AbstractThe Yukon-Tanana terrane in the Finlayson Lake district, Yukon, represents one of the first arc–back-arc systems that formed adjacent to the Laurentian continental margin in the mid-Paleozoic. Back-arc rocks contain many large and high-grade volcanogenic massive sulfide (VMS) deposits. This study integrates U-Pb zircon geochronology, lithogeochemistry, and Hf-Nd isotopes to establish precise controls on tectonomagmatic activity adjacent to the western Laurentian margin in the Late Devonian to Early Mississippian. High-precision chemical abrasion- (CA-) ID-TIMS U-Pb zircon geochronology defines coeval arc (ca. 363.1 to 348 Ma) and back-arc (ca. 363.3 to 355.0 Ma) magmatism in the Finlayson Lake district that intruded continental crust of Laurentian affinity (e.g., Snowcap assemblage). Mafic and felsic rocks display geochemical and isotopic characteristics that are consistent with being formed from mixtures of depleted asthenosphere and enriched lithospheric mantle sources. These melts variably entrained Laurentian continental crust via high-temperature crustal melting due to basaltic underplating. The high-temperature back-arc felsic magmatism occurs at specific time periods coinciding with VMS deposits and supports previous genetic models for VMS mineralization that suggest elevated heat flow and hydrothermal circulation were due to regional-scale rift-related magmatism rather than from local subvolcanic intrusions. The short timescales and transient nature of tectonomagmatic events in the Finlayson Lake district suggest that rapid and complex subduction initiation of oceanic and continental crust fragments facilitated coeval compression, extension, and magmatism in the arc and back-arc regions. We thus reevaluate the presently accepted tectonostratigraphic framework of the Finlayson Lake district and suggest revised interpretations that shed light on VMS depositional environments and a possible broader association with the ca. 358 Ma Antler Orogeny. Results of this study have implications for incipient tectonics, magmatism, and mineralization along the western Laurentian continental margin and other orogenic belts globally.

Comprehensive understanding of the pre-Paleogene kinematic evolution of the North American Cordillera in the context of evolving global plate interactions must begin with an understanding of the complex Late Cretaceous-early Eocene structural geometry and evolution of the northwestern Cordillera of Alaska, United States, and Yukon, Canada. Here, I present a kinematic model of the region that shows how regional strike-slip fault systems, including plate-boundary transform faults, interacted with each other, and with north-striking oroclinal folds and fold-and-thrust belts, which formed progressively during coeval shortening between Eurasia and North America. These Late Cretaceous-early Eocene interactions are manifestations of the plate reorganizations in the Pacific and Atlantic-Arctic regions that took place at that time, and that led to rifting and seafloor spreading within the globe-encircling Eurasian-North American plate and to the formation of transform-dominant North American-Pacific (sensu lato) and possibly North American-Arctic plate boundaries.

The Whitehorse trough is an Early to Middle Jurassic marine sedimentary basin that overlaps the Intermontane terranes in the northern Cordillera. Detrital zircon dates from eight Laberge Group sandstones from various parts of the trough all display a major Late Triassic–Early Jurassic peak (220–180 Ma) and a minor peak in the mid-Paleozoic (340–330 Ma), corresponding exactly with known igneous ages from areas surrounding the trough. Source regions generally have Early Jurassic (ca. 200–180 Ma) mica cooling dates, and the petrology of metamorphic rocks and Early Jurassic granitoid plutons flanking the trough suggests rapid exhumation during emplacement. These data suggest that subsidence and coarse clastic sedimentation in the trough occurred concurrently with rapid exhumation of the shoulders. Isolated occurrences of sandstone and conglomerate units with similar detrital zircon signatures occur west and east of the trough, as well as overlapping the Cache Creek terrane, indicating that either the trough was once more extensive, or isolated basins tapped similar sources. Development of these sedimentary basins and accompanying rapid exhumation in the northern Cordillera were coeval with the onset of orogenic activity in the hinterland of the southern Canadian Cordillera, and subsidence in the western Canada foreland sedimentary basin. The Whitehorse trough is interpreted as a forearc basin that progressively evolved into a collisional, synorogenic piggyback basin developed atop the nascent Cordilleran orogen. Upper Jurassic–Lower Cretaceous fluvial deposits overlapping the Whitehorse trough have detrital zircons that were mainly derived from recycling of the Laberge Group, but they also contain zircons exotic to the northern Intermontane terranes that are interpreted to reflect windblown detritus from the Late Jurassic–Early Cretaceous magmatic arc that developed either atop the approaching Insular terranes to the west or southern Stikinia.

