Regional-scale, northeast-trending structures control mineralization throughout east-central Alaska, including at the Pogo and Fort Knox gold mines. The Maple Leaf Property is adjacent to two such structures: the Black Mountain Tectonic Zone to the west, which appears to host high-grade mineralization at Tectonic’s Tibbs Project as well as Northern Star’s Brink prospect, and the Mount Harper lineament to the east.
Cretaceous aged intrusives and gneissic and schistose country rocks host sugary textured quartz veins and local quartz vein stockworks. Historic rock grab and hand trench sampling completed by exploration service company, Avalon Development Corporation (“Avalon”), for Rubicon returned gold values from trace to 19.1 g/t Au, with gold occurring in association with elevated bismuth, tellurium, and arsenic.
Rubicon completed a limited drill program at the Maple Leaf prospect in 2007, consisting of 1,105m of diamond drilling in four holes. Drilling intersected weakly anomalous gold (0.25 g/t Au over 0.8m) but failed to intersect the sugary quartz veins observed at surface. No work has since been completed on the property.
In addition to Maple Leaf, two other prospects are currently known at the property and suggest the presence of a substantial fluid-rich mineralizing system: American Eagle and Tourmaline Ridge. The American Eagle prospect is located 5.6km northeast of Maple Leaf and consists of a 400 x 50m ridgetop cut by 5-10% sheeted white quartz veins with coarse grained bismuthinite. Limited historic grab sampling returned values from trace to 3.03 g/t Au, up to 3,880 ppm bismuth, up to 5,160 ppm arsenic, and up to 494 ppm molybdenum. Tourmaline Ridge is located 2.4km west of Maple Leaf and consists of tourmaline-bearing paragneiss containing massive tourmalinite (> 50% tourmaline), with lesser quartz veins and tourmaline-vein breccias. Historic sampling of the tourmaline-rich rocks by Avalon returned weakly elevated gold values (maximum 164 ppb Au), up to 804 ppm bismuth, and up to 2,620 ppm arsenic. The intensity and extent of the tourmaline suggest high levels of fluid flow related to intrusive activity.