Geology and lithogeochemistry of hydrothermal mudstones from the upper block near the Duck Pond volcanogenic massive sulfide (VMS) deposit, Newfoundland, Canada: evidence for low-temperature venting into oxygenated mid-Cambrian seawater

Pyrite- and pyrrhotite-rich mudstones are spatially associated with Cambrian (~ 512–509 Ma) volcanogenic massive sulfide (VMS) deposits throughout the Tally Pond group, central Newfoundland, Canada. At the Duck Pond mine, sulfide-rich mudstones are hosted within a weakly mineralized upper block that structurally overlies the deposit but is older (~ 513 versus 509 Ma). The mudstones are laminated, 10–30-cm thick, and pyrite- and pyrrhotite-rich and occur along pillow lava selvages, or in between pillow lavas, rhyolite flows, and volcaniclastic rocks. The mudstones are laterally extensive and proximal to the mudstone host rocks are hydrothermally altered to epidote-quartz-chlorite (basalt host) and sericite-quartz (rhyolite host). Lithogeochemical data for the sulfide-rich mudstones reflect the varying contributions of elements from sedimentary detritus, hydrothermal discharge, and hydrogenous scavenging from middle Cambrian seawater. The mudstones have minor detrital element abundances and significant hydrothermal element enrichments (i.e., elevated Fe 2 O 3 , S, Pb, Zn, Cu, and Ba concentrations, high Fe/Al ratios). The hydrothermal mudstones are also enriched in oxyanions (i.e., P 2 O 5 , U, V, Cr, Ni, Co, and Hg), interpreted to have been enriched via oxidative scavenging from seawater by Fe-oxide/oxyhydroxide particles. The mudstones also have REE-Y signatures similar to modern oxygenated seawater with high Y/Ho and negative Ce anomalies (Ce/Ce* = 0.40–0.86; average = 0.58), which correlate with adsorbed oxyanion concentrations. The low Eu/Eu* (1.02–1.86; average = 1.22) in the mudstones suggest that they were deposited from low-temperature (