In situ sensitive high-resolution ion microprobe monazite geochronology and garnet isopleth thermobarometry reveal a previously unrecognized Middle Jurassic to earliest Cretaceous mid-crustal tectono-metamorphic event in the eastern part of the Yukon-Tanana terrane (Finlayson Lake district, southeast Yukon) in the northern Canadian Cordillera. Intersection of garnet end-member compositional isopleths applied to single-stage, growth-zoned garnet records progressive garnet growth from 550 degrees C and 6.1-6.6 kbar to 600 degrees C and 7.5 kbar. Monazite textures, chemical zoning, and in situ U-Pb ages record a single protracted episode of monazite growth from ca. 169 to 142 Ma coeval with the development of transposition fabrics and the late stages of garnet growth. This event post-dates widespread Early Jurassic exhumation of Yukon-Tanana terrane rocks west of the Tintina fault in west-central Yukon, which were previously ductily deformed and metamorphosed in the Permo-Triassic. The lack of evidence for Permo-Triassic ductile deformation and high-grade metamorphism within the Finlayson Lake district, and its position east of the Permian arc center and west of Permian blueschists and eclogites, suggests this eastern part of the terrane occupied the cool forearc at this time. These data indicate younger, more protracted mid-crustal orogenesis in the northern Cordillera than was previously recognized, with deformation and metamorphism migrating toward the foreland and downwards in the Middle Jurassic to Early Cretaceous, in part contemporaneous with and analogous to that in the southeastern Canadian Cordillera.

Eikland Mountain chromitites, located in SW Yukon, Canada, comprise small layers and schlieren associated with almost fresh mantle peridotites. They have an homogeneous composition (#Cr 0.54 and TiO2 up to 0.62 wt%) and display an enrichment in PGE (2.4 ppm), especially in Rh+Pt+Pd. The following PGM have been found, accounting for these geochemical data: potarite, alloys in system Pt-Fe-Cu-Ni and rare sperrylite and irarsite. The PGM occur solely in the silicate matrix, in contact with the chromite grains, pentlandite and awaruite. These data suggest that the Eikland Mountain chromitites have no affinity with Uralian-Alaskan type complexes and therefore may not be considered the source of PGM nuggets previously reported from Yukon placer deposits. The investigated PGM probably crystallized because of the presence of alkaline-rich magmatic fluids.

The Slide Mountain terrane is part of a North American Cordillera-long backarc basinal assemblage that developed between the ensialic arc terranes (Yukon-Tanana and affiliated pericratonic terranes) and the North American craton in the middle to late Paleozoic. The Slide Mountain basin started to open in the Late Devonian, and spreading continued through the late Paleozoic in an oblique (transform-dominated) manner such that the pericratonic terranes were translated into southerly latitudes. The basin closed, also in an oblique manner, by the Early Triassic, resulting in the reaccretion of the Yukon-Tanana terrane to the northwestern Laurentian margin. Both the opening and closing likely involved hundreds to possibly thousands of kilometers of intra-ocean and/or intra-arc strike-slip displacement, sinistral during the ocean's Late Devonian to mid-Permian opening and dextral during its Late Permian closing.In southeastern Yukon, Canada, the Early Permian Slide Mountain terrane is dominated by mafic and ultramafic volcanic and plutonic rocks of the Campbell Range Formation. These rocks are narrowly distributed, for over 300 km, on either side of the Jules Creek-Vangorda fault, a fault that separates Slide Mountain terrane from Yukon-Tanana terrane. The Campbell Range basaltic volcanic and high-level intrusive rocks have geochemical and isotopic signatures that vary systematically across the Jules Creek-Vangorda fault: ocean-island basalt (OIB) and enriched mid-ocean ridge basalt (E-MORB) suites with lower epsilon Nd-t occur exclusively south of the fault, whereas north of the fault they have normal mid-ocean ridge basalt (N-MORB) and backarc basin basalt (BABB) signatures with higher epsilon Nd-t values. The epsilon Nd-t values are inversely correlated with Nb/Th-pm and Nb/La-pm, suggesting that the lower epsilon Nd-t values present in the E-MORB and OIB are mantle source features of these basalts and not due to continental crustal contamination. Isotopic and multi-element mixing calculations illustrate that the OIB-like basalts were derived primarily from enriched continental lithospheric mantle, whereas the N-MORB and BABB suites were sourced primarily from the upwelling backarc asthenospheric mantle; E-MORBs represent mixtures of depleted asthenospheric and enriched lithospheric mantle.The geochemical and isotopic variations in the Campbell Range Formation across the Jules Creek-Vangorda fault is attributed to formation in different parts of an extending continental-backarc basin and then their subsequent juxtaposition by continued displacement along the fault.Despite the juvenile isotopic signatures present in the Slide Mountain terrane, they occur as thin klippe atop rocks of recycled continental crustal affinity, suggesting that they were likely only minor contributors to Cordilleran crustal growth.

