The Yukon-Tanana Terrane (YTT) in the Finlayson Lake region (FLR), southeastern Yukon, Canada is host to five volcanic-hosted massive sulphide (VHMS) deposits (total -34 Mt) that have been discovered since the mid-1990's. In this thesis, field, lithogeochemical and Nd isotopic data are presented for felsic and mafic igneous rocks in the FLR to understand the tectonic setting, style of magmatism, and their relationships to VHMS mineralization. All rocks in the FLR were built upon a continental (or continent-derived) substrate of pre-Mississippian (>365 Ma) age. The Fire Lake unit (FLU) reflects Devonian-Mississippian (-365-360 Ma) arc and back-arc magmatism built upon a composite basement of oceanic and continental (or continent-derived) crust above an east-dipping subduction zone. Models proposed herein for the magmatic and tectonic evolution of FLU include: 1) arc magmatism punctuated by back-arc basin generation; 2) ridge propagation into an evolving arc with subsequent evolution to back-arc magmatism; and/or 3) ridge-subduction (slab-window) with eventual back-arc basin magmatism. The Kudz Ze Kayah (KZK) unit overlies the FLU and consists predominantly of crustally derived Devonian-Mississippian (-360-356 Ma) felsic volcanic and high-level subvolcanic rocks and variably carbonaceous sedimentary rocks; the latter are crosscut and overlain by alkalic mafic rocks. The high field strength element (HFSE)-enriched (A-type) felsic rocks and alkalic mafic rocks in the KZK unit are inferred to represent magmatism within an ensialic back-arc basin upon evolved crust. The Wolverine succession (WS) unconformably overlies the KZK unit and consists of a lower succession of felsic volcanic and subvolcanic rocks with carbonaceous sedimentary rocks; the upper portion of the succession, above the Wolverine VHMS deposit, consists predominantly of aphyric rhyolitic rocks that are overlain basalt flows. Felsic rocks ofthe WS are broadly similar to those in the KZK unit and represent ensialic back-arc basin magmatism. However, the succession is younger (-356-346 Ma), and post-dates a period of uplift, deformation, and erosion prior to commencement of back-arc magmatism. Back-arc spreading eventually evolved to true seafloor spreading within the WS. Massive sulphide deposits in the FLR are preferentially associated with rocks indicative of high temperature magmatism (e.g., boninites, A-type felsic rocks) and extensional tectonic activity (e.g., back-arc rifting and spreading).

The Marg (Cu-Zn-Pb-Au-Ag) volcanogenic massive sulphide deposit is hosted within metasedimentary and metavolcanic rocks of the Devonian-Mississippian Earn Group and Mississippian Keno Hill Quartzite. These rocks form part of the Selwyn Basin, an off-shelf sequence that developed at the continental margin prior to Cordilleran deformation and accretion. Geological mapping and re-analysis of drill core was completed to re-assess the deposit and property-scale economic potential. The Marg deposit is deformed by at least three generations of structures that developed during Late Jurassic to Early Cretaceous time and are geometrically correlative with regional-scale structures such as the Robert Service Thrust and the Tombstone strain zone. The Marg deposit occurs within a southeasterly plunging, complex fold structure, a significant part of which has been removed by erosion. Discovery of additional stratigraphy comparable to the Marg sequence and new sulphide occurrences within the claims underscores both property and regional exploration potential. The presence of probable rift-related volcanism and mineralization within the Selwyn Basin, and the similarities of this mineralization to that within 'suspect' terranes, has implications for both regional tectonics and exploration.

During the 2000 field season, a project was initiated to study the geology, geochemistry and alteration characteristics of high-level subvolcanic porphyritic intrusions associated with the Wolverine volcanic-hosted massive sulphide deposit in the Finlayson Lake district, Yukon. Subvolcanic porphyritic intrusions within the Wolverine deposit are located approximately 10-20 m beneath exhalative sulphide bodies or iron-formation in four zones (Wolverine/Lynx, Fisher, Sable and Puck). Most intrusions are K-feldspar porphyritic (Fisher and Wolverine/Lynx Zones); however, a few are quartz and K-feldspar porphyritic (Puck and Sable zones). Feldspar-porphyritic intrusions consist of euhedral to subhedral grains of K-feldspar in a grey fine-grained matrix. Quartz-feldspar porphyritic intrusions contain slightly smaller feldspar crystals and blue to black glassy quartz eyes set in a fine-grained matrix. Most of the intrusions have non-peperitic upper margins with carbonaceous argillite (Wolverine/Lynx, Fisher, Puck). Some of the quartz- feldspar porphyritic intrusions are in contact with fine-grained volcaniclastic rocks along their upper margins (Sable); both types of intrusions have lower contacts with fine-grained volcaniclastic sedimentary rocks. These intrusions are, for the most part, unaltered and have only minor sericite-silica ±chlorite ±pyrite alteration and small mm-to cm-scale veinlets of quartz-sericite ±chlorite ±pyrite ± sphalerite. This suggests a pre-to syn-mineralization timing for the emplacement of the intrusions. The contribution of these intrusions to the heat and metal budget of the Wolverine deposit is the focus of ongoing research.

