Trace element geochemistry of the Keana brines field, middle Benue trough, Nigeria

摘要

A trace elements study of various samples from the Keana brines field, middle Benue Trough was carried-out to determine the extent to which Pb-Zn-S and BaSO_4 mineralisations have affected the quality of the brines and the waters in the area. Different sample media such as well-water, pond water, brine spring pool water, stream water, stream sediments etc. were analysed. Geochemical results show that Cu, Zn, Pb, As and S are concentrated in the waters (0.3, 0.36, 0.05, 0.07 and 1 1,5 ppm respectively). These elements are more concentrated in both the spring and pond waters, suggesting that the spring water could have acted as the transport medium for these elements released from deep-seated sources. Transitions elements (Ti, V, Cr, Fe, Co, Ni and Sr) are concentrated in the waters. Compared to the World Health Organization (WHO) admissible limits, the well waters present very high concentrations in Cd (0.56 ppm) and Sb (0.40 ppm) (200x and 70x WHO admissible values respectively). There is a preferential concentration of transition elements (Ti, V, Fe, Co and Ni) in the sediments (41.38, 362, 52.21, 269 and 54 ppm respectively) than in the waters (0.70, 0.05, 5.6, 0.04 and 0.02 ppm respectively). Similarly, Cu, Zn, Pb and As are concentrated in the sediments (44, 72, 41 and 14 ppm respectively). The concentrations of transition elements (Ti, V, Cr, Fe, Co and Ni) in the refined salt were highly elevated (784, 363, 283, 105, 59.2 and 42.6 ppm respectively) (7000-10,000x well water). Similarly, the concentrations of As, Pb, Br and Sr in the refined salt were also alarming (11.6, 16.4, 16.4 and 122 ppm respectively), (1000, 700, 3000 and 20,000x well water values respectively). S on the other hand is absent. One of the striking features is the absence of I, Cd, Sb and Se in the refined salt crystals which were detected in the waters and the brines. Compared to WHO admissible values, the refined salt crystal concentrations for Ni (426 ppm) and Cr (283 ppm) were also very high (2000x WHO values respectively) and to a lesser extent Cu (26.9 ppm) and Zn (21.7 ppm) (12 and 7x WHO values respectively).