Geochemical Evidence for a Topographically Driven Regional Mineralizing Fluid in the Polaris Zn District, Arctic Canada

Abstract

AbstractThe Polaris district in Canada’s Arctic Archipelago contains numerous carbonate rock-hosted Zn + Pb showings and rare, anomalous Cu showings in a 450- × 130-km area. As in many metallogenic districts, a genetic relationship between the mined deposit and surrounding showings has been assumed but not tested. This study uses an in situ, multianalytical approach combining optical and scanning electron microscopy petrography, fluid inclusion microthermometry, evaporate mound analysis, trace element analysis, and in situ stable isotope analysis on sphalerite and carbonate gangue to characterize the fluid histories of individual showings and the district as a whole. Results indicate that a regional, marine-derived fluid dissolved subsurface evaporite minerals, interacted with their connate brines, and transported metals and sulfate to sites of mineralization. Initial fluid mixing with local reduced sulfur accumulations resulted in precipitation of sulfides with lower δ34S values; after exhaustion of the local reduced sulfur pool, thermochemical sulfate reduction (TSR) of transported sulfate became dominant, resulting in higher δ34S. Differences in main-stage δ34S values among different showings indicate a variable extent of TSR among sites. The mineralized volume of each showing is predominantly a function of local fluid flux and availability of a local reductant. The nature and consistency of geochemical characteristics throughout the district confirm the genetic relationship between the large deposit (Polaris) and surrounding showings and indicate that a uniform mineralizing fluid, topographically mobilized during the mid-Paleozoic Ellesmerian orogeny, was responsible for the main, district-wide mineralization, after initially mixing at a smaller scale with local, on-site fluids.