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Sarah-jane Barnes - One of the best experts on this subject based on the ideXlab platform.

  • the role of black shales as a source of sulfur and semimetals in magmatic nickel copper deposits example from the partridge river intrusion duluth complex minnesota usa
    Ore Geology Reviews, 2017
    Co-Authors: Nadege Samalens, Sarah-jane Barnes, E W Sawyer
    Abstract:

    The basal unit of the Duluth Complex (Minnesota, USA) contains Ni-Cu Sulfide deposits. The S in these is thought to be derived from a Sulfide-rich black shale unit known as the Bedded Pyrrhotite Unit, a stratigraphic unit within the Virginia Formation host rocks. However, the mechanism of S transfer has not been clearly established. In order to understand how this transfer occurs we have undertaken petrography and whole rock geochemistry of the rocks from the contact aureole and the basal unit. In the contact aureole, the Bedded Pyrrhotite Unit consists of a very fine-grained graphitic shales with thin beds of Sulfides consisting of pyrrhotite with minor chalcopyrite (< 1%). The basal unit contains numerous Bedded Pyrrhotite Unit xenoliths surrounded by norites. The Bedded Pyrrhotite Unit xenoliths are partially melted and the Sulfide beds are disrupted. Leucosomes are present and these contain blebs of Sulfides consisting of pyrrhotite, pentlandite, cubanite and chalcopyrite. In the mafic rocks surrounding the xenoliths small patches of Sulfide-bearing leucosome are found. In addition to being rich in S the Bedded Pyrrhotite Unit is rich in As 38 ppm, Sb 4.1 ppm and Bi 0.6 ppm and Te 0.4 ppm and has high δ34S values. The δ34S, As/S, Bi/S and Sb/S decrease with distance from the xenoliths. Similarly, the Ni/S, Cu/S, Se/S and (platinum-group elements)/S ratios are higher in the mafic rocks and increase with distance from the xenoliths. Our model proposes that droplets of Sulfide melt derived from the Bedded Pyrrhotite Unit xenoliths were entrained in the anatectic silicate melt of the xenoliths and transferred to the mafic magma. The Sulfide droplets equilibrated with the mafic magma. Those close to the xenoliths did not have the opportunity to react with a large quantity of magma, and hence their composition is similar to the Sulfides of the Bedded Pyrrhotite Unit, i.e., rich in semimetals and poor in Ni, Cu and PGE. Farther away from the xenoliths, the Sulfide droplets could have reacted with more magma, and the composition of these Sulfides approach that of Sulfides derived mainly from mafic magma.

  • the timing and formation of platinum group minerals from the creighton ni cu platinum group element Sulfide deposit sudbury canada early crystallization of pge rich sulfarsenides
    Economic Geology, 2010
    Co-Authors: Sarah A S Dare, Sarah-jane Barnes, Hazel Margaret Prichard, Peter Charles Fisher
    Abstract:

