How do geologists find ore deposits?
That is the multimillion dollar question! "looking for surface formations" is indeed one way, and it was the main method of exploration in the past. This does not necessarily mean that you directly see the ore deposit in front of your eyes. Many ore-forming systems are accompanied by different kinds of alteration (for example potassic or argillic alteration) that are not too hard to see in the field. Once you see them, there is a possibility that an ore deposit is nearby. 

Other surface methods include, among others, looking at rivers sediments. Since rivers transport soils and rocks from upstream, sampling the sediments may reveal an anomaly in a certain commodity of interest that may lie somewhere upstream. It is also possible to use satellite data - by looking at certain wavelengths it is possible to estimate the mineralogical composition of the surface. This may give hints on the possibility of mineralisation. I've even seen cases where people used different kinds of vegetation that grows on different lithologies!

Surface methods, however, require that the mineralisation will be close to the surface, and the truth is that most of the ore deposits that satisfy that requirement have already been found. This is where geophysical methods come into place. Gravimetric, magnetic and seismic studies probe the earth below the surface and may provide exploration targets, which are then drilled to see what's actually in there.

Mineral exploration is a hard business with much more failures than successes. That said, cases of serendipity are not unknown in exploration. Also, changes in global economics, production costs and increasing/decreasing metal prices may change what is actually an economically feasible ore deposit. The metals are always there - but is it actually worth taking them out?