Extracting more gold than expected from an area of ore sounds like a great outcome.
But an undercall can present problems over time, says AMC Consultants senior geologist Maree Angus.
There are issues of market perception, understanding of the project’s value, government expectations, mine scheduling and even waste allocation.
“In a mine, things like tailings dam walls and roads are built from the waste material – so if you are not generating the waste predicted in the pit it can sometimes be as problematic as if you are not generating the gold predicted in the pit,” Ms Angus said.
Ms Angus is among the speakers at the Complex Orebodies Conference running in Brisbane, 19-21 November.
She holds an Honours degree in Economic Geology from James Cook University and has notched up 20 years of experience in the mining industry, including at the Osborne and Mt Rawdon gold projects in feasibility stage.
Her paper at the conference will focus on the Martabe gold mine in Indonesia, discussing steps taken there to address an ongoing positive reconciliation; that is higher gold metal production than predicted.
A range of factors can impact on the accuracy of predictions for metal recovery, including the number of drill holes and quality of information they provide.
Adjustments to improve the accuracy of estimates can include increasing the volume of samples from each drill hole and changes to drill hole spacing.
“Many gold deposits are very variable by nature, so having as much high quality information as possible is really important,” Ms Angus said.
In the case of the Martabe mine, where Ms Angus has been working as a consultant, there had been an undercall of around 20 per cent since production commenced in 2012.
Recently that has been reduced by incorporating the use of grade control drilling in the resource estimates.
Despite the recent improvement in reconciliation, infill RC holes last year were still producing significantly higher grades than the block model.
Owner PT Agincourt Resources (PTAR) commissioned a variety of studies to quantify the undercall and look at its causes.
Ms Angus will tell the Complex Orebodies Conference how the outcome of those studies led to the development of a set of tools to be used at the resource estimation stage to mitigate the undercall at Martabe going forward.
The AusIMM is partnering with the Sustainable Minerals Institute to host Complex Orebodies 2018.
The event will feature seven keynote speakers and a range of technical presentations drawn from a mix of corporate leaders, operators, service providers, financial institutions and researchers. More at http://complexorebodies.ausimm.com/