    Platinum-group elements (PGE) are typically hosted in base metal Sulfides and by platinum-group minerals (PGM) in Ni-Cu-PGE Sulfide deposits. At Sudbury, it appears that the majority of PGE are hosted in PGM. In order to understand why this is the case we have investigated the origin of PGM from the 402 trough ore-bodies of the Creighton deposit located on the South Range of Sudbury. These predominantly pyrrhotite-rich Sulfides, with low (Pt + Pd)/(Os + Ir + Ru + Rh) whole-rock ratios, represent cumulates of monoSulfide solid solution (MSS) that crystallized early from the Sulfide melt, collected in troughs and embayments at the base of the Sudbury Igneous Complex, and formed small pendants of ore in the footwall country rock. The majority of PGE (Ir, Rh, Pt ± Os, Ru) show a stronger affinity for the sulfarsenide phases than the cocrystallizing Sulfide phases which are strongly depleted in these PGE. The precious metal mineralogy is dominated by PGE sulfarsenides (86%) with subordinate sperrylite (PtAs2: 9%), michenerite (PdBiTe: 5%), and electrum (AgAu2: 0.1%). These discrete minerals are predominantly hosted within pyrrhotite and pentlandite except, however, a large proportion of michenerite is hosted either entirely by silicates and/or juxtaposed against silicates. The PGE sulfarsenides are euhedrally zoned with an irarsite (IrAsS) core, an outer layer of hollingworthite (RhAsS), and a PGE-rich Ni cobaltite rim (CoAsS). Rhenium Sulfides, some of which are Os bearing, are documented for the first time at Sudbury. Platinum-group minerals may crystallize directly from Sulfide melt, form by exsolution during cooling of the base metal Sulfides or recrystallize from them during metamorphism. We propose that zoned PGE sulfarsenides and sperrylite crystallized from a Sulfide melt at high temperatures (1,200°–900°C) and were subsequently surrounded by MSS cumulates, even by disseminated Sulfides, that crystallized from the now Ir, Rh, Pt ± Os, Ru-depleted immiscible Sulfide liquid. The base metal Sulfides recrystallized with secondary hydrosilicates at a late magmatic and/or hydrothermal stage (<540°C) at which time michenerite formed. The magmatic zoning of the PGE sulfarsenides was preserved during later deformation in shear zones but these PGM were corroded, fractured, and juxtaposed against silicates.

  • The Kabanga Ni Sulfide deposits, Tanzania: II. Chalcophile and siderophile element geochemistry
    Mineralium Deposita, 2010
    Co-Authors: Wolfgang D. Maier, Sarah-jane Barnes
    Abstract:

    The Kabanga deposit constitutes one of the most significant Ni Sulfide discoveries of the last two decades (indicated mineral resource 23 Mt of ore at 2.64% Ni, inferred resource 28.5 Mt at 2.7% Ni, November 2008). The Sulfides are hosted by predominantly harzburgitic and orthopyroxenitic intrusions that crystallized from magnesian basaltic and picritic magmas. However, compared with other Sulfide ores that segregated from such magmas (e.g., Jinchuan, Pechenga, Raglan), most Kabanga Sulfides have low Ni (

  • The Kabanga Ni Sulfide deposit, Tanzania: I. Geology, petrography, silicate rock geochemistry, and sulfur and oxygen isotopes
    Mineralium Deposita, 2010
    Co-Authors: Wolfgang D. Maier, Sarah-jane Barnes, Chusi Li, Arindam Sarkar, Ed Ripley, Tim Livesey
    Abstract:

    The Kabanga Ni Sulfide deposit represents one of the most significant Ni Sulfide discoveries of the last two decades, with current indicated mineral resources of 23.23 Mt at 2.64% Ni and inferred mineral resources of 28.5 Mt at 2.7% Ni (Nov. 2008). The Sulfides are hosted by a suite of ∼1.4 Ga ultramafic–mafic, sill-like, and chonolithic intrusions that form part of the approximately 500 km long Kabanga–Musongati–Kapalagulu igneous belt in Tanzania and Burundi. The igneous bodies are up to about 1 km thick and 4 km long. They crystallized from several compositionally distinct magma pulses emplaced into Sulfide-bearing pelitic schists. The first magma was a siliceous high-magnesium basalt (approximately 13.3% MgO) that formed a network of fine-grained acicular-textured gabbronoritic and orthopyroxenitic sills (Mg# opx 78–88, An plag 45–88). The magma was highly enriched in incompatible trace elements (LILE, LREE) and had pronounced negative Nb and Ta anomalies and heavy O isotopic signatures (δ^18O +6 to +8). These compositional features are consistent with about 20% contamination of primitive picrite with the sulfidic pelitic schists. Subsequent magma pulses were more magnesian (approximately 14–15% MgO) and less contaminated (e.g., δ^18O +5.1 to +6.6). They injected into the earlier sills, resulting in the formation of medium-grained harzburgites, olivine orthopyroxenites and orthopyroxenites (Fo 83–89, Mg# _opx 86–89), and magmatic breccias consisting of gabbronorite–orthopyroxenite fragments within an olivine-rich matrix. All intrusions in the Kabanga area contain abundant Sulfides (pyrrhotite, pentlandite, and minor chalcopyrite and pyrite). In the lower portions and the immediate footwall of two of the intrusions, namely Kabanga North and Kabanga Main, there occur numerous layers, lenses, and veins of massive Ni Sulfides reaching a thickness of several meters. The largest amount of high grade, massive Sulfide occurs in the smallest intrusion (Kabanga North). The Sulfides have heavy S isotopic signatures (δ^34S wr = +10 to +24) that broadly overlap with those of the country rock Sulfides, consistent with significant assimilation of external sulfur from the Karagwe–Ankolean sedimentary sequence. However, based partly on the relatively homogenous distribution of disseminated Sulfides in many of the intrusive rocks, we propose that the Kabanga magmas reached Sulfide saturation prior to final emplacement, in staging chambers or feeder conduits, followed by entrainment of the Sulfides during continued magma ascent. Oxygen isotope data indicate that the mode of Sulfide assimilation changed with time. The heavy δ^18O ratios of the early magmas are consistent with ingestion of the sedimentary country rocks in bulk. The relatively light δ^18O ratios of the later magmas indicate less bulk assimilation of the country rocks, but in addition the magmas selectively assimilated additional S, possibly through devolatization of the country rocks or through cannibalization of magmatic Sulfides deposited in the conduits by preceding magma surges. The intrusions were tilted at ca. 1.37 Ga, during the Kibaran orogeny and associated synkinematic granite plutonism. This caused solid-state mobilization of ductile Sulfides into shear zones, notably along the base of the intrusions where Sulfide-hornfels breccias and lenses and layers of massive Sulfides may reach a thickness of >10 m and can extend for several 10 s to >100 m away from the intrusions. These horizons represent an important exploration target for additional nickel Sulfide deposits.

Mostafa Fayek - One of the best experts on this subject based on the ideXlab platform.

  • extreme sulfur isotope fractionation in the late devonian dry creek volcanogenic massive Sulfide deposit central alaska
    Chemical Geology, 2019
    Co-Authors: John F. Slack, Ian W Ridley, Cynthia Duselbacon, Joel W Desormeau, Jahandar Ramezani, Wayne C Shanks, Mostafa Fayek
    Abstract:

    Abstract The Dry Creek Zn-Pb-Cu-Ag-Au volcanogenic massive Sulfide (VMS) deposit, in east-central Alaska, occurs in a Late Devonian sequence of peralkaline rhyolite tuff, minor graphitic argillite, and local peralkaline quartz-porphyry rhyolite intrusions. Principal mineralized facies are semi-massive and massive Sulfide in variably silicified and graphitic rhyolite tuff, massive Sulfide in graphitic argillite, disseminated Sulfides in graphitic and non-graphitic rhyolite tuff, and vein-hosted Sulfides in a subvolcanic, peralkaline quartz-porphyry intrusion. In situ analysis of the sulfur isotope composition of Sulfide minerals from all facies of the deposit shows a total range in δ34S values from −48.0 to 23.1‰. This remarkable 71.1‰ variation is more than twice the largest range known for Sulfides in nearly all individual VMS deposits, both modern and ancient, which typically is High-precision CA-ID-TIMS U-Pb geochronology of zircons from a synvolcanic peralkaline quartz porphyry intrusion yields a weighted mean 206Pb/238U date of 363.02 ± 0.43 Ma (2σ total uncertainty). This date indicates that the formation of graphitic and sulfidic sediments at Dry Creek, and contemporaneous VMS mineralization, occurred at least 3.6 m.y. before, and hence are unrelated to, widespread black shale deposition during the Hangenberg Event at ca. 359 Ma.

