I'd have to see further sources on this. It sounds speculative. The open pit mine I visited this summer in Arizona says they have 50 years of easily extractable ore at current rates. That was just one mine, there are others with similar or larger unrecovered deposits. There are also vast underground deposits with proposed mines awaiting approval. It's worth noting the environmental impact of these mines. The one I was at is a huge ugly scar on an otherwise beautiful landscape.