James A. Walker

Back-arc basin constraints on the genesis of Ordovician volcanogenic massive sulfides in the Flat Landing Brook Formation, Bathurst Mining Camp, Canada

Volcanic sediment hosted massive sulfide (VSHMS) deposits and coeval iron formation in the Middle Ordovician Bathurst Mining Camp (BMC) are generally hosted by tuffaceous sedimentary rocks of Nepisiguit Falls Formation. However, several volcanogenic massive sulfide (VMS) deposits occur within effusive volcaniclastic rocks and felsic domes associated with felsic dominated bimodal volcanism of the Flat Landing Brook Formation. Their setting higher in the stratigraphic pile is accompanied by base-metal contents that are atypical of the deposits hosted by the Nepisiguit Falls formation within the BMC. The Louvicourt deposit, which occurs within felsic hyaloclastite (Flat Landing Brook Formation) at the contact with an overlying sequence mafic volcanic rocks (Little River Formation) has a Pb/Zn ratio of 2.6, the highest recorded for any massive sulfide deposit in the BMC (Pb/Zn avg. 0.39). The persistence of exhalative hydrothermal activity at the terminal stages of felsic volcanism, with an evolution towards extensional mafic magmatism, highlights the exploration potential for VMS systems along the contact between the Flat Landing Brook and Little River formations within the Middle Ordovician Tetagouche Group.