As Hoov explained previously, the 3% cutoff is for direct shipping of ore to a smelter; it requires no further processing. Therfore, maximum profits for 3% and higher grades. The rest is still economical (down to around 1% IIRC, with tradeoffs for cost of recovery increasing with depth), for sure, just less profitable. With Nickel going for about $10/lb now, that picture keeps improving.