|
Jianhui Cai, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
Guangdi Zhang, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
Jiuling Li, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
Yuanyi Zhao, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
Qunyao Xiong, Institute of Mineral Resources, Chinese Academy of Geological Sciences (China)
|
|
Investigation on environmental effects of Dexing porphyry copper ore field, the largest opencast copper ore field in China, has been attracting significant attention. In this paper, a comparative mineralogical study of soils from Dexing mining environment has provided scientific basis for environmental evaluation and improvement of metallic mineral deposits. Twenty-three soil samples are collected from some typical sites in Dexing area: the mine waste dumps of Tongchang mining zone, No. 1 and No. 4 tailing reservoirs, and the upper, mid, and lower reaches of Dawu River basin. Both of the samples from the mine waste dumps and tailing reservoirs are surface soils, but those from Dawu River basin consist of soils in three soil vertical profiles and some bottom sediments. Soil minerals are determined by quantitative X-ray powder diffraction (XRD) analysis, and heavy metal contents in bulk soils are measured by atomic absorption spectrophotometry (AAS) for Cd, Pb, Zn, Cu, As, Mo, Hg, Se, and Cr. The results have shown the presence of clay and nonclay minerals in the analyzed samples with an average content of 38.9% and 61.1%, respectively. The clay mineral assemblage encountered in the soils is mainly characterized by illite, kaolinite and chlorite, whose relative contents vary from 21% to 90%, 5% to 38%, and 9% to 35%, respectively. Besides, muscovite/vermiculite mixed-layer and illite/smectite mixed-layer mineral are also observed in soils of some sites, the former with a content range of 9% ∼ 24% is only seen in soils of tailing reservoirs and Dawu River basin, and the latter ranging from 26% to 46% merely exists within soils from the mine waste dumps. The identified nonclay minerals are mainly composed of quartz, feldspar, pyrite, goethite, potassium feldspar, gypsum, and calcite arranged according to their decreasing abundances.
Quartz and feldspar grains are major primary minerals in soils of the study area, which may be derived from local main lithology such as granodiorite, quartz diorite-porphyrite, granite-porphyry and dacite-porphyrite. So these soils are all considered to be residual laterites with weak weathering intensity, but soils from either different sites or different depths have different mineral composition features, which can affect chemical and physical characteristics of related soils. According to heavy metal contents of soils, the main pollution problem in the study area is high contents of Cu, Pb, As, Mo, and Hg, furthermore, heavy metal contents exhibit changes with the sampling sites and throughout the soil vertical profiles. Finally, it is suggested that mineralogical features of soils and distribution of heavy metals in soils of the study areas restrain from each other, the difference of soil mineral components directly influences the composition and relative amount of pollution elements, conversely, various heavy metal elements added in soils could probably change the components and properties of soils.
|
