Eocene fault-controlled fluid flow and mineralization in the Paradox Basin, United States

Sedimentary rocks of the Paradox Basin of the Colorado Plateau (southwestern USA) record widespread manifestations of paleo-fluid flow and fluid-rock reactions including Cu, U-V, and Fe-Mn mineral deposits, Si and Ca metasomatism, hydrocarbon accumulations, and bleached sandstones. Many of these are spatially associated with faults. Here we show evidence for a widespread phase of fault-related fluid migration and mineralization at 41-48 Ma in the Paradox Basin. We measured K-Ar dates of multiple size fractions of clay-rich fault gouge, yielding statistically overlapping dates of authigenic (1Md) illite for the Salt Valley (47.0+ or -3.0 Ma), Kane Springs (47.7+ or -3.8 Ma), Cliffdweller (43.4+ or -4.6 Ma), Courthouse (41.9+ or -2.3 Ma), Lisbon Valley (45.3+ or -0.9 Ma), and GTO (48.1+ or -2.6 Ma) faults. The latter two have an illite Rb-Sr isochron age of 50.9+ or -3.5 Ma, and fault-adjacent bornite has a Re-Os isochron age of 47.5+ or -1.5 Ma. Authigenic illite from a paleo-oil reservoir near the Courthouse fault formed from the interaction of reduced fluids with oxidized red-bed sandstones at 41.1+ or -2.5 Ma. The Moab and Keystone faults have older authigenic illite ages of 59.1+ or -5.7 Ma and 65.2+ or -1.0 Ma, respectively. Our results show a close temporal relationship between fault gouge formation, red-bed bleaching, and Cu mineralization during an enigmatic time interval, raising questions about drivers of Eocene fluid flow.