3D Inversion of Time Domain Data with Integrated Application to Mineral Exploration

We present a 3D time domain inversion algorithm. The forward problem is solved using finite volume methods in the spatial domain and an implicit method (Backward Euler) in the time domain. A modified Gauss-Newton strategy is employed to solve the inverse problem. The practical modifications include the use of a Quasi-Newton method to generate a preconditioner for the perturbed system, and implementing an iterative Tikhonov approach in the solution to the inverse problem. In addition, we show how the size of the inverse problem can be reduced through a corrective source procedure. We invert UTEM data at San Nicolas and compare the results to previously obtained images from gravity, magnetics, and IP and with geologic information from drill holes. A consistent interpretation for the location of a massive sulfide is achieved.