Interpretation of regional geophysical data for mapping subsurface geology and hydrogeology

点击翻译按钮获取中文摘要

An important component of the resource exploration process is the collection of regional airborne geophysical data. When integrated with geological and geochemical data, an interpreter can use the geophysics to select sites for more detailed work that will assist in the discovery of minerals, hydrocarbons and groundwater. My research program is to develop innovative tools that will substantially improve the efficacy of airborne magnetic and electromagnetic methods. Airborne data are normally collected along flight traverses with samples every 5 to 15 m, but the traverses can be 100 m apart or more. These data are interpolated between the lines to generate a data set on a uniform “grid”. This interpolation process generally works well, but narrow features that trend at angles oblique to the flight lines are not well sampled, so the grid is not a good representation of the underlying geology, showing aliasing artifacts. The first project is to have a student develop a computer algorithm that is capable of generating a grid free of artifacts that better represents the underlying geology. This new algorithm would provide geoscientists with tools that they could use on a daily basis to generate better grids and hence understand the sub-surface geology and find earth resources more effectively. The second project will be for a graduate student to use the improved gridded data to determine the underlying geological source. The SLUTH method, developed previously, is good for estimating the depth to faults or dykes. A theoretical development would allow a student to develop an innovative new method for interpreting the depth and thickness of the geological feature. Airborne electromagnetic data are most important when looking for discrete highly conductive bodies. The way to determine if the conductive body is a valuable mineral deposit is to drill a hole aimed to intersect the body. A drill hole will only intersect the target if the depth and orientation of the target can be estimated correctly from the electromagnetic data. Project 3 will build on theoretical work that shows that the electromagnetic response of a body at an arbitrary inclination (dip) can be decomposed into the response of horizontal and vertical dipoles at the same depth. This enables a simple interpretation scheme to be developed for electromagnetic data that is similar to the automatic schemes used for magnetic data. It might also be possible to extend the theory to the case of arbitrary strike direction. A fourth project would involve calculating the response of the discrete conductor below conductive overburden, which is very important for exploring for resources in the "ring of fire" area in northern Ontario, an area where nickel and cobalt have recently been discovered. The fifth project would allow airborne electromagnetic data to be processed so as to directly map water in the subsurface using magnetic resonance imaging (MRI). These MRI methods are used with ground systems, but a cruder form of the technique that uses existing airborne electromagnetic data might be used to select areas that would warrant follow up with a ground system. The first four projects will develop into further projects in subsequent grant applications to improve our ability to map geology, understand geological processes, monitor the environment and explore for scarce mineral deposits. The fifth project is a proof of concept project; the technology will be further developed in subsequent grants, developing a cost effective technique for regional exploration for water. With the growing population on the planet and the development in Africa and Asia, water and mineral resources will be in strong demand and monitoring the environment will be very important.