Laboratory spectral induced polarization (SIP) measurements on 29 carbonaceous schist samples from the Wadi Bidah district show that most are associated with very long polarization decays or, equivalently, large time constants. In contrast, measurements on two massive sulfide samples indicate shorter polarization decays or smaller time constants. This difference in time constants for the polarization process results in two differences in the phase spectra in the frequency range of from 0.06 to 1 Hz. First, phase values of carbonaceous rocks generally decrease as a function of increasing frequency. Second, phase values of massive sulfidebearing rocks increase as a function of increasing frequency. These results from laboratory measurements agree well with those from other reported SIP measurements on graphites and massive sulfides from the Canadian Shield.

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Fourier spectral analysis in recent years has become a widely utilized tool for the processing and interpretation of potential field data.It is particularly well suited to analysis of aeromagnetic maps and profiles, where coverage commonly is of broad scope and statistical treatment is appropriate.The techniques developed by earlier workers for map data are readily adapted for depth estimates using aeromagnetic profiles.Three subroutines are presented: "FRQAN", which employs the complete Fourier transform to convert field intensity to the frequency domain and then computes the logarithmic energy spectrum; "CSIZE", which refines the spectrum to correct for the finite horizontal dimensions of magnetic sources, and "ENSMTH", which smooths the spectrum to clarify its decay characteristics.The average depths to sources of ensembles are obtained by manually fitting a straight line to each linear interval of the logarithmic energy-decay curve.If proper account is taken of the constraints of the method, it is capable of providing depth estimates to within an accuracy of about 10 percent under suitable circumstances. The estimates are unaffected by source magnetization and are relatively insensitive to assumptions as to source shape or distribution. The validity of the method is demonstrated by analyses of synthetic profiles and profiles recorded over Harrat Rahat, Saudi Arabia, and Diyur, Egypt, where source depths have been proved by drilling.

El Sadat City is a new urban community established in the Western Desert of Egypt near the Hile Delta. The district of the city and vicinity is covered by a thick Pleistocene section of sand and gravel facies based by a thick Pliocene layer of plastic clays.An area, selected from the previous hydrological studies, was covered by 27 deep electric soundinss in order to locate the fresh water aquifers that may occur and to identify the probable geometry of these aquifers. Data collection, reduction and analysis were achieved in site using field computers ~o produce the equivalent layering model and the n-layers model of each sounding. The models were used to construct the subsurface true resistivity bar sections as well as the resistivity contour sections along three profiles using the set of soundings located on each profile. Besides, subsurface horizontal contour sections were produced at different depths.The interpretations of the analysed data revealed that most of the Pleistocene sediments act aa a fresh water aquifer which is charged from the water circulated from the Delta. It was also possible to distinguish subsurface gravel rich channels which yield most of the groundwater potential in the area. The depth to fresh groundwater ranges from 35 m to 65 m according to the relative topography of each sounding site. In addition, the study indicated that another saline aquifer, of probably fossil water, occurs at greater depths beneath the fresh water aquifer. The two aquifers are vertically separated by a thick layer of impervious formations. Recommendations for drilling, in some selected Sites, were reached from the present study. The subsequent drilling operations resulted in the construction of a number of heavy duty water wells (water field B with capaCity of 70,000 m 3 /day) which satisfy the water demand ot the city.

Detailed geophysical measurements have been made in the Rabathan area, Wadi Bidah district, Kingdom of Saudi Arabia, at the site of diamond drill holes RAB-1, -2, and -3; these measurements suggest that the causative source for the anomalous EM (electromagnetic) and SP (self-potential) responses is probably highly conductive zones of Precambrian siliceouscarbonaceous rocks.Although many of the zones are no more than a few meters wide, they commonly contain 50 to 80 percent carbonaceous material and locally abundant pyrite.In places, several thin layers of highly concentrated carbonaceous material interlayered with chert form a multiple conductive zone that is seen in the geophysical data as complex anomaly patterns. In the geologic environment of Wadi Bidah, massive sulfide-bearing zones cannot be distinguished from siliceous-carbonaceous zones on the basis of the EM-SP responses.In North America in similar environments, complex resistivity methods used in experimental research have successfully discriminated between sulfide and carbonaceous conductors.Tests of such methods in the Wadi Bidah district are recommended. Geologic, geochemical, and geophysical data at the Jabal Mohr prospect suggest the possibility of mineralized rocks at depth over a possible strike length of 400 m.