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Cook Inlet has been recognized as the second-largest petroleum province in Alaska, second only to the North Slope. The south-central Tyonek Quadrangle is an area of significant geologic interest because it is the only location in Cook Inlet where the entire producing stratigraphy of the basin is exposed on the surface. Additionally, this area encompasses the structural boundary between the forearc basin and its sediment source rocks. To better understand the petroleum system and the geologic relationships between the exhumed arc intrusive rocks and adjacent Cenozoic stratigraphy of the Cook Inlet forearc basin, during the summer of 2010 the Alaska Division of Geological & Geophysical Surveys conducted a federally-funded...
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From June 12-21, 2017, the Alaska Division of Geological & Geophysical Surveys (DGGS) geologists carried out geologic mapping and geochemical sampling in the northeastern Tanacross D-1, and parts of the C-1, and D-2 quadrangles. The project area lies within the Yukon-Tanana Uplands, and encompasses the boundary between Fortymile and Lake George assemblages. It includes porphyry copper-molybdenum-gold deposits and prospects including: Taurus, Fishhook (also known as SW Pika), and Pika Canyon, and is adjacent to the Fortymile Mining District to the north. Highlights of this geochemical report include sampling and characterization of the Pika Canyon, Fishhook, and Taurus prospects. This dataset contains four samples...
Tags: Analyses, Analyses and Sampling, Analytical Lab Results, Analytical Results, Base Metals, All tags...
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40Ar/39Ar analyses were performed on igneous rocks from the Ray Mountains area of west-central Alaska. The plutonic samples have ages from about 89 Ma to 109 Ma, while the volcanic samples show ranges from about 30 Ma to 64 Ma. The three volcanic samples fall into two age groups: the younger sample, a basalt, has an age of about 30 Ma, while the two older, rhyolitic samples fall between 58 Ma and 64 Ma. Analyses were performed by the University of Alaska Fairbanks Geochronology Laboratory, and results were reported by Paul Layer and Jeff Benowitz. Products included in this data release are: a summary of sample collection method; the laboratory report, analytical data tables and associated metadata; and plots of...
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This report provides detailed (1:63,360-scale) mapping of the Tanana A-1 and A-2 quadrangles (500 square miles; equivalent to eight 7.5-minute quadrangles). The area is part of the Manley Hot Springs-Tofty mining districts and adjacent to the Rampart mining district to the south of the Tanana B-1 Quadrangle. This report includes detailed bedrock, surficial, structural, and stratigraphic data. Based on the resulting geologic maps, field investigations, and laboratory materials analyses, the report also includes derivative maps of geologic construction materials and geologic hazards. The Tanana A-1 and A-2 Quadrangles and surrounding area comprise several isolated mountainous ridges in the western Yukon-Tanana Upland...
Tags: 40Ar/39Ar, Aerial Photography, Aeromagnetic Map, Aeromagnetic Survey, Age Dates, All tags...
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We report U-Pb zircon geochronology results for one metavolcanic and one metaplutonic rock sample from the Mount Hayes A-6 Quadrangle of central Alaska. These samples are representative of rock units assigned to the Clearwater terrane of Jones and others (1987), a sequence of greenschist-grade metavolcanic and metasedimentary rocks of poorly constrained age and tectonic origin. Our results indicate a crystallization age of 277.33 +/- 11.84 Ma for a felsic metavolcanic rock, and a 268.05 +/- 11.64 Ma crystallization age for a granitic metaplutonic unit intruding the former.
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This data release presents zircon U-Pb LA-ICP-MS geochronology from igneous rocks exposed in a coastal exposure at Ursus Head, Iliamna C-2 Quadrangle. Sills and dikes exposed in a coastal exposure at Ursus Head are deformed within the Bruin Bay fault zone. Common dikes intruding late Triassic Kamishak Formation strata composing the hanging-wall of the Bruin Bay fault are cut by numerous small-scale, low-angle, bedding-parallel, and high angle contractional faults. Sample 09MAW006A collected from one of many dikes deformed in the fault zone produced a uni-modal distribution of zircon ages of with a weighted mean of 206.92 +/-0.96 (2 sigma, n=47) and an MSWD of 1.1. Sample 09BG020C collected from a sill of more mafic...
