Ann: Diggers & Dealers Conference Presentation, page-42

One of the issues of the Mt Ida site is that it has significant UG workings. Without those it would probably be a simple task to design the open pit mine to extract the gold.

I suspect these UG workings complicate the planning for any open pit. It may take a few more planning attempts than usual to create a design that avoids instances of haul trucks or diggers requiring roads that either don't exist due to voids or would be unwise to use because the layer of rock over that void is not thick enough and creates a risk of a cave-in. Its an area where money spent on planning will be well spent.