Epithermal vein and porphyry-related gold-silver deposits in the Mount Nansen area are mainly hosted in Paleozoic Yukon-Tanana Terrane metasedimentary rocks and Early Jurassic Big Creek Batholith intrusive rocks. Mineralization is spatially, and probably temporally, related to a northwest-trending belt of mid-Cretaceous hypabyssal felsic intrusions and dykes along the Mount Nansen Trend. The proximal relationship between the veins and mid-Cretaceous intrusive rocks suggests that mineralization may be genetically related to felsic magmatism. The Dickson stock yields a U-Pb zircon age of 108.3 ± 0.7 Ma, and proximal dykes in the Flex, Dickson, Brown-McDade and Weber zones give ages of 107.9 ± 0.9 Ma to 109.0 ± 0.7 Ma, similar to the age of the Mount Nansen Group volcanic rocks. Granodiorite that hosts the Dickson deposit gives a U-Pb titanite age of 191.5 ± 2.9 Ma, and is likely part of the Big Creek Batholith. Previous studies indicated two periods of mineralization in the Dawson Range: mid-Cretaceous and Late Cretaceous. Dating indicates that Mount Nansen mineralization is associated with the mid-Cretaceous emplacement of the high-level felsic intrusions.

We report here the results of U-Pb zircon analyses for samples collected during regional mapping of the northern Whitehorse trough. Three samples of the Nordenskiold formation, a crystal-rich volcaniclastic unit that occurs at several stratigraphic horizons in the Laberge Group, yielded concordant U-Pb zircon ages of 188.1 ± 0.4 Ma, 187.2 ± 0.4 Ma and 186.5 ± 0.3 Ma, respectively. These results clearly indicate multiple eruptive events rather than recycling of the volcaniclastic material. Zircons from a thin layer of ash tuff in the Tanglefoot formation (Laberge Group) yielded a concordant U-Pb age of 187.1 ± 0.7 Ma, confirming correlation with the Nordenskiold formation. A sample of porphyritic granite from the only pluton intruding the northern Whitehorse trough, near Carmacks, yielded a concordant U-Pb zircon age of 112.8 ± 0.2 Ma, whereas a precise age could not be resolved from zircons extracted from a porphyry dyke intruding the Tantalus Formation in the southern Whitehorse trough.

Plutonic rocks of Early and mid-Cretaceous age are associated with tungsten-molybdenum porphyry and skarn-style mineralization in the Logtung area (Yukon MINFILE 105B 039, Deklerk and Traynor, 2005) in southwestern Wolf Lake map area (105B), and with tin-tungsten (-copper, lead, zinc) skarn mineralization at the Mindy and Ork occurrences (Yukon MINFILE 105C 038 and 054, respectively, Deklerk and Traynor, 2005) in the Thirtymile Range in eastern Teslin map area (105C). We have determined laser ablation U-Pb zircon ages of 109.4 ± 0.9 Ma and 110.5 ± 0.8 Ma for two samples of a biotite monzogranite stock that is inferred to be comagmatic with the felsic dyke system that partially hosts the Logtung mineralization. The latter sample is from the same locality from which a U-Pb zircon age of ~58 Ma was previously reported for zircons inferred to be hydrothermal in origin. Two separate phases of the Thirtymile Stock gave U-Pb ages of 102.7 ± 1.1 Ma and 100.9 ± 1.4 Ma.

for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

This data set contains U-Pb isotopic data and associated ages of detrital zircon from sedimentary and metasedimentary rocks collected in northern Yukon, Canada. The samples were originally collected as part of geological mapping and research conducted by the Geological Survey of Canada. They were recovered from archived collections and sent to the U.S. Geological Survey for analysis of detrital zircon using U-Pb geochronology methods. Detrital zircon grains were separated and analyzed by GeoSep Services (GSS) in 2015 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques.

This data set contains U-Pb isotopic data and associated ages of detrital zircon from sedimentary and metasedimentary rocks collected in northern Yukon, Canada. The samples were originally collected as part of geological mapping and research conducted by the Geological Survey of Canada. They were recovered from archived collections and sent to the U.S. Geological Survey for analysis of detrital zircon using U-Pb geochronology methods. Detrital zircon grains were separated and analyzed by GeoSep Services (GSS) in 2015 using laser-ablation-inductively-coupled-plasma-mass spectrometry (LA-ICP-MS) techniques.

