Abstract The Placer Amex Inc. - Locke Jacobs Aurora uranium prospect is located southwest of the Bretz Mercury Mine and adjacent to the Cordex Syndicate uranium prospect, within the northern rim of the McDermitt caldera complex. Uranium mineralization occurs dominantly as very fine grained uraninite and coffinite localized in highly altered, vesicular to scoriaceous flow tops and breccia layers within a complex intermediate lava sequence. Mineralization was apparently introduced by a hydrothermal mechanism which added altering fluids and uranium-bearing solutions along an arcuate steeply dipping fracture system sub-parallel to the axis of the mineralized zone. A supergene mechanism may then have spread the altering and mineralizing solutions laterally along the more permeable layers within the lava sequence.