bonanza

(n) an especially rich vein of precious ore
(n) 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
bunce, godsend, gold rush, manna from heaven, windfall, boom, gravy,

bunce godsend gold rush manna from heaven windfall boom gravy