The Alu showing, northeast of Tarr inlet, is in an area which is underlain by Siluran to Devonian (?) metasediments and metavolcanics of the Icefield and Alsek Ranges sequence, which are intruded by Jurassic to Cretaceous gneissic granodiorite and diorite of the St. Elias Intrusions. The metasediments strike approximately north with near vertical dips. Greyish-yellow calc-silicates with limestone and marble bands and lenses are cut by a network of quartz veins which are erratically mineralized with chalcopyrite, bornite, and pyrite. The mineralized zone is about 100 to 400 metres wide and a kilometre in length along a north strike. Sporadic molybdenite occurs in larger quartz lenses and scheelite has been reported associated with garnet-diopside skarn.