Terra Petrophysics Services
Terra Petrophysics provides cost effective physical measurements that can be readily integrated and used to solve exploration problems.
Induced Polarisation Standard (SCIPR)
Terra Petrophysics have recently developed a petrophysical standard that has set induced polarisation and resistivity values. These standards can be used to not only ensure that your instruments are functioning correctly but to test time windows and frequency used to take measurements on core.
The standards can be purchased individually for $749 + GST (if applicable)
Samples for physical property measurements should be careefully selected for quantity and typical characteristics for meaningful results. The physical property measurements are no better than the degree that the samples represent the formation or mineralized zone under study. A suite of samples from within the area under investigation, or from available core from a drillhole should be selected.
In general, samples should be selected so that they are between the size of 10cm to 15cm. It is best to send an excess of samples in either size or quantity so that the laboratory staff can select suitable samples for physical property determinations. Depending upon the physical property procedures desired, samples can be surface or underground grab samples and drill core of any diameter.
In the laboratory, physical property determinations are generally nondestructive procedures except for coring or sawing of the core samples which may be necessary for certain procedures. The normal sample preparation is square the ends of a sample by cutting them with a rock saw to a length no shorter than 10cm. This sample size and shape is necessary for magnetic remanence and susceptibility measurements and can also be utilized for electrical and density determinations. Samples are handled carefully during physical property studies. All samples, cores and cut off remnants will be returned to the client, and may be subsequently analyzed chemically or petrographically for correlation purposes.
All samples submitted to the laboratory should be carefully marked, preferably with waterproof ink, and bagged or otherwise wrapped with sample identification clearly indicated. Samples for which magnetic remanence vector measurements are requested should be oriented in space. All samples should be accompanied by a letter describing the samples, sample designations, requested property procedures, appropriate parameters such as IP time cycle, orientation, etc. and final disposition of the samples.
Measurements of the magnetic remnant vector require that the in situ orientation in space for the sample be documented.
Most holes are drilled at an angle, not vertical. Orient the sample as it was in situ, with the appropriate end pointed towards the surface, and rotated so the appropriate cylindrical “side” is oriented “up”. Mark an arrow on the “top” of the cylindrical side, pointed downhole. Document the declination and inclination for this arrow.
Susceptibility & Remanence
The volume magnetic susceptibility measurement is made in the physical property laboratory utilising a magnetic susceptibility meter. The susceptibility is measured by using the meter to apply an external magnetic field to the sample at an operating frequency of 8 kHz. Magnetic susceptibility is calculated from the frequency difference between the sample and free air measurements. The limits of detectability are approximately 1 x 10E-07 SI units and resulting data is presented in SI units. Magnetic susceptibility measurements can be made on half or full core of various size and on surface samples.
For highly magnetic samples the magnetic remanence can be measured. The measurement of remanence (Jr) in the field and the ratio of remanence to the induced magnetisation (Jr/Ji = Q) has in the past been problematical. The induced magnetisation can be estimated using the susceptibility (k, where Ji = kH and typically H = 40 – 50 Am-1) which can be measured using a handheld meter, but magnetic remanence is more difficult. A recent development in field instrumentation uses a miniature fluxgate magnetometer and a pendulum arrangement in which a magnetic rock may be swung generating a transient signal at the fluxgate which is converted to a magnetic moment and magnetisation.
Inductive Conductivity (Frequency Domain)
The inductive conductivity determinations performed in the physical property laboratory are measured in the frequency domain at 10,000 Hz.
The inductive conductivity measurement is made in the physical property laboratory utilising a inductive conductivity meter. The conductivity is measured in the frequency domain at 10kHz by using the meter to apply an external magnetic field and inducing a small current in the the sample.
Inductive conductivity is calculated from the difference in amplitude between the sample and free air measurements. The limits of detectability are appoximately 1 S/m and resulting data are presented in S/m. Inductive conductivity measurements can be made on half or full core of various size and on surface samples.