Nickel Sulfide Mineralization Research Articles

Methanogens acquire and bioaccumulate nickel during reductive dissolution of nickelian pyrite.

Nickel (Ni) is a key component of the active site metallocofactors of numerous enzymes required for methanogenesis, including [NiFe]-hydrogenase, carbon monoxide dehydrogenase, and methyl CoM reductase, leading to a high demand for Ni among methanogens. However, methanogens often inhabit euxinic environments that favor the sequestration of nickel as metal-sulfide minerals, such as nickelian pyrite [(Ni,Fe)S2], that have low solubilities and that are not considered bioavailable. Recently, however, several different model methanogens (Methanosarcina barkeri, Methanococcus voltae, Methanococcus maripaludis) were shown to reductively dissolve pyrite (FeS2) and to utilize dissolution products to meet iron and sulfur biosynthetic demands. Here, using M. barkeri Fusaro, and laboratory-synthesized (Ni,Fe)S2 that was physically isolated from cells using dialysis membranes, we show that trace nickel (<20 nM) abiotically solubilized from the mineral can support methanogenesis and limited growth, roughly fivefold less than the minimum concentration known to support methanogenesis. Furthermore, when provided direct contact with (Ni,Fe)S2, M. barkeri promoted the reductive dissolution of (Ni,Fe)S2 and assimilated solubilized nickel, iron, and sulfur as its sole source of these elements. Cells that reductively dissolved (Ni,Fe)S2 bioaccumulated approximately fourfold more nickel than those grown with soluble nickel and sulfide but had similar metabolic coupling efficiencies. While the mechanism for Ni uptake in archaeal methanogens is not known, homologs of the bacterial Nik uptake system were shown to be ubiquitous across methanogen genomes. Collectively, these observations indicate that (Ni,Fe)S2 is bioavailable in anoxic environments and that methanogens can convert this mineral into nickel-, iron-, and sulfur-containing metalloenzymes to support methanogenesis and growth. IMPORTANCE Nickel is an essential metal, and its availability has changed dramatically over Earth history due to shifts in the predominant type of volcanism in the late Archean that limited its availability and an increase in euxinic conditions in the early Proterozoic that favored its precipitation as nickel sulfide minerals. Observations presented herein indicate that the methanogen, Methanosarcina barkeri, can acquire nickel at low concentration (<20 nM) from soluble and mineral sources. Furthermore, M. barkeri was shown to actively reduce nickelian pyrite; use dissolution products to meet their iron, sulfur, and nickel demands; and bioaccumulate nickel. These data help to explain how M. barkeri (and possibly other methanogens and anaerobes) can acquire nickel in contemporary and past anoxic or euxinic environments.

Effect of copper/nickel ratio on the efficiency of biobeneficiation of bulk copper-nickel sulfide concentrates

The dependence of the efficiency of biobeneficiation (via bioleaching) of bulk copper-nickel sulfide concentrates on the ratio of copper to nickel sulfide minerals was studied. The copper content in the concentrates ranged from 10.8 to 19.1% (copper occurred in chalcopyrite), while the content of nickel was within 4.6–9.5% (nickel occurred in pentlandite and violarite). Although the copper content was higher than the content of nickel in all concentrates, the rate of nickel leaching significantly exceeded that of copper leaching. For the concentrates characterized by copper/nickel ratio (k) equal to 1.15 and 1.5, the average nickel leaching rate was ˃8 times higher than the copper leaching rate. Bioleaching of all studied concentrates allowed the obtainment of copper concentrates in solids (copper content of 15.6–18.7%) in which nickel content was low (0.27–1.49%). The high level of nickel dissolution and the maximum increase in the copper content in the solids were shown for the concentrate with the initial copper and nickel content of 10.9 and 7.2%, respectively (k of 1.5). In this bioleach residue, the copper content increased by 4.7%, while the nickel content decreased by 6.86% compared to the original concentrate. Thus, bioleaching of copper-nickel concentrates can be considered biobeneficiation, and the highest efficacy of the process may be achieved at a copper/nickel ratio of ∼1.5.

