20 September 1886
Though gold was discovered near Krugersdorp in July 1852 and mining activities started successively in various places on the Witwatersrand (meaning Ridge of White Waters), the first gold from the Main Reef on the Witwatersrand was obtained in 1885, after which Johannesburg was laid out in 1886. Commissioner of mines for the Witwatersrand, Friedrich Peter Jacob (Carl) von Brandis, who was later appointed as the first landdrost of Johannesburg, proclaimed the first mining activities on 20 September 1886 on the farm Randjeslaagte, a piece of rocky 'left-over' ground, after surrounding farms had been surveyed. The digging was to start on 4 October 1886. Within a few years more than a hundred small mines came into being along the whole Witwatersrand, stretching from what is now known as Randfontein in the west to Springs and Nigel in the east. As workings became deeper, the mines had to amalgamate to form economic units.
References

Potgieter, D.J. et al. (eds)(1970). Standard Encyclopaedia of Southern Africa, Cape Town: NASOU, v. 5, p. 224;  v. 6, p. 212; v. 7, p. 444; v. 11, p. 472.|

Wallis, F. (2000). Nuusdagboek: feite en fratse oor 1000 jaar, Kaapstad: Human & Rousseau).