What source? All depends on the area you are digging... did your river or creek cut thru another ancient gold bearing river? or is the area known for lode deposits ect ect....
I go to this place and it never fails to treat me well..I have done well in this spot!! 90%of the gold is dust every once in a while I get a chunkie or a decent picker but not often..Anyway behind me there is a narrow channel with mostly sand.. it cuts up the mountain that is filled with sand and broken rock and very small river rock. and I have sampled this channel for about 30 feet or so and the buckets were all dusted well in gold..But its also a pretty steep grade and alot of brush, ticks and thorns..I have been up there a few times and regretted every trip but if you go high enough river rock will start to appear..and down river about a quarter mile ,the whole cliff side is old river bed and up river just around the bend there is evidence of a channel...but my source I think it is an old bend in the river long forgotten and I just found where it happens to run off into the new course of the river.. But who knows? I really need to kidnap a geologist for a few days....
