The Fyre Lake volcanogenic massive sulphide (VMS) copper-cobalt-gold property is situated 160 kilometres northwest of Watson Lake in the Finlayson Lake area of the Yukon-Tanana Terrane. Columbia Gold Mines Ltd. conducted an integrated exploration program there between late June and early October, 1996. The Fyre Lake property is underlain by a sequence of metamorphosed sedimentary and volcanic rocks known as the Layered Metamorphic Sequence (LMS). Copper-cobalt-gold VMS mineralization within the Kona Creek cirque area is hosted by deformed and metamorphosed chlorite-actinolite-quartz schist of the middle unit of the LMS which is interpreted to be a succession of basic to possibly intermediate flows with intercalated volcaniclastics and volcanically-derived fine-grained sedimentary rocks. These rocks are structurally overlain by a thick sequence of phyllitic metasedimentary rocks with a basal unit of micaceous quartz-chlorite-mica schist. The copper-cobalt-gold (± zinc, silver) VMS mineralization within the central portion of the Kona deposit occurs in three distinct horizons of massive to semi-massive sulphide and magnetite mineralization over a combined thickness of 70 to 80 metres, a continuous strike length of more than 1,000 metres and widths in excess of 100 metres. The geological setting and mineralogy of the copper-cobalt-gold VMS mineralization within the Kona zone is that of a mafic, volcanic-hosted Besshi-type VMS deposit. The Fyre Lake contains copper-cobalt-gold mineralization with significant thickness, grade and continuity.

The Fyre Lake volcanic-hosted massive sulphide (VMS) deposit is located about 160 km northwest of Watson Lake in the Finlayson Lake district of southeastern Yukon. The deposit is hosted by Devonian (?) and Mississippian rocks of the Yukon-Tanana Terrane and occurs close to the contact between chlorite schist and overlying carbonaceous phyllite. Copper-cobalt-gold mineralization occurs in two parallel zones: West Kona and East Kona. The chemical composition and rare earth element (REE) pattern of chlorite schist which hosts the Kona zones is unique in the Fire Lake area. The data indicate that the protolith of these meta-volcanic rocks has a boninitic affinity and was likely derived from a depleted source region. Mafic meta-volcanic rocks (chlorite schist) elsewhere in this area are tholeiitic and may have developed in an arc or rift-related setting. Analyses of psammitic schists in the hanging wall of the West Kona zone indicate the rocks are felsic in composition and were likely deposited in a mature arc or continental-margin setting.

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Columbia Gold Mines Fyre Lake project is located immediately to the east of Fire Lake, approximately 160 km north of Watson Lake in the Yukon Territory. The 1997 program, consisting of 44 diamond drill holes, doubled the known size of the Kona deposit. Mineralization within the Kona deposit has a defined strike length of 1500 m and a width of 250 m. The Kona deposit is hosted within a strongly deformed and metamorphosed mafic to intermediate volcanic succession of chlorite-quartz and chlorite-actinolite-quartz schists. This volcanic package is overlain by a metasedimentary succession composed primarily of finely laminated carbonaceous phyllite that locally contains 1 to 20 m thick beds of micaceous volcanic-derived sediments. An intercalated unit of quartz-biotite schist and chlorite-mica-quartz schist marks the base of the metasedimentary succession. The Kona deposit consists of two parallel northwest trending zones of copper-cobalt-gold volcanogenic massive sulphide mineralization: East Kona and West Kona. East Kona is made up of two distinct horizons: the Upper Horizon and the Lower Horizon. The Upper Horizon occurs immediately below the contact of the metasediments and the metavolcanics while the Lower Horizon occurs 40 to 70 m deeper, within the mafic volcanics. The mineralization of East Kona consists primarily of pyrite with lesser amounts of pyrrhotite and chalcopyrite occurring as massive to banded sulphides with local lenses of massive magnetite. The mineralization across West Kona changes from magnetite, pyrite, and chalcopyrite hosted within a grey siliceous matrix in the east, or down dip, through massive pyrite and lesser chalcopyrite into massive pyrrhotite in the west. The mineralization of West Kona occurs immediately below the metasedimentary and metavolcanic contact; the same stratigraphic position as the Upper Horizon of East Kona. All of the mineralized zones that make up the Kona deposit have an eastern dip and plunge to the southeast. The Kona deposit, as defined to date, consists of a 15 million tonne mineralized container with the northern, near-surface portion amenable to open pit extraction. The last two holes of the 1997 program intersected mineralization 450 m along strike from previous drilling. The deposit remains open for expansion to the southeast.

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 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 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.

The Hunker Creek area is located 30 km southeast of Dawson City, Yukon. Gold and sulphide-bearing quartz veins (MINFILE 115O 067, 068) crosscut metamorphic rocks of the Klondike Schist. The veins are enclosed by envelopes of sericitic (inner) and propylitic (outer) alteration. Locally, carbonatization occurs between propylitized and sericitized rocks. Three stages of vein mineralization can be distinguished:: (1) quartz, carbonates, gold, arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and galena; (II) quartz, carbonates, chalcopyrite, sphalerite, tetrahedrite, freibergite, polybasite, 'polyargyrite', argentite, pyrostilbnite and galena; (III) quartz and gold. Fluid inclusion data indicate that stage I minerals precipitated from hydrothermal solutions containing CO2. Homogenization temperatures range from 260° to 390°C. Stage II aqueous fluid inclusions homogenize between 190° and 260°C. Stage III inclusions homogenize between 120° and 210°C. Salinities of the three stages range from 0 to 7.2 wt-% NaCl equiv. and show no significant changes with time. It is suggested that stage I mineralization was initiated by unmixing of an original single-phase H2O and CO2 bearing fluid, and that subsequent hydrothermal evolution was controlled mainly by decreasing temperature.

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.