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A case study of two and three‐dimensional inversion of dipole‐dipole data: the Enfermarías Zn‐Pb (Ag, Sb, Au) Prospect (Moura, Portugal)
- Source: Near Surface Geophysics, Volume 3, Issue 1, Jan 2005, p. 21 - 31
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- 01 Mar 2003
- 01 Jun 2004
- 01 Jun 2004
Abstract
The Enfermarías Zn‐Pb(Ag, Sb, Au) prospect, located in the Moura‐Ficalho region (Alentejo, Portugal), was intensively explored during 1980s. A drilling programme was successful, intersecting massive and disseminated sulphide mineralizations. The geological and geophysical data set available for Enfermarias is quite vast and comprises 13 borehole geological logs, as well as gravity, magnetic and resistivity data. In this paper, the dipole‐dipole resistivity surveys are re‐examined and interpreted using both 2D and 3D inversion to provide an interesting comparison of the two different approaches. Results from gravity data modelling and data from borehole logs are used as independent validity tests on the quality of the results.
The 2D and 3D models indicate a conductive overburden covering more resistive bedrock, which appears at a depth of 70–100 m in the western part of the profiles. Results obtained from 3D inversion, however, show a very clear separation of the most resistive domains in the two different bodies, whereas this separation does not appear in the 2D models. The 3D model also shows a higher degree of spatial continuity than the partial 2D models, which are, in general, richer in short‐wavelength anomalies, and show a higher variation from profile to profile.
Comparison of the resistivity results with gravity in two coincident profiles reveals an excellent agreement between the main shallow features of both 2D and 3D models. This suggests that the resistivity model does indeed satisfy the main features of the available geological and geophysical data.