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 1Hz. First, phase values of carbonaceous rocks generally decrease as a function of increasing frequency. Second, phase values of massive sulfide-bearing 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.
Four SIP lines, measured by using a 50-m dipole-dipole array, were surveyed at the Rabathan 4 prospect to test how well the results of laboratory sample measurements can be applied to larger scale field measurements. Along one line, located entirely over carbonaceous schists, the phase values decreased as a function of increasing frequency. Along a second line, located over both massive sulfides and carbonaceous schists as defined by drilling, the phase values measured over carbonaceous schists decreased as a function of increasing frequency, whereas those measured over massive sulfides increased. In addition, parts of two lines were surveyed down the axes of the massive sulfide and carbonaceous units. The phase values along these lines showed similar differences between the carbonaceous schists and massive sulfides.
To date, the SIP survey and the SIP laboratory measurements have produced the only geophysical data that indicate an electrical difference between the massive sulfide-bearing rocks and the surrounding carbonaceous rocks in the Wadi Bidah district. However, additional sample and field measurements in areas of known mineralization would fully evaluate the SIP method as applied to various geologic environments and styles of massive sulfide mineralization. Additionally, the efficiency of SIP surveys in delineating areas of sulfide mineralization might be improved by surveying lines down the axes of known electrical conductors. An evaluation of the applied research done on the SIP method to date suggests that this technique offers significant exploration applications to massive sulfide exploration in the Kingdom of Saudi Arabia.
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Preliminary results of spectral induced polarization measurements, Wadi Bidah District, Kingdom of Saudi Arabia