Integrated Geochemical and Geophysical Approach to Mineral Prospecting – A Case Study on the Basement Complex of Ilesa Area, Nigeria - Advances in Data, Methods, Models and Their Applications in Geoscience - page 74

The magnetometer used for this work is the GEM - 8 Proton magneto-meter which
measures the Earth`s total field. The potable VLF-EM equipment used for this work was the
GEONICS-EM16 (with GBR station) and on frequency of 16 kHz and it measures the real
and imaginary part of the signal. The ABEM Terrameter was used for the electrical
resistivity measurement.
5. Geoscientific methods used, data analysis and results
5.1 General
The geoscientific methods that can be used in mineral prospecting include, magnetic,
gravity, electrical, electromagnetic, radiometric, geothermal and seismic methods. However,
the choice of method (s) would depend basically upon their resolution with respect to
problems encountered or conditions sought after within a given locality. More often,
consideration is given to the cost, time, portability and reliability of instruments used in
small scale surveys (Adewusi, 1988). The methods considered in this work include the
geochemical, electrical resistivity, VLF - EM and magnetic methods.
5.1.1 The geochemical data, analysis and results
Geochemical methods of exploration should be viewed as an integral component of the
variety of weapons available to the modern prospector. As the goal of every exploration
method is, of course the same - to find clues that will help in locating hidden ore, the
geochemical prospecting for minerals, as defined by common usage, includes any method of
mineral exploration based on systematic measurement of one or more chemical properties of
a naturally occurring material (Suh, 1993). The chemical property measured is most
commonly the trace content of some element or group of elements; the naturally occurring
material may be rock, soil, gossan, glacial debris, vegetation, stream sediment or water. The
purpose of the measurements is the discovery of abnormal chemical patterns, or
geochemical anomalies, related to mineralization.
Sampling and analysis of residual soil is by far the most widely used of all the geochemical
methods. The popularity of residual-soil surveying as an exploration method is a simple
reflection of the reliability of soil anomalies as ore guides (Gill, 1997). Practical experiences
in many climates and in many types of geological environments has shown that where the
parent rock is mineralized, some kind of chemical pattern can be found in the residual soil
that results from the weathering of that rock. Where residual soil anomalies are not found
over known ore in the bedrock, further examination usuallyshows either that the material
sampled was not truly residual or that an unsuitable horizon or size fractionof the soil was
sampled, or possibly that an inadequate extraction method was used. In other words, when
properly used, the method is exceptionally reliable in comparison with most other
exploration methods.
By definition, an anomaly is a deviation from the norm. A geochemical anomaly, more
specifically, is a departure from the geochemical patterns that are normal for a given area or
geochemical landscape. Strictly speaking, an ore deposit being a relatively rare or abnormal
phenomenon is itself a geochemical anomaly. Similarly, the geochemical patterns that are
related either to the genesis or to the erosion of an ore deposit are anomalies (Hawkes and
Webb,1962). Anomalies that are related to ore and that can be used as guides in exploration
are termed significant anomalies. Anomalies that are superficially similar to significant
anomalies but are unrelated to ore are known as non-significant anomalies.