Aeromagnetic surveys	Reduced to the pole	Vertical gradient	Upward continuation 10km	An interactive view of the aeromagnetic map along with the mineral occurrences

Twenty three aeromagnetic surveys have been carried out under the auspices of the Ministry of Petroleum and Mineral Resources of the Kingdom of the Saudi Arabia and the supervision of the BRGM and USGS. These surveys which covered the whole Arabian Shield (655,000 km2) have been conducted from 1962 to 1983 in several blocks and by different companies. The terrain clearance of the surveys was for the large part 150 m, 300 m and 500 m. The line spacing was in general 800 m. (see attached table and figure). The 1962 and 1965-67 surveys supervised by the BRGM on behalf of the Directorate General of Mineral Resources which covered the whole shield were flown using fluxgate Gulf Mark III magnetometers with analog recording. In addition to these 5 surveys, several less extensive surveys were carried out over targets of economic interest. They used a CSF cesium-vapor magnetometer with digital recording for the 1976 and 1981 surveys and a Geometrics G 813 proton precession magnetometer with digital recording for the 1983 survey.
Magnetic surveys measure variations in the earth's magnetic field. These variations are related to changes of magnetic properties of the rocks, but also to spatial and temporal variations of the Earth's magnetic field which are corrected.
The 1962 and 1965-67 data was originally presented as a series of total-intensity contour maps compiled at 20-gamma intervals to a scale of 1:50,000. This data was later on graphically recompiled to as series of colored 1:500,000-scale 100-gamma interval total intensity maps (Andreasen and Petty, 1973, 1974) and subsequently photographically compiled and reduced to a 1:1,000,000 scale map by Blank and Andreasen (1991). Until now, only this incomplete photographic compilation of graphically reduced contour maps was available along with its filtering effects.

To produce the aeromagnetic map  we used the original analog analytic data that was digitized by using the original records and not the contoured maps. Although more arduous than griding the contour maps, this method allows to capture all the original data without the filtering effect of the contouring (Georgel et al., 1985).

The original data obtained by digitalisation of the different magnetic profiles does not correspond to the total magnetic field nor to its anomalies. Thus a regional field has been calculated and substracted to the original profile data. We recalculated pseudo-anomalies for each block.
The data was then compiled to produce a map with an terrain clearance of 300 m, a 500m grid spacing in an UTM 38 projection. The absence of discontinuities between the different blocks implies that the regional fields were well calculated.

The obtained aeromagnetic map is of very good quality, except between latitudes 22-25° and longitudes 43-45° where a NE-SW linear fabric has been observed and corresponds probably to the flight direction. They result certainly from a bad leveling which could not be corrected in the absence of the flight original measurements.

To produce the reduced-to-the-pole aeromagnetic map, we subdivided the Shield into three parts and applied the following parameters supposing that induced field is largely predominant.

Panneau Sud : I = 21.1°, D = 0.76°
Panneau Centre : I = 29.6°, D = 1.22°
Panneau Nord : I = 37.06°, D = 1.6°


The attached data is subdivided into three directories :

Data-description
    Read.txt
    Figure (localisation of aeromagnetic surveys)
    Table (parameters of the different surveys)

Data
    Arabxx.Dat.Z (XYZ ascii files, UTM 38 coordinates)

Images
    Anorpm.tif (reduced to pole)
    Anorpm.tifw (georeference)
    Anorpvgm.tif (vertical gradient)
    Anorpvgm.tifw
    Anorpp10m.tif (upward continuation to 10 km)
Anorpp10m.tifw
    And attached legends


the different surveys...

Consortium = Aero Service Corp. + Hunting Geology and Geophysics Ltd. + Lockwood Survey Corp. ( +Arabian Geophysical Surveying Co. For Blocks 3, 4 et 5)