Feldspathic lherzolite and harzburgite are reported here for the first time in the southern Lac des Iles Complex; an 2.69-Ga arcuate mafic intrusion that hosts world-class Pd mineralization within varitextured and brecciated gabbronoritic rocks. The olivine-bearing rocks (Mg#75.9–80.8) are medium- to coarse-grained, weakly to strongly serpentinized, and bordered by variably altered norite. They possess relatively high Al2O3 contents (4.8–10.3 wt.

The Mount Ayliff Complex comprises five cognate mafic–ultramafic bodies emplaced along the southern margin of the Kaapvaal Craton. This study examines the Ingeli and Horseshoe lobes and assesses their magmatic sulfide prospectivity with respect to the Insizwa lobe, which hosts massive sulfides at its Waterfall Gorge occurrence. The Ingeli lobe consists of 465 m of olivine–chromite cumulates overlain by 340 m of (olivine-)gabbronorite, while the Horseshoe lobe consists of 45 m of olivine gabbronorite overlain by 5 m of gabbro. The Ingeli lobe possesses sparsely disseminated sulfides at its mafic–ultramafic transition, whereas disseminated sulfides are present throughout the Horseshoe lobe. A petrogenetic model is proposed, where magma accumulated and fractionated nickeliferous olivine and chromite in an upper-crustal staging chamber hosted by Proterozoic basement rocks. Magma then ascended and deposited olivine–chromite cumulates at the level of the complex. Prolonged magma flux in the staging chamber facilitated the assimilation of basement rocks, triggering sulfide saturation and the crystallization of Ni-poor olivine. Contaminated magma then ascended and interacted with pre-existing cumulates, depositing sulfide melt that may have backflowed as magmatic activity waned. Basaltic magma then flowed over the ultramafic cumulates, depositing disseminated sulfides whilst undergoing closed-system fractionation. Basal depressions and underlying feeder structures are the most prospective locations for magmatic sulfide mineralization.

The ~3033 Ma Stella layered intrusion is hosted by supracrustal rocks of the Kraaipan–Madibe greenstone terrane, South Africa. The studied portion of the intrusion consists mainly of magnetite leucogabbro and magnetite anorthosite, as well as several massive magnetite layers. The intrusion hosts a laterally continuous, ~60-m-thick, PGE mineralized interval, with total resources amounting to 108t Pt + Pd + Au, constituting one of the oldest known PGE reef-style mineralizations on Earth. The richest reef, with a grade of 4.4 ppm Pt+Pd over a width of 5–8 m, occurs in semi-massive magnetitite. It is suggested that the mineralized oxide and silicate layers formed through a combination of primary magmatic, late magmatic, and hydrothermal processes, including granular flow and phase sorting of a magnetite- and sulfide-bearing gabbroic crystal mush that crystallized from a tholeiitic basalt, as well as remobilization of S and metals by late magmatic and hydrothermal fluids that led to crystallization of platinum-group minerals.

