John A. Chalmers was an associate of the Royal School of Mines, and seems to have been a mining engineer. In February 1894 he was living in Johannesburg and became a member of the South African Association of Engineers and Architects (founded in 1892). In 1895 he became a naturalized citizen of the South African Republic (Transvaal). That same year he was a foundation member of the Geological Society of South Africa and served on its council for 1895 and 1896. He was the co-author of a book, with F.H. Hatch*, The gold mines of the Rand, being a description of the mining industry of Witwatersrand, South African Republic (London, 1895, with a second edition appearing the same year). Chalmers next wrote "Notes on the geology of Mashonaland and Matabeleland", with Hatch as co-author, for the Geological Magazine (London, 1895). In 1898 he published a paper, "On the drilling of the Bezuidenbore near Johannesburg", in the Transactions of the Institution of Mining and Metallurgy (London). Finally, his "Notes on the Namaqualand Copper District" was read before the same institution in April 1900 and also published in its Transactions.
By 1906 Chalmers was living in Bulawayo and had become a member of the South African Association for the Advancement of Science. He should not been confused with another John Alexander Chalmers, an iron and steel worker who lived in Benoni but died in Pretoria in 1933 at the age of 52 (National Archives Repository (TAB). Source MHG, Reference 80839, Estate papers).