The estimating process is interesting to follow. For what it's worth, Voisey's Bay Nickel Company says that the Ovoid deposit "has surface dimensions of approximately 800 metres by 350 metres, extends to depths of about 125 metres and will be mined using open pit methods."

It looks to me like most here are using a density of about 3 in your calculations. It looks to me like 4 would be a better figure for the massive sulfides. But hey, whats a billion ($) between friends?