Layered intrusions are fossilized natural laboratories that historically have constrained many fundamental principles of igneous petrology. Layered intrusions are typically stratiform, usually sill-like bodies of cumulate rocks, at least a few hundred metres to as much as 10 km thick, characterized by the presence of a variety of different types of layering over a range of length scales. They are the solid record of crystallization, differentiation and solidification processes of mainly basaltic magmas. The importance of layered intrusions also lies in hosting a significant proportion of the world's known reserves and resources of important critical metals: particularly, the majority of the global resource of platinum-group elements (PGE), chromium (Cr) and vanadium (V) and also very large resources of nickel (Ni), copper (Cu) and cobalt (Co). This paper summarizes the progress that has been made in the study of layered intrusions during the last three decades. The progress is marked by a number of novel observations from layered intrusions. Among them are: (1) draping of igneous layering over a few-km-high sloping step in the chamber floor; (2) development of igneous layering on the overturned to undercutting portions of a chamber floor; (3) magmatic karstification of the floor cumulates, (4) existence of threedimensional framework of crystals in (oxide) cumulates; (5) systematic variations in dihedral angles between touching grains, and other microtextural features; (6) Cr-rich structures at the base of magnetitite layers; (7) coexistence of melt inclusions of contrasting composition in minerals; (8) thermal and chemical histories recorded by plagioclase; (9) textural and chemical features of minerals revealed by X-ray microscopy, (10) intrusion-scale to mineral-scale isotopic heterogeneity; (11) out-of-sequence zircon ages; and (12) skeletal/dendritic growth of minerals revealed by minor element zonation. The progress is also evident from development of several new concepts and refinement of some established ones. These include: (1) time and length scales in layered intrusion processes, (2) catastrophically fast growth of magma chambers, (3) out-of-sequence emplacement in layered intrusions, (4) large-scale slumping and mineral sorting in layered intrusions, (5) production of monomineralic cumulates from single phase-saturated melts, (6) origin of non-cotectic cumulate by in situ growth, (7) the arrival of new phases on the liquidus, (8) inward propagation of solidification fronts, (9) mushy and hard chamber floor, (10) absence of roof sequences due to their disruption, (11) basal reversals and chilled margins, (12) adcumulus growth theory, (13) compositionally stratified magma chambers, (14) melt-sediment interactions during magma chamber growth, (15) lateral reactive infiltration in a crystal mush, (16) reactions involving conjugate immiscible liquids in crystal mushes, and (17) constraints on subsolidus processes from non-traditional Fe-Mg-Cr stable isotopes. Finally, we show that the major controversies regarding layered intrusions currently revolve around whether: (a) the microstructure of igneous rocks are primary or secondary , (b) compaction in layered in-trusions is pervasive or non-existent (c) large, long-lived and entirely-molten magma chambers exist or not. The review shows that layered intrusions provide ground-truth information on the processes of magma crystalliza-tion, differentiation , solidification in crustal chambers as well as on mechanisms of ore-forming elements concentration into economically viable mineral deposits. We propose a few lines for future research that may potentially raise igneous petrology to a new level of understanding of the processes that govern the evolution of terrestrial magmatic systems.

The Flatreef of the northern limb of the Bushveld Complex is a world-class platinum-group element (PGE) deposit representing the down-dip extension of the Platreef. Exploration drilling in the central portion of the project area intersected a particularly thick PGE-mineralised portion of the Flatreef exposed in drill core TMT006 and its two deflections, containing 4.5 ppm PGE (Pt + Pd + Rh + Au) over 90 m and ~ 3.7 ppm PGE over 150 m. Data obtained using whole rock geochemical analysis, field emission scanning electron microscopy, micro X-ray fluorescence and X-ray computed tomography indicate that the PGE are hosted by, or are spatially closely associated with, disseminated sulfides that occur interstitial to the cumulus silicate minerals. PGE grades show a broad, albeit irregular trend of progressive downward decrease, whereas most metal ratios (Cu/Ni, Pt/Rh, Cu/Pd and, to a lesser degree, Pt/Pd) remain broadly constant throughout the 90 m main ore zone. These features are interpreted to reflect two stages of ore formation: (i) hydrodynamic concentration of sulfidic ultramafic crystal mushes and (ii) localised downward percolation of sulfide melt in response to fluidisation of the cumulate mush caused by infiltration of ascending magmatic or crustal fluids. The model is consistent with the close spatial association of the sulfides with interstitial plagioclase as well as accessory phlogopite, quartz, apatite and rutile, whereas cumulus orthopyroxene is largely free of sulfide.

