pay dirt

US /ˈpeɪ dɜrt/
UK /ˈpeɪ dɜrt/
"pay dirt" picture
1.

soil or gravel containing a valuable mineral, especially gold, in sufficient quantities to be worth mining

:
After days of digging, the prospectors finally hit pay dirt.
The old mine was abandoned, but some believed there was still pay dirt deeper down.
2.

a source of profit or success

:
The new marketing strategy proved to be pay dirt for the company.
He finally found pay dirt with his innovative invention.