Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin?
Laurite, ideally (Ru,Os)S<sub>2</sub>, is a common accessory mineral in podiform and stratiform chromitites and, to a lesser extent, it also occurs in placer deposits and is associated with Ni-Cu magmatic sulfides. In this paper, we report on the occurrence of zoned laurite found in the...
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MDPI AG
2020-04-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/10/4/373 |
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| author | Federica Zaccarini Giorgio Garuti |
| author_facet | Federica Zaccarini Giorgio Garuti |
| author_sort | Federica Zaccarini |
| collection | DOAJ |
| description | Laurite, ideally (Ru,Os)S<sub>2</sub>, is a common accessory mineral in podiform and stratiform chromitites and, to a lesser extent, it also occurs in placer deposits and is associated with Ni-Cu magmatic sulfides. In this paper, we report on the occurrence of zoned laurite found in the Merensky Reef of the Bushveld layered intrusion, South Africa. The zoned laurite forms relatively large crystals of up to more than 100 µm, and occurs in contact between serpentine and sulfides, such as pyrrhotite, chalcopyrite, and pentlandite, that contain small phases containing Pb and Cl. Some zoned crystals of laurite show a slight enrichment in Os in the rim, as typical of laurite that crystallized at magmatic stage, under decreasing temperature and increasing sulfur fugacity, in a thermal range of about 1300–1000 °C. However, most of the laurite from the Merensky Reef are characterized by an unusual zoning that involves local enrichment of As, Pt, Ir, and Fe. Comparison in terms of Ru-Os-Ir of the Merensky Reef zoned laurite with those found in the layered chromitites of the Bushveld and podiform chromitites reveals that they are enriched in Ir. The Merensky Reef zoned laurite also contain high amount of As (up to 9.72 wt%), Pt (up to 9.72 wt%) and Fe (up to 14.19 wt%). On the basis of its textural position, composition, and zoning, we can suggest that the zoned laurite of the Merensky Reef is “hydrothermal” in origin, having crystallized in the presence of a Cl- and As-rich hydrous solution, at temperatures much lower than those typical of the precipitation of magmatic laurite. Although, it remains to be seen whether the “hydrothermal” laurite precipitated directly from the hydrothermal fluid, or it represents the alteration product of a pre-existing laurite reacting with the hydrothermal solution. |
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| publishDate | 2020-04-01 |
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| series | Minerals |
| spelling | doaj.art-9b4f398e8c4e43d8a8a11e709b47673a2023-11-19T22:15:03ZengMDPI AGMinerals2075-163X2020-04-0110437310.3390/min10040373Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin?Federica Zaccarini0Giorgio Garuti1Department of Applied Geological Sciences and Geophysics, University of Leoben, A-8700 Leoben, AustriaDepartment of Applied Geological Sciences and Geophysics, University of Leoben, A-8700 Leoben, AustriaLaurite, ideally (Ru,Os)S<sub>2</sub>, is a common accessory mineral in podiform and stratiform chromitites and, to a lesser extent, it also occurs in placer deposits and is associated with Ni-Cu magmatic sulfides. In this paper, we report on the occurrence of zoned laurite found in the Merensky Reef of the Bushveld layered intrusion, South Africa. The zoned laurite forms relatively large crystals of up to more than 100 µm, and occurs in contact between serpentine and sulfides, such as pyrrhotite, chalcopyrite, and pentlandite, that contain small phases containing Pb and Cl. Some zoned crystals of laurite show a slight enrichment in Os in the rim, as typical of laurite that crystallized at magmatic stage, under decreasing temperature and increasing sulfur fugacity, in a thermal range of about 1300–1000 °C. However, most of the laurite from the Merensky Reef are characterized by an unusual zoning that involves local enrichment of As, Pt, Ir, and Fe. Comparison in terms of Ru-Os-Ir of the Merensky Reef zoned laurite with those found in the layered chromitites of the Bushveld and podiform chromitites reveals that they are enriched in Ir. The Merensky Reef zoned laurite also contain high amount of As (up to 9.72 wt%), Pt (up to 9.72 wt%) and Fe (up to 14.19 wt%). On the basis of its textural position, composition, and zoning, we can suggest that the zoned laurite of the Merensky Reef is “hydrothermal” in origin, having crystallized in the presence of a Cl- and As-rich hydrous solution, at temperatures much lower than those typical of the precipitation of magmatic laurite. Although, it remains to be seen whether the “hydrothermal” laurite precipitated directly from the hydrothermal fluid, or it represents the alteration product of a pre-existing laurite reacting with the hydrothermal solution.https://www.mdpi.com/2075-163X/10/4/373lauritesulfidesfluidsplatinum group elements (PGE)platinum group minerals (PGM)Merensky Reef |
| spellingShingle | Federica Zaccarini Giorgio Garuti Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin? Minerals laurite sulfides fluids platinum group elements (PGE) platinum group minerals (PGM) Merensky Reef |
| title | Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin? |
| title_full | Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin? |
| title_fullStr | Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin? |
| title_full_unstemmed | Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin? |
| title_short | Zoned Laurite from the Merensky Reef, Bushveld Complex, South Africa: “Hydrothermal” in Origin? |
| title_sort | zoned laurite from the merensky reef bushveld complex south africa hydrothermal in origin |
| topic | laurite sulfides fluids platinum group elements (PGE) platinum group minerals (PGM) Merensky Reef |
| url | https://www.mdpi.com/2075-163X/10/4/373 |
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