4   THE LOCATION AND PROPERTIES OF ROAD BUILDING MATERIALS

 

The following section deals with the physical properties and locations of major rocks and their weathered derivatives for road construction materials in Namibia. The materials are classified according to their geological isotopic ages. As a basis for this classification the Geological Map of Namibia, 1980, 1:1.000.000 [18] is used. Some simplifications are made in order to make the classification of rocks according to their road building properties simpler to understand for road builders and civil engineers.

The physical properties of road building materials in their geological context can only be given in a global, summarised form because too many variations and different parameters like gradings, Atterberg limits, construction techniques etc. do exist. A systematic evaluation of road pavements for paved and unpaved roads will be undertaken in chapters 7 to 9 in order to develop quality and cost optimised models and revised material specification on the basis of ' VOC' and acceptance and rejection criteria for a broad scope of roads all over Namibia.

In Namibia five main periods of lithogenic activity can be determined (see Appendix Map 4):

1. Vaalian Age (Ma = Millions of anni) (> +- 2.100 to +-2.000 Ma)
2. Mokolian Age (+- 2.000 to +- 1.000 Ma)
3. Namibian to Cambrian Ages(Damara Sequence, Gariep Complex, Nama Group)(+- 900 to 450 Ma)
4. Carboniferous to Cretaceous (Karoo Sequence) (345 to 120 Ma)
5. Tertiary to Recent (from 65 Ma)

 

4.1  THE VAALIAN AGE

 

The oldest rocks of the Vaalian age are the Epupa Metamorphic Complex in the northern parts of the Kaokoveld which is intruded by the younger Kunene Anorthosite Complex. Complexes of similar kind and age occur as inliers in the Damara Orogen west of Outjo, in the Tsumeb- Grootfontein area, between Okahandja and Swakopmund as well as south and south-west of Windhoek. These metamorphic complexes consist largely of various intensely deformed granitic para- and orthogneisses. In places hornblende gneiss, amphibolite, marble, quartzite and schist can be found.

 

4.2  THE MOKOLIAN AGE

 

The oldest systems of the Mokolian age are various formations like the Abbabis, the Hohewarte, the Huab, the Grootfontein and the Neuhof formations. All these formations consist of paragneiss and various metasedimentary rocks which can be found in many parts of Namibia.

 

4.2.1  THE KHOABENDUS GROUP

 

The Khoabendus Group is younger than above oldest Mokolian formations. It is composed predominantly of a volcanic lower portion and a large sedimentary upper portion. These rocks can be found in many parts of the Kaokoveld, around Kamanjab and Otjovasandu. Granites of the Franzfontein Granitic Suite intrude the whole succession. The Elim Formation of the Rehoboth area consists of interbedded sedimentary rocks and lavas which have undergone low-grade metamorphism.

 

4.2.2  THE REHOBOTH AND SINCLAIR SEQUENCES

 

The Mokolian Rehoboth Sequence has three formations, the Marienhof, the Gaub Valley and the Billstein formations. These formations consist of hard blue-grey fine quartzites, which can be found in many parts of the western Rehoboth district. Furthermore these formations are composed of phyllite, schist, conglomerates, quartz, porphyry, basalt and rhyolite. The rocks of the Rehoboth Sequence are very often intruded by younger rocks, mainly granite, syenite, diorite and gabbro. These gneissic-granitic injections into the older Rehoboth Sequence can be found in many parts of Namibia, as for instance in the Gamsberg area, at the Namib border around the farm Namibgrens and others.

The Sinclair Sequence is the youngest sequence in the Mokolian age and reaches into the early Namibian age. This sequence accumulated in the Helmeringhausen- Solitaire area during three broad cycles of volcanism, plutonism and sedimentation. Parallel to these formations the Namaqua Belt of metamorphism and granitisation is stretching.

The Mokolian Namaqua Complex consists of granites and gneiss and can be found in the areas between Lüderitz and Aus, between Warmbad and the Fish River and in the area around Grünau.

