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

Geophysical framework of the Elkhead Mountains in northwest Colorado interpreted from newly acquired Earth MRI data

Paper number: 110-3
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Eocene to Miocene Elkhead volcanic field in northwestern Colorado is a result of widespread volcanism associated with diffuse extension after the Laramide Orogeny (< 40 Ma). The region experienced uplift of ~1 km and denudation since the Late Miocene (<10 Ma), leaving much of the Elkhead Mountains as sub-volcanic plutons (dikes and sills). The compositions of the igneous rocks include basalt, minette, andesite, dacite and rhyolite.

Recently collected (2024-2025) high resolution USGS Earth MRI airborne magnetic and radiometric data significantly improve our ability to geologically and geophysical identify and characterize the spatial distribution and size of igneous bodies, faults, and mineralizing systems of the Elkhead Mountains. There are sizable magnetic susceptibility contrasts between the volcanic rocks and surrounding older host rock, as well as distinct potassium anomalies associated with some known outcrops.

Both negative and positive large (100’s up to 1000 nT) mostly elliptical anomalies (up to 1000 m by 7000 m) result from exposed or relatively shallow extrusive or intrusive volcanic bodies. The similarity between some observed RTP [reduced to pole] magnetic anomalies with forward magnetic models of the topographic support the inference of exposed volcanic bodies. The negative anomalies suggest reversely polarized magnetic rocks.  In addition, there is a large circular (~4500 m diameter) relative negative magnetic anomaly (~200 nT) coincident with Hahn’s Peak, which will help better define the geometry of the stock of the volcano.

Our current characterization of the size and extent of the igneous rocks has been limited to mapping surface geology, with the best mapping in the area from the USGS done in the late 1970’s.  We will present preliminary interpretations of the character and depth extents of igneous bodies in the Elkhead Mountains, integrated with recent geochronologic work and magnetic susceptibility measurements.  In addition to better characterizing the Elkhead volcanic field, the new data are crucial for exploration of critical minerals and interpretation will head towards understanding the geophysical framework for mineral systems in the future.

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

doi: 10.1130/abs/2025AM-414180

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