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Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (15 October 2023) | Viewed by 13559

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Prof. Dr. Mohamed Zaki Khedr

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Department of Geology, Faculty of Science, Kafrelsheikh University, Kafr El- Sheikh 33516, Egypt
Interests: petrology and geochemistry of ophiolitic/Alaskan-type rocks and their mineralizations (magnetite, chromitites, platinium group elements); geochemistry of iron and titanium-bearing mafic-ultramafic layered intrusions (ilmenite-magnetite ore deposits); mantle processes (melting process, mantle metasomatism/heterogenity, thermal anomaly of mantle, mantle geodynamic, mantle upwelling/recycle etc.); carbonization of mantle (Rodingites and Listvenite)
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Dear Colleagues,

Mafic–ultramafic assemblages are mainly classified into three groups according to their origin and emplacement in different tectonic settings: 1) Ophiolitic rocks representing remnants of the oceanic lithosphere (mantle and crust). 2) Alaskan-type ultramafic–mafic rocks that occur as concentrically zoned intrusions, representing the roots of Neoproterozoic island arcs. 3) Layered mafic–ultramafic intrusions related to late extensions or continental margin settings. This Special Issue aims to build a community of authors and readers to discuss the latest research and develop new ideas and research directions for mafic–ultramafic assemblages. This includes detailed mineralogy, petrology, and geochemistry of mafic–ultramafic assemblages and the use of these data to address the origin and significance of rocks that host economic ores, such as magnetite, titanomagnetite, ilmenite deposits, banded chromitites, podiform chromitited, sulphide deposits vanadium, cobalt, nickel, and platinum group minerals (PGM). Factors controlling these economic ore deposits are also discussed in this issue. This Special Issue aims to shed light on the petrogenesis and geodynamic evolution of mafic–ultramafic assemblages, understanding magmatic types and processes in the mantle, crust, and mantle–crust boundary. Papers discussing mantle processes (melting process, mantle metasomatism/heterogeneity, mantle upwelling/recycle, etc.) and the carbonization of the mantle (Rodingites and Listvenite) are welcome.

Prof. Dr. Mohamed Zaki Khedr
Guest Editor

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Keywords

petrology and geochemistry of ophiolitic and Alaskan-type rocks
mineralogy and geochemistry of mafic–ultramafic intrusions
genesis of chromitites and platinum group minerals (PGM)
genesis of Fe-Ti oxide ores
magnetite formation during serpentinization processes
carbonation of mantle and different mantle processes

Published Papers (7 papers)

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Research

16 pages, 8542 KiB

Open AccessArticle

Tectonic-Thermal Evolution of the Wadi El-Dahal Area, North Eastern Desert, Egypt: Constraints on the Suez Rift Development

by Sherif Mansour, Noriko Hasebe, Mohamed Zaki Khedr, Akihiro Tamura and Amer A. Shehata

Minerals 2023, 13(8), 1021; https://doi.org/10.3390/min13081021 - 30 Jul 2023

Viewed by 812

Abstract

The Suez Rift developed as a northern extension of the Red Sea rift during the Oligocene-Miocene, whose flanks were constructed from the Neoproterozoic basement rocks of the Arabian–Nubian Shield. These basement rocks are comprised of the whole tectonic history since their formation. The Suez Rift initiation model and proposed thermal overprint role in the rifting process and flank development remain uncertain. Additionally, the amplitude of different regional tectonic events’ effects on the region is still debatable. Integration of fission-track thermochronology data with modeling of the time-temperature history has demonstrated efficiency in addressing such issues. In the context of this study, eleven representative samples were collected from the different rock units in the Wadi El-Dahal area at the northern tip of the western flank of the Suez Rift. These samples revealed Carboniferous zircon fission-track cooling ages of 353 ± 9 Ma and 344 ± 11 Ma. Meanwhile, the apatite fission-track analysis provided two spatially separated age groups: Permian-Triassic and Late Cretaceous, with average ages of 249 ± 11 Ma and ca. 86 ± 10 Ma, respectively. The time-temperature modeling revealed four possible cooling pulses representing exhumation events, which were initiated as a response to four tectonic activities: the accretion-subsequent event of erosion during the Neoproterozoic, the Hercynian (Variscan) tectonic event during the Devonian-Carboniferous, the Mid-Atlantic opening during the Cretaceous, and the Suez Rift opening during the Oligocene-Miocene. The western flank of the Suez Rift suggests a passive mechanical type with no extra thermal overprint, as indicated by the dominance of older thermochronological ages, modest rift flank elevations, and a reduction in the heat flow. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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35 pages, 39306 KiB

Open AccessArticle

Impact of DEMs for Improvement Sentinel 2 Lithological Mapping Utilizing Support Vector Machine: A Case Study of Mineralized Fe-Ti-Rich Gabbroic Rocks from the South Eastern Desert of Egypt

by Ali Shebl, Hatem M. El-Desoky, Ahmed M. Abdel-Rahman, Wael Fahmy, Hamada El-Awny, Anas El-Sherif, Mahmoud M. El-Rahmany and Árpád Csámer

