1. How mining company can benefit from
ground-based electromagnetic geophysics
Q&A with Professor David Thiel, Director of the Centre for
Wireless Monitoring and Applications Griffith University
Mining IQ
How can surface-based electromagnetic geophysics help those who are
conducting a feasibility study?
Professor David Thiel
The discovery of green-field deposits is usually verified by chemical analysis
of samples from surface rock, drill holes, cuttings, streams and alluvium. A
feasibility study needs to provide answers to management, investors and
often government about the viability of the planned operation. Surface-based
electromagnetic geophysics coupled with topographic mapping provides
information to a depth of 50 – 100 metres. Thus it is usually not a complete
technique in predicting the dimensions of the deposit or the purity of the ore.
Despite this, the technique can be used for overburden mapping, fault
location, intrusions, aquifers, old workings, old land-fills etc. Whether the mine
is planned to be surface-based or underground, unobtrusive surface based
mapping techniques are of significant value in mine planning. Once the upper
extent (surface projection) of the deposit is known, mine infrastructure
planning for road-ways, stock-piles, muck-piles, crushers, buildings, power
networks, etc can be planned. This impacts on the size of the mining precinct
including buffer zones for vibration, dust and noise abatement.
Surface based geophysics is usually used in conjunction with drilling, but can
reduce the number of boreholes through highly targeted drilling. This speeds
up the assessment process and the efficiency of the exploration program. The
technique is quick, simple, cheap to run and can be run with only one person.
Mining IQ
What kinds of results or information can a mining company get from ground-
based electromagnetic geophysics?
Professor David Thiel
Electromagnetic geophysics distinguishes between the rock and soil types on
the basis of conductivity. Three dimensional profiles can be developed from
one or more bore-holes. Dislocations in rock and soil are readily identified in
the field and can be pegged during the survey. The surveys can be
implemented with minimal environmental and cultural impact, very little health
and safety risk to company employees and the local population, and at very
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2. low cost. Hand-held equipment can be quickly deployed without substantial
forward planning or cost. The positional accuracy of the data is better than 1
m so that detailed mine plans can be developed with the necessary precision.
Speed and cost minimisation during the feasibility study are valued highly by
all stake holders including the local community.
Electromagnetic geophysics can identify and map:
o LOX
o Faulting
o Intrusion
o Pronounced effects in sedimentary environments
It provides a good response to changes in geology and lithology, and can
assist in mine planning – LOX, structural information
Mining IQ
How accurate is this form of scoping? Are there any areas users should be
careful of?
Professor David Thiel
Electromagnetic geophysics profiles are sometimes dominated by large peaks
and troughs in the profiles resulting from “scattering” of the electromagnetic
waves from surface and subsurface discontinuities. Some of these features
are of significant value and others constitute unwanted interference from
pipelines and power lines. An experienced operator will note these effects
during the measurements and interpret the data appropriately. As the earth is
anisotropic and the direction of the radiation affects the measured response,
mapping in only one direction (i.e. using only one source field) can result in
some major and important features being over-looked.
The technique can be influenced by the presence of surface water, vegetation
and steep terrain. Careful positioning of the instrumentation at every location
is essential to obtaining reliable data.
Due to the nature of geophysics there are a variety of interpretations which
can fit the same data points, so a pre-existing geological knowledge from
borehole data allows the most accurate interpretation of the data
Mining IQ
Feasibility studies tend to be very expensive; is electromagnetic geophysics
cost effective?
Professor David Thiel
Feasibility studies are required to address the mine economics and the social
and cultural and the environmental effects of the mine in three stages:
• the construction of the mine,
• the operation of the mine, and
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3. • the site rehabilitation during mining and at its end of life.
Given that not all feasibility studies result in progress to the construction of a
mine, the withdrawal from a site following the completion of the feasibility
study needs to ensure minimal evidence of the on-site work. Common
complaints from land-holders following a feasibility study include the presence
of compacted road-ways on arable land, drill holes, costeans, damaged
fences, graded edges in flood plains, and cleared sections of bush. Ground
based geophysical methods can operate successfully without leaving any of
these disruptions.
Ground based methods reduce the need for large scale grid drilling through
more targeted drilling and chemical ore assessment of the drill tailings/core.
This can greatly reduce the cost of the feasibility study.
Less boreholes = less time drilling and more efficient = cost effective. The
technique is thus very cost effective.
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