The possibility of a ZnS-bearing sulfide melt at 600°C: Evidence from the Rajpura–Dariba deposit, India, supported by laboratory melting experiment

ABSTRACT This paper focuses on a nanoscale study of nano- and micrometer-size Os-rich mineral particles hosted in a Ni-Fe-Cu sulfide globule found in an olivine megacryst from the Udachnaya pipe (Yakutia, Russia). These platinum-group element mineral particles and their host sulfide matrices were investigated using a combination of techniques, including field emission gun electron probe microanalyzer, field emission scanning electron microscopy, and focused ion beam and high-resolution transmission electron microscopy. The sulfide globule is of mantle origin, as it is hosted in primitive olivine (Fo90–93), very likely derived from the crystallization of Ni-Fe-Cu sulfide melt droplets segregated by liquid immiscibility from a basaltic melt in a volume of depleted subcontinental lithospheric mantle. Microscopic observations by means of field emission scanning electron microscopy and single-spot analysis and mapping by field emission gun electron probe microanalyzer reveal that the sulfide globule comprises a core of pyrrhotite with flame-like exsolutions (usually <10 μm thickness) of pentlandite, which is irregularly surrounded by a rim of granular pentlandite and chalcopyrite. Elemental mapping by energy dispersive spectroscopy (acquired using the high-resolution transmission electron microscopy) of the pyrrhotite (+ pentlandite) core reveals that pentlandite exsolution in pyrrhotite is still observable at the nanoscale as fringes of 100 to 500 nm thicknesses. The sulfide matrices of pyrrhotite, pentlandite, and chalcopyrite contain abundant nano- and micrometer-size platinum group element mineral particles. A careful inspection of eight of these platinum group element particles under focused ion beam and high-resolution transmission electron microscopy showed that they are crystalline erlichmanite (OsS2) with well-developed crystal faces that are distinctively oriented relative to their sulfide host matrices. We propose that the core of the Ni-Fe-Cu sulfide globule studied here was derived from a precursor monosulfide solid solution originally crystallized from a sulfide melt at >1100 °C, which later decomposed into pyrrhotite and the pentlandite flame-like exsolutions upon cooling at <600 °C. Once solidified, the solid monosulfide solid solution reacted with non-equilibrium Cu-and Ni-rich sulfide melt(s), giving rise to the granular pentlandite in equilibrium with chalcopyrite now forming the rim of the sulfide globule. Meanwhile, nano- to micron-sized crystals of erlichmanite crystallized directly from or slightly before monosulfide solid solution from the sulfide melt. Thus, Os, and to a lesser extent Ir and Ru, were physically partitioned by preferential uptake via early formation of nanoparticles at high temperature instead of low-temperature exsolution from solid Ni-Fe-Cu sulfides. The new data provided in this paper highlight the necessity of studying platinum group element mineral particles in Ni-Fe-Cu sulfides using analytical techniques that can image nanoscale textural features in order to better understand the mechanisms of platinum group element fractionation in magmatic systems. These processes may play a crucial role in controlling the background geochemical budgets for siderophile and chalcophile elements in a wide range of mantle-derived magmas.

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Wetting Properties of Fe-Ni-Co-Cu-O-S Melts against Olivine: Implications for Sulfide Melt Mobility

Economic Geology ◽

10.2113/96.1.145 ◽

2001 ◽

Vol 96 (1) ◽

pp. 145-157 ◽

Cited By ~ 6

Author(s):

L. A. Rose

Keyword(s):

Wetting Properties ◽

Sulfide Melt

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Up, down, or sideways: emplacement of magmatic Fe–Ni–Cu–PGE sulfide melts in large igneous provinces

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2018-0177 ◽

2019 ◽

Vol 56 (7) ◽

pp. 756-773 ◽

Cited By ~ 6

Author(s):

C.M. Lesher

Keyword(s):