  • microscale sulfur isotopic compositions of Sulfide minerals from the jinding zn pb deposit yunnan province southwest china
    Gondwana Research, 2014
    Co-Authors: Yongyong Tang, Mostafa Fayek, Xianwu Bi, Ruizhong Hu, Liyan Wu, Caixia Feng, Xinsong Wang
    Abstract:

    Abstract The Jinding Zn–Pb deposit, located in the Lanping basin in Northwest Yunnan Province, is the largest Zn–Pb deposit in China, and also probably the youngest sediment-hosted super giant Zn–Pb deposit in the world. Its genesis differs from the well-known major types of sediment-hosted Zn–Pb deposits. Based on mineral paragenesis and textures, there are two stages of mineralization: stage 1 that is typically characterized by fine-grained Sulfide minerals (galena, sphalerite, pyrite and marcasite) disseminated in sandstones of the Lower Cretaceous Jingxing Formation (K1j), and massive Sulfides in limestone breccias of the Paleocene Yunlong Formation (E1y); and stage 2 which mainly occurs as coarse-grained galena veins crosscutting stage 1 Sulfides, and minor amounts of colloform sphalerite intergrown with galena. In situ sulfur isotopic analyses of galena, sphalerite and pyrite were determined by secondary ion mass spectrometry (SIMS), and showed highly variable δ34S values (− 42.1‰–7.7‰) of different ore types. Stage 1 mineralization has δ34S values from − 42.1‰ to − 10.2‰ with the majority ranging from − 26‰ to − 14‰. Stage 2 mineralization has higher δ34S values (− 8.3‰–7.7‰). Combined with the geological settings and mineral paragenesis, the sulfur isotopic data presented here suggest multiple sulfur sources (biogenic sulfur + evaporites) and formation mechanisms for reduced sulfur (H2S). H2S responsible for stage 1 Sulfide precipitation was associated with bacterial sulfate reduction (BSR). However, H2S of stage 2 was likely derived from thermochemical sulfate reduction (TSR). The most reasonable scenario for the stage 1 mineralization is a metal-bearing brine mixing with an H2S-rich fluid, thereby causing rapid Sulfide precipitation. Till the stage 2, the ore-forming fluid shifted to the meteoric water that infiltrated and reacted with evaporitic rocks, leached metals and transported them as sulfate- or sulfite-complexes to the Jinding dome where the oxidized sulfur was reduced by organic matters to H2S, leading to precipitation of metal Sulfides. In contrast to other Sulfide deposits in the Lanping basin, biogenic sulfur might have played a key role in the mineralization process, especially during the early stage of formation of the Jinding Zn–Pb deposit.

John F. Slack - One of the best experts on this subject based on the ideXlab platform.

  • extreme sulfur isotope fractionation in the late devonian dry creek volcanogenic massive Sulfide deposit central alaska
    Chemical Geology, 2019
    Co-Authors: John F. Slack, Ian W Ridley, Cynthia Duselbacon, Joel W Desormeau, Jahandar Ramezani, Wayne C Shanks, Mostafa Fayek
    Abstract:

    Abstract The Dry Creek Zn-Pb-Cu-Ag-Au volcanogenic massive Sulfide (VMS) deposit, in east-central Alaska, occurs in a Late Devonian sequence of peralkaline rhyolite tuff, minor graphitic argillite, and local peralkaline quartz-porphyry rhyolite intrusions. Principal mineralized facies are semi-massive and massive Sulfide in variably silicified and graphitic rhyolite tuff, massive Sulfide in graphitic argillite, disseminated Sulfides in graphitic and non-graphitic rhyolite tuff, and vein-hosted Sulfides in a subvolcanic, peralkaline quartz-porphyry intrusion. In situ analysis of the sulfur isotope composition of Sulfide minerals from all facies of the deposit shows a total range in δ34S values from −48.0 to 23.1‰. This remarkable 71.1‰ variation is more than twice the largest range known for Sulfides in nearly all individual VMS deposits, both modern and ancient, which typically is High-precision CA-ID-TIMS U-Pb geochronology of zircons from a synvolcanic peralkaline quartz porphyry intrusion yields a weighted mean 206Pb/238U date of 363.02 ± 0.43 Ma (2σ total uncertainty). This date indicates that the formation of graphitic and sulfidic sediments at Dry Creek, and contemporaneous VMS mineralization, occurred at least 3.6 m.y. before, and hence are unrelated to, widespread black shale deposition during the Hangenberg Event at ca. 359 Ma.

