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The Cabullona Basin of northeastern Sonora is a structural depocenter that was formed during Late Cretaceous time. The 2.5 km-thick sedimentary fill of this basin, the Cabullona Group, is composed in ascending order of the Corral de Enmedio formation, Camas Sandstone, Packard Shale, Lomas Coloradas formation, and, laterally equivalent to the last two units, El Cemento conglomerate. Abundant vertebrate and invertebrate as well as pollen identifications from these units indicate the Cabullona Group is of middle Santonian to Maastrichtian age. The Corral de Enmedio formation represents shallow lacustrine deposits. Lithofacies of the Camas and Lomas Coloradas formations indicate they were deposited by braided- and meandering-fluvial systems, whereas the eight members of the Packard Shale represent complex fluvio-deltaic-and-lacustrine systems. The El Cemento conglomerate is a thick clastic wedge of coarse-grained alluvial deposits that was deposited adjacent to the structural margin of the basin. Clast composition and paleocurrent directions of the El Cemento conglomerate indicate it was derived from strata of the nearby uplift of the Sierra Anibacachi-Cerro Cabullona. The low-angle, southwest directed Cabullona thrust fault that separates the uplift from the basin formed the structural margin of the basin. The tectono-sedimentary history of the Cabullona Group, its age and regional tectonic setting support the idea that this basin was formed because of typical Laramide-style deformation and indicates that the Rocky Mountain foreland province of Laramide deformation extended southward to northeastern Sonora.

El Alacran, northern Sonora, Mexico, is a high-level, Laramide porphyry copper deposit encompassing an east-west elongated altered and mineralized area of 2.7 by 6 km. A small quartz latite porphyry plug forcefully intrudes comagmatic(?) Late Cretaceous or Early Tertiary andesitic to quartz latite volcaniclastic rocks.Veinlet-controlled and pervasive potassic, Type I phyllic, and transition type alteration with related base-metal mineralization postdates pervasive propylitic alteration and is related in space and time to the intrusive and its associated intrusion-breccia annulus. Potassic alteration is dated by K-Ar at 55.4 +- 1.2 m.y. Later pervasive and veinlet-controlled Type II phyllic and minor advanced argillic alteration is associated with intrusive breccia dikes and pipes which are genetically related to degassing of the system. Minor veinlet-controlled late-stage alteration followed. Hypogene zoning is exhibited by alteration, mineralization, total sulfide volume, mineralized fracture density, and geochemistry with zoning being centered over or to the east of the exposed intrusive. Supergene enrichment processes have modified hypogene sulfides, oxides, and silicates and have formed a copper enriched blanket which underlies a leached cap. The blanket is characterized by a chalcocite zone which grades downward into a bornite-digenite-covellite zone and then into low-grade protore. Although the enriched blanket appears to be subeconomic, this study indicates potential for a deep, high-grade protore zone.