Platinum-group Element Deposits Research Articles

Low-sulfide platinum–metal deposits in the Kola region: A comparative analysis of the Yuzhnosopchinskoye ore occurrence and the Fedorova Tundra deposit

Research subject. Platinum–metal objects of the Kola region (contact type mineralization), including the Yuzhnosopchinskoye ore occurrence within the same-name massif belonging to the Early Proterozoic Monchetundra intrusion and the Fedorova Tundra deposit located in the western part of the Early Proterozoic Fedorovo-Pansky layered complex. Aim. To establish the formation conditions of platinum-metal ores in the Yuzhnosopchinskoye ore occurrence and the Fedorova Tundra deposit. Methods. Comparison of the geological structure and petro-geochemical features of rocks and ores from the two objects using statistical analysis. Results. Both the Yuzhnosopchinskoye ore occurrence and the Fedorova Tundra deposit belong to the contact type of platinum group element deposits. The main characteristic feature is confinement of the ore zone to the contact of two magmatic phases. In the contact zone, igneous breccia, pegmatoid, and vein bodies are widespread, with the latter being especially common in the Yuzhnosopchinskoye ore occurrence. In Yuzhnosopchinskoye ore occurrence, breccia fragments are represented by orthopyroxenites and melanocratic norites of the early magmatic phase (layered series of rocks). They were cemented by barren gabbroids of the later magmatic phase. In the Fedorova Tundra deposit, breccia zone fragments are also composed of orthopyroxenites and melanocratic norites of the early magmatic phase (layered series of rocks). They were cemented by taxitic ore-bearing gabbronorites of the late magmatic phase. Rocks of the two objects with a similar nomenclature demonstrate slight systematic differences in the composition of petrogenic components, as well as in REE and rare elements. Taxitic gabbronorites (rocks of the marginal series) from the Fedorova Tundra deposit have no rock analogues in Yuzhnosopchinskoye ore occurrence. A comparison of similar amounts of two data sets (more than 2000 samples each) of Pt, Pd, Au, Ni, and Cu sampling showed that the content of all precious metals in the Fedorova Tundra deposit was consistently higher than that in the Yuzhnosopchinskoye ore occurrence. The Fedorova Tundra deposit is homogeneous, with an average Pd/Pt ratio of 4.5. The Yuzhnosopchinskoye ore occurrence is heterogeneous and, on average, slightly more ‘platinum’ and less ‘palladium’ than the Fedorova Tundra deposit. Conclusions. The two ore objects of the contact type are similar in many respects, mainly differing in the conditions of mineralization formation. The Yuzhnosopchinskoye ore occurrence entered the contact zone from the rocks of the layered series due to the activation of the ore matter during intrusion of the late gabbroid intrusive phase. The Fedorova Tundra deposit entered the contact zone together with the late ore-bearing gabbronorite magmatic phase.

Sources of Ore Material in the Platinum-Group Element Deposits of Polar Siberia and the Middle Urals Based on the Data from Radiogenic (Re–Os, Pt–Os) and Stable (Cu, S) Isotopes

Abstract —Understanding the main events of platinum-group element (PGE) ore formation is impossible without analysis of the sources and behavior of major ore-forming components, namely, platinum, osmium, sulfur, and copper, which are important indicators of magmatic and hydrothermal processes. In contrast to the Re–Os isotope system, the radiogenic Pt–Os isotope system, as well as stable isotopes of Cu and S in PGE deposits, are still relatively understudied. Our comprehensive research is aimed at filling this gap. The paper presents data for the Guli massif of ultramafic and alkaline rocks and carbonatites in Polar Siberia and on the zonal Nizhny Tagil and Svetly Bor clinopyroxenite–dunite massifs in the Middle Urals, which include: (1) the contents of the highly siderophile elements (HSE) in whole rocks and platinum-group minerals (PGM), (2) the Re–Os and Pt–Os isotope systematics of chromitite, Os–Ir alloys, and Ru–Os sulfides, (3) the sulfur isotope composition in Ru–Os and Ir–Rh sulfides in primary and secondary PGM assemblages, and (4) the copper isotope composition in Pt–Fe minerals from chromitites and placers. The research was performed using scanning electron microscopy, electron probe microanalysis, and high-precision isotope-geochemical analysis. The high-precision Re–Os and Pt–Os isotope data show that the HSE contents in chromitites and PGM of the Guli massif were controlled by the composition of the mantle source that evolved with near-chondritic time-integrated Re/Os and Pt/Os ratios, which are also typical of the sources of most komatiites and abyssal peridotites. The δ65Cu values of the studied samples of ferroan platinum and isoferroplatinum are identical within the analytical uncertainty and are close to 0‰, which is typical of high-temperature Cu-containing minerals. The sulfur isotope compositions of the Ir–Rh sulfides of the kashinite–bowieite series and of the Ru–Os sulfides of the laurite–erlichmanite series in the primary PGM assemblages indicate that the source of sulfur has a chondritic isotope composition, which is in agreement with the osmium isotope composition of the Ru–Os sulfides and Os–Ir alloys. The heavy sulfur isotope composition (δ34S = 5.6 ± 1.5‰) of As-containing erlichmanite is consistent with its secondary origin. The new data on the isotope compositions of osmium, copper, and sulfur can be used as new important parameters that characterize the sources of PGE mineralization.

