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Paper Number: 33
A
Comparative Study of Hand-Held Magnetic Susceptibility Instruments
Deng, D.N.1, Smith, R.S.2
1Laurentian
University, Sudbury ON, Canada.
2Laurentian
University, Sudbury ON, Canada.
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A study to compare six magnetic susceptibility (MS) instruments (the
KT-10 sold by Terraplus Inc., RT-1 produced by Fugro, SM30 produced by
ZH Instruments, MS2K & MS2C produced by Bartington Instruments and
MPP-EMS2+ probe produced by GDD Instruments (denoted as GDD)) was
conducted to characterize the equipment on the basis of their
accuracies, resolution, range, reproducibility, ease of use and response
to short term and medium term temporal drifts.
The results will help geoscientists decide which instrument has the
characteristics most appropriate for their project. Two of the
instruments we assessed (KT-10 ad GDD) are also capable of measuring the
conductivity. Knowing the how physical properties such as the magnetic
susceptibility and conductivity can vary with lithology and alteration
can be useful in geological mapping. Studies have shown MS measurements
to correlate with resources (sulphide mineralogy and even oil and gas)
as well as other natural occurrences [1], [2], [3].
The first step was to select the mode of data acquisition that is
most appropriate for our project. Our comparison study was achieved by
collecting MS data on 65 samples from BQ core from 3 holes, 2 NQ core
samples, 2 rock samples and 2 calibration samples. These data sets were
processed by plotting correlations diagrams, scatterplots and applying
statistical methods. We also assessed the lower limits of accuracy for
each instrument
The results showed that the GDD and MS2K are most affected by
temporal drift whereas the KT-10 and MS2C gave more repeatable results
in both paramagnetic and ferromagnetic samples. All instrument performed
rather poorly in diamagnetic samples, the GDD and RT-1 do not give any
negative readings. The MS2C, MS2K and GDD generally gave higher
susceptibility readings than the rest of the meters. It was also noted
that measurements on the flat face of half-core samples were always
higher compared to measurements on their respective whole core samples
because of a larger surface for coupling between the sensor and the half
core. There is a correlation between instruments, frequencies and
sensitivities, but no relationship between operating frequencies and the
temporal drifts of these instruments.
The project concluded with suggested scenarios where each instruments
and their given modes are more useful. In mineral exploration industry,
the most useful meters are GDD and KT-10 S/C because they measure both
magnetic susceptibility and conductivity measurements. In scientific
expeditions and geological surveys, the KT-10, SM30 and MS2C provide
more repeatable results and are able to measure negative
susceptibilities as well. MS2C is less useful in the field and is
recommended for laboratory use only. RT-1 is useful in paramagnetic and
ferro-/ferrimagnetic rocks. Users of SM30 are strongly discouraged from
using scanning mode if they require reproducible results.
References:
[1]Potter D (2005): 2005 International Symposium of the Society of
Core Analysis, Toronto, Canada, Paper SCA2005-02
Borradaile G.J and Henry B (1997): Earth-Science Reviews 42:
49-93; Elsevier
McDowell GM et al. (2004): SEG Int'l Exposition and 74th Annual
Meeting, Denver, Colorado, 1-4.
