The Eureka is a well defined, narrow fissure trending 55 degrees with a vertical dip. The fissure contains a narrow vein of white quartz with minor disseminated pyrite, a very little limonite and a high gold content. The vein crosscuts hard, white quartzites of the Lower Cambrian Quartzite Range Formation (correlative with rocks of the Hamill Group) where they are exposed on the eastern limb of the Eastern anticline of the Sheep Creek camp. The fissure is crosscut and slightly offset by a fault containing a diorite porphyry dyke which is 6 metres thick. A second, smaller dyke is also reported. At least 100 metres of underground work occurred on the property.