This issue contains abstracts from a variant of the biennial International Platinum Symposium that was held virtually in May 2022. This symposium di ff ered from previous events in that the organising committee, keynote speakers, and symposium presenters were made up entirely of students and early-career researchers. The event was organised to facilitate dis-cussions, networking, and collaboration amongst bud-ding researchers, something that has been hampered throughout the COVID-19 pandemic. The organising committee and reviewers are thanked for their contributions to this abstract volume, and hopefully these studies become full journal articles in the future. The presented research encompassed traditional meet-ing themes of igneous petrology and economic geology pertaining to ma fi c-ultrama fi c rocks, as well as novel themes of non-conventional platinum-group element repositories and the applications of machine learning in mineral exploration. Several studies focussed on the world-class Bushveld Complex of South Africa, particularly the complex ’ s northern limb which has become one of the world ’ s most exciting exploration frontiers for platinum-group elements, nickel, copper, chromium, and vanadium. The mobility of magmatic sulphide liquids intrans-crustalsystemsalsofeaturesinseveralstudies,and more speci fi cally, the roles in which volatile phases may play to facilitate the migration of immiscible sulphide liquid. Lastly, someabstracts focus on petrogenetic aspects of established ma fi c-ultrama fi c complexes, such as the Noril ’ sk-Talnakh, Coldwell, and Stillwater complexes. Not only did our symposium celebrate the academic achievements of early-career researchers in our fi eld, but it also celebrated diversity and inclusivity. Amongst the presenters, six continents and thirty countries were represented. Approximately 73% of participants were early-career researchers, ranging from those currently studying for bachelors ’ degrees to those completing post-doctoral studies. One third of participants were female, a statistic that extends to the keynote speakers and organising committee. I am very pleased to be part of a The northern limb of the Bushveld Complex, South Africa, is globally recognised as one of the world ’ s largest resources of platinum-group elements (PGEs). These metals are essential to the growth of sustainable and environmentally friendly technologies, particularly within the electric vehicle industry; a market which is expected to grow exponentially in the coming decades. The PGE-Ni – Cu – Co mineralisation is hosted within the Platreef, a magmatic package thought to be analo-gous to the Critical Zone of the western and eastern limbs. It has PGE grades comparable with the Merensky Reef, commonly 3 – 4 g/t (Pt + Pd + Rh + Au), but up to 15 g/t, over a much greater thickness, along with sub-stantially more associated Ni – Cu – Co in the form of magmatic sulphides. The Platreef is thought to have formed from discrete magmatic units or sills, each with their own variable metal budgets and thicknesses. Previous workers have divided the Platreef into three to four discrete magmatic units at various locations in the southern sector of the northern limb. At Turfspruit, this has been achieved via examining changing mineralogy, Pt:Pd and Ni:Cu ratios [1], and at Townlands, via trace element and S isotope analysis [2]. In the central sector, north of Sandsloot, the Platreef has been divided into three units based on mineralogy and grade [3]. Better understanding the stratigraphy of the Platreef, both in terms of along strike and down-dip variations, is vital for developing genetic and exploration models, which will in turn aid in the prediction of the locations of economically important horizons within the intrusion. In study, the Exploration geoscience practitioners use spatial data to derive insights into the spatial distribution and other characteristics of target geological objects (e.g., an orebody). However, interpretation of large datasets by human interpreters is often highly subjective. This study tests the possibility of using data science techniques on complex and very large databases in order to produce more systematic and robust results. The stratigraphy of the Rustenburg Layered Suite in the northern limb is di ff erent from that of the eastern and western limbs south of the Thabazimbi-Murchi-son Lineament. In the northern limb, the Lower Zone occurs as chonolith-like bodies that intruded into Archaean granite-gneisses and metasedimentary rocks of the Transvaal Supergroup [1]. These bodies host Cr and Ni – Cu – PGE sulphide deposits, whereas the Lower Zone in the rest of the complex is barren. The Uitloop Lower Zone intrusion is exposed as two separate bodies (Uitloop I and Uitloop II) which lie along the eastern periphery of the northern limb. Nickel sulphide mineralisation in Lower Zone serpentinised ultrama fi c rocks as well as PGE – Cu – Ni mineralisation in Critical Zone lithologies are targets of the recent exploration campaign by Lesego Platinum Uitloop (Pty) Ltd on the Uitloop II body [2] (Figure 1). An extension of the Platreef intrusion, nestled between metasedimentary packages of the Transvaal Supergroup, has been recognised in southeastern part of the Uitloop II body. styles of PGE – Cu-Ni mineralisation are hosted in the Critical sequences: basal the intrusions and within the footwall and (ii) reef-style (strata-bound) PGE horizon the upper part of the intrusions The northern limb of the Bushveld Complex, South Africa, contains various mineralised horizons, one of which is the Flatreef. The Flatreef is the correlative equivalent of the Upper Critical Zone in the eastern and western limbs of the Bushveld Complex. In the northern limb, the Flatreef is emplaced in direct contact with the Transvaal Supergroup sediments and shows signi fi cant petrological and geochemical evidence for magma-footwall interaction. Ultrama fi c rocks in the Lower Flatreef comprise distinctive hybrid lithologies that form the Footwall Assimilation Zone (FAZ) and are associated with fragments of partially melted sedimentary xenoliths. In this study, we investigate the petrography and geochemistry of the various mineral assemblages that are associated with dolomitic xenoliths with the aim of providing further understanding of the processes of carbonate assimilation that occurred. We have identi fi ed di ff erent types of mineral assemblages in the hybrid units by means of phase relations, mineral chemistry, and whole-rock chemistry. These mineral assemblages are derived from the interaction of dolomitic material with either a primitive melt or a di ff erentiated melt. Samples containing olivine (Fo 84 – 86 ) + clinopyroxene (19 – 35 mol-% Ca-Tscher-mak) and intercumulus spinel were classed as being derived from the interaction of a carbonate melt (CaO-, CO2-rich) with primitive melt. Samples that were derived from an interaction of a dolomitic xenolith with di ff erentiated melt contained olivine The Bushveld Complex is an economically important and scienti fi cally fascinating intrusion due to the thick chromitite layers contained in its Critical Zone (Figure 1). These laterally extensive chromitite layers are mined for chromium and, for some layers, platinum-group elements. They are subdivided into Lower Group, Middle Group and Upper Group chromitites (LG, MG and UG respectively) of which the LG and MG chromitites were analysed in this study. Field observations from open pit and underground exposures in the eastern and western Lobes of the Bushveld Complex were used to describe the chromitite morphology on a regional scale. The studied chromitite layers are traceable over long distances and may occur as one, two or three chromitite layers at distinct locations, with several changes in the number of their layers and their thickness occurring along a distance of a few kilometres. This is best understood as a structure of regionally bifurcating chromitites with small-scale bifurcations being visible even at the scale of individual outcrops. This study reports evidence of magmatic erosion of fl oor cumulates, as several chromitite layers transgressing their footwall have been observed. Among these features are large inclusions of orthopyroxenite in chromitite that are partly attached to the footwall rocks, suggesting that they are erosional remnants of these rocks. Fur-thermore, two potholes, roughly circular depressions in the chamber fl oor, were documented, which reveal transgressive relations of chromitites with their footwall rocks. To explain the regional bifurcations, we propose a model of chromitite formation involving the in fl ux of several pulses of superheated melt. Each pulse caused thermochemical erosion of the chamber fl oor, as shown by transgressive relationships between chromitites and their Platinum-group element (PGE) mineralisation in the northern limb [1] of the Bushveld Complex is located in disseminated base metal sulphides and subordinate chromitites hosted in ma fi c-ultrama fi c cumulates. Visual logging to di ff erentiate between and mineralised rocks interpretation of the technique samples. re (Pt, and (Co, and (Drenthe, determine a of The orebodies of Norilsk contain some of the world ’ s most valuable accumulations of Ni, Cu and platinum-group elements (PGEs). The PGEs occur throughout the deposit, but are particularly abundant within the upper ‘ taxitic ’ zones (i.e. zones with variable grain size distributions, reworked country rock xenoliths, and mm to cm-scale irregular spinel-rich aggregates that occur as patches or disrupted seams and strin-gers). These taxitic gabbrodolerites contain ore-grade PGE concentrations alongside 2 – 3 wt-% magmatic sulphides, associations that are referred to as low-sul-phide PGE-rich mineralisation. A key feature in these units are the spherical and sub-spherical features that we interpret as former gas bubbles, partially or entirely with low-temperatu

