Layered mafic intrusions (LMI) are stratified igneous bodies, with many examples that are economically significant for a number of metals including chromium, platinum group elements, vanadium, titanium, and iron. The Windimurra Igneous Complex (WIC) of the central Murchison Domain, Western Australia, the largest layered mafic intrusion in Australia, comprises a giant (2500 km2) LMI, with an interpreted thickness of approximately 11 km. The Upper Zone is free of primary hydrous minerals and contains ore-grade Fe-enrichment discoveries up to 66.6 wt% FeOt. Elevated Ti, V and Cr in magnetite at the base of the Upper Zone, and high Cr in the Middle Zone, combined with structural observations in the field, are consistent with injection of two separate magmatic pulses. In this study, four deep diamond drill cores and 92 reverse circulation drill holes from the Upper Zone and uppermost Middle Zone of the WIC sample a near continuous section of 820 m in the Upper Zone, including numerous magnetite-rich horizons. An increase in the whole-rock TiO2/V2O5 upward in the Upper Zone, a decrease in the frequency of magnetite-rich horizons, and an increase upwards in P content, have been used in combination with airborne magnetic surveys, to develop a magnetic stratigraphy for the Upper Zone. The stratigraphy reflects the prospectivity for magnetite, vanadium and chromium, all of which are more abundant at or near the base of the Upper Zone. Such exploration vectors can be used to better target local iron, vanadium as well as chromium mineralization, much of which appear spatially associated with the Upper Zone's basal contact.

Kimberlites of Jurassic age occur in various parts of South Australia. Thirty-nine of these kimberlites, which are mostly new discoveries, were studied to characterize their structural setting, their petrography, and the composition of their constituent minerals. Although some of the kimberlites in South Australia occur on the Archean to Paleoproterozoic Gawler Block, most are part of a northwest-trending, semi-continuous kimberlite dike swarm located in the Adelaide Fold Belt. The kimberlites typically occur as dikes or sills, but diatremes are also present. In the Adelaide Fold Belt, diatremes are restricted to the hinge zones of regional-scale folds within thick sedimentary sequences of the Adelaidean Supergroup. Despite widespread and severe alteration, coherent and pyroclastic kimberlites can be readily distinguished. U-Pb and Sr/Nd isotopic compositions of groundmass perovskite indicate that all kimberlites belong to the same age group (177-197 Ma) and formed in a near-primitive mantle environment (Sr-87/Sr-86: 0.7038-0.7052, epsilon Nd: -0.07 to +2.97). However, the kimberlites in South Australia are compositionally diverse, and range from olivine-dominated varieties (macrocrystic kimberlites) to olivine poor, phlogopite-dominated varieties (micaceous kimberlites). Macrocrystic kimberlites contain magnesium rich groundmass phlogopite and spinel, and they are typically olivine macrocryst-rich. Micaceous kimberlites, in contrast, contain more iron- and titanium-rich groundmass phlogopite and less magnesian spinel, and olivine macrocrysts are rare or absent. Correlations between phlogopite and spinel compositions with modal abundances of olivine, indicate that the contrast between macrocrystic and micaceous kimberlites is primarily linked to the amount of mantle components that were incorporated into a compositionally uniform parental mafic silicate melt. We propose that assimilation of xenocrystic magnesite and incorporation of xenocrystic olivine from dunitic source rocks were the key processes that modified the parental silicate melt and created the unique hybrid (carbonate-silicate) character of kimberlites. Based on the composition of xenoliths and xenocrysts, the lithospheric mantle sampled by the South Australian kimberlites is relatively uniform, and extends to depths of 160-170 km, which is slightly below the diamond stability field. Only beneath the Eurelia area does the lithosphere appear thicker (>175 km), which is consistent with the presence of diamonds in some of the Eurelia kimberlites. (C) 2019 Elsevier B.V. All rights reserved.

