Geological-Constrained3D Gravity And Magnetic Inversion Research

Gravity and magnetic survey, the two most widely used and cheaply acquired geophysical datasets in ore deposit exploration, play an important role in the different stages of the mineral exploration. The inversion models can be used to target regions of physical properties anomalies for further data acquisition or drilling. In recently years, methods have been developed to calculate inverse solutions that predict the3D distribution of physical properties required to explain the observed geophysical responses. The inverse calculation, deriving a physical property model from the data, is hampered by numerical problems and non-uniqueness. There may be an infinite number of models that explain the observed potential field data equally well. The non-uniqueness of inversion results is tackled either by increasing the amount of gravity and magnetic data, or by imposing a set of constraints. Focusing on increasing the amount of observed data is not an efficient and feasible approach. The non-uniqueness of inversion demands that geological information be included. Mathematically, the geological constrained can reduce the number of ill-conditioned equations.This thesis started from model test, and provided a comparison of the inversion results constrained by different geological priori information. The model test revealed that, as more geological constraints are included, the inversion result is more similar with the true density model. A synthetic example of3D gravity and magnetic inversion using geological constraints in Lu-Zong ore concentration district provided a3D model within5km depth which shows the distribution of the main lithology volumes, the structures and the strata. It has proved in this thesis that the geological constrained inversion can enhance the resolution, optimize the inversion results and is very effective in making the ore concentration district transparent and prospecting the deep mineral.