Nigeria’s Nationwide High Resolution Airborne Geophysical Surveys

Nigeria has gained near nationwide airborne geophysical coverage, with high resolution horizontal gradiometer magnetic and radiometric surveys, flown at 500 m line spacing and 80 m mean terrain clearance, totalling almost 2 million line-km. The surveys were flown, per the index map, as follows: 2003 – Pilot Project – Ogun State, 2005-07 – Phase 1 – Blocks A+C and B, 2007-09 – Phase 2 – Blocks D1, D2, D3 and D4. All surveys were carried out by Fugro Airborne Surveys on behalf of the Nigerian Geological Survey Agency. Phase 2 forms part of the World Bank-supported Sustainable Management for Mineral Resources Project. As part of Phase 1, time-domain electromagnetic surveys were flown at 200 m line spacing in 2008-09 with the Tempest system over three blocks, totalling 24,000 line-km. Additional TDEM surveys are planned for Phase 2. To complete the airborne coverage, the Niger Delta block will be flown in 2010 with magnetics at 1 km line spacing. In addition, a quarter of the block will incorporate airborne gravity. The survey data are currently being interpreted by Fugro Airborne Surveys (Phase 1) and by Paterson, Grant & Watson Limited (Phase 2). PGW has prepared nationwide merged grids, and will integrate the two interpretations. The data have proven extremely valuable for: -Depth-to-source mapping of the inland sedimentary basins, delineating areas of interest for oil & gas exploration, as well as mapping shallow basement with extensions of known mineral belts -Determining signatures of known occurrences such as gold deposits, lead-zinc deposits and kimberlite pipes -Mineral potential mapping -Characterization of the “Older” and “Younger” granites -Mapping intrasedimentary igneous sources, sedimentary horizons and structure -The complementary mapping capabilities of radiometric and electromagnetic data in both hard rock terrains and exposed sediments (e.g. Benue Trough). An oral presentation will provide an overview and key highlights. It will also discuss the challenges of compiling and integrating data from a multi-year campaign, utilizing as many as seven aircraft in a survey block. A poster presentation will provide a more in-depth analysis of specific areas of geophysical and geological significance, as well as the contrast of the new surveys with the low resolution magnetic data from the 1970s.