Diamonds in South Australia occur in kimberlites at Eurelia (Orroroo), and in placer deposits, which include the Springfield Basin and the historic Echunga goldfield. To identify the kimberlitic and mantle sources of the placer diamonds, and to determine any possible connections between the placer diamonds and the diamonds from the Eurelia kimberlites, we examined the physical and compositional characteristics, and the mineral inclusion content of 122 diamonds from the Springfield Basin and 43 diamonds from kimberlites at Eurelia. Additional morphological data for three Echunga diamonds are also given. Most of the diamonds from the Springfield Basin are similar to the diamonds from Eurelia with respect to their crystal shapes, surface textures, and colors. The diamond populations from both areas are characterized by a high abundance of low-nitrogen (<100 ppm) diamonds with variable nitrogen aggregation states. The stable carbon isotope compositions of the Springfield Basin diamonds are similar to the Eurelia diamonds with delta(13)C values in the range -20.0 to -2.5 parts per thousand, and a mode at -6.5 parts per thousand. Ferropericlase inclusions in two diamonds from the Springfield Basin are consistent with ferropericlase-bearing mineral inclusion assemblages found in the Eurelia diamonds and indicate that part of the diamond population from both areas is of sublithospheric origin. One diamond from the Springfield Basin contained an inclusion of lherzolitic garnet. The overall similarities between the Springfield Basin and Eurelia diamonds indicates that the bulk of the Springfield Basin diamonds are derived from kimberlitic sources that are similar (or identical) to those at Eurelia. However, three diamonds from the Springfield Basin are markedly distinct. These have well-developed crystal shapes, large sizes, yellow body colorations, and brown irradiation spots. The brown irradiation spots and abrasion textures provide evidence that these diamonds are much older than the other diamonds in the Springfield Basin, and that they are derived from distal kimberlitic sources. The diamonds are most likely derived from Permian glacigene sediments and may ultimately be sourced from kimberlites on the East Antarctic craton. Abrasion textures and brown irradiation spots are also present on diamonds from Echunga. This provides a link to the three "old" Springfield Basin diamonds and other alluvial diamonds in Eastern Australia, and suggests that Permian glaciations caused a widespread distribution of diamonds over large parts of southern Australia, which at that time was part of the supercontinent Gondwana. (C) 2009 Elsevier B.V. All rights reserved.

Australia (SA), kimberlites are reported north of Adelaide, intruding the Late Neoproterozoic to Early Palaeozoic Adelaide Fold Belt (AFB) and from the Gawler Craton further west (Fig. 1).In the AFB these kimberlites occur as swarms of numerous, relatively thin (0.5-3 m) dykes and sills as well as rarer diatremes or pipes up to ~1 hectare.

Layered mafic intrusions (LMI) are large, stratified igneous bodies of great economic significance. The constitutive crustal magma chamber(s) supplied by mantle-derived magma pulses exhibit complex mineralogical and chemical layering. Current magma chamber models invoke mineral density separation, liquid density inversion, and small-scale convection, superimposed on possible magma recharge and crustal assimilation, but petrogenetic interpretation is difficult. Four new drill cores from the Upper Zone and uppermost Middle Zone of the Windimurra Igneous Complex, the largest layered mafic intrusion in Australia, sample a continuous section of similar to 1300 m including several magnetitite horizons. The Upper Zone is free of primary hydrous minerals and exhibits ore-grade Fe-enrichment up to 62.7 wt% FeOT in some sections. Relatively high Cr in magnetite at the base and sustainedly lower Cr in the remainder of the Upper Zone is consistent with injection of a single magmatic pulse at the commencement of the zone. Major and trace element analyses of representative samples from macroscopically layered horizons from throughout the Upper Zone sequence define three magmatic trends that reflect physical separation of phases within a single magma chamber. Magnetite accumulated at the base of the Upper Zone and geochemical trends in major and trace elements indicate an early formation of magnetite with a subtle effect on oxygen fugacity in the magma chamber. Bulk Nb/Ta < 14 indicate that Fe enrichment was not the result of large-scale liquid immiscibility, but is interpreted here as the normal result of an advanced tholeiitic fractionation trend. Accumulation in magnetitite horizons close to the base of the Upper Zone is interpreted to result from density separation of magnetite crystals. Field evidence indicates a density inversion in the course of magma differentiation, probably caused by ongoing crystallisation that resulted in late-stage mass movement of magnetitites and anorthositic blocks. Strontium isotope data point to a mantle-derived origin with 87Sr/86Sr[2.8Ga]similar to 0.701, indicating little, if any crustal contamination. The Windimurra Upper Zone sequence is an ideal example to study closed system magma chamber processes in an evolving, dry mafic system in the absence of or with only very limited crustal interaction.

