Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring - Ekiti State, southwestern Nigeria

Abstract

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.

Discussion on `Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring - Ekiti State, southwestern Nigeria’

“…Considering a data window of 55 × 55 km used by Abraham et al (2014), only depth information to a depth of 8.75 km could be satisfactorily resolved by spectral analysis. Consequently, the CPD values reported in the paper could likely be erroneous.…”

“…Consequently, the CPD values reported in the paper could likely be erroneous. The 55-km dimension windows will neither be adequate to analyze 11.48-nor 21.91-km base depths as reported by Abraham et al (2014). To obtain a reliable and accurate CPD result that is up to 21.91 km as reported in the paper, a data window not less than 138 × 138 km must be utilized.…”

“…In the recent paper by Abraham et al (2014) 'Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring -Ekiti State, southwestern Nigeria' , 22 randomly selected blocks of dimension 55 × 55 km (data window) were utilized for CPD evaluation using spectral centroid method. Consequently, they obtained CPD results ranging between 11.48 and 21.91 km.…”

“…Background: The recent paper by Abraham et al (2014) 'Spectral analysis of aeromagnetic data for geothermal energy investigation of Ikogosi Warm Spring -Ekiti State, southwestern Nigeria' applied spectral analysis in the interpretation of aeromagnetic data for estimation of curie-point depths using a data window of 55 × 55 km; however, the employment of such small window may not be consistent with derived curie-point depth results. Discussion: Here, I would like to clarify and point out the possible errors in the paper.…”

“…There has been an agreement among researchers in the field that the dimension of the window analyzed may need to be, in some cases, up to ten times the depth to the bottom (Chiozzi et al 2005;Ravat et al 2007). Therefore, the purpose of this review is to clarify and point out the possible errors in the recent paper authored by Abraham et al (2014) regarding data window. This would tremendously assist researchers in appropriate spectral calculation and CPD investigations.…”