The Wallapai district is in the Cerbat Mountains, an eastward-tilted fault-block composed of Precambrian metamorphic and igneous rocks that have been intruded by granite porphyry of Tertiary (?) age. Small patches of Tertiary and Quaternary volcanic rocks occur along the flanks of the range.Mineralization is believed to have occurred after the close of Tertiary volcanic activity. The first phase consisted of "porphyry copper" mineralization in a strongly shattered portion of a granite porphyry stock. This was succeeded by the formation of veins that contain lead-zinc ores. The veins are superimposed upon and grouped symmetrically around the "porphyry copper" mineralization. Tectonic action is postulated as the fundamental control for the emplacement of the granite porphyry stock and for the two types of sulfide mineralization that are areally associated with the stock. Turquoise deposits have developed by supergene processes in the capping of the "porphyry copper" deposit.A late fault cuts both bedrock and alluvium at the western base of the range. This fault and a surrounding area of the alluvial blanket have been mineralized by chrysocolla to form the Emerald Isle copper deposit. The chrysocolla is believed to be hypogene in this deposit.