It is estimated that there is 80,000 tons of gold in the ground (in the World) and we currently mine 2500 tons a year. At the current rate of mining there is less than 30 years of gold left in the ground. Silver is running out even faster with only 20 years of silver mining remaining. I guess you can see that with gold and silver running out and the ever growing world requiring more and more of it, then you would expect their values to increase.