Opal mining is done by 2-3 person operations rather than big companies because opals don't run in seams like gold, they are quite random so you just have to strike it lucky. The miners peg their claim and start digging through the sandstone, albeit using more sophisticated equipment today. Beware wandering about there is deep uncovered hole beside nearly every one of those dirt piles.
The tiny camera's tiny battery ran out so I went back to my reading. The note with the sculpture says "This bronze and copper sculpture contrasts a series of small human forms with the architectural weight of on oversize staircase. The artwork has a philosophical aspect by reflecting on the effect of reading on the spirit - 'the more I read the smaller I feel'." Crikey, I dunno about you but if reading made me feel like that I'd stop.