The optimization and interpretation of induced polarization surveys in cyprus.

It is known from the geology that the pillow lava sequence overlying the Troodos igneous complex of Cyprus ought to contain many concealed sulphide orebodies. It has been shown in the past that the only geophysical technique capable of locating such deposits is the induced polarization method. However problems still remain in the implementation of surveys and in discriminating between different IP sources. In-situ measurements using a short spacing Wenner array were carried out over mineralization and barren rocks. The decay curves, after normalization to the value at 0.063 seconds after current cut-off, were all fitted, by a least squares method, to a three component exponential function. The exponential factors showed no discrimination between metallic and membrane IP, but indicated a longer decay for large magnitude chargeability. An estimate of the energy spectral density under each decay curve produced the same result, but did discriminate between Lower Pillow Lavas and mineralization for large chargeability values. IP surveys over two known, but contrasting sulphide deposits showed that the dipole-dipole array is the most applicable when only one traverse per line is carried out. However when combined profiling is undertaken the pole-dipole array is the most suitable due to its asymmetrical nature. Mixed plotting of the data has also been found to be a useful aid to interpretation. Inductive coupling was not a serious problem, but some of the decay curves were dominated by noise for the larger array separations. Criteria were developed for assessing data quality. Computer modelling using the finite-element method has demonstrated its applicability for interpretation and empirical relations have been developed which assist in the selection of survey parameters. The changes produced in the pseudosections by altering various geological parameters have been investigated with simplified models of the Cypriot environment. The resistivity data was found not to correlate with the IP data, but there was an indication of a resistivity decrease with depth.