It proceeded up the front range of the Andes to Ollagüe on the Bolivian border, requiring a notable piece of civil engineering, the Loa viaduct.

The Collahuasi branch reached 4,815 m (15,797 ft) above sea level, regarded at the time of construction as the highest railway in the world.

The total length of the 2 ft 6 in (762 mm) gauge lines, including branches and subsidiaries, was 1,537 km (955 mi).

Construction started in 1873, with the first section opening late in that year, motive power provided by mules.

The line reached Oruro in Bolivia, the end of the 2 ft 6 in (762 mm) section, in 1892, and branches continued to be added over subsequent years.

In 1909 the FCAB purchased the FC Caleta Coloso a Aguas Blancas, a railway operating in the mineral-rich desert regions south of Antofagasta.

The FCAB already interchanged with metre gauge railways running north–south in western Chile, and there was the prospect of connections with lines from Argentina.

In the meantime, the railway became proficient in changing bogies on freight cars between gauges at interchange points.

[1] In 1982, control of the company passed on to Chilean interests, and the head office moved from London to Antofagasta.

Primary traffic on the railway has always been mineral, first with nitrate (an essential ingredient of explosives prior to World War I) and as of 2020 copper being very important.

As the railway laid heavier rails, larger locomotives were introduced, built by both Baldwin and other American builders.

Post war developments included a fleet of modern 4-8-2 locomotives from Vulcan Foundry in England in 1954, as well as further Beyer-Garratts.