scholarly journals Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes

2014 ◽  
Author(s):  
Klaus J. Schulz ◽  
Laurel G. Woodruff ◽  
Suzanne W. Nicholson ◽  
Robert R. Seal ◽  
Nadine M. Piatak ◽  
...  
Keyword(s):  
Platinum Group Element ◽  
Group Element ◽  
Nickel Copper ◽  
Magmatic Sulfide ◽  
Platinum Group

The effects of post-cumulus alteration on the distribution of chalcophile elements in magmatic sulfide deposits and implications for the formation of low-S-high-PGE zones: The Luanga deposit, Carajás Mineral Province, Brazil

2021 ◽  
Vol 59 (6) ◽  
pp. 1453-1484
Author(s):  
Eduardo Mansur ◽  
Sarah-Jane Barnes ◽  
Cesar F. Ferreira Filho
Keyword(s):  
Base Metal ◽  
Platinum Group Element ◽  
Platinum Group Elements ◽  
Group Element ◽  
Metal Sulfides ◽  
Chalcophile Elements ◽  
Platinum Group Minerals ◽  
Base Metal Sulfides ◽  
Magmatic Sulfide ◽  
Platinum Group

ABSTRACT Most of the World's platinum-group element ore deposits occur as thin stratiform layers within layered intrusions. These layers generally contain disseminated base-metal sulfides or chromite. However, cryptic platinum-group element deposits also occur without chromite or base-metal sulfides in what are known as low-S-high platinum-group element deposits. The origin of these deposits is not clearly understood. The Luanga Complex hosts the largest platinum-group elements resource in South America (i.e., 142 Mt at 1.24 ppm Pt + Pd + Au and 0.11% Ni) and hosts both a platinum-group element deposit containing disseminated base-metal sulfides (style 1) and a low-S-high platinum-group element deposit (style 2). It therefore offers the opportunity to compare the two deposit types in the same overall geological setting and consider how the low-S-high platinum-group element deposit could have formed. The first deposit style is termed the Sulfide zone and consists of a 10–50 meter-thick interval with disseminated base metal sulfides, whereas the second style is named low-S-high-Pt-Pd zone and consists of 2–10 meter-thick discontinuous lenses of 1–5 meter-thick sulfide- and oxide-free harzburgite and orthopyroxenite with discrete platinum-group minerals. Secondary assemblages commonly replace primary igneous minerals to a variable extent throughout the deposit, and thus allow for investigating the effects of post-cumulus alteration on the distribution of a wide range of chalcophile elements in a magmatic sulfide deposit at both whole-rock and mineral scale. This study presents the whole-rock distribution of S, platinum-group elements, and Te, As, Bi, Sb, and Se in both mineralization styles and the concentration of trace elements in base-metal sulfides from the Sulfide zone. The Sulfide zone has Pt/Pd ratios around 0.5 and high concentrations of Te, As, Bi, Sb, and Se, whereas the low-S-high-platinum-group element zone has Pt/Pd ratios greater than 1 and much lower Se, Te, and Bi concentrations, but comparable As and Sb contents. This is reflected in the platinum-group element assemblage, comprising bismuthotellurides in the Sulfide zone and mostly arsenides and antimonides in the low-S, high platinum-group elements zone. Moreover, the base-metal sulfides from the Sulfide zone have anomalously high As contents (50–500 ppm), which suggest that the sulfide liquid segregated from a very As-rich silicate magma, possibly illustrated by an average komatiitic basalt that assimilated a mixture of upper continental crust and black shales. We interpret the low-S-high platinum-group elements zone as a product of S loss from magmatic sulfides during post-cumulus alteration of the Luanga Complex. Selenium, Te, Bi, and Pd were also lost together with S, whereas As and Sb were expelled from base-metal sulfide structures and combined with platinum-group elements to form platinum-group minerals, suggesting they may play a role fixating platinum-group elements during alteration. The remobilization of chalcophile elements from magmatic sulfide deposits located in the Carajás Mineral Province may represent a potential source for hydrothermal deposits found in the region.

