Identification_Information: Citation: Citation_Information: Originator: Newberry, R.J. Originator: Moshrefzadeh, J.A. Publication_Date: 2026 Title: Interior Alaska amphibolite mineral compositions: A key to distinguishing metamorphic assemblage Geospatial_Data_Presentation_Form: spreadsheet Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2026-2 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 33 p. Online_Linkage: https://doi.org/10.14509/32081 Description: Abstract: Interior Alaska amphibolite mineral compositions: A key to distinguishing metamorphic assemblage, Preliminary Interpretive Report 2026-2, provides electron microprobe mineral compositional data used to distinguish metamorphic assemblages in eastern Interior Alaska. Metamorphic rocks in this region have historically been grouped into several packages and, more recently, assemblages that are often differentiated using 40Ar/39Ar age dating, which is a costly and time consuming method. Although some assemblages show clear differences in metamorphic grade, others do not, and three amphibolite facies units (the Fortymile River, Lake George, and Fairbanks Chena assemblages) contain similar lithologies with no obvious hand specimen distinctions. Localized contact and retrograde metamorphism have further complicated classification. This study analyzes amphibole and plagioclase compositions from 79 metamafic samples collected between 1981 and 2024, with most collected between 2021 and 2024. Most analyses were conducted using energy dispersive spectrometry (EDS), while samples collected in 2024 were analyzed using the more accurate wavelength dispersive spectrometry (WDS). Several samples were analyzed by both methods and show broadly comparable results. Amphibole compositions provide the strongest discrimination among assemblages because plagioclase is more susceptible to recrystallization during both higher temperature contact metamorphism and lower temperature retrograde alteration. Results generally support the assemblage assignments proposed by Dusel Bacon 2006 and indicate that the Fairbanks Chena assemblage is more extensive than previously recognized. In addition to the interpretive discussion, this report includes comprehensive data tables containing sample identifiers, geographic locations and descriptions, petrographic context, mineral phases, oxide weight percentages, and calculated cation proportions for amphibole and plagioclase populations. These data and accompanying discussion are released as a DGGS Preliminary Interpretive Report, and all publication components are available from the DGGS website. at: http://doi.org/10.14509/32081. Purpose: The Yukon Tanana Upland of east central Alaska is a region with significant critical mineral potential and complex metamorphic geology. The purpose of this dataset is to contribute to ongoing efforts to modernize geologic mapping across east central Alaska by providing mineral chemistry information that improves the interpretation of rock units and regional geologic relationships. Supplemental_Information: >electron‑microprobe mineral‑chemistry data: Sample identifiers, geographic locations and description, petrographic locations, mineral phases, oxide weight percentages, and calculated cation proportions for amphibole and plagioclase populations. 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: -148.202609 East_Bounding_Coordinate: -141.721891 North_Bounding_Coordinate: 65.249229 South_Bounding_Coordinate: 63.261399 Keywords: Theme: Theme_Keyword_Thesaurus: ISO 19115 Topic Category Theme_Keyword: geoscientificInformation Theme: Theme_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Theme_Keyword: Actinolite Theme_Keyword: Albite Theme_Keyword: Amphibole Theme_Keyword: Amphibolite Theme_Keyword: Analyses Theme_Keyword: Batholith Theme_Keyword: Bedrock Theme_Keyword: Chemistry Theme_Keyword: Clinopyroxene Theme_Keyword: Clinozoisite Theme_Keyword: DGGS Theme_Keyword: Diopside Theme_Keyword: Epidote Theme_Keyword: Garnet Theme_Keyword: Geochemical Analysis Theme_Keyword: Geochemical Composition Theme_Keyword: Geochemical Data Theme_Keyword: Geochemistry Theme_Keyword: Geologic Theme_Keyword: Geology Theme_Keyword: Greenschist Theme_Keyword: Greenstone Theme_Keyword: Hornblende Theme_Keyword: Ilmenite Theme_Keyword: Metamorphic Theme_Keyword: Metamorphism Theme_Keyword: Methods Theme_Keyword: Microprobe Analysis Theme_Keyword: Mineral Assessment Theme_Keyword: Mineral Composition Theme_Keyword: Mineral Exploration Theme_Keyword: Mineral Resources Theme_Keyword: Mineralogy Theme_Keyword: Minerals Theme_Keyword: Petrology Theme_Keyword: Plagioclase Theme_Keyword: Plutonic Theme_Keyword: Resources Theme_Keyword: Rocks Theme_Keyword: Schist Place: Place_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Place_Keyword: Alaska Place_Keyword: Alder Creek Place_Keyword: Bedrock Creek Place_Keyword: Boulder Creek Place_Keyword: Buckskin Creek Place_Keyword: California Creek Place_Keyword: Cement Creek Place_Keyword: Chatham Creek Place_Keyword: Chena River Place_Keyword: Circle Mining District Place_Keyword: Cleary Creek Place_Keyword: Cleary Hill Mine Place_Keyword: Coffee Dome Place_Keyword: Cottonwood Creek Place_Keyword: Cripple Creek Place_Keyword: Deep Creek Place_Keyword: Demar Creek Place_Keyword: Engineer Creek Place_Keyword: Ester Dome Place_Keyword: Eva Creek Place_Keyword: Fairbanks Mining District Place_Keyword: First Chance Creek Place_Keyword: Fortymile Mining District Place_Keyword: Frenchman Creek Place_Keyword: George Creek Place_Keyword: Goldstream Creek Place_Keyword: Goodpaster Mining District Place_Keyword: Gulch Creek Place_Keyword: Happy Creek Place_Keyword: Johnson Creek Place_Keyword: Joseph Creek Place_Keyword: Kokomo Creek Place_Keyword: Last Chance Creek Place_Keyword: Lawson Creek Place_Keyword: Liwa Lake Place_Keyword: Miller Creek Place_Keyword: Molly Creek Place_Keyword: Montana Creek Place_Keyword: Moose Creek Place_Keyword: Mount Neuberger Place_Keyword: Munson Creek Place_Keyword: Newsboy Mine Place_Keyword: Ohio Creek Place_Keyword: Olympia Creek Place_Keyword: Ottertail Creek Place_Keyword: Paldo Creek Place_Keyword: Porcupine Creek Place_Keyword: Ready Bullion Creek Place_Keyword: Richardson Mining District Place_Keyword: Rock Creek Place_Keyword: Sand Creek Place_Keyword: Serpentine Creek Place_Keyword: Sheep Creek Place_Keyword: Smallwood Creek Place_Keyword: Sorrels Creek Place_Keyword: Steele Creek Place_Keyword: Stibnite Creek Place_Keyword: Stuart Creek Place_Keyword: Tok Mining District Place_Keyword: Victoria Creek Place_Keyword: Volkmar Lake Place_Keyword: Walnut Creek Place_Keyword: Wigwam Creek Place_Keyword: Williams Creek Place_Keyword: Willow Creek Place_Keyword: Wolf Creek Place_Keyword: Yukon-Tanana Upland Stratum: Stratum_Keyword_Thesaurus: Alaska Division of Geological & Geophysical Surveys Stratum_Keyword: Fairbanks-Chena Assemblage Stratum_Keyword: Fortymile River Assemblage Stratum_Keyword: Klondike Assemblage Stratum_Keyword: Lake George Assemblage Temporal: Temporal_Keyword_Thesaurus: Walker, J.D., Geissman, J.W., Bowring, S.A, and Babcock, L.E., comp., 2012, Geologic Time Scale v. 4.0: Geological Society of America Temporal_Keyword: Mesozoic Temporal_Keyword: Paleozoic Temporal_Keyword: Permian Temporal_Keyword: Proterozoic 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: The authors thank J. Wes Buchanan for his review, which improved the quality of the manuscript, and the University of Alaska Fairbanks Advanced Instrumentation Laboratory (UAF-AIL) manager, Dr. Nathan Graham, who helped set up the 2024 WDS analyses. We also thank Evan Twelker, Travis Naibert, Mike Barrera, Dave Szumigala, Alicja Wypych, Michelle Gavel, Wes Buchanan, Alec Wildland, Sean Regan, David Harvey, Izzy Muller, Serena Fessenden, Noel Blackwell, Lily Norwood, and Marisa Acosta, who mapped with the authors at various times between 2021 and 2024, procured samples used in this study, and provided helpful observations and ideas. K. Clautice, D. Solie, T. Bundtzen, G. Laird, and R. Reifenstuhl mapped with Newberry in 1995 and provided samples and discussion. Dr. Ken Severin assisted with those WDS analyses. Much of this work was performed at the UAF-AIL, and the authors gratefully acknowledge use of the UAF-AIL electron microprobe acquired with support from the National Science Foundation, Major Research Instrumentation Program Award Number 1126898. We profusely thank past and present personnel of UAF-AIL. This project was jointly funded by the State of Alaska and the U.S. Geological Survey Earth Mapping Resources Initiative (Earth MRI) through cooperative agreements G20AC00156, G21AC00336, G22AC00288, G23AC00372, and G24AC00323. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Geological Survey. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey. Cross_Reference: Citation_Information: Originator: Buchanan, J.W. Originator: Wypych, Alicja Originator: Barrera, M.L. Originator: Biegel, J.M. Originator: Gavel, M.M. Originator: Harvey, D.A. Originator: Ketcham, R.A. Originator: Muller, I.P. Originator: Naibert, T.J. Originator: Newberry, R.J. Originator: Regan, S.P. Originator: Szumigala, D.J. Originator: Twelker, Evan Originator: Wildland, A.D. Publication_Date: 2025 Title: Geochemical data from samples collected in 2023 for the Chena and Mount Harper projects, Big Delta, Circle, Fairbanks, and Eagle quadrangles, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2024-2 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 5 p Online_Linkage: https://doi.org/10.14509/31123 Cross_Reference: Citation_Information: Originator: Gavel, M.M. Originator: Wypych, Alicja Originator: Naibert, T.J. Originator: Twelker, Evan Originator: Newberry, R.J. Originator: Barrera, M.L. Originator: Szumigala, D.J. Originator: Truskowski, C.M. Originator: Muller, I.P. Originator: Fessenden, S.N. Originator: Blackwell, N.J. Originator: Harvey, D.A. Originator: Wildland, A.D. Publication_Date: 2025 Title: Bedrock geologic map of the Mount Harper-Middle Fork area, Eagle Quadrangle, Alaska Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2025-2D Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 1 sheet, scale 1:100,000 Online_Linkage: https://doi.org/10.14509/31652 Cross_Reference: Citation_Information: Originator: Joy, B.R. Originator: Keskinen, M.J. Originator: Newberry, R.J. Publication_Date: 1996 Title: Preliminary thermobarometry and microprobe mineral compositions, Fairbanks area schists and amphibolites Series_Information: Series_Name: Public Data File Issue_Identification: PDF 96-12 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 15 p Online_Linkage: https://doi.org/10.14509/1736 Cross_Reference: Citation_Information: Originator: Moshrefzadeh, J.A. Originator: Newberry, R.J. Publication_Date: 2025 Title: Electron probe microanalyzer data collected on samples from the Chena and Steese projects, Yukon-Tanana Uplands, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2025-13 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 6 p Online_Linkage: https://doi.org/10.14509/31537 Cross_Reference: Citation_Information: Originator: Naibert, T.J. Originator: Wypych, Alicja Originator: Newberry, R.J. Originator: Twelker, Evan Originator: Gavel, M.M. Originator: Wildland, A.D. Originator: Barrera, M.L. Originator: Avirett, D.F. Originator: Muller, I.P. Originator: Blackwell, N.J. Originator: Szumigala, D.J. Publication_Date: 2024 Title: Bedrock geologic map of the Taylor Mountain area, Eagle and Tanacross quadrangles, Alaska Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2024-6B Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 1 sheet, scale 1:100,000 Online_Linkage: https://doi.org/10.14509/31168 Cross_Reference: Citation_Information: Originator: Naibert, T.J. Originator: Newberry, R.J. Originator: Twelker, Evan Originator: Wypych, Alicja Originator: Gavel, M.M. Originator: Barrera, M.L. Originator: Szumigala, D.J. Originator: Truskowski, C.M. Originator: Muller, I.P. Originator: Fessenden, S.N. Originator: Buchanan, J.W. Originator: Blackwell, J.M. Originator: Harvey, D.A. Originator: Wildland, A.D. Publication_Date: 2025 Title: Bedrock geologic map of the Volkmar River-Healy River area, Big Delta and Mount Hayes quadrangles, Alaska Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2025-2C Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 1 sheet, scale 1:100,000 Online_Linkage: https://doi.org/10.14509/31651 Cross_Reference: Citation_Information: Originator: Newberry, R.J. Originator: Bundtzen, T.K. Originator: Clautice, K.H. Originator: Combellick, R.A. Originator: Douglas, Tom Originator: Laird, G.M. Originator: Liss, S.A. Originator: Pinney, D.S. Originator: Reifenstuhl, R.R. Originator: Solie, D.N. Publication_Date: 1996 Title: Preliminary geologic map of the Fairbanks mining district, Alaska Series_Information: Series_Name: Public Data File Issue_Identification: PDF 96-16 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 17 p., 2 sheets, scale 1:63,360 Online_Linkage: https://doi.org/10.14509/1740 Cross_Reference: Citation_Information: Originator: Robinson, M.S. Originator: Smith, T.E. Originator: Metz, P.A. Publication_Date: 1990 Title: Bedrock geology of the Fairbanks mining district Series_Information: Series_Name: Professional Report Issue_Identification: PR 106 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 2 sheets, scale 1:63,360 Online_Linkage: https://doi.org/10.14509/2287 Cross_Reference: Citation_Information: Originator: Twelker, Evan Originator: Newberry, R.J. Originator: Wypych, Alicja Originator: Naibert, T.J. Originator: Wildland, A.D. Originator: Sicard, K.R. Originator: Regan, S.P. Originator: Athey, J.E. Originator: Wyatt, W.C. Originator: Lopez, J.A. Publication_Date: 2021 Title: Bedrock geologic map of the Ladue River-Mount Fairplay area, Tanacross and Nabesna quadrangles, Alaska Series_Information: Series_Name: Report of Investigation Issue_Identification: RI 2021-5A Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: p. 1-32, 1 sheet, scale 1:100,000 Online_Linkage: https://doi.org/10.14509/30735 Cross_Reference: Citation_Information: Originator: Twelker, Evan Originator: Newberry, R.J. Originator: Naibert, T.J. Originator: Wypych, Alicja Publication_Date: 2025 Title: Bedrock geologic map of the Richardson Mining District, Big Delta Quadrangle, Alaska Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2025-2A Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 1 sheet, scale 1:100,000 Online_Linkage: https://doi.org/10.14509/31649 Cross_Reference: Citation_Information: Originator: Twelker, Evan Originator: Newberry, R.J. Originator: Naibert, T.J. Originator: Wypych, Alicja Originator: Gavel, M.M. Originator: Barrera, M.L. Originator: Szumigala, D.J. Originator: Truskowski, C.M. Originator: Muller, I.P. Originator: Fessenden, S.N. Originator: Blackwell, N.J. Originator: Harvey, D.A. Originator: Wildland, A.D. Publication_Date: 2025 Title: Bedrock geologic maps of the Mount Harper-Middle Fork area, Volkmar River-Healy River area, Goodpaster River-Shaw Creek area, and the Richardson Mining District, Alaska Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2025-2 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 38 p Online_Linkage: https://doi.org/10.14509/31648 Cross_Reference: Citation_Information: Originator: Wypych, Alicja Originator: Naibert, T.J. Originator: Athey, J.E. Originator: Newberry, R.J. Originator: Sicard, K.R. Originator: Twelker, Evan Originator: Werdon, M.B. Originator: Willingham, A.L. Originator: Wyatt, W.C. Publication_Date: 2018 Title: Major-oxide and trace-element geochemical data from rocks collected in 2018 for the Northeast Tanacross project, Tanacross C-1, C-2, D-1, and D-2 quadrangles, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2018-4 Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 4 p Online_Linkage: https://doi.org/10.14509/30113 Cross_Reference: Citation_Information: Originator: Wypych, Alicja Originator: Gavel, M.M. Originator: Naibert, T.J. Originator: Avirett, D.F. Originator: Barrera, M.L. Originator: Hubbard, A.K. Originator: Newberry, R.J. Originator: Regan, S.P. Originator: Twelker, Evan Originator: Wildland, A.D. Originator: Wyatt, W.C. Publication_Date: 2022 Title: Geochemical data from samples collected in 2021 for the Taylor Mountain project, Tanacross and Eagle quadrangles, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2022-4 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/10.14509/30843 Cross_Reference: Citation_Information: Originator: Wypych, Alicja Originator: Gavel, M.M. Originator: Naibert, T.J. Originator: Avirett, D.F. Originator: Barrera, M.L. Originator: Hubbard, A.K. Originator: Newberry, R.J. Originator: Regan, S.P. Originator: Twelker, Evan Originator: Wildland, A.D. Originator: Wyatt, W.C. Publication_Date: 2022 Title: Geochemical data from samples collected in 2020 and 2021 for the Western Tanacross project, Tanacross Quadrangle, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2022-5 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/10.14509/30844 Cross_Reference: Citation_Information: Originator: Wypych, Alicja Originator: Twelker, Evan Originator: Naibert, T.J. Originator: Gavel, M.M. Originator: Newberry, R.J. Originator: Szumigala, D.J. Originator: Wildland, A.D. Originator: Barrera, M.L. Originator: Harvey, D.A. Originator: Muller, I.P. Originator: Fessenden, S.N. Originator: Blackwell, N.J. Publication_Date: 2023 Title: Geochemical data from samples collected in 2022 for the Mount Harper geologic mapping project, Big Delta, Mount Hayes, and Eagle quadrangles, Alaska Series_Information: Series_Name: Raw Data File Issue_Identification: RDF 2023-24 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/10.14509/31089 Cross_Reference: Citation_Information: Originator: Wypych, Alicja Originator: Naibert, T.J. Originator: Newberry, R.J. Originator: Twelker, Evan Originator: Gavel, M.M. Originator: Wildland, A.D. Originator: Szumigala, D.J. Originator: Regan, S.P. Originator: Avirett, D.F. Originator: Barrera, M.L. Originator: Bernard, C.M. Originator: Blackwell, N.J. Originator: Fessenden, S.N. Originator: Harvey, D.A. Originator: Hubbard, A.K. Originator: Masterman, S.S. Originator: Muller, I.P. Originator: Turner, M.M. Originator: Wyatt, W.C. Publication_Date: 2024 Title: Bedrock geologic map of the Western Tanacross area, Tanacross Quadrangle, Alaska Series_Information: Series_Name: Preliminary Interpretive Report Issue_Identification: PIR 2024-6C Publication_Information: Publication_Place: Fairbanks, Alaska, United States Publisher: Alaska Division of Geological & Geophysical Surveys Other_Citation_Details: 1 sheet, scale 1:100,000 Online_Linkage: https://doi.org/10.14509/31169 Data_Quality_Information: Attribute_Accuracy: Attribute_Accuracy_Report: These data are being released in the DGGS Preliminary Interpretive Report (PIR) series. PIRs present emergent interpretations of geologic mapping or analytical investigation. These publications are reviewed for clarity and consistency and receive limited peer review. The accompanying report provides a comprehensive discussion of processing methods, with errors reported in the tables where applicable. Logical_Consistency_Report: Not applicable Completeness_Report: This data release is complete. Positional_Accuracy: Horizontal_Positional_Accuracy: Horizontal_Positional_Accuracy_Report: Location data for field stations were collected using GPS-enabled tablets or smartphones running the Esri Field Maps app with an estimated location error of 10.0 m. Lineage: Process_Step: Process_Description: Sample analysis - Geologists collected rock samples during field mapping from 2021 to 2024 and selected specimens suitable for polished thin section preparation. All thin sections were examined, and only metamafic samples with minimal weathering or retrograde alteration were chosen for analysis. Thin sections showing alteration of hornblende to actinolite or chlorite, or alteration of plagioclase to white mica, calcite, or chlorite were rejected. At least four sites containing amphibole and plagioclase were randomly selected on each thin section, and multiple grains of each mineral were analyzed using standard modified energy dispersive spectrometry (EDS) on the JEOL JXA 8530 electron probe microanalyzer at the University of Alaska Fairbanks Advanced Instrumentation Laboratory. Additional spot analyses were performed as needed to confirm mineral identification. Samples collected in 2024 were also analyzed using wavelength dispersive spectrometry (WDS) to obtain higher accuracy results and to verify EDS measurements. For each mineral grain, three or more analyses were averaged to reduce analytical variability. Previously unpublished hornblende and plagioclase analyses generated using the Cameca SX 50 microprobe at the same facility were reviewed and checked against new EDS data collected in 2025. Process_Date: 2025 Spatial_Data_Organization_Information: Direct_Spatial_Reference_Method: point Spatial_Reference_Information: Horizontal_Coordinate_System_Definition: Geographic: Latitude_Resolution: 0.0000001 Longitude_Resolution: 0.0000001 Geographic_Coordinate_Units: decimal degrees Geodetic_Model: Horizontal_Datum_Name: NAD83 Ellipsoid_Name: GRS 80 Semi-major_Axis: 6378137 Denominator_of_Flattening_Ratio: 298.257222101 Entity_and_Attribute_Information: Detailed_Description: Entity_Type: Entity_Type_Label: pir2026-2_plagioclase_data.csv, pir2026-2_plagioclase_data_dictionary.csv, pir2026-2_amphibole_data.csv, pir2026-2_amphibole_data_dictionary.csv Entity_Type_Definition: Sample identifiers, geographic locations and description, petrographic locations, mineral phases, oxide weight percentages, and calculated cation proportions for amphibole and plagioclase populations. Entity_Type_Definition_Source: DGGS Entity_Attribute_Layer_Name: electron‑microprobe mineral‑chemistry 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: PIR 2026-2 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: spreadsheet Format_Version_Date: 20260515 Format_Information_Content: table Digital_Transfer_Option: Online_Option: Computer_Contact_Information: Network_Address: Network_Resource_Name: https://doi.org/10.14509/32081 Fees: Free download Metadata_Reference_Information: Metadata_Date: 20260515 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