Arc volcanism is a key process influencing Earth’s climate, continental growth, and the formation of mineral deposits. Therefore in this contribution, we have compiled whole-rock geochemistry of frontal arc and rear-/back-arc basalts, crustal thickness, and slab parameters (e.g., slab age, slab dip, and convergence velocity) from global convergent margins to investigate the factors controlling along-arc and across-arc variations. Crustal thickness or lithosphere thickness plays a dominant role in elements immobile in aqueous fluids (e.g., Zr/Yb and Nb/Yb). The effect is imposed through mantle partial melting for both frontal arc and rear-/back-arc rocks. Slab thermal structure also affects these immobile elements and gives rise to along-arc variations. Both slab sediment and altered oceanic crust can melt especially in hot subduction zones which yield across-arc variations (e.g., Nd isotope). Aqueous fluids (represented by element ratios such as Ba/Nb and Sr/Nd) also show across-arc variations as they decrease toward rear-/back-arc. This meanwhile decreases mantle wedge melting as rear-/back-arcs show higher Zr/Yb and Nb/Yb. However, no correlations between aqueous fluids and slab parameters suggest aqueous fluids in arc rocks are controlled by complex processes. We summarize factors such as slab alteration, slab dehydration, and mantle metasomatism might impose an effect on the content of fluid mobile elements in arc rocks.