Genesis of sulfide vein mineralization at the Sakatti Ni-Cu-PGE deposit, Finland

2021 ◽  
Vol 59 (6) ◽  
pp. 1485-1510
Author(s):  
Fabian Fröhlich ◽  
Janne Siikaluoma ◽  
Inga Osbahr ◽  
Jens Gutzmer
Keyword(s):  
Solid Solution ◽  
Base Metal ◽  
Platinum Group Element ◽  
Group Element ◽  
Sulfide Liquid ◽  
Intermediate Solid Solution ◽  
Platinum Group Minerals ◽  
Magmatic Sulfide ◽  
Platinum Group ◽  
Residual Melt

ABSTRACT The Sakatti Ni-Cu-platinum-group element deposit is situated in northern Finland and comprises massive, disseminated, and vein sulfide mineralization. A stockwork is formed by chalcopyrite-rich sulfide veins, which contain exceptionally high platinum-group elements and Au grades. The mineralogy and geochemistry of this stockwork zone ore is documented in this investigation. The results are used to develop the first robust genetic concept and its relationship to massive and disseminated mineralization of the Sakatti deposit. This model is similar to that proposed for many Cu-rich magmatic sulfide ores, most importantly the Cu-rich footwall veins described from the Sudbury Complex in Canada and the Cu-rich ore at Noril'sk-Talnakh in Russia. Detailed petrographic studies using a sample suite from exploration drill core intersecting vein-style mineralization revealed a classic magmatic sulfide assemblage of chalcopyrite ± pyrrhotite, pentlandite, and pyrite. More than 1000 platinum-group mineral grains belonging almost exclusively to the moncheite (PtTe2) – merenskyite (PdTe2) – melonite (NiTe2) solid solution series were identified in the studied samples. Notably, almost two thirds of the platinum-group element-bearing minerals consist of melonite. Some of the platinum-group minerals contain inclusions of Ag-rich gold (AgAu2) and muthmannite (AuAgTe2). Most of the platinum-group minerals occur as inclusions in chalcopyrite, although a few grains are located at base-metal sulfide grain boundaries and in fractures in base-metal sulfides. The whole-rock compositions of the stockwork veins are Cu-rich and are interpreted to represent a fractionated Cu-rich sulfide liquid enriched in Pt, Pd, Au, Ag, As, Bi, Pb, Se, Te, Zn, which separated from a monosulfide solid solution (mss). An intermediate solid solution (iss) solidified from the Cu-rich sulfide liquid, recrystallizing chalcopyrite at <550 °C. Simultaneously, small volumes of intercumulus residual melt contained mainly the precious metals, Bi, and Te due to their incompatibility in iss. Solitary and composite platinum-group minerals as well as Au-minerals crystallized first from the residual melt (<600 °C), followed by a succession of various Bi-, Ag-, and Pb-tellurides (∼540 °C), and finally sphalerite and galena. Melonite crystallized as mostly large, solitary grains exsolved directly from Ni-bearing intermediate solid solution (∼600 °C), shortly after the formation of moncheite and merenskyite from the residual melt. Finally, remobilization of the platinum-group minerals occurred at temperatures of <300 °C, as suggested by the presence of minor amounts of Cl-bearing minerals and ragged grain shapes.

Distribution of noble metals in magmatic sulfide occurrences in the Montagnais Sill Complex, Labrador Trough, Canada

2021 ◽  
Vol 59 (6) ◽  
pp. 1599-1626
Author(s):  
William D. Smith ◽  
Wolfgang D. Maier ◽  
Ian Bliss
Keyword(s):  
Inductively Coupled Plasma ◽  
Precious Metal ◽  
Platinum Group Element ◽  
Noble Metals ◽  
Trace Element Analysis ◽  
Group Element ◽  
Element Analysis ◽  
Sulfide Melt ◽  
Magmatic Sulfide ◽  
Platinum Group

