|
With those Fe rich basalts (basalt does contain a lot of Fe anyway), the reason why you don't pick it up on a metal detector is because the Fe is disseminated throughout the rock in the minerals making it up, e.g. Biotite, Olivine, Hornblende etc. To actually pick it up, you need to have it congeal into a lump within the rock....you need lumps of metallic Fe to appear. One way you could possibly get that is if you metamorphosed the basalt, but even then the chances of that occurring are slim. The other way would be to weather it out in a lateritic profile...that would produce an Fe rich gossanous cap or layer within the weathered rock. Which would be the most likely route to getting Fe concretions.
|