I'm disappointed they collected the leaves by hand.
I thought the article was going to say they can measure the gold-content in leaves using drone imagery
Yeah, same. I thought they would be using satellite imagery. Archaeologists have found Mayan ruins that way because the ruins have a ton of lime plaster and the trees growing above them absorb it the same way. The leaves of the trees above the ruins reflect specific frequencies differently than the other surrounding trees and you can see blotches where the ruins are in the images (when shifted into the visible spectrum). I always wondered if you could find other things that way.
Similar techniques for viking sites in canada.
From memory, this is how Gina Rhineheart's (Australia's mining magnate) father discovered the location for the Pilbara (the world's largest iron deposit) -- by flying overhead and noticing how red the soil was[1].
They are detecting 4 parts per billion gold content in the leaves; I don't think we are close to having the technology to detect that from a satellite. Reading another article it looks like they used the Australian Synchatron (x-ray).