ABSTRACT We have characterized the distribution of noble metals among six styles of magmatic sulfide mineralization in the Montagnais Sill Complex of the Labrador Trough in northern Québec using optical and electron microscopy combined with laser ablation-inductively coupled plasma-mass spectrometry trace element analysis of sulfides. The principal sulfide minerals include pyrrhotite, chalcopyrite, and pentlandite with accessory sphalerite and sulfarsenides. In addition, cubanite, troilite, and mackinawite are present in ultramafic-hosted assemblages. The precious metal mineral assemblages are dominated by tellurides, Ag-rich gold, and sperrylite which generally occur at the margins of sulfides. Few iridium-group platinum group element- and Rh-bearing grains were identified and mass-balance calculations show that these elements are generally hosted in pyrrhotite and pentlandite. Virtually all Pt and Au are hosted in precious metal grains, whereas Pd is distributed between precious metal grains and pentlandite. Where present, sulfarsenides are a key host of iridium-group platinum group element, Rh, Pd, Te, and Au. The presence of troilite, cubanite, and mackinawite and the absence of pentlandite exsolution lamellae in the ultramafic-hosted sulfides indicates an initial sulfide melt with a high metal/S ratio. Sulfarsenides present among globular sulfide assemblages derive from an immiscible As-rich melt that exsolved from the sulfide melt in response to the assimilation of the As-bearing floor rocks. In this study, the composition of sulfides is consistent with those derived from Ni-Cu-dominated deposits and not platinum group element-dominated deposits.

scholarly journals Multiple Magma Conduits Model of the Jinchuan Ni-Cu-(PGE) Deposit, Northwestern China: Constraints from the Geochemistry of Platinum-Group Elements

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 187 ◽  
Author(s):  
Xiancheng Mao ◽  
Longjiao Li ◽  
Zhankun Liu ◽  
Renyu Zeng ◽  
Jeffrey Dick ◽  
...  
Keyword(s):  
Platinum Group Element ◽  
Parental Magma ◽  
Major Elements ◽  
Group Element ◽  
Sulfide Ores ◽  
Massive Sulfides ◽  
Nickel Copper ◽  
Magma Sources ◽  
Sulfide Melt ◽  
Platinum Group

The giant Jinchuan nickel-copper-platinum-group element (PGE) deposit is hosted by two individual sub-vertical intrusions, referred to as the western and eastern intrusions (including segment II-W and segment II-E). Exactly how the Jinchuan deposit was formed by a system of sub-vertical magma conduits is still not well understood. This paper reports new major elements, trace elements and PGEs data from the Jinchuan deposit to study the formation mechanism of sulfide ores with different textures and their relationship with the magma conduit system. Our study shows that the PGE tenors of disseminated and net-textured sulfide in segment II-E are significantly lower than segment II-W and the western intrusion, but the Cu/Pd ratios are opposite. In addition, net-textured sulfides in segment II-W show a negative correlation between IPGE (Ir, Ru and Rh) and PPGE (Pt and Pd) in contrast to the positive correlation in segment II-E and the western intrusion. These features indicate the parental magma sources of the western intrusion, segment II-W and segment II-E were originally three different surges of PGE-depleted magma. Modeling of parental magma in the western intrusion, segment II-W and segment II-E suggests that they were formed by the same initial picritic basalt (100 ppm Cu, 1 ppb Ir and 10 ppb Pd) with different prior sulfide segregations (0.0075%, 0.0085% and 0.011%). The three parts of Jinchuan sulfides show that the Pt/Pd and (Pt + Pd)/(Ir + Ru + Rh) ratios decrease from section III-5 toward both sides in the western intrusion and decrease from section II-14 toward all sides, whereas no regular spatial variations occur in segment II-E, showing the different fractionation processes of sulfide melt. The massive sulfides in the western intrusion and segment II-E experienced a ~20% to 40% and ~40% to 60% fractionation of sulfide melt, respectively. We propose that the Jinchuan deposit was generated in a metallogenic system of multiple magma conduits, where sulfides entrained in parental magma experienced different amounts of prior removal.

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