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Martian meteorites are rare; therefore, the discovery of new meteorites has the potential to significantly expand our current understanding of Mars. In this study, we describe four new shergottites, all found within the past 5 yr, in Northwest Africa (NWA): NWA 10441, NWA 10818, NWA 11043, and NWA 12335. To determine the geochemical and mineralogical composition of these new shergottites, a number of traditional and nontraditional analytical techniques were utilized, such as high-resolution X-ray computed tomography (for 3-D modal abundance determination) and electron backscattered diffraction (for identification of shock features). This enabled a comprehensive, nondestructive investigation of the in situ and bulk characteristics of these meteorites. From the results, we confirm the preliminary classifications of NWA 10441 and NWA 12335 as basaltic (diabasic), and NWA 10818 and NWA 11043 as poikilitic, shergottites. Chondrite-normalized rare earth element (REE) patterns of shergottites distinguish likely source reservoirs in the Martian mantle. NWA 10441 and NWA 12335 have bulk enriched REE patterns. NWA 10818 has an intermediate REE pattern, being slightly depleted in the light REE. Although published data for bulk rock REE in NWA 11043 indicate an enriched pattern, here we show that targeted in situ analyses of unaltered minerals reveal an intermediate REE pattern, suggesting that terrestrial weathering combined with shock processes experienced by these meteorites on ejection may affect the bulk analysis. Extensive fracturing in NWA 11043 likely acted as conduits for terrestrial alteration products. We suggest that in situ spot checking of REE in meteorites will constrain any weathering effect on the REE pattern of the bulk rock.

Recently discovered Au in boulder conglomerate between the Mesoarchaean West Pilbara superterrane basement and the overlying volcano-sedimentary stratigraphy of the Neoarchaean Fortescue Group in Western Australia has renewed comparisons with the Witwatersrand conglomerate Au deposits in South Africa. This has reignited the question of the Pilbara and Kaapvaal cratons being linked as part of the postulated Vaalbara continent during the Archaean. However, little is known about the origin of the Pilbara conglomerate Au and its host conglomerates. A detailed study is presented here on the textures, composition, and sedimentology of one newly discovered Pilbara conglomerate Au deposit at the base of the Neoarchaean Fortescue Group in the northwestern Pilbara craton. The Pilbara conglomerate Au occurrences are characteristically Ag-bearing but Hg-poor polycrystalline discoid masses overgrown by Au-poor chloritic halos, which are further enveloped by a hydrothermal alteration halo of disseminated Au within chlorite. It is argued that the Pilbara conglomerate Au represents a modified placer deposit from a primary orogenic Au source, with surface evidence for sedimentation removed by partial dissolution during later hydrothermal alteration in the host conglomerate and the crystalline basement. While the basal Fortescue Group conglomerate Au shares commonalities with the time equivalent Venterspost Conglomerate Formation, which overlies the Witwatersrand Supergroup, inconsistencies remain prior to deposition of the conglomerate sequences older than 2.7 Ga. This collectively indicates the drivers of Au metallogenesis and ultimate Au deposition in conglomerate facies were fundamentally different in the Pilbara and Kaapvaal cratons., Recently discovered Au in boulder conglomerate between the Mesoarchaean West Pilbara superterrane basement and the overlying volcano-sedimentary stratigraphy of the Neoarchaean Fortescue Group in Western Australia has renewed comparisons with the Witwatersrand conglomerate Au deposits in South Africa. This has reignited the question of the Pilbara and Kaapvaal cratons being linked as part of the postulated Vaalbara continent during the Archaean. However, little is known about the origin of the Pilbara conglomerate Au and its host conglomerates. A detailed study is presented here on the textures, composition, and sedimentology of one newly discovered Pilbara conglomerate Au deposit at the base of the Neoarchaean Fortescue Group in the northwestern Pilbara craton. The Pilbara conglomerate Au occurrences are characteristically Ag-bearing but Hg-poor polycrystalline discoid masses overgrown by Au-poor chloritic halos, which are further enveloped by a hydrothermal alteration halo of disseminated Au within chlorite. It is argued that the Pilbara conglomerate Au represents a modified placer deposit from a primary orogenic Au source, with surface evidence for sedimentation removed by partial dissolution during later hydrothermal alteration in the host conglomerate and the crystalline basement. While the basal Fortescue Group conglomerate Au shares commonalities with the time equivalent Venterspost Conglomerate Formation, which overlies the Witwatersrand Supergroup, inconsistencies remain prior to deposition of the conglomerate sequences older than 2.7 Ga. This collectively indicates the drivers of Au metallogenesis and ultimate Au deposition in conglomerate facies were fundamentally different in the Pilbara and Kaapvaal cratons.

