scholarly journals Chemical Characteristics of Ore-Bearing Intrusions and the Origin of PGE–Cu–Ni Mineralization in the Norilsk Area

Minerals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 819
Author(s):  
Nadezhda Krivolutskaya ◽  
Sheida Makvandi ◽  
Bronislav Gongalsky ◽  
Irina Kubrakova ◽  
Natalia Svirskaya
Keyword(s):  
Carbonate Rocks ◽  
Platinum Group Element ◽  
Parental Magma ◽  
Group Element ◽  
Silicate Rock ◽  
Ore Formation ◽  
Trace Element Contents ◽  
World Class ◽  
Host Rocks

The composition of the parental magmas of Cu–Ni deposits is crucial for the elucidation of their genesis. In order to estimate the role of magma in ore formation, it is necessary to compare the compositions of silicate rock intrusions with different mineralization patterns, as observed in the Norilsk region. The rock geochemistry of two massifs located in the same Devonian carbonate rocks—the Kharaelakh intrusion, with its world-class platinum-group element (PGE)–Cu–Ni deposit, and the Pyasinsky–Vologochansky intrusion, with its large deposit—was studied. Along with these massifs, the Norilsk 2 massif with noneconomic mineralization intruded in the Ivakinskaya–Nadezhdinskaya basalts was studied as well. Their settings allow the estimation of the parental magma composition, taking into account the possible assimilation of host rocks. Analyses of 39 elements in 97 samples demonstrated the similarity of the intrusions in terms of their major components. The Pyasinsky–Vologochansky intrusion contains the highest trace element contents compared with the Kharaelakh and Norilsk 2 massifs, evidencing its crystallization from evolved parental magma. No influence of host rocks on the silicate rock compositions was found, except for narrow (1–2 m) endo-contact zones. There is no correlation between the mineralization volume and the rock compositions of the studied intrusions. It is assumed that the intrusions were formed from one magma crustal source irregularly rich in sulfur (S). This source inhomogeneity in terms of the sulfur distribution resulted in deposits of varying sizes. The magmas served as a transporting agent for sulfides from deep zones to the surface.

Variant Offset-Type Platinum Group Element Reef Mineralization in Basal Olivine Cumulates of the Kapalagulu Intrusion, Western Tanzania

2021 ◽  
Author(s):  
M. D. Prendergast
Keyword(s):  
Precious Metal ◽  
Platinum Group Element ◽  
Early Stage ◽  
Precious Metals ◽  
Parental Magma ◽  
Group Element ◽  
Metal Enrichment ◽  
Reef Development ◽  
Platinum Group ◽  
Olivine Cumulates

Abstract The Kapalagulu intrusion in eastern Tanzania hosts a major, 420-m-thick, stratiform/stratabound platinum group element (PGE)-bearing sulfide zone—the Lubalisi reef—within a prominent, chromititiferous, harzburgite unit close to its stratigraphic base. Several features of the vertical base and precious metal distributions (in a composite stratigraphic section based upon two deep exploration drill holes) display similarities to those of offset-type PGE reefs that formed under the overall control of Rayleigh fractionation: (1) composite layering (at several scales) defined by systematic vertical variations of sulfide and precious metal contents and intermetallic ratios, indicating repeated cycles of PGE enrichment and depletion in the order Pd-Pt-Au-Cu, and (2) in the lower part of the reef, stratigraphic offsets of the precious metal peaks below peak sulfide (Cu) content. The form and geochemistry of the reef are consistent with overturns of basal liquid layers within a liquid layering system (i.e., stable density-driven stratification of a magma chamber), plus at least two minor inputs of parental magma during which the resident magma was recharged with sulfur and metals, and the effective depletion of precious metals in the magma midway through reef development. The Lubalisi reef differs from classic offset-type PGE reefs, however, principally because individual Pd, Pt, and Au enrichment peaks are coincident, not offset. The reef is set apart from other offset-type PGE reefs in three additional ways: (1) its association with olivine cumulates that crystallized soon after initial magma emplacement and well below the first appearance of cumulus pyroxene or plagioclase (implying attainment of sulfide saturation and precious metal enrichment without prolonged concentration of sulfur and chalcophile metals by normal magma cooling and differentiation), (2) the probable role of chromite crystallization in not only triggering sulfide segregation during reef formation but also facilitating precious metal enrichment in the early stages of reef development, and (3) its great width. The early stage of fractionation may also help explain the coincident precious metal peaks through its effect on apparent precious metal partition coefficients.

