High-Precision CA-ID-TIMS U-Pb Zircon Geochronology of Felsic Rocks in the Finlayson Lake VMS District, Yukon: Linking Paleozoic Basin-Scale Accumulation Rates to the Occurrence of Subseafloor Replacement-Style Mineralization

Abstract

Felsic igneous complexes and associated volcano-sedimentary rocks in continental back-arc environments host large-tonnage and/or high-grade volcanogenic massive sulfide (VMS) deposits. The emplacement mechanisms, style, and preservation of these deposits is thought to be partially dependent on depositional rates of the host lithofacies (i.e., discrete volcanic eruptions) relative to the setting of massive sulfide genesis on the seafloor as mounds and/or via subseafloor replacement of existing strata. The localization and occurrence of subseafloor replacement-style VMS deposits is therefore strongly influenced by the characteristics of the volcano-sedimentary facies in the hosting basin and the rates of their emplacement; the latter are poorly constrained in the literature due to the difficulty of obtaining high-precision dates that make this possible in Phanerozoic and older rocks. New high-resolution U-Pb geochronology and detailed regional stratigraphic investigation indicate that Devonian-Mississippian volcanic rocks and associated VMS mineralization in the Yukon-Tanana terrane in the Finlayson Lake district, Yukon, Canada, were erupted or emplaced during distinct time periods (ca. 363.3, 362.8, and 355.2 Ma) in two discrete submarine basins: the Kudz Ze Kayah formation and the Wolverine Lake group. The VMS deposits in both settings are contained within intrabasinal rocks that accumulated at rapid rates of ~350 to 2,000 m/m.y. over 0.6 to 1.4 m.y. Locally, these rates reach peak rates up to 7,500 m/m.y. in the Wolverine Lake group, which are interpreted to reflect facies deposition by mass transport complexes or turbidity currents. These new dates indicate that rapid accumulation of volcanic rocks in the back-arc basins was critical for localizing subseafloor replacement-style mineralization and the development of the Zn-enriched GP4F, Kudz Ze Kayah, and Wolverine VMS deposits. Rapid depositional processes observed in these deposits and their host basins are interpreted to have an important role in developing highly porous and permeable, water-saturated lithofacies that provide optimal conditions for enhancing zone refining processes and subsequent preservation of massive sulfide mineralization, which are key in the development of high-grade and large-tonnage VMS deposits. It is herein suggested that quantitative basin-scale accumulation rates, as a result of new U-Pb geochronological methods and increased precision combined with detailed stratigraphic and facies analysis, may provide important perspectives on the formation of continental back-arc basins and the localization of VMS deposits in other continental margin environments globally.

Age and Rate of Accumulation of Metal‐Rich Hydrothermal Deposits on the Seafloor: The Lucky Strike Vent Field, Mid‐Atlantic Ridge

“…Using these constraints, the Archean Kidd Creek deposit in Ontario, Canada, formed at a minimum rate of ∼170 t/yr (Bleeker & Parrish, 1996; Bleeker & van Breemen, 2011; Hannington et al., 2017). Similarly, calculated accumulation rates for deposits within the Devonian‐Mississippian Finlayson Lake VMS district in the Yukon Territory, Canada, include 75–800 t/yr for the Kudz Ze Kayah deposit, ∼8 t/yr for the GP4F deposit, and 40–200 t/yr for the Wolverine deposit (Manor et al., 2022). Therefore, although the lack of subseafloor data prevents direct comparisons between the modern seafloor and ancient deposits, the estimated accumulation rates from VMS deposits are comparable (within the same order of magnitude) to rates from the modern seafloor hydrothermal deposits.…”

Mineralogy and mineral chemistry of the ABM replacement-style volcanogenic massive sulfide deposit, Finlayson Lake district, Yukon, Canada

“…data) deposit is described as similar to the GP4F deposit (Boulton 2002 ). Subseafloor replacement is interpreted to be the primary mineralization style in all three deposits (Peter et al 2007 ; van Olden et al 2020 ; Denisová and Piercey 2022 ; Manor et al 2022a ). The ABM deposit is hosted by rocks formed at ca.…”

“…The deposit is located in the Finlayson Lake VMS district, Yukon, Canada, which contains > 40 Mt of polymetallic VMS mineralization with varying styles of deposits hosted by arc and back-arc rocks of the Yukon–Tanana and Slide Mountain terranes (Peter et al 2007 ). Following a drilling program in 2015, the massive sulfide mineralization at the ABM deposit was re-interpreted as replacement style based on lithofacies, textural, and structural studies (van Olden et al 2020 ; Denisová and Piercey 2022 ; Manor et al 2022a ). Previous work on the massive sulfide mineralization at the ABM deposit focused on the distribution and sources of Se (Layton-Matthews et al 2008 , 2013 ), but comprehensive research has not been presented on the mineralization facies, mineralogy, textures, metal residence, and genesis of the massive sulfide mineralization in the deposit.…”

“…The Fire Lake formation hosts the Kona Cu–Co–Au mafic–siliciclastic VMS deposit (Piercey et al 2001a ; Sebert et al 2004 ; Murphy et al 2006 ; Peter et al 2007 ). The Kudz Ze Kayah formation is interpreted to be coeval to the Fire Lake formation (Manor et al 2022b ); it comprises dominantly felsic volcanic and sedimentary rocks with back-arc geochemical affinities (Piercey et al 2001b ; Murphy et al 2006 ; Denisová and Piercey 2022 ; Manor et al 2022a ). The Wind Lake formation sits conformably atop the Kudz Ze Kayah formation (Piercey et al 2002 ).…”

“…The GP4F deposit is situated roughly 5 km SE from the ABM deposit (Fig. 1 ) and sits ~ 500–600 m stratigraphically below the ABM deposit (Peter et al 2007 ; Manor et al 2022a ). The R15 deposit occurs immediately along strike east of the GP4F deposit and occupies the same stratigraphic position (MacRobbie and Holroyd, unpub.…”