You would need to delay independance for a decade or more, PNG has the problem of being a state cobbled together from thousands of disparate, isolated or warring tribes who rarely speak the same language. On top of this, many of the resources are in the highlands, which are nigh inaccesible from the more developed coastal regions, and again, with the amount of tribal animosity, the highlanders aren't exactly OK with letting the lowlanders (or any other tribe really) come and develop and mine their country. Even today getting approval for development is a nightmare, and most workers need to be armed at all times on site in case of violence.
So yeah, a decade or more development on the part of Australia to connect the highlands to the coast and a greater emphasis on national education would go a long way to enriching PNG.