Murrili, the third meteorite recovered by the Desert Fireball Network, is analyzed using mineralogy, oxygen isotopes, bulk chemistry, physical properties, noble gases, and cosmogenic radionuclides. The modal mineralogy, bulk chemistry, magnetic susceptibility, physical properties, and oxygen isotopes of Murrili point to it being an H5 ordinary chondrite. It is heterogeneously shocked (S2–S5), depending on the method used to determine it, although Murrili is not obviously brecciated in texture. Cosmogenic radionuclides yield a cosmic ray exposure age of 6–8 Ma, and a pre-atmospheric meteoroid size of 15–20 cm in radius. Murrili’s fall and subsequent month-long embedment into the salt lake Kati Thanda significantly altered the whole rock, evident in its Mössbauer spectra, and visual inspection of cut sections. Murrili may have experienced minor, but subsequent, impacts after its formation 4475.3 ± 2.3 Ma, which left it heterogeneously shocked.

Reduction spheroids are small-scale, biogenic, redox-controlled, metal enrichments that occur within red beds globally. This study provides the first analysis of the compositionally unique reduction spheroids of the Tumblagooda Sandstone. The work aims to account for their composition and consequently improve existing models for reduction spheroids generally, which presently fail to account for the mineralogy of the Tumblagooda Sandstone reduction spheroids. Interstitial areas between detrital grains contained in the cores of these reduction spheroids are dominated by microplaty haematite, in addition to minor amounts of svanbergite, gorceixite, anatase, uraninite, monazite and illite. The haematite-rich composition, along with an absence of base metal phases and the vanadiferous mica roscoelite, makes these reduction spheroids notable in comparison to other global reduction spheroid occurrences. Analyses of illite crystallinity provide values for samples of the Tumblagooda Sandstone host rock corresponding to heating temperatures of ca 200°C. Consequently, while Tumblagooda Sandstone reduction spheroids formed via the typical metabolic processes of dissimilatory metal-reducing bacteria, the combination of a unique mineralogy and illite crystallinity analysis provides evidence of more complex late-stage heating and reoxidation. This has not previously been recognised in other reduction spheroids and therefore expands the existing model for reduction spheroid genesis by also considering the potential for late-stage alteration. As such, future reduction spheroid studies should consider the potential impact of post-formation modification, particularly where they are to be used as evidence of ancient microbial processes; such as in the search for early evidence of life in the geological record on Earth or other planets. Additionally, because of their potential for modification, reduction spheroids serve as a record of the redox history of red beds and their study could

The poorly constrained nature of the physical transfer of sulfides along magmatic conduits has implications for the genesis and localization of mineral deposits as well as for understanding the large-scale mobility of volatiles and metals across different geochemical reservoirs. Our natural laboratory to address this topic is a sulfide-bearing ultramafic pipe emplaced in the deep crust of the Ivrea-Verbano Zone, northwest Italy. The pipe is composed of volatile-rich peridotite that contains disseminated, blebby, and semimassive sulfides enriched in nickel, copper, and platinum-group elements (PGEs). The integration of electron backscatter diffraction orientation data and three-dimensional (3-D) X-ray computed tomography analyses from this study indicated that (1) most of olivine crystallized upon emplacement of the magma; (2) the shape and texture of the intragranular sulfide blebs, principally hosted within the central portions of the pipe, reflect early sulfide saturation; and (3) marginal areas record higher strain compared to the cores of the pipes. The differences in the size distribution of the sulfide grains between the central and marginal areas of the pipe are due to magma emplacement dynamics. The larger sulfide aggregates forming the bulk of the Ni-Cu-PGE sulfide mineralization along the margins of the pipe are interpreted to have formed by coalescence of a large number of smaller sulfide droplets. The observed sulfide size distribution between the central and marginal areas of the Valmaggia pipe is principally due to the dynamics of the magma upon emplacement, and it locally records the role of water- and carbon dioxide-bearing volatiles in the physical entrainment of dense sulfide liquids. These processes provide a viable mechanism to transport sulfides enriched in chalcophile and siderophile metals from the upper mantle into the lower continental crust, where they may be available for later remobilization into ore systems that may form subsequently in

