Nicole Schoenherr, BSc

Hydrothermal alteration in volcanogenic massive sulfide (VMS) deposits arises from the interaction of upwelling fluids with host lithofacies, driving geochemical and mineralogical changes that result in zoned alteration halos surrounding mineralization. The Snow Lake camp hosts numerous VMS deposits with economically significant endowments of critical metals. These deposits formed during a single time-stratigraphic ore interval coinciding with contemporaneous volcanism, leading to the stratabound accumulation of sulfide minerals in gently NNE-dipping ore lenses enriched in Zn, Au, and Cu. The Lalor deposit, the largest of these, is currently mined by Hudbay Minerals, with combined resources and reserves totaling 25.3 Mt at average grades of 2.9 g/t Au, 25 g/t Ag, 5 wt% Zn, and 0.79 wt% Cu, including 8.8 Mt at 4.6 g/t Au (Hudbay Minerals). The neighboring 1901 deposit holds combined resources and reserves of 5.3 Mt at average grades of 1.7 g/t Au, 18 g/t Ag, 7 wt% Zn, and 0.34 wt% Cu (Hudbay Minerals). These volcanic successions have undergone extensive syn-VMS hydrothermal alteration, followed by polyphase deformation and amphibolite-grade metamorphism. Metamorphosed hydrothermal alteration styles have been categorized into distinct chemical associations, including K, K-Mg-Fe, Mg-Fe, and Mg-Ca. Extensive mapping and sampling in the Snow Lake camp have yielded valuable data and insights into these deposits. However, there remain opportunities to refine our understanding of alteration assemblages and their relationships to mineralization, building on the strong foundation established by prior work. This study aims to evaluate the effectiveness of short-wave infrared (SWIR) spectroscopy in quantifying alteration halos and to use Leapfrog Geo modeling software with the implicit modeling method to visualize their spatial distribution. SWIR spectroscopy, being an accessible and cost-effective technique, was employed to analyze spatial trends across the Lalor and 1901 deposits. The resulting spatial model integrates lithological and structural data from publicly available cross-sections and maps and compares these with SWIR-derived alteration data and petrographic analyses, providing a comprehensive framework for understanding hydrothermal alteration patterns.