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.

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.

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Between the Cretaceous granitic rocks (Hake Batholith on the west; Cassiar Batholith to the east) are three belts of metamorphic rocks, collectively part of Yukon-Tanana terrane. These are remnants of oceanic and continental volcanic arcs, and marginal basin sediments of Early to mid-Paleozoic age. At the head of Borden Creek are thick carbonate and andesitic volcanic rocks correlated with Klinkit Group. The Ram Creek fault and Hidden Lake fault are not exposed but deduced to be steeply dipping brittle structures with northeastward thrust or transpressional offset, based upon more complete exposure to the southeast in 105B/3 map area. The former is likely of Cretaceous age; the latter was active between mid-Permian and Early Jurassic time.

The Rackla River area is underlain by normal faulted and gently folded sedimentary strata of the Paleoproterozoic Wernecke Supergroup, Mesoproterozoic Pinguicula Group, Neoproterozoic Hematite Creek Group and Windermere Supergroup, and Paleozoic Bouvette Formation. Gabbro dikes and sills that are likely age equivalent to the ca. 1380 Ma Hart River Sills cut the Wernecke Supergroup rocks. The presence of a mafic volcaniclastic horizon within the Bouvette allows its informal subdivision into a lower and upper member. These volcaniclastic rocks may the distal equivalent to volcanic rocks near the Tiger deposit, located ~20 km to the southwest. Three major angular unconformities are documented in the map area: at the base of the Rapitan Group, the base of the lower Bouvette, and the base of the upper Bouvette Formation.

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.

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.

Galena and pyrrhotite occur in manganese-stained quartz-carbonate breccia beneath rusty limestone. Surface geology of the area suggests that the mineralization is a replacement of brecciated limestone in the footwall of a low-angle fault. Results from previous exploration have proved disappointing but the host structure is probably regional in extent and larger deposits may exist along strike.

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.