Now this is my 2 cents and it's worth less than I'm charging for it, so take it with a grain of salt. Zinc contamination in lead is becoming more popular with most wheel weights going to steel or zinc now. Is the lead you've found already in ingots? A lot of guys don't like to bother with zinc contaminated lead and I was really paranoid about this when I started smelting and pouring my own weights and jigs but at this point, several years later, I feel it's a non issue. If they're wheel weights, just keep your temp around 700 degree's (or lower) in the smelting pot. If theres doubts as to if a weight is zinc I drop it in the pot and see if it floats after a few seconds. If it it floats, it gets skimmed and trashed. The guys that get in trouble with it are the one's that fill a huge pot, set it on the turkey fryer and then forget about it til it's too late, if youre doing small runs, a few pounds at a time and watching, skimming clips and monitoring the temp you'll NEVER run into a problem.