Controls on mineralization of the Naartok East gold deposit, Hope Bay volcanic belt, Nunavut
University of New Brunswick
The Hope Bay volcanic belt (HBVB), Nunavut, extends about 80 kms long and up to 20 kms wide, within the Bathurst Block of the Archean Slave Province. The HBVB consists mainly of mafic metavolcanic rocks with lesser felsic metavolcanic rocks, with local metasedimentary rocks, and is bounded by Archean granite and gneisses. Three gold deposits are recognized in the belt; these include the northern Doris deposit, the Madrid group of deposits 6 kms to the south, and the southern-most Boston deposit. The Madrid deposits consist of the Naartok East, Naartok West, Rand, and, Suluk deposits, where gold is commonly hosted within Mg-rich basaltic rocks and controlled by complex brittle-ductile deformation zones and splays preferentially developed along the interface between volcanic-sediment horizons. The Naartok East deposit is located wit11in a faulted/sheared hangingwall succession of moderately west dipping, coalesced variolitic pillowed flows that have a Mg-tholeiite composition. The stratigraphic footwall consists of Fe-Ti-tholeiites, which form pillowed to massive flows and flow breccias, with associated interflow sediments. In the hanging wall rocks gold mineralization is spatially associated with zones consisting of with multiphase brecciation, quartz-carbonate stockwork, and pervasive silicification within a broader sericite-albite-ferroandolomite alteration halo; these volcanic rocks have been preferentially altered and sulfidized, indicating that stratigraphy has an important control on the distribution of mineralization. At Naartok East, proximal silicate, carbonate, and sulfide assemblages from the goldbearing hydrothennal breccias and stockwork quartz-carbonate vein systems include; ferroan dolomite, sericite, albite, quartz, chlorite, pyrite, and rntile, +/- chalcopyrite, +/- arsenopyrite, +/Co-rich gersdorffite +/- sphalerite, and+/- electrum. Alteration and sulfide assemblages intermediate to proximal and distal zones include; ferroan dolomite with variations in Fe content (7 .69 to 13 .3 wt. % FeO), chlorite, sericite, muscovite, quartz, albite, pyrite and rutile, +/fuchsite, +/- apatite, +/- chalcopyrite, and +/- monazite. Distal alteration and sulfide assemblages include; chlorite, calcite, ferroan dolomite, quartz, and albite, +/- pyrite, +/- biotite, +/- ilmenite, +/- titanite, and +/ - apatite. Gold-bearing pyrite consistently exhibits strong As zonation with an As-poor core (0 to 0.17 wt.% As) surrounded by an As-rich rim (0.13 to 3.84 wt.% As) and an As-poor outer rim (0.2 to 1.1 wt.% As) containing Au. Electrum, less than 23 μm in diameter, are found in proximal assemblage occurs as rounded to elongated inclusions within growth zones or along grain boundaries and fractures within euhedral to subhedral pyrite; it exhibits notable enrichments in Ag (0.84 to 12.65 wt.% Ag) and Cu (0 to 0.89 wt.% Cu).