Investigating high zircon concentrations in the fine fraction of stream sediments draining the Pan-African Dahomeyan Terrane in Nigeria

Abstract

Sixteen hundred stream sediments (<150 μm fraction) collected during regional geochemical surveys in central and SW Nigeria have high median and maximum concentrations of Zr that exceed corresponding Zr concentrations found in stream sediments collected from elsewhere in the World with similar bedrock geology. X-ray diffraction studies on a sub-set of the analysed stream sediments showed that Zr is predominantly found in detrital zircon grains. However, the main proximal source rocks (Pan-African 'Older Granites' of Nigeria and their Proterozoic migmatitic gneiss country rocks) are not enriched in zircon (or Zr). Nevertheless, U-Pb LA-ICP-MS dating with cathodoluminescence imaging on detrital zircons, both from stream sediment samples and underlying Pan-African 'Older Granites' confirms a local bedrock source for the stream sediment zircons. A combination of tropical/chemical weathering and continuous physical weathering, both by 'wet season' flash flooding and 'dry season' unidirectional winds are interpreted to have effectively broken down bedrock silicate minerals and removed much of the resultant clay phases, thereby increasing the Zr contents in stream sediments. The strong correlation between winnowing index (Th/Al) and Zr concentration across the study area support this interpretation. Therefore, 'anomalous' high values of Zr, as well as other elements concentrated in resistant 'heavy' minerals in Nigeria's streams may not reflect proximal bedrock concentrations of these elements. This conclusion has important implications for using stream sediment chemistry as an exploration tool in Nigeria for primary metal deposits associated with heavy minerals.

Hydrogeochemical evolution and groundwater quality assessment using chemical systematics, statistical techniques, and pollution index of groundwater (PIG): a case study

“…Estimation based on the pollution index of groundwater (PIG) indicate an insignificant pollution state of less than 1 (0.27-0.737) for the groundwater samples collected from all the 30 boreholes in the study area. Ferré et al, 1996 andKey et al, 2012). Distribution of rocks within the Cameroon volcanic line (after Ngako et al, 2006).…”

“…1. Regional geological map of Nigeria (after Ferré et al, 1996 andKey et al, 2012). Distribution of rocks within the Cameroon volcanic line (after Ngako et al, 2006).…”

Geochemical Assessment for Gold in Sediments of Gora River in Minna Area, North-central Nigeria

“…Zr, Ba and V are considerately high in comparison to other trace elements in the samples. Zr ranges from 21-640 ppm with an average of 285 ppm probably due to the complete weathering of the source bedrocks in the Minna area [6] Pb but negatively correlated to Au, Sb, Ba, As, Pb, Cu, Mo and Cr. The result from the correlation analysis indicated that the oxides of Fe and Mn played principal role in the concentrations of the aforementioned elements, which were adsorbed by hydrated Fe-and Mn-oxyhydroxide grains dispersed in a secondary environment [7], or by the co-precipitation processes with Fe-and Mn-oxyhydroxides.…”

Geochemical fingerprinting and source discrimination of agricultural soils at continental scale

“…from fertilizers). It is worth noting that relatively immobile elements (Ti and Zr) show similar mean values accompanied by a low standard deviation, suggesting that the concentration of heavy minerals has a negligible impact on the chemical composition as suggested byKey et al, (2012).…”