Geochemical, isotopic and U-Pb dating studies of volcanic rocks of the Tlansanlin Formation in central Aishihik Lake map area (115H) show that these are Late Cretaceous (75.8 ± 0.4 Ma to 77.3 ± 1.3 Ma), relatively primitive magmas that were emplaced in a continental arc setting. Intrusive rocks in the immediate area, associated with the Hopper porphyry and skarn and Sato porphyry occurrences (Yukon MINFILE 115H 019, 021, respectively), are similar in age and composition to the Tlansanlin Formation rock units, confirming the presence of a significant Late Cretaceous igneous and mineralizing event in the area. Significant porphyry and skarn occurrences associated with the Late Cretaceous intrusions in the Aishihik Lake area, as well as the important mineral deposits and occurrences associated with this magmatic event in the Dawson Range to the northeast (e.g., Casino, Revenue-Nucleus, Sonora Gulch), underscore the metallogenic potential of this previously poorly recognized magmatic event.

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.

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.

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 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.

not_specified

This report presents the geochronology results for one sample from a Late Triassic Pyroxene Mountain pluton collected in the Mount Nansen area and analyzed for U-Pb zircon dating at Boise State University. These data complement the large dataset released in the Atlas of Sack et al. (2020).

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

This Atlas presents an extensive geoscience data set for the Late Triassic to Jurassic plutons that intrude the Intermontane terranes in Yukon. Plutons of this age are associated with significant porphyry Cu ± Au ± Mo deposits in British Columbia. In Yukon, Cu–Au–Ag deposits at Minto and Carmacks Copper are hosted by an Early Jurassic batholith but are not typical porphyry deposits. This project aims to provide the regional framework for Late Triassic to Jurassic plutons and associated mineral occurrences in southern Yukon. We systematically describe over 34 plutons and present new data for most of these, including 47 U-Pb zircon dates, 44 Ar-Ar dates, 187 whole-rock geochemical analyses, 30 whole-rock Sr and Nd isotope analyses, 27 feldspar Pb isotope analyses, zircon Hf isotope analyses for 22 samples and 26 pressure estimates from aluminum-in-hornblende analyses. Complementing these analytical data are extensive photomicrographs, photographs and maps.