Geologists have uncovered what they believe could be the world’s largest lithium deposit inside an ancient supervolcano along the Nevada-Oregon border in the US.Clay containing up to 40 million metric tons of lithium was identified throughout the  McDermitt Caldera – nearly double what has been found in Bolivia’s salt flats that have long held the record for the most lithium deposits.While the amount of lithium is based on estimates – no drilling has taken place – scientists have found high concentrations of lithium in the caldera since the 1970s.