Malmberget Poster

8/2/2019 Malmberget Poster

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Liberated Magnetite Ore

Liberation of Magnetite

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Mineralogical, chemical and textural properties of theMalmberget iron ore deposit

- A process mineralogical characterisationC. Lund* & O. Martinsson

Division of Geosciences, Lule University of Technology*[email protected]

Introduction & AimsThis project combines two different but closely connected disciplinesin a mining process to each other, ore geology and processmineralogy by studying mineralogical-textural features of the ore andthe ore concentrate in an apatite iron ore deposit in Malmberget.

The first discipline is ore geology; the object is to describe themineralogy and chemical variations of different ore bodies and oretypes but also to characterise the mineral chemistry of the oreminerals. By understanding the metamorphic influence, particular thechemical and textural effect on the ore minerals this study could alsocontribute to the controversial discussion of the origin of the apatiteiron ore (Kiruna type). The second discipline is process mineralogy;the object is to characterise the ore minerals, its ability of liberation,the mineral associations and textures but also to identify specificmineral associations, common for a certain type of ore body and oretype. These mineral associations could act as a signature and createtraceability in the process chain during the concentration. Byimproving the mineralogical understanding of the minerals and theirtextures, a certain process problem of mineralogical character couldbe identified and solved.

MethodologyThree different ore bodies from the Malmberget deposit are includedin this study; Hens, ViRi and Fabian, morphologically divided in twotypes; massive ore and ore breccia. The analytical methods that are

used are QEMSCAN and PTA in a process mineralogical point ofview and microprobe (EMPA) analysis for the chemical composition.

Results & ConclusionsOre Geology All three ore bodies and the ore types have different chemicalsignatures, particular a variation of the minor elements V2O3, TiO2,Al2O3, and MgO. Hens ore body has a content of TiO2 which is highin hematite and low in magnetite which is suppose to be aredistribution of the element during recrystallization at high oxygenfugacity. The oxidation textures in magnetite indicate that the orebodies are exposed for different stages of oxidation. Magnetite andilmenite occur as coexistence minerals and show textures both of thelowest oxidations stage (C1 & R1) which is homogeneous magnetiteor ilmenite and of the highest oxidation stage (C5 & R5) which isreplacement textures of hematite and ferrianrutile.

Process Mineralogy The results show a rather distinct difference between these two oretypes, both in the mineralogy but particularly in their texturalproperties. The particle liberation of magnetite is high for massiveore being much lower for ore breccia and decreases in the finerfractions. It is depending on mineralogy, grain size and textures ofmagnetite and gangue minerals. A binary magnetite/FeTi-oxideassociation is the most common one in both ore types whilemagnetite/amphiboles and magnetite/apatite are characteristic forore. Ore breccia has more associations of both binary and complexmagnetite bearing particles. Typical associations aremagnetite/feldspar and magnetite/quartz. A mineral texturefrequently found in ore breccia is small magnetite grains occurringas inclusions in feldspar.

Ore geology; Our data support a model with the massive ore formedfrom an iron oxide melt while the ore breccia is part of the same oreforming system but of hydrothermal origin. Process mineralogy; Orebreccia is an ore type where some of the magnetite bearingassociations will cause an increasing amount of silica in theconcentrate or iron content to the tailings.

Quantitative particle liberation of magnetite in ore and ore breccia divided in four classes. Liberated >90 %, highgrade intergrown 60-90 %, low grade intergrown 30-60 % and locked is < 30 %. Fractions: -300/+100 = 150 m,-200/+100 = 75 m and -100/+20 = 38m

Photomicrographs of oxidation textures of magnetite and ilmenite at the Malmberget deposit (reflected light).A) Exsolution lamellae of ilmenite in magnetite oxidation (stage C2-C3) B) Magnetite showing oxidationassemblage of rutile and ilmenite (stages C4-C5) and ilmenite with hematite lamellas (stage R5).

Mineral chemical plots of magnetite and hematite from Hens, ViRi and Fabian A) The TiO2 content in magnetite(left axis) and hematite (right axis) vs. the V2O3 content in Hens and ViRi. C) The TiO2/V2O3 content inmagnetite from massive ore and ore breccia, massive ore is subdivided into fine grain and coarse grainmagnetite textures.

Photomicrographs showing mineral associations from ore breccia and ore. A) Magnetite grains as inclusion infeldspar. B) Magnetite and apatite as mixed grain.

An image grid report created in iDiscoverTM visualising the different binary and complex mineral associations inore and ore breccia. Fractions: -300/+100 = 150 m, -200/+100 = 75 m and -100/+20 = 38m. Abbreviation,Mag magnetite, Amph amphibole, Qtzquartz, Fspfeldspar, Ap apatite, Chl chlorite.

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Malmberget Poster

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