14-10 Coevolution of tectonism, basin sedimentation, and volcanism in Big Sandy Valley, northwestern Arizona, USA: Implications for mineral exploration, modeling, and tectonics

Session: Linking Mineral Resources and the Geologic Framework of North America: The USGS Earth Mapping Resources Initiative (Earth MRI) and Related Activities

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Big Sandy Valley in northwestern Arizona is an exceptionally well-exposed extensional basin comprised of two generations of Oligo-Miocene to Pliocene sedimentary and volcanic rocks deposited on Proterozoic rocks that were intruded by three Late Cretaceous plutons. Hydrothermal alteration is present in all stocks with coarse muscovite alteration present in the northern plutons. A poorly exposed, east-dipping, low-angle normal fault was previously identified along the western margin of the basin based on drilling and seismic reflection. Thermal modelling of Cretaceous plutonic rocks (AHe, AFT, ZHe) from the footwall of the fault suggests rapid middle Miocene exhumation, though permits exhumation initiating as early as the late Oligocene; whereas thermal modelling of a hanging-wall sample (AHe, ZHe) from the Aquarius Mountains suggests Cretaceous rocks there reached upper crustal levels shortly after emplacement. Extension and exhumation were accompanied by basin-fill sedimentation of the Tule Wash formation, where up to 2,000 m of sedimentary rocks, rock-avalanche deposits, basalt flows, and minor pyroclastic rocks accumulated in an endorheic basin, and were subsequently deformed by normal faulting and broad antiformal doming. New U-Pb and Ar-Ar ages of basalt flows and tephra show that Tule Wash sedimentation locally began ca. 25 Ma, prevalent by ~12 Ma,  and ended ~10 Ma, followed by a basin-wide erosional event and angular unconformity over the Tule Wash formation. In the southern Aquarius Mountains, near the southern boundary of the basin, bimodal volcanism erupted high- and low-silica rhyolite domes, pyroclastic rocks, and mafic lava flows, forming the Kaiser Spring volcanic field. Field relations and new Ar-Ar ages show that ~15-8 Ma volcanism was contemporaneous with Tule Wash deposition and subsequent erosion, suggesting that volcanism dammed the basin’s southern terminus and created a second, younger endorheic basin that was filled with conglomerate, sandstone, mudstone, and limestones of the ~10-5 Ma Big Sandy Formation. [LT1] Lithium mineralization is hosted within the muddy lithofacies of the Big Sandy Formation, and in volcano-sedimentary claystones penecontemporaneous with the Tule Wash formation in an adjoining basin. The second episode of deposition ended ~5 Ma via dry spillover to the south, recorded by a series of off-lapping, incised terraces. These results provide new insight into the previously poorly understood evolution of Big Sandy Valley that improves our understanding of regional mineral, groundwater, and geothermal resources.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10938

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