The US Geological Society is encouraging people to comb through the left-overs of old mining operations and look for materials they may not have known were valuable in the past.

Reports say a gold-rush of sorts is taking off, with budding prospectors taking to the mounds of tailings from mines dug over the last two hundred years.

The USGS and Department of Energy are on a nationwide scramble for deposits of the elements that make magnets lighter, bring balanced hues to fluorescent lighting and colour to the touch screens of smartphones, in order to break the Chinese stranglehold on supplies. The rare earth elements were unknown to earlier miners and discarded as useless.

Larry Meinert, director of the mineral resource program for the US Geological Survey, says “if they turn out to be valuable that is a win-win on several fronts - getting us off our dependence on China and having a resource we didn't know about... Uncle Sam could be sitting on a gold mine.”

Rare earth mineral mining is already a significant industry in Australia, but reports of high concentrations in the tailings of old mines in the US will likely have some companies digging back through the waste piles of previous generations.