Black sand is an accumulation of dense, iron-rich minerals like magnetite and hematite that settle at the bottom of sluice boxes, riverbeds, and wash plants. Because gold is also extremely dense, it drops out of the water flow alongside these heavy iron minerals. Placer miners closely watch for black sand deposits as a strong indicator that precious metals are trapped in the same gravel layer.
Heard on the job
We hit a thick layer of black sand at the bedrock contact, so make sure to pan the concentrates carefully.