Reconnaissance geologic and geochemical sampling was made during the 1978 field season at most of the 50 or so electromagnetic anomalies detected in the 1977 airborne electromagnetic (AEM) survey of the Wadi Bidah district. These Phase 1 studies also included reconnaissance geophysical traverses of nine of the AEM conductors. In addition the AEM anomalies were classified on the basis of this reconnaissance work into a list of priority targets for use in economic studies, and six AEM anomalies were selected for further studies.
During Phase 2 conducted in the 1979 field season, ground geophysical work consisting of electromagnetic (EM), self-potential (SP), and selected magnetic surveys were carried out in the six targets selected in the Phase 1 studies. These target areas in aggregate cover about 30 km 2, and are approximately half of the Wadi Bidah Class 1 and Class 2 priority targets found during the 1977 airborne electromagnetic (AEM) survey of parts of the Arabian Shield.
The results indicate possible extension of known reserves at the Rabathan area (AEM anomaly B-29), with possible potential for mineralization in the area extending 15-20 km north (anomaly B-13), where the geologic and geophysical environment is similar.
An important observation is that mineralization in the B-29 (Rabathan) zone is coincident with narrow SP anomalies superimposed on the larger, broader, and more formational-type SP anomalies encountered in both areas B-29 and B-13.
AEM anomaly B-25-26 areahas geophysical characteristics that show in the groundwork and that make it an attractive drill target. EM and SP anomalies are associated, in part, with magnetic anomalies and with exposures of significant limonitic gossan.
Wadi al Khadra prospect, not included in the 1977 AEM survey, and the AEM anomaly B-25-26 area were also high-mineralization-potential products of the Phase 2 studies. Target area B-35 remains an unknown quantity, and AEM anomaly B-24 is almost certainly due to a carbonaceous schist.
Geochemical results, along with detailed geologic mapping and the geophysical data, indicate several potential mineralized targets. Further detailed geophysics (EM and SP) will assist in understanding the geophysical data thus far collected.
Further ground follow-up studies are recommended.
Additional Publication Details
USGS Numbered Series
Preliminary report on geophysics ground follow-up of the 1977 airborne survey in the Wadi Bidah District, Kingdom of Saudi Arabia