Both mines get both resources.

The way it works is that for each resource a building can gather, it looks at its tile and its adjacent tiles and will produce equal to the highest amount of those tiles. So if it is a metal mine and it is on a low iron, but there's a high iron adjacent to it and you get slant drilling, it will be producing iron at the high rate. It works the same for all resources. For aluminum, it would do the same evaluation. A metal mine could produce high levels of iron and aluminum from a plot that is on neither but adjacent to both. 

Does that make sense?

-Scott-