When ex-FIFO worker and musterer Johnathon Campbell found gold in 2017 in an area south of Karratha (Western Australia), it sparked an unprecedented interest over the “Pilbara Gold” on the Australian Securities Exchange (ASX), as it was compared to the Witwatersrand Basin which is host to the largest gold reserve on earth. But is the Pilbara Gold what it seems to be?
Gold is known to occur across most of the Australian continent, especially along prospective geological settings. Western Australia in particular has an outstanding number of gold mineral occurrences, as shown in the map below. So, what is so special about the new gold findings in the Pilbara?
The fire was sparked when explorers realised that, unlike the majority of gold in the Eastern Goldfields which is hosted in greenstones, gold in the Pilbara was hosted in a basal conglomerates such as the Fortescue Formation and Hardey Formation.
The fire was sparked when explorers realised that, unlike the majority of the gold that is found in the Eastern Goldfields of WA which is hosted in greenstones, gold in the Pilbara was hosted in conglomerate.
When mining and exploration companies in the area started comparing gold in the Pilbara with gold in Witswatersrand, the ASX responded with enthusiasm, as this could be a lifetime discovery. The Witwatersrand Basin occurs in South Africa, and is host to the largest (by far) economic concentrations of gold in the world.
FACT: Witwatersrand has produced to date over 40,000 tons of gold, representing about 50% of all gold ever mined on earth!
Gold was originally found in Witwatersrand on a farm in 1886, 5 km west of Johannesburg. As gold was embedded in conglomerate, it was assumed that this was alluvial gold in an old riverbed, tilted as a result of tectonic movements. However, when traced down below surface, it was found that this conglomerate was part of a much larger sedimentary sequence.
It is important to understand that the only similarities between gold in the Pilbara and gold in Witwatersrand is that gold is hosted in sediments. Everything else is pure speculation.
However, this does not rule out the great possibilities that the area has to offer. Witwatersrand is far better understood than the Pilbara gold, as it has been explored and studied for much longer and with far better detail. Additionally, the Pilbara is much larger, so at this stage is too early to make predictions in the foreseable future.
What does this mean for prospectors around the world?
The History of Gold in the Pilbara
Gold has been known to occur in the Pilbara for well over a century. The discovery history of gold in the Pilbara dates back to 1887, when gold was discovered at Mallina (east from Whim Creek).
As early as 1892, a gold rush was initiated across the Pilbara, although only a small amount of gold was found. In 1895, a shaft 35 feet deep was sunk through a conglomerate; the area was known as the Just in Time lease. A 1907 map by Gibb Maitland, Government Geologist, summarises the relationship between gold and conglomerate in this area:
Numerous gold occurrences were found across the Pilbara since that time, most notoriously around Marble Bar, and in the area south and east from Karratha:
However, the Pilbara Region has been most well known for its economic concentrations of iron ore. Like gold, iron ore in the Pilbara was first identified a long time ago, in 1861.
Today, Western Australia is the world’s largest iron ore producer and exporter. In 2017, it accounted for 38% of global production and 57% of global seaborne exports.
The vast majority of iron ore in Western Australia comes from the Pilbara. The demand for iron ore has consistently increased over the last 20 years driven by demand from developing countries, particularly China. Hence, this commodity is a critical part of Australia’s economic development.
Although there are numerous gold mineral occurrences across the Pilbara, gold prospecting and exploration has been overlooked since the first iron ore mine in the Pilbara was developed back in 1965 (Goldsworthy mine, east of Port Hedland).
What is Conglomerate Gold?
Conglomerate gold refers to gold that is “attached” to a conglomerate. A conglomerate is a clastic rock, meaning that is composed of fragments, of pre-existing minerals and rocks, known as “clasts”.
Conglomerates are predominantly composed of a mixture of subrounded clasts, such as those found on a river bed. The shape and size of the rounded clasts depends on the conditions of weathering, erosion, and sedimentation. The clasts are bound together with finer grained sand and silt plus a mixture of iron oxides (known as “matrix”) which cements the particles together.
Conglomerates are formed from clasts of different rock types, derived from the local and regional rock formations, such as granites or basalts. As these are transported by water, they might travel a long distance before they are deposited.
Unlike gold found attached to quartz, which is most typically derived from “primary” reefs derived from mineralised local outcrops, “conglomerate gold” contains gold nuggets as one of the clast (or matrix) components, suggesting that the gold might have travelled an unknown distance from its original source.
Is the Pilbara a Good Place for Gold Detecting?
Yes! the gold in the Pilbara is nuggety in nature, which makes it very dificult to mine using traditional mining methods. However, it is very easy to find with metal detectors.
Surface material is relatively easy to find, and even though several promising targets have been identified by miners and explorers in the last couple of years, these are very hard to drill and build a traditional resource because drillholes are likely to miss the nuggets.
This means that most gold is left untouched, providing a lifetime opportunity for gold prospectors.
There are four key advantages of prospecting in the Pilbara compared to the Eastern goldfields:
- Unlike the Eastern Goldfields, the Pilbara has been underexplored by prospectors and mining companies alike, making it a once in a lifetime opportunity.
- Very few modern metal detectors have been used over the Pilbara.
- Gold in the Pilbara has very high purity (over 96% gold and almost no silver).
- Gold nuggets in the Pilbara can be very large. Most nuggets are small and flat such as “watermelon seeds” (the most common), but some can be smooth and large (several ounces per nugget).
- Mining companies have a hard time drilling these targets, making it very difficult to establish resources and ultimately mine the ground. Hence, a lot of ground remains untouched.
Conclusion
The Pilbara gold offers an outstanding opportunity for gold prospectors, perhaps a once in a lifetime event. Although organised company mining activity is perhaps prohibitive at this stage, small scale metal detecting warrants the best strategy for discovering new gold patches in this area.