Lateritised gravel bed: A new guide horizon for lateritic gold? |
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| Authors: | ABhaskara Rao |
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| Institution: | Departamento de Geociências, Universidade de Brasília, 70910, Brasília, Brazil |
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| Abstract: | Geological studies made in the area of Mara Rosa in Goias State, Brazil, where small occurrences of gold are known in river placers, have revealed an interesting and extensive “lateritised gravel bed” overlying an inexpressive nodular lateritic crust horizon. The gravel has pebbles of vein quartz, quartzites and gneisses, which are interlocked and compacted by intense lateritisation with brown hydrous Fe-oxide (goethite). The underlying nodular crusts grade from deep brown to mottled, and occasionally have cavities. They possibly represent an interface between the bed rock and the gravel bed. The intensity of lateritisation is attributed to the existence of volcanogenic mafic sequences in the rock. The presence of pebbles of the same nature in the small placers with Au, suggest that Au has been dissolved and precipitated during the lateritisation process. Its abundance is mainly restricted to the lateritic gravel bed, which in turn has contributed Au to the stream placers. Thus, it is considered as a new guide horizon for lateritic Au. |
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