Masters Degrees (Earth Sciences)

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Browsing Masters Degrees (Earth Sciences) by Author "Creus, Pieter Koenraad"

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    Geology and structural controls of lode-gold mineralisation around the Navachab Gold Mine in the Pan-African Damara Belt of Namibia
    (Stellenbosch : Stellenbosch University, 2011-12) Creus, Pieter Koenraad; Kisters, Alex; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Numerous quartz-vein hosted gold prospects in the Karibib district in central Namibia testify to the presence of a large hydrothermal system during Pan-African times in rocks of the Damara Belt and centred around the Navachab Gold Mine. This study presents the results of the regional and detailed mapping of the Navachab synform, a NE-SW trending, regional-scale structure hosting a number of these gold prospects, locally referred to as the “zoo prospects”, in the direct vicinity of the main Navachab Gold Mine. The zoo prospects are located in the marble-dominated, up to 800 m thick Karibib Formation, which forms the core of the Navachab synform. Regional mapping of the synform identified six main lithological units comprising massive and banded dolomitic and calcareous marbles, intraformational breccias and interlayered calc-silicate felses. Despite characteristic thickness variations, the six units can be correlated throughout the synform, allowing for a lithostratigraphic correlation of units in the otherwise monotonous marble sequence. All of the prospects are spatially closely associated with and adjacent to unit 5, an up to 100 m thick, competent dolomitic marble unit. This suggests a strong lithological control of the mineralisation. The first-order Navachab synform formed during the regional D2 phase of deformation. The strongly non-cylindrical, doubly-plunging fold shows open- to close interlimb angles and a pronounced NW vergence in the SW, but is tight- to isoclinal and upright in the NE. Higher fabric intensities and detachment folding are confined to the subvertical limbs of the synform in the north. Here, structures record a subhorizontal, NW-SE directed co-axial shortening strain interpreted to have developed in response to the geometric hardening and layer-normal shortening following the rotation of the fold limbs to subvertical attitudes during progressive D2 shortening. The mineralisation of the zoo prospects is located where D2 high-strain zones intersect unit 5. This suggests an additional structural control of the mineralisation. The detailed mapping of the zoo prospects identified five distinct quartz-vein sets. The geometry, orientation and progressive deformation of the vein sets indicate that veining occurred during the late stages of the D2 event and during NW-SE directed, subhorizontal shortening. Areas of increased veining and mineralisation occur preferentially in areas of strain incompatibilities, where the combined effects of D2 strains and prominent lithological contacts created zones of localized dilatancy. This includes most prominently dilational jog geometries developed between anastomosing D2 shear zones, where hydrothermal fluid flow has produced pervasive quartz-vein stockworks. This also includes areas of detachment folding, where deformation of the rheological stiffer dolomitic marbles and less competent calcareous marbles has led to detachment surfaces and, locally, dilatancy. Zones of increased permeability are also created where two or more vein sets intersect, which is particularly common within and adjacent to boudin interpartitions of competent dolomite units and along rheologically prominent contacts. The zoo prospects illustrate the interplay of (1) prominent rheological contrasts between adjacent lithologies, (2) the presence of high-strain zones, and (3) the geometry of host structures for the formation of auriferous quartz veins in the Karibib district.