The amount generated by a miner is not the raw value of what is mined, but that value minus what value would have been without that miner. If someone else would have mined the gold only a little bit later and/or at only slightly higher cost, then the actual miner isn't creating much wealth.

Something else to consider is that, by definition, people with < 90th percentile IQs are ten times as common as people with > 90th percentile, so even if the per person income generation of high IQ people is higher, the total income isn't necessarily higher.