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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.

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Stratigraphic and structural relationships within Stikinia, and overlap assemblages of the Whitehorse trough, are investigated in the Teslin Mountain area, southern Yukon. The Middle Triassic Joe Mountain Formation is dominated by a thick sequence of aphyric basalt produced by subaqueous volcanism. The Upper Triassic Lewes River Group displays complex lateral and vertical lithological and facies changes. It illustrates synvolcanic terrane exhumation, with erosion of the volcanic upland leading to deposition of thick volcaniclastic sequences, in parallel with ongoing clastic and carbonate sedimentation in marginal basins. Unravelling the Lewes River Group stratigraphy is critical in understanding the latest stages of Stikinia arc volcanism and the onset of Whitehorse trough marine sedimentation in the Early-Middle Jurassic. Further mapping and analytical work will focus at characterizing the Joe Mountain Formation and Lewes River Group, to determine how Stikinia evolved prior to final amalgamation of the Intermontane terranes with North America.

In this paper, we present a preliminary assessment of the lithogeochemical characteristics of meta-volcanic rocks in the Finlayson Lake region. Unit 2 mafic meta-volcanic rocks are subdivided into three suites: 1) low Ti tholeiites and boninites (suite 2a); 2) transitional (oceanic island basalt, OIB?), Light Rare Earth Element (LREE) -enriched tholeiites (suite 2b); and 3) normal mid-ocean ridge basalts (suite 2c; N-MORB). Suite 2a has similarities to rocks formed in ancient suprasubduction zone ophiolites and in forearcs in modern intraoceanic arcs. Unit 3 felsic meta-volcanic rocks comprise two subdivisions: 1) a low Eu/Eu*, Zr/Y, and Ce/Yb N suite (3a); and 2) a higher Eu/Eu*, Zr/Y and Ce/Yb N suite (3b). All unit 3 felsic meta-volcanic rocks have calc-alkalic continental arc signatures. Meta-basaltic rocks of the Campbell Range belt (CRB) fall into three suites: 1) moderately LREE enriched E-MORB type rocks (CRB 1 ); 2) LREE depleted N-MORB t ype rocks (CRB 2 ); and 3) a high Mg#, High Field Strength Elements (HFSE) and LREE-enriched tholeiitic suite (CRB 3 ). All CRB meta-basaltic rocks have features consistent with generation in an ocean basin and/or back-arc/marginal basin setting. The most prospective suites for volcanogenic massive sulphide mineralization in the Finlayson Lake region are 2a, 3a, and CRB 1 and CRB 2 .

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.

Paleozoic rocks of the Pelly Mountains, central Yukon, preserve greater than 150 m.y. of sedimentation, magmatism and base-metal mineralization. To identify secular trends in regional tectonics and metallogeny, a multi-year project on the stratigraphy of the Pelly Mountains in the Quiet Lake (105F) and Finlayson Lake (105G) map areas was initiated. Field studies during summer 2015 focused on two stratigraphic intervals: (1) mafic volcanic, volcaniclastic and clastic rock successions assigned to the Cambrian-Ordovician Cloutier and Groundhog formations (Kechika group); and (2) felsic volcanic, volcaniclastic and clastic rock successions assigned to the Devonian-Mississippian Black Slate and Felsic Volcanic formations (Seagull group). Cambrian-Ordovician strata were deposited in a marine environment characterized by episodic mafic volcanism and extensional tectonism. Devonian-Mississippian strata record the transition from an extensional turbidite basin to a metalliferous volcanic rift basin, and resemble key rock assemblages of the Selwyn basin (Earn Group) and Yukon-Tanana terrane (Grass Lakes and Wolverine Lake groups).

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The Finlayson Lake district in southeastern Yukon is a remnant of a Late Paleozoic arc–back-arc system that consists of metamorphosed volcanic, plutonic, and sedimentary rocks of the Yukon-Tanana and Slide Mountain terranes. These rocks host more than 40 Mt of polymetallic resources in numerous occurrences and styles of volcanogenic massive sulphide (VMS) mineralization. Geochemical data from these rocks support previous interpretations that volcanism and plutonism occurred in arc–marginal arc (e.g., Fire Lake formation) and continental back-arc basin environments (e.g., Kudz Ze Kayah formation, Wind Lake formation, and Wolverine Lake group) where felsic magmatism formed from varying mixtures of crust and mantle-derived material. The rocks have elevated high field strength element (HFSE) and rare earth element (REE) concentrations in VMS-proximal stratigraphy relative to VMS-barren assemblages, suggesting that the petrogenetic conditions that generated felsic rocks likely played a role in the localization of VMS mineralization. Future work aims to constrain magmatic processes and outline prospectivity criteria for delineating productive VMS assemblages within the district, and in similar geodynamic settings globally.