New Mexico Aeromagnetic Compilation

Aeromagnetic anomalies are due to variations in the Earth's magnetic field caused by the uneven distribution of magnetic minerals (primarily magnetite) in the rocks that make up the upper part of the Earth's crust. The features and patterns of the aeromagnetic anomalies can be used to delineate details of subsurface geology including the locations of buried faults, magnetite-bearing rocks, and the depth to the base of sedimentary basins. This information is valuable for mineral exploration, geologic mapping, and environmental studies.

The New Mexico aeromagnetic map is constructed from grids that combine information (see data processing details) collected in 58 separate aeromagnetic surveys conducted between 1946 and 1998. The data from these surveys are of varying quality. The design and specifications (terrain clearance, sampling rates, line spacing, and reduction procedures) varied from survey to survey depending on the purpose of the project and the technology of that time. Every attempt was made to acquire the data in digital form. Most of the available digital data were obtained from aeromagnetic surveys flown by the U.S. Geological Survey (USGS), flown on contract with the USGS, or were obtained from other federal agencies and state universities. Much of the pre-1975 data are available only on hand-contoured maps and had to be digitized. These maps were digitized along flight-line/contour-line intersections, which is considered to be the most accurate method of recovering the original data. Digitized data are available as USGS Open File Report 99-557.  All surveys have been continued to 304.8 meters (1000 feet) above ground and the surveys are blended or merged together. An index plot gives an overview of the original surveys and a data table summarizes the detailed specifications of the surveys. The map can be downloaded as a grid with a 500 meter grid interval.

Also included are maps and grids of some of the individual surveys at their original flight elevation that were generated with a finer grid spacing due to a closer flight line spacing. These were then regridded to the final grid spacing of 500 meters for use in the state merge.

The entire study area is covered by aeromagnetic data collected as part of the National Uranium Resource Evaluation (NURE) program of the U.S. Department of Energy. These data are available in digital form and provided the framework for the map compilation. However, because magnetic surveying was not the primary objective in the design of the NURE surveys, these data are subject to certain limitations. Although the NURE surveys were flown at elevations close to the reduction datum level, the spacing between flight lines ranged from 4800 meters to 9600 meters (3 to 6 mile). The wide spacing between flight lines flown at low altitudes over surface rock units having high magnetizations causes anomalies with short spacial wavelengths to be elongated between flight lines, producing lineations perpendicular to the flight-line direction and 'pearl string' anomalies along the flight line. Problems related to the reduction of navigation control and inconsistent datum levels between surveys causes herringbone features which can be observed within and at the boundaries of 1° x 2° quadrangles. Consequently, data from higher resolution surveys other than NURE were incorporated into the framework of NURE surveys wherever possible.

This project was supported by the Mineral Resource Program / Crustal Imaging & Characterization Team of the USGS. The authors wish to thank our USGS colleague Mike Webring for the in-house software used to prepare the aeromagnetic data.

The USGS also acknowledges the U.S. Bureau of Indian Affairs Division of Energy and Minerals and the Unocal Corporation for allowing us to include their data sets in the composite grid of New Mexico.

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