The Applicability and Limitations of the Induced Polarization Method in the Search for Sulphide Mineralization in the Troodos Igneous Complex, Cyprus
thesisposted on 15.08.2012, 13:56 by George Maliotis
The Pillow Lava sequence overlying the Troodos Igneous Complex of Cyprus contains sulphide mineralization within tectonic zones of variable width and extent, and some of these have been mined since ancient times. Previous I.P. and other geophysical work showed that the location of concealed zones presents considerable problems. In this study a new attempt using modern highpower equipment was made to assess the usefulness of the I.P. method in Cyprus. After an orientation survey over a sulphide body 125 m deep, Time-Domain I.P. and Resistivity surveys using the pole-dipole configuration with a spacing of 50 m were carried out over six different areas where the mineralization occurs in different modes and grades. The data were plotted on pseudosections which conveyed very useful information on the location, extent and depth of the polarizing body. The resistivities of the barren rocks were generally low, between 5 and 30 ohm-meters. The zones of high grade sulphide mineralization had equally low resistivities which increase with decreasing sulphide content. The N.T.I. was found to attain high values over the mineralization. The amplitude varied mainly according to the size, depth and location of the body with respect to the geophysical grid. The highest anomalous values were observed when both poles of the receiver were over concealed or exposed mineralized bodies. This clearly imposes limitations on the detection of narrow zones, particularly at depth. The values of the I.P. voltage were observed at sixteen times between 0.035 and 0.78 sec. for n = 2 on all the lines. The I.P. decay was investigated both as an exponential decay and as a log time decay. In the first the electromagnetic and true chargeabi¬lity components were found to attain in general high values over the mineralization but without any significant variations between the disseminated and higher grade mineralization. On the log time axis the I.P. decay was found to consist of a short and fast decaying linear component, and a later and slower curved component. Some of the parameters which describe this shape were found to have much different values over the different grades of mineralization implying thus a distinction between disseminated and high grade mineralization on the basis of the decay curve.