This Wikipedia article on tin sources and mining makes the claim: "Pliny mentions that in 80 BC, a senatorial decree halted all mining on the Italian Peninsula"
But the article lists no sources or background information, and a basic Google search fails to find any mention of this that isn't linked to the Wikipedia article.
Is this accurate? If so, what was the reasoning behind banning mining on the Italian Peninsula?
Ah good old Pliny the Elder - definitely one of my favourite Roman sources!
The passage I assume the article refers to is this one (3.24):
In abundance of metals of every kind, Italy yields to no land whatever; but all search for them has been prohibited by an ancient decree of the Senate, who gave orders thereby that Italy shall be exempted from such treatment.
Exactly what Pliny means here is hard to determine. In the notes for the Loeb translation, two possibilities are given: either he means that no mining was to take place in Italy at all, or that Italian minerals were kept in reserve, to be used as a last resort. It would be bold of Pliny to claim that there was absolutely no mining in Italy whatsoever, especially as he praises the quality of iron from Sulmona in another section of his work (34.145). Certainly there were well-known marble quarries at places like Carrara, but quarrying stone is different to mining metal ore, so might not have come under the ban Pliny is talking about. I'm afraid I don't know the archaeology well enough to say whether that could shed more light onto this question.