I believe it is probably Johannesburg. I now know (thanks to the kind members of this forum) that Alexander Bingle McLean died in Turffontein, Johannesburg on 13 October 1918 and I know that Alexander and Maria's son Charles Henry McLean was born at Elandsfontein, Johannesburg on 8 September 1901. I see on Alexander's Death Notice that his wife (presumably Maria) had deserted him 12 years before his death which would make her leaving about 1906.