The mine, known as Excelsior, operated intermittently between 1873 and 1884, utilizing older workings and yielding 5 tons of tin ore. A tunnel, called the Excelsior Tunnel, was excavated southwestward from Deerpark Wood towards the North Engine Shaft of Kit Hill, in search of tin and copper lodes. Construction of the tunnel commenced in 1877 and continued sporadically over the next six decades until 1938 when the effort was abandoned, still approximately 310 meters short of its intended destination. Despite falling short of its goal, the tunnel extends nearly 1 kilometer in length and is remarkably straight, with the portal visible from its far end. In 1959, the tunnel attracted the interest of the Military/Atomic Energy Authority as a potential site for testing the feasibility of masking seismic signals emitted by underground nuclear tests. For further information and photographs, a comprehensive history can be accessed at http://www.subbrit.org.uk/sb-sites/sites/e/excelsior_tunnel/index3.shtml. However, it’s worth noting that as of June 2005, several areas of the tunnel have collapsed, and the remaining timbering appears increasingly unstable. Additionally, there are no mineral exposures within the tunnel, and any minerals listed were likely retrieved from the now densely overgrown dumps surrounding the area.