51821-THE ROLE OF BASEMENT STRUCTURES IN THE LOCALIZATION OF LARAMIDE MINERALIZATION: EXAMPLES FROM THE PATAGONIA MOUNTAINS, SOUTH-CENTRAL ARIZONA

2000 GSA Annual Meeting -- Reno, Nevada

Abs. No. 51821

THE ROLE OF BASEMENT STRUCTURES IN THE LOCALIZATION OF LARAMIDE MINERALIZATION: EXAMPLES FROM THE PATAGONIA MOUNTAINS, SOUTH-CENTRAL ARIZONA

Author(s): BERGER, Byron, R., PHILLIPS, Jeffrey D., and RIDLEY, W. Ian, U.S. Geological Survey, Federal Center, MS964, Denver, CO 80225-0046

Keywords: Basement Structures, Patagonia Mountains

Base-and precious-metal mineralization is associated with Late Paleocene to Early Eocene intrusive activity in the Patagonia Mountains, Arizona. The major tectonic blocks and a biotite-hornblende granodiorite stock in the range are elongated NW-SE reflecting the structural dominance of en chelon NW-striking, right-lateral strike-slip faults and NNE-striking normal faults. Right steps in the en chelon NW-striking faults are important sites for localizing hydrothermal activity. A detailed aeromagnetic survey suggests NW fault trends are regional, deep brittle-crust scale structures linked by N to NE structures. Derivative aeromagnetic maps show additional E-W to ENE lineaments in most highly mineralized areas. East-westerly fractures are observed in outcrop as sheeted fracture zones and faults. In the Late Paleocene to Eocene regional stress field, E-W faults should be neither primary displacement shear zones nor antithetic shear zones and, therefore, represent an older structural fabric. Mineralization at Trench Camp and at the World's Fair and Three R mines, in the northern Patagonia Mountains, includes veins on E-W fractures implying they were hydraulically conductive and, therefore, accommodated some strain. At the World's Fair mine, the E-W fractures bound a small extensional step between NW-striking faults within which the orebodies occur. The Three R mine is localized in a fan of N to NNW faults between en chelon NW faults where an ENE shear zone crosscuts them. Thus, although regional NW fault systems control magma flow in the crust, it is the interplay of these systems with locally reactivated faults where the stress/permeability relations are most favorable for ore-deposit formation.

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