Xieyan Song - One of the best experts on this subject based on the ideXlab platform.

  • implications of nano and micrometer size platinum group element minerals in base metal Sulfides of the yangliuping ni cu pge Sulfide deposit sw china
    Chemical Geology, 2019
    Co-Authors: Qinglin Liang, Xieyan Song, Richard Wirth, Liemeng Chen
    Abstract:

    Abstract The concentrations of platinum-group elements (PGE) and semimetal elements (As, Sb, Se, Te and Bi) in the base metal Sulfides from the Yangliuping deposit were determined using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS). Mass balance calculation reveals that the base metal Sulfides only contain Cu-(PGE) Sulfide deposits. Euhedral shape and similar chemical composition of the nanometer-size PGE-arsenides and sulfarsenides in the base-metal Sulfides suggest that they crystallized from the Sulfide melt before the crystallization of monoSulfide solid solution (MSS) and intermediate solid solution (ISS). It is proposed that the nanometer-size PGE-arsenides and sulfarsenides formed from PGE-As molecular or polymolecular clusters in the Sulfide liquid at high temperature. The PGE-As molecular or polymolecular clusters prevent As and PGE from partitioning into the base metal Sulfide lattice and tend to form discrete nanometer-size PGE-arsenides and sulfarsenides. Thus, semimetal elements, particularly As, play an important role on behaviour of PGE during solidification of magmatic Sulfide liquids.

  • controls on the metal compositions of magmatic Sulfide deposits in the emeishan large igneous province sw china
    Chemical Geology, 2008
    Co-Authors: Xieyan Song, Meifu Zhou, Jiafei Xiao
    Abstract:

    Abstract Magmatic Sulfide deposits in the Emeishan large igneous province, SW China, have variable chalcophile and siderophile metal contents and can be divided into PGE, Ni–Cu–PGE and Ni–Cu deposits. PGE Sulfide deposits include the Jinbaoshan and Zhubu deposits and have ores with very low Sulfide contents (~ 1 to 2 vol.%) and very high Pt and Pd (0.3 to 10 ppm) and Ir (0.02 to 0.5 ppm). Typical Ni–Cu–PGE Sulfide deposits include the Yangliuping and Qingkuangshan deposits, which contain Sulfide ores with more than 10 vol.% Sulfides (0.1–6.2 wt.% Ni, 0.03–11 wt.% Cu) and have moderate PGE contents (0.1–5 ppm Pt, 0.01–1.8 ppm Pd, On the 100% Sulfide basis, Pt and Pd correlate positively with Ir in the ores from the PGE deposits, whereas they correlate negatively in the Ni–Cu–PGE and Ni–Cu deposits. PGE geochemistry and model calculations indicate that the PGE-rich Sulfides were separated from primary basaltic magmas, whereas the Ni–Cu–PGE Sulfides were produced from magmas that had experienced minor Sulfide removal (about 0.01%), and the Ni–Cu Sulfides were separated from magmas that experienced about 0.025% Sulfide segregation. Fractionation of monoSulfide solid solution resulted in differentiation between IPGE and PPGE in the Ni–Cu–PGE and Ni–Cu deposits.

Sebastian Staude - One of the best experts on this subject based on the ideXlab platform.

  • Interspinifex Ni Sulfide ore from Victor South-McLeay, Kambalda, Western Australia
    Mineralium Deposita, 2020
    Co-Authors: Sebastian Staude, Stephen J. Barnes, Gregor Markl
    Abstract:

