mining city, Queensland, Australia, located at the northern end of the Selwyn Range. The city's name is attributed to John Campbell Miles, who in 1923 discovered deposits of silver-lead ore and named one of his leases after his sister Isabelle. Subsequently, Mount Isa Mines, Ltd., the principal leaseholder, developed the minefields, which are Australia's main source of silver, lead, zinc, and copper. In the early 1970s large silver, lead, and zinc deposits found at Hilton, about 20 miles (32 km) north of Mount Isa, made Mount Isa Mines, Ltd. the world's largest single producer of silver, lead, and zinc. Cattle are raised in the area, and there is an annual rodeo held there. Lake Moondarra nearby was formed in 1958 by damming the Leichhardt River. Pop. (2006) local government area, 19,664.