Geo-tourism Analysis

ETUSIS-LODGE,  Karibib, Namibia

von Diplom-Geologin Nicole Grünert Terra Africana Safaris (Pty) Ltd

3. Geological attractions on Etusis  in detail

3.1 Abbabis Complex

In the Abbabis Complex the visitor can observe one of the oldest rock formations of Namibia, which already existed when life was only possible in the form of micro organisms in the overall ancient ocean and out of which mainland's such as the Abbabis Complex rose as large desolate islands. Further here the visitor can stand on the deepest roots of the African continent. Due to their age of about 2000 million years the rocks of the Abbabis Complex underwent extreme pressure and temperature conditions several times. This lead to the formation of unusual high pressure and high temperature minerals as well as to a partial schistosity of the origin rocks. Therefore the rocks of the Abbabis Formation are mainly gneiss's and schist's.

A freshly hammered hand specimen of rock definitely represents a very valuable souvenir of a Namibian safari. Unfortunately the Abbabis Complex, which is situated on the northern boundary of the farm is not very accessible.

Rock description Gneiss:

3.2 Etusis Formation

The Etusis Formation consists of reddish quartzitic rocks, which are so dominating on this farm that geologists choose Etusis as the type locality. Quartzite's are sandstone's which have been under high pressure and temperature conditions during a mountain building event, so that they underwent a so-called metamorphism.The original material of the quartzite's was the erosion  debris of the surrounding mainland areas, for example the Abbabis Complex which was still high mountains in those  times. The erosional material was transported into  depressions by rivers and there deposited as boulders and  later solidified (see Chapter 2). After subsidence of the Abbabis Complex below the ocean level in the newly formed arm of the sea continued sedimentation of the Etusis Formation occurred. Thus mainly sands were deposited on the solidified boulders (conglomerate). The sands were solidified into sandstone's by pressure of the overlying layers. During the following folding of the sediments in the arm of the sea by the Damara mountain building (see chapter 2) these rocks were transformed into very hard quartzite's. It is interesting that besides quartzite's orquartzitic conglomerate also schist's occur in the Etusis Formation. These  schist's are termed biotite mica-schists and are mainly found in the southwest of Etusis. They represent the depositional product of the deeper, further off-shore  areas of the former arm of the sea, were no sands but mainly fine, clay-containing sediments were deposited.
These sediments were also altered by the mountain building event and metamorphosed into mica-schist's by high pressures and temperatures, hence the black-brown, iron-containing mica biotite is formed.










Rock description Quartzite:



Rock description Biotite mica-schist:

(see also Mineral description: Biotite)

3.3 Karibib Formation

The white marble of the Karibib Formation not only represents a remarkable starting product for the diamention stone industry, but can also tell a very interesting geological history. After flooding of huge parts of the submerged Abbabis high area shallow sea regions (shelf seas) were formed on its fringes. Here  deposition of large amounts of lime mud, consisting of fine calcite, occurred. This sedimentation deposition took place under such favorable conditions that later a  very pure limestone was formed by pressure of the overlying layers, which became thicker and thicker.This limestone was then altered by the Damara mountain building event and transformed into the snow white marble, which is economically of importance for the whole Karibib region. Grey marble, which also occurs gives evidence of changes in the deposition conditions within the shelf seas. Larger amounts of sand interbedded with lime mud's occurred, thus this "pollution" is responsible for the color changes seen today. Therefore it is not surprising, that the Grey marbles are found at the contact with the quartzite's. Besides the depositional history also the layering of the marbles is interesting. The lime mud's, which were originally deposited  horizontally, nowadays as marbles dip nearly vertically. This is a consequence and an evidence of the intrusion of a huge granite pluton into the earth's crust below Etusis, thus the marble layers were pushed upwards and tilted steeply. Surface signs of weathering are of a much younger age, which characterize the Karibib Formation. The marble shows deeply incised gullies (karren), which over thousands of years deepened even further and which can be seen as a form of karstification.

Rock description: Marble

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3.4 Granite Intrusions

As already mentioned in chapter 2 many granite bodies intruded up from the deeper interior of the earth into the overlying rock layers during the late stage of the Damara mountain building event between about 580 and 490 million years ago. These granite plutons are also to be admired on Etusis.

On Etusis interesting granite occurrences are mainly in the southwest of the farm and on the plains south of the Otjipatera Mountains. Beside the typical weathering forms such as temperature weathering, formation of grus, polygon and woolsack formation the granites on Etusis also show forms of chemical weathering, which are caused by coastal fog invading deep into the interior. In the southwestern corner of the farm the granite shows a very brittle surface structure, which is caused by regular moistening with fog.

A further particularity can be observed in these granites, because the rock also contains garnet besides the typical granite minerals quartz, feldspar and mica.

Besides garnet another granite mineral is often found at this outcrop. This is the black tourmaline variety schorl. The schorl crystals, which sometimes occur here often show a considerable size, however they have no importance in the jewelry industry due to lack of transparency.

