In my view, arealmente is an adverb derived from areale, the second meaning of which is (Garzanti):
¶ s. m. in biogeografia, zona di insediamento e mantenimento di una specie.
I would be inclined to translate it as:
We had at our disposal (or, at hand) a compelling and important element from a geographical point of view, namely a highly visible access to the mine...
Vincolante basically means binding but I am guessing that here it is used to express a highly important geographical feature.
My best guess!