Porphyritic rhyolite sills form an important component of the footwall of the Wolverine volcanogenic massive sulfide (VMS) deposit, Yukon, Canada, and occur proximal to mineralization in the immediate deposit area (Wolverine/Lynx zone) and at similar stratigraphic levels along strike (Fisher, Puck, and Sable zones). Porphyritic rhyolites are of two types: an older quartz-feldspar porphyritic (QFP) rhyolite suite; and a younger feldspar porphyritic (FP) suite. Both the QFP and FP suites of intrusions are semiconcordant, suggesting a silllike morphology, and are altered and crosscut by veinlet mineralization, suggesting that they are pre- to synmineralization. The margins of QFP suite of intrusions contain minor xenoliths of surrounding shales and poorly developed chilled margins suggesting emplacement into partially consolidated sedimentary rocks, whereas the FP suite of intrusions shows well-developed chilled margins indicative of emplacement into fully solidified sedimentary rock. These features suggest that the QFP suite of intrusions represents an older phase of rhyolitic magmatism, whereas the FP suite represents a younger event. This is supported by U-Pb zircon ages, which indicate a 352.4 ± 1.5 Ma emplacement age for the FP suite and a ~347 to 346 Ma emplacement for the FP suite (two ages at 347.8 ± 1.3 and 346.0 ± 2.2 Ma). Both suites of porphyries have inherited Proterozoic zircon and have ratios of La/SmUCN ~1 and Nb/ThUCN ~1 (UCN ‐ upper continental crust normalized), indicating derivation from and/or extensive interaction with ancient upper continental crustal materials. The FP suite, however, has elevated high field strength element (HFSE) and rare earth element (REE) contents, high zircon saturation temperatures, and higher Nb/Ta ratios and lower Ti/Sc ratios than the QFP suite. These features are interpreted to reflect that the FP suite of magmas was hotter (>900°C) melts with a greater mantle component in their genesis. Both suites, however, are interpreted to have formed due to basaltic upwelling, crustal melting, and crust-mantle mixing during ensialic back-arc basin activity. The presence of mantle heat within the Wolverine basin from ~352 to ~347 to 346 Ma, a minimum of 5 m.y., suggests that sustained mantle heat flow was critical to the genesis of the Wolverine porphyries. It is also suggested that this sustained mantle heat was responsible for the Wolverine hydrothermal system and that upwelling mantle may be essential in providing the heat to drive hydrothermal systems even in continental margin-type VMS environments (e.g., Bathurst, Iberian pyrite belt). The Wolverine porphyries are among the most HFSE- and REE-enriched felsic rocks associated with VMS mineralization globally. The high HFSE and REE concentrations in these rocks are interpreted to be due to

