27 Jun 2022

Under Brisbane lies coal, gold, quartz in small geological pockets

Brisbane is famous for a subtropical climate and being one of Australia's most liveable cities, but there is much more going on underneath its streets than most residents might think.

Parts of the Queensland capital's hilly terrain are home to reserves of coal, quartz and gold.

Traces of coal were first noticed on the banks of Kedron Brook in the 1880s, according to the Nundah & Districts Historical Society (NDHS).

Historian John McDonnell told ABC Radio Brisbane that the Nundah Colliery, in the northern suburb of the same name, was opened at the turn of last century.

Businessman Charles Gardner opened the pit in 1906 and that year, with four men working, it produced 70 tonnes of coal.

But the quality was not as high as what was being mined in nearby Ipswich and the mine was never economical.

Still, at one stage there were up to 12 men employed at Nundah Colliery and it reached 790 feet into the earth.

By the time it closed in 1910, 1,803 tonnes valued at 460 pounds had been extracted, pulled out over Buckland Rd bridge and sold to the Brisbane gasworks, Eagle Farm meatworks and old Virginia brickworks.

Mr McDonnell said "possibly due to the war", it reopened again from 1913 to 1915, and then again in 1929 but shut down soon after.

What lies beneath

Geologist Warwick Willmott said coal sedimentary layers lying underneath the city were about 220 million years old, but the earth changes that created them started a few million years before that.

"There's a belt of country that sits between Chermside, Lutwyche, New Farm and Kangaroo Point, which is underlined by something called the Brisbane tuff," he said.

"That resulted from a big volcanic eruption somewhere north of Brisbane that roared down a valley in the older rocks and that ash cloud settled and consolidated and made a very hard rock and we can see that [in the cliffs] at Kangaroo Point.

"After that time, erosion removed a lot of material off the hills of older sedimentary rocks and they collected in small basins or low areas in silt and mud.

"In some of those basins, swamps developed, they built up vegetation that died, got compressed and was made into coal.

"Most of those basins were out to the west around Ipswich but there were some in Brisbane itself out towards Nundah, Clayfield and also Tingalpa."

Mr Willmott said they were "only fairly minor seams compared to the major seams out at Ipswich where the coal mining industry got going and continued until recently".

No diamonds, but a little bit of gold

Most of Brisbane, and "certainly the hilly suburbs like the western suburbs and south-eastern suburbs", said Mr Willmott, sits on "hardened, old sedimentary rocks that have been heated up, cooked up, compressed, crumbled and stood on end" 300–350 million years ago.

"Those old hardened sediments that got crumpled and squeezed together, when that squeezing was happening some gold and quartz got squeezed out and formed some little veins in the rocks and some small gold mines were established from those veins in the old days," he said.

"There was one on Mt Coot-tha and some in Brisbane Forest Park but none of them were very significant, they were only very small.

"Syndicates of men worked them mainly in the Depression [so] they could get a little bit of money out of it but they were mostly unsuccessful.

"The only company mine was down in Kingston and that closed in the 50s I think."

Rather than coal and gold, the ground around Brisbane was more valuable for the presence of clay, used in brickmaking, and is still unearthed from the outskirts of the city.

Mr Willmott said at an old Albion clay pit for bricks, workers even found dinosaur footprints among the rocks.

Surprise discovery while drilling for water

When Peter Cox hired a contractor to drill for bore water on his Clayfield property in 2007, he thought the black liquid spilling onto his lawn was oil at first.

However, he was informed it was coal dust mixed with pressurised water from the drilling machine which had hit a nine-metre deep seam of coal.

"At that stage we were in the millennium drought, and we were watching our garden wither away so we decided to get the bore done," Mr Cox said.

"When the man was drilling the hole, and I've reviewed my records and found his drilling log, at about 15 metres he struck coal and the depth of that seam continued through to about 24 metres, that's in vertical thickness.

"And then under that, he struck beautiful clear, pure water."

Clayfield is a neighbouring suburb to Nundah and when he heard of the Nundah Colliery, presumed that seam ran under his property as well.

SOURCE: https://www.abc.net.au/news/2022-05-12/brisbane-old-coal-gold-mines-geological-history/101055136

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