The deepest gold mine in South Africa is only 11,762 feet (2.23 miles) deep.
The Kola Superdeep Borehole SG-3 is the deepest hole at 40,230 feet (7.62 miles).
Earth’s crust varies in depth, from 3 miles under oceans
to 60 miles under continents.
See also in The book of science:
Readings on wikipedia: