They're building a beneficiation plant as part of the mine,...

They're building a beneficiation plant as part of the mine, which will result in a final product of just over 400MT at 60% ore. The details are provided in past announcements. Quote from 25 May 2018 announcement;

The Marillana project has a total estimated Probable Ore Reserves of 967 Mt of DID plus 46 Mt of direct ship CID (Table 3). The total saleable product from the processed iron ore feed is estimated at 404 Mt averaging 60% Fe, 6.1% SiO2, and 3.1% Al2O3 (Table 4). Life of mine strip ratio is 1.0:1 (tonnes of Waste to tonnes of Ore).

Apparently it will be a low cost mine due to the ore body not requiring blasting.