Black line faults tend to cut and displace various lithologies, dykes, and gold-bearing veins and are a common feature found in the Red Lake gold mines. They are characterized by their distinct black color and may have anomalous traces of gold but are usually barren. Black line faults along the Red Lake mine trend may vary in size, geometry, and significance, but they all share the same general composition of mostly tourmaline, chlorite, and interstitial quartz. They have previously been described as faults associated with brittle late stage deformation; however, some are overprinted by ductile deformation. Black line faults are significant in that they represent a time of brittle-ductile deformation and the presence of complex hydrothermal fluids, typically related to orogenic gold mineralization.