IIRC nickle is a tricky metal in that it is often the byproducts of other mines. So if a lead mine makes 10% of earnings off nickle byproduct.... Then whether it does more exploration or mining is dependent on the lead price not the nickle price
Silver often has this problem. It is often the byproduct of a mine, say a copper mine.
When I think of nickel, Sudbury, Ontario jumps to mind. And Timmins too. http://www.pfncapital.com/s/NewsReleases.asp?ReportID=190474&_Type=News-Releases&_Title=Major-Timmins-Nickel-Acquisition-Program-Underway-Pacific-North-West-Capita...