b'What lies beneath revisitedFeatureFigure 4.Ujina deposit geology-upper image; TEM section-lower image (Nickson 1993).This work was carried out in 1993 and the results circulated by Quantec to interested parties (Nickson 1993). One such group was BHP who have been investing considerable effort at upgrading airborne EM technology along with Aberfoyle LLC and Geoterrex Ltd (Smith etal., 2003). Based on the Quantec work, and other trials carried out by BHP near the Escondida Mine, BHP then undertook a major programme of airborne EM looking for the supergene part of undiscovered porphyry systems. This work was summarised in Harrison (2002).The scope of the exploration programme allowed for a more careful examination of actual conditions within the ore body. Figure 5 shows a downhole resistivity log from Escondida Norte. Harrison (2002) also provided the following comments about what was observed:Figure 5 is a physical property log from Escondida Norte showing the strong correlation between conductivity and total sulphide content (Pyrite, Chalcopyrite, Chalcocite and Covellite). Chalcopyrite tends to be more disseminated and not as well connected in hypogene ore and is generally not seen as a source of conductivity. Pyrite is the most abundant mineral, and although it does not have the lowest resistivity, it makes up for it in connectivity. In addition, chalcocite can form as sur\x1fcial covering on incompletely oxidised pyrite crystals, increasing the connectivity and lowering the resistivity for non-economic occurrences of chalcocite. Metallic chalcocite is well connected and very conductiveAlmost concurrent with this work, Aerodat Ltd., a Canadian airborne survey group, was commissioned by the Iran NationalFigure 5.Graph showing strong correlation between downhole conductivity Copper Company to carry out an extensive airborne EM,and total sulphide content for ZERD62 at Escondida Norte.DECEMBER 2023 PREVIEW 46'