gold rush

nouns

a sudden happening that brings good fortune (as a sudden opportunity to make money)
"the demand for testing has created a boom for those unregulated laboratories where boxes of specimen jars are processed like an assembly line"
bonanza, boom, bunce, godsend, gold rush, gravy, manna from heaven, windfall
a large migration of people to a newly discovered gold field
gold rush
is a type of (narrower)
the movement of persons from one country or locality to another
migration