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Evolution of Late Cretaceous Kasalka Group volcanics, Nechako Plateau, central British Columbia

University of British Columbia

As new mineral deposits located at or near-surface becomes exhausted, innovations in exploration are required to ensure the future supply of mineral resources. One of these innovations includes the examination of under-explored regions. The discovery and development of the Blackwater Au-Ag deposit has brought about renewed interest in the Nechako Plateau region. The mineralization at Blackwater is hosted in Late Cretaceous volcanic rocks, that are interpreted to be a part of the Kasalka Group. Historic work and mapping suggest that the Kasalka Group volcanic rocks crop out across the Nechako Plateau region, however, limited data is available for their timing and field descriptions bear strong similarities to other volcanic packages in the region. Furthermore, their context and association with mineralized deposits are limited to the areas immediately proximal to known deposits, and the respective impact on regional metallogeny is not constrained. Detailed and regional mapping, along with multi-faceted sample analyses has allowed for the identification and description of distinct lithologies of the Kasalka Group. High-precision geochronology confirms and identifies several pulses of Kasalka Group volcanism across the Nechako Plateau through Late Cretaceous time, between 82 and 63 Ma. Lithogeochemical characterization has also identified two main compositional groups: a trachyandesite intermediate suite and a high-silica felsic suite. Both compositions may be petrogenetically related, and are also geochemically distinct from older and younger volcanic packages in the region. Integration of age and geochemistry provides key insights to the tectonic setting and provenance of melts that produced the Kasalka Group volcanic rocks. A potential driving factor for Kasalka Group volcanism may be post-subduction melting in continental crust during middle to Late Cretaceous time, instead of a typical subduction-related arc configuration as observed through the Jurassic or along the Coast Plutonic Complex through Cretaceous to Eocene time. Post-subduction crustal thickening may induce melting and result in arc-like volcanic rocks in areas without active subduction or arc magmatism. Similarities to volcanic rocks produced in subduction-related arc settings may indicate that post-subduction magmatic processes in the Cordillera in British Columbia may serve a larger role in the tectono-magmatic evolution and mineral endowment than previous interpretations suggest.

Text

2020-08-27

Attribution-NoDerivatives 4.0 International

http://hdl.handle.net/2429/75734

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nd/4.0/