How do seams/veins of metal form in the ground? Magma looks so homogenous – wouldn’t all the metallic components get mixed in with everything else when it cools?
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It is very rare that you find metal in a metallic form in the ground, most of it is in a compound with another element.
There are multiple ways ores can form. one is that different minerals crystalise at different temperatures when magma cools down slowly for example in a magma chamber the minerals with the lowest melting temperature can crystalize on the chamber walls.
Sometimes minerals can be dissolved in warm water but not in colder. Warm water in th ground can dissolve the mineral, it travels up to the surface where it cools down and the mineral gets deposited, over time the ore builds up. It does not have to be on the ground you can get it sticking to walls of cracks in the ground too. That way low concentration in a large amount of volume can be converted to high concentration in another location
https://en.wikipedia.org/wiki/Ore_genesis
It should be said that some ore contains very little of the material we look for. Low-quality gold ore in underground mining contains 1-4 grams of gold per tonne, the highest grade ore they are minded today is at around 44 grams per tonne. There is 1 million gram in a tonne, which gives you an idea of how low the concentration can be in ore, It will be a lot higher in for example Iron ore, there is a reason gold costs more than iron…
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