Every day we see many visitors happily panning for gold at the Museum, excited by what they find. Not as happy though as one lucky amateur prospector who recently unearthed the find of a lifetime in Australia - a 5.5 kg nugget of gold! Worth close to $300,000 CAD we can be sure it made his day. Nuggets this size are extremely rare, yet how do nuggets form and where does our gold come from?
For many years there has been speculation about how nuggets of gold and other precious metals form. Some proposed bacterial action, others believed them to be formed by the sticking together of smaller grains over time. But more recent research on Australian nuggets seems to prove that the process is much simpler. Whatever size the nuggets are, they are formed in their host rock and then weathered out.
But further than that, where does our gold come from? It seems that the gold we find on the surface today came from meteorites early in the earth's formation. Any gold that had formed in our earliest earth sunk to the core when it formed. This would have left the rock in the mantle and crust bereft of gold. However in the first few hundred million years, the earth was being regularly bombarded by meteorites. They brought gold and other precious metals which got caught up in the rock. Fast forward a few billion years and we find that most of our gold deposits have formed when these rocks have been brought to the surface through volcanic action. Black smoker deposits on the ocean floors and hydrothermal vents such as at Yellowstone are breeding grounds for gold deposits.
Did You Know? The largest known nugget to date is named Welcome Stranger. Weighing in at around 78 kg it was found in 1869 in Australia. However it might have been eclipsed by Canaã. Found in 1983 at a mine in Brazil, it broke into pieces when being excavated though would have weighed around 150 kg. The largest piece that survived is now the second largest nugget at 61 kg.
Impressed by the gold in the photo above? It is a beautiful piece of gold in matrix from the Braelorne gold mine, near Lillooet, BC and is on display at the Britannia Mine Museum.