There's uselessly tiny gem fragments in them thar ancient alluvial gravel beds.
Model is bought from: https://cults3d.com/en/3d-model/various/gold-sluice-box-v2-modular-expandible-included-4-mats-classifier although easy enough to design yourself. It works great though and the price is fair if you do want one.
Sluice body is petg, mats are tpu as I thought it would make cleaning easier. TBH petg would probably be a better candidate as long as you did a high contrast material. The flex doesn't add much as it's short sections that fit in a pan anyway.
The sluiced fragments (some of) hairtie for scale.
Not practical, but I want a tiny 3d printed chest of gem rough so for now I'm collecting it all.