Geospatial Insights into Ophiolitic Complexes in the Cimmerian Realm of the Afghan Central Block (Middle Afghanistan)

Ophiolites are remnants of oceanic crust that have been thrust onto continental crust due to tectonic processes. They are composed of mostly mafic and ultramafic rocks, which are genetically associated with gold, silver, platinum group element (PGE), chrome, manganese, titanium, cobalt, copper, and nickel deposits. The main objective of this research was to identify the spatial distribution of Mesozoic ophiolitic complexes within the Central Afghan Block in Middle Afghanistan using optical remote sensing data and spectral analyses. Distinct algorithms, such as false color composite (FCC), proposed band ratios (PBR), principal component analysis (PCA), and spectral angle mapper (SAM), were used to map the targeted ophiolitic complexes. New band ratios were proposed in this study based on the spectral properties of mafic-ultramafic minerals and rocks, which showed high efficiency. Based on the results, four different ophiolitic complexes were delineated within this study area. These complexes are consistent with previous studies. The accuracy assessment of this study showed an overall accuracy of 72.2%. The findings of this study can significantly contribute to further studies on the emplacement mechanism and paleo-Tethys history of Middle Afghanistan. Also, the spatial distribution of the ophiolitic complexes identified in this study can be used to constrain models of the tectonic evolution of the Central Afghan Block. Additionally, the identification of new band ratios for mapping ophiolitic complexes can be used in future studies of other ophiolite-bearing regions.

Microbial communities from weathered outcrops of a sulfide-rich ultramafic intrusion, and implications for mine waste management.

The Duluth Complex (DC) contains sulfide-rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally-weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long-term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally-weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse uncultured Ktedonobacteria, Acetobacteria, and Actinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally-weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide-rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large-scale mining operations.

Platinum-group elements (PGE) in the New Afton alkalic Cu-Au porphyry deposit, Canadian Cordillera, I: relationships between PGE, accessory metals and sulfur isotopes in pyrite

The second part of this article can be found here: 10.3389/feart.2023.819109 (DOI). At the late Triassic New Afton alkalic porphyry Cu-Au deposit (British Columbia, Canada), pyrite is a widely distributed minor sulfide phase within hypogene ore where it predates Cu mineralization and hosts significant concentrations of Pd and Pt. Here we characterize pyrite major, minor and trace element composition by EPMA and LA-ICP-MS, and S isotopes (bulk pyrite and in situ SIMS in individual growth zones) to elucidate compositional variations at different stages of pyrite growth with respect to PGE deposition. At least two cycles of zoned Co-Ni-Pd-Pt-Se-As co-enrichment are recorded over two stages of pyrite growth at the New Afton deposit. Concentrations of Co (up to ∼5.5 wt%; highest observed in any reported ore-forming system) and Ni (up to 1 wt%) overlap with pyrite from mafic-ultramafic platinum-group element (PGE) deposits, iron oxide±apatite and iron oxide-copper-gold deposits (IOA-IOCG), and mantle peridotite-associated base metal exhalative deposits. In early hypogene (type I) pyrite, high Pt (up to ∼24 ppm) occurs in crystal cores that have high Co/Ni ratio (>∼7), high Co (>∼ 1 wt%) and are poor in Ni, Se, and As. With progressive growth, early hypogene pyrite rims and late hypogene (type II) cores record an initial Ni-Pd-As-Se (±Co) co-enrichment stage, followed by oscillations in composition (from “barren” to variably Co-Ni-Pd-Pt-As-Se-enriched). Pd in pyrite (up to ∼70 ppm) is inversely correlated to Co/Ni ratio, being enriched when Co/Ni < ∼7 and Ni > ∼1000 ppm. The highest levels of Pd enrichment occur in the most Ni- and Se-enriched growth zones. The transition from early, high Co/Ni (Pt-enriched) to later, low Co/Ni (Pd-enriched) growth zones is accompanied by a decrease in pyrite δ34SVCDT of up to ∼7‰ (4‰ range in single grains) with a total range in composition measured between −5.5‰ and +1.4‰. Subsequent to the shift to lower values, overgrowths of high Co/Ni pyrite formed with values of δ34SVCDT similar to the earliest Co-Pt-rich growth zones. Some combination of fluctuations in temperature and oxygen fugacity related to episodic cooling and hydrothermal recharge involving new pulses of metal-rich magmatic fluids is required to explain the observed metal enrichment patterns and variations in S isotope values. Co-Ni-rich pyrite may be a valuable exploration vector to PGE enrichment in porphyry deposits.

