Opaline concretions in Weichselian Late-glacial lake marl from Flanders, northern Belgium     

Luc Denys  Patrick Kiden  Cyriel Verbruggen 《Journal of Paleolimnology》1998,20(1):91-98

Macroscopic opal-A concretions were observed in lake marl deposited in a small Flemish lake (Belgium) during the Allerød biozone of the Weichselian Late-glacial (ca. 12–11 ka BP). The silica from these concretions was derived within the profile, by the leaching of siliceous microfossils – mainly diatom frustules. Formation of the concretions probably resulted from pH- and/or evaporation related precipitation of the silica at a lower stratigraphic level, presumably corresponding more or less to a former low position of the groundwater table. The presence of these concretions is probably related to alternatingly wet and dry local conditions during the middle and later part of the Allerød.  相似文献   

Geochemical Fingerprint and Iron Ore Potential of the Siliceous Itabirite from Palaeoproterozoic Nyong Series,Zambi Area,Southwestern Cameroon          下载免费PDF全文

Sylvestre Ganno  Cyriel Moudioh  Adjija Nzina Nchare  Gus Djibril Kouankap Nono  Jean Paul Nzenti 《Resource Geology》2016,66(1):71-80

The study area forms part of an emerging iron ore province of southern Cameroon. Geochemistry analyses reveal that the siliceous itabirite has a very simple chemical composition, with Fe₂O₃ and SiO₂ representing more than 96 wt.% of the average composition; suggesting chemical precipitates of silica and iron. Low Al₂O₃ and TiO₂ concentrations and a weak positive correlation between them point to a minor detrital component in the precipitated marine sediments. The Si/Al ratio (average 52.7) indicates the hydrothermal origin of the studied itabirite. The Al–Si discrimination diagram supports this interpretation through the plot of all data in the hydrothermal field. The studied samples have low iron content (about 39.32% Fe), high gangue content (40.97% SiO₂ and 1.3 % Al₂O₃) and low concentration of the deleterious elements (0.16 % P and < 0.01% S). The main gangue mineral is silica which can be efficiently removed from iron ores during preparation of raw materials for the blast furnace process. According to commercial standards for crude iron ores, it may be concluded that the Zambi iron ores are a low‐grade magnetic ore that can be profitably exploited for the production of iron for steel production.  相似文献