The supergiant Obuasi gold deposit is the largest deposit in the Paleoproterozoic Birimian terranes of West Africa with 62 Moz of gold (past production + resources). The deposit is hosted in the Paleoproterozoic Kumasi Group sedimentary rocks composed of carbonaceous phyllites, slates, psammites, and volcaniclastic rocks intruded by different generations of felsic dikes and granites. A three-stage deformation history is defined for the district. The D1Ob stage is weakly recorded in the sedimentary rocks as a layer-parallel fabric and indicates that bedding parallel shearing occurred during the early stage of deformation at Obuasi. The D2Ob is the main deformation stage affecting the Obuasi district and corresponds to a NW-SE shortening. Tight to isoclinal folding, as well as intense subhorizontal stretching, occurred during D2Ob, parallel with the plane of a pervasive NE-striking subvertical foliation (S2Ob). Finally, a N-S shortening event (D3Ob) refolded previously formed structures and formed a distinct ENE-striking, variably dipping S3Ob cleavage that is domainal in nature throughout the deposit. Two economic styles of mineralization occur at Obuasi and contribute equally to the gold budget. These are (1) gold-bearing sulfides, dominantly arsenopyrite, mainly disseminated in metasedimentary rocks and (2) native gold hosted in quartz veins that are as much as 25 m wide. Microstructural evidence, such as strain shadows surrounding gold-bearing arsenopyrite parallel with S2Ob, but folded by S3Ob, indicates that the sulfides were formed during D2Ob. Concentrations of as much as 700 ppm Au are present in the epitaxial growth zones of the arsenopyrite grains. Although the large mineralized quartz veins are boudinaged and refolded (indicating their formation during D2Ob), field and microanalytical observations demonstrate that the gold in the veins is hosted in microcracks controlled by D3Ob, where the S3Ob cleavage crosscuts the quartz veins in the main ore zones. Thu

The Monts de Cristal Complex of Gabon consists of several igneous bodies interpreted to be remnants of a tectonically dismembered, >100 km long and 1–3 km wide, ultramafic–mafic intrusion emplaced at 2765–2775 Ma. It is the most significant mafic–ultramafic layered complex yet identified on the Congo Craton. The complex consists largely of orthopyroxenite cumulates, with less abundant olivine-orthopyroxenite and norite, and rare harzburgite and dunite. Mineral compositions (Fo ol 84, Mg# Opx 85, An plag 60–68, Cr/Fe chromite 1–1·45) and whole-rock data suggest that the parent magma was a low-Ti basalt containing approximately 10% MgO and 0·5% TiO2. Trace element and Rb–Sr and Sm–Nd isotope data indicate the presence of an enriched component, possibly derived from crustal contamination of a magma generated in the sub-lithospheric mantle. Most rocks show a highly unusual pattern of strong Pt enrichment (10–150 ppb) at low concentrations of Pd (1–15 ppb), Au (1–2 ppb), Cu (1–20 ppm), and S (<500 ppm), suggesting that unlike in most other PGE-rich intrusions globally, platinum in the Monts de Cristal Complex is not hosted in magmatic sulfides. Synchrotron X-ray fluorescence mapping has revealed the location of buried small Pt particles, most of which are associated with As. We propose that this constitutes some of the strongest evidence yet in support of magmatic crystallization of a Pt–As phase from S-undersaturated magma.

