2010 Geoscience BC Scholarship

Dikun Yang, PhD student, University of British Columbia



PhD Thesis - Dikun Yang
Geophysical survey decomposition and efficient 3D inversion of time-domain electromagnetic data - University of British Columbia, 2014 - Available digitally through University of British Columbia (pdf, 23.09MB)


Biography: Dikun Yang, an international student from China, started his post-secondary education in the Department of Geophysics, China University of Geosciences Wuhan in 2001. He received his B.S. with major of geophysics in 2005. He then was admitted to the graduate school of China University of Geosciences. From 2005 to 2008, Dikun specialized in electromagnetic methods of applied geophysics, including both theoretical aspects and applications of magnetotelluric, control source frequency domain EM, time domain EM, etc. Most of his researches during that period were aiming at solving the practical problems arising from industry by geophysical tools, for example, detection of groundwater, exploration of metallic and coal deposits and evaluation of geohazard. In 2008, Dikun obtained his Master's degree with his thesis on three-dimensional magnetotelluric inversion of field data. Dikun started his PhD program in Geophysical Inversion Facility, Department of Earth and Ocean Sciences, UBC in January 2009, where he has been researching electromagnetic methods and their applications in mineral exploration under the supervision of Dr. Doug Oldenburg. Currently, his is studying three-dimensional inversions and interpretations of time domain electromagnetic data and other types of geophysical data.

Project: Inversion of Time Domain Electromagnetic Datasets to Produce Realistic 3D Conductivity Models

Time domain electromagnetic (TEM) data provides unique information about the ground conductivity which is directly associated with minerals and their geologic signatures. However,because of the complexity of numerical modelling and the cost of computation, three-dimensional TEM data inversion that reveals realistic distribution of subsurface conductivity has not been fully
developed. My PhD thesis focuses on the practical inversions of two types of TEM data, viz. airborne TEM and inductive source resistivity (ISR).

Airborne TEM is a very important type of data that gives unique insight of ground conductivity at the depth of most exploitable mineral deposit. The main difficulty of 3D airborne TEM inversion is that too many transmitters are involved, so the computation of multi-source problem may be extremely expensive. This results that mining exploration heavily depends on the data-based method and 1D inversion. However, my study has shown that 1D inversion may produce completely incorrect conductivity model due to the considerably large footprint of airborne TEM system and this problem can only be tackled by 3D inversion. As the first pass I have inverted a VTEM dataset from Mt. Milligan deposit in BC and produced a 3D conductivity model in
accordance with known geology. My next step will be presenting a practical workflow for the industy, by which geophysicists can invert large-scale airborne TEM data with smart selection of soundings for inversion to achieve desired resolution with reasonable computational cost.

The other type of dataset is inductive source resistivity (ISR), which employs large transmitter loop but measures transient electrical field (E-field). ISR has been proven to be sensitive to deep and poorly conductive structure and thus very promising to be an effective alternative to the conventional magnetic field TEM in resistive geology. However ISR data have not been 3D inverted because of the complexity of the survey. I am now working with synthetic model
inversions and a field dataset from Shea Creek uranium deposit. The next step is to do some researches in the aspects of survey design and a detailed workflow of ISR inversion. With the knowledge learned in this study, the prospectors can have more insight about the E-field TEM and are able to better use this technique in deep exploration.

Roundup 2011 Poster: Delineation of Porphyry Deposit by 3D Airborne Time Domain Electromagnetic Inversion


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