The compositions of resistant indicator minerals are diagnostic of their original host environment. They may be used to fingerprint different types of mineral deposit as well as vector towards them. We have characterised the composition of apatite and Fe–Ti oxides in variably mineralised mafic–ultramafic rock units of the Montagnais Sill Complex in the Labrador Trough to assess their suitability for vectoring towards magmatic sulphide occurrences. Two broad types of apatite were identified: (i) fluoro- to hydroxy-apatite (Cl/(Cl+F) < 0.2); and (ii) chloro- to hydroxy-apatite (Cl/(Cl+F) > 0.5). The former reflects variable degrees of degassing and Cl loss during Rayleigh fractionation and is not indicative of Ni–Cu mineralisation or host rock. The latter exists only in sulphidic olivine cumulate units and thus may be used to vector towards similar rock types in the Labrador Trough. Ilmenite is the dominant oxide, except for the upper parts of differentiated gabbroic sills in which titanomagnetite is dominant. Magnetite occurs only as a secondary phase in serpentinised olivine cumulates and is not discriminative for magmatic sulphides. Ilmenite and titanomagnetite in the sulphidic olivine-bearing units have characteristically high Mg (∼1000–10 000 ppm), Cr (∼100–1000 ppm), and Ni (∼10–1000 ppm) concentrations relative to those from other rock units. Their composition is consistent with Fe–Ti oxides derived from evolved sulphide melts in ultramafic-hosted Ni–Cu–(PGE) sulphide deposits and thus may be used to vector towards similar magmatic sulphide occurrences in the Labrador Trough.

We have combined high-resolution element maps of the Merensky Reef and Boulder Bed of the western Bushveld Complex with compositional and microtextural data of plagioclase grains in associated anorthosite units. We describe several key petrographic observations from these units that we feel are crucial to further our understanding of their formation. All analysed cumulus plagioclase grains show some degree of reverse zoning. However, grains directly underlying the Merensky Reef and the boulders of the Boulder Bed show the most pronounced reverse zoning. We observed no microscopic evidence for deformation in the anorthosite units. We propose that a combination of chamber replenishment, partial melting of proto-cumulates, static recrystallisation, and reactive flow was responsible for the formation of these enigmatic rocks.

The Boulder Bed of the western Bushveld Complex is an m-scale unit of mottled anorthosite containing sub-circular dm-scale ‘boulders’ of pyroxenite, harzburgite, or norite. To better understand this unit, we have combined high-resolution element mapping and electron back-scatter diffraction analysis with electron-probe microanalysis of plagioclase crystals from the boulders and their host anorthosite. Several key features pertinent to understanding the formation of this unit have been described, including (i) anhedral olivine is concentrated at the base of boulders, whereas clinopyroxene is concentrated towards the tops; (ii) the upward decrease in grain size through the boulders; (iii) the occurrence of chromite along the base of boulders and seldom along the top; (iv) the presence of strongly reverse-zoned cumulus plagioclase (An 75-95 ) in the so-called marginal zone underlying boulders; (v) the absence of deformation in the host anorthosite but the prevalence of intra-crystalline deformation in intercumulus pyroxene of the marginal zone; (vi) that amphibole (± apatite ± phlogopite) partially line the base of some boulders; (vii) traces of pyrrhotite (± pentlandite ± chalcopyrite) occur within the lower halves of boulders. We propose that the boulders formed in response to the disaggregation of a locally PGE-rich pyroxenite, triggered by heat- and (or) volatile-induced partial melting of the noritic host rocks. Several of the petrologic features arose from the reaction between the boulders and the noritic partial melt prior to late-stage viscous compaction.

Arc volcanism is a key process influencing Earth’s climate, continental growth, and the formation of mineral deposits. In this contribution, we have compiled whole-rock geochemistry of arc basalt, crustal thickness, and slab parameters ( e.g. slab age, slab dip, convergence velocity) from global convergent margins to investigate the factors controlling along-arc and across-arc variation. Previous work has shown that crustal thickness and slab thermal structure play an important role in along-arc chemical variations. However, the role that slab-derived aqueous fluids play in controlling the along-arc variability of erupted melts is commonly overlooked, despite their apparent influence on across-arc chemical variations, i.e. lower Sr/Nd and Ba/Nb ratios are observed in rear-/back-arc regions where lower volumes of slab fluids are released. From our database, we demonstrate that slab-derived aqueous fluids and crustal thickness of the overriding plate control the intensity of mantle melting, by affecting the wet solidus and mantle thermal structure respectively. Furthermore, both the contribution of slab-derived aqueous fluids and the slab thermal parameter correlates with, and are likely controlled by the crustal thickness of the overlying plate. As a result, this enhances the correlation between crustal thickness and trace element indices of mantle melting ( e.g. , Zr/Yb, Nb/Yb). The connection between slab fluid contribution, crustal thickness and the extent of mantle melting is supported by observations of the pre-Pliocene arc in western Panama. From the early Cretaceous to the late Miocene, crustal thickening caused a reduction in the flux of aqueous fluids liberated from the subducting plate, which along with the effect of thickened crust on mantle wedge thermal structure, give rise to lower degrees of mantle melting.

