Major and trace elements pollution of sediments associated with Abandoned Barite Mines in parts of Oban Massif and Mamfe Embayment, SE Nigeria

• The concentrations of trace elements varied among the dump sites; decreased with depth and distance away from mine dump sites.
• Comparison of average trace element concentrations with background values indicated that the sediments were polluted in all sites.
• The index of geoaccumulation (Igeo) indicated varying degrees of pollution.

The present study was carried out to assess stream sediment quality and pollution level by major and trace elements near six abandoned barite mines in the Oban massif and Mamfe Embayment (SE Nigeria). Results showed that the stream sediments are sandy (> 70%) and slightly acidic (pH, 4.1- 6.3) with LOI ≤ 4%, qualitatively indicating low organic matter contents. The concentrations of trace elements varied widely among the dump sites and decreased with depth and distance away from mine dump sites. Comparison of average trace element concentrations in the sediments with background concentrations revealed that most of the sediments were polluted with Fe, As, Cu, Hg, Pb and Zn at all the mine sites. Pollution by Cd was documented at locations underlain by shale rock, while Cr pollution was at area underlain by basement. Pollution by Co was mainly within shale and basement areas. Concentrations of Al, Ni and V across all mine sites and Co at sedimentary area were below background values. Lowest concentrations of elements were recorded with the sandstone area and the highest concentration in the basement area. Moderate values of elements characterized the shale area. The index of geoaccumulation (Igeo) based on average values for the depth range 0-30 cm indicated varying degrees of pollution with Al, Fe, Cd, Co, Cr, Hg, Mn, Ni and V (practically unpolluted, Class 0); As, Ba, Cu and Zn (slightly polluted, Class I) and Pb (moderately to strongly polluted, Class III). However, these levels of pollution are milder compared to when maximum Igeo values were used. The sediments were slightly to strongly polluted with Pb across all the sample sites irrespective to the lithology. The Itot defined as the sum of Igeo for all trace elements obtained from the different mine sites indicated that the basement areas are most polluted compared to the areas underlain by sedimentary rocks. The spatial distribution of different pollution level by trace elements was irregular and not defined to any geologic terrains.