Weathering profile on carbonate rocks of the Nyanga syncline, Gabon

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Even without remarkable minerals, I find regolith fascinating. Given the questions raised by my last post, I suggest staying in Gabon and see what the weathering profile looks like a few kilometres away from the Ikoundou Mountains and their hyaline quartz.

Let’s head for the plain of Tchibanga which is characterized by a beautiful savannah clearly visible on satellite imagery. It constitutes the south-western flank of the Nyanga syncline, the heart of it being the Schisto-Greseux group while the flanks are made up of the Schisto-Calcaire group. A particularly good example of the geological control of vegetation.

The carbonate units have been weathered much more easily than the metamorphic and igneous units surrounding them (Mayombe in the South and Chaillu in the North). The result is a karstic relief with rare pinnacles of limestone rock emerging from the savannah.

The Stone Line is much thicker and consists of large cuirasse blocks, some of them metric in size. While it works rather well on the surrounding relief, unsurprisingly, surface geochemical exploration is not applicable in this context.

Cédrick Gineste

Cédrick Gineste has 35 years of experience in field mineralogy. An exploration geologist since 1997, his field missions have taken him to more than twenty countries across five continents. He has a naturalistic approach to mineralogy and collects deposits and their parageneses rather than minerals.

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Mineralogique Blog

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Quartz crystals in the Gabonese Stone Line

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A few years ago, road works between Ndende and Tchibanga uncovered beautiful sections of Gabon's distinctive weathering profile. We used the opportunity to sample the saprolite in order to obtain valuable geochemical information. The yellowish layer at the top of the embankment is the Cover Horizon, which is actually wind-blown silt (loess) from southern Africa, deposited around 35,000 years ago. It varies in thickness from 1 to 4 metres and is found almost everywhere in Gabon. It covers much of the bedrock, but is currently being eroded.

Cornetite from the Blue Mine, South Africa

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