Abstract

The purpose of this study is to determine geochemical characteristics for stream sediments in the Gwangju area. We collect the stream sediments samples by wet sieving along the primary channels and dry these samples slowly in the laboratory and grind to under 200mesh using an alumina mortar for chemical analysis. Major elements, trace and rare earth elements are determined by XRF, ICP-AES and NAA analysis methods. For geochemical characteristics on geological groups of stream sediments, we separate geologic groups which are derived from Precambrian granite gneiss area, Jurassic granite area and Cretaceous Hwasun andesite area. Contents range of major elements for stream sediments in the Gwangju area are SiO₂ 51.89~70.63 wt.%, Al₂O₃ 12.91~21.95 wt.%, Fe₂O₃ 3.22~9.89
wt.%, K2O 1.85~4.49 wt.%, MgO 0.68~2.90 wt.%, Na2O 0.48~2.34 wt.%, CaO 0.42~6.72 wt.%, TiO2 0.53~1.32wt.%, P2O5 0.06~ 0.51 wt.% and MnO 0.05~0.69 wt.%. According to the AMF diagram for stream sediments and rocks, the stream sediments are plotted on boundary of tholeiitic series and calk alkaline series, which shows that contents of Fe2O3 are higher in stream sediments than rocks. According to variation diagram of SiO₂ versus (K₂O+Na₂O), stream sediments are plotted on subalkaline series. Contents range of trace and rare earth elements for stream sediments in the Gwangju area are Ba 590~2170 ppm, Be 1~2.4 ppm, Cu 13~79 ppm, Nb 20~34 ppm, Ni 10~50 ppm, Pb 17~30 ppm, Sr 70~1025 ppm, V 42~135ppm, Zr 45~171 ppm, Li 19~77 ppm, Co 4.3~19.3 ppm, Cr 28~131 ppm, Cs 3.1~17.6 ppm, Hf 5~27.6 ppm, Rb 388~202 ppm, Sb 0.2~1.2 ppm, Sc 6.4~17 ppm, Zn 47~389 ppm, Pa 8.8~68.8 ppm, Ce 62~272 ppm, Eu 1~2.7 ppm and Yb 0.9~6 ppm.

Keywords stream sediments, major & trace elements, geochemical characteristics, geological group, Gwangju area