Interpretation Of Borehole Gravity Data For Vms Deposits In The Context Of Complex Geology

A forward modeling and inversion code has been developed to study the use of the borehole gravity method for exploration of VMS deposits. Different problems are associated with the gravity method and to analyse them, synthetic data has been modeled and then inverted. The first problem encountered is the data acquisition settings including the number of boreholes, their location and data collection sampling in the boreholes. They highly influence the results of the inversion. A minimum of three boreholes within appropriate distance from the target is required to locate any structure. In the case where the geology is complex, the boreholes have to be well positioned around the deposit to be able to properly locate it. In the scenario where the borehole gravity method is used to calculate the excess mass of a deposit and to define its structure, at least one borehole should intercept the deposit. Also, fixed density constraints are highly recommended to be able to calculate precisely the excess mass of a deposit. The regional-residual anomaly separation is a very important aspect of the data interpretation. Up to now no technique is effective in performing an optimal separation. In this paper we apply four different methods and compare the inverted density model to the initial model. These methods are the graphical method, the vertical gradient, a non-linear filter and a wavelet filter. Then these methods were applied to GraviLog data that was acquired over and in the vicinity of the Virginia Gold’s Coulon deposit (Quebec, Canada). All methods were able to help locate the deposit, but densities are all underestimated.