Margaux Le Vaillant

Commonwealth Scientific and Industrial Research Organisation

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Stephen J. Barnes

Australian Resources Research Centre

Bélinda Godel

Commonwealth Scientific and Industrial Research Organisation

Marco L. Fiorentini

University of Western Australia

Louise Schoneveld

Australian Resources Research Centre

David R. Mole

Geoscience Australia

Mark A. Pearce

Commonwealth Scientific and Industrial Research Organisation

David Fox

Mineral Resources

Michael Verrall

Australian Resources Research Centre

Sam Spinks

Australian Resources Research Centre

Giada Iacono–Marziano

Institut des Sciences de la Terre

Cooperative Institutions

Commonwealth Scientific and Industrial Research Organisation

Mineral Resources

Australian Resources Research Centre

University of Western Australia

ARC Centre of Excellence for Core to Crust Fluid Systems

Target (United States)

Curtin University

Health Sciences and Nutrition

Australian Research Council

Chinese Academy of Sciences

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Oxide-Sulfide-Melt-Bubble Interactions in Spinel-Rich Taxitic Rocks of the Norilsk-Talnakh Intrusions, Polar Siberia

Economic Geology (2020)

Louise Schoneveld Stephen J. Barnes Bélinda Godel Margaux Le Vaillant Marina A. Yudovskaya

Abstract Oxide-rimmed, spherical structures interpreted as former gas bubbles have been discovered within a chromitiferous taxitic lithology of the Norilsk-Talnakh intrusions. These rocks are represented by variable grain size, presence of reworked country-rock xenoliths and millimeter- to centimeter-scale irregular spinel-rich aggregates, patches, or disrupted seams and stringers. They contain spherical and subspherical agglomerations that we interpret as amygdules, partially or completely filled with low-temperature hydrothermal minerals and locally with magmatic phases including sulfide globules. In places these amygdules form clusters that are interpreted as former bubble foams. The wetting relationships visible between vapor bubbles, silicate melt, sulfide liquid, and oxide were investigated in detail using 3-D μX-ray tomography and detailed 2-D X-ray fluorescence maps. They also reveal short-range spatial variability in silicate and oxide minerals, reflecting small-scale advanced fractionation of silicate melt. Three possible mechanisms are considered for the formation of these bubble-spinel foams: (1) the abundant spinel allows for the in situ nucleation of vapor bubbles, (2) the vapor bubbles ascend through the magma and collect spinel, or (3) the vapor bubbles cause rapid nucleation of chromite within these layers. Although none of these mechanisms can be exclusively ruled out, the texture and chemistry of the Norilsk-Talnakh chromitiferous taxitic lithology is most indicative of in situ nucleation of vapor bubbles on spinel surfaces (i.e., mechanism 1).

Lithology

Stishovite

10.5382/econgeo.4748

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Citations (26)

The genesis of Carlow Castle: A unique Australian orogenic Cu-Co-Au deposit in the Archean Pilbara Craton

ASEG Extended Abstracts (2019)

David Fox Sam Spinks Mark A. Pearce Margaux Le Vaillant Robert Thorne

SummaryCarlow Castle is a Cu-Co-Au deposit situated within the western Pilbara Craton of Western Australia. Whilst Carlow Castle is the oldest discovered copper deposit in the Pilbara region, having been initially discovered in 1882, no detailed study of the ore mineralisation has ever been undertaken. After being long abandoned, a recent drilling campaign through 2018 uncovered an economically significant and geologically complex system of Cu-Co-Au mineralisation with a current resource estimate for Carlow Castle of 7.7Mt @ 1.06g/t Au, 0.51% Cu, and 0.08% Co, making it one of Australia’s most significant Cu-Co-Au deposits. This mineralisation was analysed using a variety of geochemical and mineralogical techniques in order to provide the first constraint on its genesis. This analysis suggests that Carlow Castle is a hydrothermal Cu-Co-Au deposit, with mineralisation hosted in sulphide-rich quartz veins throughout a pervasively chloritised shear zone in an Archaean mafic volcano-sedimentary sequence. Within these ore veins, the sulphide mineralogy is dominated by pyrite (FeS2), chalcopyrite (CuFeS2), chalcocite (Cu2S), and cobaltite (CoAsS). Here we present the findings of the first detailed study on the nature of the Cu-Co-Au mineralisation at Carlow Castle and propose an orogenic model for the genesis of this unique deposit. It is proposed that the orogenic event that gave rise to Carlow Castle is related to the initial assembly of the Pilbara Craton during the Archean.