The Jaguar hydrothermal nickel sulfide deposit: Evidence for a nickel-rich member of IOCG-type deposits in the Carajás Mineral Province, Brazil

The Jaguar Ni sulfide deposit (mineral reserves of 58.6 Mt at 0.95 wt% Ni) occurs along a regional fault zone in the Carajás Mineral Province in the Amazonian Craton, Brazil. This study presents the first detailed description of the Jaguar deposit and provides a basic framework to constrain the origin of the Ni sulfide mineralization. Jaguar nickel sulfide orebodies are associated with ductile-brittle hydrothermal alteration zones developed over felsic subvolcanic or granitic country rocks. Prominent features of the Jaguar deposit include: i. its location along regional scale deep fault systems, ii. extensive zones of biotite-chlorite alteration overprinted by magnetite-apatite-quartz alteration zones, iii. sulfide mineralization occurring as steeply dipping orebodies closely associated with magnetite-apatite rich bodies, iv. sulfides that are disseminated or form the matrix of breccias consisting of pyrite and millerite, with minor pentlandite, chalcopyrite and pyrrhotite, v. pyrite, magnetite and apatite occur mostly as euhedral to subhedral crystals enclosed in irregular aggregates of fine-grained anhedral millerite, vi. sulfide mineralization with high Ni (Ni/S ~ 0.15–0.30) and Co (Co/S ~ 0.005–0.015) contents, high Ni/Cu ratios (~5–25) and low Zn and PGE contents, vii. metal association consisting of LREE, Fe, U, P, Pb, Bi, Te, Ni, and Co, and viii. mineralized zones with high F contents and a positive correlation of F with S, Ni and P2O5. The geological setting and characteristics of the Jaguar deposit are similar to the iron-oxide-copper-gold (IOCG) deposits in the Carajás Mineral Province, indicating that they all belong to a regional hydrothermal system. The existence of nickel-rich members of IOCG type mineralizations in the Carajás Mineral Province was previously suggested for other deposits (e.g., GT34, Castanha) and interpreted as deeper portions of the IOCG mineral system. The close association of nickel sulfide mineralization in the Jaguar deposit with magnetite-apatite-rich breccias may be interpreted as an iron-oxide-apatite (IOA) member within the regional hydrothermal system. In contrast to most hydrothermal nickel deposits in the world, the Jaguar deposit is neither hosted by mafic-ultramafic rocks nor associated with black shales. Therefore, the Jaguar deposit is interpreted as an uncommon hydrothermal Ni deposit associated with the IOCG mineral system in the Carajás Mineral Province. Our results provide new insights for worldwide exploration for Ni sulfide deposits in geological environments different from those traditionally considered prospective.

Exploration of a novel depressant polyepoxysuccinic acid for the flotation separation of pentlandite from lizardite slimes

Lizardite is representative of a group of serpentine minerals that coexists with nickel sulfide minerals, and the lizardite slime coating that easily forms on surfaces during mineral processing, making it difficult for beneficiation. In this study, a biodegradable polyepoxysuccinic acid (PESA) was introduced as a novel depressant to eliminate the adverse effects of lizardite slimes on pentlandite flotation. The results of microflotation tests and adsorption measurements showed that PESA addition considerably increased the separation efficiency of pentlandite from lizardite slimes, which could be attributed to the improvement of collector adsorption density on the pentlandite surface. Zeta potential measurements and DLVO calculations showed that the lizardite surface charge changed from positive to negative in the presence of PESA, and the resulting electrostatic repulsion caused hetero-dispersion between pentlandite and lizardite particles. Consequently, a collector could adsorb onto the exposed pentlandite surface, restoring the floatability of pentlandite. X-ray photoelectron spectroscopy (XPS) analysis was used to characterize the chemical interactions between PESA and the Mg sites on the lizardite surface. These results demonstrate that PESA can be used as an effective depressant for removing lizardite slimes from the pentlandite surface in a flotation system.

