11th SAGA Biennial Technical Meeting and Exhibition

EXIGE (www.exigesa.com) and its partner AirWatch, a joint venture between Wagtail Aviation (www.wagtail.co.za) and Alto Air (www.Alto-Air.com), developed the next generation airborne geophysical platform – GyroLAG (Gyrocopter Light Airborne Geophysics). GyroLAG is a single pilot operated, smart tailored, ultra-high resolution airborne geophysical platform, which combines the merits of dense data sampling, accurate positioning, low clearance above ground or sea level, slow speed, multiple parameter measurements, automatic data quality control and real-time quality assurance, with the benefit of being highly efficient, cost effective, commercially attractive, safe, easy to operate and reliable. The aviation platform, a Kriek type gyrocopter, is a South African designed and built machine with a license for commercial operations. It originated from 6 years of development, which are presented in more detail. The platform will undergo production in the fourth quarter of 2009. The final setup of the remote sensing and geophysical instrumentation on-board is at an early stage of implementation. GyroLAG will accommodate up to 7 distinct remote sensing technologies including a range of digital cameras covering the entire IR to UV spectrum, lightweight magnetic, radiometric and gravity sensors. Instrumentation’s agility and ruggedness have been proven during a sequence of separate survey and test conditions and their preliminary performances are illustrated. The platform’s positioning information is acquired utilising a DGPS and/or real time GPS. A notebook computer is used as digital acquisition system and proprietary software for flight preparation, data acquisition, and automatic flight data quality control against user-set technical specifications are being developed. Commercial launch of GyroLAG in its full capacity is planned for the first quarter of 2010 but it is worth pointing out that the platform in a magnetic, radiometric and/or still camera configuration is already operational.

The Prince Albert and Collingham formations of the lower Karoo succession contain organic rich shales deposited in the extensive anoxic to dyoxic Gondwana basin during the early to middle Permian. A total of 15 samples were subjected to Rock-eval pyrolysis and X-ray florescence spectrometry for the determination of its source rock characteristics, thermal maturity and palaeoenvironments. These were then compared to 6 analyzed samples from the Agbada formation of the Niger Delta. The total organic carbon content of the Karoo shales varied between 0.07-1.30 wt%, with an average of 0.46 wt%. Rock-Eval pyrolytic yields and calculated values of hydrogen and oxygen indexes imply that organic matter type is predominantly inert kerogen (Type IV). The measured Tmax values as determined by Rock-Eval Pyrolysis range between 215oC-424oC, this corresponds to thermally immaturity. Despite the age of the samples the thermal maturity of these kerogens are generally low, therefore suggesting uplift and exposure of these sediments. This claim is further confirmed by low trace metal concentrations relative to those of the Niger Delta samples. Preliminary studies indicate the Karoo basin holds no significant hydrocarbon generating potential, apart from gas. Further geochemical studies and petroleum systems analysis may however reveal hydrocarbon accumulations within the Karoo basin.

The Spectrem waveform and processing has many advantages. The possibility of implementing this on a central-loop helicopter platform was investigated. Data was acquired in early 2008 with ground and flight tests. The amplitude of the anomalies produced by the Step Response processing are modulated by the amount of primary field present at the receiver. The smaller the primary field (larger “Bucking Factor”), the larger the anomaly amplitudes, however this makes the system more sensitive to geometric changes. The ground and flight tests suggest that the Spectrem waveform and processing is not suitable for a central loop helicopter system due to it’s sensitivity to geometric changes.

This review focuses on our understanding of the structural and tectonic setting of the Cape Fold Belt (CFB) based on contributions made by academics and professional geologists, mainly during the last two decades. Most of the research concentrated on the identification and mapping of thrust faults in the southern arm of the CFB, as well as seismic surveys which provided data for putting forward tectonic models to account for structural and stratigraphic features of the fold belt. Thrust stacking is a common characteristic in all three stratigraphic sequences of Palaeozoic Cape Supergroup rocks. A complex pattern of ductile and brittle deformation occurs in the Table Mountain Group whereas in the overlying Bokkeveld and Witteberg Groups there is a close association of folding with development of thrust faults. Thin-skinned characteristics are prevalent in the southern arm of the CFB, but give way to thick-skinned features in the southernmost central part of the fold belt where basement rocks have been thrusted northwards towards the foreland. A variety of tectonic models proposed for the CFB have generated some controversy among researchers. Currently popular are the Andean and the strike-slip (transpression) models. The former accounts for the northward vergence of structures in the southern arm of the fold belt, but thicknesses of crustal substrate obtained from recently carried out deep sounding seismic surveys across the fold belt do not entirely corroborate this model. Structural characteristics in cover rocks that favour the transpression model are en echelon folds and faults as well as flower structures which are commonly associated with strike-slip regimes.

