Using 3D modelling to avoid ore dilution

In coal mining it is important to know if localized areas of coal have been rendered worthless through contact metamorphism adjacent to volcanic dykes or sills.  This high temperature metamorphic process results in “coked” or “cindered” coal, which is graphitised and is highly electrically conductive.  Coked coal should be excluded from the ore reserve model and is ideally discarded during the mining process. To avoid dilution of high-quality coal with waste, accurate coked coal boundaries are traditionally mapped by expensive drilling prior to mine planning.

Case study: Bowen Basin mine site, Queensland

Surface electromagnetic and electrical methods were trialled at a mine in the Bowen Basin, Queensland, with the objective of mapping the extent of coked coal.  The methods trialled included moving-loop time-domain electromagnetics (MLTEM), Sub-Audio Magnetics (SAM), and conventional direct-current resistivity/induced polarization (DCIP).

MLTEM was found to be an effective tool for mapping the coked coal.  Figure 1 below shows a one-dimensional (1D) inversion using the UBC code EM1DTM.  The strong flat-lying conductor on the southern two-thirds of the line is associated with coked coal (KC).  The dipping feature on the northern third of the line is a 1D inversion artifact.  The artifact arises because the measured data are 3D, due to the abrupt edge of the conductor two thirds of the way along the section, whereas the 1D inversion assumes that the earth is horizontally stratified.

Figure 1 One-dimensional inversion results from one of the MLEM survey lines (no vertical exaggeration). The strong flat-lying conductor on the southern two-thirds of the line is associated with coked coal (KC). The dipping feature on the northern third of the line is a 1D inversion artifact.

SAM total field electromagnetic (TFEM) data was also acquired, using a grounded wire transmitter.  3D inversion of TFEM data was feasible because only a single transmitter was employed – the computation time for electromagnetic inversions scales with the number of transmitters.  The 3D TFEM inversion used the MLEM 1D inversion result as a reference model.  Figure 2 shows a cross-section through the 3D TFEM model, on the closest section to that shown in Figure 1.  The extent of the coked coal has been well mapped by the TFEM, and the 3D inversion has greatly suppressed the dipping artifact from the 1D inversion.

Figure 2 Conductivity section through the grounded-source TFEM 3D inversion. The closest corresponding MLTEM 1D inversion is shown in Figure 1. The constrained 3D TFEM inversion has greatly supressed the 1D inversion artifact.

Although this case study applies to coal mining, the 3D modelling approaches described are applicable in general to SAM, total field electromagnetic and TEM data.  We can model data acquired for base metals and gold exploration using similar techniques.

The results of this work have been published at the 2nd Australian Exploration Geoscience Conference by  Lowe et al (2019), and can be downloaded from here.  We would like to thank our co-authors Jonathan Lowe (BHP), Eric Battig and Dan Eremenco (GAP Geophysics).  Permission to show these results was kindly granted by BHP.

James Reid is the Director of our Asia-Pacific consulting services and a Principal Consultant with an extensive geophysical consulting background. He has extensive expertise in the planning and quantitative interpretation of electromagnetic and electrical methods, particularly the application of airborne electromagnetics to mineral and groundwater exploration. He has an MSc in geophysics from the University of Sydney and a PhD in geophysics from Macquarie University. James is based in Perth.

Scott Napier is a Principal Geophysicist who brings general expertise in geophysical inversion, along with extensive borehole, ground, marine, and airborne EM interpretation and processing experience. He has worked in Canada and internationally on oil and gas, uranium, and base metal exploration teams, with a track record of proven discovery. Scott has an MSc in geophysics from UBC. Scott is based in Vancouver.

Latest news

Stratigraphic interpretation and modelling
March, 06 2020

Coal industry solutions

Our coal solution provides users the simplicity of 2D grid modelling with the geological complexity of 3D volumetric surface modelling...
Read more
Case studies
February, 04 2019

Darlot Gold Mine Area, Australia

3D Interpretation of geological, 3D seismic, and conventional geophysical data for brownfields exploration targeting...
Read more
Case studies
April, 30 2019

ERO Copper Curaçá Valley, Brazil

Maximizing value: 3D data integration and interpretation. One of the main challenges in exploration is increasing our subsurface knowledge...
Read more
Case studies
September, 01 2019

Machine learning in mineral exploration

We have applied machine learning as part of custom solutions to complex exploration and geotechnical problems since 2015...
Read more
Software tips
July, 20 2020

Data set summaries

In Geoscience INTEGRATOR The Data set explorer provides simple, immediate ‘dashboard’ access to all the data sets, and their summary information...
Read more
Geoscience ANALYST
October, 10 2019

Geoscience ANALYST Pro Geophysics Consortium

Today we are highlighting our new, industry-led, research consortium focused on delivering software and methods that make the use of advanced geophysics a day-to-day, practical reality for industry...
Read more
Software tips
October, 12 2020

Create regions – Crossplot 2D

In GOCAD Mining Suite you can filter data dynamically before creating regions and save the filters as templates for later use...
Read more
Case studies
June, 10 2019

Let the data speak!

Four years ago, along with DMT Group, we started working with  JSC Apatit on their Kirovski and Rasvumchorr mines that...
Read more
Geoscience ANALYST
February, 17 2020

Bridging the gap

Industry uptake of academic exploration and mining research is often slower than it should be. Academics must focus on innovation and education...
Read more
About us
January, 10 2018

UDMN Award of Excellence

Geoscience INTEGRATOR wins - Last December, UDMN presented us with an Outstanding Achievement in Commercialization...
Read more
Software tips
February, 01 2021

Show and hide

In Geoscience ANALYST you can show and hide everything, individual objects, container groups or drillhole groups...
Read more
Software tips
April, 03 2020

Using hot keys

Use hot keys in GOCAD Mining Suite to optimize your experience to help navigate the interface and execute commands more quickly and easily. Try them out!
Read more

Please contact our team for additional information about our products and services