[mr beer]

Australia is rich in iron and uranium, amongst other natural resources. So goo could plausibly assemble using those elements.

Silica is a versatile substance, what did you want it to build? A vast twinkling glass fortress, that gradually eats the wasteland? Von neuman rocky 'beetle' swarms with razor steel pincers and feet? Underground bunkers full of nuclear missiles and guarded by killer robots? Because with sufficient tech, those should all be doable.