There is a “very good” chance the Pilbara’s Hardey Formation will support a large-scale gold mine, says Franco Pirajno, Adjunct Professor at the University of Western Australia’s Centre for Exploration Targeting.
Walk us through the history of the Pilbara and how it was formed.
The Witwatersrand Basin is the largest known gold province in the world and the deposits have now been worked for well over 100 years and are believed to have produced about one third of all gold mined in the world.
Before continental drift, the South African basin was connected to the Pilbara, forming a small ancient continent called VaalBara (combined Kaapvaal and Pilbara blocks). Continental drift separated the two blocks, with the Pilbara now in Western Australia.
The gold discoveries in Australia have been known for some time, based on the similarities in the formation of the rocks in each area, but only now are we seeing it start to be fulfilled.
When we come to the Hardey Formation in the Pilbara it is considered to be the equivalent rock as the Witwatersand, although it has gone through different conditions, so we think of them more like a sibling to each other. The Witwatersand is much larger though.
How is the Hardey Formation gold similar to that in Witwatersand?
The Witwatersrand gold (and uranium) mineralisation are of two main types:
1) associated with ancient organic matter (called kerogen) derived from algal mats similar to those of Shark Bay in Western Australia (known as stromatolites) and
2) as nuggety gold together with the mineral pyrite (called buck shot pyrite), resulting from fluvial reworking (braided river systems, quite similar to those on the western side of the Alpine Fault of the South Island in New Zealand which, by the way, do have alluvial gold).
The Hardey Formation in the Pilbara may have gone through similar processes as in the Witwatersrand, although the latter was at a later stage affected by geological phenomena, such as a large meteorite impact, which may have further enriched the original mineralisation
If we knew the potential, why haven’t we mined the gold in the Hardey Formation in the Pilbara before?
The Pilbara Hardey Formation has been largely ignored for a long time, and we see this happen all the time around the world – while we might know of a particular area, miners wait for the gold price to make it financially possible to be mined and it appears that it has come to that time in the Pilbara now.
Mr Creasy singlehandedly started the latest boom when he recognised the potential for the likely wealth of mineralisation in the area.
There have always been plenty of alluvial mining in the Pilbara region – where prospectors scrape the surface or use metal detectors to find nuggets, but there has never been the extent of drilling specifically aimed at exploring a Witwatersrand equivalent we are seeing now.
In places like Far-East Russia gold placers in rivers escaped attention for so long, but now they are having a gold rush of their own. It all depends on the trends at the time and who can afford to mine it.
We’ve come a long way from panning for gold, is technology a key player in the rise of Pilbara gold?
Exploration technology is good enough now to target mineral deposits but it is still difficult to know just how much is below ground.
If you drill deep enough you can find gold in the Hardey formation, but the question is whether there is enough to warrant a mine. Some of the deepest gold mines in the Witwatersrand extend to 3. km below the surface and I am optimistic that we could find mineralisation in the Hardey Formation, perhaps not as deep, but still economically viable at current prices
I remember a time when the price of gold was just $30 an ounce and now it is well over $1000, the price changes over time and that is ultimately what makes a mine viable or not.
From a geological perspective, how likely is it that there will be a significant mine in the Pilbara?
The chance of the Hardey Formation uncovering potential for a large scale mine is reasonably good, I give it the big tick but cannot say which of the current explorers will make it.
Drilling results will tell the story, once they come up with good results, it will drive more and more targeting and more exploration.
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