well, the actual source, it doesn't really matter, whether the fluids came from the pluton or from somewhere else, that's not the key thing.

the most important thing is where it ended up, in the case of rice lake (same goes for red lake, val d'or and timmins) the gold was deposited in shears, in fractures and weaknesses in the rock, what controlled the shears and predicting where they occured is the key here. how was the rock folded? how was it sheared? Instead of finding out where the gold comes from you try to find out what trapped it and is now holding it.

once you find the cracks, you'll find the fluid, and you might get lucky and get a 52oz/ton sample out of it.