I made an example, that I hope will help you understand this in a clearer way:

So in here you have rain water, entering the Earth in a large area and getting hotter as they descend down. It becomes possible for them to dissolve the gold from the large volume of rock. But also, because the water (now steam or a supercritical fluid) are hot they start to ascend upwards, usually through a narrow zone. When they cool down again, gold forms as a solid. For example, gold associated with quartz veins commonly forms through this process.

Now, what happens if these gold-bearing quartz veins are exposed on the surface? They may erode by rain and snow and get concentrated in river beds. So you can either mine the original quartz vein or the nearby river bed.

Australia recorded only 180 impacts, compared to other countries recording over 900. Both Western and Northern Australia record three times more impacts than the East coast. The west coast produced veins of gold while the east coast produced huge nuggets and flecks. The east coast of Australia suffered volcanic eruptions. While the western and northern have few if any inactive volcano's. The vast plans would explain the veins, spread of impact over distances. All confirming the theory but not why uranium is found in the crust in these areas. Perhaps uranium was formed over time from impact of these asteroids or took longer to cook than gold during the big bang. Its odd though that uranium is proficient in the same areas.

I'm just a backyard scrub but for my two bob answer to your question, I'd say gold is more evident on larger continents that are more accessible. Remember Australia is wide as the USA with fewer mountain ranges and a tenth of the population.

In the 1900 a man near death and surely out of his mind returned to town claiming to of found a reef of gold a mile long. Harold Bell Lasseter had rode west to find his fortune, on finding it he lost his way home and the location of his fortune. For 30yrs Lasseter insisted on continuing the trek looking for his goldern mile, until eventually he died of malnutrition and exhaustion. Kalgoorlie in Western Australia was dicovered soon after. Kalgoorlie mines produce 850,000 ounces (28 tonnes) of gold per year. Lasseter reef has never been found.