The Paleoproterozoic Wernecke Supergroup is a >13 km-thick metasedimentary succession exposed in the Wernecke, Ogilvie and Richardson mountains of central and northern Yukon. A program of field and laboratory investigations was initiated in 2007 in order to constrain the provenance, age and environment of deposition of the Wernecke Supergroup, as well as to better constrain the age of subsequent Proterozoic deformation (Racklan orogeny). Clastic and carbonate samples were collected from the Wernecke Supergroup for analysis of detrital and metamorphic minerals, as well as whole rocks, using a range of isotopic methods. Preliminary results from U-Pb analysis of detrital zircons from quartz sandstone beds, using ion probe mass spectrometry, are provided in this report. Patterns of the detrital zircon ages are broadly comparable to other Paleo- to Mesoproterozoic basins in Canada, suggesting a common Laurentian source. The maximum age of the Supergroup of 1.61 ± 0.03 Ga is provided by the age of the youngest detrital grain, which is ~0.1 Ga younger than expected.

This interim report has reviewed stratigraphic characteristics of the lowermost succession of Proterozoic rocks exposed in the northern Wernecke Mountains. This sequence of rocks, which is in excess of 13 km thick, is named the Wernecke Supergroup. The Wernecke Supergroup is composed of three groups which from oldest to youngest are given the informal names Fairchild Lake Group, Quartet Group and Gillespie Lake Group. Several tentative subdivisions of formational status have been described in each of these groups. The Fairchild Lake Group is composed of at least 4 km of generally light grey weathering siltstones, slates and argillites. It is divided into four formations, two of which contain carbonate members:: one formation near the middle of the group, contains ribbed weathering, thinly bedded, siltstone-limestone rhythmites; the other formation at the top of the group consists of interbedded shaly siltstone and dolostone with a distinctive white weathering limestone marker horizon. The Quartet Group, which conformably overlies the Fairchild Lake Group, consists of up to 5 km of monotonous dark grey weathering siltstone, argillite and slate with minor sandstone. The Quartet Group is transitional into the overlying Gillespie Lake Group which is compposed of at least 4 km buff to orange to locally grey weathering dolostone with minor siltstone and sandstone. Metamorphism, faulting, complex folds, the monotonous and cyclical nature of stratigraphy, the lack of distinctive marker horizons and the possibility of facies changes have greatly hindered attempts at stratigraphic reconstruction in rocks of the Wernecke Supergroup. Thus much of the stratigraphic detail within the groups must be considered tentative in nature. Field investigations to be undertaken during the summer of 1978 will help further refine the stratigraphic relationships outlined above. An Appendix to this report contains 19 representative stratigraphic sections which illustrate the main features of these rocks and a 1::250 000 location map showing where the sections are from.

Three events of Paleoproterozoic deformation are recognized in schist of the Fairchild Lake Group (Wernecke Supergroup) in the Wernecke Mountains. The first event produced a chloritoid ± garnet and opaque porphyroblastic, chloritoid-chlorite-muscovite-quartz schist. Pressure-temperature conditions have been estimated to lie between 3-6 kbar and 450-550°C. The second event produced a crenulation, and the third generated kink bands. All of these features are crosscut by 1.60 Ga Wernecke Breccia. These events are regarded as products of the Racklan Orogeny, a Paleoproterozoic interval of orogenesis, which favourably correlates with the Fifteenmile Orogeny in the Ogilvie Mountains of western Yukon and the Forward Orogeny in the Northwest Territories.

The Early Cambrian Quartet Mountain lamprophyres are volatile-rich ultramafic alkaline dikes that crosscut the Wernecke and Mackenzie mountains supergroups in the Wernecke Mountains of northern Yukon. Their emplacement may have been triggered by Early Paleozoic extension of the Cordilleran miogeocline. Numerous small-volume alkalic igneous rocks that range in age from Cambrian to Devonian occur elsewhere in the miogeocline and may reflect a similar tectonic setting. The Quartet Mountain lamprophyres contain phenocrysts of phlogopite ± diopside ± olivine within a dark-grey aphanitic groundmass and were likely generated by low-percentage melting of mantle at depths >90 km. One of the lamprophyres contains abundant pseudomorphed olivine xenocrysts and xenoliths of inferred crustal and mantle affinities. Although this dike resembles kimberlite because of its abundance of mantle xenoliths and xenocrysts and its ultramafic composition, it differs from kimberlite in its abundance of phlogopite phenocrysts. It is best described as an ultramafic lamprophyre with kimberlitic affinity. The lamprophyres have modest potential to host diamonds.

