Duncan I.R. Simpson, a metallurgist in Johannesburg, became a member of the Chemical, Metallurgical and Mining Society of South Africa in 1903. A few years later he published a paper entitled "A new method of obtaining the density of settled sand" in the society's Journal (1906/7, Vol. 7, pp. 158-). In 1905 he worked at New Goch Gold Mines, Ltd, Johannesburg.
He may be the same person as Duncan Simpson, Fellow of the (British) Chemical Society (FCS) and associate of the (British) Institution of Mining and Metallurgy (AIMM), of Vryheid, Natal, who took out a patent in 1907 in connection with the treatment of complex ores, and in 1908 proposed to form a society for the advancement of mining in the Natal Colony.