Mining deeper has always
been synonymous with
challenges. In 1905, 150
.metros was considered
deep for Canada; by 1935, this classifica-
tion had been pushed to 1,500 metres,
and today 3,000 metres is a more com-
mon benchmark. Elsewhere, mines
greater than 4,000 metres are considered
ultra-deep.
Canadian mining journal October 2019 Stephen Hardcastle