The gold collectors would retrieve jewellery from thieves, melt it into ingots in France, and sell them to a gold-buying company in Germany, said prosecutors in Nancy in northeast France.
“This illegal gold trafficking could be worth a couple dozen million euros,” they added.
On top of the 30 kilos (1,058 ounces) of gold seized — worth €1.5 million (around $1.7 million) — police also found 12 vehicles worth a total of €340,000, 30 luxury watches and around €121,000 in cash.
The suspects were arrested between mid-May and late June and face charges of “stealing as part of an organised group” and “aggravated laundering”, the prosecutor's statement said.
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“The investigations continue, in particular based on accounting vouchers seized during raids in Germany and Belgium,” it added.
A French jeweller and nine accomplices were arrested in another gold trafficking case between France and Germany last October, in a case thought by Europol to be worth at least €1 million.
The 56-year-old jeweller was arrested on a train at the border between France and Germany in possession of €37,000 in cash, Europol said at the time.