Volcanology, geochemistry and geodynamic setting of the Neoarchean Sunrise volcanogenic massive sulfide deposit, Beaulieu River volcanic belt, Slave craton, Northwest Territories, Canada

Abstract

The Sunrise volcanogenic massive sulfide (VMS) deposit is a banded, polymetallic Zn-Pb-Cu-Ag sulfide lens hosted by felsic volcanic rocks of the Neoarchean Beaulieu River volcanic belt in the western Slave craton in the Sunset Lake area of the Northwest Territories, Canada. With historic indicated resources of 1.52 Mt at 5.99% Zn, 2.39% Pb, 0.08% Cu, 262 g/t Ag, and 0.67 g/t Au—it is the largest known VMS deposit in the Northwest Territories.The footwall stratigraphy is interpreted to be the product of subaqueous, largely effusive, bi-modal volcanism with periods of pyroclastic eruptions and concomitant subsidence. It consists of basalt to basaltic-andesite lavas with minor associated volcaniclastic rocks, rhyolite lobe-hyaloclastite flows and rhyolite domes, and felsic volcaniclastic rocks. Though hosted within felsic volcaniclastic lithofacies, the mineralization is spatially associated with the thickest portions of a quartz-feldspar porphyritic lobe-hyaloclastite flow and rhyolite dome. Felsic tuff to lapillistone units, characterized by fine ash, pumice and broken crystal clasts indicate derivation from pyroclastic volcanism and deposition by eruption-fed density currents. Felsic tuff breccia units are characterized by block-sized fragments of quartz-feldspar porphyritic rhyolite and were deposited during mass wasting events along fault scarps or by the oversteepening of domes. Massive to stringer-style sulfide mineralization is dominantly within felsic (seldom heterolithic) tuff to tuff breccia units, but laterally discontinuous argillite units occur at the top of the footwall and commonly contain stringer to semi-massive sulfide mineralization, indicating a hiatus in volcanism before the onset of basaltic andesite lavas that form the hanging wall to the deposit.Volcanic stratigraphy and architecture, and the occurrence of a volcanogenic massive sulfide deposit, combined with major and trace element geochemistry and Nd, Hf, and Pb isotopic data indicate the volcanic rocks and the Sunrise deposit formed on rifted Mesoarchean crust.