Nodular chromite is a characteristic feature of ophiolitic podiform chromitite and there has been much debate about how it forms. Nodular chromite from the Troodos ophiolite in Cyprus is unusual in that it contains skeletal crystals enclosed within the centres of the nodules and interstitial to them. 3D imaging and electron backscatter diffraction have shown that the skeletal crystals within the nodules are single crystals that are surrounded by a rim of polycrystalline chromite. 3D analysis reveals that the skeletal crystals are partially or completely formed cage or hopper structures elongated along the <111> axis. The rim is composed of a patchwork of chromite grains that are truncated on the outer edge of the rim. The skeletal crystals formed first from a magma supersaturated in chromite and silicate minerals crystallised from melt trapped between the chromite skeletal crystal blades as they grew. The formation of skeletal crystals was followed by a crystallisation event which formed a silicate-poor rim of chromite grains around the skeletal crystals. These crystals show a weak preferred orientation related to the orientation of the core skeletal crystal implying that they formed by nucleation and growth on this core, and did not form by random mechanical aggregation. Patches of equilibrium adcumulate textures within the rim attest to in situ development of such textures. The nodules were subsequently exposed to chromite under-saturated magma resulting in dissolution, recorded by truncated grain boundaries in the rim and a smooth outer surface to the nodule. None of these stages of formation require a turbulent magma. Lastly the nodules impinged on each other causing local deformation at points of contact.

Motivated by the challenge of capturing complex hierarchical chemical detail in natural material from a wide range of applications, the Maia detector array and integrated realtime processor have been developed to acquire X-ray fluorescence images using X-ray Fluorescence Microscopy (XFM). Maia has been deployed initially at the XFM beamline at the Australian Synchrotron and more recently, demonstrating improvements in energy resolution, at the P06 beamline at Petra III in Germany. Maia captures fine detail in element images beyond 100 M pixels. It combines a large solid-angle annular energy-dispersive 384 detector array, stage encoder and flux counter inputs and dedicated FPGA-based real-time event processor with embedded spectral deconvolution. This enables high definition imaging and enhanced trace element sensitivity to capture complex trace element textures and place them in a detailed spatial context. Maia hardware and software methods provide per pixel correction for dwell, beam flux variation, dead-time and pileup, as well as off-line parallel processing for enhanced throughput. Methods have been developed for real-time display of deconvoluted SXRF element images, depth mapping of rare particles and the acquisition of 3D datasets for fluorescence tomography and XANES imaging using a spectral deconvolution method that tracks beam energy variation. © Published under licence by IOP Publishing Ltd.

Komatiite-hosted nickel sulphides from the Yilgarn Craton (Australia) consist of two main sulphide phases: pyrrhotite (Fe7S8) and pentlandite ((Fe,Ni)9S8); two minor sulphide phases: chalcopyrite (CuFeS2) and pyrite (FeS2) and trace arsenides. Samples of massive sulphides from three deposits with diverse deformation and metamorphic histories (the Silver Swan, Perseverance and Flying Fox deposits) have been studied by electron backscatter diffraction and laser ablation inductively coupled plasma mass spectrometry and nano-scale secondary ion mass spectrometry. These ore bodies were selected to investigate the relationship between microstructures and mineral trace element chemistry in three dominant sulphide species in each deposit. In all three samples, pyrrhotite preserves a strong evidence of crystal plasticity relative to both pentlandite and pyrite. The trace element composition of pyrrhotite shows significant variation in specific elements (Pb, Bi and Ag). This variation correlates spatially with intragrain pyrrhotite microstructures, such as low angle and twin boundaries. Minor signatures of crystal plasticity in pyrite and pentlandite occur in the form of rare low angle boundaries (pentlandite) and mild lattice misorientation (pyrite). Trace element compositions of pentlandite and pyrite show no correlation with microstructures.Variations in pyrrhotite are interpreted as a result of intragrain diffusion during the syn- and post-deformation history of the deposit. Intragrain diffusion can occur either due to bulk diffusion, dislocation–impurity pair diffusion, or by “pipe diffusion”, i.e. along fast diffusion pathways at high and low angle, and twin boundaries. This contribution examines three different diffusion models and suggests that dislocation–impurity pair diffusion and pipe diffusion are the most likely processes behind increased trace element concentration along the microstructures in pyrrhotite. The same phenomenon is observed in samples from three di

