As s often the case in Cornwall it is difficult to pinpoint one mine and mineral. This from mindat.org.
Harrowbarrow & Prince of Wales Mines (Wheal Newton (Barnard); Harrowbeer; Harrowbarrow Consols; Wheal Goodluck; East Wheal Brothers; Wheal Pleasant; Calstock United; Calstock Mines ), Callington, Callington District, Cornwall, England, UK
This group of mines also included Wheal Fortune, Wheal George, Wheal Queen and West Edward, South Harrowbarrow
Ref: Hamilton Jenkin XV, 1969.
The first referance to the mines being worked was in 1580, as Wheal Goodluck. The lode was discribed as a great Margasly (?pyrite)lode bearing silver.
In 1774 Harrowbarrow mine was offered for sale as a copper and tin mine. The next recorded working was in 1805, but was soon abandoned. In 1825-6 Harrowbarrow was reopened as Wheal Goodluck again and produced 37 tons of copper ore. 10 years later the mine was at work under two names one called East Wheal Brothers. This working lasted untill 1848, and is belived some copper and tin, and 700 uk pounds worth of silver was produced. Intrestingly at this time the mine was drained by a Sims double cylinder (compound) beam engine 38inch/20inch (Higher presure steam entered the small cylinder, and was then reused at a lower presure in the larger cylinder). In about 1822-23 Prince of Wales may have been worked under the name Calstock mines, and produced 92 tons of copper ore. In 1850 Prince of Wales (Wheal Pleasant) with Harrowbarrow mine was included under the name of Calstock United. The group of mines continued to be reworked in various amalgemations and names untill 1914. Prince of Wales was propected in 1928 but no production resulted.
The most recent activity was was around 1977 when a level was driven northward towards Hingston Down, again no production resulted. It would appear that most of the silver ore came from the Wheal Queen section, which was developed on a tracked of the Wheal Brothers lode. Another mine which was also rich for silver ore.
This group of mines developed some seven east by south trending mineralised faults, and a north-south mineralised cross-course fault, probably silver berring. It would seem that only the Prince of Wales lode was developed to any great depth to 193 fathoms below surface (353mts), for a lenth of about 200 fathoms (366mts). Ore values are indecated by the stope patten as being inconsistant in all the mines of this group. Development on the other lodes is to no more than a 50 fathom level below adit.
18000 tons of copper ore.
1110 tons of tin ore.
23 tons of lead ore.
27 tons of manganese.
10120 tons of pyrite.
6753 tons of arsenical pyrite (?arsenopyrite)
532 tons of arsenopyrite.
2 tons of arsenic.
20 tons of silver ore.
421 oz silver.
The recorded minerals anatase, childrenite, molybdenite, ramsbeckite, schulenbergite, scorodite. Where found in the Price of Wales portion of this group, other minerals where found in the various mines that make up this group.
I believe there is acccess to underground lead/silver workings.