Good thing they are forever...

Reading about an odd commodity deflation story I found this fact I would never have guessed:

The immediate outlook for the industry might look bleak, but some analysts said that once the production overhang worked itself through the system, prices would recover. Without new discoveries, Mr. Even-Zohar expects the world to run out of new diamonds within 20 years. [More]

Of course, by then artificial diamonds may be indiscernible from "real" diamonds.

Diamonds are a girl's best friend, they say - and soon they could be every girl's best friend.
A team in the US has brought the world one step closer to cheap, mass-produced, perfect diamonds. The improvement also means there is no theoretical limit on the size of diamonds that can be grown in the lab.
...
Zaitsev considers low-pressure annealing at temperatures greater than 2000 °C to be a "breakthrough in diamond research and technology".
The improving quality of synthetic diamonds threatens the natural diamond market. While 20 tonnes of natural diamonds are mined annually, some 600 tonnes of synthetic diamonds are produced each year for industrial use alone.
They are used in a range of high-end technologies, such as lasers and high-pressure anvils. Some companies have also started to sell synthetic diamonds as gemstones. In response, diamond giant De Beers has set up a "Gem Defensive Programme" with the aim of finding ways to tell apart synthetic and natural diamonds. [More]

The technology of renewable sources for the stuff we use to live is pressuring the entire extraction industry.  It won't be rapid, but at some point most mines - especially deep-shaft - could become curiosities.