In 2021 the Northwest Territories Geological Survey (NTGS) continued bedrock mapping project approximately 330 km northeast of Yellowknife, within the Point Lake greenstone belt “Arrowhead” outlier and the surrounding granitoid complex. This mapping was conducted at 1:20,000 scale in conjunction with targeted 1:2000 scale mapping by collaborators at the University of Saskatchewan. This work aims at improving the knowledge of ore-forming processes and to better understand controls on base and precious metal endowment. Through mapping, details about the nature of emplacement and the thermotectonic history of volcanic and sedimentary rocks, and associated volcanogenic massive sulfide (VMS) style mineralization, is being revealed. This mapping is utilizing a 65,000 line-km high-resolution magnetic survey to provide 3D insights into the outlier geometry. Magnetic susceptibility data were collected in the field to support the creation of more robust 3D geophysical inversions.
Within the “Arrowhead” outlier volcanic and sedimentary rocks have recorded multiple thermotectonic events and are bounded along their margin with granitoids by steeply dipping faults. Massive mafic rocks (volcanic and associated intrusive) and pillow basalts dominate the volcanic stratigraphy. Minor mafic breccias, mafic and intermediate tuffs, and rare local felsic tuffs were also observed. The metasedimentary rocks range in composition from psammites to pelites. The thin to medium bedded sedimentary rocks contain corderite and andalusite +/- sillimanite +/- partial melt in the northwest corner of the outlier. The metamorphic grade increases towards the south and west where the rocks are gneissic migmatites and contain sillimanite and anatectic melt. Towards the margin of the “Arrowhead” outlier the percentage of anatectic melt and intrusion pre- to syn-kinematic granitoids increases. The percentage of intrusive material increases outward from the greenstone belt until xenoliths and schlerin make up 5% or less of the rock. Also, along the greenstone belt margin interlayering of volcanic and sedimentary rocks was observed, indicating synchronous deposition for at least part of its history.
Although the “Arrowhead” outlier has a lack of previously known mineralization, our work aims at testing correlating these volcanic rocks with those in the Point Lake greenstone belt that host the IZOK Lake VMS deposit. Through our work a significant number of volcanic rock-hosted VMS style mineralization was observed in the course of our work. Variable grades of VMS-style mineralization ranged in size from a few inches to meters to 400 by 800 meters. Quartz vein-hosted mineralization was also observed cross-cutting volcanic and metasedimentary rocks.