Smelting a pack full of gold, 40 for example, takes about 15 minutes while digging it will take anything from an hour on up, usually more.

Yes, but what you are forgetting is that in order to smelt gold you have to spend a large quantity of time and trias in order to progress to the level of skill it takes to smelt gold. It is not a one or two day task. It involves a lot of progress points and time. So to say it takes only 15 minutes to process the gold is true, but it took a heck of a long time to get to that ability. It is like in real life, your Med.School trained surgeon makes all the money even if the assistant is doing more work. There is a premium for knowledge and learned skill. So it is fair.