Geoscience Reference
In-Depth Information
CHAPTER
1
Introduction
Geophysical methods respond to differences in the
physical properties of rocks.
Figure 1.1
is a schematic
illustration of a geophysical survey. Over the area of
interest, instruments are deployed in the field to meas-
ure variations in a physical parameter associated with
variations in a physical property of the subsurface. The
measurements are used to infer the geology of the
survey area. Of particular significance is the ability of
geophysical methods to make these inferences from a
distance, and, for some methods, without contact with
the ground, meaning that geophysics is a form of
remote sensing (
brownfields, and is increasingly used during the
mining of orebodies. It is widely used because it can
map large areas quickly and cost effectively, delineate
subtle physical variations in the geology that might
otherwise not be observed by field geological investi-
gations and detect occurrences of a wide variety of
mineral deposits.
It is generally accepted that there are few large ore-
bodies remaining to be found at the surface, so mineral
exploration is increasingly being directed toward
searching for covered and deep targets. Unlike geo-
chemistry and other remote sensing techniques,
geophysics can see into the subsurface to provide
information about the concealed geology. Despite this
advantage, the interpretation of geophysical data is
critically dependent on their calibration against geo-
logical and geochemical data.
). Surveys may be conducted
on the ground, in the air or in-ground (downhole).
Information about the geology can be obtained at
scales ranging from the size of a geological province
down to that of an individual drillhole.
Geophysics is an integral part of most mineral
exploration programmes, both greenfields
sensu lato
and
