Mining activity at Captain's Flat began in 1882 on copper ore bodies. A railway connection from Bungendore to Captains Flat to support mining operations was considered as early as 1897, but the poor performance of the mine meant a railway was economically unfeasible. As the depth of mining increased, the constitution of the lode changed and the ore proved too complex to treat for extraction of mineral. From 1899 to 1926, production continued on a restricted basis, however within that period technological improvements were made which meant that the lode could again be economically handled. A pilot plant was erected to demonstrate the practicability of renewed mining. A trial survey of a railway to Captains Flat was completed in May, 1928. The proposal was referred to the Parliamentary Standing Committee on Public Works on 27 March 1929. Legislation authorising the construction of the line was passed on 16 June 1930. Due to the prevailing worldwide financial depression, in 1929 the New South Wales government petitioned the federal government for the Commonwealth Railways to construct the line and make it available to the New South Wales Government Railways, under a similar arrangement to the Queanbeyan to Canberra railway. This proposal was rejected the following year and the railway was shelved.
Construction
The line was re-surveyed, a further Ratification Act was passed on 15 December 1937 and construction commenced in February, 1938, with 600 men employed. By June, work on the foundations for piers of bridges spanning Thurralilly Creek and Molonglo River was in hand. The strengthening girders used came from the original viaducts over Wollondilly, Boxers and Barbers Creeks on the Main South line which had been superseded by duplication work in the 1912–14 period. Some of the rails used in the construction of the line came from the Matakana – Mount Hope branch which closed on 6 July 1924. The line was made available on 7 February 1939, for traffic to a point beyond Hoskinstown where a temporary siding and unloading facilities were provided. Loads of concentrate were conveyed from Captains Flat by road to this transfer point. The line was open to Captain's Flat under construction conditions from 28 November 1939, however Mines Department records indicate that conveyance of concentrates from the mine began in October, 1939. The Captain's Flat line opened for general traffic on 17 June 1940 when the tri-weekly rail motor service began.
Operations
The new line was worked under Ordinary Train Staff and Ticket conditions. The length of the line was. During November, 1940, a halt with a small passenger platform was built at Hoskinstown, and a stopping place was also provided at Foxlow where stops were made to pick and set down passengers and parcels. The station at Captain's Flat was an island platform, however the station building was at ground level, on the down side of the platform. Local passenger traffic was never significant. On one occasion, a direct railmotor service was provided on Saturdays between Captain's Flat and Queanbeyan and return, without proceeding into Bungendore, for the convenience of passengers wishing to spend the afternoon in Queanbeyan. By November 1960, passenger traffic had dropped off considerably due to the improvement of the road to Queanbeyan, which was substantially shorter than travelling via Bungendore. Dedicated passenger service was discontinued in 1960; subsequently, a small number of passengers were able to be transported in the brake van of the tri-weekly freight run. Mining operations ceased on 9 March 1962. During operations, nearly 4 million tons of ore were obtained. By April, 1964, services were reduced to just one goods train a week. The line was closed to traffic on 28 August 1968. Sunday, 10 August 1969 saw the temporary re-opening of the line as the location for the railway scenes in the feature film, Ned Kelly, starring Mick Jagger. The special train scheduled for the film was hauled by Locomotive 1243. It was renumbered 176 for the film, and fitted with a kerosene headlamp.
Subsequent developments
In 1974, the derelict railway station at Captains Flat was converted into a private home. In 1993, the NSW Department of Transport called for Expressions of Interest on the future use of the line. Registrations closed in August that year. It was understood that there was an interest in creating a walking track or a tourist railway over the last section of the line into Captain's Flat. By this date, the town was a fraction of its peak size. A Canberra resident registered his interest in returning the line into an operational condition. Whilst he expected to complete his rehabilitation within 2 years, no further progress has been accomplished.
