GEOPHYSICAL EXAMINATION OF THE SUPERIOR PROVINCE IN WESTERN MINNESOTA: IMPLICATIONS FOR MINERAL EXPLORATION FROM GRAVITY AND MAGNETIC DATA ANALYSIS

The Superior Province, an Archean-aged craton, extends across approximately 132,000 square miles in south-central Canada and the north-central United States. Within Minnesota, it predominantly comprises diverse granitic and granitic-type intrusions, complemented by lesser amounts of metamorphic lithologies resulting from orogenies dating back to 2.8 to 2.6 billion years ago. The Minnesota Orogeny, the final orogenic event, significantly impacted west-central Minnesota. However, northwestern Minnesota within the Superior Province contains minor Cretaceous clastic sediments, overlain by a thin layer of glacial deposits upon the bedrock units making the determination of bedrock units difficult.

The Superior Province is renowned for hosting several world-class ore deposits, including banded-iron formations, volcanogenic massive sulfides, and granitoid-hosted gold and copper deposits. However, the potential ore deposits in northwestern Minnesota remain largely unexplored due to the scarcity of outcrops and comprehensive geophysical and geochemical surveys. Addressing this gap, a high-resolution aeromagnetic and radioactivity survey was conducted as part of the USGS Critical Mineral program. Utilizing the available gravity data, a geophysical analysis was initiated that generated various residual and derivative anomaly maps, as well as two and three-dimensional gravity and magnetic models, to be correlated with existing geochemical data.

Preliminary examination of gravity and magnetic anomaly maps reveals gravity and magnetic minima on the Bouguer gravity, reduced to the pole magnetic, and residual gravity and magnetic anomaly maps, which are associated with Archean granite intrusions. Conversely, gravity and magnetic maxima are linked to banded-iron formations and basaltic dikes. The larger scale gravity and magnetic anomalies, as depicted on the maps, trend SW-NE, while anomalies related to the iron formations and dikes trend SE-NW. The derivative analysis not only validates these findings but also provides more precise identification of the source bodies. Subsequent efforts will entail the creation of additional residual anomaly maps, subsurface models, and the application of machine learning techniques in conjunction with geochemical data to predict optimal areas for detailed mineral exploration.