Petrology, Hf-Nd isotope geochemistry, and U-Pb geochronology of volcanogenic massive sulfide (VMS)-related felsic rocks and crustal evolution of the Northern Canadian Cordillera, Yukon

Manor, Matthew John (2022) Petrology, Hf-Nd isotope geochemistry, and U-Pb geochronology of volcanogenic massive sulfide (VMS)-related felsic rocks and crustal evolution of the Northern Canadian Cordillera, Yukon. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (295MB)

Abstract

The Yukon-Tanana terrane in the Finlayson Lake district, Yukon, represents one of the first arc–back-arc systems that formed adjacent to the western Laurentian continental margin in the mid- Paleozoic. Back-arc rocks contain many large-tonnage and high-grade volcanogenic massive sulfide (VMS) deposits, including the felsic-hosted Kudz Ze Kayah, GP4F, and Wolverine deposits. This study integrates field mapping with petrology, U-Pb zircon geochronology, and whole-rock and zircon geochemistry and tracer isotopes to establish precise controls on tectono-magmatic activity for the Late Devonian to Early Mississippian Laurentian continental margin and create new criteria to evaluate the role of magmatism in regional VMS genesis and its importance in mineral exploration. 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. Rapid depositional processes in the basins hosting VMS deposits (e.g., Kudz Ze Kayah formation and Wolverine Lake group) are interpreted to have had an important role in developing highly porous and permeable, water saturated lithofacies that provided optimal conditions for enhanced zone refining processes and subsequent preservation of massive sulfide mineralization, which are key features required for the development of high grade and large-tonnage VMS deposits. Geochemical and isotopic analysis of rocks in a refined chronostratigraphic framework indicates that VMS-proximal rocks have distinctly elevated high field strength element (HFSE), rare earth element (REE), Th, and Hf-Nd isotopic excursions relative to VMS-distal back-arc rocks and coeval arc assemblages. Further, zircon geochemistry indicates that VMS-proximal magmas were hotter, less fractionated, and contained greater contributions of mantle-derived (i.e., asthenospheric) juvenile melts compared to VMS-distal magmas. These results indicate that high-temperature back-arc felsic magmatism occurred at specific time periods coinciding with VMS deposit formation and supports previous genetic models for VMS mineralization that suggest elevated heat flow and hydrothermal circulation were due to regional-scale rift-related magmatism (i.e., basaltic underplating) rather than from local subvolcanic intrusions. This study underscores the importance of integrating mineral-scale petrology, geochemistry, and geochronology with traditional whole-rock methods to define the primary tectono-magmatic environments that generated VMS-related felsic rocks on the Laurentian continental margin, of which can be applied to VMS exploration in other orogenic belts globally.

Actions (login required)

View Item