Nickerson Et Al:Layout 1
© 2010 Society of Economic Geologists, Inc. Special Publication 15, pp. 299–316 Chapter 17 Characterization and Reconstruction of Multiple Copper-Bearing Hydrothermal Systems in the Tea Cup Porphyry System, Pinal County, Arizona PHILLIP A. NICKERSON,† MARK D. BARTON, AND ERIC SEEDORFF Institute for Mineral Resources, Department of Geosciences, University of Arizona, 1040 East Fourth Street, Tucson, Arizona 85721-0077 Abstract This study exploits a cross-sectional view of the Laramide magmatic arc in the northern Tortilla Mountains, central Arizona, that was created by tilting during severe Tertiary extension of the Basin and Range province. Building upon earlier work, we combine the results of geologic mapping of rock types, structures, and hydrothermal alteration styles, with a palinspastic reconstruction, to provide a system-wide understanding of the evolution of the composite magmatic and hydrothermal Tea Cup porphyry system. Geologic mapping revealed the presence of at least three, and possibly four, mineralizing hydrothermal sys- tems in the study area that are associated with widespread potassic, sericitic, greisen, sodic (-calcic), and propy- litic alteration. The alteration envelops both porphyry copper and porphyry molybdenum (-copper) mineral- ization. Two areas flanking compositionally distinct units of the composite Tea Cup pluton are characterized by intense potassic and sericitic alteration. Intense alteration and mineralization akin to iron oxide-copper-gold systems was recognized in several areas. The U-Pb dating of zircons from porphyry dikes suggests that hydrothermal activity in the study area was short lived (~73−72 Ma). Subsequently, between ~25 and 15 Ma, the Tea Cup porphyry system was tilted ~90° to the east and extended by >200 percent due to movement on five superimposed sets of nearly planar normal faults.
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