First-Principles Study of the Elastic Properties of Nickel Sulfide Minerals under High Pressure

Nickel sulfide minerals, an important type of metal sulfides, are the major component of mantle sulfides. They are also one of the important windows for mantle partial melting, mantle metasomatism, and mantle fluid mineralization. The elasticity plays an important role in understanding the deformation and elastic wave propagation of minerals, and it is the key parameter for interpreting seismic wave velocity in terms of the composition of the Earth’s interior. Based on first-principles methods, the crystal structure, equation of state, elastic constants, elastic modulus, mechanical stability, elastic anisotropy, and elastic wave velocity of millerite (NiS), heazlewoodite (Ni3S2), and polydymite (Ni3S4) under high pressure are investigated. Our calculated results show that the crystal structures of these Ni sulfides are well predicted. These Ni sulfides are mechanically stable under the high pressure of the upper mantle. The elastic constants show different changing trends with increasing pressure. The bulk modulus of these Ni sulfides increases linearly with pressure, whereas shear modulus is less sensitive to pressure. The universal elastic anisotropic index AU also shows different changing trends with pressure. Furthermore, the elastic wave velocities of Ni sulfides are much lower than those of olivine and enstatite.

The fluid evolution of the Nimbus Ag-Zn-(Au) deposit: An interplay between mantle plume and microbial activity

The Nimbus Ag-Zn-(Au) volcanic-hosted massive sulfide (VHMS) deposit represents an exceptional orebody in the Yilgarn Craton of Western Australia. It is located in a zone of juvenile crust running N-S through the Eastern Goldfields Superterrane. However, unlike most other VHMS occurrences associated with the 2690–2680 Ma rift sequence (Teutonic Bore, Jaguar, Bentley, Erayinia), it is hosted by the ca. 2705 Ma plume-related stratigraphy, which is more typically associated with komatiite-hosted nickel-sulfide mineralization. The Nimbus deposit displays hybrid VHMS-epithermal characteristics resulting from low temperature and shallow water conditions, which developed a quartz-carbonate-sericite dominated alteration assemblage in the dacite host rocks. Sulfide mineralization comprises pyrite, sphalerite, galena, arsenopyrite, Ag-Sb-Pb-Bi sulfosalts, and rare chalcopyrite. In this study, we applied a combination of in-situ analytical techniques to monitor the evolving sulfur isotope signature of the mineralizing fluids, and propose that the Nimbus VHMS deposit developed as a result of a bimodal fluid history. In the first stage, the hydrothermal system – powered by plume-related magmatism – deposited a series of barren pyrite lenses with colloform textures. Their variable but consistently negative mass-independent sulfur isotope fractionation signature (Δ33S = −0.81%) reflects the interaction between mantle-derived magmatic fluids and Archean seawater. The ubiquitous presence of carbon-rich porous textures and the remnants of carbonaceous “nests” in colloform pyrite also indicate a significant contribution of microbial sulfate reducers during the incipient stages of sulfide precipitation. The gradual formation of colloform lenses eventually sealed the hydrothermal system establishing a physical barrier that limited the interaction with seawater. This process promoted the onset of higher temperature and pressure conditions required to form the high-grade Zn-Ag mineralization, sourcing sulfur and fluids largely from a magmatic reservoir (Δ33S = +0.09%). Whereas the identification of a predominantly magmatic sulfur source is supported by sulfur isotope signatures, the recognition of a magmatic origin of the fluid may only be inferred indirectly. It is consistent with the observed quartz-sericite alteration style and the proposed mechanism of sulfide deposition via decompression, which does not require any interaction with seawater. The trace element distribution of the ore-related sulfides also supports a closed hydrothermal system developed through multiple fluid pulses. Indeed, this ore-forming scenario is commonly favored by high confining pressures, which at Nimbus were established following the deposition of the colloform pyrite lenses that progressively sealed the hydrothermal system creating the favorable conditions for mineralization.

