Roles of xenomelts, xenoliths, xenocrysts, xenovolatiles, residues, and skarns in the genesis, transport, and localization of magmatic Fe-Ni-Cu-PGE sulfides and chromite

Lesher, C. Michael

doi:10.1016/j.oregeorev.2017.08.008

Cited by 61 publications

(12 citation statements)

References 99 publications

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“…Magmatic sulfides typically have δ 34 S values of 0.1 ± 0.5 ‰ (Sakai et al 1984). Some modern studies of MORB lava sulfides suggest larger ranges (Eckardt 2001, Seal 2006, Labidi et al 2012, but the original values presented by Sakai et al account for seafloor sulfate/sulfide fractionation and are thus more precise and reliable (Lesher 2017). The local pristine magmatic δ 34 S signature of the Scottish BPIP has been found to be −2.3 ± 1.5 ‰ (Hughes et al 2015a) based on the mean composition of the picritic Trotternish Sills (Hughes et al 2015a), which is comparable with that of Icelandic basalts (Torssander 1989) and MORB (Labidi et al 2012).…”

Section: Discussionmentioning

confidence: 98%

Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: implications for Ni – Cu – platinum group element mineralisation in the North Atlantic Igneous Province

et al. 2019

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The ∼60 m thick Magilligan Sill is part of the British Palaeogene Igneous Province in the North Atlantic. The sill comprises layers of dolerite and olivine gabbro, and it intrudes a thick sequence of Mesozoic mudstones and marls, which are locally baked at the sill margins. Since 2014, the sill has been an exploration target for orthomagmatic Ni – Cu – platinum group element (PGE) sulfide mineralisation analogous to the Noril’sk-Talnakh intrusion in Russia. We present new petrological, geochemical, and S isotope data to assess the prospectivity of the sill and the underlying magmatic plumbing system. Most sulfides in the dolerite portions of the sill are <50 μm in size and comprise only pyrite with PGE abundances below the detection limit. In the olivine gabbros, >150 μm size pentlandite, chalcopyrite, and pyrrhotite grains contain <4 ppm total PGE, 1460 ppm Co, and 88 ppm Ag. Pyrite from the dolerites have δ34S ranging from −10.0‰ to +3.4‰ and olivine gabbro sulfides range from −2.5‰ to −1.1‰, suggesting widespread crustal contamination. The S/Se ratios of sulfides in the dolerites and olivine gabbros range from 3500 to 19 500 and from 1970 to 3710, respectively, indicating that the latter may have come from upstream in the magma plumbing system. The Magilligan Sill records multiple injections of mafic magma into an inflating sill package, each with distinct mechanisms towards S saturation. Whilst the sulfide minerals in the sill do not constitute significant mineralisation themselves, detailed in situ studies highlight a divergence in S saturation histories and suggest that a larger volume of olivine gabbro sulfides at depth may be prospective.

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Section: Discussionmentioning

confidence: 98%

Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: implications for Ni – Cu – platinum group element mineralisation in the North Atlantic Igneous Province

et al. 2019

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“…What I would like to argue for here is some genetic link between the podiform chromitite produced in the mantle and the stratiform one in the crust; some of the chromite grains in the latter are possibly precipitated in the mantle prior to the entrainment by magma to the crust. Many factors for the formation of chromiteoversaturated magmas in the crust have been proposed, such as compression of magmas due to vesiculation [79], an increase in oxygen fugacity [8,80], assimilation of Fe-oxiderich rocks [81,82] and decompression of magmas [14], reflecting the various geologic and petrologic contexts of the host's layered intrusions.…”

Section: Discussionmentioning

confidence: 99%

Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis

Arai¹

2021

Minerals

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No genetic link between the two main types of chromitite, stratiform and podiform chromitites, has ever been discussed. These two types of chromitite have very different geological contexts; the stratiform one is a member of layered intrusions, representing fossil magma chambers, in the crust, and the podiform one forms pod-like bodies, representing fossil magma conduits, in the upper mantle. Chromite grains contain peculiar polymineralic inclusions derived from Na-bearing hydrous melts, whose features are so similar between the two types that they may form in a similar fashion. The origin of the chromite-hosted inclusions in chromitites has been controversial but left unclear. The chromite-hosted inclusions also characterize the products of the peridotite–melt reaction or melt-assisted partial melting, such as dunites, troctolites and even mantle harzburgites. I propose a common origin for the inclusion-bearing chromites, i.e., a reaction between the mantle peridotite and magma. Some of the chromite grains in the stratiform chromitite originally formed in the mantle through the peridotite–magma reaction, possibly as loose-packed young podiform chromitites, and were subsequently disintegrated and transported to a crustal magma chamber as suspended grains. It is noted, however, that the podiform chromitites left in the mantle beneath the layered intrusions are different from most of the podiform chromitites now exposed in the ophiolites.

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“…There are <2-cm-thick chromite layers in strongly differentiated komatiite flows where chromite has reached saturation after significant degrees of fractional crystallization (e.g., Kambalda: Lesher, 1989) and rare occurrences of Cr-rich lavas (e.g., Halkoaho et al, 2000), but the amount of chromite is very small and it is clear that it formed via fractional crystallization. The absence of thick chromite seams in komatiitic, picritic, or basalt lavas suggest that despite its fine grain size and theoretical high transportability (see Lesher, 2017), chromite is normally trapped at the same stratigraphic levels where it forms and is not normally transported significant distances vertically, likely because it forms larger untransportable "pseudoslugs".…”

Section: Discussionmentioning

confidence: 99%

Genesis of chromite deposits by dynamic upgrading of Fe ± Ti oxide xenocrysts

Lesher

Carson

Houlé

2019

Geology

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Roles of xenomelts, xenoliths, xenocrysts, xenovolatiles, residues, and skarns in the genesis, transport, and localization of magmatic Fe-Ni-Cu-PGE sulfides and chromite

Cited by 61 publications

References 99 publications

Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: implications for Ni – Cu – platinum group element mineralisation in the North Atlantic Igneous Province

Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: implications for Ni – Cu – platinum group element mineralisation in the North Atlantic Igneous Province

Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis

Genesis of chromite deposits by dynamic upgrading of Fe ± Ti oxide xenocrysts

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