South Deep Gold Mine’s development to its present status as Gold Fields’ “flagship ore reserve” has been preceded by a history of complications punctuated by several changes of ownership. So too has the mapping of its complex reef formations been a prolonged and challenging process.
Only recently has the mine’s geological team responsible for its geological modelling, a vital aspect of mine planning, succeeded in fully coming to grips with it. They did this by bringing the dynamic 3D geological modelling software Leapfrog Geo into play.
Accurate geological modelling is essential in the case of South Deep because of the exceptional complexity of the alluvial deposit. It comprises 16 reef horizons in a west-to-east fan formation that is up to 130 m at its thickest and is highly faulted throughout. In addition the reefs “pinch out” at various points as the fan narrows towards the west.
“In the absence of regularly updated and accurate geological modelling the risk of off-target reef mining frequently occurring is a very real possibility. Any mining not perfectly compliant to the mine plan in exact three-dimensional space could be detrimental for the grade and cost profile of any operation,” Hendrik Pretorius, South Deep’s Chief Evaluator, explains.
The fast, fully-mechanised production rate is the second factor that makes regular up-to-date geological modelling essential at South Deep.
“Leapfrog Geo fully meets our requirements in this respect by keeping ahead of the production rate. It provides accurate, genuinely three-dimensional profiles of the individual sections that are currently being mined, based on all known geological data,” Pretorius states.
By contrast the digital terrain 3D modelling program used previously for this purpose, while proving useful for processing and consolidating data, was unwieldy and slow.
To make the analysis of the ore body more manageable for geological modelling purposes it has been divided into segments, which have been further subdivided into smaller segments designated “fault blocks”. Not only is Leapfrog Geo more user friendly, but it builds a model more than three times faster than the digital terrain program can. To illustrate this Pretorius explains: “When using the digital terrain program a geologist cannot quite finish building a model of one fault block in a day, whereas with Leapfrog Geo he can easily build models for three complete fault blocks in a single day.”
Furthermore, when an existing model requires updating as new data becomes available, with the digital terrain modelling program it has to be completely reconfigured from scratch, whereas Leapfrog Geo updates it dynamically. In addition, Leapfrog Geo produces a complete 3D model that more closely resembles the actual structure of any fault block. “Leapfrog Geo produces the fault block as a model with a volume that can be rotated to isolate individual faults in it, which can be examined and analysed more closely. A further advantage of the software is that all the available data can be stored within it, which makes it more integrated, more easily accessible and more secure.” South Deep’s geological team however continues to use the digital terrain program as part of its armoury of data collection tools that provide the information required to build and update its geological models in Leapfrog Geo.
South Deep, which is situated near the town of Westonaria about 50 km southwest of Johannesburg, adopted Leapfrog Geo – an internationally proven software solution – in October 2012. Leapfrog’s local distributor office provided the initial training for the mine’s core senior geological team.
Since Leapfrog Geo has been rolled out, in-house training has also been provided to the underground production geologists who use it on a day-to-day basis.
“We have now reached the point where we can start using it to its full capability, which is to have it operate as close to real time as possible. As new information comes to hand we can instantly update the model to reflect the geological formations accordingly, which creates the optimal conditions from a mine planning point of view,” Pretorius states.
He adds: “Although the use of Leapfrog Geo has proven to be of crucial importance in enabling South Deep to operate more efficiently, I have no doubt that other mining operations in which the geological conditions are less complicated also stand to benefit by adopting it.
“Many mines in South Africa are still using rudimentary 2D geological modelling programs for mine planning,” he points out. Desmond Subramani, Principal Geologist and official Leapfrog distributor for the African region, says that no special customization of Leapfrog Geo was required to meet South Deep’s complex geological modelling requirements.
“It already contained the design elements capable of meeting the unique characteristics of the ore body there. This amply illustrates the program’s innate flexibility to cater to a great variety of geological settings. “The mining industry has been – and continues to be – severely hit by difficult economic conditions and various other disruptive factors. In such a climate it is all the more important for mining operations to ensure that costs are kept to a minimum and all opportunities to maximize profits are taken advantage of. As the South Deep example illustrates, accurate and timeous geological modelling provides an opportunity to increase production efficiencies and reduce costs. “This is what Leapfrog Geo is designed to deliver.”