I bought a book in Canada which lists men (and a few women) who died in the gold rush town of Barkerville. One of them might just be your missing person !
James Bennett, from Pont i hyr v Fryn, Glamorgan (spelling as on his MI) D. 1/8/1868 aged 31 (or 37)
W. F. Davidson 'Native of Wales', d. 25/9/1864
John Dunn from Wick, Glamorgan. D. 6/10/1863 aged 24
David Edwards from 'Machymlleth' (sp. as on MI) Montgomeryshire. D. 26/4/1911, aged 87
(John) Rosser Edwards, from Tredegar, Monmouthshire. D. 29/11/1867 aged 45
Wm. L. Jones, native of Beaufort, Wales. B. 5/7/1836, d. 18/8/1888
Griffith Lewis native of Pulleg, Breconshire. D. 12/4/1867, aged 31
Roland Rowland from Carnarvon. D 5/8/1872, aged 29
There is more information in the book about several of these people ...
