Word of Miles's lead spread fast. By the end of 1923, 118 leases had been pegged across the Mount Isa field, and a seasoned mining engineer, William Henry Corbould, quietly secured 51 of them. In January 1924 he floated the Mount Isa Mining Company. Within two years he had pulled off something almost unheard of in Australian mining: by December 1925 his company had absorbed its rivals, so that a single firm held virtually the entire mineralised area of what promised to be a major field. The early going was brutal. Through 1924 the company sank thirty-three shafts and grasped, with mounting alarm, just how much money it would take to build a mine out here. Corbould crossed to London again and again between 1924 and 1927, hunting for capital.

The oldest surviving works tell the story of those lean exploration years. Robert Lawlor held a small lease at Top Camp when the government geologist inspected the area in September 1923; absorbed into the company by the end of 1924, his shaft became the main way down into the ore of the Rio Grande lode during the proving phase. What remains today is humble and evocative: a partly intact two-cylinder steam winding engine, built by May Brothers of Gawler in South Australia, resting on its concrete mounts, a return-flue boiler nearby, its iron chimney toppled alongside. The shaft mouth is sealed now with a grid. The recycled Australian-made engine is a rare survivor from the days before the heavy English machinery arrived - a glimpse of make-do beginnings.

Everything changed in 1927, when the London-based Russo-Asiatic Consolidated, chaired by the financier Leslie Urquhart, took control and brought capital and American engineers to build, in their own words, 'the most modern mine of the age'. The engineer Charles Mitke moved the main ore shaft to the town side of the long dividing ridge and supervised the sinking, in 1929, of the shaft that bears Urquhart's name. The Urquhart Shaft drove half a mile straight down - though it struck an underground reservoir and never reached its planned depth - and over the years hauled three million long tons of ore and rock annually. Its steel headframe, raised in 1930-31, was an American A-frame rather than the four-poster towers usual at the time, and that innovation helped popularise the form. Silhouetted on its hilltop, it has been a community landmark and the very symbol of Mount Isa Mines for more than ninety years.

Power came next. The American engineer J M Callow designed a steel-framed station of coal-fired boilers and generators at the base of the ridge, overlooking the tent settlement on the riverbank. Operational by 1931, it was described that year as having 'twin chimneys rising like black cigars above a roof of dazzling iron'. It lit the town and ran the mine; later it was adapted to make compressed air, a job it still does. But the oldest thing of all is the easiest to miss. Back in 1923, water was named the field's great 'temporary disability', and in a narrow gully men threw up a small stone weir - the Experimental Dam. Just a curved wall of rendered stone, later raised with concrete, now largely silted up and tucked away on the lease. Set against the colossal modern tailings dams and smelter stacks, this modest weir is the humble truth at the bottom of it all: before there could be a great mine, there first had to be water.