Recovering geodetic parameters such as tropospheric delay and geodetic site positions and monitoring their variations in time has important applications for studying the processes of the dynamic Earth. Geodetic position time series exhibit non-linear motions that are associated with seasonal signals caused by loading effects, and seismic deformation processes such as earthquakes etc. This implies that the fluctuations in the station coordinates and tropospheric parameters could be synchronized because they are driven by common underlying processes. In the analysis of space geodetic measurements, space geodetic solutions are often co-assessed in order to determine geophysical signals present in both parameters. The main objective presented in the current contribution is to determine the linkage between temporal structure of the zenith tropospheric delay and the geodetic station height coordinates fluctuations in the time-frequency-energy space. The temporal structures of the combined solution of the zenith tropospheric wet delay (ZWD) and the geodetic station height at the Hartebeesthoek geodetic station (HartRAO) have been studied. The oscillation patterns in these geophysical signals have been analysed by using the noise-assisted data analysis (NADA) methodology known as ensemble empirical mode decomposition (EEMD). The instantaneous phase differences among the associated modes of the intrinsic mode functions (IMFs) have been computed and used to assess the degree of synchronisation between the two series. Our results show that the ZWD and the HartRAO geodetic station height show modes that are temporally correlated and some of the IMF modes exhibit temporal structures that can be associated with both local and global forcing mechanisms.

Space Geodesy provides many important products. These products are applicable in numerous scientific, industrial and commercial applications. The current hub for Space Geodetic activities is the Space Geodesy Programme at the Hartebeesthoek Radio Astronomy Observatory. A new fundamental space geodetic observatory for South Africa has however been proposed and various workshops were held to date in this regard. The main drivers for a new station are the ageing and subsequent breakdown of current equipment as well as deteriorating atmospheric seeing conditions at HartRAO. Current equipment that still functions also does not provide the resolution and sensitivity needed by modern techniques. Initial surveys highlighted Matjiesfontein as a very good option in terms of numerous factors. These factors will be discussed. The actual site is located about 4 km south of the village in a shallow valley in the mountains and is ideal to become a new fudicial site for Africa. A GPS Reference station as well as a weather station has already been installed on this site. Current equipment at the Matjiesfontein site as well as planned equipment and infrastructure will be discussed.

A structural study of Witteberg Group Rocks was conducted along the Soutkloof River, approximately 14 km east of Steytlerville, Eastern Cape Province of South Africa. Here a north to south geotraverse was studied in an attempt at unravelling the structural geology of the rocks belonging to the Upper Devonian to Lower Carboniferous Witteberg Group (Upper Cape Supergroup). These rocks are mostly arenaceous and include quartzite, sandstone, siltstone and shale which have been folded, faulted and metamorphosed. Thrust, normal and strike-slip faulting occur in the area. Shallow south dipping low-angle thrust fault planes are displaced by steep south-dipping thrust planes and subordinate north-dipping backthrusts. Displacement along thrust planes is predominantly northwards. Steeply dipping thrust fault planes are often reactivated by east-west striking normal faults. Strike-slip faulting post dates all structural features and displaces normal and thrust fault planes. Open to tight folds are present and are mostly north-vergent and often steepened or truncated by steep south-dipping thrust fault planes. South-vergent folds are related to backthrusting and post-fold faulting. The study has revealed that the current geologic map and the local stratigraphy were compiled without recognising major structural features such as thrust, normal and strike-slip faulting, and its validity is therefore questioned. Extensive faulting suggests that the conventional stratigraphic interpretation of the Witteberg Group strata should be revised.

In the local mineral exploration environment the high resolution imaging capabilities of 2D seismic reflection surveys continue to provide rapid, cost-effective mapping solutions over areas of structural mapping concern not otherwise speedily available from borehole data. This is particularly so where time-lines are short. 2D seismic sections sourced from the Wits Gold, Karoo coal, Canadian diamond and Bushveld platinum exploration sectors demonstrate in particular; • technique versatility in mapping orebodies or marker horizons having a tabular sheet geometry, and satisfying minimum thickness plus physical property requirements • a large spectrum of structural environments ranging from the benign to the complex. This spectrum ranges from flat dips with minor rolls and grabens through large scale wrench and listric faulting, to moderate dips with structural terraces or large grabens above Floor doming.

The determination of in situ rock density is an important process in most opencast mining operations where an accurate estimate of total resource tonnage allows forecasting of metal production and life-of-mine. At the Skorpion zinc mine in Namibia, various techniques have been tried to improve density measurements, which are used to estimate mined tonnage and predict ore recovery based on laboratory measurements of ore yield per rock mass. Hitherto, the Archimedean submersion technique has been the basis of measurement. Downhole wireline density logging was put forward as a technology that could assist in getting accurate density determinations, particularly in the porous and vuggy arkose host rock. A borehole logging trial was conducted where a dual spaced gamma-gamma density sonde and other complementary downhole measurements, such as the photo electric density and optical televiewer, were surveyed for comparison with core density measurements. The wireline logs were run successfully in both wet and dry borehole conditions and a high degree of precision was achieved. The accuracy of the logs was based on industry standard calibration and borehole compensation with some quality assurance using core data in non-porous sections of the borehole sample. Results showed good agreement between core and wireline density in the non-porous rocks, but the wireline logs measured somewhat higher density in porous and vuggy zones. Analysis of the Archimedean technique used at Skorpion showed that the precision achieved was good, but accuracy was compromised by unsaturated and unmeasurable drill core porosity. The extreme geological environment and predominantly dry boreholes highlights the limitations of the gamma-gamma density measurement and demonstrates the critical requirement for sound data quality control and adherence to rigorous calibration standards. The availability of complementary measurements is found to be important to developing the right understanding of the wireline density response in an unfamiliar geological environment. Skorpion mine has recognised the differences in density measured by the Archimedean and the wireline logging techniques, particularly in porous and vuggy formations and supports further test work for quantitative calibration of the response. Following the successful outcome of that work, the wireline method could be deployed on an ongoing basis to supplement and enhance the accuracy of the core-based measurements.