Ann: Positive Interim Metallurgical Test Results, page-36

I'm not an engineer, but silica and alumina are the main deleterious elements when it comes to IO. In unoxidised Banded Iron Formations, silica tends to occur in the form of chert bands, as well as alongside alumina in clays that make up shale bands. The silica present in the chert bands can be removed to a large extent via typical magnetic separation processes, however the silica and alumina present in clays/shales typically needs to be run through a wet plant and washed out.
Someone with a mining engineer degree please feel free to come in and clarify/add more detail.