By Chanyaporn Chanjaroen Oct. 9 (Bloomberg) -- Gold and platinum prices will gain on constrained supply, BlackRock Investment Management Managing Director Graham Birch said. The metals are becoming harder to mine because of a shortage of available deposits, a lack of power and political instability, Birch said today at the Commodities Week conference in London. ``The depletion rate of gold mines exceeds the rate of gold mines being developed,'' he said. ``We cannot see an increase in aggregate world gold production. Platinum is one of my favorites.'' The global financial crisis that has shaken equity markets pushed mining stocks such as BHP Billion Ltd. and Anglo American Ltd. down too far, Birch said. The ``negative'' short-term outlook for natural resources doesn't change the ``positive'' long-term outlook, he said. Aluminum supply isn't limited in the same way as some other metals, Birch said. ``The amount of aluminum to be produced is not limited by any geological constraint. As prices rise, so can supply,'' he added. To contact the reporter on this story: Chanyaporn Chanjaroen in London at cchanjaroen@bloomberg.net

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