Background: Aeromagnetic data of the Ikogosi warm spring region was used to calculate the basal depth of the magnetic layer (Curie point depth) in the region. The warm spring issues from a crossing of fractures from a metasedimentary suite of Effon Psammite formation which form part of the Precambrian basement complex in Nigeria. Method: The adopted computational method transforms the spatial data into the frequency domain and provides a relationship between radially average power spectrum of the magnetic anomalies and the depths to the respective sources. Heat flow density and equivalent depth extent of heat production from radioactive isotopes in the area were also evaluated. Results: The average Curie point depth for the Ikogosi warm spring area is 15.1 ± 0.6 km and centres on the host quartzite rock unit. The computed equivalent depth extent of heat production provides a depth value (14.5 km) which falls within the Curie point depth margin and could indicate change in mineralogy. The low Curie point depth observed at the warm spring source is attributed to magmatic intrusions at depth. This is also evident from the visible older granite intrusion at Ikere -Ado-Ekiti area, with shallow Curie depths (12.37 ± 0.73 km). Conclusions: Results indicate that the area is promising for further geothermal explorations.

The Wikki Warm Spring (WWS) is located on the Kerri-Kerri formation of tertiary age. This forms part of the Benue Basin, which links up with the Chad Basin in the north and extends southwest to the Anambra Basin in Nigeria. The stratigraphy of the WWS region consists of alluvium, the Kerri-Kerri formation, the Gombe formation, the Pindiga formation, the Yolde formation, the Bima formation, and basement rocks as the oldest. We estimate the depth to the bottom of magnetic sources (DBMS) in the WWS region using the fractal sources distribution approach on aeromagnetic data to identify the geothermal system of the WWS region. The adopted computational method is based on statistical methods of depth determination from the radial power spectrum assuming a fractal distribution of magnetic sources. The average estimated DBMS at the WWS source location is 10.72 ± 0.54 km. The obtained results imply an average thermal gradient of 54.11 °C km -1 and heat flow value of 135.28 mW/m 2 . Generally, shallow DBMS values are obtained in the northeastern region of the WWS area and these increase towards the southwestern region when regional variation patterns of estimated depths are considered. The generally shallow DBMS obtained in the study area is attributed to magmatic intrusion or diapirism in the subsurface and emphasizes the effects of large-scale tectonic events, particularly the basin-initiating event, as major influences on the thermal history. Results will contribute to decisions on where to drill boreholes for further geothermal energy exploration in the region.

The Saudi Arabia government announced the $500 billion mega project “NEOM City”, to build a cross-border mega city to connect Saudi Arabia, Egypt, and Jordon for attracting foreign investments to the region. NEOM city is situated on the eastern region of the Gulf of Aqaba with its western side in the Sinai Peninsula. The selected site for NEOM city is geographically remarkable; nevertheless, this site needs a detailed geological and geophysical investigation. Sinai Peninsula is a microplate between the Arabian and African plates. Its southern tip is located at a triple junction comprising the Gulf of Aqaba–Dead Sea Transform fault, the Gulf of Suez, and the Red Sea, leading to relatively higher seismic activities in the region. The current study aims to understand the thermal structure of the vicinity of NEOM city to address the potential geohazards and indicate geological attractions within and around the planned city. We use the magnetic data from which geothermal images can be obtained. The preliminary results indicate that there is geologic similarity between the southern part of Sinai Peninsula and the northern part of the Arabian shield. This is because the Gulf of Aqaba separates what was once a continues Neoproterozoic crust. In addition, the magnetic data showed the presence of prominent lineaments on either side of the Gulf of Aqaba. The notable lineaments might represent faults that could still be active. Hence, selecting a site of NEOM city to be east of the Gulf of Aqaba needs to be guided by the careful understanding of the potential hazards. In addition, shallow Curie depths near the Gulf of Aqaba are recognized as a source for renewable geothermal energy.

In reply to Geothermal Energy 2:11 comments about possible errors in our recent paper Geothermal Energy 2:6, 1-21 with title 'Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring -Ekiti State, southwestern Nigeria', we show that there are no errors in the published paper. Our choice of 55 × 55 km block dimension slide across the magnetic anomaly map is consistent with the derived Curie point depths. This choice was adopted because of complexity of the geology in the area and the need to sample more data points while preserving the spectral peak. All depth estimates were carefully and thoroughly performed and assessed using tectonic framework, geological and geophysical evidence, heat flow, seismicity, and other independent information.

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