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The
magnetic susceptibility is measured with
low-frequency (1025 Hz) AC-bridges, which are composed of two coils and
two resistors. The measuring field parallel to the coil axis is roughly
of same intensity as the Earth’s magnetic field in Tanzania. The
temperature dependence of the magnetic susceptibility can be determined
accurately on a wide temperature range (from ca. -192 o C to +700 oC).
Densities are determined by weighing
the samples in air and water and calculating the dry bulk density. The
accuracy of the balance is 0.1 g and the repeatability for average-size
(200 cm3) hand specimens is better than 0.1%.
Porosities
are determined by the
water saturation method. The water-saturated samples are weighed before
and after drying in oven. The accuracy of the balance used for porosity
measurements is 0.01 g. The effective porosity is calculated and water
saturation curves are compiled to clarify the nature of rock porosity
and the relationship between the degree of saturation and immersion
time.
The
remanent magnetization is measured with fluxgate magnetometers
inside magnetic shielding. The accuracy is ca. 3*10-3
A/m
for
weakly magnetic samples of average size. In addition to the
intensity of the remanent magnetization, also its directional
properties can be determined.
The
specific resistivity is determined by inductive or galvanic
methods. The galvanic equipment includes 2- or 4-point systems with wet
electrodes and different frequencies, e.g. 0.1, 10 and 500 Hz, which
allows the determination of induced polarization (IP).
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