Nickel dropped about 3.7% today, going from $5.98/lb. to $5.76/lb. according to kitcometals.com. Other than being a quiet day before a holiday, I don't see anything to account for this big of a drop in a single day. The problem with quiet days is that individual traders might be able to push things around more than they usually could. I just bought some more .999 Canadian nickels yesterday and will look to add even more based on the price drop...if I can find them.
Also, I noticed that copper, lead, zinc and aluminum didn't go down sharply like nickel did. So I am suspecting this could be a trader trying to manipulate things to make a quick profit on an otherwise quiet day.