The Mammoth magnetic anomaly, Pinal County, Arizona
Links
- More information: Publisher Index Page (via DOI)
- Data Releases:
- USGS data release - Airborne magnetic and radiometric data acquired over parts of Cochise, Graham, Greenlee, Pima, Pinal, and Santa Cruz Counties, Arizona
- USGS data release - Ground Magnetic Observations of the Mammoth Magnetic Anomaly, Pinal County, Arizona, May 2025
- Open Access Version: Publisher Index Page
- Download citation as: RIS | Dublin Core
Abstract
A high-resolution Earth Mapping Resources Initiative airborne geophysical survey was flown in the southwest North American porphyry copper province to improve bedrock geologic maps and to identify areas that have unrecognized critical mineral resource potential. During the review of the aeromagnetic data, a distinctly monopolar-shaped, negative magnetic anomaly was observed at a flight elevation of 200 m above the ground with a maximum amplitude of –9500 nT. We have named this the Mammoth magnetic anomaly (MMA) because it is centered 12 km northeast of the town of Mammoth, Arizona, USA. The total field anomaly (TFA) contour of –500 nT enclosing the MMA defines an elongate shape measuring 2.5 km long by 1 km wide that trends northwest–southeast. Given the striking nature of this negative, monopolar-shaped magnetic anomaly, we conducted a ground campaign in May 2025 to determine its authenticity and potential relationship to critical mineral endowment. The MMA was confirmed on the ground with a TFA approaching –46,000 nT. Total magnetic intensity (TMI) observations routinely fell below the 18,000 nT operating floor of an industry-standard cesium-vapor total field magnetometer, and extremely low TMI measurements were corroborated along coincident traverse lines using two high dynamic range, but lower sensitivity, smartphone vector magnetometers. The lowest TMI values recorded by both smartphone magnetometers were 1000 nT and confirmed with multiple adjacent and crossing lines. Field observations suggest that this magnetic feature is caused by strong remanent magnetization within fine-grained magnetite hosted within locally altered Pinal Schist.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | The Mammoth magnetic anomaly, Pinal County, Arizona |
| Series title | The Leading Edge |
| DOI | 10.1190/tle44110879.1 |
| Volume | 44 |
| Issue | 11 |
| Year Published | 2025 |
| Language | English |
| Publisher | The Society of Exploration Geophysicists |
| Contributing office(s) | Geology, Minerals, Energy, and Geophysics Science Center |
| Description | 10 p. |
| First page | 879 |
| Last page | 888 |
| Country | United States |
| State | Arizona |
| County | Pinal County |