska to support geologic mapping and mineral resource evaluation. This survey provides high resolution geophysical data that help identify concealed lithologic contacts, structural features, and alteration zones associated with gold and other metallic mineral deposits within the Kuskokwim Mountains. The resulting resistivity models and derived 3D datasets offer a framework for assessing mineral potential in an area of historically productive mining districts and geologically favorable host rocks. Supplemental_Information: >ascii_data: ASCII format line data, other ASCII data >databases_geosoft: Geosoft format database of final line data, other Geosoft format databases >documents: Project report, calibration reports >grids_geosoft: Oasis montaj Geosoft GRD format gridded data >grids_tif: Geographically registered data value rasters of gridded data, GeoTiff format >maps_pdf: Printable and geographically registered maps in pdf format. >models_resistivity: Models of subsurface resistivity inverted from measured EM response; agf_sci is the recommended model for end-users. >vector_data: Line path and survey boundary in Esri shapefile (shp) format Time_Period_of_Content: Time_Period_Information: Single_Date/Time: Calendar_Date: 2025 Currentness_Reference: ground condition Status: Progress: Complete Maintenance_and_Update_Frequency: None planned Spatial_Domain: Bounding_Coordinates: West_Bounding_Coordinate: -157.498114 East_Bounding_Coordinate: -156.583921 North_Bounding_Coordinate: 62.473379 South_Bounding_Coordinate: 62.151097 Keywords: Theme: Theme_Keyword_Thesaurus: ISO 19115 Topic Category Theme_Keyword: geoscientificInformation Theme: Theme_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Theme_Keyword: Aeromagnetic Theme_Keyword: Aeromagnetic Data Theme_Keyword: Aeromagnetic Map Theme_Keyword: Aeromagnetic Survey Theme_Keyword: Airborne Geophysical Survey Theme_Keyword: Analytic Signal Theme_Keyword: Apparent Resistivity Contours Theme_Keyword: Apparent Resistivity Data Theme_Keyword: Apparent Resistivity Map Theme_Keyword: Apparent Resistivity Survey Theme_Keyword: Bedrock Geology Theme_Keyword: Conductivity Survey Theme_Keyword: Critical Minerals Theme_Keyword: Derivative Theme_Keyword: DGGS Theme_Keyword: Differential Resistivity Theme_Keyword: Domain Theme_Keyword: Economic Geology Theme_Keyword: Economic Study Theme_Keyword: Electromagnetic Anomalies Theme_Keyword: Electromagnetic Data Theme_Keyword: Electromagnetic Data Inversion Theme_Keyword: Electromagnetic Survey Theme_Keyword: Exploration Theme_Keyword: First Vertical Derivative Theme_Keyword: Frequency Domain Electromagnetic Data Theme_Keyword: Geologic Theme_Keyword: Geology Theme_Keyword: Geophysical Map Theme_Keyword: Geophysical Survey Theme_Keyword: Geophysics Theme_Keyword: Geophysics Search Tag Theme_Keyword: Gridded Data Theme_Keyword: Helicopter Survey Theme_Keyword: HEM Survey Theme_Keyword: Interpretation Theme_Keyword: Inversion Theme_Keyword: Methods Theme_Keyword: Mineral Assessment Theme_Keyword: Mineral Exploration Theme_Keyword: Mineral Resources Theme_Keyword: Minerals Theme_Keyword: Modeling Theme_Keyword: Remote Sensing Theme_Keyword: Resistivity Theme_Keyword: Resistivity Model Theme_Keyword: Resistivity Survey Theme_Keyword: Rocks Theme_Keyword: Structure Theme_Keyword: Subsurface Place: Place_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Place_Keyword: Beaver Creek Place_Keyword: Bismarck Creek Place_Keyword: Eldorado Creek Place_Keyword: George River Place_Keyword: Granite Creek Place_Keyword: Granite Mountain Place_Keyword: Homestake Creek Place_Keyword: Julian Creek Place_Keyword: McGrath Mining District Place_Keyword: Michigan Creek Place_Keyword: Moose Creek Place_Keyword: Munther Creek Place_Keyword: Starr Creek Place_Keyword: Willow Creek 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. Point_of_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: Alaska Division of Geological & Geophysical Surveys Contact_Position: Metadata Manager Contact_Address: Address_Type: mailing and physical Address: 3354 College Road City: Fairbanks