You will always find black sand with gold but finding black sand alone is not an indication for gold. If your area is a known gold producing region your on the right track. If you are trapping the magnetite(black sand) and lead then you should also be trapping the heavier gold. Even if there's no gold in your area you might still find gems sluicing or panning. Garnets sapphires and other gems with a high specific gravity are sometimes found in your concentrates...so keep an eye out. Sorry for the non answer answer.