Covellite

Chalcocite

Ore genesis

10.1080/22020586.2019.12073037

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Poikilitic Textures, Heteradcumulates and Zoned Orthopyroxenes in the Ntaka Ultramafic Complex, Tanzania: Implications for Crystallization Mechanisms of Oikocrysts

Journal of Petrology (2016)

Stephen J. Barnes David R. Mole Margaux Le Vaillant M. J. Campbell Michael Verrall

The late Proterozoic Ntaka Ultramafic Complex is a body of dominantly pyroxenitic cumulate rocks containing cyclic alternations of olivine–orthopyroxene cumulates. Chemical zoning in the pyroxenes has been imaged at 25–40 µm resolution using desktop microbeam X-ray fluorescence mapping followed up with laser ablation–inductively coupled plasma mass spectrometry analysis for minor and trace elements on selected samples. Poikilitic and granular harzburgites are finely intermingled, in some cases on a centimetre scale in the same thin section. Poikilitic varieties display spectacular textures, ranging from isolated equant orthopyroxene oikocrysts within olivine-rich heteradcumulate harzburgites to rocks composed entirely of interlocking centimetre-sized anhedral orthopyroxene oikocrysts containing sharply bounded idiomorphic Cr-enriched cores. The poikilitic harzburgites are interlayered with cumulate pyroxenites in which orthopyroxene grains show a variety of zoning patterns: Cr-rich cores similar to those in the oikocrysts; sharply bounded oscillatory zoned cores; and reverse zoning with Cr-poor cores and Cr-enriched rims. A further variation is the presence of a mingled harzburgite lithology in which dunite or poikilitic harzburgite is invaded on a centimetre scale by diffuse vein networks or patches of coarse orthopyroxenite. This range of textures and lithologies attests to a more complex set of processes than implied by the standard cumulus theory model in which oikocrysts are considered to have crystallized from intercumulus liquid within a permeable crystal mush. A range of hypotheses is proposed, including infiltration metasomatism of original olivine cumulates by migrating orthopyroxene-saturated pore fluid; however, the textural relationships, whole-rock chemistry and Cr zoning within the grains can best be explained by a model in which the orthopyroxene oikocrysts form in part or whole as mechanically accumulated cumulus grains. The complexity of zoning patterns is attributed to stirring of entrained olivine and orthopyroxene crystals within a heterogeneous flowing crystal mush, where the transporting magma has a wide range of silica contents owing to poorly stirred incorporation of siliceous country-rock material. The Cr-rich orthopyroxenite component grew from Si-enriched chromite-saturated magma. Mingled lithologies developed after accumulation as a result of percolation and infiltration metasomatism by Si-enriched liquid derived by melting of xenoliths within the crystal pile. The model may be more generally applicable: dunite–harzburgite cycles, common in many layered intrusions, may reflect variable degrees of contamination rather than cycles of fractional crystallization and replenishment.

Ultramafic rock

Lithology

Metasomatism

Fractional crystallization (geology)

10.1093/petrology/egw036

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Citations (64)

Extent and survival of zoned pyroxene within intrusions hosting magmatic sulfides: Implications for zoned pyroxene as a prospectivity indicator

Mineralium Deposita (2024)

Louise Schoneveld Stephen J. Barnes Kirsi Luolavirta Siyu Hu Michael Verrall

Abstract Chromium-zoning patterns in pyroxene from the economically significant Ni-Cu sulfide deposits at Nova-Bollinger (Western Australia) and Kevitsa (Northern Finland) were investigated using XRF mapping, automated mineralogy, and EPMA analyses. At Nova-Bollinger, complex Cr-zoning patterns are found widely throughout the cumulus orthopyroxene and clinopyroxene within the Lower Intrusion, a small chonolith that hosts the vast extent of the sulfide mineralisation. Cumulus pyroxenes with visible sector and abrupt zonation patterns have been found up to 150 m vertically away from the massive sulfide ore. Complex zoning patterns are observed throughout the Kevitsa intrusion, in the form of strong oscillatory zoning in cumulus clinopyroxene and sector zoning in idiomorphic orthopyroxene oikocrysts. Kevitsa pyroxenes show varying degrees of hydration, leading to epitaxial replacement by amphibole. Cr zonation is visible through the early stages of this alteration, with preservation enabled by the presence of Cr-rich epitaxial amphibole; however, the remnant zoning is lost as the amphibole alteration progresses. Results suggest that Cr zonation in pyroxene may be an effective indicator of dynamic recharged conduits and therefore an indicator of favourable conditions for metal enriched magmatic sulfide ore formation. Such indicators have significant vertical extent from the ore body and can survive partial alteration, which makes them a useful tool for prospectivity assessment of drilled intrusions. Furthermore, our data show that there is potential for complexly zoned pyroxene to be used as an ex-situ prospectivity indicator in glacial till.