scholarly journals Introduction to the special issue on the Flatreef PGE-Ni-Cu deposit, northern limb of the Bushveld Igneous Complex

2020 ◽  
Author(s):  
Wolfgang D. Maier ◽  
Marina Yudovskaya ◽  
Pedro Jugo
Keyword(s):  
Ore Deposits ◽  
Special Issue ◽  
Ore Formation ◽  
Igneous Complex ◽  
Northern Limb ◽  
Pge Mineralization ◽  
World Class ◽  
Bushveld Igneous Complex ◽  
Mine Development ◽  
Host Rocks

AbstractMore than 30 years ago, Cox and Singer (1986) suggested that magmatic platinum-group element (PGE)-Ni-Cu deposits are amongst the best understood of ore deposits, yet the origin of PGE mineralization in the Bushveld Igneous Complex (BIC) remains controversial after a century of study. In the northern limb of the BIC, the unravelling of ore formation proved particularly difficult due to relatively poor outcrop, which is typically affected by contamination of the intruding magmas with the host rocks and expressed in the form of abundant xenoliths, footwall rafts and disturbance of magmatic stratigraphy. In this thematic issue, we present contributions on the Flatreef, a recently discovered world-class PGE-Ni-Cu deposit constituting a downdip extension of the mineralized unit of the Platreef of the northern limb. Two deep shafts are currently being sunk, making the Flatreef one of the most significant new mine development on the Bushveld in several decades.

scholarly journals Platinum-Group Element Geochemistry of the Escondida Igneous Suites, Northern Chile: Implications for Ore Formation

2019 ◽  
Vol 60 (3) ◽  
pp. 487-514 ◽  
Author(s):  
Hongda Hao ◽  
Ian H Campbell ◽  
Jeremy P Richards ◽  
Eizo Nakamura ◽  
Chie Sakaguchi
Keyword(s):  
Platinum Group Element ◽  
Group Element ◽  
Northern Chile ◽  
Element Geochemistry ◽  
Ore Formation ◽  
Platinum Group

Hybrid Nature of the Platinum Group Element Chromite-Rich Rocks of the Norilsk 1 Intrusion: Genetic Constraints from Cr Spinel and Spinel-Hosted Multiphase Inclusions

2020 ◽  
Vol 115 (6) ◽  
pp. 1321-1342
Author(s):  
Ivan F. Chayka ◽  
Vadim S. Kamenetsky ◽  
Liudmila M. Zhitova ◽  
Andrey E. Izokh ◽  
Nadezhda D. Tolstykh ◽  
...  
Keyword(s):  
Platinum Group Element ◽  
Sedimentary Rocks ◽  
Alkali Feldspar ◽  
Group Element ◽  
Genetic Constraints ◽  
Silicate Inclusions ◽  
Chromium Spinel ◽  
Platinum Group ◽  
Host Rocks

Abstract The Norilsk 1 intrusion (Russia), renowned for its abundance of sulfide ores, contains an upper contact zone, which hosts sulfide-poor and Cr spinel and platinum group element (PGE)-rich discontinuous reefs with significant economic potential. Located within strongly inhomogeneous contact rocks of various compositions, the origin of these reefs is complex and debated. Enrichment in PGEs in these rocks is distributed heterogeneously, occasionally occurring in extremely dense disseminations of Cr spinel, which are unusual for other rocks of the Norilsk 1 intrusion. The compositions of Cr spinel vary significantly between individual samples, even within the same samples across clusters of several Cr spinel grains and single grains. Chromium spinel grains are broadly characterized by low Mg# (3–50 mol %), moderate to extremely high TiO2 content (1–18 wt %), diverse Fe2+/Fe3+ ratios, and elevated V and Zn. Multiphase silicate inclusions hosted by Cr spinel are dominated by orthopyroxene, alkali-feldspar, clinopyroxene, Na phlogopite, high-Al amphibole, chlorite, and albite, along with minor felsic glass, sulfide, apatite, baddeleyite, titanite, calcite, halite, and cordierite. Heating experiments (1,250°C) on the silicate inclusions failed to produce homogeneous glasses but showed evidence of partial melting and reactions with precursor minerals that crystallized new phases. The experimentally obtained glasses are characterized by compositions that strongly differ from any known igneous rock in the Norilsk region, and the assemblage of phases in these inclusions is not supportive of the entrapment of a homogeneous silicate melt. Trace element patterns of the glasses of the experimentally heated inclusions are compositionally distinct from the Norilsk trap basalts, and instead are closer to the sedimentary rocks of the Norilsk region. We suggest that an in situ interaction between the mafic melt and the sedimentary rocks was responsible for Cr spinel mineralization and the formation of the host rocks. The subsequent subsolidus modification of the initial rocks expanded the Cr spinel compositional range and formed muscovite-albite-chlorite assemblages, which replaced the original silicate minerals.