    Spinifex-textured olivine plates hosted in Sulfides are usually named “interspinifex ore” in komatiite-hosted Sulfide deposits. This ore type is rare but provides important genetic information on Sulfide deposits, komatiite volcanology and thermomechanical erosion processes. Occurrences in Victor South-McLeay and Moran South (Kambalda, Western Australia) differ significantly from previously reported occurrences in their stratigraphic location, position within the ore profile and textural appearance. Thus, their formation process has to be reconsidered. Interspinifex ore reported here is situated in the lower portion of the basal lava flow between massive and net-textured Sulfides in the centre of the embayment and between massive Sulfides and older basalt in a “pinchout” where the Sulfides melted sideways into older basalt on the embayment edge. Interspinifex ore is composed of up to 10-cm-long aggregates of parallel plates in the upper portion of massive Sulfides and is overlain by barren komatiite. The texture does not allow for a classic single explanation. Thus, two possible formation mechanisms are envisaged: (1) A younger komatiite melt intrudes into its own olivine and Sulfide liquid cumulate pile, while the Sulfides are still liquid. The injection on top of the Sulfides causes the formation of an emulsion, from which the spinifex forms due to the temperature gradient between the melts. (2) Interspinifex ore is a relic of an early komatiite flow formed in a series of successive pulses of komatiite and Sulfide liquid. The spinifex of the komatiite is invaded by a younger batch of Sulfide liquid replacing interstitial silicate melt.

  • Sulfide silicate textures in magmatic ni cu pge Sulfide ore deposits massive semi massive and Sulfide matrix breccia ores
    Ore Geology Reviews, 2018
    Co-Authors: Stephen Barnes, Sebastian Staude, Margaux Le Vaillant, Ruben Pina, Peter C Lightfoot
    Abstract:

    Abstract Much of the value of magmatic Ni-Cu-PGE Sulfide orebodies is contained within massive or semi-massive ores that show a wide variety of textural relationships to included or adjacent silicate rocks. We identify five mutually gradational textural types: (1) pure inclusion-free massive Sulfide ores; (2) Sulfide matrix ore breccias, of sharp-wall, soft-wall or mixed character; (3) emulsion textured ores formed by frozen mixtures of molten silicate and Sulfide, most commonly developed as melt films at thermal erosion contacts; (4) vein-hosted Sulfides formed at late magmatic or high temperature post-emplacement deformation stage close to the brittle-ductile transition in the country rocks or host igneous bodies; and (5) tectonic “durchbewegung” breccias, formed by mechanical inter-shearing of less-ductile silicate inclusions and more-ductile solid Sulfides. Some deposits, the Moran Shoot at Kambalda being the type example, record the invasion of country rock footwall by downward- or sideways-percolating superheated molten Sulfide liquid generating vertical sequences of pure massive Sulfide, emulsion textured ores and finely-spaced invasive Sulfide veins; these are referred to as Sulfide melting-infiltration fronts and may provide a clue to the mechanism of formation of Sulfide-rich magmatic ores as whole. Sulfide matrix ore breccias are particularly well developed in the Voisey’s Bay and Aguablanca deposits, where they developed by flooding of percolating Sulfide melt through the silicate matrix of magmatic intrusion breccias, displacing silicate melt. The lithology of the silicate or carbonate rock inclusions determines the nature of the inclusion-matrix relationships. Non-refractory inclusions typically disaggregate along original grain boundaries to leave coherent inclusions surrounded by clouds of inclusion-derived or matrix-derived crystals, with the low-melting silicate component preferentially displaced by Sulfide liquid, whereas refractory inclusions retain sharp boundaries. Zonation of inclusions and overgrowths preserves reaction between inclusion and silicate matrix that pre-dates invasion of the intrusion breccia by Sulfide liquid. The process of percolation of dense, low-viscosity Sulfide liquid into pore space and fractures within partially molten (or melting) silicate rock is a unifying theme that links Sulfide matrix ore breccias and emulsion textured ores with distinctive textures in less Sulfide rich rocks such as net-texture (matrix ore texture), leopard texture (poikilitic net texture) and interspinifex ore. Vein-hosted massive Sulfides may be emplaced under magmatic conditions where the excess pressure of the Sulfide liquid column drives or enhances fracturing of the country rock and injection of Sulfide into the cracks. Such veins are commonly referred to as “remobilised”, a term which may obscure process understanding and should be reserved for cases where tectonic solid-state mobilisation of Sulfide can be demonstrated on textural and structural grounds. The tendency of Sulfide liquids to invade country rocks and potentially to drive the propagation of their own magmatic containers may be a critical feedback loop in the development of magmatic Sulfide mineral systems.