The earliest, and indeed the only, known occurrence of rock salt mining in Ireland took place in the halite beds of south-east Antrim. Although rock salt was not successfully mined at Carrickfergus until the 1850s, there had been an awareness of the existence of salt springs in the area for at least a century before that date. As early as 1757 Dr John Rutty, a Dublin physician, had noted the salinity of the Carrickfergus springs in the course of his survey of Irish mineral waters, one of which no doubt was the ‘salt hole’ which featured in an earlier post.
In his quest for coal the Marquis of Downshire in 1852 discovered a bed of rock salt, at a depth of around 550 feet, at Duncrue, about two miles north-west of Carrickfergus town. A mine was developed and operated there by the newly-formed Belfast Mining Company, and by 1857 it was producing upwards of 20,000 tons of salt annually.
Duncrue was exploited using the traditional ‘pillar and stall’ method of mining. As excavation progressed horizontally within the galleries substantial pillars of salt were left standing at intervals to support the roof. At Duncrue some of these were described as being about 8 yards by 6 yards in width and depth. The dimensions of the gallery itself were about 60 feet in width by 45 feet in height. It was excavated in three stages, each level being about 15 feet high. Excavated rock salt was broken up into more manageable lumps before being loaded into wagons and taken to the shaft where it was winched to the surface. A tramway was constructed in 1856 to convey salt from the mine to the deep water harbour of Belfast for shipment.
The majority of salt was exported as rock to Scotland, England and further afield. Some was also sent to Irish refineries, such as those at Belfast, Dundalk, Drogheda, Balbriggan and Cork. It seems likely that the availability of locally-produced rock salt was a factor in the survival, or even establishment, of some of the late 19th century Irish salt works. A number of works are listed in the Belfast directories long after the earlier phase of salt refining had ended (by 1837).
Other mines – French Park, Maiden Mount and Burleigh Hill – were later opened in the general vicinity of Duncrue, and these continued in use after the Duncrue mine became unstable and was abandoned around 1870. The unstable mines have been subject to collapse and some of the sink holes have developed into large ponds similar to the ‘flashes’ in the vicinity of the Cheshire mines.
The Carrickfergus salt trade temporarily declined after 1884, and in 1886 the Belfast Mining Co. went into liquidation. The existing mines were amalgamated into the Salt Union in 1888, and the trade eventually recovered.
The last of the old mines closed in 1958, and for a time, until the opening of the present one at Kilroot in 1965, no salt was produced at Carrickfergus. Kilroot continues to supply much of the salt used for gritting icy Irish and British roads in winter.