The following is summarized from Bundtzen and Clautice (1986). In the vicinity of the Golden Eagle occurrence, the Porcupine Slate that host this prospect is a dark-gray, pyrite-rich, micaceous, carbonaceous slate to phyllite, with minor siltstone and metasandstone. Tan to brown, micaceous silica-carbonate bands are either beds or altered mafic dikes. The Golden Eagle lode is a quartz-pyrite-pyrrhotite-sphalerite fissure vein that cuts a 11- to 15-foot-wide, tan, silica-carbonate band. On the west side of McKinley Creek, the vein ranges from 3 inches to 27 inches thick, strikes N35-65W, and dips steeply northeast to vertical. The hanging wall of the vein contains a highly gossanous 3.5-foot-long by 0.5 to -1-foot wide wedge of bronze-colored pyrite, pyrrhotite, and minor sphalerite. Oxidation of the sulfides has left a vug of euhedral quartz crystals, ferricrete gossan, and local concentrations of very fine-grained free gold. Native sulfur spheres and masses up to 2 inches in diameter envelope clots of sulfide grains, particularly sphalerite. Vertically higher on the vein exposure, smaller pods of massive to disseminated pyrite, pyrrhotite, and minor sphalerite are localized along the hanging wall. The average sulfide content of the vein is only 5% to 8%. At least two phases of silica injection are apparent. The weighted average of six samples taken along 14 feet of exposed vein is 0.653 ounce of gold per ton, 0.227 ounces of silver per ton, and 0.45% zinc, with traces of copper, lead, and cobalt. Grab samples of five similar, smaller, quartz-sulfide veins downstream from the Golden Eagle lode averaged 0.495 ounce of gold per ton, and 0.043% zinc, with traces of cobalt, copper, and lead.

Still and others (1991) assert that the silica-carbonate bands are altered dikes of original mafic composition. Most of the quartz veins are transverse fracture fillings confined to the silica-carbonate-altered dikes.