I tried finding some info on metallic deer teeth and read a journal of pathology from 1895 that stated samples of deer teeth from Great Britain often had a metallic luster to the enamel layer. It gave no explanation why and I found no mention of it anywhere else.
I wonder if it could have come from a mineral lick of some kind. It might be worth a call to your states game commission, just to make sure it's not a symptom of disease. Better safe than sorry.