Preliminary geology of the McGrath - upper Innoko River area, western interior Alaska

Bundtzen, T.K.Laird, G.M.1980Preliminary geology of the McGrath - upper Innoko River area, western interior AlaskageodatabaseAlaska Open-File ReportAOF 134Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys39 p., 2 sheetshttps://doi.org/10.14509/53Preliminary geology of the McGrath - upper Innoko River area, western interior Alaska, Alaska Open-File Report 134, presents results of geologic mapping and resource assessment across approximately 900 square miles in parts of the McGrath, Iditarod, and Ophir 1:250,000 quadrangles of western interior Alaska. DGGS staff completed a total of ninety-four field days in 1972, 1978, and 1979. The map area contains a Late Paleozoic chert-argillite-limestone unit, Early(?) Cretaceous limy sandstone and impure limestone, and a thick section of mid- to Late Cretaceous lithic sandstone, siltstone, shale, and conglomerate. Layered sedimentary rocks form low, rounded ridges, and igneous complexes and associated hornfels form steep massifs. Bedrock exposures are limited below timberline but are well developed along stream bluffs and in the Beaver Mountains. Late Cretaceous alkaline plutonic complexes, dike swarms, and associated mafic volcanic rocks intrude and overlie the layered units. Surficial deposits include glacial, eolian, alluvial, and colluvial sediments. Dominant structures consist of northeast-trending folds and high-angle faults. Placer gold deposits occur in modern and older stream terraces in the Ophir mining area and the Candle Hills. Gold placers are associated with basaltic-to-rhyolitic dike swarms and faults that cross stream channels. The dike swarms contain anomalous concentrations of gold, nickel, yttrium, chromium, and zirconium, and fractures in plutons and nearby hornfels zones locally contain anomalous base and precious metals interpreted as probable lode sources for gold placers in the Candle Hills. The geologic relationships recorded by this map have important implications for understanding mineral resources and guiding future exploration throughout this region of Alaska. The dataset provides geologic, structural, stratigraphic, and geochronologic information organized according to the GeMS and AK GeMS mapping schemas. The complete report, geodatabase, and ESRI fonts and style files are available from the DGGS website: https://doi.org/10.14509/53.This report provides geologic mapping and resource information for parts of the McGrath, Iditarod, and Ophir 1:250,000 quadrangles of western interior Alaska. The mapping improves understanding of bedrock geology, surficial deposits, and structural features, and documents the distribution and geologic controls of placer gold deposits in the Ophir mining precinct and Candle Hills. These data support mineral resource evaluation, land management, and future geologic investigations in the region.This geodatabase is organized according to the AK GeMS mapping schema Hendricks, M.D., Macpherson, A.E., Athey, J.E., Wyatt, W.C., Montayne, Simone, Buchanan, Wes, Rivera, P.G., and Steinleitner, A.M., 2024, AK GeMS data dictionary: A description of the Alaska geologic mapping schema: Alaska Division of Geological & Geophysical Surveys Miscellaneous Publication 170 v. 2, 13 p. https://doi.org/10.14509/31172. The distribution package includes ESRI fonts and style files, along with usage instructions. Further documentation of the symbology is provided by Ekberg, P.G., Hendricks, M.D., and Athey, J.E., 2021, AK GeMS symbology: A description of the AK GeMS style file: Alaska Division of Geological & Geophysical Surveys Miscellaneous Publication 169, 7 p. https://doi.org/10.14509/30584.19721979ground conditionCompleteNone planned-157.182321-155.50411263.17527962.719700ISO 19115 Topic CategorygeoscientificInformationAlaska Division of Geological & Geophysical