The Hamersley Province in Western Australia hosts large iron ore deposits. Each deposit displays various iron ore types defined by their metallurgical properties, especially in terms of porosity and mineralogy. Conventional porosity and mineralogy information on iron ore types are provided for 2D thin sections using automated image analysis with scanning electron microscopy (SEM)-based techniques combined with chemical analysis. However, these techniques cannot accurately quantify the 3D porosity. High-resolution X-ray computed tomography (HRXCT) is a non-destructive technique providing a 3D image of the sample with a resolution close to 0.5-0.7 micrometres for samples up to few centimetres in length. 3D image analysis using customised algorithms now provides accurate quantitative porosity and mineralogy of iron ore types., The Hamersley Province in Western Australia hosts large iron ore deposits. Each deposit displays various iron ore types defined by their metallurgical properties, especially in terms of porosity and mineralogy. Conventional porosity and mineralogy information on iron ore types are provided for 2D thin sections using automated image analysis with scanning electron microscopy (SEM)-based techniques combined with chemical analysis. However, these techniques cannot accurately quantify the 3D porosity. High-resolution X-ray computed tomography (HRXCT) is a non-destructive technique providing a 3D image of the sample with a resolution close to 0.5-0.7 micrometres for samples up to few centimetres in length. 3D image analysis using customised algorithms now provides accurate quantitative porosity and mineralogy of iron ore types.

X-ray fluorescence images acquired using the Maia large solid-angle detector array and integrated real-time processor on the X-ray Fluorescence Microscopy (XFM) beamline at the Australian Synchrotron capture fine detail in complex natural samples with images beyond 100M pixels. Quantitative methods permit real-time display of deconvoluted element images and for the acquisition of large area XFM images and 3D datasets for fluorescence tomography and chemical state (XANES) imaging. This paper outlines the Maia system and analytical methods and describes the use of the large detector array, with a wide range of X-ray take-off angles, to provide sensitivity to the depth of features, which is used to provide an imaging depth contrast and to determine the depth of rare precious metal particles in complex geological samples. © 2013 SPIE.

The Merensky Reef of the Bushveld Complex consists of two chromitite layers separated by coarse-grained melanorite. Microstructural analysis of the chromitite layers using electron backscatter diffraction analysis (EBSD), high-resolution X-ray microtomography and crystal size distribution analyses distinguished two populations of chromite crystals: fine-grained idiomorphic and large silicate inclusion-bearing crystals. The lower chromitite layer contains both populations, whereas the upper contains only fine idiomorphic grains. Most of the inclusion-bearing chromites have characteristic amoeboidal shapes that have been previously explained as products of sintering of pre-existing smaller idiomorphic crystals. Two possible mechanisms have been proposed for sintering of chromite crystals: (1) amalgamation of a cluster of grains with the same original crystallographic orientation; and (2) sintering of randomly orientated crystals followed by annealing into a single grain. The EBSD data show no evidence for clusters of similarly oriented grains among the idiomorphic population, nor for earlier presence of idiomorphic subgrains spatially related to inclusions, and therefore are evidence against both of the proposed sintering mechanisms. Electron backscatter diffraction analysis maps show deformation-related misorientations and curved subgrain boundaries within the large, amoeboidal crystals, and absence of such features in the fine-grained population. Microstructures observed in the lower chromitite layer are interpreted as the result of deformation during compaction of the orthocumulate layers, and constitute evidence for the formation of the amoeboid morphologies at an early stage of consolidation.An alternative model is proposed whereby silicate inclusions are incorporated during maturation and recrystallisation of initially dendritic chromite crystals, formed as a result of supercooling during emplacement of the lower chromite layer against cooler anorthosite during