Yukon–Tanana terrane in the southern Campbell Range is composed of rocks that have different metamorphic, exhumation, and structural histories, and that have formed in disparate parts of the Paleozoic Yukon–Tanana volcanic arc. The geological relationships in the southern Campbell Range reveal the tectonic and structural history of the Klatsa metamorphic complex, which represents the remnants of an Early Mississippian subduction zone beneath the Yukon–Tanana arc. The Klatsa metamorphic complex is composed of foliated to massive serpentinite, leucogabbro, amphibolite, and retrogressed eclogitic quartz–muscovite schist with lenses of metabasite. It was structurally juxtaposed on Upper Mississippian to Lower Permian metasedimentary rocks of the White Lake, King Arctic, and Money Creek formations. Regional and local structural and stratigraphic relationships suggest that the Klatsa metamorphic complex is part of the Cleaver Lake thrust sheet, the structurally highest thrust sheet in a north- to northeast-vergent thrust belt that deformed the Yukon–Tanana terrane during the Early Permian. Restoration of the displacement on the Cleaver Lake and underlying thrust faults places the Klatsa metamorphic complex on the western margin of Yukon–Tanana terrane. Late Devonian to Early Mississippian subduction is thought to have occurred along this margin based on previous paleogeographic reconstructions. Generally north- to northeast-vergent D1 to D3 folds deformed the Klatsa metamorphic complex and adjacent metasedimentary rocks. Jurassic(?) D4 imbricate thrust faulting has, in part, reactivated the Cleaver Lake thrust fault contacts and imbricated the Klatsa metamorphic complex with metasedimentary rocks in fault panels that are repeated at a scale of 10 to hundreds of metres.

In the 25 years since the first application of the terrane concept to the North American Cordillera and the introduction of the term “suspect,” a pattern of interterrane stratigraphic and intrusive linkages and shared isotopic and faunal elements has emerged. Far from being restricted to late, postamalgamation overlaps, these linkages can be as old as the oldest rocks within the terranes. In the Canadian Cordillera, these linkages give a coherent sense to terranes that otherwise might appear to be a collection of isolated and unrelated fragments. Such observed linkages effectively eliminate some of the paleogeographic uncertainties that were previously inferred between adjacent terranes (although not necessarily with respect to the Laurentian continent) and highlight their common history. In light of these relationships, it is now possible to interpret terranes of the Canadian Cordillera in terms of shared geodynamic scenarios, such as repeated arc superposition on older arcs and/or basement and coexisting arc system components. A primary result of this analysis is that the Intermontane terranes represent one interrelated set of arcs, marginal seas, and continental fragments that once formed a Paleozoic to early Mesozoic fringe to North America, the peri-Laurentian realm. By contrast, the Insular terranes, along with the Farewell and Arctic-Alaska terranes, include crustal fragments that originated from separate sites within the Arctic realm in Paleozoic time.

Rocks assigned to the Windy McKinley Terrane occur in Stevenson Ridge and Kluane map areas of western Yukon. Based on new mapping in Stevenson Ridge area, rocks mapped as Windy McKinley Terrane have been divided into three fault-bound assemblages: 1) a structurally lowest assemblage of muscovite-quartz schist, calcsilicate schist, and minor marble, carbonaceous quartzite and schist, pebble meta-conglomerate and granitic meta-plutonic rocks; 2) an imbricated ophiolitic assemblage of meta-chert, probably intrusive greenstone, leucogabbro, variably serpentinized dunite and harzburgite, and mafic greywacke; and 3) an assemblage of fine-grained clastic and calcareous rocks intruded and variably hornfelsed by voluminous Early Triassic (Mortensen and Israel, 2006) gabbro. Assemblage 1 probably correlates with Yukon-Tanana Terrane. Assemblage 2 more strongly resembles the Chulitna Terrane of Alaska rather than either the Windy or McKinley terranes as originally defined. Assemblage 3 resembles part of McKinley Terrane, as well as the Aurora Peak and Pingston terranes. These terrane re-assignments have implications for the area’s mineral potential.

The Finlayson Lake massive sulphide district of southeastern Yukon is underlain by variably deformed, metamorphosed and imbricated midto late Paleozoic rocks of Yukon-Tanana and Slide Mountain terranes and affiliated overlap assemblages. Yukon-Tanana terrane comprises three fault-bounded successions of Upper Devonian-Lower Mississippian metavolcanic and metaplutonic rocks that were deposited on a pre-Late Devonian ensialic basement in westor southData Repository items Murphy_Appendix1.pdf (Appendix 1) and Murphy_Appendix2.pdf (Appendix 2), are available on the CD-ROM in pocket.

