ZTEM Airborne AFMAG EM and Ground Geophysical Survey Comparisons over the Pampa Lirima Geothermal Field in Northern Chile

Abstract

A ZTEM (Z Tipper Axis Electromagnetic) airborne AFMAG survey was conducted over the Pampa Lirima geothermal project where a number of other ground geophysical surveys had been previously undertaken, including magnetotelluric (MT), time domain transient electromagnetic (TDEM), and DC resistivity soundings. Resistivity methods such as MT are typically used to map structure, lithology and alteration, especially the low resistivity cap over the outer margins of the geothermal reservoir at depth. The ZTEM survey at Pampa Lirima overflew the area for comparison purposes. The ZTEM results appear to correlate well with previous geophysics and the known geology, including known fault structures and contacts, as well as a prominent conductivity high over the Lirima hot spring field. 2D inversions of the airborne ZTEM appear to agree quite well with 3D inversion of ground MT for shallower depths (<2km), in particular the conductive clay-cap attributed to the deep 3D MT conductive heat source and a resistive NE-SW lineament that extends between the Lirima and San Andrés hot springs. Joint 3D MT-ZTEM inversion results should improve the accuracy and the areal extent of the known subsurface resistivity structures at Pampa Lirima.