INSIGHTS INTO THE MAGNET COVE ALKALINE CARBONATITE COMPLEX OF ARKANSAS FROM NEW GRAVITY AND MAGNETIC MODELS

Alkaline carbonatite systems are simultaneously known for their wealth of mineral resources and the enigma of their formation and emplacement. The alkaline carbonatite complex at Magnet Cove (MC) in south-central Arkansas is a Cretaceous-age ring-dike complex that has intruded into Paleozoic sedimentary layers of the Ouachita Mountains. Magnet Cove and the surrounding Arkansas alkaline province (AAP) were previously mined for critical minerals such as Al, Ba, Ti, V, Nb, Li, and is permissive for rare earth elements (REEs). In 2020, the AAP was identified by the U.S. Geological Survey and the Arkansas Geological Survey as an Earth MRI focus area based on its potential critical mineral endowment. In 2022-23, high-resolution airborne magnetic and radiometric data were collected over most of Arkansas and southern Missouri. The 12 km² surface exposure of the MC complex is associated with strong positive gravity (40 mGal) and magnetic anomalies (7,000 to 9,500 nT). Advancements in geophysical data acquisition and software have allowed for an improved rendering of the subsurface geometry of the complex. We present new 2D forward and 3D inversion models using aeromagnetic and ground-based gravity and magnetic data. Our models suggest that the MC complex extends to a depth of between 10 and 25 km, with a lateral subsurface extent that ranges from 5 to 25 km, resulting in a total volume of nearly 1000 km³. The models support previous suggestions that the MC complex is likely connected to other intrusions of the AAP at depth. The modeled extent of the MC complex, in conjunction with its proximity to the intersection of the Ouachita thrust front and the failed Reelfoot rift in Arkansas, suggest that the alkaline intrusions follow deep crustal boundaries in the underlying Precambrian basement. The methods employed can guide the use of the new Earth MRI airborne geophysical survey in future geophysical models of these Cretaceous intrusions.