SurveysAlluvialAlluviumAnalysesAndesiteAntimonyArgilliteArsenicAugiteBariteBasaltBedrockBedrock GeologyBiotiteBismuthBrachiopodsBrecciaChemistryChertChloriteChromiteChromiumCinnabarClayClinopyroxeneColluviumConglomerateDaciteDikeDioriteDredgeDriftEnergyEnvironmentEolianErosionExplorationFanFaultsFelsicFelsiteFlyschFoldingFoldsFossilsFractureGarnetGastropodsGeneralizedGeochemistryGeochronologyGeologicGeologyGlacialGlaciationGoldGossanGraphiteGravelGraywackeGreisenHelminthopsisHornfelsIgneousIlmeniteInoceramusInterpretationIntrusiveJasperLeadLimestoneLithologyLodeLoessMagnetiteManganeseMarineMegafossilsMeltwaterMercuryMetalsMetamorphicMineral AssessmentMineral DepositsMineral DevelopmentMineral ExplorationMineral LocalitiesMineral ResourcesMineralogyMineralsMiningMolybdenumMonzoniteMudstoneNickelNonmarineOlivineOreOrogenyOrthoquartziteOutcropOutwashPaleobotanyPaleocurrentPaleontologyPetrologyPhyllitePlacerPlagioclasePlatinumPlutonicPlutonsPyriteQuartzResourcesRhyoliteRocksSandSandstoneScheeliteSedimentSedimentaryShaleShearShonkiniteSideriteSiltSiltstoneSilverSlateSlopeStratigraphyStream SedimentsStructureSulfidesSurfaceSurficialSyeniteTailingsTalusTephraTerraceThermokarstThoriumTillTourmalineTransportationTrenchingTuffTungstenTurbidityUpliftUraniumVanadiumVolcanicVolcaniclasticYttriumZincZirconiumAlaska Division of Geological & Geophysical SurveysAnvil CreekBeaver CreekBeaver MountainsBeef Steak CreekBilly Goat CreekBrown CreekCalifornia CreekCamp CreekCanadian CreekCandle CreekCandle HillsCandle PlacerCarl CreekCash CreekCrater MountainDodge CreekDollar CreekDome CreekEster CreekFrench Joe MountainGanes CreekGoldbottom CreekHarrell IslandIndependence CreekInnoko Mining DistrictInnoko RiverKatlitna RiverKuskokwim MountainsKuskokwim RiverLast Chance CreekLincoln CreekMaiden CreekMoore CityMount JoaquinNaden CreekOphirOphir CreekReady Bullion CreekRex CreekRoundabout MountainRoundabout MountainsSpalding CreekSpruce CreekSteak CreekSteel CreekSunset CreekTakotnaTakotna MountainTakotna RiverTamarack CreekTatalina RiverTolstoi CreekTolstoi LakeWarner CreekWilson LakeWindy CreekYankee CreekWalker, J.D., Geissman, J.W., Bowring, S.A, and Babcock, L.E., comp., 2012, Geologic Time Scale v. 4.0: Geological Society of AmericaCretaceousPaleozoicPhanerozoicQuaternaryThis 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 SurveysMetadata Managermailing and physical

3354 College Road

FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysPlease 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.Thomas K. Bundtzen led the project and was assisted by Gregory M. Laird during all three seasons, and by Virginia F. Ferrell, Nicki D. Coursey, and Karen S. Emmel in 1979. Specialists contributed fossil locality data, paleocurrent measurements, K-Ar age determinations, geochemical analyses, gold production figures, and uranium and thorium analyses. Additional geological comparisons were provided by U.S. Geological Survey staff familiar with nearby quadrangles. Long-time local residents shared information on past mineral activity, and the Rossander mining camp on Yankee Creek served as the 1979 base camp. The report was reviewed by DGGS staff. This map was converted to GeMS or digitized into GeMS by Kinney Engineering, LCC., quality controlled, and then finalized by DGGS staff (Chris Wyatt and Mike Hendricks). Ally M. Steinleitner implemented final database quality control and packaging. This geologic map (or report or conversion or product, etc.) was funded by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G24AC00521, 2024, and the State of Alaska General Fund. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.Bundtzen, T.K.Laird, G.M.1982Geologic map of the Iditarod D-2 and eastern D-3 quadrangles, AlaskaGeologic ReportGR 72Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys1 sheet, scale 1:63,360https://doi.org/10.14509/432Bundtzen, T.K.Laird, G.M.1983Geologic map of the Iditarod D-1 Quadrangle, AlaskaProfessional ReportPR 78Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys1 sheet, scale 1:63,360https://doi.org/10.14509/2252Bundtzen, T.K.Laird, G.M.1983Geologic map of the McGrath D-6 Quadrangle, AlaskaProfessional ReportPR 79Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys1 sheet, scale 1:63,360https://doi.org/10.14509/2253Bundtzen, T.K.Laird, G.M.1983Preliminary geology of the northeastern Iditarod C-3 Quadrangle, AlaskaReport of InvestigationRI 83-13Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys1 sheet, scale 1:63,360https://doi.org/10.14509/2352Bundtzen, T.K.Laird, G.M.Lockwood, M.S.1988Geologic map of the Iditarod C-3 Quadrangle, AlaskaProfessional ReportPR 96Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys13 p., 1 sheet, scale 1:63,360https://doi.org/10.14509/2277Burns, L.E.Graham, G.R.C.Barefoot, J.D.Naibert, T.J.Fugro Airborne Surveys Corp.2019Iditarod electromagnetic and magnetic airborne geophysical survey data compilationGeophysical ReportGPR 2019-15Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys15 phttps://doi.org/10.14509/30222Burns, L.E.Graham, G.R.C.Barefoot, J.D.Naibert, T.J.CGGFugro Airborne Surveys Corp.2019Fox Hills electromagnetic and magnetic airborne geophysical survey data compilationGeophysical ReportGPR 2018-6Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys14 phttps://doi.org/10.14509/29820Fusso, L.A.Petersen, E.I.Emond, A.M.EON Geosciences Inc.2026Kuskokwim airborne magnetic and radiometric geophysical survey, Ganes Creek, Alaska (2026)Geophysical ReportGPR 2026-1Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys16 phttps://doi.org/10.14509/31746Fusso, L.A.Petersen, E.I.Emond, A.M.EON Geosciences Inc.2026Kuskokwim airborne magnetics and radiometric geophysical survey, McGrath, AlaskaGeophysical ReportGPR 2026-2Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys17 phttps://doi.org/10.14509/31804Meyer, J.F.Krouskop, D.L.1986Preliminary gravity data of the Minchumina basin, southcentral AlaskaReport of InvestigationRI 86-1Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys14 p., 2 sheets, scale 1:500,000https://doi.org/10.14509/2400Petersen, E.I.Fusso, L.A.Geotech Ltd.Aqua Geo Frameworks LLC2026Candle Hills airborne electromagnetic survey, Kuskokwim region, AlaskaGeophysical ReportGPR 2026-3Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys9 phttps://doi.org/10.14509/31963Reger, R.D.Campbell, K.M.Stevens, D.S.P.Smith, R.L.2003Survey of geology, geologic materials, and geologic hazards in proposed access corridors in the Ophir Quadrangle, AlaskaMiscellaneous PublicationMP 100Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys5 sheets, scale 1:250,000https://doi.org/10.14509/3286Reger, R.D.Cruse, G.R.Stevens, D.S.P.Smith, R.L.2003Survey of geology, geologic materials, and geologic hazards in proposed access corridors in the Iditarod Quadrangle, AlaskaMiscellaneous PublicationMP 76Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys4 sheets, scale 1:250,000https://doi.org/10.14509/2930Reger, R.D.Stevens, D.S.P.Cruse, G.R.Livingston, H.R.2003Survey of geology, geologic materials, and geologic hazards in proposed access corridors in selected quadrangles, AlaskaMiscellaneous PublicationMP 129Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys72 phttps://doi.org/10.14509/2946Attribute fields within each feature class are populated using the map symbology and corresponding applicable values from the GeMS and AK GeMS specifications. When known, certainty in attribute interpretation is indicated in the relevant fields. Attribute accuracy varies throughout the map and is scale-dependent.All polygon features were topologically validated according to the AK GeMS geologic mapping schema specifications.This publication is a DGGS Alaska Open-File Report (AOF). An AOF contains