Pyroxene

Prospectivity mapping

Amphibole

10.1007/s00126-024-01292-1

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Citations (3)

New observations by X-ray fluorescencemicroscopy provide insights for the origin ofAguablanca sulfide-matrix breccias in SW Spain

Macla: revista de la Sociedad Española de Mineralogía (2019)

Sarah‐Jane Barnes Rubén Piña García Margaux Le Vaillant Lorena Ortega Menor Rosario Lunar Hernández

Sulfide-matrix breccia ores are common features of deposits hosted within mafic conduit-style intrusions. They account for a large proportion of Ni-Cu sulfiderich ores in a number of deposits including the sub-layer and offset dyke deposits at Sudbury (Lightfoot, 2016), deep portions of the feeder dyke system and margins of the Ovoid and Eastern Deeps orebodies at Voisey’s Bay, (Barnes et al., 2017), Nebo-Babel (Seat et al., 2007) and particularly in the subject of this contribution, the Aguablanca deposit in SW Spain (Pina, 2019). Genetic interpretations of sulfide matrix breccias have fallen into four main categories (Barnes et al. 2019): tectonic “durchbewegung” origins, upward emplacement of sulfide-rich slurries due to late stage compression in intrusive complexes, downward emplacement as sulfiderich gravity flows during backflow in sill-dyke complexes or into footwall offset dykes, and gravity-driven downward percolation of sulfide liquid through the matrix of original silicate-matrix intrusion breccias. This study presents microbeam XRF mapping to reveal petrographic features, textures and chemical zoning patterns in Aguablanca sulfide-matrix breccia ores at a scale of mm-cm.

Breccia

Stockwork

Sill

Source

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Rapid mineralogical and geochemical characterisation of the Fisher East nickel sulphide prospects, Western Australia, using hyperspectral and pXRF data

Ore Geology Reviews (2017)

Lauren L. Burley Stephen J. Barnes Carsten Laukamp David R. Mole Margaux Le Vaillant

Mineral exploration

Felsic

10.1016/j.oregeorev.2017.04.032

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Citations (19)

3D textural evidence for the formation of ultra-high tenor precious metal bearing sulphide microdroplets in offset reefs: An extreme example from the Platinova Reef, Skaergaard Intrusion, Greenland

Lithos (2016)

David A. Holwell Stephen J. Barnes Margaux Le Vaillant Reid R. Keays Louise Fisher

Chromitite

Breccia

10.1016/j.lithos.2016.03.020

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Citations (22)

Platinum-group element and gold contents of arsenide and sulfarsenide minerals associated with Ni and Au deposits in Archean greenstone belts

Mineralogical Magazine (2018)

Margaux Le Vaillant Stephen J. Barnes Marco L. Fiorentini Sarah‐Jane Barnes Adam Bath

ABSTRACT Post-magmatic alteration of certain magmatic Ni sulfide ores in Western Australia, the Miitel deposit and the Sarah's Find prospect, produced Ni–As–PGE haloes around massive sulfides. A study of the composition of arsenide grains from these hydrothermal haloes, along with arsenides from various magmatic and hydrothermal mineralized environments in other localities, was conducted in order to compare their composition, and assess their potential use as indicator minerals for exploration vectoring, as well as to gain knowledge on their crystallization history. Concentrations in trace elements such as platinum-group elements (PGEs), Au and other metals was obtained by laser ablation inductively coupled plasma mass spectroscopy analyses. Results show that variations in PGEs and Au compositions can be related to the magmatic vs. hydrothermal origin of the grains; and to their provenance from deposits enriched in either Ni, Au or both. Magmatic NiCoFe sulfarsenides have strongly correlated, high IPGE (Os, Ir, Ru, Rh) contents up to 100 ppm Ir, compared with maximum values in hydrothermal sulfarsenides of ~1 ppm. Gold in hydrothermal sulfarsenides from Au-mineralized ultramafic rocks extends up to 500 ppm, with typical values of 3–30 ppm; similar values are also found in nickeline (also called niccolite). These results suggest that nickel arsenides could potentially be used as indicator minerals for nickel and gold exploration. Trace-element contents of arsenide grains in shear zones could be used to deduce the presence of Ni or Au mineralization upstream in the fluid pathway.