Role of volatiles in intrusion emplacement and sulfide deposition in the supergiant Norilsk-Talnakh Ni-Cu-PGE ore deposits

Abstract The Norilsk-Talnakh orebodies in Siberia are some of the largest examples on Earth of magmatic Ni–Cu–platinum group element (PGE) deposits, formed by segregation of immiscible sulfide melts from silicate magmas. They show distinctive features attributable to degassing of a magmatic vapor phase during ore formation, including: vesiculation of the host intrusions, widespread intrusion breccias, and extensive hydrofracturing, skarns, and metasomatic replacement in the country rocks. Much of the magmatic sulfide was generated by assimilation of anhydrite and carbonaceous material, leading to injection of a suspension of fine sulfide droplets attached to gas bubbles into propagating tube-like host sills (“chonoliths”). Catastrophic vapor phase exsolution associated with a drop in magma overpressure at the transition from vertical to horizontal magma flow enabled explosive propagation of chonoliths, rapid “harvesting” and gravity deposition of the characteristic coarse sulfide globules that form much of the ore, and extensive magmatic fluid interaction with country rocks.

Paleoproterozoic East Pana Layered Intrusion (Kola Peninsula, Russia): Geological Structure, Petrography, Geochemistry and Cu-Ni-PGE Mineralization

The East Pana intrusion is a part of the Paleoproterozoic Fedorova–Pana complex (FPC), which belongs to the group of Fennoscandian layered mafic–ultramafic massifs. This article discusses the magmatic stratification of the East Pana intrusion, as well as Cu-Ni and platinum-group elements (PGE) mineralization (PGE zones A, B and C) in its various parts with a total length of more than 20 km, including the East Chuarvy PGE deposit. Based on the whole-rock data on the distribution of major, trace, and ore-forming elements, it is assumed that PGE zone A belongs to the main ore–magmatic system of the FPC, while PGE zones B and C belong to the minor ore–magmatic systems. At the same time, additional magmatic injection played an important role in the formation of economic Cu-Ni-PGE mineralization (PGE zone B), characterized by high PGE concentrations and moderate palladium enrichment. On the normalized distribution spectra of trace elements, the crystallization products of this injection (Gabbronorite Zone 2) have a positive Zr-Hf anomaly, which distinguishes it from host rocks with an anomaly of the opposite sign (Gabbronorite Zone 1, Gabbro Zone). It is assumed that this portion of magma was intruded as a sill of crystal mush, the fractionation of which at depth led to its enrichment with residual liquid.

Rhenium mineral resources: A global assessment

Rhenium (Re) is essential to modern transportation because of its key role in the aerospace and petrochemical sectors and has been assessed as critical due to its complex supply chains and limited options for effective substitutes. Efforts to estimate global Re resources are complicated by its production as a ‘by-product of a by-product’ – i.e., its extraction as a by-product from molybdenum (Mo) concentrates, which in turn are commonly by-products from copper (Cu) mining, leading to very limited reporting of Re grades in mineral deposits. This has rendered past estimates of global Re resources subject to high uncertainty and variability.This study addresses this key issue using a new detailed database of mineral deposits reported to host Re that also includes deposits which are inferred to contain Re based on their Cu and Mo contents (using Re proxies). We also present an analysis of historical Re production and uses, and a review of Re mineralogy and key mineral deposit types. We estimate that 618 deposits hosting resources of Cu, Mo and other metals, which are dominated by porphyry Cu ± Mo deposits, host somewhere between ∼55,000–140,000 t Re. Our best estimate of ∼83,000 t Re is 3–4 times that of previous global Re resource estimates, and yet does not include other nickel, platinum group element or tungsten-related deposits that may also host Re. With current global demand at only ∼50 t Re/yr, our minimum global estimate would be sufficient to meet global demand for centuries, unless a major shift in the use of Re takes place to boost future demand. As has been demonstrated to be the case for other critical metals, the pertinent questions around future supply of Re appear not to be related to total quantity of mineral resources, but rather which mines and refineries will offer lower costs and more environmentally/socially sustainable and responsible supply chains.

