Do not discount the "pretty" rocks found along with gold. The sapphires you see are worth many times more than gold. Sapphire (& Ruby, (corundum), is like garnet, a relatively high specific gravity that will catch in a sluice readily. These gems act as gold, they will drop behind a boulder, in bedrock cracks, and set up in the stratiform layers of a bar on the inside bend of a stream. In a perfect (laboratory world) a river bar sets up from front to back: Gold, Platinum, Lead, Iron Ore (black sand), Gems, Sand. and in a stratiform layer (top to bottom) Sand, Gems, Iron Ore, Lead, Platinum, Gold. In the real world big gold drops out at the head of the bar and as the bar is formed, it forms an airfoil shape which sucks light gold flakes (and gems) to the back of the bar. What you want to look for is concentrations of black sands at the back of the bar to know there is gold (and gems) likely. At the front of the bar will be the heaviest gold (nuggets) and gems, but they may be too deep or covered by massive layers of boulders to get to. Just remember to follow the black sands and move slightly ahead of them for the richest concentrations of fine & flake gold (and gems).