Gravimetric detections for characterizing intrusive geometry in the Precambrian basement of northwestern Nigeria

The study was inspired by the need to diversify the country’s economy from oil-based to non-oil-based, of which solid mineral resources are prominent, in addition to some scientific research interests derivable from the clear understanding of the petrological settings in the area. The Nigeria geological setting comprises basically of basement complex, which hosts most of the mineral resources in the country, and a sedimentary basin. Over 95% is the basement complex in the study area. The aim was to infer 2D models for characterizing the lithological series of rock intrusions within the host rocks. Gravity data were collected over 4 months using LaCoste-Romberg Gravimeter G446 from 1579 stations over 23,235.3525 km 2 . The stations were tied to the International Gravity Standardization Net (IGSN). Mean density values from 142 samples of rocks are as follows: granite 2.61 ± 0.07 g cm −3 , pegmatite 2.63 ± 0.06 g cm −3 , granodiorite 2.67 ± 0.05 g cm −3 , dolerite 2.65 ± 0.07 g cm −3 , and gabbro 2.68 ± 0.06 g cm −3 . The Bouguer anomaly field ranges from − 300 to − 20 mGal, while the residual anomaly varies between − 200 mGal and 120 mGal. The general NE–SW trend obtained in all the anomaly fields agrees with the regional trend in the Nigeria Basement Complex. High gravity gradients (maximum 5 mGal/km) from most intrusions in the area confirmed sharp vertical contacts. The largest depth and thickness of the low-density intruding granites are 27 and 44 km; the high deep root here suggests a magmatic mode of emplacement. Their density contrast ranges from − 0.57 to − 0.3 g cm −3 . Isolated denser ultra-basic intrusions, whose density range is 0.2–0.4 g cm −3 , occurred with depth and thickness of 14 and 44 km in the area. These intrusions were suspected to be of metasomatic origin. Furthermore, a low-density sill-shaped structure, 18-km deep and 2.5-km thick, was mapped in the southern part of the study area. In conclusion, the occurrence of deep-rooted gravity-low causative bodies confirmed low-density mineralogical presence in some parts of the area. Also, metasomatic intrusions confirmed the occurrence of chemical alterations whereby the host rocks were replaced by denser/mafic rocks of high-gravity field mineralogical compositions.