Determination of density value in the Nong Son - Da Nang by Petrov's 3D gravity inversion

Abstract

The paper presents the results of Petrov’s 3D inversion applied to gravity data to determine the continuous distribution of rock density from the surface down to a depth of Z = 7250 m in the Nong Son - Da Nang area, supporting the delineation of potential zones associated with ore-forming processes. The inversion method was performed continuously on the residual gravity field using a two-dimensional “live-window” energy filter, with window sizes varying from 600÷8600 m. The reliability of the inversion results strongly depends on the accurate determination of residual gravity anomalies. Therefore, in this study, we apply a statistical-probabilistic approach to identify adaptive filter-window geometries that are consistent with the regional anomaly trend, thereby enhancing the accuracy of residual gravity anomaly separation. The results show that, at the southwestern ore-point locations, the subsurface rock density is heterogeneous, forming blocks with positive residual-density values ranging from 0.1÷0.35 g/cm³, corresponding to residual gravity anomalies of 1÷3.5 mGal. The residual density anomalies within local block structures at the ore-point sites extend to depths of approximately 4000 m. The density increases from about 2.25 g/cm³ at the surface to 3.05 g/cm³ at a depth of 7250m. In the ore-bearing zones, the density varies from 2.8 g/cm³ near the surface to 3.0 g/cm³ at depths of around 4000 m, forming a continuous band extending upward from depth toward near-surface levels. The interpretation results indicate potential mineralized zones associated with the upward migration and near-surface accumulation of magma-derived materials.