Although the Gryfe valley downstream from Bridge of Weir contains valuable minerals, such as coal and limestone which have been worked at various times, the geology of the higher ground above Bridge of Weir is quite different, consisting mainly of volcanic rock. This rock is of little obvious value, beyond whin for rubble dykes. However, the Renfrewshire Heights contain numerous rare minerals. The only difficulty has been finding these minerals in large enough quantities to make working them worthwhile. Copper was found and worked above Gourock and Lochwinnoch, but the most elusive mineral was barytes.
Barytes has many uses, including the making of paint, paper, textiles and leather. Renfrewshire barytes is an attractive mineral of high purity, with pink and white banding. It is a dense rock, which was originally formed in vents and cracks in the surrounding volcanic rocks.
Although more than forty barytes veins have been identified in what is now Muirshiel Country Park, only two have been worked to any extent. These were on Queenside Muir, in the valleys of two nameless burns, which drop from the shoulders of Hill of Stake to the Calder Water. As the crow flies, the mines are equidistant between Bridge of Weir and Largs, and can be accessed by a track up the Calder from Muirshiel Visitor Centre.
The barytes at Muirshiels was originally quarried opencast in a series of steps in the hillside. Mines were then driven down almost vertically into the vein from the floor of the workings. Although the seam is about six metres thick, this varies greatly, and workings extended off into side vents and fissures as they were found.
Workings date from the 1750s and have continued intermittently since then. Like many rare minerals, the value of barytes depends on global economics. In the 1890s output was often less than 1,000 tons a year. By the 1950s Muirshiels was one of four barytes mines in S.W. Scotland, including Eaglesham in Renfrewshire, and Glen Sannox on Arran. By this time Muirshiel’s output approached 20,000 tons a year and together these mines accounted for a third of UK production.
From the mine, the barytes was carried a short distance on a mineral railway, then six kilometers down a rough track to the crushing mill on the Calder Water. The mill was built about 1850. It had three grinders in cast iron vats which processed about three tons per day. The mill ground, processed and dried two varieties or colours of barytes, pinkey-grey and white. The mine owner also owned Queenside Dam, to store water to drive the mill. By the 1940s the mill was derelict and the raw mineral was taken to a dressing plant in Kingston, Glasgow.
Social research by Brian Skillen has shown that during wartime in the 1940s, only six men were employed, living a frugal existence in a cottage at Muirshiels. The lorry which took them back and forth from the mine could barely stand up to the rough road, and eventually crashed, killing one of the miners.
The mine closed in the 1960s. Infrequent press interest shows that the working of barytes is likely to become economic again in the future. Whether it will be worked inside what is now a Country Park remains to be seen.
© 2013 Stuart Nisbet