Mine Site Geophysics
Welcome to this special issue of FastTIMES entitled: Mine Site Geophysics. Mine sites have long lives, starting with their discovery and ending with their closure. During the mine-life cycle many decisions are required that impact the economics and safety of the mine (for example, the location of tailings ponds). Environmental issues must be addressed as well such as ensuring the isolation of contaminated water from surface and ground water sources. Placement of infrastructure at a mine site requires knowledge of the locations of potential satellite ore bodies in the mine area so that construction can bypass these areas and save expensive modifications later. Prolonging mine life by locating additional resources nearby is also important for profitability. The list of decisions that are required during a mine’s life is long and complex.
Geophysical data provide important information at mine sites that can be used to solve a wide range of potential issues: 1) post exploration discovery 2) geotechnical and infrastructure studies 3) minimizing ore contamination, waste dilution and mining hazards 4) waste management – rocks, tailings and mine waters 5) management of ground water, surface water and mine water, and
6) environmental management, rehabilitation, and mine closure (for more information see the article by Pettifer, 2018).
In this issue we provide examples of using geophysics to address some of the concerns mentioned above. We have divided the issue into several focussed themes.
A – Focus on Brownfields and Green fields
We start with Reid’s paper entitled The Complete Mine Site Geophysicist – Assisting Mining Operations with EM, Radiometric and Seismic Measurements which provides 3 interesting examples from Africa using innovative solutions to locate additional reserves close to existing mines. One interesting example uses in-mine reflection seismic to locate pods of chromite ore. Another example uses gamma spectroscopy to locate felsic dykes that are high in potassium. The mining company had discovered there was a relationship between high grade gold and where these dykes intersect. Gordon and Cortes make use of deep penetrating electromagnetic (EM) systems for risk mitigation in an article titled Deep Imaging Technologies Applied to Mine Planning and Exploration: Applications for Risk Mitigation at the Mine Site. In their paper they use a combination of detailed MT and deep DC resistivity and induced polarization (DCIP) systems for imaging to depths of 1500 m. They combine these techniques with 3D imaging technologies to enhance resolution at depth. Gibson
et al. leads the reader through a detailed inversion scheme for integrating geological and gravity (density) models is an article entitled Searching for Excess Density via Inversion of 3D Geology and Gravity Data – a Possible Brownfields Exploration Method. They use high quality ground gravity data from a Sedex deposit combined with a 3D geological model to demonstrate the technique.
The article by Ryan et al entitled An Evaluation of Placer Deposit Exploration Through GPR, DC Resistivity, Drone Imagery and Lidar outlines a systematic approach to explore for placer gold deposits in the Klondike area near Dawson City, Yukon. This region has been explored using the same methods introduced in the early 1900’s. They developed an interesting approach to obtain estimates for the dielectric constant of permafrost and non-permafrost sediments are converted to radar velocities. They then are used to convert GPR two-way travel times to more accurate depth sections.
In addition, there are two articles in the Government Geophysics News column on recent releases of geophysical data. One is from the Illinois State Geological |survey that has published the results of approximately 90 yeas of recently digitized near surface geophysical surveys. The other is from the Geological Survey of Canada and the Saskatchewan government on a combined airborne/EM/magnetic survey at Wapawekka Lake near La Ronge.
B – Focus on tailings storage facilities (TSF)
We start with a paper in the industry news column by Elliott entitled Reducing the Risk of Tailings Storage Facilities. She talks about integrating various data types into a single database that can be used by all stakeholders. The article discusses the importance of monitoring and collecting these data to ensure long-term stability and safety of TSF’s by ensuring it is available to make informed decisions. The next paper is by Balding entitled High Level Case Studies in Tailings Storage Facility Design, Construction and Management using Geophysics. He begins with the evaluation of palaeo-karst features using seismic refraction, microgravity and ERI and continues with 5 more studies using these 3 geophysical methods, as well as MASW and EM-31 surveys. There is a case study paper in the Hydrogeophysics and Environmental Geophysics column entitled TSF Leakage Temporal Changes – A Case Study. Four EM31 surveys carried out over a 12-year period around a TSF, illustrate the dynamic nature of leakage from a TSF and a how in favourable circumstances in a saline environment, repeat, simple EM31 surveys can be used with bore control as a way of environmental monitoring of saline groundwater levels that threaten surrounding vegetation root zones.