Fluid Dynamic ◽

Experimental Studies ◽

Natural Systems ◽

Large Igneous Provinces ◽

Ultimate Explanation ◽

Preferential Localization ◽

Igneous Provinces ◽

Sulfide Melt ◽

Analog Systems ◽

Almost All

The preferential localization of Fe–Ni–Cu–PGE sulfides within the horizontal components of dike–sill–lava flow complexes in large igneous provinces (LIPs) indicates that they were fluid dynamic traps for sulfide melts. Many authors have interpreted them to have collected sulfide droplets transported upwards, often from deeper “staging chambers”. Although fine (<1–2 cm) dilute (<10%–15%) suspensions of dense (∼4–5 g/cm3) sulfide melt can be transported in ascending magmas, there are several problems with upward-transport models for almost all LIP-related deposits: (1) S isotopic data are consistent with nearby crustal sources, (2) xenoliths appear to be derived from nearby rather than deeper crustal sources, (3) lateral sheet flow or sill facies of major deposits contain few if any sulfides, (4) except where there is evidence for a local S source, sulfides or chalcophile element enrichments rarely if ever occur in the volcanic components even where there is mineralization in the subvolcanic plumbing system, and (5) some lavas are mildly to strongly depleted in PGE >>> Cu > Ni > Co, indicating that unerupted sulfides sequestered PGEs at depth. Two potential solutions to this paradox are that (i) natural systems contained surfactants that lowered sulfide–silicate interfacial tensions, permitting sulfide melts to coalesce and settle more easily than predicted from theoretical/experimental studies of artificial/analog systems, and (or) (ii) sulfides existed not as uniformly dispersed droplets, as normally assumed, but as fluid-dynamically coherent pseudoslugs or pseudolayers that were large and dense enough that they could not be transported upwards. Regardless of the ultimate explanation, it seems likely that most high-grade Ni–Cu–PGE sulfide deposits in LIPs formed at or above the same stratigraphic levels as they are found.

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Mineralogy of Nickel and Cobalt Minerals in Xiarihamu Nickel–Cobalt Deposit, East Kunlun Orogen, China

Frontiers in Earth Science ◽

10.3389/feart.2020.597469 ◽

2020 ◽

Vol 8 ◽

Author(s):

Yixiao Han ◽

Yunhua Liu ◽

Wenyuan Li

Keyword(s):

Hydrothermal Process ◽

Cobalt Sulfide ◽

Sulfide Deposit ◽

Crustal Material ◽

Mechanism Model ◽

Electron Probe Microanalyzer ◽

Nickel Cobalt ◽

East Kunlun ◽

Metallogenic Mechanism ◽

Sulfide Melt

Located in the East Kunlun Orogen, China, the Xiarihamu magmatic nickel–cobalt sulfide deposit is the country’s second largest deposit of this type. It was formed in special early Paleozoic with low copper grade (0.14 wt%) compared with other deposits of the same type. The mineralogy of nickel and cobalt minerals, which are direct carriers of these elements, can clearly reflect their behavior in the process of mineralization; however, such information for this deposit remains unreported. In the present study, we use an electron microscope and electron probe microanalyzer to delineate and analyze many nickel and cobalt minerals such as maucherite, nickeline, cobaltite, violarite, gersdorffite, parkerite, and arsenohauchecornite in various rocks and ores. With the increase in crustal material contamination, it can reach arsenide saturation locally in sulfide melt, then a separate Ni-rich arsenide (bismuth) melt exsolves somewhere. This melt will crystallize into nickeline, parkerite, arsenohauchecornite, and maucherite first. Second, most of nickel and cobalt tend to enter cobaltite and pentlandite phases, rather than existing in chalcopyrite and pyrrhotite phases as isomorphism during sufficient fractional crystallization of sulfide melt, which gathered nickel and cobalt elements widely. Also, more than one magma might result in the superposition of ore-forming elements. Later, the ore-forming elements redistribute limitedly through a hydrothermal process. The metallogenic mechanism model of nickel and cobalt established in the present study not only explains the process of nickel–cobalt mineralization in Xiarihamu but also can be applied to similar deposits and has a wide universal replicability.

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