Geophysics for Mineral Exploration

This Special Issue contains ten papers which focus on emerging geophysical techniques for mineral exploration, novel modeling, and interpretation methods, including joint inversions of multi physics data, and challenging case studies. The papers cover a wide range of mineral deposits, including banded iron formations, epithermal gold–silver–copper–iron–molybdenum deposits, iron-oxide–copper–gold deposits, and prospecting forgroundwater resources

Study on 3D forward modeling & inversion of surface-borehole electromagnetic data.

The purpose of this research is to develop an interpretive tool to meet the requirements of deep mineral exploration. Therefore, we carried out a series of research work as part of a doctoral training program and achieved the relevant objectives below. The core of this doctoral thesis is the development of 3D modeling tools to interpret the electromagnetic data collected in boreholes. First, a 3D model creation tool is designed, with which we can easily build a 3D geological model from sections and quickly discretize it. The sections could be true geological cross-sections or from a conceptual geological model. The utility of this tool is to facilitate the tests of the algorithms developed within the framework of this thesis, in order to model the electromagnetic responses in various geological situations and allow to easily change the parameters of the geophysical measurement system. Two parallelization algorithms, MPI-based and hybrid MPI/OpenMP-based methods, are designed for surface borehole time domain electromagnetic (BHTEM) forward modeling. The BHTEM responses are calculated from anomalous regions distributed in a 3D model (discretized into cells). The forward modeling additionally uses multiple meshes, fine meshes are used for the anomalous region in the high-frequency range and coarser meshes for geological background in the low-frequency range. Based on varying meshes for different frequency ranges, the parallel computation greatly reduces the computation time of the TEM forward modeling. An optimal survey design benefits from quick forward modeling. We found that the target BHTEM response depends upon the transmitting pulse width, target time constant, and the duration of measurement time. We proposed the formula with respect to the three variables to design optimal pulse widths in advance for different off-times in order to maximize the efficiency of TEM measurement in the field. Finally, a 3D BHTEM inversion algorithm is developed based on the Gauss-Newton method with high spatial resolution. By introducing the isosurface, neighborhood anomalies search, 3D trace envelope, and false targets elimination into the inversion process, the predicted model is improved through iterations and interactions between the computation and the user intervention

Energy: A continuing bibliography with indexes, issue 39

This bibliography lists 1377 reports, articles and other documents introduced into the NASA scientific and technical information system from July 1, 1983 through September 30, 1983