You can search for gold the easy way, with a pan or a pickaxe. Or you could examine the local Eucalyptus trees. This is geobotanical and biogeochemical prospecting.
Eucalyptus trees in arid environments have deep roots, and sometimes they’re deep enough to suck little particles of gold up out of the soil into their leaves and branches. These particles are tiny and not really worth much in themselves, but they’re a good indicator that the area might have gold deposits. You have to grind them up and run them through expensive equipment, of course, so this falls under the category biogeochemical prospecting.
It turns out that plants can be good indicators of a number of geological features. The copper flower in central Africa thrives in soils that have a high concentration of copper (quelle surprise!); the Red Alpine Catchfly from Scandinavia grows well in the same conditions. Both are used to identify copper deposits, purely by their presence. No geochemical analysis is necessary, so we call this geobotanical prospecting.
Probably the most impressive plant of this kind is the chandelier tree of tropical Africa: it grows best above kimberlite, the rocks that produce diamonds. Yup, it’s a diamond-prospecting plant.