9th SAGA Biennial Technical Meeting and Exhibition

Determining the orientation or trajectory of any geological borehole is every bit as important as the core or other
information that may be extracted from the borehole. Uncertainties in the location of geological contacts, structures,
etcetera, which propagate into uncertainties in resource volume calculations, increase the risk associated with resource
evaluation projects and may even lead to resource discounting factors being introduced.

During the first quarter of 2005, a due diligence study on caliper techniques, was conducted at a De Beers
operation. The purpose of the study was to determine the accuracy and precision of a newly acquired GeoVista 4
arm caliper for down-hole measurements. The survey was conducted in one of the large diameter drill holes (LDD)
drilled as part of the Resource Extension Project currently underway at the operation. These holes are being used for
resource evaluation, with the grade analysis performed on samples in the range of 1 tonne. The reason for acquiring
the caliper was to obtain more accurate estimations of down-hole sample volumes, which has the effect of
increasing confidence in grade values.

Nondestructive testing (NDT) methods have been recognized as powerful tools for investigating mechanical
properties in geotechnical engineering and have recently been applied to earth science materials (de Beer, 2003) In
this study experiments were conducted on several rock samples to investigate the abilities of non-destructive
techniques (NDT) on geological samples.

Anglo Base’s Namakwa Sands heavy mineral sands operation is located on the West Coast of South Africa. Heavy
minerals are extracted from paleo-beach sands, but in certain areas of the deposit relative hard calcretised or
silcretised horizons occur. Although this material is mineralised, it is discarded to waste as the current plants are
not equipped to liberate mineral from the hard layers. It has become essential to determine the amount of hard
material in the ore body to justify the construction of a new plant for treating the hard material.

Data from part of the Southern African Magnetotelluric Experiment (SAMTEX) have been analysed using an
impedance tensor decomposition method in order to gain a better understanding of geoelectric directionality and
dimensionality and its variation with depth, and the electrical anisotropy properties of the region. The SW-NE transect
from Sutherland to Messina, South Africa, is coincident with part of the Kaapvaal Craton Project’s Southern Africa
Seismic Experiment (SASE) deployment. Shear-wave splitting analyses on the SASE data, reported in the literature,
showed that splitting delay times appear to exhibit geological control, with the Late-Archean regions showing generally
greater anisotropy.

Typical problems on coal mines include determining the thickness of coal left in the floor by historic mining
(potentially a large reserve of coal that can still be extracted), and identification and determination of the thickness
of sandstone partings located within coal seams. An additional problem encountered at Anglo Coal’s Bank Colliery
was determining the risk to planned underground workings beneath a dam- critical information required being the
bathymetry of the dam and the amount of sludge in the dam.

We present a new approach to the simultaneous pre-stack
inversion of PP and, optionally, PS angle gathers for the
estimation of P-impedance, S-impedance and density. Our
algorithm is based on three assumptions. The first is that
the linearized approximation for reflectivity holds. The
second is that PP and PS reflectivity as a function of angle
can be given by the Aki-Richards equations (Aki and
Richards, 2002).

The viewshed of a topographic dataset is the region around a given observation point that is visible from that
location. It has many uses, such as in urban environment planning, or in siting television and radio transmitters. The
viewshed is used here as a data enhancement tool to aid in the interpretation of geophysical potential field data. The
fraction of the area of a moving window visible from each point on the dataset (considered as if it were topography)
is computed. Since this area changes if the observer is raised above the surface, its vertical derivative can also be
computed. This derivative was found to be a useful method of enhancing subtle features, and is demonstrated on
aeromagnetic and gravity datasets from South Africa.

Drilling galleries with tunnelers is subjected to strict technical requirements. The anticipation of
obstacles in advance of the tunnelling is essential to the operations and the in-site day-by-day safety.
The recognition of the fractured zones and the circulation of water are the objectives of this
methodology combining high-resolution seismic and 3D tomography.