when smelting metals they add silica, lime, alumina and other things to pull the bad things out. they then dump off the top layer (slag) and then make the gold/silver/misc. ingot. Slag can have trace metals in it but not worth anything.
In anaconda mt (where I use to live for a while) there are piles (billions of tons) of this from copper... yes it contains gold, silver, copper and other things (so does ocean water) but worthless
Selling Ryedale sorted USA cents 1.5 each + shipping over 500fv 1.5 each +1/2 shipping If you pick up 1.35 each located MT/ND boarder. after Ryedale sorting they are hand sorted to remove canadian then rechecked with Ryedale to insure all copper and count out $50 FV then placed in cloth bags and sealed with #1 copper wire.
Man, he sure has a following.... They can have 'em.
Deal
Live free or die. Plain and simple.
"If you love wealth more than liberty, the tranquility of servitude better than the animating contest of freedom, depart from us in peace. We ask not your council or your arms. Crouch down and lick the hand that feeds you. May your chains rest lightly upon you and may posterity forget that you were our countrymen." - Samuel Adams