ABSTRACT The Laramide continental arc formed in southwestern North America at about the same time the Sierra Nevadan arc was shutting down, and the Laramide arc was active concurrent with the progress of the Laramide orogeny, from ca. 80 Ma to ca. 45 Ma. East-central Arizona offers an excellent opportunity to explore aspects of tectonics, structural geology, magmatism, and hydrothermal systems in a segment of the Laramide arc that is exceptionally well endowed with porphyry copper deposits. The structure of this region is especially complicated, with multiple generations of normal faults commonly superimposed on originally moderate-angle reverse faults with associated fault-propagation folds. A large new porphyry copper deposit, Resolution, was discovered near Superior in the mid-1990s. The discovery started a new round of development in the mining life cycle at the Resolution deposit; in the region, it contributed to copper exploration again becoming vigorous in the last decade. In the years since discovery of Resolution, important new scientific insights have been gained, including at the regional scale. Post-ore crustal extension exposed multiple levels of Laramide and older igneous and hydrothermal systems at the surface where they can be more easily mapped and sampled, and palinspastic reconstructions of post-mineral normal faulting permit the exposures to be restored to their original positions. The porphyry-related products that are observed at higher levels include local advanced argillic alteration and Cordilleran-style veins and associated mantos, such as at the Magma mine, Resolution deposit, and Old Dominion mine in the shallowest levels of the Superior-Globe-Miami area. Most porphyry copper ore bodies were developed at intermediate depths, where porphyry intrusions exhibit sericitic and potassic alteration and carbonate rocks were converted to skarn, such as in the heart of the Miami-Inspiration, Resolution, Ray, and Christmas deposits. Plutonic rocks are exposed at deeper paleodepths, where pegmatites, quartz veins, and greisen muscovite are locally observed, especially directly beneath porphyry copper orebodies, as in the Schultze and Granite Mountain plutons. Likewise, sodic-calcic alteration may be developed on the deep flanks of porphyry systems, such as adjacent to the Tea Cup pluton. Subsequent Cenozoic extension variously buried or exhumed the hypogene portions of these hydrothermal systems, leading to the development of various supergene products, both in situ and exotic.

Abstract The southwestern North America porphyry copper province comprises adjacent parts of the U.S. states of Arizona, New Mexico, and Texas, and the Mexican states of Sonora, Chihuahua, northern Sinaloa, and Baja California. The province has an estimated total endowment (production + reserves + resources) of 295 million tonnes of copper metal, 96% of which is in deposits of Laramide (∼80–45 Ma) age. This is one of the major accumulations of the element known in the Earth's crust. In addition to having played a major historical role with regard to the discovery, development, mining, and scientific study of porphyry copper deposits, large remaining reserves and resources assure that the this porphyry province will continue to be a factor in world copper supply for many years to come. The southwestern North America province is largely underlain by mid-Proterozoic continental crust covered by upper Proterozoic to mid-Paleozoic miogeoclinal sedimentary rocks. Arc magmatism commenced in the area in the Triassic and continued until extinguished by ridge subduction that started in early Miocene time; this resulted in its conversion from a convergent to a transform margin. A long-lived series of NW-trending sedimentary basins evolved parallel to the arc from Jurassic through mid-Cretaceous time. The Laramide porphyry deposits were emplaced during a continental-scale episode of flat subduction and strong compression. This was accompanied by metaluminous to weakly peraluminous calc-alkaline I-type magmatism. Hypogene porphyry copper mineralization is dominated by chalcopyrite (± bornite), accompanied by K-silicate, transitional K-silicate-sericitic, and sericitic alteration. Subsequent to porphyry emplacement, much of the region was subjected to an episode of weathering and erosion, followed in the mid-Tertiary by a switchover to an extensional tectonic regime and the eruption of silicic volcanic rocks that blanketed much of the region. Two episodes of weathering-related oxidation, leaching, and enrichment, one prior to mid-Tertiary volcanisim (Eocene-Oligocene) and the second of Miocene age, produced rich supergene copper ores that were the mainstay of production in the province through the 1970s. Southwestern North America Laramide porphyry copper deposits are very near the median of worldwide porphyry deposit distributions in regard to size, contained Cu metal, median Cu grade, and median Mo grade. Median Au grades are significantly lower than the global median. The depth of erosion of pre-Laramide arcs in southwestern North America probably accounts for the relative paucity of porphyry deposits, and there are segments of the Laramide arc that have been tectonically denuded during mid-Tertiary extension, also resulting in a lack of deposits. There are, however, segments of the Laramide arc with similar, apparently appropriate, levels of erosion and preservation that have widely different deposit densities and/or copper endowment that is as yet unexplained. The apparent lack of Eocene to Oligocene porphyry deposits is also difficult to account for; hypabyssal rocks of this age are quite common and copper-bearing polymetallic skarn and high-temperature replacement and vein deposits are locally associated with them, but there is only one small, low-grade porphyry deposit of this age documented in southwestern North America. Although the region has been heavily explored for exposed porphyry copper deposits, there remain excellent opportunities for discovery, given that an estimated 54% of the porphyry trend is covered by post-Laramide rocks or unconsolidated sediments. Exploration targets include undrilled or poorly drilled extensions of known deposits—both laterally and, especially, at depth; deposits or dismembered parts of deposits under structural cover in areas of post-Laramide extension; and deposits under postore volcanic and alluvial cover. Future production will increasingly be dominated by open pit low-grade and underground high-grade hypogene milling ores, with an important molybdenum by-product credit.