Evidence of magmatic degassing in Archean komatiites: Insights from the Wannaway nickel-sulfide deposit, Western Australia

Magmatic degassing from komatiite lava flows potentially influenced the geochemical evolution of the Archean atmosphere and hydrosphere. We argue that the escape of SO2-rich volatiles from komatiites impacted on the mineralogical, geochemical and isotopic composition of associated nickel-sulfide mineralization leaving behind detectable and measurable footprints that can be best observed where the polarity of the magmatic sequence is clearly recognizable. Here we focus on the ore-bearing sequence of the Archean komatiite-hosted N01 nickel-sulfide orebody at Wannaway, Yilgarn Craton, Western Australia. This deposit displays a volcanic sequence with a well-defined succession of stratigraphically-correlated facies comprising a massive sulfide horizon at the base of the channelized komatiite flow, overlain by matrix and disseminated sulfide mineralization. Pyrrhotite is the dominant sulfide phase in the lower part of the ore profile. The amount of troilite gradually increases from the base of the matrix ore over several meters up-sequence, eventually becoming dominant at the expense of pyrrhotite. In the upper portion of the mineralized sequence troilite is associated with accessory Mn sulfide alabandite (MnS), which is usually reported in reduced terrestrial and extra-terrestrial environments. Such mineralogical and volcanological features are consistent with upwards decreasing in fS2 and fO2 away from the basal contact of the komatiite flow. After evaluating the possible role of metamorphism, the pyrrhotite-troilite-alabandite assemblage and the progressive up-sequence decrease of the pyrrhotite/troilite ratio across the upper part of the mineralized sequence are interpreted as magmatic and indicative of progressive loss of sulfur with concomitant establishment of reducing conditions within the sulfide melt ponding at the base of the komatiite lava. In this context, the investigation of spatially constrained sulfur isotopic signatures allows to isolate the multiple sulfur fractionation processes that impacted on sulfide mineralization and ultimately permits the identification of the isotopic shift associated with magmatic degassing. Following this approach we recognize two distinct sulfur isotope exchanges processes triggered by 1) assimilation of sulfidic shales during emplacement of the komatiite flow, and 2) equilibration between the sulfide melt and the sulfur dissolved in the silicate melt. We finally correlate the remaining δ34S depletion up-stratigraphy with the loss of heavy sulfur isotopes through magmatic degassing of SO2-rich volatiles from the ultramafic flow. The emission of SO2 upon emplacement and cooling of the magma flow would also explain the progressive reducing fO2 and fS2 conditions indicated by variations in mineral assemblages from the base of the komatiite upwards.

High-performance reagent modes for flotation recovery of platiniferous copper and nickel sulfides from hard-to-beneficiate ores

The paper presents the results of the recent research performed in IPKON Russian Academy of Sciences that deals with development and substantiation of new selective reagents for effective flotation recovery of non-ferrous and noble metals from refractory ores. The choice and development of new selective reagents PTTC, OPDTC, modified butylxanthate (BXm) and modified diethyl-dithiocarbamate (DEDTCm) to float platiniferous copper and nickel sulfide minerals from hard-to-beneficiate ores is substantiated. The mechanism of reagents adsorption and regulation of minerals floatability is discussed. The study of reagent modes indicates that by combining PTTC with the modified xanthate results in 6 – 7 % increase in the recovery of copper, nickel and PGM in the flotation of the low-sulfide platiniferous Cu-Ni ore from the Fedorovo-Panskoye deposit. The substitution of OPDTC for BX makes it possible to increase recovery of Pt by 13 %, Pd by 9 % and 2 – 4 times the noble metal content in the flotation concentrate.

Chromite compositions in nickel sulphide mineralized intrusions of the Kabanga-Musongati-Kapalagulu Alignment, East Africa: Petrologic and exploration significance

Chromite is a ubiquitous accessory mineral in the olivine-pyroxene cumulate bodies that host massive and disseminated nickel sulphide mineralization in intrusions of the Kabanga-Musongati-Kapalagulu Alignment in East Africa. Its composition is related to the conditions of emplacement and petrologic evolution of its host magma in a spectrum of intrusions ranging from classical lopolithic layered intrusions to groups of smaller, discrete sill-like chonoliths.The Kapalagulu lopolithic intrusion, emplaced into polymetamorphosed Archæan-Palæoproterozoic crust, contains abundant chromite with relatively oxidized compositions, whereas chromites from the highly-mineralized Kabanga chonolith intrusions, emplaced into graphitic and sulphidic schists, are strongly reduced in terms of their Fe3+/Fetotal ratio. Ni in chromite correlates with Ni in olivine: Ni in both is depleted in the more strongly sulphide-mineralized intrusions. The Musongati intrusion, also emplaced through graphitic schists, but much larger and less-well mineralized in sulphides than Kabanga, has chromites intermediate in character. The compositions of the chromites can be used to determine the petrologic history of the intrusions, and may prove to be a useful exploration tool in such mineralized belts.

