Chemostratigraphy of Late Ordovician to Early Devonian Strata Hosting the Prairie Creek Zn-Pb-Ag Deposit, Southern Mackenzie Mountains, Northwest TerritoriesOnline pre-recorded
The Prairie Creek Zn-Pb-Ag deposit comprises vein-style and stratabound mineralization hosted in Upper Ordovician to Early Devonian basinal strata. This study is designed to characterize the background geochemical signature of the host rocks at Prairie Creek, providing foundational information to support a robust evaluation of geochemical anomalies in regional exploration surveys. Furthermore, geochemical proxies for paleodepositional and diagenetic redox conditions offer relatively new tools for interpreting historically cryptic, fine-grained mudstones. Paleodepositional and diagenetic redox conditions played an important role in the formation of stratabound Zn-Pb mineralization in other districts and a better understanding of these processes could have important implications for exploration strategies in the Prairie Creek area.
To this aim, drill hole PC-10-186 and wedge PC-11-206 were sampled every ~15 m. This deep drill hole constrains the presence of prospective host strata ~2 km from the main Prairie Creek deposit and provides fantastic access to unaltered samples of almost the entire section of host strata. Samples were 15-20 cm in length and targeted homogenous, dark-colored, fine-grained mudstone. Veins and alteration related to minor vein-style mineralization were excluded from samples. Bulk samples were analyzed for multielement geochemistry, δ13C and δ18O composition of carbonates, and total organic carbon (TOC) and hydrocarbon speciation by Rock-Eval pyrolysis.
Preliminary analysis of results shows that the mudstone of each of the four sampled formations (Upper Whittaker, Road River, Cadillac, and Arnica) are characterized by distinct geochemical characteristics. Major element chemistry shows that the contribution from terrigenous detrital material, carbonates (dolomite and calcite), and biogenic silicon varied over time. Redox proxies (e.g., MnO, non-detrital Mo, Ce/Ce*) indicate that the paleodepositional conditions were primarily suboxic to anoxic with the strongest evidence for anoxia and euxinia (free H2S) in the upper part of the Silurian-Devonian Cadillac Formation. Vanadium is poorly correlated with other redox-sensitive metals, which indicates that concentrations may have been modified by mobilization of hydrocarbons. This is consistent with results from Rock-Eval pyrolysis that show samples are overmatured. Bulk δ13C composition of carbonates in the samples fall within the range of expected values for the Phanerozoic and the major excursions correlate well with the δ13C curve for strata of similar age in the Richardson trough of the Selwyn basin. Geochemical proxies for hydrothermal alteration indicate limited influence by hydrothermal fluids with Ge <0.1 ppm in all samples and rare positive Eu/Eu* excursions. The strongest positive Eu/Eu* excursion includes four samples with Eu/Eu* > 1.25, spatially correlated with the presence of minor vein-style mineralization.