Godio, A.

A Spectral Induced Polarization (SIP) survey was carried out in a mining test site in Sardinia (Italy). Measurements were developed along a profile by using an axial dipole-dipole array with 10 AB positions and 6 MN positions for cach AB. The amplitude and phase spectra of the apparent resistivity were acquired in the 0.25-4096 Hz frequeney range. The results obtained through the processing and inversion step seem to confirm that, with respect to the classical TD/FD Induced Polarization, SIP allows better discrimination of some important characteristics of mineral deposits such as mineral content and grain size.

A magnetic and an electromagnetic survey using low induction equipment were performed on a test site in an industrial landfill; the main goal of the geophysical survey was to check the reliability of data processing techniques for detecting iron masses inside the upper part of the landfill. Physical and chemical characterisations of the test area, performed on some samples, supplied the geophysical investigations. This paper outlines the data processing of the magnetic data, which was mainly based on the solution of Euler’s equation to detect near surface magnetic sources, associated with iron concentrations. The results of the magnetic survey delineate the existence of high concentration of ferro-metallic objects; the magnetic behaviour of the waste disposal is affected by the presence both of fine iron materials disseminated in sandy and clayey materials, derived from the cast iron foundry industrial process, and ferro-metallic objects such as drums or parts of heavy machines. Some trenches, excavated in the test area, proved that the magnetic behaviour of the landfill is mainly caused by the high concentration of fine iron materials disseminated in the waste. Therefore, magnetic surveys could be useful tools for detecting zones of high concentrations of iron particles in the landfill; this material can be recovered from the landfill and recycled.

The paper deals with some aspects of the planning and the interpretation of the IP and resistivity measurements in the San Priamo coastal plane (Sardinia, Italy). The plane presents some hydrogeological problems related to previous flowages and salt water intrusion from the sea. The geophysical results verified the good resolution of the joint elaboration of the IP and the resistivity soundings, in order to delineate some hydrogeological aspects of the San Priamo coastal plane. In particular, the technique was suitable for detecting salt water intrusion in a fresh acquifer, with good reliability.