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This DGGS Raw Data File presents 40Ar/39Ar age dating results for selected igneous rocks encountered in the Styx River area of the western Alaska Range. Crystallization ages on biotite and hornblende from plutonic rocks range from about ~60 to ~63 Ma, while a sericite alteration age in plutonic rocks altered by a dike swarm also is around ~63 Ma. Sericite alteration associated with a copper-molybdenum porphyry ranges from ~10 to ~11 Ma. Analyses were performed by the University of Alaska Fairbanks Geochronology Laboratory, and results were reported by Paul Layer and Jeff Benowitz. This data release includes the following products: a summary of sample collection methods, the laboratory report, analytical data tables...
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The Tok project area is adjacent to the Delta mineral belt volcanogenic massive-sulfide (VMS) district, the Peak gold-silver-copper skarn, and structurally controlled gold and antimony mineralization in the Stibnite Creek and White Gold areas. The project area also includes the Noah prospect, an intrusion-related copper prospect. Whereas the Delta mineral belt has been extensively mapped and explored, the detailed mapping does not continue into the 2015 Tok project area. In this area, only reconnaissance mapping has been conducted. The combination of a lack of detailed mapping, the industry interest in the adjacent areas, and the geophysical data findings prompted the Alaska Division of Geological & Geophysical...
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This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) Wrangellia Mineral Assessment project, part of a multi-year effort focusing on improving the publicly available geoscientific information for the western Wrangellia terrane. The samples described in this report were selected and analyzed to improve our understanding of the geology and structural history of the Wrangellia Mineral Assessment project area. A metagabbro rock sample returned a Late Triassic crystallization age consistent with regional ages for Nikolai Greenstone-related magmatism; however, the two amphibole separates ages do not overlap,...
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U-Pb analyses were performed on igneous rocks from the Ray Mountains area of west-central Alaska. These new age analyses will allow us to better evaluate the geochronology of the granitic rocks that are the apparent source of the alluvial REE and tin resources. The plutonic samples have ages ranging from 98.0 +/- 0.9 Ma to 111.6 +/- 1.0 Ma. The sample location coordinates and analytical data tables associated with this report are available in digital format as comma-separated value (CSV) files.
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The State of Alaska's Strategic and Critical Minerals (SCM) Assessment project, a State-funded Capital Improvement Project (CIP), is designed to evaluate Alaska's statewide potential for strategic and critical mineral resources. The SCM Assessment project is being implemented by the Alaska Division of Geological & Geophysical Surveys (DGGS), and involves obtaining new airborne-geophysical, geological, and geochemical data. For the geochemical part of the SCM Assessment project, thousands of geochemical-sample analyses and locations from historical U.S. Bureau of Mines (USBM), U.S. Geological Survey (USGS), Bureau of Land Management (BLM), DGGS, Alaska Territorial Department of Mines, Alaska Division of Mines and...
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This Division of Geological & Geophysical Surveys (DGGS) Raw Data File presents U-Pb geochronology and Lu-Hf isotopic compositions, age-dating results, and additional trace-elemental composition of zircons from four granitoids sampled during investigations by DGGS geologists in the western Alaska Range and the Talkeetna Mountains. The purpose of the Lu-Hf and U-Pb isotopic study was to better understand the Jurassic through early Tertiary magmatic and tectonic evolution of the Alaska Range and the significance of that magmatism for the formation of metallic mineral deposits. The U-Pb isotopic data also serve to further refine the crystallization age of plutons, which were previously ambiguous in 40Ar/39Ar geochronology...
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In 2016, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) and University of Alaska Fairbanks carried out a two-part geologic mapping and geochemical sampling project in the Tok River area of the Tanacross A-5 and A-6 quadrangles (June 12-26 and July 8-26). This report provides results of stream-sediment sampling for trace-element geochemistry. An initial suite of sediment samples was collected from streams draining known gold occurrences, including the Stibnite Creek and Noah prospects, and numerous prospects in the White Gold area. These samples were split in half and the two splits were sieved to -200 mesh and -80 mesh, respectively. The splits were then both analyzed to determine...
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The State of Alaska's Strategic and Critical Minerals (SCM) Assessment project, a State-funded Capital Improvement Project (CIP), is designed to evaluate Alaska's statewide potential for strategic and critical mineral resources. The SCM Assessment project is being implemented by the Alaska Division of Geological & Geophysical Surveys (DGGS), and involves obtaining new airborne-geophysical, geological, and geochemical data. For the geochemical part of the SCM Assessment project, thousands of geochemical-sample analyses and locations from historical U.S. Bureau of Mines (USBM), U.S. Geological Survey (USGS), Bureau of Land Management (BLM), DGGS, Alaska Territorial Department of Mines, Alaska Division of Mines and...
Tags: Alaska Statewide Quadrangle, Alaska, State of, Analyses, Analyses and Sampling, Analytical Lab Results, All tags...
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During the 2017 field season, geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted geologic mapping and sampling of part of the Richardson Mining District southeast of Fairbanks, including parts of the Big Delta B-4, B-5, and C-5 quadrangles. The project area is about 30 miles west of the Pogo gold mine and covers the currently active Montecristo and Uncle Sam gold-exploration properties. The goal of DGGS's work in this area is to conduct a mineral-resource assessment and to build an improved understanding of the area's geology and controls on gold mineralization to facilitate industry exploration targeting. This report is based on 17 days of fieldwork completed June 23-July 3,...
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This report presents 40Ar/39Ar step-heating geochronology results for igneous and metamorphic rocks from the Alaska Division of Geological & Geophysical Surveys' (DGGS) Talkeetna Mountains C-4 Quadrangle and Adjoining Areas geologic mapping project. Hornblende-bearing gabbro returned a Late Triassic crystallization age consistent with regional results for Nikolai Greenstone-related magmatism. We determined Early Jurassic metamorphic ages for hornblende and sericite from two samples of upper greenschist to amphibolite grade metavolcanic rocks. Our results indicate that a granodiorite pluton intruding Wrangellia in the study area has a Middle Jurassic age consistent with the Talkeetna Arc, indicating that the Wrangellia...
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Geologists from the Alaska Division of Geological & Geophysical Surveys (DGGS) and University of Alaska carried out a two-part geologic mapping and geochemical sampling project in the Tok River area of the Tanacross A-5 and A-6 quadrangles (June 12-26 and July 8-26). The Tok River area is adjacent to the Delta mineral belt volcanogenic massive-sulfide (VMS) district, the Peak gold-silver-copper skarn, and the structurally controlled gold and antimony mineralization in the Stibnite Creek and White Gold areas. The Tok River project area includes the Noah (also called Hona) prospect, an intrusion-related copper prospect. The combination of insufficient detailed geologic mapping, historical and current industry interest...
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This data release presents 40Ar/39Ar step-heating geochronology results from rocks collected roughly 7 km southwest of Contact Point, Iliamna B-3 Quadrangle. Samples obtained from a felsic dike intruding the principal Bruin Bay fault plane near Contact Point produced biotite and plagioclase 40Ar/39Ar ages of 36.5 +/- 0.8 Ma and 31.5+/-0.7 Ma, respectively. The age dates inform stratigraphic, structural, and geochronologic studies along the western margin of lower Cook Inlet basin. The accompanying report also presents zircon U-Pb LA-ICP-MS geochronology results for dikes near Ursus Head.
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The Iniskin-Tuxedni Bay area contains excellent exposures of nearly all of the lower Cook Inlet Mesozoic succession, including most of the stratigraphic sections that define the interval and the petroleum source rocks that comprise the basin. An underdeveloped understanding of the Mesozoic petroleum system has led the Alaska Department of Natural Resources' Division of Geological & Geophysical Surveys and Division of Oil and Gas, and the U.S. Geological Survey to collaborate on a multi-year project that includes two major mapping campaigns. Geologic mapping between Chinitna Bay and the Johnson River during the 2015 field season encompassed volcanic arc rocks northwest of the Bruin Bay fault system, and Mesozoic...
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40Ar/39Ar analyses of igneous rocks from the Alaska Highway corridor between Delta Junction and the Canada border show a range of Cretaceous ages from about 68 Ma to about 112 Ma. The 25 samples fall into two broad age groups. The younger group ranges from about 68 Ma to 73 Ma; the older group ranges from a minimum age of about 84 Ma to about 103 Ma. One sample, a mafic dike, yielded an older age of about 112 Ma.


