it depends how confident you are the next 5 years of iron ore prices will match the past 5 years...if we continue to see strong gains then magnetite resources may be okay...personally I would rather stick to high grade DSO haematite as it's going to be in demand and high margin regardless of economic conditions, so it's insulated. Magnetite is far riskier but if things go your way you'll reap the rewards.
What is a tonne of magnetite worth? I don't know but UMC's DSO is probably valued less than $1.50 per tonne, not JORC'ed yet but certainly much much further down the track than ACS. So that's where my money is at.