Platinum group

Arsenide

Ultramafic rock

Greenstone belt

Rare-earth element

Trace element

10.1180/minmag.2017.081.100

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Citations (19)

The Occurrence and Origin of Pentlandite-Chalcopyrite-Pyrrhotite Loop Textures in Magmatic Ni-Cu Sulfide Ores

Economic Geology (2020)

Stephen J. Barnes Valentina Taranovic Louise Schoneveld Eduardo T. Mansur Margaux Le Vaillant

Abstract Pentlandite is the dominant Ni-hosting ore mineral in most magmatic sulfide deposits and has conventionally been interpreted as being entirely generated by solid-state exsolution from the high-temperature monosulfide solid solution (MSS) (Fe,Ni)1–xS. This process gives rise to the development of loops of pentlandite surrounding pyrrhotite grains. Recently it has been recognized that not all pentlandite forms by exsolution. Some may form as the result of peritectic reaction between early formed MSS and residual Ni-Cu–rich sulfide liquid during differentiation of the sulfide melt, such that at least some loop textures may be genuinely magmatic in origin. Testing this hypothesis involved microbeam X-ray fluorescence mapping to image pentlandite-pyrrhotite-chalcopyrite intergrowths from a range of different deposits. These deposits exemplify slowly cooled magmatic environments (Nova, Western Australia; Sudbury, Canada), globular ores from shallow-level intrusions (Norilsk, Siberia), extrusive komatiite-hosted ores from low and high metamorphic-grade terranes, and a number of other deposits. Our approach was complemented by laser ablation-inductively coupled plasma-mass spectrometry analysis of palladium in varying textural types of pentlandite within these deposits. Pentlandite forming coarse granular aggregates, together with loop-textured pentlandite where chalcopyrite also forms part of the loop framework, consistently has the highest Pd content compared with pentlandite clearly exsolved as lamellae from MSS or pyrrhotite. This is consistent with much of granular and loop pentlandite being formed by peritectic reaction between Pd-rich residual sulfide liquid and early crystallized MSS, rather than forming entirely by subsolidus grain boundary exsolution from MSS, as has hitherto been assumed. The wide range of Pd contents in pentlandite in individual samples reflects a continuum of processes between peritectic reaction and grain boundary exsolution. Textures in metamorphically recrystallized ores are distinctly different from loop-textured ores, implying that loop textures cannot be regenerated (except in special circumstances) by metamorphic recrystallization of original magmatic-textured ores. The presence of loop textures can therefore be taken as evidence of a lack of penetrative deformation and remobilization at submagmatic temperatures, a conclusion of particular significance to the interpretation of the Nova deposit as having formed synchronously with the peak of regional deformation at temperatures within the sulfide melting range.

Pentlandite

10.5382/econgeo.4757

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Citations (37)

Sulfide and Fe-Ti-P liquid immiscibility in the Ni-Cu-Co ovoid deposit of the Voisey’s Bay complex, Labrador, Canada

Mineralium Deposita (2024)

Stefano Caruso Margaux Le Vaillant Stephen J. Barnes Ville J. Virtanen Giada Iacono–Marziano

Abstract In the Voisey’s Bay complex, sulfide-matrix breccias developed through the percolation of dense sulfide melt, leading to the displacement of the silicate melt within partially molten silicate-matrix breccias. In these sulfide matrix-breccias, hydrous silicate rims are commonly present at the interface between the sulfide matrix and the silicate framework. Multiple lines of evidence support a magmatic origin of these hornblende-biotite rims, which was largely coeval with the emplacement of the sulfide melt in the magmatic breccias. The formation of the hornblende-biotite rims required the addition of alkalis and water that could not have entirely been sourced from either the sulfide melt or the silicate framework. Through the integration of compositional maps with major and trace element analyses of the main accessory minerals, we propose that the critical components required for the development of the hydrous silicate rims in sulfide-matrix breccias originated from an immiscible Fe-Ti-P melt. Distinct textural and compositional features of apatite, hercynite, ilmenite and magnetite support the presence of small amounts of Fe-Ti-P melt in the sulfide melt. This Fe-Ti-P melt likely formed through melt immiscibility in the early stages of the development of the Voisey’s Bay complex, and was transported in the magma conduits together with the sulfide melt.

Breccia

Matrix (chemical analysis)

10.1007/s00126-024-01319-7

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