Spectral Geophysics

An example of the response of a conductive plate (sulphide body) under weakly conductive overburden, measured by the VTEM® helicopter-borne EM/Mag/Radiometric system.

Airborne EM can be applied very efficiently to cover large areas for precious and base metals, diamond and uranium exploration. The system can detect conductors at depths of several 100 meters, depending on the geological environment.

SPECTRAL GEOPHYSICS has the latest software and expertise to extract the maximum information from Airborne electro-magnetic, magnetic and radiometric data.

It is important to be able to present all available geophysical data sets in a manner which allows direct correlation between different geological responses and additional data sets such as satellite imagery, geological maps, digital terrain models, borehole information, resistivity depth sections, radio-active elements, etc.

The figure below shows a 3D IP/resistivity model derived with UBC software package DCIP3D from pole-dipole data over an existing orebody at 320m depth.
The data presentation was done with the program VOXLER, but can be done with Profile Analyst or Oasis Montaj.

CDI’s are a 2D display of conductivity variations with depth along a survey line (ground or airborne). Uranium could be associated with conductive lithologies i.e.. graphite, carbonaceous shale, massive sulphides, etc. which can be very effectively mapped with EM. A CDI is a very cost and time efficient way to derive conductivity variations with depth directly from raw EM data. Formational conductors can readily be identified on the CDI sections.

SPECTRAL GEOPHYSICS has extensive experience in creating CDI’s using the latest available software such as EMFLOW.

The Time Domain Electromagnetic and Induced polarization methods, used in isolation or in combination, are very efficient geophysical tools to locate base metal sulphides containing, e.g. copper, nickel, lead and zinc.

SPECTRAL GEOPHYSICS uses the 24 bit EM/IP Smartem 24 receiver to record the full wave-form at very high sampling rates (120,000Hz) enabling us to record very weak signatures in very noisy terrains such mine sites.

The EM surveys usually consist of either large fixed loop or moving loop configurations, followed by downhole logging using 3D EM probes.

The figure on the left illustrates the 3 component EM response down hole for a base metal target.



Airborne magnetic surveys can cover large tracts of land in a relatively short space of time, delineating large regional geological features.

Processing of the data thus gathered will enhance the signatures of the geological features.

The example on the left shows a paleochannel (in red) detected below approximately 5m of Kalahari cover in southern Botswana.

The accurate delineation of the channel  will have a significant influence on the probability to locate diamondiferous gravels or potable water.

SPECTRAL GEOPHYSICS geo-scientists apply sophisticated filters to accentuate subtle features of interest in high resolution aeromagnetic data.

The figure on the right shows the detection capabilities of Electrical Resistivity Tomography (ERT). The example is from the software manual of RES2DINV by MH Loke.  The pipe of approximately 1.2m diameter is indicated by a conductive circular feature.

The non-invasive nature of the technique as well as the ability to operate in areas with high AC interference makes it the ideal tool to apply in urban environments.

The directional downhole IP technique is used to determine the direction from the hole to chargeable material located around it. Current electrodes are located on the surface in the plane of the drill section and in the plane perpendicular to it. The potential readings  taken with one electrode in the hole and one on surface. Using the two sets of readings from each current position, it is possible to determine the vector direction to the bypassed chargeable material.

The example above is from a test survey in the Copper District in Namaqualand, South Africa. Interpretation of the results indicate that the bulk of the body is located southwest of the hole at a depth of approximately 100m and a distance of approximately 25m from the hole.