Rock description Granite:

3.5 Pegmatite Dykes

Pegmatite's are products of the late cooling-off stage of granite plutons, mentioned in chapter 3.4. They can be described as rock melts in a very unusual gas-like liquid condition caused by temperatures of between 400 and 700 degree Celsius, which have been intruded into the surrounding rock. By virtue of the high pressure and their high mobility these melts also intrude into the smallest fissures of the granite which was already solidified into the surrounding neighboring rocks. As the more usual chemical elements within the granite are already solidified, pegmatite's often contain rare elements. After cooling-off of the melts therefore often unusual elements are found in the pegmatite's (for example caesium, beryllium and lithium ores) and precious stones (for example tourmaline and aquamarine). In chapter 4 "Mining Activities" the economical importance of the pegmatite's becomes clear. These are intrusive rocks with a relatively high concentration of possible economic minerals. Pegmatite's are also interesting for small miners and single prospectors, of whose activities the small diggings in the pegmatite's on Etusis and especially on the neighboring farm Neuschwaben give evidence.

Rock description (Granite) Pegmatite:

3.6 Gabbro Intrusions

The keen visitor has maybe already seen the green-black rocks on the way to Etusis Lodge, which are observed in small gullies along the way. On a drive around the farm these rocks catch the eye as numerous dark hilltops between the typical granite koppies in the plains of Etusis. This rock is called gabbro. Gabbro as well as granite belongs to the magmatic intrusive rocks, which means that they crystallize subsurface out of molten magma, after they rose along weak zones from the depths of the earth, which mainly open up during mountain building events. Intrusive rocks are classified according to their chemical composition, mainly relating to the SiO2 (Quartz) content. The rocks of granitic composition with a high SiO2 content predominate by far. Gabbro however has a very low SiO2 content which already the dark color indicates. The fact that gabbro intrusions are very rare, points out the particularity of this rock occurrence on Etusis.

Therefore it is assumed that the Etusis gabbros, which rose beneath the area, are nothing more than volcanic hearth, which have not forced the way onto the earth's surface. Due to erosion, which took off huge amounts of overlying rocks of the Damara mountains, these impressive rocks are evidence of seldom magmatic activity and are to be seen on Etusis.

At the moment it is being investigated if the numerous gabbro plutons are connected subsurface and in which times they were formed.

Rock description Gabbro:

4. Previous mining activities on the Farm Etusis

4.1 Mica Mines

Several mica occurrences are found on Etusis, which are associated with pegmatite dykes and which were mined for industrial mineral use. These are light muscovite mica, which is mainly used in electronics and as a high fire resistant heat isolator. Lithium containing mica (lepidolite) however also occurs in the northeast of the farm, which is used as lithium ore and as such is of some importance for the manufacturing of special metal material for example in aviation. Lepidolite is also used in glass and ceramics manufacturing.

Mineral description: Mica

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4.2 Tourmaline Mine

Tourmaline certainly radiates the biggest fascination of all the minerals occurring on Etusis. Namibia and especially the region around Karibib is famous for this semi-precious stone, which occurs in different colored, beautiful columnar crystals.

these small old tourmaline workings on Etusis give an interesting example of the immense energy, with which the local people are on the track of these treasures of the earth. The black-colored tourmaline (schorl) dominates within the pegmatite's which is only of collectors' interest, but not usable for cutting purposes. More rare are red, green or even blue crystals. A watermelon tourmaline has been found on Etusis from time to time, which shows a red center and green edges. Mining of tourmaline normally is pure hand-work, however sometimes air drills and much more seldom explosives are used. The point is to find a tourmaline filled hollow (druse, pocket) and to extract it as intact as possible. Such druses often contain valuable quartz-crystals, which are sold as collectors' items.

Mineral description: Tourmaline

4.3 Copper Mine

The ore-containing quartzite layer shows a thickness of approximately 15 m and the highest mineral concentrations are within the lowest 6 meters. The mineral concentration is connected to cleavage and bedding planes within the quartzite. The ore-enrichment originates from rising granite plutons at the end of the Damara mountain building event. In this late colling-off hot watery liquids were pressed from the nearly solid granite into fissures and gaps into the surrounding quartzite's. These hollows were filled with crystallized copper minerals by solidification of these melts. After erosion had exposed the quartzite's, the copper ore underwent chemical weathering by the influence of atmospheric oxygen.

Mineral description: Malachite

Mineral description: Chrysocolla


4.4 Marble quarries

Several small quarries also give evidence on Etusis of this valuable metamorphic rock of Damaran aged times. A significant occurrence of white marble is situated in the southwestern corner of the farm, which however is only mined on the neighboring farms Ubib, Kubas and Gamikaub West. Generally the marble of the region is classified in different color categories. On Etusis mainly white marble is found, which is termed "African White Marble". Criteria like purity, less fissuring, broad homogeneity (no alternating layering with other rock types), none or minor overlying rock layers are of the greatest importance to ensure economic mining.

5. Final Remarks

Etusis represents one of the geologically most interesting regions of western Namibia. This is based on the occurrence of metamorphic and magmatic rocks and the gabbro intrusions. The ancient Abbabis Complex and additionally the special tectonics released by the unique up-doming of the area by intruding magma masses directly underneath Etusis are especially emphasized. It is not surprising that such an interesting geological area is combined with such an impressive landscape in which geological features are just "crying out" to be observed. The occurrence of mineral prospects and old mines completes the attraction of Etusis as a geological destination. The good accessibility and especially the extremely comfortable accommodation at Etusis Lodge make the farm an ideal setting for a one to several day geological stay. The geological training of the lodge operators during the examination of the area and the report available ensures that the visitor can expect qualified guiding.

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