Francis Drake's expedition, during his circumnavigation voyage around the world, drifts off course and discovers the OTL Bass Strait, eventually landing near OTL Melbourne.
Effects, anyone?
How soon before gold is discovered?
(Please, no Draka jokes.)
As a first guess: nothing of consequence. After all, the Dutch sailed around Australia for a century and half, and the Spanish and Portuguese had been occasionally exploring other islands in Oceania since even earlier, to almost no noticeable effect outside the occasional clash with the natives. Nobody in Europe seems to have seriously cared for a colony in the area or seen much worth in such an attempt before the second half of the eighteenth century, although some schemes were devised.
The area simply had no apparent usefulness to offset the enormous distance involved.
Think about California. The area was considerably closer to major European colonies, and its location was roughly know since late sixteenth century, still almost no effort to colonize it was undertaken for more than a century and gold remained undiscovered for another century thereafter.
Drake would report about a strange place with some curious fauna and some dark-skinned savages. Some other exploring expeditions might go there, and the whole of Australian coastline would be explored somewhat earlier. Some dead platypus might end in a European Wunderkammer, sparking some interesting cultural and scientific debate at best.
But I don't see any major obvious effect.