The geology in the Mount Nansen area, of the Dawson Range, comprises a metamorphic basement overlain and intruded by mid and Late Cretaceous magmatic rocks. Mid-Cretaceous epithermal deposits are recognized in the Brown-McDade cluster in the south, and Late Cretaceous porphyry and epithermal occurrences in the centrally located Klaza cluster. Here we report eight new U-Pb zircon crystallization ages, two CA-TIMS and six LA-ICPMS, and Pb isotopic data for igneous feldspar from six samples. A 199.06 ± 0.96 Ma crystallization age demonstrates the host rock to the Brown-McDade deposit is the Late Triassic to Early Jurassic Minto suite. We report crystallization ages of 111 ± 1.8 Ma for the Dickson Hill porphyry, 107.96 ± 0.03 and 107.86 ± 0.03 Ma for the central and border phases of the Bow Creek granite, respectively, and 107.0 ± 0.72, 107.0 ± 0.78 and 107.5 ± 0.67 Ma for equigranular and porphyritic phases of the Dawson Range granodiorite. These ages confirm a mid-Cretaceous Whitehorse suite affinity for these rocks with porphyritic textures suggesting high-level emplacement. Feldspar Pb isotopic data of igneous rocks in the Mount Nansen area become more radiogenic with time and are distinct for Late Triassic to Early Jurassic plutonic rocks versus Cretaceous rocks. Cretaceous feldspar isotopic data broadly overlaps Pb isotopic values of galena from deposits throughout the Dawson Range suggesting coeval magmatic rocks are a significant source of metals.

This dataset contains U-Pb isotopic data and associated ages of zircons within the lithologic framework of igneous, metaigneous, and metasedimentary rocks collected from the Seldovia quadrangle in southcentral Alaska. The samples were collected as part of geological mapping and research conducted from 2020 to 2023 and funded by the Mineral Resources Program of the U.S. Geological Survey. Zircon grains were separated and analyzed by GeoSep Services (GSS). All analyses were conducted between 2021 and 2023 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques. Also described in this report are the major and trace element geochemical analyses for samples collected as part of the mapping project. Analyses were conducted by ALS Global. Major elements were determined from fused bead, acid digestion, and ICP-AES analysis. Loss on ignition (LOI) was determined by furnace or TGA. Also included are rubidium (Rb), strontium (Sr), samarium (Sm), and neodymium (Nd) analyses conducted by the ALS Scandinavia laboratory in Lulea, Sweden. Samples were prepared by alkali fusion. Sr was separated using Sr-specific column (TrisKem). Nd was separated from matrix first as sum of REE using a AG50-x8 column (AlfaAesar) and then from Sm on a Ln column (TrisKem).

This dataset contains U-Pb isotopic data and associated ages of zircons within the lithologic framework of igneous, metaigneous, and metasedimentary rocks collected from the Seldovia quadrangle in southcentral Alaska. The samples were collected as part of geological mapping and research conducted from 2020 to 2023 and funded by the Mineral Resources Program of the U.S. Geological Survey. Zircon grains were separated and analyzed by GeoSep Services (GSS). All analyses were conducted between 2021 and 2023 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques. Also described in this report are the major and trace element geochemical analyses for samples collected as part of the mapping project. Analyses were conducted by ALS Global. Major elements were determined from fused bead, acid digestion, and ICP-AES analysis. Loss on ignition (LOI) was determined by furnace or TGA. Also included are rubidium (Rb), strontium (Sr), samarium (Sm), and neodymium (Nd) analyses conducted by the ALS Scandinavia laboratory in Lulea, Sweden. Samples were prepared by alkali fusion. Sr was separated using Sr-specific column (TrisKem). Nd was separated from matrix first as sum of REE using a AG50-x8 column (AlfaAesar) and then from Sm on a Ln column (TrisKem).

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Lower Paleozoic miogeoclinal calcareous rocks of the Cassiar Terrane are intruded by the Early Cretaceous Glenlyon Batholith. Garnet-biotite and garnet-muscovite-biotite-aluminum silicatequartz geothermobarometry on the intrusive wall rocks indicate metamorphism to lower amphibolite facies at temperatures of approximately 700°C and pressures of approximately 3 kbar. Progressive deformation, indicated by porphyroblast-matrix relationships, are interpreted to be a result of minor displacements of the country rock associated with and facilitated by intrusion of the Glenlyon Batholith, followed by static heating. Isolated skarn units exist along contacts between the batholith and its wall rocks. A skarn unit is also present along a nearby north-northeast-trending dextral strike-slip fault that predates and is intruded by the batholith.

