Don't bet your whole portfolio on metals. Use metals as an addition to your overall diversification strategy.
I am in agreement with William Tucker and John Myers… Be careful, seek professional guidance, and don’t bet it all on metals. If you are sensing that you will not have sufficient savings for a comfortable retirement then start changing things now as there are no shortcuts. Reduce your expenses, increase you income, adjust your retirement goals, and save more…
There are a number of mutual funds that specialize in gold and special metals...here's a link to a U.S News and World Report article: http://money.usnews.com/funds/mutual-funds/rankings/equity-precious-metals and here is a list of metals and mining exchange traded funds from which you can choose: http://etfdb.com/type/sector/materials/metals--mining/ Be careful however, these funds can be quite volatile and past performance is no guarantee of future results. You might want to seek some professional guidance in choosing.
While the demand for metals could possibly go up or remain where it is, the world is no where close to running out of anything anytime soon. 30 years ago world was expected to run out of oil in about 30 years according to popular press. Well now 30 years later we probably have 100 year supply left based on reserves. I would not be suprised if the reserve amount left keeps going up. Most of this is due technology. You would expect the price of any metal to rise as the reserves go down, however, technology keeps improving the amount of use from each precious metal comes down there is less spoliage in production, alternative methods of mixing metals with plastic has taken place. Also the technology to extract the metals keeps getting better as in the case of oil. We may have better technology one day to dig deeper into earth using robots replacing human mine workers. Robots don't need oxygen and go down much deeper. Don't count on the earth running out of any metals any time soon. We may be also mine other planets using robots.