If it was Devon then Hope's Nose would be a good source! MinDat gives the following sources for Gold in Cornwall, but I have no idea which of these are or were commercial
Wheal Gorland, St Day, Gwennap
Wheal Sparnon, Redruth, Camborne -
Mudgeon Vean, St Martin-in-Meneage
Perran Great St George Mine, Perranzabuloe,
Redmoor Placers (Upper & Lower Creany; Wheal Prosper), Lanivet Area,
Ladock placers, St Stephen Area
St Ewe, St Stephen Area, St Austell District,
Godrevy Cliff, Gwithian, St Erth - Gwithian Area,
Botallack, Botallack - Pendeen Area, St Just District,
Wheal Hazard (Hazard Section), Botallack Mine
Treore Mine, St Teath, Area East of Wadebridge, Wadebridge District
Carnon Valley, Helford - Falmouth Area