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U-Pb Zircon ages from bedrock samples collected in the Tanacross D-1, and parts of the D-2, C-1, and C-2 quadrangles, Alaska
This Alaska Division of Geological & Geophysical Surveys (DGGS) Preliminary Interpretive Report presents U-Pb ages of zircons from 14 sedimentary, metamorphic, and igneous samples collected during 2017 and 2018 field investigations in the northeastern Tanacross Quadrangle, Alaska. The DGGS Northeast Tanacross project is a part of multi-year effort to investigate the geology and mineral-resource potential of the Yukon-Tanana Uplands region in collaboration with the U.S. Geological Survey. The purpose of the U-Pb isotopic study is to better understand the Devonian-to-Mississippian and Mesozoic-to-Early Paleogene episodes of magmatic and tectonic events within the Yukon-Tanana Uplands and the relationship of magmatism to the metallic mineral deposits. This area is characterized by the presence of two Late Devonian to Mississippian metamorphic assemblages--Lake George and Fortymile River. Both assemblages are composed of metasedimentary and metavolcanic rocks that have been intruded by Devonian to Eocene intrusive rocks of varying composition and texture. Paleozoic intrusive rocks are deformed and metamorphosed and include prevalent Late Devonian-Early Mississippian augen orthogneiss, herein called the Divide Mountain suite, that was emplaced into and deformed together with the Lake George assemblage. The Fortymile River assemblage is primarily cross cut by Mississippian to Permian intrusive rocks that are also pervasively deformed and metamorphosed. Following Jurassic to mid-Cretaceous regional metamorphism and deformation, all metamorphic rock packages were intruded by Mid- to Late-Cretaceous volcanic and plutonic rocks, some of which have known or suspected potential for gold together with silver, zinc, copper, and lead mineralization. Products included in this data release are: A summary of sample-collection methods, the laboratory report, analytical data tables, and associated metadata. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30465.
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U-Pb zircon ages from bedrock samples collected in the Tanacross and Nabesna quadrangles, eastern Alaska
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This Alaska Division of Geological & Geophysical Surveys (DGGS) Preliminary Interpretive Report presents uranium-lead (U-Pb) ages of zircons from 37 igneous and metamorphic samples collected during the 2019 field season in support of a 4,800-sq-km (1,860-sq-mi) bedrock geologic map of eastern Interior Alaska surrounding Mount Fairplay and the Ladue River drainage. The area lies north of the Alaska Highway and is approximately 65 km (40 mi) east of Tok, Alaska; it runs west from the Alaska-Yukon border to encompass the Taylor Highway. DGGS and U.S. Geological Survey (USGS) staff identified this area as having underexplored potential to host deposits of critical minerals, including rare earth elements (REE), uranium, niobium, zirconium, tin, tungsten, bismuth, and rhenium, as well as conventional mineral resources including gold, copper, molybdenum, lead, zinc, and silver. The goal of this U-Pb isotopic study is to better understand the Devonian through Paleogene magmatic and tectonic events, which have been linked to most of the known mineralization in the Yukon-Tanana Uplands. The Mount Fairplay and Ladue River areas are characterized by amphibolite- to greenschist-facies metamorphic rocks-the Lake George assemblage, Ladue River unit, and the Klondike assemblage-which have Mississippian-Devonian and Permian protolith ages. Voluminous volcanic and plutonic rocks of varying composition and texture from the mid-Cretaceous (ca. 100-115 Ma), Late Cretaceous (ca. 65-71 Ma), and Paleogene (ca. 57-58 Ma) magmatic episodes were observed to be emplaced in both the Lake George and Ladue River metamorphic units. Alaska DGGS and the USGS staff have identified both generations of Cretaceous magmatism as having potential to host deposits of the critical minerals mentioned above. All components of this data release are available on the DGGS website: http://doi.org/10.14509/30732.
