The Ag/Pb mine was a later one, still going in the 1920s. Here is an extract from a Northern Mines Reasearch paper:
Harold William Gloucester-Trotman died in Nigeria in November, 1940, at the age of 43.
He joined H.M. Forces at the outbreak of the Great War, and after demobilization studied at Chelsea Polytechnic and Camborne School of Mines. In 1924 he joined the staff of the St. John d’el Rey Co. and was occupied in research work on the dressing of bauxite. Returning to England in the same year, he was for eighteen months manager of the Bodithiel silver-lead mine in Cornwall, and in 1925 he went to Northern Nigeriau where he was for some time assistant engineer on the staff of the Bisichi Tin Company, and later worked on his own account.