In this paper we tackle the problem of inverting geophysical magnetic data due to simple shape anomalies caused by thin sheet, cylinder and fault models using Occam's inversion scheme. A significant aspect of using Occam's inversion is the choice of the regularization parameter controlling the trade-off between the data fidelity and regularization term in the cost function of optimization problem, and consequently, reliable estimation of subsurface models. Two criteria L-curve and weighted generalized cross validation are considered in order to choose an optimum value of the regularization parameter. The proposed strategy was first evaluated on three theoretical synthetic models for each of the magnetic simple-shaped structures with different random errors, where a considerable agreement was obtained between the exactly known and estimated models. The validity of the technique was also applied to one real data set from Morvarid ironapatite deposit, in Northwest Iran. The resulting inverted parameters using the proposed algorithm correspond reasonably closely with the known geology and nearby borehole information.

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As geophysical parameters are not always functionally related, treating multiple geophysical data sets to have a realistic geological model is not straightforward. An effective strategy to derive a geological interpretation is a combination of several geophysical methods with geological and well observations, each with its advantages and limitations. Gravity and magnetic methods are encouraging tools to investigate salt domes due to enough density and susceptibility contrasts between salt minerals and the background sedimentary rocks. In this paper, the dome-shaped salt unit in the Qarah-Aghaje area in Zanjan, located in the northwestern part of Iran, is investigated through the integration of 3D inversion models obtained from gravity and magnetic data and geological and well information. The 3D inversion of both data sets is made using a weighted damped minimum length solution for which model weighting is constructed from multiplying depth weighting and compactness constraints. At first, a synthetic case with a high degree of similarity to the real case is considered to evaluate the efficiency of the adopted inverse algorithm. Then, the inversion algorithm is implemented on the collected gravity and magnetic methods, and interpretation is made utilizing 3D obtained inverse models and geologic and well data. The result shows a dome-shaped potash-bearing salt unit that starts from a depth of 12 m and continues to the depth of 200 m. The drilled well in the centre of the main source of the salt (Well 3) demonstrates a depth range of 11-115 m.

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