A geochemical, petrographic, and metallogenic analysis of volcanogenic sulphide deposition within the Connaigre Bay Group, Hermitage Peninsula, southern Newfoundland

Abstract

The Hermitage Peninsula, southern Newfoundland, is underlain by the late Precambrian Connaigre Bay Group, a sequence of felsic to mafic flows, tuffs, and associated volcaniclastic sedimentary rocks. The Connaigre Bay Group was intruded by the Ordovician or older Hermitage Bay Complex, Simmons Brook Batholith, and Straddling Granite, and by the Devonian or Carboniferous Pass Island Granite and Harbour Breton Granite. -- The Connaigre Bay Group is host to two significant (≥ 2-3% combined Zn+Pb±(Cu)) volcanogenic massive sulphide showings (Winter Hill and Frenchman Head) and several base-metal-poor massive pyrite occurrences. The mineralized zones occur within a limited stratigraphic interval consisting of the top sequences of the lowermost, dominantly felsic, Tickle Point Formation and the lower portions of the conformably overlying, mainly mafic volcanic, Sam Head Formation. -- The main showing, Winter Hill, displays some characteristics similar to the world class Kuroko deposits. The showing can be divided into two distinct zones. The lower zone is a discordant stringer-zone containing chalcopyrite and pyrite in a gangue dominated by recrystallized quartz, along with minor cordierite, chlorite, and rare andalusite. The upper zone is concordant and contains disseminated to layered massive sphalerite-galena-pyrrhotite-pyrite ± chalcopyrite in a carbonate- and Ca-Mg-silicate-rich gangue. -- The showings and occurrences probably represent deposition during a hiatus in volcanism (i.e. a change from felsic-dominated to mafic-dominated volcanism). The mineralization is situated near, and parallel to, major faults, implying that the faults exerted a structural control on mineral deposition, and provided a conduit along which mineral-rich fluids could be focussed to the seawater-seafloor interface. -- The Connaigre Bay Group displays transitional calcalkaline-tholeiitic characteristics (Tickle Point Fm.), and entirely tholeiitic characteristics (Sam Head Fm. and the conformably overlying mafic volcanic Doughball Point Fm.). Major, trace, and rare earth element chemistry, along with the regional geology, suggest that sulphide deposition occurred in an extensional environment within an island arc environment. Nb depletions and LREE-enriched patterns typify island arc environments, yet high (>3) Zr/Y ratios suggest that there is some crustal contamination within the arc system.