Mafic volcanic and clastic strata of the Middle Triassic Joe Mountain Formation, east of Lake Laberge, Yukon, represent a juvenile volcanic arc sequence. Mafic volcanic rocks of the Upper Triassic Lewes River Group were formed in the spatial and temporal continuity of Joe Mountain volcanism. Carbonate sedimentation took place in shallow oceanic subbasins adjacent to the arc from the Carnian to Rhaetian; these subbasins were separated by physiographic boundaries inherent to the arc, resulting in lateral stratigraphic variations. Polymictic conglomerate and turbiditic sequences of the Lower-Middle Jurassic Laberge Group unconformably overlie Triassic rocks. Two north-northwest strike-slip faults, the Laurier Creek and the Goddard, control the distribution of units. Joe Mountain Formation rocks are characterized by an east-west structural trend, whereas the Upper Triassic and Jurassic sequences are characterized by north-northwest trending tight folds and thrust faults. At least five post-accretion igneous suites intrude or overlie older stratigraphy, including the Late Cretaceous Open Creek volcanic complex.

Mica-quartz schist and olivine serpentinites form the Kluane metamorphic assemblage, a 150-km-long belt that is wedged between the Yukon-Tanana Terrane and the Insular Superterrane in the northern Coast Belt. The olivine serpentinites are serpentinized dunites that occur as lens-shaped bodies, interlayered along strike, with the mica-quartz schist. The larger ultramafic bodies developed a foliation and shear sense that is similarly oriented to those in the adjacent schist, suggesting 'Alpine-type' emplacement. Tectonic juxtaposition of schist and ultramafic rocks occurred during collapse and subduction of a back-arc basin underneath the North American continental margin in the Late Cretaceous. Oxygen isotope analyses point to values similar to known ophiolitic serpentinites. The ultramafic rocks are interpreted to be part of an oceanic crust that formed topographic highs during subduction and were subsequently sheared off and tectonically interleaved with metasedimentary rocks during the accretionary process.

The "Wernecke Breccias" are enigmatic, but significant features of the Middle Proterozoic Wernecke Supergroup in the Wernecke and Ogilvie Mountains. This report describes the breccias near Quartet Mountain and the Igor prospect in the Wernecke Mountains. Widespread, pervasive metasomatism and greenschist facies metamorphism of both the breccias and wall rocks is demonstrated by the development of chlorite, calcite, dolomite, siderite, albite, hematite, sericite, biotite and quartz. Altered fragments are multicoloured and give the appearance that they are transported, and exotic, but all are locally derived. Structures in relatively unaltered breccias suggest that brecciation was accompanied by mylonitization and faulting. Repeated brecciation, metasomatism, and faulting characterize development of the breccias. Small gabbro and diabase dykes and sills are associated with the breccias. The breccias contain numersouss, small occurrences of copper, iron, barium, molybdenum, uranium, cobalt, gold, and silver. Crustal extension and detachment faulting, and large buried intrusions beneath the breccias are suggested as possible genetic mechanisms.

Studies of biogeochemical and evolutionary change in the Neoproterozoic require a detailed understanding of stratigraphic successions and their intrabasinal correlation to integrate those records into regional and global frameworks. The early Neoproterozoic Fifteenmile Group in the Ogilvie Mountains has previously been shown to archive important information on the evolution of the biosphere, including ocean redox and early evolution of eukaryotes. Here, we formally define the Chandindu Formation, a 150 to 420-m-thick siltstone-dominated mixed carbonate-siliciclastic succession of the lower Fifteenmile Group in the Coal Creek and Hart River inliers. We present ten sections of the Chandindu Formation and propose a type section and formalization to promote the development of a consistent stratigraphic framework for Proterozoic successions in northwest Canada.The Chandindu Formation begins with muddy tidal flat facies, which are succeeded by shale-siltstone-sandstone coarsening-upward cycles deposited in a predominantly subtidal environment. However, carbonate occurrences throughout the entire unit suggest localized carbonate buildups, likely nucleated on fault-bound paleohighs where siliciclastic background sedimentation was low. These paleohighs originated from rift-inherited complex basin topography and syn-depositional faulting during deposition of the upper Chandindu Formation.

The Joe Mountain area of the Yukon contains Middle Triassic to Upper Triassic volcanic, sedimentary and intrusive rocks of the Stikine Terrane. The Ladinian (~237 to 228 Ma) rocks of the Joe Mountain Formation of Stikinia are divided into four units, including: 1) a lowermost mafic-ultramafic complex (mTJM4); 2) a lower basalt-flow-dominated unit (mTJM3); 3) a volcaniclastic- and sedimentary-rockdominated unit; and 4) and uppermost unit of black pillow basalts and volcaniclastic rocks (mTJM4). In the Joe Mountain Formation there is a general increase in the abundance of volcaniclastic and sedimentary material, and a decrease in flow material, away from Joe Mountain suggesting that Joe Mountain is a volcanic centre. Hematite-magnetite iron formation was discovered in 2004 interlayered with unit mTJM3 basalts. These iron formations have anomalous metal concentrations, but more importantly, have hydrothermal geochemical signatures (e.g., high Fe/Al ratios) similar to volcanogenic massive sulphide-associated iron formations globally.