ABSTRACT This field trip integrates economic geology with structural geology and tectonics, as well as petrology, geochemistry, and regional geology, to examine a segment of the Laramide arc that includes part of the Laramide porphyry copper province of southwestern North America. The province arguably is the second-largest porphyry copper province in the world, hosting six of the world’s 25 largest porphyry deposits on the basis of contained copper metal. The Globe–Superior–Ray–San Manuel area includes about a dozen Laramide (Late Cretaceous to early Paleocene) porphyry copper deposits and the related granodioritic to granitic plutons. These plutons and their wall rocks were tectonically dismembered and variably easterly or westerly tilted (locally >90°) during Laramide contraction and subsequent mid-Cenozoic extension. The style of both shortening and extension here remains a subject of debate. Although this trip includes one brief mine visit and examination of drill core at the Resolution deposit, it will principally focus on: (1) different parts of various plutons and the associated alteration aureoles, including review of resultant mineralization, and the original sides, roots, and deep flanks of the hydrothermal systems; and (2) structure in the adjacent wall rocks and the implications for the style and timing of deformation in absolute and relative terms to hypogene ore formation. An increased understanding of the structural geology and the alteration-mineralization zonation of the dismembered hydrothermal aureoles allows an integrated view of the original geometry and size of the porphyry systems, the relationship between porphyry copper mineralization and crustal shortening, and possible origins of deep hydrothermal alteration.

ABSTRACT We describe the time-space evolution of a segment of the Laramide arc in east-central Arizona that is associated with porphyry copper mineralization, as constrained by U-Pb zircon geochronology conducted by laser ablation–multicollector–inductively coupled plasma–mass spectrometry. Mid-Cenozoic normal faulting dismembered and tilted many of the plutons and the associated porphyry copper deposits and produced a wide range in depths of exposure. The study area reconstructs to a 75-km-long slice along the arc, with exposures from <1 to >10 km depth. The copper deposits are related to granodioritic to granitic plutons that exhibit variable magmatic sources and locally severe degrees of zircon inheritance. U-Pb zircon ages of plutons in the study area range from 75 to 61 Ma, with dioritic rocks at the older end of the range. The age range of magmatism and mineralization in a cluster of deposits near the Schultze Granite, including the Globe-Miami, Pinto Valley, and Resolution deposits, is from ca. 69–61 Ma. To the south in the Tortilla and Dripping Spring Mountains, the porphyry systems range from ca. 74 Ma at Kelvin-Riverside to ca. 69 Ma at Ray and ca. 65 Ma at Christmas. At several localities where geologic constraints exist, mineralizing plutons were emplaced following Laramide shortening. The ages of the inherited zircon cores correspond fairly closely to the ages of basement rocks in the immediate vicinity of sample sites, implying that similar basement ages and lithologies contributed to the source areas of magmas that produced Laramide porphyry deposits. The U-Pb results on hypabyssal rocks are typically 1–5 m.y. older than previous K-Ar ages, and U-Pb ages on more deeply emplaced plutonic rocks are as much as 5–10 m.y. older. These results are consistent with predictions from thermal modeling and suggest that temporal evolution of the entire Laramide arc needs revision. For this segment of the arc, magmatism was stagnant for ~15 m.y., with minimal migration over time and mineralization occurring episodically over most of that lifespan. There is no simple geographic progression in ages along or across the strike of the arc. Thus, it is difficult to call upon time-specific far-field or plate margin triggers for magmatism or mineralization. The intrusive flux of the Laramide arc appears to be similar to that of the Sierra Nevada arc during the Mesozoic during its “background” periods, rather than during episodes of flare-up. The wide compositional diversity of the Laramide arc is more akin to northeastern Nevada during the onset of extension in the mid-Cenozoic than to the Mesozoic of the Sierra Nevada.

In this section, only the stratigraphy of the rocks deposited before and during the violent events of the Cuban orogeny will be described. The deformation probably reached its peak during the early–middle Eocene. The reason for this rather indefinite time assignment is that no index faunas have been found to separate the middle from the lower Eocene in the syn-orogenic flysch sediments, much less in the wildflysch that characterizes the culmination of the orogeny. The only evidence that the orogeny is pre–upper Eocene is a widespread, well-defined unconformity below an upper Eocene orbitoid-rich limestone that, although occasionally deformed, was not involved in the strong orogenic tectonism. As will be seen later, the tectonic events that marked the end of the orogeny were not exactly synchronous all over Cuba. In the south, the orogenic deformation started in the late Maastrichtian to Paleocene, whereas in the north, the deformation started in the early Eocene. The molasse (or erosion of already inactive topography) cycle startedinthe southinthe early Eocene while thrusting proceeded in the north in the middle Eocene with the production of associated flysch deposits (or erosion of an active orogenic front). The mo-lasse was carried piggyback by the northward advancing thrusts while contemporaneous flysch was being generated in the north. Stratigraphy and structure are intimately intertwined in Cuba; the significance of structural features can be understood only through the knowledge of stratigraphy. Therefore, in this chapter, the stratigraphy will be described first to establish a plausible preorogenic paleogeography.As previously mentioned, many