Lithogeochemistry in exploration for intrusion-hosted magmatic Ni–Cu–Co deposits

Magmatic Ni–Cu–Co–platinum group element deposits are notoriously difficult exploration targets owing to a lack of alteration haloes or other extended distal footprints. Success requires prediction of prospective terranes, followed by identification of suitable host intrusions and deposition sites within those intrusions. At the regional scale, potential ore-hosting magmas tend to have lithophile trace element trends falling on mixing lines between primitive or slightly depleted source mantle and typical upper continental crust, with several significant exceptions. Most known deposits have parent magmas that are in the upper range of FeO content for given MgO compared with baseline data sets for continental large igneous province magmas. At the scale of individual intrusions, the presence of cumulate rocks, both mafic and ultramafic, is key. These can be recognized in regional datasets using combinations of magnesium number (molar MgO/(MgO + FeO), Al 2 O 3 , TiO 2 and Zr contents. Combinations of alteration-resistant element ratios between Ni, Cr and Ti are also useful and can also be applied to moderately weathered samples. Concentrations and ratios of Cu and Zr are useful in discriminating chalcophile-enriched and depleted magma suites. In combination, these approaches can be combined to discriminate highly prospective cumulate-dominated magmatic suites and individual intrusions from non-cumulate suites with limited potential. Supplementary material: Supplementary Appendix 1, procedure for determination of FeO–MgO contents of magmas from olivine-liquid mixing lines, and Supplementary Appendix 2, procedure and error analysis for correcting major element whole rock analyses volatile and sulfide free, are available at https://doi.org/10.6084/m9.figshare.c.6267664

Diversity of Net-Textured Sulfides in Magmatic Sulfide Deposits: Insights from the Eagle’s Nest Ni-Cu-(Platinum Group Element) Deposit, McFaulds Lake Greenstone Belt, Superior Province, Canada

Abstract The Eagle’s Nest Ni-Cu-(platinum group element; PGE) deposit occurs within the 2.73 Ga Esker intrusive complex of the Ring of Fire intrusive suite in the McFaulds Lake greenstone belt of northern Ontario. Mineralization occurs along the northern margin of a formerly ~500-m-high, ~85-m-thick, >1,500-m-long subvertical structurally rotated blade-shaped dike composed of harzburgite, lherzolite, and wehrlite. Three sulfide textural facies are present (percentage as proportion of total mineralization): (1) disseminated (~5%), (2) net texture (~80%), and (3) semimassive to massive (~15%). Five subfacies of net texture have been identified: (1) bimodal olivine-bearing leopard net texture (~50%), (2) inclusion net texture (~5%), (3) orthopyroxene-bearing pinto net texture (<1%), (4) localized zones of disrupted net texture (~30%) containing 3- to 5-cm-thick zones of barren amoeboid crosscutting pyroxenite, and (5) fine-grained patchy net texture (~15%). All textural facies are characterized by typical magmatic pyrrhotite-pentlandite-chalcopyrite-(platinum group mineral) assemblages. Massive sulfides are localized in two embayments along the basal contact separated by a topographic high, grading upward to rare semimassive, laterally more continuous net-textured, and disseminated sulfides, with gradational contacts between all textures except massive. Similar mean ore tenors of different sulfide textural facies (Ni100 ~7.5, Cu100 ~4.8), suggest that the majority of the mineralization formed from similar magma compositions at similar magma/sulfide ratios, but the presence of different inclusion populations (peridotite, gabbro, chromitite) and the presence of disrupted net texture indicates that the olivine, inclusions, and sulfide melts accumulated from multiple pulses in a dynamic system. The smaller, blade-shaped, sulfide-rich, chromite-poor Eagle’s Nest body does not appear to be the feeder to the overlying larger, oblate, sulfide-poor, chromite-rich Double Eagle body. This highlights the need to understand the fluid dynamics of entire plumbing systems when exploring for these deposit types and the significance of smaller, more dynamic magmatic conduits as environments favorable for Ni-Cu-(PGE) mineralization.

Suitability of surficial media for Ni–Cu–PGE exploration in an established mining camp: a case study from the South Range of the Sudbury Igneous Complex, Canada

A geochemical study over the southwestern part of the South Range of the Sudbury Igneous Complex was completed to assess the suitability of surficial media (humus, B-horizon soil and C-horizon soil) for delineating geochemical anomalies associated with Ni–Cu–PGE (platinum group element) mineralization. Another objective was to test whether Na pyrophosphate can eliminate the effects of anthropogenic contamination in humus. Results of this study suggest that the natural geochemical signature of humus is strongly overprinted by anthropogenic contamination. Despite no indication of underlying or nearby mineralization, metal concentrations in humus samples by aqua regia collected downwind from smelting operations are higher compared to background, including up to 13 times higher for Pt, 12 times higher for Cu and nine times higher for Ni. The high anthropogenic background masks the geogenic signal such that it is only apparent in humus samples collected in the vicinity of known Ni–Cu–PGE deposits. Results of this study also demonstrate that anthropogenically derived atmospheric fallout also influences the upper B-horizon soil; however, lower B-horizon soil (at >20 cm depth) and C-horizon soil (both developed in till) are not affected. Glacial dispersal from Ni–Cu–PGE mineralization is apparent in C-horizon till samples analysed in this study. Compared to the background concentrations, the unaffected C-horizon till samples collected immediately down-ice of the low-sulfide, high precious metal Vermilion Cu–Ni–PGE deposit are enriched over 20 times in Pt (203 ppb), Au (81 ppm) and Cu (963 ppm), and over 30 times in Ni (1283 ppm).Supplementary material: supplementary tables and figures are available at https://doi.org/10.6084/m9.figshare.c.5691080