The Fire Lake formation of the Yukon-Tanana terrane in the Finlayson Lake region, Yukon, Canada, consists primarily of Late Devonian (ca. 365-360 Ma) mafic metavolcanic rocks and smaller volumes of mafic and ultramafic subvolcanic metamorphosed intrusions. In this paper, field, geochemical, and Nd isotope attributes of these rocks are presented in an attempt to understand their tectonic setting, the magmatic processes involved in their formation, and their roles in Cordilleran crustal growth. The mafic rocks of the Fire Lake formation exhibit a wide diversity of geochemical signatures and are classified into seven chemically defined suites: (1) backarc-basin basalt, (2) enriched mid-oceanic-ridge basalt (E-MORB), (3) oceanic-island basalt (OIB), (4) Th-rich OIB, (5) boninite, (6) island-arc tholeiite, and (7) light rare earth element (LREE)-enriched island-are tholeiite. The diversity of geochemical signatures is interpreted to represent variable mixtures of asthenospheric (MORB-type) mantle, subarc mantle wedge, and lithospheric (OIB-type) mantle with or without elemental contributions from the subducted slab and/or continental crust. These suites of rocks are also associated with fine-grained basinal sedimentary facies, variations in metavolcanic and metasedimentary unit thickness, extensional synvolcanic faults, and apparent extensional-fault-controlled emplacement of mafic intrusive rocks and hydrothermal volcanic-hosted massive sulfide mineralization. The suites also exhibit a broad spatial distribution; those with "arc" signatures (Nb/Th-mn < 1; mn-normalized to primitive mantle values) are located primarily in the western parts of the formation, and suites with "nonarc" signatures (Nb/Th-mn < 1) are located primarily within the eastern parts of the formation. Collectively, these geologic and geochemical attributes are interpreted to stem from the transition from are magmatism to the initiation of an extensional backarc basinal environment associated with an east-dipping subduction zone.The initiation of backarc-basin magmatism recorded in the Fire Lake formation was part of a much larger Late Devonian backarc basinal system forming along the western edge of the margin of North America. The Fire Lake formation is interpreted to represent (1) the commencement of Yukon-Tanana arc rifting and separation from the North American cratonic margin, and (2) the initiation of a marginal (backarc) basin (now the Slide Mountain terrane) inboard of the Yukon-Tanana arc system. This tectonic evolution likely occurred either as a result of slab rollback toward the west within the convergent margin responsible for Yukon-Tanana arc activity or as a result of the propagation of the Slide Mountain backarc-basin spreading ridges into the Yukon-Tanana are system. This Yukon-Tanana arc rifting episode was also broadly coincident with rifting and hydrothermal activity within rocks of the North American craton.The geochemical and isotopic signatures of magmatic rocks in the Fire Lake formation have some features similar to intraoceanic arc rocks (e.g., boninites, island-arc tholeiites), and many have juvenile Nd isotope signatures (i.e., epsilon(Nd(t)) > 0; most have epsilon(Nd(t)) > +5), suggesting that the pericratonic terranes of the northern Cordillera have a significant juvenile component. If this is the case throughout the Yukon-Tanana terrane, then the pericratonic terranes may have contributed much more juvenile material to Cordilleran crustal growth in the Phanerozoic than has previously been considered.

This paper provides an integrated field and geochemical study of weakly alkalic, ~360 Ma mafic rocks from the Yukon–Tanana terrane in the Finlayson Lake region, southeastern Yukon. These mafic rocks occur as dykes and sills that crosscut older felsic metavolcanic rocks and metasedimentary rocks (Kudz Ze Kayah unit) or as flows interlayered with carbonaceous metasedimentary rocks. The mafic rocks have signatures similar to those of ocean-island basalts, moderate TiO2 and P2O5 contents, elevated high field strength element and light rare earth element contents, and εNd350 = +1.1. A subset of the dykes (group 4b) has similar geochemical characteristics but with higher Th/Nb and lower Nb/U ratios, higher Zr and light rare earth element contents, and εNd350 = –2.8. The geochemical and isotopic attributes of these rocks are consistent with formation from either lithospheric or asthenospheric sources during decompression melting of the mantle, with some rocks exhibiting evidence for crustal contamination (group 4b). The alkalic basalts are interpreted to represent ~360 Ma ensialic back-arc rifting and basin generation. It is envisioned that east-dipping subduction, represented by slightly older magmatic suites (Fire Lake unit), was disrupted by subduction hinge roll-back, westward migration of arc magmatism, and the onset of back-arc extension. Decompression melting of the mantle associated with back-arc generation resulted in mantle melting and the formation of the alkalic basalts. The spatial association of this mafic magmatism with crustally derived felsic volcanic rocks and contained volcanogenic massive sulphide mineralization suggests that the associated deposits (Kudz Ze Kayah, GP4F) formed within an ensialic back-arc environment.

