Total organic carbon in soils and its relation with manganese concentrations in soils and vegetation close to an abandoned manganese mine

This study aimed at quantifying the total organic carbon (TOC) present in soils within the proximity of the Kgwakgwe Mn oxide ore abandoned mine, Botswana, and establish its relationship with Mn concentrations in soils and vegetation based on multivariate and Geographical Information Systems (GIS) analytical techniques. Four hundred soil samples and 200 vegetation set samples were obtained from a 4 km² area close to the abandoned mine. The TOC in soil samples were determined using a carbon/hydrogen/moisture determinator, and Mn concentrations in soils and vegetation by atomic absorption spectrophotometry. Results were processed using the statistical package for social science (SPSS), GIS, and Remote Sensing (RS) techniques with the Integrated Land and Water Information System (ILWIS), Geosoft Oasis Montaj and ArcGIS software packages. The values for TOC in the soil samples from the study area ranged from 0 wt % to 7.91 wt %, with a mean of 1.90 wt %, and at the control area, from 4.07 wt % to 4.86 wt %. The range of concentrations of Mn in soils was from 36 mg/g to 24908 mg/g and for Mn concentrations in the vegetation samples from 26 mg/g to 3611 mg/g with a mean of 598 mg/g. Results of correlation coefficients depicted very weak negative association except Mn in soils/Mn in leaves which was weak but positive. The statistical data yielded four clusters as follows: cluster one consisted mainly of Mn in leaves, cluster two was constituted of Mn in soils, and cluster four had TOC. Cluster three was dominated by the three parameters but with negative t statistic. The spatial presentation of data presented revealed little or no vegetation in the south eastern area and those close to the mine workings, and some significant vegetation in the north western part of the study area. The low TOC in the soils is associated to low vegetation cover which is considered to have been influenced by the soil clay fraction mineralogy and high concentrations of Mn.     

Copper, nickel and zinc contamination in soils within the precincts of mining and landfilling environments

This study determined copper, nickel and zinc concentrations in soils within the precincts of a copper-nickel mining and urban landfilling environments, and used obtained values to appraise the degree of soil contamination and pollution based on geoaccumulation index, contamination factor and pollution load index. Mean concentrations of copper (252.4?mg/kg), nickel (153.0?mg/kg) and zinc (30.4?mg/kg) in soils around the mining area were considerably higher than those around the landfill (4.3, 0.91, and 13.7?mg/kg, respectively, for copper, nickel and zinc). The mining area was moderate to heavily contaminated with copper, nickel and zinc (1?<?I _geo?<?4), whereas the landfill area was moderately contaminated (1?<?I _geo?<?3). In both areas, the level of copper contamination was higher than that of nickel and zinc. Contamination around the mining environment was attributed to mining activities whereas around the landfill area, migration of leachate from the disposed waste could have been responsible.     

Paleoclimatic implications of hydrogen and oxygen isotopic compositions of Cretaceous–Tertiary kaolins in the Douala Sub-Basin,Cameroon

Increased interest in paleoenvironmental studies is a result of climatic changes occurring at present and predicted for the future. Such studies could be done using the stable isotope compositions (δ²H and δ¹⁸O) of kaolins, which provide knowledge on the paleoenvironmental conditions prevailing during the time of kaolinisation. In this study, the stable isotopic compositions of clay-size fraction of kaolins occurring in Cretaceous and Tertiary Formations of the Douala Sub-Basin in Cameroon are presented, with the aim of reconstructing the paleoenvironmental conditions of the Sub-Basin. To achieve this, the clay-size fraction (< 2 μm fraction) of 8 kaolinite-rich samples were analysed for their δ²H and δ¹⁸O compositions, and results were reported as part per mil (‰) relative to the SMOW standard. The δ¹⁸O values of kaolins found in the Cretaceous–Tertiary Formations of the Douala Sub-Basin varied between +18.2 and +21.0‰, whereas the δ²H values varied between –69 and –53‰. Nine of the eleven samples plotted on the right of the supergene–hypogene line. Five of these nine samples plotted very close to the kaolinite line, which represents the composition of kaolinite in equilibrium with meteoric water at 20 °C; suggesting a supergene weathering origin of these kaolins. The determination of the temperature of kaolinisation yielded mean formation temperatures of 22 ± 2 °C and 27 ± 6 °C for Cretaceous and Tertiary kaolins, respectively. Excluding the two samples falling in the hypogene field, averages of kaolinisation temperatures were 20 and 25 °C during the Cretaceous and Tertiary periods, respectively. These temperatures are slightly below the present mean annual temperature in Douala (27 °C), thereby suggesting that the climate was becoming warmer from the Cretaceous to the Present. Therefore, Douala had a cooler and rainy climate during the Cretaceous, and the climate is gradually becoming hotter and more humid, favouring the refinement of existing kaolins and the kaolinisation of kaolin-forming minerals in the Sub-Basin.