reports of research by DGGS personnel. Its objective was to make information available to the public as soon as possible, and therefore reports of this series were not subjected to rigorous critical review and formal editing and did not use professional cartographic services.Certainty in feature boundaries or location varies throughout the map. Data fields within each feature class and the accompanying orientation and location confidence lookup tables record the authors' degree of confidence in the location of applicable features.Ekberg, P.G.Hendricks, M.D.Athey, J.E.2021AK GeMS symbology: A description of the AK GeMS style fileMiscellaneous PublicationMP 169Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys7 phttps://doi.org/10.14509/30584paper2021publication dateEkberg, P.G. and others, 2021GIS analysis and digital cartographyHendricks, M.D.Ekberg, P.G.Athey, J.E.Wyatt, W.C.Willingham, A.L.Naibert, T.J.2021AK GeMS data dictionary: A description of the Alaska geologic mapping schemaMiscellaneous PublicationMP 170Fairbanks, Alaska, United StatesAlaska Division of Geological & Geophysical Surveys10 phttps://doi.org/10.14509/30669paper2021publication dateHendricks, M.D. and others, 2021GIS analysis and digital cartographyU.S. Geological Survey National Cooperative Geologic Mapping Program2020GeMS (Geologic Map Schema) - A standard format for the digital publication of geologic mapsTechniques and MethodsTM 11-B10United StatesU.S. Geological Survey1 phttps://dggs.alaska.gov/pubs/id/30585paper2020publication dateU.S. Geological Survey National Cooperative Geologic Mapping Program, 2020GIS analysis and digital cartographyGeologic mapping - DGGS completed geologic mapping during ninety-four field days in 1972, 1978, and 1979. Mapping documented bedrock lithologies, intrusive and volcanic relationships, structural features, and surficial deposits across parts of the McGrath, Iditarod, and Ophir quadrangles. Field investigations included measurement of paleocurrent indicators, identification of fossil localities, and collection of rock and sediment samples for geochemical and age-dating analyses. Supporting data included fossil identifications, K-Ar age determinations, and uranium and thorium analyses. Information on historical mineral activity was gathered from local residents, and geological comparisons with nearby quadrangles were incorporated into final interpretations.1979Data packaging - DGGS organized and attributed the geologic and geographic features according to the AK GeMS schema, then programmatically transformed the data into four distribution formats: (1) an AK GeMS data package containing the full database and supporting files, (2) a GeMS data package converted to the USGS base standard, (3) a SQLite database file, and (4) a simplified shapefile package with shapefile representations of the data.2026vectorUniversal Transverse Mercator40.999600-1590500000.0000000coordinate pair.00000001.00000001MetersNAD27Clarke 18666378206.4294.9786982mcgrath_upper_innoko_river_ak_gems_dbGeodatabase, layer files, style files, and fontsDGGSmcgrath_upper_innoko_river_ak_gems_dbmcgrath_upper_innoko_river_gems_dbGeodatabase, layer files, style files, and fontsDGGSmcgrath_upper_innoko_river_gems_dbmcgrath_upper_innoko_river_gems_geopackageSQLite Database fileDGGSmcgrath_upper_innoko_river_gems_geopackagemcgrath_upper_innoko_river_gems_shapefileShapefiles and open data filesDGGSmcgrath_upper_innoko_river_gems_shapefileAlaska Division of Geological & Geophysical SurveysMetadata Managermailing and physical

3354 College Road

FairbanksAK99709-3707USA(907)451-5020(907)451-5050dggspubs@alaska.gov8 am to 4:30 pm, Monday through Friday, except State holidaysFGDC Content Standard for Digital Geospatial MetadataFGDC-STD-001-1998If 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.https://dggs.alaska.gov/metadata/dggs.extdggs metadata extensions