According to Poseidonius, one of the most careful and accurate observers and scholars in world history, the discovery of the atom predates Leucippus and Democritus and goes back to even before Trojan times.
"The Sidonians, according to tradition, are skilled in many beautiful arts, as the poet [Homer] also points out; and besides this they are philosophers in the sciences of astronomy and arithmetic, having begun their studies with practical calculations and with night-sailings; for each of these branches of knowledge concerns the merchant and the ship-owner; as, for example, geometry was invented, it is said, from the measurement of lands which is made necessary by the Nile when it confounds the boundaries at the time of its overflows. This science, then, is believed to have come to the Greeks from the Aegyptians; astronomy and arithmetic from the Phoenicians; and at present by far the greatest store of knowledge in every other branch of philosophy is to be had from these cities. And if one must believe Poseidonius, the ancient dogma about atoms originated with Mochus, a Sidonian, born before the Trojan times. However, let us dismiss things ancient." -- Strabo, geographer, 7
"Can we not read into them some justification for the belief that some former forgotten race of men attained not only to the knowledge we have so recently won, but also to the power that is not yet ours?" -- Frederick Soddy, radiochemist, The Interpretation of Radium, 1909
"We've located series of civilizations, nine of them definitely, and indications of others as well, all of which have reached heights comparable to our own, and all of which, without exception, were destroyed by fire at the very height of their culture." -- Isaac Asimov, writer, 1941
"I mean, there were huge battles that took place in Europe during World War II. And you can go back to those places now. I mean, there should be, you know, just tons of equipment and stuff lying around. But it's not there. You can hardly find a thing. So I think, over millions of years, there can be a lot of destruction." -- Michael A. Cremo, author, August 2006
Grattan, J.P., et al., Radon and ‘King Solomon's Miners’: Faynan Orefield Jordanian Desert, Science of the Total Environment, Volume 319, Issues 1-3, Feb 2004
Whilst the copper ores were the main objectives of the ancient mining, numerous other toxic metals are present in significant quantities, including minerals such as thorium and uranium