The effects of post-cumulus alteration on the distribution of chalcophile elements in magmatic sulfide deposits and implications for the formation of low-S-high-PGE zones: The Luanga deposit, Carajás Mineral Province, Brazil

ABSTRACT Most of the World's platinum-group element ore deposits occur as thin stratiform layers within layered intrusions. These layers generally contain disseminated base-metal sulfides or chromite. However, cryptic platinum-group element deposits also occur without chromite or base-metal sulfides in what are known as low-S-high platinum-group element deposits. The origin of these deposits is not clearly understood. The Luanga Complex hosts the largest platinum-group elements resource in South America (i.e., 142 Mt at 1.24 ppm Pt + Pd + Au and 0.11% Ni) and hosts both a platinum-group element deposit containing disseminated base-metal sulfides (style 1) and a low-S-high platinum-group element deposit (style 2). It therefore offers the opportunity to compare the two deposit types in the same overall geological setting and consider how the low-S-high platinum-group element deposit could have formed. The first deposit style is termed the Sulfide zone and consists of a 10–50 meter-thick interval with disseminated base metal sulfides, whereas the second style is named low-S-high-Pt-Pd zone and consists of 2–10 meter-thick discontinuous lenses of 1–5 meter-thick sulfide- and oxide-free harzburgite and orthopyroxenite with discrete platinum-group minerals. Secondary assemblages commonly replace primary igneous minerals to a variable extent throughout the deposit, and thus allow for investigating the effects of post-cumulus alteration on the distribution of a wide range of chalcophile elements in a magmatic sulfide deposit at both whole-rock and mineral scale. This study presents the whole-rock distribution of S, platinum-group elements, and Te, As, Bi, Sb, and Se in both mineralization styles and the concentration of trace elements in base-metal sulfides from the Sulfide zone. The Sulfide zone has Pt/Pd ratios around 0.5 and high concentrations of Te, As, Bi, Sb, and Se, whereas the low-S-high-platinum-group element zone has Pt/Pd ratios greater than 1 and much lower Se, Te, and Bi concentrations, but comparable As and Sb contents. This is reflected in the platinum-group element assemblage, comprising bismuthotellurides in the Sulfide zone and mostly arsenides and antimonides in the low-S, high platinum-group elements zone. Moreover, the base-metal sulfides from the Sulfide zone have anomalously high As contents (50–500 ppm), which suggest that the sulfide liquid segregated from a very As-rich silicate magma, possibly illustrated by an average komatiitic basalt that assimilated a mixture of upper continental crust and black shales. We interpret the low-S-high platinum-group elements zone as a product of S loss from magmatic sulfides during post-cumulus alteration of the Luanga Complex. Selenium, Te, Bi, and Pd were also lost together with S, whereas As and Sb were expelled from base-metal sulfide structures and combined with platinum-group elements to form platinum-group minerals, suggesting they may play a role fixating platinum-group elements during alteration. The remobilization of chalcophile elements from magmatic sulfide deposits located in the Carajás Mineral Province may represent a potential source for hydrothermal deposits found in the region.

Genesis and mechanisms of metal enrichment in the Baimazhai Ni-Cu-(PGE) deposit, Ailaoshan Orogenic Belt, SW China

