Volcanic Stratigraphy and Alteration of the Sunrise Volcanogenic Massive Sulfide Deposit, Beaulieu Volcanic Belt, Northwest TerritoriesSoapbox Wednesday, November 21, 2018 - 13:42 to 13:48 Theatre 2
The Sunrise deposit is a volcanogenic massive sulfide (VMS) deposit located within the Beaulieu volcanic belt (ca. 2.6 Ga) in the Slave craton, about 110 km east northeast of Yellowknife, Northwest Territories. The Beaulieu belt is part of the Yellowknife Supergroup, and is underlain by the ca. 2.8 Ga Sleepy Dragon Complex of the Central Slave Basement Complex. The belt is comprised of mafic volcanic flows with minor felsic volcanic rocks. The Sunrise deposit has a historic indicated resource of 1.52 Mt at 5.99% Zn, 2.39% Pb, 0.08% Cu, 262 g/t Ag, and 0.67 g/t Au. While the deposit has been explored since the late 1980’s, the detailed volcanic stratigraphy and the nature of alteration associated with it remains poorly characterized.
The aim of this study is to characterize the rhyolite lapilli tuff hosting the VMS deposit, and the alteration associated with mineralisation, through detailed mapping (completed summer 2018), petrography, and lithogeochemistry (to be completed winter 2019). The deposit is spatially associated with a rhyolite flow-dome complex and associated felsic volcaniclastic rocks; however, the majority of the footwall stratigraphy consists of andesite and basalt pillow lavas. The ore is banded massive sulfide, hosted in a rhyolitic lapilli tuff that has been pervasively, strongly sericitized and silicified (predominantly composed of recrystallized K-feldspar and quartz, with lesser amounts of sericite and trace epidote in fractures). Ore is not exposed at surface, but the rhyolite lapilli tuff is pervasively Fe-stained from the weathering of disseminated pyrite, and locally contains sphalerite (<1mm, <1%) and chalcopyrite (<1 mm). The lower contact of the rhyolite lapilli tuff is not exposed. The upper contact with pillow basalt of the hanging wall is marked by an ~1 m wide shear zone of intensely foliated basalt. Moderate carbonate and chlorite alteration and trace amount of pyrite and sphalerite (<1 mm, <1%, in pillow selvages) were observed in the basalt.
The Sunrise VMS deposit of the Beaulieu volcanic belt is hosted by a strongly silicified and sericitized rhyolite lapilli tuff with a maximum thickness of 40 m and strike length of 350 m as exposed at surface. The immediate hanging wall is composed of moderately carbonate and chlorite altered basalt that also contains trace pyrite and sphalerite, indicating the hydrothermal system was still active post-basalt eruption. Future work using whole rock geochemistry, and detailed mineralogy (X-ray diffraction) will allow us to quantify alteration zones within and petrogenesis of the rocks that host the Sunrise deposit; this new information will potentially aid in exploration for other VMS deposits in the Beaulieu belt.