The R500 Isortoq project in South-West Greenland contains two titanomagnetite-rich troctolite veins striking 15 km with an inferred resource of 70 Mt and potential products of Fe, Ti and V. As with many modern exploration assessments there is a need to quantify the mineral proportions of the ore, along with the key mineral carriers of the target elements. For any complex ore where the target elements are hosted at different concentrations, in different minerals, this process of characterisation usually necessitates using multiple techniques.
Generally, the concentrations of vanadium in vanadiferous titanomagnetite deposits are low (0.3 – 1.9 %V2O5) and mostly contained as solid-solution with vanadiferous titanomagnetite. It is normally recovered as a co-product with major elements Fe and Ti, which themselves may be hosted by multiple other phases. As such the assessment of mineralogy particularly benefits from combining techniques to resolve the overall mineralogy, trace element and major element deportment and liberation characteristics (Figure 1).
Figure 1: Comprehensive Mineralogical Characterisation
In isolation, any one of these techniques would be insufficient. Although deductions may be made, assays on their own won’t determine how much of the target elements are hosted in recoverable phases but is nonetheless the best method for determining the concentration of target elements in the ore. Optical petrography provides excellent qualitative textural information (Figure 2) but would be cost prohibitive to obtain quantitative information.
Figure 2: Reflected photomicrograph showing finer-grained ilmenite and exsolution textures in titanomagnetite.
XRD gives excellent bulk mineral deportment and has advantages when it comes to identifying the clay minerals but provides no information on textures, and struggles to detect phases present at concentrations <2-3%. Furthermore, as in this case, it is unable to distinguish well between minerals in close solid solution and may overestimate key phases relative to others (i.e. overestimating ilmenite content relative to vanadiferous titanomagnetite). Auto-SEM provides substantial bulk mineral, deportment and quantitative liberation data (e.g. Figure 3) – indeed that is one of the most powerful aspects of this type of work.
Figure 3: Theoretical grade-recovery charts.
However, it cannot detect trace element contents within phases (e.g. V in titanomagnetite) and can struggle with clay group mineral speciation. Manual SEM or EPMA can provide long acquisition times and/or standards backed analysis for the determination of trace element mineral contents (similar techniques such as Laser ICP-MS can be used if an even greater resolution is required) but needs to be coupled with the other techniques for that data to be extrapolated to a full sample deportment (as in Figure 4).
Figure 4: Relative deportment for vanadium
For the Isortoq project, the combination of these techniques provided a robust overall mineralogical interpretation giving confidence for critical metallurgical interpretations along with on-going commercial and development decisions.