Discovery of the volcanic-associated massive sulphide (VMS) Kudz Ze Kayah (KZK) deposit in 1994, closelyfollowed by the discovery of the Wolverine VMS deposit, resulted in a period of intense exploration activity in Yukon. This led to the discovery of additional VMS mineralization that includes GP4F, Ice and significant new reserves at Fyre Lake. Numerous VMS prospects were identified. The Fyre Lake, KZK, GP4F, Wolverine, and Ice VMS deposits are hosted by the Yukon-Tanana Terrane (YTT) in the Finlayson Lake district of southeastern Yukon. The Fyre Lake deposit (8 200 000 tonnes of 2.1% Cu and 0.73 g/t Au) is stratigraphically lowest and occurs in mafic metavolcanic rocks of the Devonian to Mississippian Grass Lakes succession. The KZK and GP4F deposits (13 000 000 tonnes of 5.5% Zn, 1% Cu, 1.3% Pb, 125 g/t Ag and 1.2 g/t Au and 1 500 000 tonnes of 6.4% Zn, 3.1% Pb, 0.1% Cu, 89.7 g/t Ag and 2.0 g/t Au, respectively) are within the Devonian to Mississippian succession but lie stratigraphically above Fyre Lake in felsic metavolcanic rocks. The Wolverine deposit (6 237 000 tonnes of 12.66% Zn, 1.33% Cu, 1.55% Pb, 370.9 g/t Ag and 1.76 g/t Au) is hosted by Carboniferous rhyolitic metavolcanic rocks and carbonaceous argillite of the Wolverine succession. The Ice deposit (4 561 863 tonnes of 1.48% Cu ) occurs highest in the stratigraphy and is hosted within late Palaeozoic mafic metavolcanic and associated metasedimentary rocks of the Campbell Range succession. The YTT underlies a large part of Yukon, east-central Alaska and parts of British Columbia. VMS mineralization occurs within rocks of the YTT in the Dawson and Glenlyon areas of Yukon, in the Teslin-Rancheria area in Yukon and adjacent British Columbia, and in several areas within Alaska, as well as in the Finlayson Lake area of the Yukon. In the Dawson area, which lays adjacent to the massive-sulphide-rich Finlayson Lake district (before approximately 425 km of right lateral movement on the Tintina Fault), VMS prospects are hosted in Late Devonian to mid-Mississippian Nasina Assemblage and Permian Klondike Schist. In the Glenlyon area, massive sulphide mineralization and chert horizons occur within a belt of rocks that is at least 20 km long. In the Teslin-Rancheria area and adjacent northern British Columbia, several VMS prospects have been identified. The Alaskan VMS occurrences are in the Delta, Bonnifield and Trident Glacier districts. Exploration during this period was not confined to the YTT but extended into rocks of the North American miogeocline that are coeval, and possibly correlative, with Devono-Mississippian strata of the YTT. This led to the discovery of additional resources at the Marg and Wolf VMS deposits. The Marg deposit (5 527 002 tonnes of 1.76% Cu, 2.46% Pb, 4.60% Zn, 62.7 g/t Ag and 1.0 g/t Au) occurs in the Selwyn Basin within a Devonian to Mississippian sequence of carbonaceous siliceous phyllite, quartz-muscovite and quartz-chlorite phyllite and massive quartzite. These strata also host the Jane prospect. The Wolf deposit (4.1 million tonnes of 6.2% Zn, 1.8% Pb and 84 g/t Ag) occurs in the Pelly-Cassiar Platform within the Devono-Mississippian Pelly Mountains volcanic belt and is hosted by felsic metavolcanic and associated metasedimentary rocks. Numerous other VMS prospects, including MM, occur throughout the length of this 80-km-long volcanic belt. The newly defined VMS deposits are comparable in size to the average Canadian VMS deposit indicating the discoveries are significant. Mineralization in the YTT occurs in Late Devonian to Permian strata thus there are several prospective horizons and the potential for additional discoveries is significant.

Upper Devonian and Lower Mississippian metavolcanic rocks of Yukon-Tanana Terrane in southern Finlayson Lake and Frances Lake map areas occur in three thrust sheets, locally modified by a Cretaceous normal fault. The lower thrust sheet, the Big Campbell sheet, comprises the Upper Devonian to Lower Mississippian metavolcanic stratigraphy that hosts the main volcanichosted massive sulphide (VHMS) deposits of the district. Metavolcanic rocks in the middle thrust sheet, the Money Creek sheet, include the Upper Devonian Waters Creek and Early Mississippian Tuchitua River formations. The former comprises primarily felsic metavolcanic rocks and carbonaceous phyllite and is extensively intruded by sheets of comagmatic porphyry. The latter comprises primarily intermediate metavolcanic, volcaniclastic and epiclastic rocks. The upper thrust sheet, the Cleaver Lake sheet, is in part made up of Late Devonian calc-alkaline basalt and rhyolite, the Cleaver Lake formation, and comagmatic felsic to ultramafic plutonic rocks. Of these, the Waters Creek formation and the formations in the Big Campbell sheet have the highest potential to host VHMS deposits.