The location and properties of road building materials for the Vaalian and Mokolian ages are summarised in table 12 [18]:

 

TABLE 12 LOCATION AND PROPERTIES OF VAALIAN AND MOKOLIAN ROCKS

 

|=================================================================================================================|
| AGE/     | GROUP/   | FORMATION/| LITHOLOGY: SEDIMENTARY,      | PROPERTIES: APPLICATIONS AND EXPERIENCES       |
| SEQUENCE | SUBGROUP |COMPL/SUITE| VOLCANIC AND INTRUSIVE ROCKS |                                                |
|----------------------------------------------------------------|------------------------------------------------|
| VAALIAN ERATHEM: ISOTOPIC AGE: >2.100 Ma TO 2.000 Ma           |                                                |
|----------------------------------------------------------------|                                                |
| >2.100 Ma|          | Epupa     | Paragneiss,metasedimentary.  |  No systematic experience as road building     |
|          |          | Complex   |                              |  material as yet.                              |
|          |          | (Ve)      |                              |                                                |
|----------|----------|-----------|------------------------------|                                                |
| 2.100 Ma |          | Kunene    | Anorthosite,dunite,gabbro,   |                                                |
|          |          | Complex   | norite,syenite,foyaite.      |                                                |
|          |          | (Vk)      | intrusive into Epupa and     |                                                |
|          |          |           |                   older      |                                                |
|----------------------------------------------------------------|------------------------------------------------|
| MOKOLIAN ERATHEM: ISOTOPIC AGE: 2.000 Ma TO 1.000 Ma           |                                                |
|----------------------------------------------------------------|------------------------------------------------|
| 2.000 Ma | Haib (Mh)|           | Andesite,dacite,rhyolite.    |                                                |
|----------|----------|-----------|------------------------------|                                                |
| 1.960 to |          |Vioolsdrift| Granodiorite,leucogranite,   |  Not very much is known about the road         |
| 1.810 Ma |          | Suite     | gabbro,diorite.              |  building properties of these rocks.           |
|          |          | (Mgv)     | intrusive into Haib and      |                                                |
|          |          |           | older                        |                                                |
|----------|----------|-----------|------------------------------|------------------------------------------------|
| 1.800 Ma |          |Huab,Grootf| Para-/orthogneiss,granite,  ,| A paragneiss of the Hohewarte Formation found  |
|and older |          | Abbabis,  | metabasite dykes,            | between Oamites and Brack was used for the     |
|          |          | Hohewarte,| metasedimentary rocks.       | subbase of TR 1/5 between Rehoboth and Aris    |
|          |          | Mooiriver,| (Mhu,Mgr,Mab,Mho,Mmo,Mnh)    | with no negative experiences on record for     |
|          |          | Neuhof    |                              | these rocks.                                   |
|----------|----------|-----------|------------------------------|------------------------------------------------|
| 1.800 Ma |Khoabendus| Okapuka,  | Rhyolite,basalt,andesite,    |                                                |
|          |  (Mk)    |   (Mok)   |ortho-amphibolite,greenschist | Only randomly used. No systematic experiences  |
|          |          | Elim (Me) |quartzite,phyllite,limestone, | known.                                         | |          |          |           | magnetite-quartzite,gneiss.  |                                                |
|----------|----------|-----------|------------------------------|------------------------------------------------|
| 1.860 to |          | Franzfont-| Granite,granodiorite.        | Only randomly used for gravel wearing courses  |
| 1.730 Ma |          | ein Suite | intrusive into Khoabendus    | in Damaraland. No systematic experiences on    |
|          |          |   (Mgf)   | Group and Huab               | record.                                        |
| Rehoboth |          | Marienhof | Quartzite,phyllite,weakly    | The Rehoboth Sequence granites which intruded  |
| Sequence |          | (Mm)      |metamorphosed basalt,rhyolite | older formations like Mk and the paragneisses  |
| 1.670 to |          |Gaub Valley| and conglomerate.            | of Mh were used for the basecourses for TRs    |
| 1.420 Ma |          | (Mvy)     |Quartzite,schist,conglomerate | 1/4 and 1/5 and gravel wearing courses:        |
|          |          | Billstein | and quartz porphyry.         | Rehoboth west area: No negative experiences.   |
|          |          | (Mbi)     |                              |                                                |
|          |          |           |  Metabasite dykes. (Mm,Mvy)  |                                                |
|          |          |           | intrusive into Gaub & older  | Nothing is known about the road properties     |
|----------|----------|-----------|------------------------------| of these rocks.                                |
| 1.500 Ma |          | Alberta   |Ortho-amphibolite,anorthosite |                                                |
| minimum  |          | Doornboom | serpentinite,hornblendite,   |                                                |
|          |          | Complexes | talc and chlorite schist.    |                                                |
|          |          | (Mal,Mu)  | intrusive into Gaub & older  |                                                |
|          |          | Piksteel  | Granodiorite,quartz diorite. | No systematic experiences are on record        |
|          |          | Weener    |                              | for these rocks.                               |
|          |          | (Mgp,Mge) | intrusive into Gaub & older  |                                                |
|----------|----------|-----------|------------------------------|------------------------------------------------|
