Exploration is beset with high costs, risks, and all kinds of challenges: where to target; how many holes to drill?
With such questions, any answers help reduce the uncertainty inherent to the process. Without doubt, the first and most important decision is selecting where to explore.
Understanding the geology of the target area allows companies to make informed decisions when choosing their exploration approach.
Understanding ore-forming processes is critical for sedimentary basin exploration
Outcomes emerging from research undertaken in CSIRO’s Deep Earth Imaging Future Science Platform (DEI-FSP) is generating new predictive tools for mineral explorers.
The DEI-FSP has been working on new ways to image and enhance our understanding of deeper geology and its evolution over time. Knowledge about this evolution is critical to enable new mineral discovery in sedimentary basins.
Sedimentary basins are natural sources for many critical minerals, but their genesis and radical transformation over time makes their composition extremely difficult to determine.
Every basin is unique.
This makes selecting exploration targets within sedimentary basins tricky.
Understanding variables of ore formation
CSIRO research scientist Dr Thomas Poulet is part of a team developing three-dimensional numerical modelling simulators which are helping to better understand ore-forming processes.
“The number of variables affecting the formation of ore deposits in sedimentary basins is so high a team of geoscientists with diverse expertise is required to reliably assess them,” says Dr Poulet, a specialist in mathematical geoscience.
“Our main hypothesis as modellers is that understanding the formation of ore deposits can help explorers targeting resources,” he says.
His research focuses on ore-forming systems in sedimentary basins.
A collaboration between researchers in DEI-FSP and CSIRO’s Discovery team is studying the mechanisms that govern localised fluid flow pathways associated with the intricate mineralisation processes that can occur in these basins.
Why are these basins so complex?
Elementary geology reminds us that over millions of years rivers and oceans have eroded rocks that have been transported and deposited as sediments.
Basins contain multiple layers (strata) of different types of sediments. After deposition, these have been subject to a myriad of processes, including burial, exhumation, and chemical reactions.
Scavenging a system
While complex to unravel, understanding a basin’s formation history is the first step in assessing its potential to contain an ore deposit.
Dr Poulet explains there are many points to consider, such as:
- the pressure and temperature history of the system
- the system’s architecture
- the nature of the fluids involved
- where the physical and chemical pathways are
- the drivers for fluid flow, and
- the parts of the system being scavenged and where minerals are precipitating.
Understanding the highly transformational nature of sedimentary strata and a basin’s structural controls is imperative.
Nature cannot defy physics, but in basins built over millions of years, it can complicate it.
“A basin may contain many layers of different rock types each with different properties,” says Dr Poulet.
“For example, imagine a permeable layer of sandstone, above it there may be an impermeable layer of shale, then above that another permeable layer of sandstone.”
“That’s where it starts to get difficult.”
“We might have one or more fluids migrating through the more permeable layers of the deformed system."
“If the conditions are right the chemistry of the fluids and rock may interact resulting in the precipitation of metal-bearing minerals."
“If the reaction is ongoing and concentrated in a particular region of the basin, then a new ore deposit forms.”
Faulted, fractured and folded
Permeable rock beds offer one fluid flow pathway.
Yet some of the rocks have been faulted, fractured, and folded – creating pathways allowing fluids to flow upwards or sideways rather than simply following across the bed itself – and then you have a geological system that defies simple analysis.
“That is why we need some very powerful computers to sort out these problems because it is too complex to do it in our heads!”
New advanced computer modelling of fluid flows
As an example, to capture the role of faults and folds as conduits for the flow of potentially mineralising fluids, the team has developed several numerical tools to build 3D models from the GIS (spatial) information of fault traces, thickness, dip, and dip orientation.
The models can be used to visualise faulted basins and generate the corresponding fluid flow simulations.
“Our work is cutting-edge,” Dr Poulet says.
“Our models can be incorporated into workflows used by exploration companies to help identify high potential areas when prospecting.”
“The approach is computationally advanced with the models able to account for a range of varying parameters and geological constraints.”
“At the back end of the process, we can use artificial intelligence to assist with calibrating the models to ensure they are refined specifically for the region of interest.”
And these tools can be used for exploration in other geological settings.
“There is the potential to adjust the parameters to account for different ore deposit types and geological settings. At this stage, we are focusing and refining our models’ development for exploring sedimentary basins. However, we can also apply the workflow to other geological settings.”
Unlocking critical battery minerals
These models have been created with industry in mind, to offer practical help to mineral exploration companies.
The search for critical and strategically important metals has become ever more urgent as the world progresses from fossil fuels to battery-powered technologies.
Finding economic ore bodies is time-consuming and extremely expensive – the costs of exploring and drilling can blow out to hundreds of millions of dollars.
“The business of exploration is about taking risks. If anything, our modelling decreases risk enormously, making that search so much more accurate and so much less expensive for the company,” Dr Poulet says.
Often the object is to tell the company where not to go.
“If we can invalidate some areas and reduce the search space and the number of drilling holes, we will have saved the company time and money.”
“That’s a win for everybody.”
Explore the Deep Earth Imaging FSP website.