Q&A with David Thiel the real benefits and concerns of Electromagnetic Geophysics
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Surface-based electromagnetic geophysics can help mining companies with feasibility studies in the following ways: 1) It provides information on overburden, faults, intrusions, aquifers, and old workings to a depth of 50-100 meters, which helps with mine planning and infrastructure development without being a fully comprehensive assessment of the deposit. 2) It can identify rock and soil types and their conductivity, as well as dislocations, which allows for detailed mine planning with precision over 1 meter. 3) While interpretations require geological knowledge and the technique can be influenced by certain surface conditions, electromagnetic geophysics is cost-effective as it reduces the need for extensive drilling and leaves no surface disruption after feasibility studies
Q&A with David Thiel the real benefits and concerns of Electromagnetic Geophysics
- 1. How mining company can benefit from ground-based electromagnetic geophysics Q&A with Professor David Thiel, Director of the Centre for Wireless Monitoring and Applications Griffith University Mining IQ How can surface-based electromagnetic geophysics help those who are conducting a feasibility study? Professor David Thiel The discovery of green-field deposits is usually verified by chemical analysis of samples from surface rock, drill holes, cuttings, streams and alluvium. A feasibility study needs to provide answers to management, investors and often government about the viability of the planned operation. Surface-based electromagnetic geophysics coupled with topographic mapping provides information to a depth of 50 – 100 metres. Thus it is usually not a complete technique in predicting the dimensions of the deposit or the purity of the ore. Despite this, the technique can be used for overburden mapping, fault location, intrusions, aquifers, old workings, old land-fills etc. Whether the mine is planned to be surface-based or underground, unobtrusive surface based mapping techniques are of significant value in mine planning. Once the upper extent (surface projection) of the deposit is known, mine infrastructure planning for road-ways, stock-piles, muck-piles, crushers, buildings, power networks, etc can be planned. This impacts on the size of the mining precinct including buffer zones for vibration, dust and noise abatement. Surface based geophysics is usually used in conjunction with drilling, but can reduce the number of boreholes through highly targeted drilling. This speeds up the assessment process and the efficiency of the exploration program. The technique is quick, simple, cheap to run and can be run with only one person. Mining IQ What kinds of results or information can a mining company get from ground- based electromagnetic geophysics? Professor David Thiel Electromagnetic geophysics distinguishes between the rock and soil types on the basis of conductivity. Three dimensional profiles can be developed from one or more bore-holes. Dislocations in rock and soil are readily identified in the field and can be pegged during the survey. The surveys can be implemented with minimal environmental and cultural impact, very little health and safety risk to company employees and the local population, and at very 1
- 2. low cost. Hand-held equipment can be quickly deployed without substantial forward planning or cost. The positional accuracy of the data is better than 1 m so that detailed mine plans can be developed with the necessary precision. Speed and cost minimisation during the feasibility study are valued highly by all stake holders including the local community. Electromagnetic geophysics can identify and map: o LOX o Faulting o Intrusion o Pronounced effects in sedimentary environments It provides a good response to changes in geology and lithology, and can assist in mine planning – LOX, structural information Mining IQ How accurate is this form of scoping? Are there any areas users should be careful of? Professor David Thiel Electromagnetic geophysics profiles are sometimes dominated by large peaks and troughs in the profiles resulting from “scattering” of the electromagnetic waves from surface and subsurface discontinuities. Some of these features are of significant value and others constitute unwanted interference from pipelines and power lines. An experienced operator will note these effects during the measurements and interpret the data appropriately. As the earth is anisotropic and the direction of the radiation affects the measured response, mapping in only one direction (i.e. using only one source field) can result in some major and important features being over-looked. The technique can be influenced by the presence of surface water, vegetation and steep terrain. Careful positioning of the instrumentation at every location is essential to obtaining reliable data. Due to the nature of geophysics there are a variety of interpretations which can fit the same data points, so a pre-existing geological knowledge from borehole data allows the most accurate interpretation of the data Mining IQ Feasibility studies tend to be very expensive; is electromagnetic geophysics cost effective? Professor David Thiel Feasibility studies are required to address the mine economics and the social and cultural and the environmental effects of the mine in three stages: • the construction of the mine, • the operation of the mine, and 2
- 3. • the site rehabilitation during mining and at its end of life. Given that not all feasibility studies result in progress to the construction of a mine, the withdrawal from a site following the completion of the feasibility study needs to ensure minimal evidence of the on-site work. Common complaints from land-holders following a feasibility study include the presence of compacted road-ways on arable land, drill holes, costeans, damaged fences, graded edges in flood plains, and cleared sections of bush. Ground based geophysical methods can operate successfully without leaving any of these disruptions. Ground based methods reduce the need for large scale grid drilling through more targeted drilling and chemical ore assessment of the drill tailings/core. This can greatly reduce the cost of the feasibility study. Less boreholes = less time drilling and more efficient = cost effective. The technique is thus very cost effective. 3