Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Godel, Bélinda

doi:10.1007/978-94-017-9652-1_9

Cited by 42 publications

(11 citation statements)

References 188 publications

(274 reference statements)

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“…A small number of mafic (-ultramafic) intrusive systems, so-called layered intrusions, are responsible for supplying most of society's Pt, Pd and Rh [1][2][3] . A wealth of field, petrological and geochemical information exists for precious metal deposits in economically significant layered intrusions 2,4,5 . However, uncertainty persists regarding the mechanisms that concentrate precious metals in centimetre-metre thick layers in these intrusions 1,6 .…”

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confidence: 99%

Rapid crystallization of precious-metal-mineralized layers in mafic magmatic systems

et al. 2020

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The solidified remnants of mafic magmatic systems host the greatest concentrations of platinum-group metals in the Earth's crust. Our understanding of precious metal mineralisation in these intrusive bodies is underpinned by a traditional view of magma chamber processes and crystal mush solidification. However, considerable uncertainty remains regarding the physical and temporal controls on concentrating these critical metals, despite their importance to modern society. We present high-precision 87 Sr/ 86 Sr analyses of plagioclase and clinopyroxene from within cm-thick precious metal-enriched layers in the approximately 60 Ma open-system Rum layered intrusion (NW Scotland). Isotopic heterogeneity is present between plagioclase crystals, between clinopyroxene and plagioclase, and within plagioclase crystals, throughout the studied section. Based on these observations, we demonstrate that platinum-group element mineralisation formed by repeated small-volume reactive melt percolation events. The preservation of

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Rapid crystallization of precious-metal-mineralized layers in mafic magmatic systems

et al. 2020

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“…The proportion, morphology, size, and distribution of sulfide aggregates observed in the rocks can be used to shed light on the processes that led to the transport, segregation, and accumulation of the sulfide liquid (Godel et al, 2006(Godel et al, , 2013Godel, 2015;Robertson et al, 2015). However, most of the existing studies were carried out on relatively dry basalt and komatiite systems erupted at surface or subvolcanic levels.…”

Section: Segregation and Transport Of Sulfide Blebs In Hydrous Silicamentioning

confidence: 99%

Microstructural constraints on magma emplacement and sulfide transport mechanisms

et al. 2018

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The poorly constrained nature of the physical transfer of sulfides along magmatic conduits has implications for the genesis and localization of mineral deposits as well as for understanding the large-scale mobility of volatiles and metals across different geochemical reservoirs. Our natural laboratory to address this topic is a sulfide-bearing ultramafic pipe emplaced in the deep crust of the Ivrea-Verbano Zone, northwest Italy. The pipe is composed of volatile-rich peridotite that contains disseminated, blebby, and semimassive sulfides enriched in nickel, copper, and platinum-group elements (PGEs). The integration of electron backscatter diffraction orientation data and three-dimensional (3-D) X-ray computed tomography analyses from this study indicated that (1) most of olivine crystallized upon emplacement of the magma; (2) the shape and texture of the intragranular sulfide blebs, principally hosted within the central portions of the pipe, reflect early sulfide saturation; and (3) marginal areas record higher strain compared to the cores of the pipes. The differences in the size distribution of the sulfide grains between the central and marginal areas of the pipe are due to magma emplacement dynamics. The larger sulfide aggregates forming the bulk of the Ni-Cu-PGE sulfide mineralization along the margins of the pipe are interpreted to have formed by coalescence of a large number of smaller sulfide droplets. The observed sulfide size distribution between the central and marginal areas of the Valmaggia pipe is principally due to the dynamics of the magma upon emplacement, and it locally records the role of water-and carbon dioxide-bearing volatiles in the physical entrainment of dense sulfide liquids. These processes provide a viable mechanism to transport sulfides enriched in chalcophile and siderophile metals from the upper mantle into the lower continental crust, where they may be available for later remobilization into ore systems that may form subsequently in the middle and upper crust.

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“…In many -but not all -of these occurrences, the PGE are hosted in chromitite seams (>60 vol.% Cr-spinel). A significant body of work demonstrates the petrogenetic link between the concentration of the PGE and the formation of chromitite (e.g., Irvine 1977;Melcher et al 1997;O'Driscoll et al 2009;González-Jiménez et al 2014a, 2014bLatypov et al 2013;Godel 2015). Layered intrusion-bearing 'stratiform' chromitite seams are associated with two of the largest deposits (reefs) of the PGE on Earth: the Merensky Reef and the UG-2 chromitite, both situated in the Critical Zone of the 2 Ga Bushveld Complex (South Africa; cf.…”

Section: Introductionmentioning

confidence: 99%

“…Here, we combine X-ray microtomography (μCT) with petrography and mineral chemistry to visualise the 3D distribution and microstructure of the base-and precious metal-rich phases and link this to their chemical signatures. Establishing the microstructural relationships between Cr-spinel, base-metal phases and the PGM in chromitite is pivotal to understanding the petrogenesis of these deposits; distinguishing between these high density phases is an objective particularly well-addressed by μCT (e.g., Ketchum and Carlson 2001;Godel et al 2010;Godel et al 2013;Godel, 2015;Prichard et al 2017). The key goal in this study is to elucidate the distribution of the PGE between specific carrier phases and link this to the chromitite microstructure and mineral chemistry to formulate a comprehensive petrogenetic interpretation.…”

Section: Introductionmentioning

confidence: 99%

Platinum-group element remobilization and concentration in the Cliff chromitites of the Shetland Ophiolite Complex, Scotland

et al. 2018

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The ~492 Ma Shetland Ophiolite Complex contains an extensive mantle section, within which numerous podiform chromitite bodies formed during melt percolation in a supra-subduction zone setting. One of the Shetland ophiolite chromitite localities has an unusual style of platinum-group element (PGE) mineralization. Specifically, the Cliff chromitite suite has relatively high (>250 ppm) Pt plus Pd, compared to other chromitites in the Shetland Ophiolite Complex. In this study, we apply petrographic observation, mineral chemistry and novel X-ray microtomography data to elucidate the petrogenesis of PGE-bearing phases at Cliff. The combined datasets reveal that the PGE at Cliff have probably been fractionated by an As-rich fluid, concentrating Pt and Ir into visible (0.1–1 µm) platinum-group minerals (PGM) such as sperrylite and irarsite, respectively. The high (>1 ppm) bulk-rock concentrations of the other PGE (e.g. Os) in the Cliff chromitites suggests the presence of abundant fine-grained unidentified PGM in the serpentinized groundmass. The spatial association of arsenide phases and PGM with alteration rims on Cr-spinel grains suggests that the high Pt and Pd abundances at Cliff result from a late-stage low-temperature (e.g. 200–300°C) hydrothermal event. This conclusion highlights the potential effects that secondary alteration processes can have on modifying and upgrading the tenor of PGE deposits.

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Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Cited by 42 publications

References 188 publications

Rapid crystallization of precious-metal-mineralized layers in mafic magmatic systems

Rapid crystallization of precious-metal-mineralized layers in mafic magmatic systems

Microstructural constraints on magma emplacement and sulfide transport mechanisms

Platinum-group element remobilization and concentration in the Cliff chromitites of the Shetland Ophiolite Complex, Scotland

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