Possibly named after a mountain in the Holy Land, where the river Jordan rises, this mine
has the distinction of being the oldest named mine in Cornwall to appear on a map, a
map from about 1560 at Hatfield House. In 1584 Norden marked it on his map of Penwith
Hundred, but without a name, as was his custom at the time. Situated at Porthnanven on
the southern side of the Cot or Kelynack Valley and extending a short way down the coast,
the mine has never had a change of name in the four and a quarter centuries of its existence,
apart from variants in spelling, though at one time it was worked with its neighbours Letcha
(late Cornish for a frying-pan) which adjoins it to the east, and Oak, adjoining Hermon
on the cliffs to the south.

The first working of which there is any record can be assumed to have started some
time before about 1560 and to have ended after 1584. A sale of black tin to the Angarrack
smelting-house is recorded in 1716. After a period of idleness it was taken up in the autumn
of 1753, and it is thanks to correspondence that has survived in private possession that
an account can be given of this working, which lasted until about 1770 at least.

via

Wheal Hermon, St. Just 1560-1976

Justin Brooke

https://www.aditnow.co.uk/documents/HERMON-Mine/Hermon.pdf