Zircon U-Pb age data, Alaska Highway Corridor, Tanacross and Nabesna quadrangles, Alaska
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Twenty-two igneous and metamorphic rock samples were collected in a 20-km-long swath centered on the Alaska Highway between Tetlin Junction, Alaska, and the Canada border. Igneous and metamorphic rock samples were submitted to the Apatite to Zircon, Inc. laboratory (A2Z), where zircon U-Pb age analysis, using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), was performed by Paul O'Sullivan. The 15 felsic plutonic rock samples and one gabbro sample yield Cretaceous zircon U-Pb weighted-mean ages ranging from 95.7 Ma to 106.2 Ma. Zircons from a metadiorite yield a Triassic weighted-mean age of about 241.9 Ma. Metamorphic zircons from two samples with felsic igneous protoliths yield Mississippian weighted-mean ages of 351.7 Ma and 354.6 Ma. Detrital zircons from two metaconglomerates yield individual grain ages from 100 Ma to 1,811 Ma, but are predominantly between 300 Ma and 345 Ma. Detrital zircons from a quartzite yield peaks at about 2,648 Ma, 1,946 Ma, and 1,807 Ma. Samples were analyzed for a variety of suites of major and trace elements depending on the sample type. The analytical data tables associated with this report are being released in digital format.
Zircon U-Pb age data, Ray Mountains area, Bettles Quadrangle, Alaska
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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.
U-Pb zircon age data from meta-igneous rocks in the Clearwater Mountains, Mount Hayes A-6 Quadrangle, Alaska
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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.
U-Pb Isotopic Data and Ages of Zircon and Titanite from Rocks from the Western Alaska Range, Northern Aleutian Range, Taylor Mountains, and Tikchik Mountains Regions, Alaska
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This data set contains U-Pb isotopic data and ages of zircon and titanite from igneous and metamorphic rocks collected from the western Alaska and northern Aleutian Range of south-central Alaska. The data sets also contain U-Pb isotopic data and ages of detrital zircon from sedimentary and metasedimentary rocks collected in the same region but also from the Taylor and Wood River Mountains of southwestern Alaska. The entire sample suite was collected as part of geological mapping and supporting geochemical and geochronological analysis conducted from 2004 to 2019 and funded by the Mineral Resources Program of the U.S. Geological Survey (USGS). Zircon and (or) titanite were obtained from igneous and metamorphic rocks to determine the crystallization age and (or) age of metamorphism for the bedrock samples. Bulk rock samples were processed into concentrated mineral separates in USGS laboratories in Denver, Colorado, or by Apatite to Zircon, Inc. (A2Z) and analyzed by USGS research scientists at the Stanford-USGS Sensitive High Resolution Ion Microprobe with Reverse-Geometry (SHRIMP-RG) at Stanford University. Detrital zircon grains were obtained from samples of sedimentary and metasedimentary rocks to determine depositional age and sediment sources. Detrital zircon grains were separated from bulk bedrock samples and analyzed at one of three different laboratories [University of British Columbia (UBC, 2004 to 2006), at A2Z (2006 to 2009), and GeoSep Services (GSS, 2015 to 2019)] using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques. The data tables accompanying this data release report the isotopic composition of uranium (U) and thorium (Th) measured in each grain, ratios of two isotopes of lead (207Pb and 206Pb) and two isotopes of uranium (235U and 238U), and the age of each grain. The SHRIMP-RG data table also reports concentrations of selected trace elements measured in each grain.
U-Pb Isotopic Data and Ages of Detrital Zircon from Selected Rocks from Southwestern Alaska and the Yukon-Tanana Upland and Environs of Eastern Interior Alaska and Eastern Yukon, Canada
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This dataset contains U-Pb isotopic data and associated ages of detrital zircon from sedimentary and metasedimentary rocks collected from southwestern Alaska and from the Yukon-Tanana upland and environs of eastern interior Alaska and western Yukon, Canada. The samples were collected as part of geological mapping and research conducted from 1996 to 2021 and funded by the Mineral Resources Program of the U.S. Geological Survey. Detrital zircon grains were separated and analyzed by four different laboratories: U.S. Geological Survey laboratories in Denver, Colorado; Apatite to Zircon, Inc. (A2Z); GeoSep Services (GSS); and the University of British Columbia. All analyses were conducted between 2007 and 2021 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques.