En septembre 1998, un des auteurs (WW) a decouvert un indice important de mineralisation en emeraude dans la region du lac Finlayson, dans le secteur sud-est du Yukon. L'indice de Regal Ridge est situe dans les roches metavolcaniques deformees de facon complexe dans le socle de Yukon-Tanana, pres du contact avec un pluton granitique mis en place au cretace moyen. Les cristaux d'emeraude se sont developpes ou des veines de quartz recoupent des niveaux micaces de l'unite schisteuse tardidevonienne de Fire Lake, mafique et a faible pendage. Au moins huit veines semblables ont ete reperees. Dans la plupart des cas, les veines sont entourees d'une masse de petits cristaux enchevetres de tourmaline foncee. Leurs sont associes localement de petites quantites de scheelite, et, dans les veines elles-memes, des sulfures. Une zone de sulfures epars coinciderait avec la zone a tourmaline, marquee par des produits d'oxydation ochres. Des cristaux de beryl vert atteignent 4 cm en longueur dans les zones a tourmaline et, dans certains cas, les veines de quartz. Certains des plus petits cristaux, et des portions des plus gros, ont une qualite gemme. La teneur en Cr (moyenne 3208 ppm) en fait le chromophore principal. Les donnees sur les inclusions fluides indiquent que la phase fluide responsable de la mineralisation avait une salinite maximale equivalente a 3% de NaCl. La composition isotopique de l'oxygene de l'emeraude est tres variable (entre 12.3 et 14.8‰), mais sans variation comparable dans les valeurs de 8D correspondantes (-57.3 et -59.8‰, respectivement), ce qui suppose une phase fluide isotopiquement homogene qui a amorce un echange isotopique avec l'encaissant sans toutefois atteindre l'equilibre. Les valeurs de δ 1 8 O du quartz et de la tourmaline des veines de quartz indiquent une temperature de formation d'environ 365 et 498°C. A la lumiere des donnees isochores des inclusions fluides, ces temperatures correspondraient a une pression entre 1.0 et 2.5 kbar, et donc une profondeur entre 3 et 7.7 km. La proximite du granite fait penser qu'il etait la source du beryllium, quoique sa teneur en Be est assez faible (entre 12 et 13.2 ppm). La source du Cr est le schiste (520 ppm Cr). Un âge 4 0 Ar/ 3 9 Ar d'un echantillon de mica du schiste, 109 Ma, pourrait temoigner de l'âge d'un rechauffement lie a la mineralisation, ou bien un refroidissement suivant la mise en place du granite, ou les deux.

Mid-Paleozoic mafic rocks in the Finlayson Lake region of the Yukon-Tanana terrane, southeastern Yukon, Canada, have the diagnostic geochemical signatures of boninites: high MgO, Cr, Ni, and Co contents, intermediate SiO2 contents, high Mg#'s (MgO/ (MgO+FeO*), Al2O3/TiO2, and Zr(Hf)/middle rare earth element (REE) ratios; low TiO2, REE, and high-field-strength element contents; and U-shaped primitive mantle-normalized trace element patterns. However, unlike most modern and ancient boninitic rocks that are typically associated with intraoceanic realms, those from the Finlayson Lake region are part of a mid-Paleozoic continental margin arc-backarc magmatic system. We propose a model in which the boninitic rocks from the Finlayson Lake region formed as a result of spreading ridge propagation into an are built on composite basement of oceanic and continental crust. In the oceanic segment, upwelling asthenosphere induced melting of a subducted-slab metasomatized refractory mantle source to form boninitic magmatism. In the continental sector, upwelling asthenospheric mantle, and/or the melts derived thereof, induced crustal melting, which explains the large volume of temporally equivalent felsic volcanic and intrusive rocks.