State_or_Province: AK Postal_Code: 99709-3707 Country: USA Contact_Voice_Telephone: (907)451-5020 Contact_Facsimile_Telephone: (907)451-5050 Contact_Electronic_Mail_Address: 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. Data_Set_Credit: This work was supported by the State of Alaska capital improvement project funds. Cross_Reference: Citation_Information: Originator: Burns, L.E. Originator: Graham, G.R.C. Originator: Barefoot, J.D. Originator: Naibert, T.J. Originator: CGG Originator: Fugro Airborne Surveys Corp. Publication_Date: 2019 Title: Beaver Creek electromagnetic and magnetic airborne geophysical survey data compilation Series_Information: Series_Name: Geophysical Report Issue_Identification: GPR 2018-7 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 14 p Online_Linkage: https://doi.org/10.14509/29821 Cross_Reference: Citation_Information: Originator: DGGS Staff Publication_Date: 2016 Title: Alaska merged geophysical data grids Series_Information: Series_Name: Digital Data Series Issue_Identification: DDS 12 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 3 p Online_Linkage: https://doi.org/10.14509/29555 Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: 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. Logical_Consistency_Report: Data were supplied by providers in accordance with DGGS contract requirements (see accompanying project report). The originating coordinate system was retained for all publication products. Completeness_Report: The dataset provides processed geophysical and positional data for the entire survey extent. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Station coordinates were positioned using a real-time or post-processed corrected differential GPS. Vertical_Positional_Accuracy: Vertical_Positional_Accuracy_Report: Not applicable Lineage: Process_Step: Process_Description: Data acquisition - Time-domain electromagnetic data were acquired with the helicopter-mounted VTEM Terrain system by Geotech Ltd. from August 12 to September 14, 2025. The crew flew 2,516 line kilometers over a single 916.5 square kilometer survey block. They flew the block along northwest-southeast lines spaced 400 meters apart and added northeast-southwest tie lines spaced 4,000 meters apart. The system maintained an average ground clearance of 47 meters and a nominal airspeed of 87 km/hr. Geotech Ltd. generated initial resistivity models using a simple inversion method called Resistivity Depth Imaging (RDI). Aqua Geo Frameworks then produced a spatially constrained inversion model that applies both along track and cross track constraints. Process_Date: 2025 Process_Step: Process_Description: Data cataloged for archival and publication - Final data were published and archived by DGGS. Process_Date: 2026 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: raster Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Planar: Grid_Coordinate_System: Grid_Coordinate_System_Name: Universal Transverse Mercator Universal_Transverse_Mercator: UTM_Zone_Number: 4 Transverse_Mercator: Scale_Factor_at_Central_Meridian: 0.999600 Longitude_of_Central_Meridian: -159 Latitude_of_Projection_Origin: 0 False_Easting: 500000.000000 False_Northing: 0 Planar_Coordinate_Information: Planar_Coordinate_Encoding_Method: coordinate pair Coordinate_Representation: Abscissa_Resolution: .00000001 Ordinate_Resolution: .00000001 Planar_Distance_Units: Meters Geodetic_Model: Horizontal_Datum_Name: WGS84 Ellipsoid_Name: WGS 84 Semi-major_Axis: 6378137 Denominator_of_Flattening_Ratio: 298.257223563 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: ascii_data Entity_Type_Definition: ASCII format line data, other ASCII data Entity_Type_Definition_Source: Geotech Ltd. and Aqua Geo Frameworks LLC Entity_Attribute_Layer_Name: ascii_data Detailed_Description: Entity_Type: Entity_Type_Label: databases_geosoft Entity_Type_Definition: Geosoft format database of final line data, other Geosoft format databases Entity_Type_Definition_Source: Geotech Ltd. and Aqua Geo Frameworks LLC Entity_Attribute_Layer_Name: databases_geosoft Detailed_Description: Entity_Type: Entity_Type_Label: documents Entity_Type_Definition: Project report, calibration reports Entity_Type_Definition_Source: Geotech Ltd. and Aqua Geo Frameworks LLC and Alaska Division of Geological & Geophysical Surveys (DGGS) Entity_Attribute_Layer_Name: documents Detailed_Description: Entity_Type: Entity_Type_Label: grids_geosoft Entity_Type_Definition: Oasis montaj Geosoft GRD format gridded data Entity_Type_Definition_Source: Geotech Ltd. and Aqua Geo Frameworks LLC and Alaska Division of Geological & Geophysical Surveys (DGGS) Entity_Attribute_Layer_Name: grids_geosoft Detailed_Description: Entity_Type: Entity_Type_Label: grids_tif Entity_Type_Definition: Geographically registered data value rasters of gridded data, GeoTiff format Entity_Type_Definition_Source: Alaska Division of Geological & Geophysical Surveys (DGGS) Entity_Attribute_Layer_Name: grids_tif Detailed_Description: Entity_Type: Entity_Type_Label: maps_pdf Entity_Type_Definition: Printable and geographically registered maps in pdf format. Entity_Type_Definition_Source: Geotech Ltd. and Aqua Geo Frameworks LLC Entity_Attribute_Layer_Name: maps_pdf Detailed_Description: Entity_Type: Entity_Type_Label: models_resistivity Entity_Type_Definition: Models of subsurface resistivity inverted from measured EM response; agf_sci is the recommended model for end-users. Entity_Type_Definition_Source: Geotech Ltd. and Aqua Geo Frameworks LLC Entity_Attribute_Layer_Name: models_resistivity Detailed_Description: Entity_Type: Entity_Type_Label: vector_data Entity_Type_Definition: Line path and survey boundary in Esri shapefile (shp) format Entity_Type_Definition_Source: Alaska Division of Geological & Geophysical Surveys (DGGS) Entity_Attribute_Layer_Name: vector_data Distribution_Information: Distributor: Contact_Information: Contact_Organization_Primary: Contact_Organization: Alaska Division of Geological & Geophysical Surveys Contact_Position: Metadata Manager Contact_Address: Address_Type: mailing and physical Address: 3354 College Road City: Fairbanks State_or_Province: AK Postal_Code: 99709-3707 Country: USA Contact_Voice_Telephone: (907)451-5020 Contact_Facsimile_Telephone: (907)451-5050 Contact_Electronic_Mail_Address: 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. Resource_Description: GPR 2026-4 Distribution_Liability: 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. Standard_Order_Process: 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. Fees: Contact DGGS for current pricing Standard_Order_Process: Digital_Form: Digital_Transfer_Information: Format_Name: GeoTiff, ESRI shapefile, Geosoft binary grid (GRD), Microsoft Office documents, PDF (with or without georeferencing), ER Mapper ERS, ASCII text files (including CSV), Geosoft database, AutoCAD DXF, Geosoft plot file (PLT), digital images (multiple formats), georeferenced photos (multiple formats), Geosoft ASCII XYZ, Geosoft ASCII files (PLY, i0, EXP), and KMZ. Format_Version_Date: 20260304 Format_Information_Content: Airborne electromagnetic geophysical survey data compilation Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://doi.org/10.14509/31964 Fees: Free download Metadata_Reference_Information: Metadata_Date: 20260304 Metadata_Contact: Contact_Information: Contact_Organization_Primary: Contact_Organization: Alaska Division of Geological & Geophysical Surveys Contact_Person: Simone Montayne Contact_Position: Metadata Manager Contact_Address: Address_Type: mailing and physical Address: 3354 College Road City: Fairbanks State_or_Province: AK Postal_Code: 99709-3707 Country: USA Contact_Voice_Telephone: (907)451-5020 Contact_Facsimile_Telephone: (907)451-5050 Contact_Electronic_Mail_Address: dggspubs@alaska.gov Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays Metadata_Standard_Name: FGDC Content Standard for Digital Geospatial Metadata Metadata_Standard_Version: FGDC-STD-001-1998 Metadata_Use_Constraints: 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. Metadata_Extensions: Online_Linkage: https://dggs.alaska.gov/metadata/dggs.ext Profile_Name: dggs metadata extensions