DIRECT DATING OF ULTRAMAFIC SILLS AND MAFIC INTRUSIONS ASSOCIATED WITH Ni-SULFIDE MINERALIZATION IN THE THOMPSON NICKEL BELT, MANITOBA, CANADA

The Paleoproterozoic Thompson nickel belt, a segment of the northwest margin of the Archean Superior craton in Manitoba, is one of the largest nickel-producing regions in the world and the second largest Ni-Cu-PGE (platinum group elements) mining camp in Canada after Sudbury. The nickel sulfide ores are hosted in or associated with ultramafic sills of komatiitic affinity that were emplaced into sulfur-rich metasedimentary rocks of the Ospwagan Group and subsequently strongly deformed and metamorphosed (amphibolite to granulite facies) during the Trans-Hudson orogeny. A U-Pb zircon age of 1880.2 ± 1.4 Ma for a metaperidotite (olivine orthopyroxenite) from the upper part of a boudinaged ultramafic sill at the Pipe 2 deposit is interpreted as the age of crystallization of the intrusion, the first age from an ultramafic sill containing mined nickel sulfide in the Thompson nickel belt. This age confirms a direct petrogenetic relationship between Ni-Cu-PGE mineralization and widespread mafic-ultramafic magmatic activity (Molson igneous events) at ca. 1.88 Ga along the Superior province craton margin (e.g., Thompson nickel belt, Fox River belt, Cape Smith belt, New Quebec orogen). At the south pit of the Thompson mine, a U-Pb zircon age of 1860.7 ± 0.7 Ma for a composite mafic intrusion (garnet amphibolite to layered metagabbro) identifies a new age of mafic magmatic activity in the Thompson nickel belt that is unrelated to nickel sulfide mineralization. The thermal effects of the Trans-Hudson orogeny are recorded by a range of zircon dates and ca. 1760 Ma metamorphic titanite from the South pit intrusion and are consistent with interpretations that regional metamorphism occurred as a single progressive event. The results of this study open up the possibility of using the high-precision U-Pb geochronology of mineralized ultramafic rocks to precisely constrain the duration of mafic-ultramafic magmatism in the Thompson nickel belt and assess potential age differences between ultramafic sills across and along strike of this world-class nickel metallotect.

Low-sulfide PGE and nickel sulfide metallogeny of Paleoproterozoic riftogenesis of the Fennoscandian Shield

By the end of the Archean, the period of active volcanism, plutonism, accretion, and cratonization had been completed by the construction of stable continental plates. Afterward, cratons were subject to intense extension owing to mainly mantle diapirism and ascent of asthenospheric flows, which gave rise to the formation of ensialic intracratonic basins, whereas other linear troughs were expressed in the formation of continental rifts. Zones of continental rifting are characterized by a wide spectrum of mineral resources (Cu, Ni, PGE, Co, Ti, V, etc.) related to igneous complexes. This paper is focused on metallogeny of nickel-sulfide and PGE mineralization in the Fennoscandian Shield. The results of metallogenic analysis of Paleoproterozoic riftogenesis, along with the account of previous achievements, have shown that the aforementioned mineralization is related to three consecutive plume-tectonic pulses of mantle activization, which are expressed in (i) upwelling of the subcontinental mantle enriched in LREE, (ii) intrusion of mafic and ultramafic melts derived from enriched and depleted Archean mantle sources, and (iii) formation of low-sulfide Pt–Pd and Pt-bearing Cu–Ni sulfide deposits.