Detailed imaging, bulk chemical analyses and laser ablation ICP-MS analyses were carried out on mineralised samples from the platinum-group element-bearing J-M Reef. The aims of the study were to determine which phases are the main hosts of the PGE, and to determine the textural relationships of the PGE-bearing minerals and the associated sulphides, silicates and secondary magnetites. Most of the platinum group minerals are closely associated with base metal sulphides, either included in them or located at the contacts between them and the oxides or silicates. The textures suggest that they exsolved from the base metal sulphides and it is suggested that the PGE, Ni, Cu and Te partitioned into a magmatic sulphide liquid that crystallised into base metal sulphide and that the Pt-Fe alloys and some of the Pd sulphides exsolved during desulphurisation at high temperatures. In contrast, skaergaardite (Pd-Cu alloy) and some Pd sulphides are found in association with secondary magnetite and probably formed at relatively low temperatures during a second fluid migration event. Pd/Pt ratios in the wall rocks and the reef indicate that some Pd in the reef was leached from the underlying rocks and deposited in the reef in association with the secondary magnetite., Detailed imaging, bulk chemical analyses and laser ablation ICP-MS analyses were carried out on mineralised samples from the platinum-group element-bearing J-M Reef. The aims of the study were to determine which phases are the main hosts of the PGE, and to determine the textural relationships of the PGE-bearing minerals and the associated sulphides, silicates and secondary magnetites. Most of the platinum group minerals are closely associated with base metal sulphides, either included in them or located at the contacts between them and the oxides or silicates. The textures suggest that they exsolved from the base metal sulphides and it is suggested that the PGE, Ni, Cu and Te partitioned into a magmatic sulphide liquid that crystallised into base metal sulphide and that the Pt-Fe alloys and some of the Pd sulphides exsolved during desulphurisation at high temperatures. In contrast, skaergaardite (Pd-Cu alloy) and some Pd sulphides are found in association with secondary magnetite and probably formed at relatively low temperatures during a second fluid migration event. Pd/Pt ratios in the wall rocks and the reef indicate that some Pd in the reef was leached from the underlying rocks and deposited in the reef in association with the secondary magnetite.

The supergiant Obuasi gold deposit with 62 Moz of gold (past production + resources) is hosted in the Palaeoproterozoic Kumasi Group sedimentary and volcaniclastic rocks intruded by different generations of felsic dykes and granites. A three-stage deformation history is defined for the district. Two economic styles of mineralisation contribute equally to the gold budget. These are gold-bearing sulphides, dominantly arsenopyrite, mainly disseminated in metasedimentary rocks and native gold hosted in quartz veins that are as much as 25 m wide. Microstructural evidence, such as strain shadows surrounding gold-bearing arsenopyrite parallel with S2Ob, but folded by S3Ob, indicates that the sulphides were formed during the main deformation stage D2Ob. Concentrations of as much as 700 ppm Au are present in the epitaxial growth zones of the arsenopyrite grains. Although the large mineralised quartz veins are boudinaged and refolded (indicating their formation during D2Ob), field and microanalytical observations demonstrate that the gold in the veins is hosted in microcracks controlled by D3Ob, where the S3Ob cleavage crosscuts the quartz veins in the main ore zones. Thus, these observations constitute the first evidence for multiple stages of gold deposition at the Obuasi deposit. The maximum age for the older disseminated gold event is given by the age of the granites at 2 105 ± 2 Ma, which is within error of hydrothermal rutile in the granites of 2 098 ± 7 Ma; the absolute age of the younger gold event is not known., The supergiant Obuasi gold deposit with 62 Moz of gold (past production + resources) is hosted in the Palaeoproterozoic Kumasi Group sedimentary and volcaniclastic rocks intruded by different generations of felsic dykes and granites. A three-stage deformation history is defined for the district. Two economic styles of mineralisation contribute equally to the gold budget. These are gold-bearing sulphides, dominantly arsenopyrite, mainly disseminated in metasedimentary rocks and native gold hosted in quartz veins that are as much as 25 m wide. Microstructural evidence, such as strain shadows surrounding gold-bearing arsenopyrite parallel with S2Ob, but folded by S3Ob, indicates that the sulphides were formed during the main deformation stage D2Ob. Concentrations of as much as 700 ppm Au are present in the epitaxial growth zones of the arsenopyrite grains. Although the large mineralised quartz veins are boudinaged and refolded (indicating their formation during D2Ob), field and microanalytical observations demonstrate that the gold in the veins is hosted in microcracks controlled by D3Ob, where the S3Ob cleavage crosscuts the quartz veins in the main ore zones. Thus, these observations constitute the first evidence for multiple stages of gold deposition at the Obuasi deposit. The maximum age for the older disseminated gold event is given by the age of the granites at 2 105 ± 2 Ma, which is within error of hydrothermal rutile in the granites of 2 098 ± 7 Ma; the absolute age of the younger gold event is not known.

