Dicker Willem Carbonatite Complex, Namibia

DICKER WILLEM
CARBONATITE COMPLEX

A spectacular inselberg rises over 600 metres above the southern Namib desert plain, contrasting sharply with the surrounding broken mountain ridges and red dunes of the Koichab sand sea. Built mainly of fine grained carbonate formed by volcanic action, the mountain owes its form to karstic weathering in an arid environment. Browse the photo gallery to gain further insight into the nature and origin of this unique feature


Dicker Willem probably traslates to Fat William and this view from the SE shows him on his back with his head partly buried in the sand on the left, with only his chin protruding, while his mightly belly dominates the centre	Vertical aerial photograph of the Dicker Willem mountain, showing the strong contrast between the dark carbonatite talus on the left and the light quartzose dune sands on the right	Simplified geological map of the Dicker Willem carbonatite complex	Familiar backdrop to the Namib horses that are often spotted from the highway through the Namib between Aus and Luderitz

Landsat TM image of the southern Namib region around Dicker Willem, which is the prominent dark body in the centre showing the distinctive talus fan stretching SW	Outcrops of granite gneiss form the country rock through which the Dicker Willem carbonatite was intruded	The SE slopes of Dicker Willem preserve the contact between the granite gneiss country rock (shallow lower slopes) and the carbonatite (steeper more blocky upper slopes)	Within the confines of the carbonatite complex are screens of brecciated country rock gneiss

The brecciated country rock close to the carbonatite are variably fenitised	The dipping foliation in the country rock gneisses are followed by thin sheets of carbonatite and trachyte	Spherulitic potassic trachyte sheet intruding the country rock gneisses near the outer contact of the Dicker Willem complex	Trachyte sheet composed of rounded to angular blocks of vesicular trachyte surrounded by matrix carbonate

Trachyte pellet breccia sheet	Trachyte pellet texture suggestive of transport of magmatic globules in a fluidised carbonatitic matrix	Northern slopes of Dicker Willem exposing white sovites cut by brown alvikite sheets	Coarse bladed spinifex-like texture developed in pyroxene sovite

Aggegates of euhedral clinopyroxene within coarse sovite	Banded sovite with dark layers of clinopyroxene and magnetite	Banded pyroxene sovite cut by a thin alvikite	Banded alvikite sheet with trains of blue apatite

Brown dolomite segregations alternating with dolomite-phyric alvikite	Between the closely packed dolomite cumulate zones the creamy coloured alvikite develops a microspinifex texture	Graded layers of dolomite-bearing alvikite	Multiple layers of dolomite cumulates and interspersed dolomite-phyric alvikite spinifex

Dolomite-phyric carbonatite	White sovite cut by multiple generations of darker brown and rusty alvikite dykes and hydrothermal carbonate veins	Another zone of white sovite cut by several generations of late ferrugineous carbonatite veins	Brown alvikite cut by later brown alvikitic veins and a carbonatite breccia dyke

Carbonatite breccia pipe cutting alvikite. The clasts include whote coarse sovite, black magnetite and brown alvikite	Block of inclusion choked sovite surrounded by brown banded alvikite sheets. Inclusions within the sovite are a variety of ijolites and nepheline-bearing sovites	The summit area of Dicker Willem is made up of brown alvikite cut by yellow carbonatite breccia pipes	Summit area of Dicker Willem looking NW. Alvikite outcrops right at the bottom of the view, which are cut by red-brown breccia pipes on the left ridge, while the dark screes on the right ridge are ferruginous silicified carbonate vein material cutting both alvikite and breccias.

The highest point of Dicker Willem forms part of plateau underlain by alvikite and breccia pipes	From the summit of Dicker Willem the lower ridges of country rock gneisses stretch off the the horizon	Dicker Willem carbonatite complex forms a solitary mountain rising 600m above the Namib Desert plain; view from the west	After the igneous carbonatites had been emplaced the complex was traversed by hydrothermal fluids that were responsible for the white calcitic druses

Dark green veins of fenite traverse altered granite in the contact aureole of the Dicker Willem carbonatite. It is this type of fenite that the Lithian mica taeniolite has been found	Close up view of a cut rock slab of clinopyroxene rich sovite (interpreted as a cpx-calcite cumulate) from Dicker Willem	Medium-grained spinifex-type texture in alvikite cone sheet. Pale coloured calcite intergrown with dark brown dolomite in divergent sheaths of plates	Dicker Willem view from south on Tsirub

Website authored by Professor David L. Reid

Last Updated: 2006/03/25