An overview of nickel mineralisation in Africa with emphasis on the Mesoproterozoic East African Nickel Belt (EANB)

Nickel production in Africa takes place principally in Botswana, South Africa and Zimbabwe, with much of the South African and Zimbabwean production being a by-product of platinum-group element mining in the Bushveld Complex and Great Dyke. Several large nickel deposits have been discovered elsewhere in Africa but until recently, their development has been hindered by political risk and limitations in energy and transport infrastructure. Most of the continent is significantly underexplored with respect to base metals, including the area covered by the East African Nickel Belt (EANB). The known nickel deposits of the EANB all occur in mafic-ultramafic intrusive rocks of the Mesoproterozoicage Kibaran igneous event. These intrusive bodies take the form of medium to large layered intrusions, small dynamic magma conduits (chonoliths and sills) and dyke swarms. Laterite deposits are developed over exposed dunite and peridotite lithologies in the basal sequence of larger layered intrusions, whereas nickel sulphide deposits are developed at the base of the small chonoliths. Geochronological and geochemical data suggests that all intrusions in the EANB formed in a single magmatic event (1350 to 1400 Ma) and were derived from a picritic parental magma, which was variably contaminated in mid to upper-crustal staging chambers by metasedimentary rocks. As a result, nickel sulphide mineralisation was formed in all of the intrusions, but in most, the grades and tenors are too low to be considered economic in the foreseeable future. In the 1970s, government-led regional surveys identified a large nickel laterite deposit at Musongati in Burundi and a nickel sulphide deposit at Kabanga in the northwest of Tanzania. These deposits have subsequently been explored and delineated by mining companies, but they remain undeveloped due to their distance to the coast and a lack of transport and energy infrastructure. The Kabanga sulphide deposit now comprises a total mineral resource of 58 million tonnes grading 2.6% nickel. The Musongati laterite deposit comprises an overall resource of 122 million tonnes with a grade of 1.4% nickel.

The Camelwood and Musket Nickel deposits - Discovery of a new Nickel Sulphide camp in the North-eastern Goldfields of Western Australia

The Camelwood and Musket nickel sulphide deposits are significant recent discoveries, located within the Mt Fisher Greenstone Belt, in the northern goldfields region of Western Australia. Camelwood was the first deposit to be discovered, in December 2012, from a reverse circulation (RC) drilling campaign designed to test a coincident airborne electromagnetic (AEM) and geochemical anomaly. The original objective of the AEM surveys was to detect massive sulphides known to be associated with gold mineralization at the old Mt Fisher gold mine. However, a number of discrete, late-time EM anomalies were identified along an interpreted ultramafic sequence on the eastern boundary of the greenstone belt. The EM anomalies represented classic nickel sulphide mineralisation targets. Ground time-domain electromagnetic (TEM) surveys, down-hole TEM (DHTEM) surveys, and extensive drilling have been carried out since then, resulting in a JORC compliant resource at Camelwood (1.6Mt @ 2.2% Ni) and the discovery of the Musket deposit. The application of the AEM method was instrumental in the discovery of the Camelwood nickel deposit. Systematic use of ground and down hole geophysical methods has been valuable in delineating the resource at Camelwood and in the discovery of the Musket deposit. The discovery of Camelwood and Musket proves the potential of the Mt Fisher Greenstone belt to host significant nickel sulphide mineralisation.

Textural Relationship of Sulfide Ores, PGE, and Sr-Nd-Os Isotope Compositions of the Triassic Piaohechuan Ni-Cu Sulfide Deposit in NE China

The ~216-Ma Piaohechuan no. 4 intrusion in northeastern China, situated in the easternmost part of the Central Asian orogenic belt, is composed of hornblende-olivine gabbro overlain by hornblende gabbro. The intrusion is about 630 m long, 40 to 250 m wide, and 50 to 150 m thick. Nickel sulfide mineralization is restricted to the lower part of the intrusion and contains 10,000 metric tons (t) of Ni with average PGE concentrations of 40 ppb Os, 30 ppb Ir, 36 ppb Ru, 26 ppb Rh, 255 ppb Pt and 161 ppb Pd in 100% sulfide.

