Recently, I sold a batch of Bourneix gold on matrix to someone who didn't just want to collect ‘raw’ gold, but to process it in order to extract the precious metal.
I thought it would be interesting to share with you all the steps that led him to obtain a nugget
Finding gold (almost) like the Gauls: from gold-bearing rock to molten gold
By M. Jacques
Gold-bearing quartz stones from a mine exploited by the Gauls certainly 1 century BC and probably 4 centuries BC. Total weight: 1.700kg Due to the hardness of the stone, a technique known to the Gauls was used: thermal billing (embrittling the stones with a blowtorch).
Batch of rough blocks
Crushing the stones into gravel, the gravel into sand, the sand into dust (more accurately, into a slurry, because I wet the sand so that it jumps less and makes less dust), all with a 1kg sledgehammer...
Cutting the mud with 2 American cutters (the kind you see in programmes about gold diggers in Alaska) (one very large to cut quickly, 1 smaller, more precise for the finish: the best colours: dark blue and green).
Progressive gold panning, from the coarsest to the finest. Indispensable: a pipette or ‘pissette’ to recover the gold and a pair of tapered recovery tweezers (like tweezers).
Once the gold concentrate has been obtained, a powerful magnet is used to remove the ferruginous sand and the material is dried.
Crushing the stones into gravel, the gravel into sand, the sand into dust (more accurately, into mush, because I wet the sand so that it jumps less and makes less dust), all with a 1kg sledgehammer...
Cutting the mud with 2 American cutters (the kind you see in programmes about gold diggers in Alaska, one very large to cut quickly, the other smaller and more precise for the finish: the best colours are dark blue and green).
Progressive gold panning, from the coarsest to the finest. Indispensable: a pipette or ‘pissette’ to recover the gold and a pair of tapered recovery tweezers (like tweezers).
Once the gold concentrate has been obtained, a powerful magnet is used to remove the ferruginous sand and the material is dried.
Mixing the sand with powdered borax (borax has the ability to lower the melting point of the gold, to facilitate the separation of the metal from the remaining minerals and to agglomerate as much waste as possible in a sort of carbonised ‘caramel’ resulting from the fusion of the borax. The denser gold flows underneath. I chose a small copper container // copper's high thermal conductivity. Remember to descale the melting container (heat to white + brush off any particles that have become detached before melting the gold) I used an old soldering coal to place the melting container on (it retains the heat and insulates the work surface). To be on the safe side, I put an old breadboard between the soldering coal and the work surface...
Once the gold + borax has melted, throw the resulting block into a jar of cold water.
Using a sledgehammer, crush the block into small pieces on a metal plate. Discard the carbon blocks containing no gold, and crush the mixed blocks containing a little gold and the ‘pure’ gold very finely to remove the small carbon particles. Rinse and redo a fine gold panning session (separation of the carbon dust from the gold: fairly simple). All that should be left at this stage is the gold (crushed, hammered, in small chips, flakes, etc.) all together in the well descaled and cleaned container or in a very clean 2nd.
Re-melting: this step will allow the ‘nugget’ to form (it doesn't matter what shape: by heating strongly enough, you will allow any residual lead to ‘evaporate’ and shape the gold to your liking (teardrop, ball, cabochon, etc). Once the nugget has formed, allow it to cool gradually or throw it into cold water.
Using a mini Dremmel and a metal brush tip, clean the nugget of the slight oxidation on its surface. Dremmel brushes are effective but soft enough not to create unsightly scratches or cause too much loss of material. After brushing, the nugget can be dipped in a gold jewellery cleaning product, rinsed and then wiped dry with a cloth. Touchstone test: the nugget passed the 18k test with flying colours, but not the 24k. As I had no acid for 20k and 22k, I determine ‘with a wet finger’ that the nugget has a purity of 20k (the remainder of the nugget being made up of silver (I saw some while crushing the ore), a little copper and undoubtedly some non-ferruginous + rare metals).
The Gauls, either to save money or because they couldn't find ore as concentrated as mine, deliberately mixed gold, silver and copper: electrum.
With 1,700kg of gold-bearing rock, I obtained a nugget of 4,446g of 830‰ (20k) gold. This result is exceptional. You don't find such a concentration in nature. It was possible because the rock had been selected for its gold content by a geologist... I estimate that I lost 0.5/0.6g of gold during the many different stages of creating the nugget (a first for me).
I'll probably recast it to make a mini sphere, which I'll polish so that it shines +++: a gold sphere of the Lemovices (Gaulish people who ruled the Limousin region and surrounding areas. An unforgettable souvenir!
Thank you, Élise, for these exceptional rocks.
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