GeoResources - Structural and Fluid System Evolution, Otavi Mountainland (Namibia, Significance for the Genesis of Sulphide and Nonsulphide Mineralisation

Content
Hydrocarbon E&P
Geothermal Energy
Metallic Ore Resources
Fundamental Research
Industry Sponsorship
Virtual Geology
Contact
Project Login
Projects / Fundamental Research / Metallic Ores / Otavi Mountainland, Sulphide and Nonsulphide Mineralisation, Abstract ...
 
 

Structural and Fluid System Evolution in the Otavi Mountainland (Namibia) and its Significance for the Genesis of Sulphide and Nonsulphide Mineralisation

  
  Abstract  
     
     

   
     
     
  Scientists
Carsten Laukamp, University of Heidelberg (now: James Cook University, Australia)
Thilo Bechstädt, GeoResources and University of Heidelberg
Maria Boni, GeoResources, University of Napoli and University of Heidelberg
  
     
  Abstract
The Otavi Mountainland (OML) in Namibia is part of the northern foreland fold and thrust belt of the Pan-African Damara Orogen, made of the Paleoproterozoic basement (Grootfontein Inlier) and Cryogenian rift sediments (Nosib Group) overlain by Neoproterozoic platform carbonates (Otavi Group), known for various types of sulphide and non-sulphide mineralisations. The Paleoproterozoic and Neoproterozoic successions were studied to establish a model of the structural and fluid system evolution of the OML, in order to constrain the sources of the ore forming fluids and to understand the timing and the formation of several types of base metal ore deposits in this target area.

The Paleoproterozoic basement comprises the Grootfontein Metamorphic Complex and the Grootfontein Mafic Body. Based on major and trace element compositions the Grootfontein Metamorphic Complex suggest a magmatic evolution from dioritic to granitic compositions in a convergent tectonic setting, related to the Eburnean orogeny. In opposite chemical compositions of gabbros of the Grootfontein Mafic Body suggest an emplacement in a continental regime, related to distinct magma sources or to contamination from older basement rocks. Beside the Grootfontein Mafic Body, intermediate to mafic rocks of the Grootfontein Metamorphic Complex could have been source rocks for base metal mineralisation in the OML.

Due to the Neoproterozoic break-up of Rodinia, a horst-graben-system evolved in the Paleoproterozoic basement, filled by siliciclastic rocks (Nabis Formation) and related rift volcanics (Askevold Formation). Geochemical studies on These rift volcanics yield a tholeiitic composition and were deformed during the Pan-African orogeny under greenschist facies conditions (M1). Pre Pan-African magnetites from the Askevold Formation (587±12 Ma) postdate the VMS-type ores of the Nosib Group to a Cryogenian deposition. Based on comparative geochemical studies it is suggested that the Askevold Formation and related VMS-type deposits are favourable sources for base metals deposited in the OML. 

Three deformational phases are observed in the OML: 1. Early Ediacaran E-W shortening (D1) caused by collisional processes in the Kaoko Belt. 2. Main deformation and related N-S shortening in late Ediacaran to early Cambrian times (D2), due to convergence and collision of the Sao Francisco - Congo and Kalahari Cratons. 3. Dextral strike slip and extensional normal faulting (D3), triggered by the late Pan-African uplift of the Northern Platform during the waning stages of the convergence between the Sao Francisco - Congo and Kalahari Cratons.

Sulphide and non-sulphide mineralisations within the platform carbonates of the Otavi Group are related to the circulation of basinal and/or metamorphic brines, linked to the successive deformational events of the Pan-African orogeny. During D1, Zn-Pb sulphides of the Berg Aukas-type were deposited in sedimentary and tectonic breccias, further refined by hydrothermal fluids. During D2 hydrothermal remobilisation of these ores took place, acting as precursor for later phases of base metal mineralisation. Later (syn-D2) hydrothermal fluids were triggered by regional metamorphism (M1) and the emplacement of syntectonic granites in the central Damara Belt, leading to Cu-As-rich sulphosalts and Pb-Cu-Zn sulphides of the Tsumeb-type in karst pipes, fault breccias and at cross junctions of different tectonic trends. During D3, repeated remobilisation of Tsumeb-type and eventually Berg Aukas-type deposits led to the direct replacement of the primary ores and/or further distribution of sulphide ores into D2-structures (e.g. Kombat). Syn- to postdepositional remobilization of primary Zn-sulphides of the Berg Aukas-type led locally to the replacement by Zn-silicates (Willemite). Precipitation of the vanadates commenced significantly after the Pan-African orogeny.

During a phase of deep continental weathering in the late Kenozoic the circulation of slightly heated meteoric fluids fostered the formation of supergene Pb-Zn-Cu vanadates in post-Damaran karst fillings, solution collapse and tectonic breccias and North- to NE-striking faults, reflecting the original composition of the primary sulphide deposits in the same area.
  


 
  Publications
Laukamp, C., Bechstaedt, T. and Boni, M., submitted, Geodynamic evolution of the Otavi Mountainland (Namibia): Implications for Pan-African Damara orogeny and metallogeny: Journal of African Earth Sciences
Laukamp, C., Schneider, J., Boni, M. and Bechstaedt, T., submitted, Geochemistry and geochronology of Paleoproterozoic basement rocks of the Grootfontein Inlier (Namibia): Precambrian Research.
Laukamp, C., Schneider, J., Boni, M. and Bechstaedt, T., submitted, Geology, geochemistry and metallogenetic significance of Cryogenian rift volcanics in the Otavi Mountainland (Namibia): South African Journal of Geology.
Schneider, J., Boni, M., Laukamp, C., Bechstaedt, T., and Petzel, V. , 2007, Willemite (Zn2SiO4) as a possible Rb-Sr geochronometer for dating nonsulfide Zn-Pb mineralization: examples from the Otavi Mountainland (Namibia): Ore Geology Reviews doi:10.1016/j.oregeorev.2006.05.012
  
     
  Funding Organizations
German Research Fund (DFG)
  
 
 
     
Drucken Kontakt