The Kalka intrusion is an ultramafic-to-mafic layered intrusion that belongs to the 1078–1075 Ma Giles Complex (Musgrave Province, South Australia). The upper, evolved portions of the intrusion are characterised by Fe-Ti-(V) oxide-rich (magnetite and ilmenite) units that bear lithostratigraphic similarities to previously reported Fe-Ti-(V) oxide occurrences (Mantamaru) from the west Musgrave Province. This study presents a detailed petrographic and geochemical characterisation of these Fe-Ti-(V) rich oxide units at Kalka and constraints on the petrogenesis of oxide-rich units and implications for vanadium mineralisation at Kalka. Basal magnetitite units from the Kalka intrusion contain moderate whole-rock TiO2 (up to 10 wt%) and high V (up to 6910 ppm) contents, indicating potential for economic vanadium mineralisation. In contrast, stratigraphically higher olivine magnetitite units contain higher modal proportions of silicate minerals and ilmenite relative to magnetite and are marked by higher TiO2 contents (up to 14.9 wt%) and lower V contents (up to 850 ppm). Magnetite and ilmenite from oxide-rich units of the Kalka intrusion record extensive subsolidus re-equilibration, as evidenced by exsolution lamellae, and is attributed to slow cooling and/or overprinting during post-emplacement regional metamorphism. We show that laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) produced much more reliable estimates of the original composition of oxides, as well as subsolidus and supersolidus temperature and oxygen fugacity, than electron microprobe analyses. The results indicate that V-rich magnetite at Kalka crystallised from a moderately oxidised magma (ΔFMQ + 1.17 – +3.40). Progressive oxidation and melt evolution led to V depletion and the stabilisation of ilmenite in the overlying olivine magnetitite units. By integrating petrographic and geochemical evidence, we demonstrate that variations in oxygen fugacity, evolving melt composition and density-driven crystal sorting contributed to the development of the magnetitite layers at Kalka.
Abersteiner et al. (Mon,) studied this question.