Genesis and mechanisms of metal enrichment in the Baimazhai Ni-Cu-(PGE) deposit, Ailaoshan Orogenic Belt, SW China

2021 ◽  
Vol 59 (6) ◽  
pp. 1543-1570
Author(s):  
Yiguan Lu ◽  
C. Michael Lesher ◽  
Liqiang Yang ◽  
Matthew I. Leybourne ◽  
Wenyan He
Keyword(s):  
Platinum Group Element ◽  
Crustal Contamination ◽  
Platinum Group Elements ◽  
Group Element ◽  
Orogenic Belt ◽  
Large Igneous Province ◽  
Type I ◽  
Monosulfide Solid Solution ◽  
Platinum Group ◽  
Host Rocks

ABSTRACT The ∼259 Ma Baimazhai Ni-Cu-(platinum-group element) deposit is located in the Ailaoshan-Red River fault zone on the southwest margin of the Yangtze Plate in the Jinping area of southeastern Yunnan Province. The intrusion is lenticular (∼530 m long × 190 m wide × 24–64 m thick) and concentrically zoned (margin to core) from gabbro through pyroxenite to peridotite. It contains ∼50 kt of Ni-Cu-(platinum-group element) mineralization, concentrically zoned (margin to core) from disseminated through net-textured to massive sulfides with an average grade of 1.03 wt.% Ni, 0.81 wt.% Cu, and 0.02∼0.69 ppm Pd+Pt. The sulfide assemblage comprises pyrrhotite, chalcopyrite, and pentlandite, with lesser magnetite, violarite, galena, and cobaltite. The mineralization is enriched in Ni-Cu-Co relative to the platinum-group elements and the host rocks are enriched in highly incompatible lithophile elements relative to moderately incompatible lithophile elements with high Th/Yb and intermediate Nb/Yb ratios. These host rocks, and those at most other Ni-Cu-platinum-group element deposits in the Emeishan Large Igneous Province, have high γOs and intermediate εNd values, indicating that they crystallized from a magma derived from a subduction-modified pyroxenite mantle source and modified by crustal contamination. The initial concentrations of metals in the primary magma are estimated to have been on the order of 200 ppm Ni and 100 ppm Cu, but only 0.4 ppb Pd, 0.2 ppb Pt, 0.005 ppb Rh, 0.02 ppb Ru, and 0.01 ppb Ir. The δ34S values of ores and separated sulfides range from 5.8‰ to 8.6‰, between the ∼10‰ value of sulfides in the metasedimentary country rocks and the 0 ± 0.5‰ value expected for magmas derived from MORB-type mantle, or the –2.5 ± 0.3‰ value expected for subduction-modified mantle, consistent with equilibration at magma:sulfide mass ratios (R factors) of 100–1000. Variations in Ir100 and Pd100 (metals in 100% sulfide) are consistent with 40–60% fractional crystallization of monosulfide solid solution to form Ni-Co-intermediate platinum-group element (Ru, Os, Ir)-rich massive ores and Cu-palladium/platinum-group elements (Pt, Pd, Rh)-Au-rich residual sulfide liquids. This process is also recorded by magnetite: Type I (early magmatic), type II (late magmatic), and type III (secondary) magnetites exhibit progressively lower Cr-Ti-V concentrations. The platinum-group element contents in base-metal minerals are low, and only pentlandite, violarite, and cobaltite contain detectable concentrations of Pd, Rh, and Ru. There is abundant textural evidence for metamorphic-hydrothermal alteration of sulfides in the Baimazhai intrusion, with secondary violarite, chalcopyrite, and pentlandite being enriched (Ag, Sb, Au, Pb) or depleted (Sn) in more mobile chalcophile elements. The different tectonic and petrogenetic settings of the Baimazhai and other deposits in China highlight the potential of Ni-Cu-platinum-group element deposits to occur in subduction or post-subduction settings and demonstrate that the key controls are magma flux and access to crustal S. Exploration potential remains for the Ailaoshan orogenic belt to host additional magmatic Ni-Cu 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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