Case Studies
Airborne electromagnetics in Pilbara manganese exploration - a case study
Airborne electromagnetic methods have been used for manganese exploration in parts of the Pilbara since 2002 when the first Hoistem survey was flown for Pilbara Manganese. A XTEM survey was commissioned by Montezuma Mining to test the effectiveness of the technique in a new manganese province near Kumarina, WA.
A series of test lines was flown over areas of known manganese ore deposits and revealed a successful correlation between the electromagnetic conductors and the known manganese zones. In addition the test lines revealed new zones of conductivity where traces of manganese had been found but not yet drilled. Based on the preliminary results the complete Butcherbird tenement was flown in December 2010.
The survey successfully mapped the extent of the known manganese zones and assisted in the identification and mapping of several new targets which were subsequently drilled and found to bear manganese oxide. The shape of the EM anomaly maps the resource outline and the strength of the EM signal correlates strongly with the grade of the resource.
The final powerpoint presentation that was delivered at Australian Society of Exploration Geophysicists Conference 2012 (Brisbane) is available for download here as a PDF.
Airborne electromagnetics for water exploration
Byro Sub-basin hydrogeophysical investigation – a case study combining airborne EM, aeromagnetics and geophysical drillhole measurements
GPX Surveys was commissioned to fly 2612 line kms of Helicopter time-domain electromagnetics (EM) using their XTEM system, over a groundwater exploration area in the Byro sub-basin, south of Gascoyne Junction. The objective of the survey was to determine the capabilities of the XTEM system with respect to mapping the conductivity variation of the different sedimentary units, to see if the XTEM EM data could define the aquifer horizon and to try and use the XTEM EM data to map the salinity in the region.
The XTEM system was selected for the project due to its characteristically high vertical and spatial resolution. The high bandwidth and square waveform allows XTEM to be a good mapping system for the objectives of this type of survey.
A series of test lines were flown over geophysical boreholes in May 2011 and revealed a successful correlation between the geology, layered conductivity and the generated Conductivity Depth Images (CDI’s). The EM data from the test lines were interpreted in the field at the completion of the acquisition flight. The decision was made based on these results to continue flying and complete a larger survey over the entire block. The survey was performed across the strike of the major syncline, with variable line spacings between 1 – 4km.
The survey successfully mapped the extent of the known conductive units within the depth-of-investigation and allowed a layered earth model to be produced. This was further constrained by inverting magnetics data and allowing for geophysical borehole measurements and geological observations to be integrated.
Work was also done to combine measured salinity information from bores in the region with the modelled XTEM conductivities and structure, resulting in modelled salinity distributions for the major geological units.
The results proved that the XTEM EM data can be used as a tool to verify the regional conceptual model where little data was available basin wide and map potential recharge zones on the flanks of the syncline.
The final powerpoint presentation that was delivered at the CSIRO Workshop "Groundwater Resource Assessment in Western Australia - The role of airborne hydrogeophysical methods", Perth, 22 February 2012 is available for download here as a PDF.