The leaves and the size of the trunk suggest Acacia melanoxylon. However it could be Acacia implexa. There are a lot of Acacia species in the area. Wait till it flowers, or better, till it has seeds and then you will be really sure. The seeds of Acacia melanoxylon have a pinky red fleshy thingy (aril) wrapped right arounf the seed. The seeds of Acacia implexa have a white aril which folds over and over on itself at one end of the seed. Acacia melanixylon grows in wet gullies and rainforest edge and regrowth, and Acacia implexa on dryer sites.