C – Focus on new technologies
The first paper by van Dam et al entitled Efficient conductivity mapping using the operator-carried time-domain electromagnetic loupe TEM system carried out a case study at a mining site in Western Australia. The objective was to map a conductive leachate from overflow runoff from the tailings pond that could be present in bedrock fractures outside the pond area. The loupe TEM results are compared with a Geonics EM-34 survey conducted several years earlier, as well as passive seismic horizontal to vertical spectral ratio (HVSR)data to estimate depths based on the resonant frequency. The results show the Loupe TEM system performs quite well and is an efficient way to collect useful conductivity data. Prikhodko et al discuss a new airborne EM system using natural occurring audio frequency magnetic fields (AFMAG). The system can image to depths between 1 and 2 km, even in the vicinity of active mines. Their paper entitled Capabilities of the Airborne Mobile MT for the expansion of Active and Historical Mines explains how the airborne mobile MT system can work in electrically noisy environments. They provide 4 case histories using examples from active and historical mines to show the effectiveness of the method. Urosevic et al carry out a comparative study of a Distributed Acoustic Sensing (DAS) system and a standard geophone system over a salt-lake environment in western Australia in an article entitled Reflection Seismic with DAS, Why and Where? Their study is the first attempt to use the DAS technology for surface reflection seismic in an area where regular geophone seismic systems often don’t work. They show that, even with issues related to directional sensitivity and low S/N, the dense sampling along the cable helps to overcome these difficulties, particularly in areas where the surface conditions cause problems for conventional geophone systems. An article in the Mining Geophysics News column entitled The 21st Century: A New Era for Mining Tech by McCown is well worth a read. It talks about the use of robots and robotics within the mining community. This section ends with the geoDRONE column, highlighting the importance of the emerging technology of using drones to acquire geophysical data and reporting on a new initiative to establish guidelines for quality control of drone geophysics data.
D – Focus on Geotechnical
Chatfield discusses the use of wireline logs to provide information on in-situ rock strength and stress. He provides examples using the sonic and variable density tools in an article entitled Wireline Sonic Logs Reviewed. The article provides an excellent overview of the capabilities and usefulness of borehole logging to the mining industry. In the infrastructure and geotechnical geophysical news column Cassidy discusses micro drones capable of working in boreholes and small underground cavities.
In addition, there are two other brief articles that relate to mining activity. These are the Archaeology and Forensics Geophysics column which looks at archaeology of historic and ancient mine sites and the Agriculture Geophysics column which examines the conflicts and symbiosis between mining and agriculture. Finally, the regular UXO Geophysics News column features news of the recent SERDP/ESTCP 2020 Conference and the upcoming SAGEEP 2021 / Munitions Response Virtual Meeting. Enjoy the issue and keep safe and healthy.
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Mel Best has more than 30 years geophysical experience in industry and government. He began his career with Shell Canada in Calgary, Alberta in the mineral department. At that time, he carried out a detailed comparison of existing airborne EM systems in anticipation of developing a system for Shell. He spent two years at Royal Dutch Shell’s research center in Rijswijk, The Netherlands developing such a system (the SWEEPEM airborne EM system). Several patents and research publications emerged from this project as well as a prototype system. He eventually moved from the minerals department to head up petroleum engineering research for Shell in Calgary. He left Shell to work for Teknica Resource Development Limited in Calgary developing artificial intelligence workstations for seismic processing and interpretation. Mel then joined the Geological Survey of Canada (GSC) as head of the Basin Analysis Subdivision in Dartmouth, Nova Scotia responsible for research related to east coast offshore and eastern Arctic hydrocarbon basins of Canada. Dr Best became Director of the Pacific Geoscience Centre (GSC) in Victoria, British Columbia heading up research in earthquake seismology and marine geosciences on the west coast and western Arctic of Canada. He stepped down as Director after 4 years to become a senior research scientist working on environmental and groundwater research. He took early retirement from the GSC in 1997 and started a geophysical consulting practice in oil and gas exploration and production as well as groundwater and environmental studies. He is past editor of the Journal of Environmental and Engineering Geophysics and the Canadian Journal of Exploration Geophysics and past associate editor of the Bulletin of Canadian Petroleum Geology. He is a recipient of a meritorious service award from the Canadian Society of Exploration Geophysicists and the John Nichol award from EEGS.