The Palaeopmterozoic Huckleberry Cu-Ni-(PGE) prospect in the Labrador Trough, northern Quebec, represents a similar to 400-m-thick, out-of-sequence sill complex that comprises a similar to 200-m-thick glomeroporphyritic gabbro, intruded in its centre by a similar to 200-m-thick differentiated gabbro-peridotite sill and in its gabbroic footwall, several thinner (<30 m) ultramafic sills. Globular sulphides are present at the base of the sill complex, whereas disseminated to net-textured sulphides occur in the ultramafic units (Cu/Ni = 0.1-0.8) as well as their gabbroic footwall (Cu/Ni = 1-3). The glomeroporphyritic gabbro sill stack (MgO similar to 4 wt%, TiO2 similar to 0.6 wt%, Na2O + K2O similar to 2-3%, Eu/Eu* similar to 1.2, An(plg) similar to 70-60) comprises several sills characterised by sharp changes in size and abundance of plagioclase glomerocrysts. We hypothesise that the glomerocrysts represent remobilised crystal mushes that were dislodged from a floatation cumulate in a staging chamber during episodic expulsion of magma. In the central gabbm-peridotite sill, mineral compositions (FOolv similar to 75-75, Mg#(opx) approximate to 78-68, An(plg) approximate to 78-70) and whole-rock data (MgO approximate to 22 - 27%, TiO2 approximate to 0.4%) suggest that the parent magma was an olivine-saturated basalt containing 8-9 wt% MgO. Whole-rock geochemical data further suggests that the parent magmas did not undergo any significant contamination (La/Sm-N < 2, S/Se < 4000). The Cu/Pd values of ultramafic units (>10,000) suggest sulphide melt saturation was attained before their final emplacement in magma feeder conduits or staging chambers at relatively low R factors (1000-5000). Downward decreasing concentrations of chalcophile elements in the drill cores suggests that sulphide melt percolated downward from the ultramafic cumulate units into the glomeroporphyritic gabbro footwall. We propose that the footwall ultramafic sills represent downward injections of olivine and sulphide melt from the overlying gabbro-peridotite sill, which mechanically concentrated high volumes of sulphide in narrow sills.

ABSTRACT We have characterized the distribution of noble metals among six styles of magmatic sulfide mineralization in the Montagnais Sill Complex of the Labrador Trough in northern Québec using optical and electron microscopy combined with laser ablation-inductively coupled plasma-mass spectrometry trace element analysis of sulfides. The principal sulfide minerals include pyrrhotite, chalcopyrite, and pentlandite with accessory sphalerite and sulfarsenides. In addition, cubanite, troilite, and mackinawite are present in ultramafic-hosted assemblages. The precious metal mineral assemblages are dominated by tellurides, Ag-rich gold, and sperrylite which generally occur at the margins of sulfides. Few iridium-group platinum group element- and Rh-bearing grains were identified and mass-balance calculations show that these elements are generally hosted in pyrrhotite and pentlandite. Virtually all Pt and Au are hosted in precious metal grains, whereas Pd is distributed between precious metal grains and pentlandite. Where present, sulfarsenides are a key host of iridium-group platinum group element, Rh, Pd, Te, and Au. The presence of troilite, cubanite, and mackinawite and the absence of pentlandite exsolution lamellae in the ultramafic-hosted sulfides indicates an initial sulfide melt with a high metal/S ratio. Sulfarsenides present among globular sulfide assemblages derive from an immiscible As-rich melt that exsolved from the sulfide melt in response to the assimilation of the As-bearing floor rocks. In this study, the composition of sulfides is consistent with those derived from Ni-Cu-dominated deposits and not platinum group element-dominated deposits.

