"According to Goldman Sachs, the world has about 20 years’ worth each of known minable reserves of gold GCJ5, +0.16% diamonds and zinc. Platinum PLJ5, +0.99%copper HGK5, -0.97% and nickel reserves only have about 40 years or less left."
http://www.marketwatch.com/story/in-20-years-the-world-may-run-out-of-minable-gold-2015-03-30?siteid=yhoof2