ABSTRACT The ∼259 Ma Baimazhai Ni-Cu-(platinum-group element) deposit is located in the Ailaoshan-Red River fault zone on the southwest margin of the Yangtze Plate in the Jinping area of southeastern Yunnan Province. The intrusion is lenticular (∼530 m long × 190 m wide × 24–64 m thick) and concentrically zoned (margin to core) from gabbro through pyroxenite to peridotite. It contains ∼50 kt of Ni-Cu-(platinum-group element) mineralization, concentrically zoned (margin to core) from disseminated through net-textured to massive sulfides with an average grade of 1.03 wt.% Ni, 0.81 wt.% Cu, and 0.02∼0.69 ppm Pd+Pt. The sulfide assemblage comprises pyrrhotite, chalcopyrite, and pentlandite, with lesser magnetite, violarite, galena, and cobaltite. The mineralization is enriched in Ni-Cu-Co relative to the platinum-group elements and the host rocks are enriched in highly incompatible lithophile elements relative to moderately incompatible lithophile elements with high Th/Yb and intermediate Nb/Yb ratios. These host rocks, and those at most other Ni-Cu-platinum-group element deposits in the Emeishan Large Igneous Province, have high γOs and intermediate εNd values, indicating that they crystallized from a magma derived from a subduction-modified pyroxenite mantle source and modified by crustal contamination. The initial concentrations of metals in the primary magma are estimated to have been on the order of 200 ppm Ni and 100 ppm Cu, but only 0.4 ppb Pd, 0.2 ppb Pt, 0.005 ppb Rh, 0.02 ppb Ru, and 0.01 ppb Ir. The δ34S values of ores and separated sulfides range from 5.8‰ to 8.6‰, between the ∼10‰ value of sulfides in the metasedimentary country rocks and the 0 ± 0.5‰ value expected for magmas derived from MORB-type mantle, or the –2.5 ± 0.3‰ value expected for subduction-modified mantle, consistent with equilibration at magma:sulfide mass ratios (R factors) of 100–1000. Variations in Ir100 and Pd100 (metals in 100% sulfide) are consistent with 40–60% fractional crystallization of monosulfide solid solution to form Ni-Co-intermediate platinum-group element (Ru, Os, Ir)-rich massive ores and Cu-palladium/platinum-group elements (Pt, Pd, Rh)-Au-rich residual sulfide liquids. This process is also recorded by magnetite: Type I (early magmatic), type II (late magmatic), and type III (secondary) magnetites exhibit progressively lower Cr-Ti-V concentrations. The platinum-group element contents in base-metal minerals are low, and only pentlandite, violarite, and cobaltite contain detectable concentrations of Pd, Rh, and Ru. There is abundant textural evidence for metamorphic-hydrothermal alteration of sulfides in the Baimazhai intrusion, with secondary violarite, chalcopyrite, and pentlandite being enriched (Ag, Sb, Au, Pb) or depleted (Sn) in more mobile chalcophile elements. The different tectonic and petrogenetic settings of the Baimazhai and other deposits in China highlight the potential of Ni-Cu-platinum-group element deposits to occur in subduction or post-subduction settings and demonstrate that the key controls are magma flux and access to crustal S. Exploration potential remains for the Ailaoshan orogenic belt to host additional magmatic Ni-Cu deposits.

Forecasting criteria for sulphide PGE-copper-nickel deposits of the Noril’sk province (In English)

Research subject. World-class sulphide platinum-group-element (PGE)-Cu-Ni deposits occur within the Noril’sk-Talnakh region of northern Siberia, Russia. The signifcance of these deposits presents opportunities to determine the most effective approaches for the search of similar deposits using commercial PGE-Cu-Ni deposit examples. Materials and methods. Petrological and geochemical analysis of the ultramafc-mafc intrusions of the Noril’sk province ranks them into three types in terms of sulphide mineralization style and economic signifcance: 1) economic intrusions containing unique and large sulphide PGE-Cu-Ni deposits (Oktyabr’sk, Talnakh and Noril’sk-1); 2) subeconomic intrusions that contain small- to medium-sized Cu-Ni sulphide deposits, and medium-sized to large PGE deposits (Chernogorsk, Zub-Marksheider, Vologochan, etc.); 3) uneconomic intrusions that contain low-grade disseminated Cu-Ni ores with ≈0.2 wt % of Cu and Ni, and low Cr and PGE (Nizhny Talnakh, Zelyonaya Griva, etc.). Results and conclusions. Principal sources used in exploration for rich sulphide PGE-Cu-Ni ores include structural, magmatic, stratigraphic-lithological, geochemical, mineralogical, metamorphic and some others. Based on an analysis of isotope-geochemical data, new indicators for locating sulphide PGE-Cu-Ni mineralization are suggested. A restricted range of S-isotope values, and a negative trend for coupled S-Cu isotope compositions can be employed as useful guides to assess the economic potential of a PGE-Cu-Ni sulphide deposit. It is proposed that the Chernogorsk ultramafc-mafc intrusion of the Noril’sk province is the most promising target in a search for rich PGE-Cu-Ni ores. It is suggested that the previously known mineralogical-geochemical and novel isotope-geochemical characteristics of sulphide and silicate minerals are important indicators in assessing the potential ore content of ultramafc-mafc intrusions of the Noril’sk province.

Existence of the Dharwar–Bastar–Singhbhum (DHABASI) megacraton since 3.35 Ga: constraints from the Precambrian large igneous province record

AbstractWe propose a Precambrian megacraton (consisting of two or more ancient cratons), DHABASI in the Indian Shield, which includes the Dharwar, Bastar and Singhbhum cratons. This interpretation is mainly based on seven large igneous provinces (LIPs) that are identified in these three cratons over the age range of c. 3.35–1.77 Ga, a period of at least 1.6 Ga. The absence of any subsequent break-up of DHABASI since 1.77 Ga suggests that this megacraton has existed for the past 3.35 Ga. In addition to their use in recognizing this megacraton, these LIP events may also provide likely targets for Cu–Ni–Cr–Co–platinum group element deposits. We suggest that the megacraton DHABASI was an integral part of supercontinents/supercratons through Earth's history, and that it should be utilized as a distinct building block for palaeocontinental reconstructions rather than using the individual Dharwar, Bastar and Singhbhum cratons.

The Sulfide/Silicate Coefficients of Nd and Sm: Geochemical “Fingerprints” for the Syn- and Epigenetic Cu-Ni-(PGE) Ores in the NE Fennoscandian Shield

One of the current directions of the Sm-Nd isotope systematics development is a dating of the ore process using sulfide minerals. Yet, the issue of the existence of rare earth elements (REE) in sulfides is still a matter for discussion. Sulfides from ore-bearing rocks of Proterozoic (2.53–1.98 Ga) Cu-Ni and platinum group elements (PGE) deposits of the Fennoscandian Shield were studied. It is found that the most probable source of REE in sulfide minerals from Cu-Ni-PGE complexes could be submicronic fluid inclusions, which are trapped at the mineral crystallization stage. In such a case, fluid or melt inclusions are specimens of the syngenetic parental melt, from which the base mineral formed, and these reflect a composition of the parental fluid. The mineral–rock partition coefficients for Nd and Sm can be used as “fingerprints” for individual deposits, and these are isotope-geochemical indicators of the ore-caused fluid that is syngenetic to sulfide. Moreover, the DNd/DSm ratio for various sulfide minerals can be used as a prospective geochemical tool for reconstructing a mineral formation sequence in ore complexes. On the other hand, differences in isotope compositions of sulfide neodymium could be markers of some ore-caused fluids and related to certain generations of sulfide minerals.

The solubility of gold and palladium in magmatic brines: Implications for PGE enrichment in mafic-ultramafic and porphyry environments

We performed experiments to determine the solubility of Au and Pd in magmatic aqueous fluids as a function of oxygen fugacity (ƒO2), temperature (T), pH and total chloride concentration (Cltotal). Experiments were conducted at 800–1000 °C and 200 MPa in an externally-heated rapid-quench Molybdenum-Hafnium Carbide (MHC) cold-seal pressure vessel assembly. We employed a synthetic fluid inclusion (SFI) technique to entrap equilibrated, hydrothermal fluids in response to in situ fracturing of quartz cylinders at experimental run conditions. The solubility of Au and Pd both have positive relationships with ƒO2, temperature, acidity and chlorinity. Concentrated aqueous brines containing 63 wt.% NaCl can dissolve wt.% levels of Au (∼1.2 wt.%) and Pd (∼1.7 wt.%) at metal saturation in relatively oxidized conditions, 1.44 log units above the Ni-NiO oxygen buffer (NNO+1.44), and mildly acidic pH at 900 °C and 200 MPa. Thermodynamic modeling of experimental results suggests that Au is mainly transported as AuCl(aq) at high pH and low Cltotal conditions, whereas HAuCl2(aq) and potentially AuCl2(aq)− predominates at low pH and high Cltotal conditions. Results from thermodynamic modeling also suggest Pd is mobilized in significant contributions by both PdCl2(aq) and PdCl3(aq)− with the latter gaining predominance in response to increasing Cltotal. Calculated fluid/melt partition coefficients for Au and Pd in low-density, magmatic vapors at 1000 °C and 200 MPa suggest that Pd may experience fractionation from Au in porphyry Au-Cu (±Pd, Pt) systems due to the restricted compatibility of Pd in the fluid phase (requiring strongly acidic and substantially high ƒO2 conditions). Moreover, high-density, concentrated aqueous brines facilitate the compatibility of Pd in the fluid phase which may be important with respect to the formation of platinum-group element (PGE)-enriched horizons in layered mafic intrusions (e.g., J-M Reef, Stillwater Complex, U.S.A.). The potential for magmatic, near-neutral pH, high-salinity brines to dissolve significant amounts of Pd as Pd(II)-chloride complexes (∼400 to ∼900 µg/g) well below the NNO buffer suggests that such fluids may be responsible for late-stage hydrothermal remobilization of Pd within mafic-ultramafic igneous environments (e.g., Cu-Ni-PGE footwall deposits and low-sulfide PGE deposits in the Sudbury Igneous Complex, Canada).

