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Integrating geologic and geophysical data through advanced constrained inversions Lelièvre, Peter George

Abstract

To be reliable, Earth models used for mineral exploration should be consistent with all available geologic and geophysical information. There are two areas of research that are important to help achieve the goal of more reliable Earth models: development of geophysical inversion methods that 1) increase the kinds of geologic information that can be incorporated, and 2) can combine several complimentary types of geophysical data collected over the same Earth region. Discussions with geologists connected to exploration studies have identified several types of geologic information which could help improve results if incorporated into geophysical inversions. A specific goal of my research was to develop methods for incorporating all of that information into inversion algorithms within a deterministic framework (i.e. minimization of an objective function). I developed several methods to reach this goal. Inversion of magnetic data is complicated by the presence of remanent magnetization. Typical magnetic inversion routines assume no remanence exists and erroneous results can be obtained if this assumption is made incorrectly. To solve this problem I developed two total magnetization vector inversion routines that allow for the incorporation of geologic information that is commonly available regarding remanence. Another important form of geologic information is orientation information. I developed methods for incorporating orientation information into geophysical inversions. This information can be incorporated by performing a rotation of an orthogonal system of smoothness operators and through the addition of linear constraints to the inverse problem. Lastly, I developed an iterative procedure for cooperatively inverting multiple types of geophysical data (from surveys responsive to different physical properties). The procedure creates models that are structurally similar and geologically realistic, in that they involve sharp interfaces (physical property jumps) between rock units (regions of nearly constant physical properties). My research provides functional methods for applying geophysics to exploration problems. None of the methods I developed involve significant complications to the inverse problem and they can be applied to current exploration problems without requiring additional computing resources.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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