New fieldwork investigating the provenance and stratigraphic setting of Triassic sedimentary rocks in the northern Cordillera focused on previously documented, but largely unstudied, exposures overlying the Yukon-Tanana, Slide Mountain and Cassiar terranes. We report on the lithologies observed and samples collected from the Sheldon Lake, Quiet Lake and Glenlyon map areas of Yukon, and McDame map area of northern British Columbia. Our research goal is to characterize sediment source regions in the Triassic and constrain early Mesozoic basin development in the northern Cordillera. We interpret the Triassic sedimentary evolution in Yukon and northern British Columbia to be intimately tied to collision of the Yukon-Tanana terrane with the ancient Pacific margin by closing of the Slide Mountain ocean. Our new samples collected from Middle to Late Triassic strata will further constrain that collisional event and add to the database that consists mainly of Early to Middle Triassic miogeoclinal rocks.

Two distinct but undeformed suites of granitic plutons intrude deformed siliciclastic rocks in western Dorsey Terrane. A calc-alkaline hornblende-bearing gabbro to granodiorite stock has been dated at 181.5 Ma (by the Rb/Sr method). The second suite consists of highly evolved late-orogenic granites of the Thirtymile stock and Hake Batholith, which are approximately 100 Ma. The penetrative fabric of the metasedimentary rocks indicates generally eastward-vergent layer-parallel shear. The deformation of the siliciclastic rocks is thus constrained at older than 181 Ma. The absence of resetting of the Rb-Sr isotopic ratios of the Jurassic pluton indicates that the mid-Cretaceous magmatism was emplaced at a shallow crustal depth. Since the Jurassic pluton has both a 'juvenile' Sr isotopic ratio of 0.7045 and chemistry indicative of a largely mantle-derived source, a subduction-related setting for magma generation is likely. The spatial relationship of craton-derived clastic rocks and these plutons requires that subduction had an eastward polarity.

We present new field and U-Pb analytical data from the Sonora Gulch Project that demonstrate a protracted history of polymetallic mineralization (Au-Ag-Cu-Zn ± Mo) associated with several pulses of Cretaceous magmatism. Recent exploration on the Sonora Gulch Project has highlighted the presence of two important mineralized zones: the Nightmusic zone, a mesothermal Au-enriched base metal skarn, and the Amadeus zone, an epithermal Au-Ag system. Four U-Pb age dates determined from each of two feldspar porphyry dykes (ca. 74 Ma), a weakly mineralized quartz porphyry stock (ca. 75 Ma) within the Nightmusic zone and the Au-Ag mineralized Amadeus stock (ca. 75 Ma), demonstrate the widespread occurrence of Late Cretaceous magmatism. The age determinations indicate that mineralization occurring within the Sonora Gulch project area are temporally equivalent to the Casino Cu-Au-Mo deposit, located roughly 40 km to the west-northwest. These new data extend the currently known eastern limit of Late Cretaceous magmatism and associated mineralization.

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The Tummel fault zone, a northwest-trending belt of rocks of uncertain age and/or tectonic affinity, separates Paleozoic miogeoclinal strata of Cassiar Terrane from Yukon-Tanana Terrane metavolcanic and metasedimentary rocks. Northeast of the fault, Cassiar Terrane comprises pelitic and semipelitic rocks with rare amphibolite, which are correlated with the Kechika Group. These are overlain by carbonate correlated with the Askin Group. Southwest of the fault, in Yukon-Tanana Terrane, Devono-Mississippian siliciclastic rocks are overlain by Mississippian arc volcanic rocks. Granodiorite and diorite of the Telegraph Plutonic Suite (348-350 Ma) intrude the siliciclastic rocks. Foliated greenstone, leucogabbro intrusions, serpentinite and chert occur in the Tummel fault zone. The Early Cretaceous Glenlyon Batholith intrudes strata of Cassiar Terrane. Contact metamorphism recognized across the Tummel fault zone is interpreted to have been imposed by the Glenlyon Batholith. If correct, this interpretation requires that post-mid-Cretaceous displacement across the Tummel fault zone has been minimal (~5 km).