Research And Application On The Joint Inversion Of 3D DC Resistivity And Gravity Data Structural Constraints

Our country's prospecting work is gradually turning to deep mineral resources.The lead-zinc mining area in the upper reaches of Xiagalaiaoyi River is located in Huzhong area of Daxinganling Mountains in Heilongjiang Province,which is rich in mineral resources.In order to more accurately infer the underground geologicalgeophysical model of the mining area,Heilongjiang Geophysical Prospecting Institute has carried out three-dimensional integrated geophysical exploration in the mining area.3D resistivity data and 3D gravity data were collected.DC resistivity method and gravity method are two important geophysical exploration methods,but both of them have their own limitations.In order to solve the limitation of single inversion,reduce the multi-solution of single inversion,and obtain the geological-geophysical model with consistent structure,a joint inversion algorithm of DC resistivity and gravity based on cross-gradient structure constraint is used to process the data.For the forward,the finite volume method is used in the resistivity method,and the regular hexahedral grid is used in the gravity calculation by using the analytical expression.The correctness of the forward numerical simulation is verified by the resistivity forward calculation and the gravity forward calculation.At the same time,the data reliability of the joint inversion theoretical model is tested.In the aspect of inversion,the cross gradient constraint is added to the inversion objective function in the form of penalty term,and the objective function is solved numerically by GaussNewton method.Finally,the resistivity and density models are obtained by alternating iteration.In this paper,the above joint inversion algorithm is tested in single and double anomalous body models,and the model test results show that,compared with the single inversion,the resistivity model is more similar to the density model in structure,the resistivity model is more effective in the vertical constraint of the density model,and the vertical resolution of the density model is significantly improved.The joint inversion can obtain more accurate spatial structure distribution of the anomalous body.Finally,the cross-gradient joint inversion algorithm studied in this paper is applied to the field actual data,and the joint inversion study is carried out on the collected threedimensional resistivity data and three-dimensional gravity data,and the resistivity model and density model obtained by the joint inversion are more similar to the single inversion structure,combined with the surface geological data and known ore body information.The geological interpretation of the joint inversion results is carried out,and two metallogenic prediction areas are delineated,which provides a strong basis for accurately judging the spatial location of deep geological bodies.