A total of 73 peridotitic mantle xenoliths and a set of garnet and clinopyroxene xenocrysts from the recently discovered Jurassic Monk Hill kimberlite (UCO-H77A) in South Australia were used to constrain the thermal and compositional structure of the lithospheric mantle beneath the Adelaide Fold Belt, which is located at the southeastern margin of the Australian craton. The xenoliths contain mostly lherzolitic mineral assemblages (garnet + cpx + opx +/- chromite), but lack preserved olivine as a result of alteration. Pressure and temperature estimates for the suite of xenoliths (73 samples) follow an array from similar to 1 center dot 2 GPa and 650 degrees C to similar to 5 center dot 0 GPa and 1300 degrees C, which reflects the conductive geothermal gradient for this region at the time of kimberlite emplacement (Jurassic, similar to 189 Ma). Based on the projected intercept of the geotherm with the mantle adiabat, the maximum depth of the lithospheric mantle beneath the Monk Hill kimberlite is estimated to be around 160-180 km, with the base of the lithosphere lying marginally outside the diamond stability field. The results challenge previously proposed paleogeotherms for this region, which are either significantly hotter or significantly cooler. Sm-Nd isotope data for high-T garnet and clinopyroxene megacrysts define a robust isochron (189 +/- 17 Ma), which reflects the Jurassic emplacement age of the Monk Hill kimberlite. This indicates that minerals from deeper parts of the lithosphere were in isotopic equilibrium and exhumed during the kimberlite eruption from temperatures above the Sm-Nd closure temperature for garnet and clinopyroxene. Within the suite of peridotite xenoliths from Monk Hill, abundant low-T (< 1000 degrees C) xenoliths can be distinguished from a less common high-T (> 1000 degrees C) population. The high-T xenolith population is characterized by titanium-enriched compositions, suggesting that the deeper parts of the lithosphere were affected by pervasive melt metasomatism. This interpretation is supported by the trace element compositions (rare earth elements, high field strength elements) of the garnet and clinopyroxene xenocrysts.

Diamonds from Jurassic kimberlites at Eurelia, South Australia, contain coexisting inclusions of ferropericlase and MgSi-perovskite that provide evidence for their deep (>670 km) lower mantle origin. Eurelia diamonds formed from mixed carbon sources, likely including subducted carbonate, as indicated by a trend toward isotopically heavy carbon compositions (δ 13 C = 0‰) and low nitrogen concentrations (

sourceofMagneticanomaliesatFranklyn Summary An air-core drilling program commenced at the Franklyn Target on Wednesday 12 July. To date nine shallow holes have been completed for 398 metres of drilling. Most of these holes have intersected kimberlite under shallow Tertiary sediments. The information in this report that relates to Exploration Results, Mineral Resources and Ore Reserves is based on information compiled by Dr K Wills who is a Fellow of the Australasian Institute of Mining and Metallurgy and acts as a geological consultant to Flinders Diamonds Limited. Dr Wills has more than five years relevant experience in the style of mineralisation and types of deposit under consideration and consents to inclusion of the information in this report in the form and context in which it appears. He qualifies as Competent Person as defined in the 2004 Edition of the "Australasian Code for reporting of Exploration Results, Mineral Resources and Ore Reserves".