One-dimensional inversion of airborne time-domain electromagnetic data from Taylor Brook, western Newfoundland, and 3D finite-element time-domain forward modeling using unstructured grids

Abstract

In this thesis, geophysical inversion and numerical modeling are carried out on a dataset collected using the Airborne Time-Domain Electromagnetic (ATEM) survey method over an area called Taylor Brook, western Newfoundland, which potentially hosts massive sulfide mineralization. ATEM profiles are interpreted using a 1D inversion code (EM1DTM). The inversion results indicate that the majority of the dataset collected in the part of the area which does not show any anomaly is highly noise-contaminated. In contrast, several observation points near the sulfide mineralization have reasonable anomalies. For a better understanding of the sulfide-bearing zone’s dip, thickness and depth in the survey area, 2D cross-sections along each profile are created by combining 1D models for each observation point. Also, 3D forward modeling is applied to several Earth models that are created using the information of boreholes and the results of 1D inversions. For 3D modeling of time-domain EM problems, the finite-element time-domain (FETD) method using unstructured tetrahedral meshes is used. The dataset for two different survey profiles that have boreholes nearby were chosen to guide the building of the 3D models. A trial-and-error method, in which the physical properties and thicknesses of the geological structures were varied, resulted in a reasonable match between the vertical component (z-component) of the calculated responses from the FETD forward modeling and the measured data. This reasonable match would mean that the final Earth model is reasonable representation of the subsurface in the survey area.