Got A Tricky One - Industrial Silver Ingots

Just a hunch here, but the remaining metal may be Zinc. That could explain the color. It sounds like some type of brazing alloy. If the remaining five percent is Zinc, the refining cost likely would consume most of the Silver value. You could try a specific gravity test for several samples and compare the results to a calculated range for expected values if the remainder is Zinc, but any variances in the composition and how the alloy could have been mixed make this a bit iffy.