BHP & RIO have great haemetite, what about the rest though.
If you will look at the comparisons many reserves such as FMG have high impurities compared to that of magnetite ore found in GBG's reserves for example.
Heres a comparison
IRON CONTENT FMG 60% GBG 68.2%
PHOSPHOROUS FMG 0.05% GBG 0.01%
ALUMINA FMG 2.00% GBG 0.01%
so yeah sure you can export haemetite out of the ground, but it wont attract the premiums high quality magnetite will.
