4-5 is a low ball figure, I'm working on the project that will bring the largest integrated Iron Ore mining hub in the world online in 2020, with first ore on track for end of 2019. Inside the iron ore space I know of 5 sizable mine expansions / developments now moving towards execution in various phases; Silvergrass, West Angeles, Firetail, Koodaideri.....plus any more in early study phases.
There is a large Nickel project (Greenbushes & Kwinana expansion), several gold mines that are being restored back to operation after being in care and maintenance for years, 3-4 lithium plants....
Its a good time in WA, not sure its boom times just yet as we need to sustain the current surge for a while yet, but its definitely rebounded.