This year's model - geological modelling techniques

Materials World magazine
,
1 Dec 2014

More miners should take a leaf out of the oil and gas sector’s book and start using advanced geological modelling techniques – early adopters are already reaping the benefits. Guy Richards reports. 

It’s no secret that many ore discoveries these days are complex in composition and variable in quality – and yet mining companies could be doing more to establish how and when best to develop new projects, according to one expert. Andy Clay is managing director of Venmyn Deloitte, a consultancy that carries out technical and economic assessments of mineral projects, and he says miners should start adopting some of the advanced geological modelling and visualisation technology that’s common in the oil and gas sector.

‘The type of visualisation I’m talking about here is comparable to the 3D techniques used in medicine on pregnant mothers,’ he explains. ‘Similar techniques are used in the oil and gas sector, and even 4D techniques that show the time variable to model flows in a reservoir.

‘The sector has had to adopt these techniques simply because of the enormous cost of drilling wells into likely reservoirs. It is not unusual for the industry to be exploring at over 10km below sea-level, with such deep wells often costing in excess of US$100m. Failure is not an option when this type of money is at stake.

‘There’s a crossover here with the mining industry, in the shale gas market, where the amount of drilling needed is similar to coal projects – but you also need the type of reservoir visualisation techniques used in the oil and gas industry. 

But they can also be applied to mining projects worldwide, for difficult orebodies, say, and to help make sure, when the time is right, to develop them according to factors such as commodity prices. You can only accurately assess this option by using these advanced techniques.’

However, he says, ‘Very few mining companies are using these techniques, partly because of their cost and partly because of the industry’s inherent resistance to change – it’s expensive and there’s a culture in mining that things are done in a certain way because that’s the way they’ve always been done. But these techniques could be a game-changer for the mining industry – companies really should take their lead from the oil and gas sector, and no matter how orebodies are assessed, we would recommend spending money on 3D modelling.’

Two companies that are exploiting this technology are Gold Fields, at its South Deep project in South Africa, and Newmont Mining, across all its global operations.

South Deep is one of the largest gold mines in the world but the company says it’s an exceptionally complex deposit, consisting of 16 reef horizons in a west-to-east fan formation, up to 130m at its thickest point and highly faulted throughout. In addition, the reefs pinch out at various points as the fan narrows towards the west.


Running a risk

Without regularly updated and accurate geological modelling, the risk of off-target reef mining frequently occurring is very real, affecting the grade and cost profile of this fully mechanised project. But as the composition of the orebody changes and new information about it is acquired, a traditional modelling package would need to be partially or completely rebuilt, which is costly and time-consuming. As such, the geologists and mine planners at South Deep use software called Leapfrog, one of a number of such products that updates geological models dynamically.

Nick King, Chief Geologist at the project, gives a detailed insight into how the software is actually used. ‘At South Deep, new geological data is collected every day, either through new borehole information or routine underground mapping,’ he says. ‘Typical geological inputs would be the records of the thickness of a particular reef unit, the orientation of the contact planes between reef units, the orientation and thickness of intrusive lithologies and the occurrence, sense of movement and orientation of fault planes.

‘With this software, we can capture that information, add it to the database and then automatically update the geological model for the area concerned, which rarely takes more than a couple of hours. Once a new model has been generated, the geologist will review it and, once satisfied that it is correct, assess the implications that the changes may hold for the optimal mining of that particular area.’

King says most model updates result in relatively minor changes that do not need any modifications to the layout or scheduling of the mining excavations. But, he adds, ‘Where new information has resulted in a significant change to the geological model for that area, the geologist will contact the mine planner, provide a copy of the new model and assist in the redesign and scheduling of the affected excavations. The new design is then forwarded to the survey department, which will provide the miner with a survey note detailing any changes in distance and direction that may be required. The miner will then translate that information into instructions to his equipment operators.

’The entire process, from the initial recording of new geological information to the implementation of the first blast in response to a new instruction, can be completed within 48 hours,’ he says.

Gold Fields adopted Leapfrog late in 2012, but Newmont has been using its own proprietary visualisation tools for more than 20 years, according to the Group Executive of Resource Modelling, Marcelo Godoy. It now also uses Leapfrog ‘on an as-needed basis’ and, since early 2014, another dynamic modelling package called Vulcan.

Godoy declines to discuss Newmont’s use of modelling software in anything other than general terms, but he does say, ‘Visualisation tools are generally integrated into full mining packages that have tools and processes to support the orebody modelling and mine planning workflows, which includes data management, geologic modelling, geostatistics and mine design.’

But, given the company’s focus on gold and copper, he adds, ‘Gold and copper deposits generally have complex morphology and a high degree of heterogeneity. Therefore, it is paramount that geologists and planners have the ability to visualise and work with orebody models directly in 3D.’

Clearly, practitioners of this technology are also among its advocates, and according to King it doesn’t have to be limited to complex orebodies. ‘Mines with less complex geological conditions could also benefit from adopting [software such as] Leapfrog. The advantage is that, regardless of the complexity of the geological conditions, it can incorporate new geological data into a self-contained software package and produce an updated geological model within hours of data capture.’

By contrast, he says, operations that rely on traditional modelling packages can only produce a limited number of model updates a year. Another drawback is that they often rely on the importation of external data files, meaning that strict data controls and protocols are needed to ensure that the correct files – and their versions – are available and accessed when a new model build is required. Geological models developed in Leapfrog can be exported in formats that are compatible with most mine planning and survey software packages.

The impression is that the only thing stopping the wider industry adopting the new technology is, well, the wider industry, and yet the pressure on miners to extract mineral resources efficiently and profitably can only grow. Whenever a new technology comes to market, potential customers will often wait to gauge its utility by looking at the experiences of the early adopters. In this case, they look to be wholly positive.