The Finlayson Lake volcanic-hosted massive sulfide (VHMS) district represents one of Canada's most recent VHMS discovery regions with similar to34 million metric tons (Mt) of massive sulfide mineralization found since the mid 1990s, Felsic volcanic rocks are associated with three units: the Fire Lake unit, the Kudz Ze Kayah unit, and the Wolverine succession. Significant accumulations of polymetallic felsic VHMS deposits (Kudz Ze Kayah, GP4F, and Wolverine) have only been discovered in the Kudz Ze Kayah unit and Wolverine succession to date. In the hanging wall of the Money Creek thrust, felsic volcanic and high-level intrusive rocks in the Fire Lake unit have calc-alkalic and tholeiitic affinities with low high field strength element (HFSE) contents and intermediate Zr/Sc (9.4-43.4) and Zr/TiO2 (254-864) ratios, These rocks are interlayered with mafic rocks with are geochemical signatures, to date devoid of significant VHMS mineralization, and represent bimodal magmatism within air evolving, Devonian-Mississippian continental-arc system. The Kudz Ze Kayah unit in the foot-wall wall of the Money Creek thrust stratigraphically overlies the Fire Lake unit and consists of felsic volcanic rocks with high HFSE contents, within-plate (A-type) signatures and high Zr/Sc (15.3-190.3) and Zr/TiO2 (630-2,185) ratios, The Kudz Ze Kayah unit felsic rocks are crosscut and overlain by alkalic mafic rocks, are associated with abundant carbonaceous sedimentary rocks, and represent magmatism within a Devonian-Mississippian ensialic back-arc rift-basin environment. The Wolverine succession unconformably overlies the Kudz Ze Kayah unit. Felsic rocks below the Wolverine deposit have geochemical attributes similar to the Kudz Ze Kayah unit with high HFSE contents, within-plate (A-type) signatures, and high Zr/Sc (29.9-84.2) and Zr/TiO2 (391-1,220) ratios. In contrast, aphyric rhyolite flows in the hanging wall of the deposit have much lower HFSE contents and the lowest Zr/Sc (3.5-27.7) and Zr/TiO2 (181-591 ratios in the district. All the felsic rocks of the Wolverine succession are interlayered with abundant carbonaceous sedimentary rocks and are overlain by midocean ridge basalt (MORB)-like basaltic rocks, The Wolverine succession is interpreted to have formed within an Early Mississippian ensialic back-arc, basin environment that eventually evolved to sea-floor spreading.The variation in the HFSE budgets of the felsic rocks of the Finlayson Lake district likely reflects variations in the source and/or temperature of crustal melting. in particular, felsic rocks of the Fire Lake unit have higher Nb/Ta and lower Ti/Sc ratios than other volcanic rocks in the district, suggesting possible derivation from mafic crustal sources and/or lower crustal fusion temperatures, The Kudz Ze Kayah unit and footwall rocks to the Wolverine deposit arc, inferred to have formed from high-temperature partial melting of continental crust. The hanging-wall aphyric rhyolites from the Wolverine deposit may have formed from either lower temperature continental crust l melting or may have been derived from the mixing of HFSE-depleted N-MORB mafic magmas and evolved continental crust,Polymetallic felsic volcanic-associated, VHMS deposits within the Finlayson Lake district are preferentially associated with HFSE-enriched felsic rocks with high Zr/Sc (15.3-190.3) and Zr/TiO2 (391-2,105) ratios. The HFSE and rare earth element (REE) systematics of VHMS-associated felsic rocks of the Finlayson Lake district are different front prospective felsic rocks from Archean VHMS environments in the Superior province and are displaced toward higher Zr/Y and La/Yb-11 ratios. Their HFSE and REE systematics are similar to many Phanerozoic VHMS environments, in particular those at least partially to fully underlain by evolved continental crust. The geochemical differences between the felsic rocks of the Finlayson Lake district and those from Archean VHMS environments most likely reflect differences in the substrates front which the felsic rocks were derived (e.g., evolved versus juvenile).