Recent exploration in the Duketon greenstone belt, Yilgarn craton, led to the discovery of a new occurrence of high-grade Ni-PGE (platinum group element) sulphide mineralisation associated with komatiites, referred to as the Rosie Ni Prospect. The mineralisation consists predominantly of disseminated and brecciated semimassive to massive base-metal sulphide with 0.5 to 5 cm thick sulpharsenide-bearing lenses. Mineral chemistry and mineralogical studies indicate that As-rich phases, either as a melt or as primary minerals, played a critical role in collecting and concentrating PGEs from the komatiitic magma. The concentrations of trace elements within the sulpharsenides and sulphides from the different mineralisation types reflect the interaction between the silicate and sulphide liquids. The smaller the proportion of the sulpharsenide relative to sulphide in the rock is, the higher the PGE concentration in the sulpharsenide will be. In-situ Se analysis of the base-metal sulphides from the different ore types indicates that Se concentrations in pentlandite and pyrrhotite from sulpharsenide-rich lenses are an order of magnitude higher than those of sulphides found in As-poor samples. The particular As-Se enrichment may have been triggered by the erosion and assimilation of black-shale sulphidic sediments enriched in organic matter by the komatiitic magma flows, leading to the formation of immiscible S-As-rich melt where PGEs partitioned preferentially into the As-rich phases., Recent exploration in the Duketon greenstone belt, Yilgarn craton, led to the discovery of a new occurrence of high-grade Ni-PGE (platinum group element) sulphide mineralisation associated with komatiites, referred to as the Rosie Ni Prospect. The mineralisation consists predominantly of disseminated and brecciated semimassive to massive base-metal sulphide with 0.5 to 5 cm thick sulpharsenide-bearing lenses. Mineral chemistry and mineralogical studies indicate that As-rich phases, either as a melt or as primary minerals, played a critical role in collecting and concentrating PGEs from the komatiitic magma. The concentrations of trace elements within the sulpharsenides and sulphides from the different mineralisation types reflect the interaction between the silicate and sulphide liquids. The smaller the proportion of the sulpharsenide relative to sulphide in the rock is, the higher the PGE concentration in the sulpharsenide will be. In-situ Se analysis of the base-metal sulphides from the different ore types indicates that Se concentrations in pentlandite and pyrrhotite from sulpharsenide-rich lenses are an order of magnitude higher than those of sulphides found in As-poor samples. The particular As-Se enrichment may have been triggered by the erosion and assimilation of black-shale sulphidic sediments enriched in organic matter by the komatiitic magma flows, leading to the formation of immiscible S-As-rich melt where PGEs partitioned preferentially into the As-rich phases.

