Archaeological discoveries

Where is half of the gold in world found?

In seawater.

Gold's average concentration is 0.00004 ppm in the Earth's crust. However, gold is highly enriched in ocean water (estimated 0.01-0.02 ppm), which means that more than 99% (conservatively) of all gold on Earth exists in the oceans. So, most of the gold on Earth exists in the ocean water, even if it is an extremely tiny amount.