Wernecke breccia comprises numerous intrusive hematitic breccia zones exposed in the Wernecke and Ogilvie mountains of central Yukon. The breccias were emplaced in Middle Proterozoic time into Middle Proterozoic strata of Wernecke Supergroup, Fifteenmile group, and possibly Pinguicula group. Significant mineralization of Cu, U, Co, Ag and Au within and near breccia zones occurred during widespread Fe, CO2, and Si metasomatism. Following a period of hydrothermal activity and intense fracturing, breccia zones in the study area were generated in open spaces produced by extensional faulting or rapid expansion of volatile-rich fluids. A strong spatial correlation between breccia and crosscutting mafic to felsic intrusions indicates a magmatic linkage. Metasomatism extended from before brecciation to after cooling of the igneous intrusions. The metasomatising fluids may have been partly derived from residual liquids of possible tholeiitic magma chambers fractionating at depth. Regional deformation and metamorphism incurred during Racklan orogeny in Middle Proterozoic time preceded brecciation; the breccias developed in fully lithified rock. Previous models of breccia genesis invoking evaporite or mud diapirism are considered invalid.

A group of hydrothermal breccias, collectively known as Wernecke breccia, formed at approximately 1.60 Ga in Yukon. The breccias consist of a hydrothermally precipitated matrix that cements clasts derived mainly from the metasedimentary Wernecke Supergroup. Locally, clasts and megaclasts of the Bonnet Plume River intrusions, the Slab volcanics, and other volcanic rocks are also present within the breccias. This paper describes a volcano-sedimentary succession interpreted as a megaclass within Wernecke breccia. The succession consists of pyroclastic and epiclastic rocks that formed in a volcanic environment in a region of evolved crust. This finding adds detail to the character of a postulated Proterozoic terrane that may have collided with the northwestern margin of ancestral North America toward the end of the Paleoproterozoic.

The 1.60 Ga hydrothermal Wernecke Breccia are hosted within metasedimentary rocks of the Wernecke Supergroup and exposed in the Wernecke, Ogilvie and southern Richardson Mountains of northern Yukon. Breccia clasts with soft sediment deformation textures were previously identified and interpreted as fragments of the Wernecke Supergroup that were torn off and carried upward during mud volcanism. This model was subsequently discounted because field relations and geochronology indicated that the Wernecke Supergroup was lithified and metamorphosed prior to brecciation. Our recent work confirms the presence of soft sediment within zones of Wernecke Breccia and demonstrates the need for an unlithified sediment source. Two types of soft sediment materials have been identified: red mudstone to sandstone, and green mudstone. These unlithified sediments were likely derived from late Paleoproterozoic water-saturated sediments. During breccia formation, the surface was breached and fragments of the unlithified sediments foundered into the breccia zones, mixing with clasts of lithified wallrock. The sediments descended to depths of at least 4 km where they were lithified and encased by hydrothermal cement. Subsequent erosion removed the source beds and exposed the breccia zones.

Ogilvie Mountains breccia (OMB) is in Early (?) to Late Proterozoic rocks of the Coal Creek Inlier, southern Ogilvie Mountains, Yukon. Host rocks are the Wernecke Supergroup (Fairchild Lake, Quartet and Gillespie Lake groups) and lower Fifteenmile group. Ogilvie Mountains breccia crops out discontinuously along two east-trending belts called the Northern Breccia Belt (NBB) and the Southern Breccia Belt (SBB). Individual bodies of OMB vary from dike and sill-like to pod-like. The NBB coincides with a north side down reverse fault—an inferred ruptured anticline—called the Monster fault. The SBB coincides with a north side down fault called the Fifteenmile fault. The age of OMB is constrained by field relationships and galena lead isotope data. The age of OMB formation is between 1.45 and 0.90 Ga. Hydrothermal alteration has locally overprinted OMB and introduced silica, hematite and sulphide minerals. Rare earth element chemistry reflects a lack of mantle or deep-seated igneous process in the formation of OMB. However, this may be only an apparent lack because flooding by a large volume of sedimentary material could obscure a REE pattern indicative of another source. This thesis is available online at https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0052352. This thesis is available at the EMR library – QE446.Y8 L36.

