The roles of rapid submarine volcanism and regional-scale basaltic underplating on the formation
of felsic-hosted volcanogenic massive sulfide (VMS) mineralization in the Finlayson Lake district, Yukon
January 27th, 2022
Matthew J. Manor
Ph.D. Candidate, Memorial University of Newfoundland
The Finlayson Lake volcanogenic massive sulfide (VMS) district contains >40 Mt of polymetallic
mineralization hosted by rocks that represent one of the first arc–back-arc systems along the western
Laurentian margin during the Late Devonian to Early Mississippian. Back-arc rocks contain many large-
tonnage and high-grade VMS deposits, including the felsic-hosted Kudz Ze Kayah, GP4F, and Wolverine
deposits. New high-precision chemical abrasion (CA)-ID-TIMS U-Pb zircon geochronological results
define the timing of back-arc–related rifting, felsic volcanism, and VMS mineralization in two continental
margin basins: 1) the Upper Devonian (ca. 363.4 to 362.3 Ma) Kudz Ze Kayah formation, which contains
the 1.5 Mt GP4F (ca. 363.4 Ma) and 18.1 Mt Kudz Ze Kayah (ca. 362.8 Ma) deposits; and 2) the Early
Mississippian (ca. 357.6 to 354.9 Ma) Wolverine Lake group, which hosts the 5.2 Mt Wolverine deposit
(ca. 355.2 Ma). Rapid depositional processes in these VMS-hosting basins are interpreted to have an
important role in developing highly porous and permeable, water saturated lithofacies that provide optimal
conditions for enhanced zone refining processes and subsequent preservation of massive sulfide
mineralization, which are key in 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 chemistry indicates that VMS-proximal magmas were hotter, less fractionated, and contained greater
juvenile melt contributions compared to VMS-distal magmas. These results indicate that high-temperature
back-arc felsic magmatism occurred at specific time periods coinciding with VMS deposits 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. Further applications of this multi-faceted analytical approach in other
convergent margins globally have the potential to vastly improve our understanding of ancient continental
margin volcanic processes and associated VMS mineralization in subaqueous environments.
A New Story Emerging in the Toodoggone: Lawyers Property, North-
Central BC
E. Laycock
The Lawyers Property, located in the Toodoggone district of north-central British Colombia is an
advanced stage Au-Ag exploration program with an indicated resource of 2.1 Moz Au equivalent. The
Au-Ag mineralization is hosted in a structurally controlled low-sulphidation epithermal deposit, located
within the prolific “Golden Horseshoe”; an arch of gold and polymetallic mineralization hosted in the
Stikinia terrain. In recent years, exploration has expanded in this district due to its favorable geology
with high discovery potential, existing infrastructure, and long history as a mining region.
The Lawyers deposit is broadly understood as a low sulfidation epithermal system which
manifests itself as narrow multiphasic breccia zones and vein sets with 20-30 m potassic alteration halos.
Recent exploration efforts have been focused on a two-prong approach of defining and expanding the
known historical mineralized zones of AGB, Cliff Creek and Dukes Ridge, and more recently expanding
into poorly understood exploration prospects with limited or no historical development. Recent
exploration results from the Lawyers property successfully demonstrate that there is property wide
mineralization along similar structural conduits that are responsible for the major mineralized zones of
the resource targets, lending itself to the larger potential of developing a major mining district with
significant expansion opportunities to the already well-defined deposits present on the Lawyers
Property.