The Tanami region is an extensive stretch of land on the border between the Northern Territory and Western Australia, with a history of mining dating back more than a century.
The region is known for gold mineralisation hosted in ancient volcaniclastic-sedimentary and mafic rocks.
However, until recently, locating that gold has proven challenging for local exploration companies due to the lack of exposure.
Prodigy Gold in the Tanami
In 2017, one of these companies, Prodigy Gold, approached the CSIRO to help them better understand the complex Tanami geology and target their gold exploration undercover.
CSIRO Senior Scientist, Dr Susanne Schmid, headed the team that developed the unique geochemical vector in response to this request.
“When we started, there were a lot of known gold occurrences in that region, usually identified by soil anomalies containing pathfinder metals that can occur with gold,” Dr Schmid says.
“But not much was known about the geology and what controls the mineralisation because of the lack of exposure.”
Developing geochemical vectors
The CSIRO team developed the Tanami gold vector in-house, tailoring existing vectors to fit the geochemical makeup of the region.
“We have developed geochemical vectors over the past 10 years, mostly targeting copper,” Dr Schmid explains.
“You can apply them for different target types, but they have to be adapted towards the geology in different regions.”
Essentially, geochemical vectors are composed of the different elements that make up a particular rock type or ore deposit signature and how it formed, creating a ‘fingerprint’ for it.
That fingerprint is then compared with samples to systematically locate rocks likely to host a particular commodity undercover.
The vector can also be integrated with geophysics and structural geology to make data more meaningful.
Creating the Tanami gold vector
To create the Tanami geochemical vectors, the CSIRO team used the local drill core data to interpret the type of environment the volcaniclastic-sedimentary rocks formed in and identify the variations in facies.
The team then defined relationships between rock units, revealing that a particular rock type was most likely to host gold mineralisation.
Dr Schmid explains such geochemical vectors are useful when no visual observation of the rocks can be made.
“You can use geochemistry, instead of seeing the actual textures, to define lithology,” she says
“We can then say there’s a particular lithology that hosts more gold than others, and so you have a vector where it tells you this is a unit predicted to host gold.”
Geochemical vectors can also be plotted on a map to show geographic trends of rocks most likely to host gold.
“Explorers use vectors to identify different rock types and where they are geographically. They can use that map for understanding geology better and for targeting their exploration,” Dr Schmid explains.
Geochemical vectors can reduce drilling
Even though exploration companies still need to drill, they need to drill fewer holes.
This reduces risks around drilling and makes it easier, faster and cheaper for companies to locate areas of interest and target their commodity despite it being undercover.
“Before, they’ve got to drill and analyse for gold, and they see some anomalies, but this didn’t narrow the search space,” Dr Schmid says.
“But if you have geochemical vectors, you see where your few metres-wide target zone might occur.”
Another benefit of this vector is that it was designed so companies can use it independently, without relying on a third party or needing extra knowledge or information.
“Companies are happy that we did the knowledge transfer, they’re not relying on us to do that for them, they can do it themselves,” Dr Schmid says.
However, it’s important to remember this vector doesn’t guarantee gold will be found.
Instead, Dr Schmid explains the vector “is like part of a recipe – the host rock is one ingredient, but it doesn’t mean that there’s gold if you haven’t got all the other ingredients.”
So far, industry interest in geochemical vectors is strong, with other exploration companies trialling it themselves.
Explorers finding value using vectors
In fact, once neighbouring company Northern Star Resources saw how effective it was for Prodigy Gold, it asked the CSIRO to apply the vector to several of its own prospects.
“They saw value in that and wanted it for themselves.”
“We worked very closely with them and greatly improved our geological understanding of the region. It is the go-to tool in the Tanami region now,” Dr Schmid says.
The go-to tool in the Tanami
Because this type of vector is adaptable, Dr Schmid believes it could be used in any region around the world to help locate any commodity undercover – as long as you have a good knowledge and understanding of the area and how it works.
Although the vectoring tool has helped exploration companies locate areas that might host gold, it doesn’t tell them how the gold is distributed in rocks in a deposit.
Complicating this is the fact such information varies across the areas between deposits – and exploration companies want to know why.
This is what Dr Schmid and her team are now investigating.
“We are currently working on geo-metallurgical aspects of the gold mineralisation across various deposits in the Tanami region,” she says.
“We will see if the host rock lithology and geochemistry play a role in the distribution of gold within the rocks, and how that knowledge can be best used for exploration.”
CSIRO is currently investigating how to apply this technique across other regions in Northern Australia in collaboration with exploration companies.
For more information, contact Dr Susanne Schmid, Susanne.Schmid@csiro.au.