G. Kubale applied for an appointment as mining inspector in the South African Republic (Transvaal) in July 1896 and held this position to the outbreak of the Anglo-Boer War in 1899. He was stationed at Klerksdorp. His report "Bijdrage tot de geologie van de Klerksdorp goudvelden der Zuid-Afrikaansche Republiek" (Contribution to the geology of the Klerksdorp goldfields of the South African Republic) was included as Appendix E (pp. 48-59) to the annual report of the State Mining Engineer for 1896, which was published together with the annual report of the Head of the Mines Department. In September 1898 he was transferred to Boksburg and reported on some coal mines near Brakpan. An extract from this report was included as an appendix to the annual report of the State Mining Engineer for 1898. In November 1899 he reported on the Rose Deep gold mine, near Germiston.
Kubale was a member of the Chemical and Metallurgical Society of South Africa in 1899 and was still listed as a member of the renamed Chemical, Metallurgical and Mining Society of South Africa in 1903.