Zircon U-Pb results from the eastern Moran area, Tanana B-6 and Melozitna B-1 quadrangles, Alaska
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Raw Data File 2023-15,Zircon U-Pb results from the eastern Moran area, Tanana B-6 and Melozitna B-1 quadrangles, Alaska, Raw Data File 2023-15, U-Pb geochronologic data from 2011 DGGS field studies in the eastern Moran area. These dates were obtained as part of an integrated geological, geophysical, and geochemical mineral inventory study in the eastern Kokrines Hills near Moran Dome in the Tanana B-6 and Melozitna B-1 quadrangles. The project area is of historical and current interest for the potential development of mineral resources. The data are available from the DGGS website: http://doi.org/10.14509/31016.
U-Pb Isotopic Data and Ages of Zircon and Titanite from Rocks from the Yukon-Tanana Upland, Alaska
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This data set contains 3 tables containing uranium-lead (U-Pb) isotopic data and crystallization ages of zircon and titanite from igneous, metamorphic, and sedimentary rocks collected from the Yukon-Tanana upland of eastern interior Alaska between 2013 and 2019. Bulk samples of igneous and metamorphic rocks were processed into concentrated mineral separates of zircon and (or) titanite in USGS laboratories in Denver, Colorado, or by Apatite to Zircon, Inc. (A2Z) and analyzed by USGS research scientists at the Stanford-USGS Sensitive High Resolution Ion Microprobe with Reverse-Geometry (SHRIMP-RG) at Stanford University. Bulk samples of sedimentary and metasedimentary rocks were processed into concentrated mineral separates of detrital zircon and analyzed by Apatite to Zircon, Inc. and GeoSep Services (GSS) using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques. The 2 data tables (geology_detritalZircon_easternAK_Jones.csv; geology_SHRIMPRGData_easternAK_Jones.csv) accompanying this data release report the isotopic composition of uranium (U) and thorium (Th) measured in each grain, ratios of two isotopes of lead (207Pb and 206Pb) and two isotopes of uranium (235U and 238U), and the age of each grain. A third table (geology_sampleSummary_easternAK_Jones.csv) reports sample locations, rock characteristics, and interpreted ages. The SHRIMP-RG data table (geology_SHRIMPRGData_easternAK_Jones.csv) also reports concentrations of selected trace elements measured in each grain.
U-Pb geochronology of igneous and detrital zircon samples from the Tok River area, eastern Alaska Range, and Talkeetna Mountains, Alaska
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This Alaska Division of Geological & Geophysical Surveys (DGGS) Raw Data File presents U-Pb zircon geochronology results from igneous, meta-igneous, and metasedimentary rocks collected during the Tok River and Wrangellia geologic mapping projects in the eastern Alaska Range and the northwestern Talkeetna Mountains. The purpose of these analyses is to better constrain the age of select geologic units encountered during the mapping projects. The samples were submitted to the U.S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center (GGGSC)-Plasma Lab in Denver, CO where U-Pb geochronology analyses were performed by Christopher Holm-Denoma in 2016-2017. All files are available from the DGGS website: http://doi.org/10.14509/30439.
U-Pb detrital zircon geochronology of Cretaceous-Cenozoic sedimentary rocks in the Ladue River-Mount Fairplay area, Alaska
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This report presents U-Pb detrital zircon dates from three sedimentary rock samples collected in the eastern Tanacross Quadrangle during 2019 geologic mapping by the Alaska Division of Geological & Geophysical Surveys. This geologic map is published concurrently by Twelker and others (2021). The data were collected to support the map interpretation by establishing maximum depositional ages (MDAs) for the sampled strata. Further, these results also bolster a regional detrital zircon dataset that will, collectively, further constrain the Cretaceous-Cenozoic paleogeography of the region. This work is of economic and scientific interest: placer gold in the Fortymile District originated in Jurassic orogenic veins and, in some areas, was transported and concentrated by Cretaceous-Cenozoic depositional systems prior to its deposition in modern placer deposits. This process is described for the Coal Creek and Woodchopper Creek placers between Circle and Eagle and may be relevant elsewhere in the eastern Yukon Tanana Uplands. The analytical data tables associated with this report are available in digital format. Users can access the complete report and digital data from the DGGS website: http://doi.org/10.14509/30683.