|          |          |Namaqualand|                              |                                                |
|          |          |Metamorphic|                              |                                                |
|          |          |Complex    |                              |                                                |
|          |          |  (Mn)*    |                              |                                                |
|          |          |           |                              |                                                |
|>1.200 Ma |          |  (Mp)     |Gneiss,metasedimentary rocks ,| No systematic experiences are on record        |
|          |          |           | ortho-amphibolite.           | for these rocks.                               |
|          |          |           |                              |                                                |
|          |          |  (Mgj)    | Charnockite,gabbronorite,    | Some granites and gneisses have favourable     |
|          |          |           | ultramafic rocks.            | road construction properties and they have     |
|±1.200 Ma |          |  (Mgb)    | Biotite-rich augen gneiss.   | been used for the basecourse construction      |
|          |          |           |                              | for TR 4/2: Lüderitz-Aus and also for coarse   |
|          |          |  (Mgw)    | Gneissic granite,pegmatite.  | concrete aggregate with good successes.        |
|          |          |           |                              | However, soluble salt contents need to be      |
|          |          |           | all are intrusive into Mp    | watched.                                       |
|----------|----------|-----------|------------------------------|------------------------------------------------|
| Sinclair |          | Tumuab    | Granites                     |                                                |
| Sequence |          |  (Mgt)    | intrusive into older         |                                                |
| 1.300 to |----------|-----------|------------------------------|                                                |
| 1.000 Ma |          | Nagatis   | Rhyolite,quartz porphyry,    | No systematic experiences.                     |
|          |          |  (Mna)    | arkose,shale,basalt.         |                                                |
|          |----------|-----------|------------------------------|------------------------------------------------|
|          |          | Houmoed   |Granodiorite,diorite,granite  | No systematic experiences.                     |
|          |          |  (Mgh)    | intrusive into Mna.          |                                                |
|          |----------|-----------|------------------------------|------------------------------------------------|
|          |          | Kunjas    | Conglomerate,arkose,shale,   |                                                |
|          |          |  (Mku)    | quartzite.                   | Randomly used for some gravel wearing courses  |
| 1.265 Ma |          | Barby     | Basalt,andesite,arkose,tuff  | No systematic experiences.                     |
|          |          |  (Mba)    |felsite,conglomerate,quartz.  |                                                |
|          |----------|-----------|------------------------------|------------------------------------------------|
|          |          | Nubib(Mgn)| Granite.                     | No systematic experiences.                     |
|          |          | Spes Bona | Syenite,diorite,monzonite    |                                                |
|          |          |  (Msy)    |intrusive into Barby & older. |                                                |
|          |----------|-----------|------------------------------|------------------------------------------------|
|          |          |Guperas(Mg)| Rhyolite,ignimbrite,basalt,  | No systematic experiences.                     |
|          |          | Nuekopf   | conglomerate,shale,quartzite.|                                                |
|          |          |  (Mnu)    |                              |                                                |
|          |----------|-----------|------------------------------|------------------------------------------------|
| 1.210 to |          | Gamsberg  | Granite intrus. into Nuekopf | Randomly used for gravel wearing courses.      |
| 1.160 Ma |          | Suite     | and older.                   |                                                |
|          |          | Sonntag   | Granite: intrusive into      | No systematic experiences.                     |
|          |          |(Mgg + Mgs)| Guperas and older.           |                                                |
|          |----------|-----------|------------------------------|------------------------------------------------|
|          |          |Aubures(Ma)| Quartzite and red quartzite, | The red quartzites and conglomerates of the    |
|          |          | Grauwater | conglomerate,shale,basalt,   | Doornpoort Sub-formation can be found around   |
|          |          |  (Mga)    |rhyolite,ignimbrite,argillite | Witvley and Gravenstein. The red quartzites    |
|          |          |Doornpoort |                              | were used as crusher-run basecourse for        |
|          |          |  (Md)     | Formations from Grauwater    | TR 6/1 between Witvley and Gobabis and also    |
|          |          | Klein Aub | to Klein Aub are the equiv.  | for coarse concrete aggregate with favourable  |
|          |          |  (Mka)    | in the Rehoboth/Witvley      | experiences. Also randomly used for gravel     |
|          |          |           | areas to the Sinclair Sequ.  | wearing courses in the Gobabis area.           |
|----------|----------|-----------|------------------------------|------------------------------------------------|
| 920 Ma   |          | Richters- | Granite (Ngr),Syenite (Nsy)  | Due to remoteness in extreme south-western     |
|          |          | feld      | intrusiv into older          | corner in Namibia no systematic experiences    |
|          |          | Complex   | formations.                  |                                                |
|=================================================================================================================|
                                                               

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