Recent discoveries of at least two types of volcanogenic massive sulphide (VMS) deposits hosted in varying terranes have greatly expanded the mineral potential of the Yukon Territory. Kuroko style deposits at Kudz Ze Kayah and Wolverine are hosted by an Early Mississippian felsic metavolcanic and carbonaceous sedimentary package within the Yukon-Tanana Terrane in the Finlayson Lake area. The massive sulphide lenses at Wolverine have spectacular grades and constitute a geological resources, as of November 1996, of 5,311,000 tonnes with 1.81 g/t Au, 359.1 g/t Ag, 1.41% Cu, 1.53% Pb and 12.96% Zn. New discoveries at the Fyre Lake and Ice properties continue to expand the volcanic hosted massive sulphide potential of the Finlayson Lake area. Fyre Lake is a copper-cobalt-gold Besshi-type deposit hosted by chlorite schist. Towards the end of the season DDH 65 at Fyre Lake intersected 31.3 m of 2.29% Cu, 0.53 gpt Au and 0.07% Co. The enigmatic, ""Cyprus-type"", Ice occurrence has copper-cobalt mineralization in mafic volcanic rocks that are interpreted to belong to the Slide Mountain Terrane. The last hole of the season, DDH IC96-34 intersected 20.56 m of massive pyrite, chalcopyrite and bornite with grades of 5.2% Cu, 0.6 gpt Au, 25 gpt Ag and 0.6% Co. Prior to discovery of Ice, volcanic hosted massive sulphide mineralization was unknown in the Slide Mountain Terrane in the Yukon. The Yukon-Tanana and Slide Mountain Terranes are not restricted to the Finlayson Lake area but cover a considerable portion of the Yukon Territory. West of Dawson the Yukon-Tanana Terrane contains several exhalite occurrences in the Devono-Missisippian Nasina Assemblage and the Permian Klondike Schist. Devono-Mississippian strata in the Yukon-Tanana Terrane may correlate with similar aged units in the Pelly-Cassiar Platform and Selwyn Basin where there are several massive sulphide occurrences. The Marg Deposit occurs at the northern edge of the Selwyn Basin; the MM, Bnob and Chzerpnough properties are hosted by extension related, pyritic, brecciated, felsic metavolcanic rocks within the Pelly-Cassiar Platform. The Yukon-Tanana Terrane extends westward into the Delta District of Alaska where there are at least 26 stratiform and replacement massive sulphide deposits and occurrences. Strata potentially correlative with the Yukon-Tanana Terrane hosts several volcanogenic massive sulphide deposits and occurrences in northern British Columbia.

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The definition of regionally extensive stratigraphy in deformed and metamorphosed rocks of the Yukon-Tanana Terrane in the Finlayson Lake district allows the recognition of at least three mineralized horizons. They are:: a Lower horizon in chlorite schist of unit 2 close to the contact with overlying carbonaceous phyllite of unit 3; a Middle horizon in felsic meta-volcanic rocks of unit 3; and an Upper horizon in pillowed mafic volcanic rocks of the Campbell Range belt. The lower horizon hosts the Fyre Lake deposit. The Kudz Ze Kayah deposit and probably the deposits near Wolverine Lake are in the Middle horizon. The Upper horizon hosts the Money deposit.

Although deformed and metamorphosed, the strata hosting volcanogenic massive sulphide deposits in the Finlayson Lake district retain characteristics that suggest the influence of syn-depositional faults near the deposits. The Fyre Lake deposit occurs within a mafic schist unit near where notable changes in thickness, rock type and amount of comagmatic metaplutonic rocks occur. These changes occur across a north-northwest-striking corridor along which deposits and prospects in the overlying felsic metavolcanic schist are distributed (including Kudz Ze Kayah). Syn-volcanic, syn-mineralization faulting would explain the association of these deposits with the observed changes in host rock characteristics. Using similar arguments, syn-mineralization faults have been inferred on the Hat Trick property southwest of Fire Lake, as well as in Pennsylvanian and Permian rocks of the Campbell Range succession. Finally, stratigraphic differences between coeval rocks in the hanging wall and footwall of the Money Creek thrust imply that the thrust may have re-activated a syn-depositional structure. The regions of hanging wall and footwall cut-offs of the Money Creek thrust would therefore be considered as highly prospective for massive sulphide deposits.

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.