How do people know where to mine gold, diamonds, and other valuable minerals?

Question

Its 1849... did I just roll out of town with a pick and a shovel and start digging? I know there were tips, sometimes good and sometimes bad, loosely based on areas near where others had struck "pay dirt" but then how did the people on which such tips were based find their plots? I know that today tech plays a big role (ground penetrating, spectral analysis, core samples, etc) but are any of the classic methods still used and just what the heck are they!?!

Answer 1

I had a brother in law that was a geologist.  His company would take pictures of the land from an airplane, and they would put the  pictures together to get a map.  (Just one such map is worth thousands of dollars!)

Anyway, apparently they can tell a lot about what's underground just by looking at what's on the ground.  For example, if the vegetation in a certain area is shorter, there could be something under the ground that is inhibiting the root growth.

I guess the same goes with the color of vegetation, and the color of the dirt if there's no vegetation.

That's all I know.

Answer 2

In the old days a river might wash gold particles away from an eroding slope (the mother lode) including nuggets when the river raged.  Prospectors would follow the stream upriver to find the mother lode.  Also, certain areas of the stream were likely to have currents strong enough to wash away sand but leave the heavier gold.  Diamonds are often found in the remains of ancient volcanic cores or in sand washed away long ago from the cores.  Geologists study terrain of existing finds and look for similar terrain.

Answer 3

there are a couple things that flash dollar signs to mineralogists and mining geologists.  The first is metasomatism.

Metasomatism is a process of mineral enrichment from hot water flowing through the formation.  It turns the rock 'greisen' which is a pastel red/orange/yellow color and are indicitive that the rock is some sort of metal ore.  So, we look for that color, or minerals in the rock that form through the process.  Examples are black hills gold, canadian shield komatiite deposits, yellowstone.

Next, we look for pegmatites.  These are granites that had an extended time to cool, giving them super large crystals.  Usually pegmatites have had so much time to differentiate that they contain crazy minerals and are enriched in some (usually lighter) elements.  Examples are tin mountain in the black hills and the gemstone mines of Minas Geras Brazil.

We still trace placer deposits too - that's where you pan for gold, or look for a spot where water would deposit what you are looking for.  We also do this in paleo-formations - in old creek deltas, uphill from glacial finds, old gravel deposits, etc.

It really depends on what you're looking for and how much you want to spend to get it out of the ground.