map background search result map search result map Geologic map of the Tanana A-1 and A-2 quadrangles, central Alaska 40Ar/39Ar data, Alaska Highway corridor from Delta Junction to Canada border, parts of Mount Hayes, Tanacross, and Nabesna quadrangles, Alaska 40Ar/39Ar data, Ray Mountains area, Bettles Quadrangle, Alaska 40Ar/39Ar data, Styx River map area, Lime Hills C-1 Quadrangle, Alaska 40Ar/39Ar data from the Talkeetna Mountains C-4 Quadrangle and adjoining areas, central Alaska Major-oxide and trace-element geochemical data from rocks collected in 2015 in the Tok area, Tanacross A-5, A-6, and parts of adjacent quadrangles, Alaska Major-oxide and trace-element geochemical data from rocks collected in 2015 in lower Cook Inlet, Iniskin - Tuxedni region, Alaska Major-oxide and trace-element geochemical data from rocks collected in 2010 in the Tyonek Quadrangle, Alaska Zircon U-Pb age data, Ray Mountains area, Bettles Quadrangle, Alaska U-Pb zircon age data from meta-igneous rocks in the Clearwater Mountains, Mount Hayes A-6 Quadrangle, Alaska Major-oxide and trace-element geochemical data from rocks collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016 Trace-element geochemical data from stream sediments collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016 Digital compilation of geochemical data for historical samples from occurrences of strategic and critical elements in Alaska: Part I - Rare-earth elements (REE) Digital compilation of geochemical data for historical samples from occurrences of strategic and critical elements in Alaska: Part II - Platinum group elements (PGE) 40Ar/39Ar data from rocks collected in the 2015 Wrangellia mineral assessment project area, Mount Hayes A-5, Mount Hayes B-6, and Talkeetna Mountains D-2 quadrangles, Alaska U-Pb and Lu-Hf isotope, age, and trace-element data from zircons at four sites in the western Alaska Range and Talkeetna Mountains, Alaska Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet Major-oxide and trace-element geochemical data from rocks collected in the Tanacross C-1, D-1, and D-2 quadrangles, Alaska in 2017 Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska Zircon U-Pb and 40Ar/39Ar results from dikes collected within the Bruin Bay fault zone, lower Cook Inlet U-Pb zircon age data from meta-igneous rocks in the Clearwater Mountains, Mount Hayes A-6 Quadrangle, Alaska Major-oxide and trace-element geochemical data from rocks collected in 2015 in lower Cook Inlet, Iniskin - Tuxedni region, Alaska 40Ar/39Ar data, Styx River map area, Lime Hills C-1 Quadrangle, Alaska Major-oxide and trace-element geochemical data from rocks collected in the Richardson mining district, Big Delta Quadrangle, Alaska 40Ar/39Ar data from the Talkeetna Mountains C-4 Quadrangle and adjoining areas, central Alaska Trace-element geochemical data from stream sediments collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016 Major-oxide and trace-element geochemical data from rocks collected in the Tanacross C-1, D-1, and D-2 quadrangles, Alaska in 2017 Zircon U-Pb age data, Ray Mountains area, Bettles Quadrangle, Alaska 40Ar/39Ar data, Ray Mountains area, Bettles Quadrangle, Alaska Geologic map of the Tanana A-1 and A-2 quadrangles, central Alaska Major-oxide and trace-element geochemical data from rocks collected in 2010 in the Tyonek Quadrangle, Alaska Major-oxide and trace-element geochemical data from rocks collected in the Tok River area, Tanacross A-5 and A-6 quadrangles, Alaska in 2016 Major-oxide and trace-element geochemical data from rocks collected in 2015 in the Tok area, Tanacross A-5, A-6, and parts of adjacent quadrangles, Alaska 40Ar/39Ar data from rocks collected in the 2015 Wrangellia mineral assessment project area, Mount Hayes A-5, Mount Hayes B-6, and Talkeetna Mountains D-2 quadrangles, Alaska 40Ar/39Ar data, Alaska Highway corridor from Delta Junction to Canada border, parts of Mount Hayes, Tanacross, and Nabesna quadrangles, Alaska U-Pb and Lu-Hf isotope, age, and trace-element data from zircons at four sites in the western Alaska Range and Talkeetna Mountains, Alaska Digital compilation of geochemical data for historical samples from occurrences of strategic and critical elements in Alaska: Part I - Rare-earth elements (REE) Digital compilation of geochemical data for historical samples from occurrences of strategic and critical elements in Alaska: Part II - Platinum group elements (PGE)