Keir and Cawder Ltd. and James Millar Son and Co. Ltd. reopened the mine in 1942. They formed the Muirshiel Barytes Co. in 1947, and constructed new shafts to depths between and . This gave access to veins of baryte of a finer quality, which was taken directly to a dressing plant in Glasgow. Production was in 1944, rising to in 1949. Up to this stage there was no electricity at the mine, and minerals were transported in wagons on rails, moved to the surface by human or horse power. The workforce came from Lochwinnoch and Kilbirnie. In 1960 the mine was taken over by Anglo Austral Mines Ltd., and electrical power was introduced to power winding gear for the wagons and lift them to the surface, where the barytes was loaded into lorries. In 1962 Rio Tinto Zinc became the operator. A new dressing plant was constructed just downhill from the mine, to process output from a lower quality vein. At this time up to 48 people from Lochwinnoch and Kilbirnie worked at the mine, including 11 skilled miners, each with an assistant, as well as maintenance and surface workers. Annual production reached a peak of in 1964. Production ended on 5 September 1969.