In July 2018, Mineral Council of South Africa announced, 75% of mines in South Africa are now unprofitable due to decline in gold reserves. Among the nation's gold mines are two of the deepest mines in the world. The East Rand Mine, in Boksburg, extends to a depth of 3,585 metres (11,762 ft).
In 1917, Johannesburg became the headquarters of the Anglo-American Corporation founded by Ernest Oppenheimer which ultimately became one of the world's largest corporations, dominating both gold-mining and diamond-mining in South Africa. Major building developments took place in the 1930s, after South Africa went off the gold standard.