Re-opening the ventilation raise on No.1 Level
An old plan of the mine showed a 'rise to surface' at the top of a stope near the end of No.1 Level, but in the early days of the project there was no evidence of this at surface. After several unsuccessful attempts to climb the stope, which is almost 100 feet high, it was decided to locate the top of the rise by carrying out an accurate survey up the hillside. This survey pin-pointed the rise in the base of one of the many old costean pits on top of Trewey Hill.
Agreement was made with the mineral owner to re-open this rise in order to improve the natural ventilation in the mine. On a cold winters day an 8-ton JCB digger was hired to excavate the costean pit. Within half-an-hour a burst of steamy air revealed that we had broken into the top of the rise. It proved to be about 15 feet deep into a short level that entered the top of the stope. The following few months were spent rebuilding the collar of the rise with concrete blocks, capped with a metal grid, and a cattle-proof fence.
Schematic of the stope and raise on No.1 Level
Re-opening the rise greatly improved the natural ventilation throughout the main parts of the mine. The air temperature underground remains constant throughout the year at 10-11 deg C, but the direction of air flow in the mine varies depending on the outside temperature. Although there are no inherent explosive gases underground, the constant air flow helps to maintain low radon levels throughout the main part of the mine.