The man you are looking for is actualy Samuel Hopewell of Samuel Hopewell & Co., St. Helena merchants. He married Emma Matilda Arnall in St. Helena in 1840. Emma Matilda was born in Redruth, Cornwall in 1815 and was a twin with Lydia Staughton Arnall. Emma Matilda was the daughter of my ancestor George Arnall b. 1775 in Lanteglos, Nr.Camelford in Cornwall. As you can imagine all of the Arnalls were associated with tin mining.
Transcript from the 1840 (Marriages) West Briton Newspaper:-
On the 19th of May Last, at the Island of St. Helena, Samuel HOPEWELL, Esq., merchant, to Emma Matilda, youngest daughter of the late Mr. George ARNALL, of Redruth.
For some reason the Arnall family wanted to keep the Hopewell name alive and used it as a Christain name quite often in successive generations. For example there was a Caharles Hopewell Arnall born in Truro in 1869 and a George Hopewell Arnall born in Sydney, Australia in 1895
Cheers for now
Bob Needham in Oz