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.

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.

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.

The Paleoproterozoic Slab volcanics occur in three localities in the Wernecke Mountains. The largest exposure is at Slab Mountain and consists of a 0.6 x 0.25 km block of thin, steeply dipping mafic to intermediate lava flows. A zone of Wernecke Breccia (1.60 Ga), which crops out along the exposed margin of this volcanic block suggests that the megaclast foundered into the breccia zone from a higher crustal level. The volcanic rocks are typically aphyric. The groundmass consists mainly of laths of plagioclase (commonly altered to scapolite), anhedral biotite and magnetite. The scapolite, and possibly the biotite and magnetite, likely grew during hydrothermal alteration associated with Wernecke Breccia emplacement. Primary igneous mineralogy is uncertain. The Slab volcanics appear geochemically similar and are probably comagmatic with some of the 1.71 Ga Bonnet Plume River Intrusions. No correlative volcanic strata have been found in the Wernecke Mountains or in the neighbouring Ogilvie Mountains.

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.

Several centres of continental volcanism are situated in southern Yukon. Two of these, the Skukum Volcanic Complex and the Bennett Lake Cauldron Complex BLCC are closely associated in space and gross geological characteristics, including their important role as hosts for epithermal precious metal mineralization. The BLCC was studied extensively by Lambert and the Skukum complex is currently under investigation by the author. The Skukum complex was previously thought to represent a similar structural and volcanic setting to the BLCC. Study of the Skukum complex began in the summer of 1982 with the idea that it represented a cauldron subsidence feature and that an improved understanding of its geology would assist in developing potential targets for mineral exploration. The geology in the area is complex due to the discontinuous nature and incomplete exposure of volcanic units and is further complicated by severe faulting. The author found that the Skukum complex differs from the BLCC in three respects:: 1) the presence of a bimodal suite of extrusive rocks (which suggests the tapping of two magma chambers), 2) its structural complexity and the absence of major cauldron subsidence and 3) the variability of depositional environments within the complex. Contrary to past speculation, the two complexes, which have been considered to be closely related in time and space, each represent a distinctive structural and volcanic setting.

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.

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.

The Eocene Skukum volcanic complex, 60 km south-southwest of Whitehorse, is elliptical in plan, covers an area of about 140 km², and unconformably overlies Cretaceous granitic rocks and Precambrian metasedimentary rocks. The complex is fault-bounded and in places has been intruded by felsic dykes and stocks. A major north-trending fault divides the area into two parts: a western part which includes a lower interlayered sedimentary-volcanic sequence and an upper unit, approximately 500 m thick, characterized by andesite lava flows, pyroclastic flows and sedimentary units; and an eastern part which comprises about 800 m of altered felsic pyroclastic flows and brecciated, flow layered and spherulitic felsic lava flows. Study of the interlayered sedimentary-volcanic formation provides a control on the paleotopography of the Skukum area, and the depositional environment and provenance of the formation..

The 1.71 Ga Bonnet Plume River intrusions (BPRI) and related volcanics are preserved only as clasts in the 1.60 Ga Wernecke breccias of Yukon that host iron-oxide copper gold (IOCG) occurrences. Field work conducted in 2009 confirmed that they did not intrude the surrounding <1.64 Ga Wernecke Supergroup. Petrography shows that they are extensively altered and/or metasomatized, although relicts of primary igneous minerals remain. The major oxides are of little use in classification. Trace element geochemistry however, reveals a mafic to intermediate, calc-alkaline volcanic arc signature. Geochemical modelling has demonstrated that crystal fractionation was dominated by pyroxenes, plagioclase and olivine. The BPRI and related volcanic rocks are thought to have originated in a calc-alkaline volcanic arc that was obducted onto the Wernecke Supergroup, subsequently partially brecciated, and finally sank within the Wernecke breccias to the level of the Wernecke Supergroup.