Beneficiation potential of low-grade iron ore from the Manganore Iron Formation through gravity concentration

About 84% of the high-grade iron ore produced in South Africa is hosted by the Manganore Iron Formation of the Ghaap Group of the Asbestos Hills Subgroup, Transvaal Supergroup. The Manganore Iron Formation (MIF) is slumped into sinkhole structures of the Campbellrand Subgroup and occurs exclusively on the Maremane Dome, an arcuate structure located between Postmasburg in the south and Sishen/Kathu in the north, in the Northern Cape Province of South Africa. In the absence of major discoveries of new high-grade iron ore deposits around the world, mining companies have to turn to materials that were once classified as waste. This study was initiated to assess the beneficiation potential of banded MIF and brecciated MIF, two texturally distinct types of partly ferruginized iron formation that occur along the contact of the MIF with the immediately underlying Wolhaarkop Breccia and the Campbellrand Subgroup. The stratigraphic thickness of the partly ferruginized materials in drill core varied between from 23.2 m to 101.9 m. Both material types were sampled in drill cores, and Hand specimen samples were also collected from dump stockpiles and open pits at the Beeshoek and Khumani mines.
Partly ferruginized banded MIF consists of alternating bands of haematite and microbanded chert varying in thickness from the millimetre to the centimetre scale, with specularite filling fissures and pore spaces. The brecciated and partly ferruginized MIF comprises angular fragments of chert, quartz, iron formation, jasper, and high-grade haematite ore with or without matrix. Light microscopy and X-ray diffraction studies revealed that haematite is the principal ore mineral and quartz (chert) the main gangue mineral. Iron- and silica-rich bands were separated using a diamond saw for density measurements and for major element geochemistry by X-ray fluorescence spectrometry. The bulk density varies between 2.7 g.cm-3 and 5.2 g.cm-3 , and correlates well with the iron concentration, which range from 13.5 to 69.4 wt.% Fe. Bulk samples of both raw material types were crushed using a jaw crusher, then sieved in different size ranges and a particle size range (-5.6+1.4 mm) was selected for gravity concentration. This crushed material was found to contain 35.9 wt% Fe (brecciated MIF) and 33.7 wt% Fe (banded MIF). The beneficiation potential of the Manganore low-grade raw material type was assessed using a mineral density separator. The Mintek fixed trailer jig was used with input parameters of 200 kpa pressure. Separation success was monitored by determining the iron concentration of different beds using X-ray fluorescence spectrometry (XRF). The best separation was observed for brecciated MIF, which yielded a gravity concentrate containing 60.7 wt.% Fe (1.69 enrichment ratio), while processing of banded MIF yielded gravity concentrates of up to 52.2 wt.% Fe (1.72 enrichment ratio). The results d e m o n s t r a t e clearly that partly ferruginized MIF holds potential to be processed into a high-grade iron ore concentrate. However, the texture of the low-grade iron formation impacts significantly on separation success.