In Bendigo, we’re always raving about our gold mining history, but Bendigo isn’t the only place in Australia where gold was discovered, so what’s the big deal?
As it turns out, there are a few reasons why the Bendigo goldfield was a bigger deal than most other places in Australia … starting with the amount of gold that was found!
From 1850 to 1954, over 700,000kg of gold was found on the Bendigo goldfield
This is over 3 times more than any other goldfield in Victoria, or over a third of all the gold found across 15 goldfields in Victoria at the time. See graph at bottom of page.
As a result of the amount of gold that was found, Bendigo was the richest goldfield in the world at the time and, to this day, is still ranked in the top ten goldfields worldwide.
Of the 700,000kg found, 200,000kg was found on the surface as alluvial gold, while the remaining 500,000kg was found as a result of quartz reef mining, a type of mining for which Bendigo is world famous.
So, how did the ground under Bendigo come to have so much gold in it?
It’s a long story that started about 500 million years ago! Back then, the land Bendigo is now on was under a vast ocean. We know this because there is evidence of ancient creatures still in the rock. It consisted of layers of sandstone and slate, otherwise known as sedimentary rock.
About 440 million years later, there were a lot of earth movements which resulted in the sedimentary rock becoming tightly folded (think of lots of layers of corrugated iron being stacked on top of one another). During the folding, gaps occurred between the layers of sandstone and slate. These gaps were filled by molten gold bearing quartz (also known as hydrothermal fluids or silica) which pushed its way up from deep in the Earth’s crust.
Then, around 150 million years ago (during the Jurassic period when dinosaurs roamed the Earth) there were further intrusions of igneous rock into the folded rock, which are called Monchiquite Dykes. These intrusions were recognised as indicators for the miners of where gold was likely to be found.
Over the next 150 million years, a lot of erosion took place that eventually resulted in the folded rock becoming exposed releasing some of the gold. It may have been there for thousands of years before being discovered by two ladies doing their washing in the creek.
Alluvial mining vs quartz reef mining
At first a lot of gold was found on the surface, so thousands of alluvial miners descended on Bendigo and spent their days using gold pans and puddling machines in the creeks to find the gold, however, once the alluvial gold ran out, some people wondered what they might find if they dug a little deeper.
This is how quartz reef mining came to be, with a few ambitious and brave men deciding to extend their search for gold into Bendigo’s underworld.
They soon discovered the layered corrugated pattern of the rock which extended approximately 4 kilometres across from East to West and 16km North to South . They named these corrugations “Saddle Reefs” and soon realised that the gold was most often present in the upper curves of the reefs (anticlines) where Monchiquite Dykes were present. See image below.
Once this geological structure was recognised, it wasn’t long before thousands of quartz reef mines began operating and seeking out the saddle reefs that had gold in them.
Between 1851 and 1954 over 5,000 registered quartz reef mines operated on the Bendigo Goldfield, within an area 16km long and around 4km wide, which is quite a large area for a goldfield. There are 37 anticlines containing saddle reefs within this area, making it one of the largest known saddle reef formations in the world. The deepest saddle reef worked was at a depth of around 1,400m.
To learn more about Bendigo’s fascinating gold story book your students in for a tour of Central Deborah Gold Mine, where they will be able to see for themselves the conditions under which the miners worked in the harsh gold rush era.