First-Principles Study on Ligand Binding and Positional Disorder in Pentlandite

Density functional theory, in conjunction with a cluster expansion model, has been used to study the structure and stability of the positionally disordered iron–nickel sulfide mineral pentlandite (Pn), (Fe,Ni)9S8, with results indicating heterogeneous nearest neighbor metal contacts are more energetically favorable than homogeneous contacts. The virtual crystal approximation was also explored as a means to address positional disorder, but while reliable results could be obtained for the bulk model, the same was not true for the surface, as local distortions which affected the surface model energies could not be reproduced. We also address the binding of ethyl xanthate (CH3CH2OCS2–), water, and hydroxide to the [111] Pn surface to understand the mode of action of industrial xanthate flotation agents better. In order to model anionic ligands bound to a periodic boundary condition surface we propose applying a correction derived from the surface work function to remove the additional charge introduced by the ligand. The results obtained from the ligand binding studies indicate that while ethyl xanthate could readily displace up to a full monolayer of water per unit cell it is likely that Fe-enriched surfaces will bind xanthate in competition with the hydroxide anion, while a Ni-enriched surface will preferentially bind hydroxide anions over xanthate.

Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic–mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

The 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic–mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite–trondhjemite–granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)–peridotite–pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length ≈30–500 m; width ≈2–15 m) are hosted by the serpentinite–peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78–86 and moderate Mg# (100 Mg/(Mg + Fe2+)) of 45–55. In situ trace-element analysis (LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe3+# versus Ti/Fe3+# diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on major-element characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe–Ti–V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic–mafic plutonic rocks in the Nuggihalli greenstone belt.

Catalytic Dissociation of Water on the (001), (011), and (111) Surfaces of Violarite, FeNi2S4: A DFT-D2 Study

The iron–nickel sulfide mineral violarite is relevant in origin of life theories and has potential catalytic activity. Here we present density functional theory simulations with a correction for the long-range interactions (DFT-D2) of the bulk and surfaces of violarite, and subsequent adsorption and dissociation of water. Relaxation of the low-Miller index surfaces shows the (001) surface to be energetically the most favorable, while the (111) is the least stable surface, but also the least reactive with respect to water. Calculation of the reaction energy pathways reveals that water adsorption is most likely to occur on the (011), as this stabilizes the low-coordinated atoms. Stronger adsorption energies are found for Fe octahedral sites, over tetrahedral Ni sites, with the dissociation of an adsorbed water molecule on the surface facilitating the adsorption of a subsequent molecule. Dissociation of water is also most likely to occur on the (011) surface, as reflected by negative values calculated for the overall reaction energies. The results ultimately show that associative adsorption of water is preferred over dissociative adsorption.

Spatial Variation in Platinum Group Element Concentrations in Ore-Bearing Komatiite at the Long-Victor Deposit, Kambalda Dome, Western Australia: Enlarging the Footprint of Nickel Sulfide Orebodies

Abstract The detectable footprints of komatiite-hosted nickel sulfide deposits are typically very small, but can potentially be enlarged by identifying subtle geochemical variations related to ore-forming processes in the host rocks. This study examines the spatial variability of whole-rock concentrations of platinum group elements (PGEs) within the host flow to massive nickel sulfide mineralization at the Long-Victor deposit, Kambalda dome (Western Australia), where a series of ore shoots occupy two subparallel channels, over a strike length of approximately 3,000 m. The basal komatiite flow unit at Long-Victor contains a wide range of platinum group element concentrations and PGE/Ti ratios in S-poor rocks outside the ore shoots. About a third of the samples analyzed show evidence for either enrichment or depletion in PGEs, as estimated from mantle-normalized ratios of Pt/Ti, Pd/Ti, and Rh/Ti, relative to background values typical of those found in Neoarchean Munro-type komatiites worldwide. The very strong correlations observed between Pt/Ti, Pd/Ti, and Rh/Ti testify to a primary magmatic origin of this signal. Depletion signatures are largely restricted to samples in the flanking environment within the basal flow, and are found both in spinifex-textured A-zone and cumulate B-zone samples. The strongest depletion signatures are preserved in the uppermost portions of the A-zone and decrease in magnitude with increasing depth from the stratigraphic top of the spinifex horizon downward. This is interpreted as the result of progressive flushing of the flow channel by PGE-undepleted lava subsequent to ore formation. Enriched signatures are largely restricted to cumulate rock types, and are found within both channels and flanks. The halo of anomalous PGE/Ti ratios, both depleted and enriched, extends more than 400 m from the cutoff of 0.4% Ni that defines the limit of disseminated ores, and is much more extensive and marked than anomalies defined by Ni concentrations, Ni/Cr ratios, or Ni/Ti ratios, which extend no more than 20 m beyond the disseminated ores themselves. The PGE enrichment halo is recognizable in rocks having no visible sulfide and having Ni values falling within the silicate background, and is attributed to the accumulation of small proportions of PGE-rich disseminated sulfide liquid formed at high R factors, with subsequent loss of S during hydrothermal alteration. Mapping of PGE/Ti ratios provides an effective and sensitive method for vectoring toward ore during mine-scale and prospect-scale exploration, and is potentially applicable to mafic systems as well as to komatiites.

