In the 18th century, an unexpected discovery occurred when an adit, driven through Pengreep estate, intersected a cobalt-bearing lode around 1754. This cobalt mine, described by Pryce in 1778, was notable for its accidental finding by Mr. Beauchamp. He stumbled upon a three-foot-wide lode containing genuine cobalt just as the Society of Arts offered a reward for the best cobalt discovery in England. Despite initial success, the mine proved difficult to sustain, with water inundating the workings shortly after its discovery.

Additionally, the lode contained bismuth ores, leading to the designation of the mine as both a cobalt and bismuth source. These bismuth ores were initially discarded until Dr. Albert Schlosser demonstrated a process to separate them from the cobalt ores in 1775.

Although there were claims of nickel ores being found in 1754, later investigations revealed this to be a mistake. In 1958, the Atomic Energy Authority reopened the adit in search of uranium ores, but none were discovered. Hamilton Jenkin, visiting the site the same year, observed that the adit was approximately 300 feet long and speculated that a nearby burrow might be a shaft dump.

The provided grid reference marks the estimated location of the adit portal, based on observations by Hamilton Jenkin.