Tin and tungsten-bearing veins, breccias and skarns occur in a 60 km long belt trending west from Keno Hill to the Tintina Fault. They are hosted by mid-Cretaceous felsic intrusions, or adjacent metasedimentary rocks of Upper Precambrian to Mississippian age. Tin occurrences are mainly associated with two-mica granites in the southern part of the belt, while the tungsten lodes are more commonly associated with biotite-hornblende granitoids. Tin- and silver-bearing veins are associated with the central granite phase of a zoned intrusion in the northwest part of the belt (the Syenite Range). The zoned intrusion ranges in composition from tourmaline orbicular granite to granite to quartz monzonite to syenite. Most skarns are tungsten-dominant, whereas most breccias and veins are tin-bearing. The skarns are calcic and reduced. Three stages of skarn mineral formation and associated minerals are recognized:: 1) isochemical contact metamorphism, including diopside, grossular, wollastonite, and tremolite; 2) metasomatic skarn formation including andradite, idocrase, hedenbergite, axinite, and some sulphide minerals; and 3) retrograde alteration including actinolite, chlorite, clinozoisite, epidote, calcite, biotite, scheelite, cassiterite and sulphide minerals. Sulphide minerals are mostly minor, with pyrrhotite and pyrite predominant. Breccias, veins and sheeted veins of tin and tungsten occur in steeply diping tabular bodies close to felsic intrusions. The veins consist of quartz, tourmaline or chlorite. Tin-bearing veins and breccias contain all three gangue minerals plus pyrrhotite, pyrite, sphalerite, chalcopyrite, arsenopyrite and galena. Tungsten is only found in quartz (~orthoclase) veins which contain minor pyrite and molybdenite. Sheeted vein systems consist of three mineral assemblages:: 1)quartz-orthoclase-scheelite, 2) quartz-orthoclase-cassiterite, and 3) tourmaline-cassiterite. The first assemblage is present both in the endo- and exocontact of felsic intrusions, whereas the second and third occur further away from the granite in metasedimentary rocks which generally lie outside the thermal aureole of the intrusion. Breccia clasts consist of quartzite, schist, and/or vein fragments (quartz, tourmaline, or chlorite). The breccias are either clast-supported with a matrix of rock flour, or matrix-supported with a matrix (groundmass) of crystalline quartz, tourmaline or chlorite similar to vein material. Geochemical studies of the McQuesten River occurrences indicate that:: 1) Some properties are exclusively tin or tungsten properties, but others contain both metals. There is a positive correlation between tungsten and tin in some tin-bearing rocks. 2) Silver is common in veins and skarns which contain over 50 ppm Sn. 3) Gold occurs in significant quantities in most skarns and in several veins. 4) There is a positive correlation between gold and bismuth in the skarns. Bismuth can be used as a pathfinder for gold in these skarns.

Detailed vertical-face mapping of 'Slab Creek' was carried out in the summer of 2001 to evaluate the relations of Wernecke Breccia bodies with alteration, veining and iron oxide-copper-gold mineralization. Slab Creek is situated near the 'Slab' mineral occurrence in the Bonnet Plume River district of the Wernecke Mountains. Meta-sedimentary rocks in the area consist of meta-siltstone, meta-silty dolomite and phyllite of the lower succession of the Early Proterozoic Wernecke Supergroup, known as the Fairchild Lake Group. These rocks were folded and metamorphosed to lower greenschist facies, and were subsequently intruded by the Wernecke Breccias during the Mid Proterozoic. Three alteration zones can be recognized within Slab Creek, an inner feldspar zone coinciding with the large breccia bodies, surrounded by a chlorite-quartz-carbonate zone, grading outward into a sericite-chlorite zone. Alteration, veining and mineralization is most intense within the albite alteration zone where iron oxide-copper-gold (cobalt-uranium) mineralization is disseminated and occurs as vein infill.

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.

Mackenzie Mountains supergroup (MMSG) strata in the Wernecke Mountains are described in detail. Three new formations are assigned to the revised and formalized Hematite Creek Group, which forms the base of the MMSG. The Dolores Creek Formation (black mudrocks and microbial dolostone) is the basal unit of the MMSG. The Black Canyon Creek Formation (cyclic peritidal dolostone) and Tarn Lake Formation (desiccation-cracked, shallow-marine siltstone and sandstone) are probably equivalent to the ‘H1 unit’ and Tsezotene Formation in NWT, respectively. The Hematite Creek Group is overlain by the Katherine Group (thick quartz arenite-dominated succession). The highest MMSG strata documented belong to the Basinal assemblage (Little Dal Group). Regional thickness and lithofacies variations in two of the new formations suggest that the basin had considerable paleobathymetric variation that is not consistent with patterns established in NWT. The economic potential of the succession is unknown.

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.