Reconstruction of the Depositional, Structural and Metamorphic History of the Arrowhead Outlier, Northwest Territories, Canada.Online pre-recorded
The Arrowhead Outlier, which is primarily composed of mafic volcanic rocks, is located in the west-central region of the Slave craton, ~300 kilometres northeast of Yellowknife in the Northwest Territories. The tectonic and metamorphic evolution of the Arrowhead Outlier is poorly understood; however, it is considered correlative to the well-studied Point Lake belt ~30 kilometres to the east. This project focuses on the geochemical, structural, and lithological study of the mafic volcanic rocks of the Arrowhead Outlier, aiming to correlate them with the Peltier Formation of the Point Lake belt.
The project objectives are to: 1) subdivide the volcanic rocks into volcanic facies; 2) document the geochemistry of the volcanic rocks in order to determine their petrogenesis; 3) determine the age relationship between the sedimentary, volcanic, and intrusive rocks; 4) assess the metamorphic grade; 5) collect structural measurements to reconstruct the deformational history; and 6) assess the style and economic potential of sulfide mineralization in the Arrowhead Outlier.
Three main hypotheses are formulated as a result of the field season. First, the volcanic rocks of the Arrowhead Outlier represent subaqueous eruptions and are a part of the Point Lake belt that have been separated by faulting and granite intrusions from the main belt. Second, the metamorphic grade of the metasedimentary rocks and the associated anatectic granites is sillimanite-zone amphibolite. Third, the main mineralization style within the Arrowhead Outlier is volcanogenic massive sulfide.
Detailed mapping at 1:2000 was completed from July to August. The mapping focused on the sedimentary rocks in the south-central fold hinge, across the thickest sequences of volcanic rock, and into the intrusive rocks that border the outlier. Preliminary results of this fieldwork found that the volcanic core of the Arrowhead Outlier is composed dominantly of massive to pillow basalt with lesser amounts of bedded mafic tuff and gabbro. Mafic volcanic rocks are dominantly amphibolite-grade and locally mylonitized. Rare occurrences of mafic breccia, bedded heterolithic tuff, and bedded felsic tuff occur adjacent to mineralization. Mineralization hosted within the mafic rocks includes pyrite, arsenopyrite, pyrrhotite, chalcopyrite, bornite, and sphalerite. Metasedimentary rocks along the fold hinge consist of interbedded semipelites and psammites. To the west the semipelite is garnet-bearing and the psammite is cordierite-bearing, while to the east the semipelite contains knotted fibrolite and the psammite is barren of cordierite. The intrusive and basement rocks are dominantly schlieren granite and syenogranite. Pegmatitic regions of the syenogranite contain schorl-variety tourmaline and garnet.
Next steps to understanding the history of the Arrowhead Outlier include petrographic analyses of major lithologies to more accurately identify their mineralogies. Analysis of whole-rock geochemical data will further subdivide volcanic facies, determine the tectonic environment and source of the mafic lava, and aid to interpret relationships between the various lithologies. Analysis of assay data from visible occurrences of sulfide mineralization will aid to determine the mineralization styles present and assess the economic potential of the Arrowhead Outlier. Finally, utilizing both field mapping observations and geochemical data, two 1:2000 scale maps will be published.