Age of the lower Cambrian Vanadium deposit, East Guizhou, South China: Evidences from age of tuff and carbon isotope analysis along the Bagong section

Abstract The early Cambrian is a critical interval of dramatic oceanic and biochemical changes in geological history. The black shale deposits, which are rich in Mo, Ni, V, and platinum group elements (PGE), are a reflection of that interval. Among all known Cambrian black shale deposits in South China, the vanadium deposits are poorly constrained by geochronology. The newly discovered tuff layer in the Sansui Bagong vanadium deposit in Guizhou Province can provide excellent constraints on the age of vanadium deposits. In this study, we obtain a new zircon U–Pb isotopic age, which can constrain the age of the vanadium deposit. This tuff occurs in the middle part of the ore bed, and the age of the tuff layer can reflect the mineralization age of the V deposit. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used in this study to obtain the zircon U–Pb age of the tuff and indicates that the event of volcanic activity took place at 520.9 ± 1 Ma. This age is close to the boundary between the Cambrian Terreneuvian and Series 2. This result provides a good constraint on the age of the vanadium deposits in South China and makes the vanadium deposits to be comparable with other Mo–Ni–PGE deposits. The alteration of organic carbon isotope (δ 13Corg) values can reflect changes in the marine environment and is widely used in stratigraphic correlation. The analysis of the δ 13Corg values of the ore bed in the present study reveals a positive excursion at the bottom of the deposit and a negative excursion in the V-enriched layer. The δ 13Corg values in the Bagong section are comparable to those in the Xiaotan and Longbizui sections. The ages of the Sansui vanadium deposit constrained by the U–Pb isotopic age of the tuff and the δ 13Corg values are consistent. All of the data lead us to infer that the vanadium deposit formed at approximately 521 Ma.

The distribution of platinum-group elements and Te, As, Bi, Sb and Se (TABS+) in the Paraná Magmatic Province: Effects of crystal fractionation, sulfide segregation and magma degassing

The concentrations of Te, As, Bi, Sb and Se (TABS+) in magmas from large igneous provinces (LIPs) are of interest because these elements are important in the formation of platinum-group minerals (PGM) found in magmatic NiCu platinum-group element (PGE) deposits. Furthermore, the TABS+ are volatile and hence they may be lost in degassing and have a role to play in the mass extinctions associated with LIPs events because these are mostly toxic elements. However, the concentrations of TABS+ in magmas from LIPs are not well documented due in part to the analytical difficulties and in part to the numerous processes that affect their distribution. We have determined the concentration of TABS+ and PGE in rocks from the Paraná Magmatic Province (PMP) in order to assess the effects of fractional crystallization, sulfide segregation and magma degassing. Decrease in the Rh, Ru and Ir concentrations with Mg and Cr indicate that these elements behaved as compatible elements during crystal fractionation. Based on changes in the Cu/Pd sulfide saturation occurred in some cases resulting into a decrease in Pd and Pt. Arsenic and Sb behave as incompatible elements, whereas Se, Te and Bi show variable behaviour. Most lavas from the PMP display negative As, Se and Te anomalies on mantle-normalized patters coupled with Te/Cu, Se/Cu and As/Th and Sb/Th ratios lower than mantle values, which we attribute to loss of the TABS+ during degassing.

Iron isotope fractionation during sulfide liquid evolution in Cu–PGE mineralization of the Eastern Gabbro, Coldwell Complex, Canada

In spite of the fact that metal stable isotopes are not expected to exhibit large equilibrium fractionations at magmatic temperatures, Fe isotope compositions of base-metal sulfides are increasingly being used to characterize the processes that generate and modify Ni–Cu–platinum-group element (PGE) deposits. In the Eastern Gabbro of the Coldwell Complex, Canada, the δ56Fe values (relative to IRMM-014) of pyrrhotite (−1.48‰ to −0.16‰) are consistently negative and exhibit no correlation with style of mineralization, whereas δ56Fe values of chalcopyrite (−0.65‰ to 1.11‰) are largely positive (except for the W Horizon) and decreases in samples from Footwall Zone, through the Main Zone ≈ Four Dams ≈ Sally, to the W Horizon. Source heterogeneity, sulfide segregation, variations in R factor, crustal contamination, hydrothermal fluids, and redox reactions have been ruled out as having had a significant effect on the Fe isotope composition of both pyrrhotite and chalcopyrite. Rather, the positive correlation between δ56FeCcp and the pyrrhotite/chalcopyrite ratio of the mineralized zones indicates that the large range in δ56FeCcp is likely due to variations in the amount of monosulfide solid solution (MSS) that crystallized before intermediate solid solution (ISS). Monosulfide solid solution favors 54Fe, thus the δ56Fe of the residual Cu-rich liquid would be higher than the initial sulfide liquid and variable depending on how much MSS crystallized before ISS. Subsequent to the solidification of MSS, it exsolved pyrrhotite with minor pentlandite, with troilite exsolving from pyrrhotite at lower temperatures. The large range in δ56FePo is likely due to the partitioning of 54Fe and 56Fe among these phases and the variability in the proportion of the phases in the samples. These conclusions have important implications for the applicability of Fe isotopes in base-metal sulfides to characterizing magmatic Ni–Cu–PGE systems as the Fe isotope composition of two of the most dominant base-metal sulfides in these systems, pyrrhotite and chalcopyrite, are not controlled by mineralizing processes, but rather subsolidus processes.