In the present paper, we have compiled data on 565 layered and differentiated igneous intrusions globally, documenting their (i) location, (ii) age, (iii) size, (iv) geotectonic setting, (v) putative parent magma(s), (vi) crystallisation sequence, and (vii) mineral deposits. Most studied intrusions occur in Russia (98), Australia (72), Canada (52), Finland (37), South Africa (38), China (33), and Brazil (31). Notable clusters of: (i) Archaean in-trusions (-15%) include those of the McFaulds Lake Area (commonly known as the Ring of Fire, Canada), Pilbara and Yilgarn cratons (Australia), and Barberton (South Africa); (ii) Proterozoic intrusions (-56%) include those of the Giles Event and Halls Creek Orogen (Australia), Kaapvaal craton and its margin (South Africa and Botswana), Kola and Karelia cratons (Finland and Russia), and Midcontinent Rift (Canada and USA); and (iii) Phanerozoic intrusions (-29%) include those of eastern Greenland, the Central Asian Orogenic Belt (China and Mongolia) and Emeishan large igneous province (China). Throughout geological time, the occurrence of many layered intrusions correlate broadly with the amalgamation and break-up of supercontinents, yet the size and mineral inventory of intrusions shows no obvious secular changes. In our compilation, 337 intrusions possess one or more types of mineral occurrences, including: (i) 107 with stratiform PGE reef-style mineralisation, (ii) 138 with Ni-Cu-(PGE) contact-style mineralisation, (iii) 74 with stratiform Fe-Ti-V-(P) horizons, and (iv) >= 35 with chromitite seams. Sill-like or chonolithic differentiated in-trusions present in extensional tectonic settings and spanning geological time are most prospective for Ni-Cu-(PGE) mineralisation. In contrast, PGE reef-style deposits are most prevalent in larger, commonly lopolithic intrusions that are generally >1 Ga in age (-75%). Stratiform Fe-Ti-V-(P) horizons are most common in the central and upper portions of larger layered intrusions, occurring in the Archaean and Phanerozoic. Approxi-mately 80% of intrusions with chromitite seams are older than 1 Ga and > 50% of them also contain PGE reefs. Based on the distribution of layered intrusions in relatively well explored terranes (e.g., Finland, South Africa, Western Australia), we propose that many layered intrusions remain to be discovered on Earth, particularly in poorly explored and relatively inaccessible regions of Africa, Australia, Russia, Greenland, Antarctica, South America, and northern Canada.

The interaction between mafic-ultramafic magma and crustal sulfide is considered a key process in the formation of magmatic Ni-Cu-platinum group element (PGE) sulfide deposits. Integrated S/Se and multiple sulfur isotope studies are the most robust in constraining the role of crustal sulfur during ore genesis. In the present study, we report the first integrated S/Se and multiple sulfur isotope study of magmatic sulfide occurrences in the Labrador Trough, namely, on the recently discovered Idefix PGE-Cu and Huckleberry Cu-Ni-(PGE) prospects. Whole-rock and in situ S/Se values (similar to 810-3115) of magmatic sulfides and their host rocks are consistent with S loss during postmagmatic hydrothermal alteration, negating their use in interpreting the origin of S. Values of Delta S-33 similar to 0 indicate no record of the assimilation of Archaean sulfur. Disseminated (-0.5 to +2.5 parts per thousand) and globular (3.0-4.5 parts per thousand) sulfides at Idefix as well as globular sulfides (2.1-9.6 parts per thousand) at Huckleberry have d34S values greater than the accepted mantle range, suggesting that crustal S played a role in the formation of these sulfides. In contrast, disseminated and net-textured sulfides at Huckleberry have variable delta S-34 values (-4.6 to +3.2 parts per thousand) that are mostly within the accepted mantle range, excluding one anomalous sample that records relatively higher delta S-34 values (11.9-15.0 parts per thousand). It is proposed that sulfide melt segregated in response to the addition of small proportions of crustal S prior to the final emplacement of the host intrusions, i.e., in a feeder conduit or staging chamber. Isotopic exchange between the sulfide melt and silicate magma has diluted and, in places, eradicated a crustal delta S-34 signature.

Bushveld anorthosites commonly contain the so-called “mottles” comprising irregular, typically centimetric domains of oikocrystic pyroxene or olivine enclosing small, embayed plagioclase grains. The mottles were traditionally interpreted to result from solidification of trapped intercumulus liquid or via in situ crystallisation at the top of the crystal mush. Here, we present microtextural and compositional data of a mottle to place further constraints on the formation of anorthosite layers. Element maps generated by scanning electron microscopy reveal that plagioclase within and around the mottle has markedly elevated An contents (up to An 95 ) relative to the host anorthosite and is strongly reversely zoned. Other unusual features, some of which were reported previously, include a halo of sub-vertically oriented, acicular phlogopite around the mottle, elevated contents of disseminated sulfides, and relatively evolved yet Ni-rich olivine (Fo 71–75 , 3000 ppm Ni). These features are interpreted to result from reactive porous flow of hot, acidic fluid enriched in nickel and sulfur through proto norite. The fluids dissolved mafic minerals and leached alkalis from the outer rims of plagioclase grains. Reconnaissance studies suggest that reversed zoning of plagioclase is a common feature in Bushveld norite and anorthosite. This implies that reactive porous flow could have been far more pervasive than currently realised and that Bushveld anorthosite layers formed through recrystallisation of norites.

