If a triggered mana ability produces mana when a basic land is tapped for mana, that additional mana is produced by the source of the triggered mana ability, not by that basic land.

If a basic land gains a mana ability, mana produced with that ability can be spent to cast Imperiosaur.

An effect that allows you to spend mana as though it were mana of any type to cast Imperiosaur won't allow you to spend mana from a source other than a basic land to cast it.