John Fleming, son of Andrew Fleming and his wife Catherine, qualified as Master of Arts (MA) but was a mining engineer in Johannesburg from the eighteen-nineties. In 1895 he became a member of the Chemical and Metallurgical Society of South Africa. At that time he experimented with the extraction of gold from slurry after cyanide treatment. His work was described only years later, in a paper he delivered before the (renamed) Chemical, Metallurgical and Mining Society of South Africa in April 1903, titled "Extraction of gold from cyanide house slimes by a wet method". The paper was published in the society's Proceedings (1903, Vol. 3, pp. 347-360). Fleming was still a member of the society in 1905 and at that time was a consulting engineer in Johannesburg. He was married to Barbara Wallace Maltman.