The Labrador Trough in northern Quebec is currently the focus of ongoing exploration for magmatic Ni-Cu-platinum group element (PGE) sulphide ores. This geological belt hosts voluminous basaltic sills and lavas of the Montagnais Sill Complex, which are locally emplaced among sulphidic metasedimentary country rocks. The recently discovered Idefix PGE-Cu prospect represents a stack of gabbroic sills that host stratiform patchy disseminated to net-textured sulphides (0.2–0.4 g/t PGE+Au) over a thickness of ∼20 m, for up to 7 km. In addition, globular sulphides occur at the base of the sill, adjacent to the metasedimentary floor rocks. Whole-rock and PGE geochemistry indicates that the sills share a common source and that the extracted magma underwent significant fractionation before emplacement in the upper crust. To develop the PGE-enriched ores, sulphide melt saturation was attained before final emplacement, peaking at R factors of ∼10 000. Globular sulphides entrained along the base of the sill ingested crustally derived arsenic and were ultimately preserved in the advancing chilled margin.

Mafic-ultramafic rocks of the Montagnais Sill Complex (MSC) are actively being explored for magmatic Ni-Cu-PGE sulfide deposits. The MSC possesses several attributes that are key for the formation of orthomagmatic deposits, but exploration remains in its infancy due to a lack in understanding of the metallotects operating in this region. The Huckleberry Cu-Ni-PGE Prospect (157 samples average 1.0% Cu, 0.2% Ni and 0.74 g/t PGE+Au) hosts multiple sulfide-rich intrusives, making it an ideal location to study the prospectivity of sills that comprise the MSC. Using a series of numerical models contrasted against measured whole-rock and mineral compositions, we constrain the petrogenesis of the mafic-ultramafic rocks, highlighting its influence on the nature of sulfide ore.

"Magmatic Ni–Cu–PGE sulphide potential of the New Québec Orogen, Northern Québec." Applied Earth Science, 128(2), pp. 60–61

Granite stocks across southwest England have played a significant role in the genesis of world-class polymetallic mineralisation. This study presents the first geochemical and geochronological dataset for the composite Crownhill stock, placing it into the newly emerging geochronological framework for the Cornubian Batholith. The Crownhill stock comprises kaolinised two-mica granite in the north and variably-grained biotite granite in the south that encloses pods of tourmaline granite. All granites are peraluminous (A/CNK > 1) and the biotite (BG) and tourmaline granites (TG) are related by the replacement of biotite by tourmaline and secondary muscovitization. Integrated LA-ICP-MS and CA-ID-TIMS geochronology indicate two-phase magmatism, where zircon cores yield 288.9 +/- 5 Ma and 286.4 +/- 5 Ma and rims yield 277.74 +/- 0.33 Ma and 278.35 +/- 0.35 Ma, for BG and TG respectively. The zircon cores crystallised during initial magmatism, that formed the two-mica and muscovite granites (e.g., Carnmenellis, Bodmin, and Hemerdon) exposed in the north of the Crownhill stock. The zircon rims crystallised from the second phase of magmatism that formed the biotite and tourmaline granites (e.g., Dartmoor and St. Austell). This indicates that zircon crystals were assimilated from older two-mica and muscovite granites and entrained in the second phase of magmatism. Trace element compositions of zircon grains suggest that the rims crystallised from a more evolved magma, where zircon grains hosted in tourmaline granites are broadly more evolved than those from biotite granites. This is likely a result of elevated volatile concentrations delaying zircon fractionation.Trace cassiterite has been observed within interstitial tourmaline in the tourmaline granites, where crystallisation was likely induced by the removal of boron through tourmaline fractionation, coupled with the addition of Sn sourced from the alteration of biotite. The assimilation and overprinting of older granites by second-stage magmatism suggests that the initial phase of magmatism could be more widespread than initially thought and that tourmalinisation may have been responsible for leaching and remobilising Sn from the biotite-rich granites. (C) 2019 Elsevier B.V. All rights reserved.