High-resolution X-ray computed tomography (HRXCT) is a nondestructive technique that allows exploration of the three-dimensional distribution of minerals and pore space in natural and synthetic rock samples. Recent technological developments allow the characterisation of samples up to few cm diameter at a resolution down to 0.7 micrometres. This, combined with the development of dedicated workflows, algorithms and softwares, is opening new doors for the quantitative three-dimensional characterisation of ores at the sample scale. When combined with three-dimensional image analysis, HRXCT provides quantitative three-dimensional mineralogical and textural measurements (volume, shape, three-dimensional relationship) that are impossible to assess accurately by any other method. The principles of HRXCT are described and dedicated methodologies presented from data acquisition through to quantitative three-dimensional measurements. These methodologies are applied to Ni-Cu-PGE ore samples but are suitable for a range of geological materials. The combination of HRXCT with quantitative three-dimensional image analysis applied to geological materials hosting ore deposits provides a better understanding of ore mineralogy, ore-forming processes and parameters required for mineral or metallurgical processing, with benefit for both academic studies and mineral industry applications. (Authors.), High-resolution X-ray computed tomography (HRXCT) is a nondestructive technique that allows exploration of the three-dimensional distribution of minerals and pore space in natural and synthetic rock samples. Recent technological developments allow the characterisation of samples up to few cm diameter at a resolution down to 0.7 micrometres. This, combined with the development of dedicated workflows, algorithms and softwares, is opening new doors for the quantitative three-dimensional characterisation of ores at the sample scale. When combined with three-dimensional image analysis, HRXCT provides quantitative three-dimensional mineralogical and textural measurements (volume, shape, three-dimensional relationship) that are impossible to assess accurately by any other method. The principles of HRXCT are described and dedicated methodologies presented from data acquisition through to quantitative three-dimensional measurements. These methodologies are applied to Ni-Cu-PGE ore samples but are suitable for a range of geological materials. The combination of HRXCT with quantitative three-dimensional image analysis applied to geological materials hosting ore deposits provides a better understanding of ore mineralogy, ore-forming processes and parameters required for mineral or metallurgical processing, with benefit for both academic studies and mineral industry applications. (Authors.)

The deposit is a high-tonnage magmatic Ni-Cu-PGE mineralisation which developed as a stratiform layer within the main cumulus sequence of a layered intrusion. The ore zone comprises a 20-200 m thick interval containing up to 5 wt% of disseminated sulphides within a sequence of mainly unaltered harzburgites and orthopyroxenites. The orthopyroxene- dominated sequence lies between the dominantly olivine-rich cumulates that make up the lower half of the intrusion and the gabbroite cumulates that make up the upper half. Consistent patterns of sulphide tenor involving gradually decreasing Ni from more than 20 to about 10 wt%, nearly constant Cu and gradually decreasing PGEs with cyclically variable Pt/Pd ratios are found within the ore zone across the entire intrusion and display little lateral variability. The position of the sulphide mineralisation envelope migrates to higher stratigraphic levels from the northern to the southern margin of the intrusion, and maximum grades and thicknesses correlate with the maximum thickness of orthopyroxene-bearing cumulates asymmetrically disposed towards the southern margin. Ni tenors of the sulphides are in the range 15-15 wt%, Cu tenors are typically 5-8 wt% and PGE tenors range from less than 100 ppb to greater than 10 ppm for Pt and Pd. The features of the deposit are attributed to mixing of an initially S-undersaturated, moderately Ni-enriched resident magma with a relatively low Ni, PGE-depleted significantly lower temperature replenishing magma charged with suspended sulphide liquid droplets., The deposit is a high-tonnage magmatic Ni-Cu-PGE mineralisation which developed as a stratiform layer within the main cumulus sequence of a layered intrusion. The ore zone comprises a 20-200 m thick interval containing up to 5 wt% of disseminated sulphides within a sequence of mainly unaltered harzburgites and orthopyroxenites. The orthopyroxene- dominated sequence lies between the dominantly olivine-rich cumulates that make up the lower half of the intrusion and the gabbroite cumulates that make up the upper half. Consistent patterns of sulphide tenor involving gradually decreasing Ni from more than 20 to about 10 wt%, nearly constant Cu and gradually decreasing PGEs with cyclically variable Pt/Pd ratios are found within the ore zone across the entire intrusion and display little lateral variability. The position of the sulphide mineralisation envelope migrates to higher stratigraphic levels from the northern to the southern margin of the intrusion, and maximum grades and thicknesses correlate with the maximum thickness of orthopyroxene-bearing cumulates asymmetrically disposed towards the southern margin. Ni tenors of the sulphides are in the range 15-15 wt%, Cu tenors are typically 5-8 wt% and PGE tenors range from less than 100 ppb to greater than 10 ppm for Pt and Pd. The features of the deposit are attributed to mixing of an initially S-undersaturated, moderately Ni-enriched resident magma with a relatively low Ni, PGE-depleted significantly lower temperature replenishing magma charged with suspended sulphide liquid droplets.