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Petrophysical studies

Petrophysical Laboratory

The Geological Survey of Tanzania (GST) has a petrophysical laboratory for measuring petrophysical properties of rock and ore samples. Petrophysical parameters can be used for quantification of geophysical interpretations and have also direct geological applications.

Petrophysical laboratory measurements include density, porosity, magnetic susceptibility and remanent magnetization and galvanic or inductive resistivity.

The GST laboratory equipment has been developed for rapid measurement of many samples with high accuracy. Measured data are currently stored in a database, and data analyses and summaries are available for scientific and commercial purposes.

Petrophysical laboratory
Petrophysical laboratory


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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