I heard an interesting interpretation of 'golden fleece'
Apparently, animal skins, especially sheep, were placed in rivers as a way of picking up gold flecks. In essence, it was a way of panning for gold without all the labor. Put the skin in, come back months later, and it would have a fair bit of gold on it.
so that's where clancy got it from?
Yup. I've heard/read that theory a number of times.
While that might work to trap gold flecks, they certainly wouldn't stay there when you picked it up or shook it.
Fines, (read "flecks" of gold), are really quite tenacious in hanging in the mat of a placer operation. Violent shaking will get MOST of the gold out of the mat, but a significant amount of gold still needs to be washed out.
Most of the fines will not just fall out of the mat. You have to work at getting them all out.
Unless, of course, you get into the paystreak very heavy, then it's a problem any miner would love to have! (The fines falling out when moving the mats, but that's why we have buckets!)