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Abstract

The Iron Mask Batholith district in southern British Columbia hosts several porphyry-style mineralized centers. This study integrates petrography, μXRF mapping, whole-rock geochemistry, and SWIR spectroscopy to characterize magmatic phases and hydrothermal features. Two previously undocumented lithologies were identified, contributing to a broader understanding of local magmatic diversity. Also, a newly developed immobile element ratio (Zr/Sc vs. Th/V), along with the Alkalic Porphyry Index (MAPIx), enhances the discrimination of alkalic systems beyond traditional classification methods. Geochemical evidence indicates a temporal transition from ~200 Ma transitional phases to ~152 Ma calc-alkalic phases, reflecting a shift from oceanic to continental arc tectonic regimes. Hydrothermal alteration in alkalic deposits exhibits concentric and structurally asymmetric zonation. Potassic and calc-potassic cores are surrounded by broader propylitic, phyllic, and argillic halos. SWIR spectroscopy reveals that deeper zones feature Fe-rich chlorite and phengitic white mica, while distal zones contain Mg-rich chlorite and muscovitic mica. Thirteen vein types were documented, transitioning from K-feldspar ± epidote ± sulfide assemblages to calcic veins; vein density decreases markedly beyond ore zones, indicating structurally focused fluid pathways. Pathfinder elements in the studied alkalic porphyry deposits extend horizontally from a central core of Pd, Pt, Cu, and Au (~100m wide) to Te, Re, and Se (~700m wide) and further distal V, As, and Sb (~1 km wide). Vertically, a higher concentration of Mo occurs at depth (~750m deep) along with depleted Zn and Mg. This is overlain by a zone of high concentrations of Cu, Au, Pd, and Pt. Near the surface, Te, V, As, and Sb have higher concentrations. Consistent with element zonation, the mineral chemistry of pyrites, chlorites, and epidotes shows distinctive anomalous element distribution with proximity to mineralized centers. The studied alkalic porphyry systems exhibit elevated concentrations of Te, As, V, Au, and Pd relative to calc-alkalic counterparts, alongside markedly smaller geochemical footprints (~1.2 km vs. ~5 km). Restricted chemical dispersion perpendicular to ore strike and limited distal alteration zones necessitate a refined exploration strategy: employing high-density sampling grids, leveraging SWIR spectroscopy to vector through thermal gradients, and integrating vein morphology and mineral chemistry analysis to enhance subsurface targeting accuracy.