3D Distributed Array IP
The distributed array 3DIP is among the most technologically advanced IP surveys available to the exploration industry. The system employs multiple full waveform 2 channel receivers which can be deployed with random dipole lengths and orientations throughout the survey area, depending on your targeting needs. Random current injections can then be made throughout the survey area allowing for concurrent resistivity and chargeability measurements in multiple directions, configurations and depths.
When processed, the dataset usually provides 10 times the data points in multiple directions than a conventional 2D IP survey. The extensive dataset then undergoes a 3D inversion to provide a full 3 dimensional model of the chargeability and resistivity results.
The power behind our distributed array 3DIP system becomes evident in many different exploration environments outside of the traditional field environment.
- Being 100% GPS based, the orientation of the dipoles does not have to be linear. The deployment of the array can be designed to fit the terrain and have a minimal impact in environmentally or culturally sensitive areas by reducing or even eliminating the need for survey grid line cutting.
- The full waveform measurements result in stronger filtering of noise, allowing for clean data in even the noisiest of environments.
- The system also provides multidirectional resistivity and chargeability data allowing for the better differentiation of multi-directional geologic systems.
Induced Polarization (IP) is a commonly used geophysical survey for measuring the electrical properties of the subsurface rock.
Both IP and resistivity measurements are made by injecting an electrical current into the ground using two current electrodes which energizes the ground. Induced polarization represents the ability of rocks to briefly hold an electrical charge after the transmitted voltage is turned off. By measuring the electrical gradient between receiver electrodes, the apparent resistivity of the ground can be calculated. The survey depth and resolution can be adjusted with an increase or decrease in the spacing of the electrodes.
Depending on the targeting parameters, many different IP survey configurations can be deployed. The most common conventional deployments are Pole-Dipole, Dipole-Dipole and Gradient. These represent 2 dimensional deployments; this means the data point collected lies below a cut grid line. Anomalies are generally related back to the cut grid coordinate and are represented in 2D space.
Determining the electrical properties of the rock can provide clues in the determination of the subsurface potential. The measured electrical properties reveal valuable information about geology, geological structures and mineralization. The increase in the induced polarization effect indicates the increase in polarizable material such as disseminated sulphides. Variations within the apparent resistivity indicate variations in the geological unit, such as a siliceous alteration.
Every kind of mineral exhibits a unique magnetic susceptibility. This means different geological units below the ground can cause local disturbances within the magnetic field. A magnetometer measures these magnetic disturbances, also known as magnetic anomalies. The processing of magnetic variations allows these magnetic anomalies to be better visualized and georeferenced.
Magnetometers used in geophysical surveys may use a single sensor to measure the total magnetic field strength or may use two spatially separated sensors to measure the gradient of the magnetic field or the difference between the sensors. As the distance between the source and sensor increases, the resolution drops as the shorter wavelengths are lost. Therefore, depending on the target, ground based systems are more advantageous.
CXS employs the Gem Systems GSM-19 Overhauser magnetometer. The GSM-19 is capable of stop and go along with Walking Mag mode and GPS integration. This results in GPS georeferenced ground magnetic readings to better locate the anomaly spatially. CXS offers ground magnetic survey options on either a cut grid or virtual grid using GPS technology.
Very Low Frequency (VLF)
Very Low Frequency (VLF) is a passive survey that uses the interaction of radio communications signals with geological features. VLF is primarily used as a first pass reconnaissance tool to look for shallow bedrock conductive features.
VLF is often employed to identify conductive features, such as sulphides. It is also widely used to identify and trace structural features, such as faults.
VLF can easily be combined with a magnetometer survey to quickly identify targets for further exploration. VLF is also frequently used to ground truth and geo-reference anomalies that were historically identified or identified through airborne surveys.
The most common horizontal loop EM (HLEM) system is the Apex MaxMin. In an HLEM survey, there are two coils or loops. One of these loops is the transmitter, which generates an alternating EM field (the primary field) in the ground beneath. If there is a conductor in the ground, then small circulating currents will flow in the conductor, and give rise to their own EM field (the secondary field) at the surface.
The other loop is a receiver. In the MaxMin the receiver loop is wound around two magnetic cores, which form the ‘horns’ on the receiver. Normally the primary field is much stronger than the secondary field. In order to detect the secondary field, a small part of the primary field is sent from the transmitter via cable to the receiver, and is used to cancel the primary field at the receiver, leaving only the secondary field to be detected. The receiver measures two quantities, the in-phase component and the quadrature component of the secondary field, expressed as a percentage of the primary field at the receiver. There is a phase shift or time delay in generating the secondary field of the conductor. The part of the secondary field that is not delayed is the in-phase component, and the part that is delayed is the quadrature component. Anomalies from good conductors have large in-phase and small quadrature components, while weaker conductors have low in-phase and high quadrature components.
The MaxMin offers a range of frequencies which depends on the model. Typical frequencies increase from 110 hertz (Hz) by factrs of two to 3550 Hz or even higher. In a mineral exploration survey, both lowest and highest frequencies are read, but not all intermediate frequencies are necessarily used.
Interpretation of HLEM data depends on the assumption that the transmitter and receiver coils are coplanar (that is, in the same plane) at a constant separation. In areas of topography, maintaining this assumption is not trivial. The MaxMin system allows the operator to measure the slope to the next station before leaving the current one. If this measurement is done at each station, the computer in the MaxMin receiver will integrate the slope readings to determine the elevation difference between the Tx and Rx coils.
Gamma-ray spectroscopy offers a rapid and reliable radiometric method of analysis of U and/or Th ores. Methods of ore analysis are described, and experimental results are presented. The U-Th ratios of rocks, which are important in strata recognition and correlation studies, can be determined directly by gamma-ray spectroscopy without the necessity of making individual U or Th assays. Analysis of potash ores is facilitated with a gamma-ray spectrometer. Erratic behavior of gamma-ray well logs can often be resolved by studying the gamma-ray spectra of these logs. Neutron-activation, followed by gamma-ray spectral analysis, of common earth materials offers a method of borehole rock analysis for elements such as Ca, H, Cl, S, and Mg. Data in studies employing radioactive tracers can often be enhanced through use of a gamma-ray spectrometer. Other present and potential applications of the gamma-ray spectrometer in mineral exploration are also discussed.
Geophysical surveys are an extremely helpful tool for identifying areas of high exploration potential so that work programmes can be prioritised. Our geophysical experts can interpret regional geophysical and satellite data and provide a report on targets, intrusion detections, structural interpretations and alteration maps.