Comparing orthomagmatic and hydrothermal mineralization models for komatiite-hosted nickel deposits in Zimbabwe using multiple-sulfur, iron, and nickel isotope data

Trojan and Shangani mines are low-grade (<0.8 % Ni), komatiite-hosted nickel sulfide deposits associated with ca. 2.7 Ga volcano-sedimentary sequences of the Zimbabwe craton. At both mines, nickel sulfide mineralization is present in strongly deformed serpentinite bodies that are enveloped by a complex network of highly sheared, silicified, and sulfide-bearing metasedimentary rocks. Strong, polyphase structural–metamorphic–metasomatic overprints in both the Trojan and Shangani deposits make it difficult to ascertain if sulfide mineralization was derived from orthomagmatic or hydrothermal processes, or by a combination of both. Multiple S, Fe, and Ni isotope analyses were applied to test these competing models. Massive ores at Shangani Mine show mass-dependent fractionation of sulfur isotopes consistent with a mantle sulfur source, whereas S-isotope systematics of net-textured ore and disseminated ore in talcose serpentinite indicates mixing of magmatic and sedimentary sulfur sources, potentially via post-magmatic hydrothermal processes. A restricted range of strongly mass-independent Δ33S values in ore samples from Trojan Mine likely reflects high-temperature assimilation of sulfur from supracrustal rocks and later superimposed low-temperature hydrothermal remobilization. Iron isotope values for most Ni-bearing sulfides show a narrow range suggesting that, in contrast to sulfur, nearly all of iron was derived from an igneous source. Negative Ni isotope values also agree with derivation of Ni from ultramafic melt and a significant high-temperature fractionation of Ni isotopes. Fe isotope values of some samples from Shangani Mine are more fractionated than expected to occur in high-temperature magmatic systems, further suggesting that hydrothermal processes were involved in either low-grade ore formation (liberation of Ni from olivine by sulfur-bearing hydrothermal fluids) or remobilization of existing sulfides potentially inducing secondary Ni-sulfide mineralization.

Nanoparticle Flotation Collectors—The Influence of Particle Softness

The ability of polymeric nanoparticles to promote glass bead and pentlandite (Pn, nickel sulfide mineral) attachment to air bubbles in flotation was measured as a function of the nanoparticle glass transition temperature using six types of nanoparticles based on styrene/N-butylacrylate copolymers. Nanoparticle size, surface charge density, and hydrophobicity were approximately constant over the series. The ability of the nanoparticles to promote air bubble attachment and perform as flotation collectors was significantly greater for softer nanoparticles. We propose that softer nanoparticles were more firmly attached to the glass beads or mineral surface because the softer particles had a greater glass/polymer contact areas and thus stronger overall adhesion. The diameters of the contact areas between polymeric nanoparticles and glass surfaces were estimated with the Young-Laplace equation for soft, liquidlike particles, whereas JKR adhesion theory was applied to the harder polystyrene particles. The diameters of the contact areas were estimated to be more than an order of magnitude greater for the soft particles compared to harder polystyrene particles.