The Yukon-Tanana terrane in Yukon, Canada, records Late Devonian (ca. 366–360 Ma) rifting and the onset of latest Devonian–Carboniferous arc and back-arc magmatism (ca. 360–325 Ma) in the Northern Cordillera. Detrital zircon U-Pb and Hf isotope analyses indicate that the metasedimentary basement of the Yukon-Tanana terrane was sourced in northwestern Laurentia. Sandstones in Late Devonian–Carboniferous successions generally have robust Late Devonian–Mississippian age peaks, and their Hf isotope signatures are characterized by strongly negative εHft values in Late Devonian zircons followed by progressively more juvenile εHft values in Carboniferous zircons. This Hf isotopic “pull-up” reflects the melting of Precambrian crust related to regional extension in the Late Devonian, followed by progressively more juvenile magmatism as the arc matured through the Carboniferous. Paleozoic rocks of the Tracy Arm terrane in southeastern Alaska, USA (formerly Yukon-Tanana south), have been compared with the Yukon-Tanana terrane in Yukon. Detrital zircons from the metasedimentary basement to the Tracy Arm terrane have distinct Precambrian populations that indicate sources along a different segment of the Laurentian margin compared to basement of the Yukon-Tanana terrane. Magmatism in the Tracy Arm terrane ranges from 440 Ma to 360 Ma and is characterized by an Hf isotopic “pull-down” in the Silurian to Early Devonian, followed by a “pull-up” in the Middle to Late Devonian and a second “pull-down” in the Late Devonian to early Mississippian. Thus, the Yukon-Tanana and Tracy Arm terranes record distinct pre-Carboniferous histories. Interactions between these two terranes are suggested by the influx of exotic early Mississippian clasts and detrital zircons on the Tracy Arm terrane that match sources in the Yukon-Tanana terrane. This paper is available via open access. You can also contact the Yukon Geological Survey (geology@gov.yk.ca) for a copy of this paper.

The Logan (MINFILE 105B 099) and YP (MINFILE 105B 001) zinc-lead-silver deposits are located in the Rancheria District, Yukon Territory. These deposits and numerous other occurrences occur in veins and breccia zones which cut clastic sedimentary rocks of Proterozoic and Palaeozoic age, along fracture zones cross-cutting Cretaceous granites and Eocene volcanic dykes of mafic and felsic composition, and form replacement bodies in Palaeozoic carbonates. At the Logan and YP deposits, four phases of mineralization can be distinguished. The main sulphide minerals are sphalerite, galena, pyrrhotite, pyrite, chalcopyrite and arsenopyrite. Silver is mostly confined to galena, but also occurs in tennantite-freibergite group minerals, stannite, Pb-Ag-Bi-sulphosalts of the matildite-galena series and lillianite homologues. Arsenopyrite geothermometry using the method of Kretschmar and Scott (1976) returned maximum formation temperatures of 465° - 490° C at YP and 335° - 385°C at Logan. Microthermometric investigations of fluid inclusions in quartz associated with the YP mineralization showed formation pressures corresponding to a depth of 2500 m. Fluid inclusion data from quartz suggest that mineralization at YP and Logan is caused by a mixture of magmatic and metamorphic fluids. The fluid inclusions have low salinities of 34 weight per cent NaCl equivalent, an unusally low value for fluids which have separated from acid magmas. The metamorphic fuids may have been derived from metamorphic dewatering of Palaeozoic sediments.

This dataset contains U-Pb isotopic data and associated ages of zircon grains from 27 sedimentary samples and one volcanic ash sample from the Cretaceous Torok and Nanushuk Formations. Seven samples were collected from outcrop and 21 samples were collected from archived core material from oil exploration wells on the North Slope of Arctic Alaska. Zircon grains were analyzed at the University of California, Santa Barbara (UCSB) between 2013 and 2018 using laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS) techniques. The study was funded by the Energy Resources Program of the U.S. Geological Survey (USGS).