The video viewed at the June 2005 meeting features club members Shirley and Larry Weilnau, who are experienced gold placerers as well as prize-winning competition gold panners. Coincidentally, the filmmaker was a Ph.D. geologist, but who had no experience or training in gold-related pursuits. But if he didn't have the answers, he knew the right questions and the video took the form of a Q-and-A session which was remarkably informative.
In a suitable division of labor, Shirley did most of the talking and Larry the hands-on demonstrating. That this was a professional production was obvious by the stunning cinematography. (Let's all head for Buena Vista in the morning!)
Filmmaker: Where does the gold come from?
Shirley: Originally it was in veins in the bedrock in the mountains above us. During the most recent ice age, mountain glaciers scoured the veins along with the country rock and carried the material down the valley. At the melting edge of the glacier, the gold and rock debris were dumped and formed hills and ridges called moraines. The glaciers have receded but the moraines are still there eroding from precipitation, especially spring run-off, dumping waste and gold into the river. The action of the river water concentrates the gold into workable deposits by washing away the less dense waste rock while the much denser gold tends to remain behind.
Larry appears in a boulder field exposed by low water. He emphasizes the need for panning (sampling) "so that you don't work all day where there is no gold." He demonstrates panning which the filmmaker shows in very good detail, including the colors in the pan.
Filmmaker: Why is there gold in the boulder field?
Shirley: Gold will accumulate wherever a stream loses energy. The boulder field obstructs stream flow, causing an energy drop and resulting in gold deposition among the boulders.
Larry and Shirley are operating a suction dredge/high-banker combo in the boulder field.
Filmmaker: How does the dredge work?
Shirley: It is a vacuum cleaner. It sucks up the gravel containing the gold, and then spews it at the inclined grizzly where the larger fragments are screened out. The remaining gravel, containing the gold, goes through into a sluice where the water washes away most of the waste while the gold is captured behind the riffles and on the floor mat. It does the same thing that the river does but on a smaller scale and more precisely.
With a smile, Larry shows the results of a sluice clean-up: a commendable payoff in gold!