7th SAGA Biennial Technical Meeting and Exhibition

The MEGATEM II system has been developed as the latest phase of a four-year program to upgrade the
GEOTEM airborne electromagnetic (AEM) survey equipment to operate on a large survey aircraft.
The initial work was driven by a desire to survey in areas previously inaccessible with fixed-wing
AEM, while the second phase marked an explicit geophysical focus – to improve the effective depth
coverage of the AEM system.

Geophysical data is frequently collected in vast quantities, resulting in large amounts of data that
oten require rapid interpretation. Semi-automatic interpretation methods, such as Euler (Hood 1963, Reid
et al 1990, Durrheim and Cooper 1998, Barbosa, Silva, and Medeiros 1999) and Werner (Hartman, Teskey,
and Friedberg, 1971) deconvolution can assist the interpreter by indicating portions of the data of interest,
which can then be modeled in detail.

Multivariate statistical techniques have been used frequently in geological and geophysical
interpretation (Eberle 1993, Lanne 1996). The deciding factor in any interpretation is the nature of the
data that is submitted to the multivariate technique. Texture analysis is examined as a possible method
of pre-processing data before the multivariate statistical analysis stage. The multivariate technique used
is k-means cluster analysis, which is a simple, yet robust, unsupervised classifier.

Electrokinetic phenomena are well known. They are defined as arising from the relative motion
between a charged surface and its associated double electric layers. Two types of electrokinetic
phenomena are used in geophysics.

A number of variously sized mud cones, mud pools and marshy patches caused by liquefaction
developed along a short segment of the Siloam Fault in Soutpansberg, Northern Province, in April
2000. As a result several houses in the vicinity of the fault segment now show evidence of severe
cracking. Since mud cones and related features appearing along faults are in most instances caused by
strong earthquakes, rumours of earth tremors having taken place, but gone unnoticed, or looming in the
very near future are widespread in this rural area.

The town of Mamre is completely dependant on groundwater for water supply. The potable
water supplied by the Atlantis wellfield is an expensive water source to use for irrigation.
This instigated a geophysical investigation into locally occurring groundwater for irrigation.
The shallow seismic reflection, electromagnetic and resistivity methods were successfully
used to delineate areas for groundwater development. The seismic data were used to
quantitatively determine depth to bedrock, whereas the electromagnetic and resistivity data
were used to give a qualitative estimation of zones of deeper weathering.

A new method for the solution of inverse problems is described that does not require either the
calculation of gradient matrices or their inversion. The method works by constructing an equation
whose attracting fixed point under iteration is the desired solution. It is demonstrated using a gravity
forward model and applied to an equivalent layer gridding problem.

Recent high resolution magnetic and radiometric surveys
flown in Namibia for the Ministry of Mines and Energy
indicate that basic assumptions and processing
techniques applied to airborne surveys must be
questioned and refined when surveys cover large areas
and are flown over an extended time span.

Three high-resolution seismic lines over a Merensky Reef target were recently
acquired using vibrators. The objective of this survey was to identify and map the depth of the
reef in the area, and the structures displacing it.

Minerals explorers are interested in understanding how a particular technology will address a given
exploration problem. Our intention is to address this question in the specific case of predicting how
effective present-day airborne electromagnetic (AEM) technology will be in discovering new deposits
of nickel sulphide.