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

Knowledge of the geologic framework and mineral resources is improving through new geologic mapping, airborne geophysics, geochemistry, and lidar acquisition, especially through Earth MRI. We welcome submissions of Earth MRI research and similar studies linking framework geology and mineral resources.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

New Earth MRI magnetic and radiometric datasets in the Wyoming-Colorado border region

Paper number: 110-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Cheyenne belt (CB) region along the Wyoming–Colorado border hosts multiple known and suspected critical mineral systems, making it a priority for new mapping and research efforts. The northeast-striking CB forms the boundary between the Archean Wyoming Province (WP) on the north and the Paleoproterozoic Green Mountain arc (GMA) on the south. The GMA was accreted to the WP during the 1,780–1,740 Ma Medicine Bow orogeny. In 2023–2024, high-quality airborne magnetic and radiometric surveys were conducted across the region. Most of the surveying was conducted with 200 m line spacing and 100 m nominal terrain clearance. Early observations are reported here. North of the CB, Archean rocks produce generally subdued magnetic anomalies that strike at high angles to anomalies produced by younger rocks. Strata of the Paleoproterozoic Snowy Pass Supergroup of the Medicine Bow Mountains and Snowy Pass Group of the Sierra Madre produce elongated, low-amplitude magnetic highs. Numerous short-wavelength magnetic anomalies are produced by small mafic intrusions north of the CB. Shear zones in the CB juxtapose rocks of differing magnetizations, producing elongate magnetic gradients. In the GMA, metasedimentary and metavolcanic rocks produce magnetic anomalies of variable character and amplitude, although anomaly amplitudes are generally greater than those north of the CB. Large mafic intrusive complexes of interest for several critical minerals (e.g., Lake Owen layered mafic complex, Elkhorn gabbro), produce complex anomalies. Mesoproterozoic granites intrude the GMA, have variable magnetic character, and include the variably magnetic Sherman Granite and strongly magnetic Log Cabin batholith. Genetically related to the Sherman Granite, the Virginia Dale intrusive complex produces a series of concentric, sub-circular magnetic anomalies. Major faults and shear zones in the GMA in the southern Medicine Bow Mountains and the southern Laramie Mountains are expressed magnetically as strong, roughly east-trending gradients and discontinuities. The magnetic expression of major structural patterns in the GMA in the Sierra Madre have more complex and diverse geometries. Miocene volcanic rocks in the Elkhead Mountains region southwest of the CB display variable magnetizations and produce complex patterns of short-wavelength magnetic anomalies. Radiometric data signatures closely track exposed bedrock and surficial units. Generally, observed K, Th, and U values are high over granites, lower over metasedimentary rocks, and very low over mafic intrusive rocks.

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

doi: 10.1130/abs/2025AM-413688

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