According to Dines Steeperton Mine (aka Knack Mine) was an unsuccessful trial on the western slopes of Steeperton Tor.
Helen Harris in her book the Industrial Archaeology of Dartmoor gives a little more information as follows:
At the foot of the western slopes of Steeperton Tor are the remains of Steeperton Tor or Knack Mine which was active for tin during the nineteenth century on the site of earlier workings up to the 1880's. The remains include a hillside reservoir, gullies, adits, shafts and pits, parts of a dam across the Taw, a leat, wheelpit and buddle site, as well as building ruins.
The mine actually has quite early origins and was working as early as 1799, indicated by documents researched by Tom Greeves. There is evidence of other licences during the first half of the 19th century. Obviously the mine was a bit more than a trial.
As with most Dartmoor mines the site aroused interest due to the Medieval openworks on the western valley slopes - evidence of tin lodes worked from surface sometime around the sixteenth century. An attempt to work these at depth probably started in the late eighteenth century. The mine at this time was known as Wheal Virgin and in 1799 Duchy records state that Wheal Virgin was owned by Gill & Co and was 'raising tin fast' (Greeves).
Nothing is then heard of the mine until 1836 when a licence was granted to three men from Tavistock – Henry Prenton, Francis Prout and John White (Greeves). The licence was to run for twelve months at the cost of 1/18 share or dues. The bounds of the mine were set as being:
From a certain rock or stone marked WV on the eastern side of the shaft known by the name of Wheal Virgin Shaft to the length of three hundres fathoms eastward and four hundred fathoms westward, being together seven hundred fathoms on the course of the lode on which the said shaft is now sinking and one hundred and fifty fathoms north and south thereof…
In 1835 the mine was referred to as Nack or Knack Mine. The following year the mine was apparently abandoned.
In 1853 a one year lease was granted to Michael Stevens from Lydford when it was called Steeperton Sett, however there in no evidence of any production in tin.
The next record of interest in the mine dates to 1875-1876 the Chief Agent was R M Jeffery, although during that time the mine was probably not worked, as in 1876 the Duchy agent reported the mine to be deserted with the workings in a dangerous condition (Greeves). However in the following year mining recommenced when the Steeperton Mining Co Ltd was formed and it is this company that installed the plant and buildings, the remains of which are still visible. The plant, waterwheel and stamps were purchased from Gobbett Mine, Hexworthy for £65 (Greeves). One ton of black tin was produced the following year, but by 1879 the company was in liquidation and the machinery and plant were auctioned shortly after. From 1880-1882 the mine was in the ownership of the Steeperton Tor Mining Co Ltd. This may be a reconstruction of the earlier company (often one or more of the original investors might encourage new investors to speculate in the mine - requiring the formation of a new company). Interestingly the Chief Agent from 1877-1882 was S M L Aldridge, which would suggest some sort of restructuring. However, the new company was not successful as according to Burt et al the mine was not worked between 1880-1881.
The employment figures for the mine suggests that 1878 was the only period of serious mining in this latter period. During that year the total number of employees were 27 (13 underground and 14 at surface). By 1879 the workforce consisted of just one man who was working at surface, presumably just undertaking surface maintenance requirements (Burt et al).
Steeperton Tor Tin Mine, Dartmoor, Devon
T A P Greeves Trans. Devon Assoc. 117, 101-127, 1985
Industrial Archaeology of Dartmoor
Helen Harris 1968
Devon and Somerset Mines – The mineral Statistics of the United Kingdom 1845 - 1913
R Burt et al.
The Metalliferous Mining Region of South-West England Vol 2
H G Dines 1956