Minerals 2023, 13(6), 826; https://doi.org/10.3390/min13060826 - 18 Jun 2023

Cited by 2 | Viewed by 1496

Abstract

Fused remote sensing datasets have greatly contributed to enhancing lithological targets and providing significant information for mineral exploration. For instance, multispectral datasets can discriminate rock units through their unique spectral signatures. Digital Elevation Models (DEMs) could be an effective tool boosting lithological discrimination based mainly on their topographic variations. Consequently, the current study applied the power of the support vector machine (SVM) algorithm and the integrated Phased Array L-type band Synthetic Aperture Radar (PALSAR) DEM and multispectral Sentinel 2 data to: 1—Create an updated lithological map of a poorly mapped arid terrain (Khashir-Ras El-Kharit district, Eastern Desert of Egypt), and 2—Compare and assess the distribution of ferrogabbros with the aim of improving the localization of these rock bodies and investigating their mineral content. Our results enhanced the lithological mapping and revealed a better generalization of mineralized ferrogabbros when the input was a fused DEM with Sentinel 2 compared to the salt and pepper effect observed when adopting the Sentinel 2 solely as the input data. Additionally, the current research strongly recommends detailed exploration programs for Fe-Ti oxide ores within the gabbroic rocks delineated through the resultant thematic map. The ferrogabbros were subjected to a comprehensive analysis involving whole rock geochemistry, XRD, EDX, and light-reflecting investigations, which revealed the existence of magnetite, titanomagnetite, and hematite. The titanomagnetite crystals display subhedral morphology and exhibit fine- to medium-grained surfaces with irregular shapes. X-ray diffraction (XRD) analysis revealed the presence of magnetite and hematite in the concentrated Fe-Ti oxides. Additionally, the whole rock geochemistry highlighted the origin of the ferrogabbros and their proposed tectonic setting as an alkaline to calc-alkaline magma type that developed in a continental arc setting. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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15 pages, 3982 KiB

Open AccessArticle

Reconstructing the Tectonic History of the Arabian–Nubian Shield in Sinai: Low-Temperature Thermochronology Implications on Wadi Agar Area

by Sherif Mansour, Noriko Hasebe, Kamal Abdelrahman, Mohammed S. Fnais and Akihiro Tamura

Minerals 2023, 13(4), 574; https://doi.org/10.3390/min13040574 - 20 Apr 2023

Cited by 2 | Viewed by 1312

Abstract

The Arabian–Nubian Shield envelops the entire regional tectonic history from its formation during the Ediacaran to the Red Sea/Gulf of Suez rifting in the Oligocene–Miocene. The occurrence and extent of the expected successive tectonic events on Sinai basement rocks remain uncertain. Integration of thermochronological techniques with time–temperature modelling has proven to be a powerful tool for thermal-tectonic history reconstruction. Therefore, we collected representative samples from the Arabian–Nubian Shield basement rocks of the Wadi Agar area at the eastern flank of the Suez rift. Zircon fission-track data show two cooling age possibilities of Ediacaran and Devonian ages. Meanwhile, apatite fission-track data represent three cooling age spans of Carboniferous, Triassic, and Cretaceous. The integration of these data with the modelled time–temperature histories reveals four different cooling events synchronous with the regional events; (1) the Neoproterozoic post-accretion erosional event that causes near-surface rock uplift, (2) the Devonian–Carboniferous Hercynian tectonic event which affected the region with rocks exhumation of ca. 4.2 ± 1.4 km, (3) the Triassic Gondwana breakup initiation, and (4) the Oligocene–Miocene Gulf of Suez rifting which caused flanks uplift in the studied region of ca. 1.2 ± 0.4 km. The Gulf of Suez is a passive rift with a dominant mechanical component that is divided into two differently exhumed northern and southern segments, where an additional far-field thermal overprint was restricted to the southern segment. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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29 pages, 9294 KiB

Open AccessArticle

Petrogenesis and Tectonic Evolution of Kab Amiri Ophiolites and Island-Arc Assemblages, Central Eastern Desert, Egypt: Petrological and Geochemical Constraints

by Sherif A. Taalab, Ahmed M. Abdel-Rahman, Hamada El-Awny, Hamdy A. Awad, Hesham M. H. Zakaly, Wael Fahmy and Antoaneta Ene

Minerals 2023, 13(4), 528; https://doi.org/10.3390/min13040528 - 09 Apr 2023

Cited by 1 | Viewed by 1356

Abstract

The Kab Amiri area in the Central Eastern Desert (CED) of Egypt comprises ophiolitic rocks, island arc metasediments, and granitic rocks. This study deals with the petrography and geochemistry of the ophiolitic and island arc rocks to understand their petrogenesis and geodynamic evolution of the CED ophiolitic belt. The Kab Amiri ophiolite is dismembered, comprising serpentinites and metabasalt (spilite). Serpentinites have low contents of Al₂O₃ (1.14 wt%) and CaO (0.65 wt%), suggesting they are depleted peridotite protoliths (e.g., depleted harzburgites to dunites). The high L.O.I. value (13.7 wt%) of serpentinite rocks indicates intense hydration and serpentinization during alteration processes. Petrographic and geochemical studies suggest that serpentinites were likely formed after depleted peridotites in a supra-subduction zone (SSZ) setting (e.g., a fore-arc setting). Spilitic basalt shows a tholeiitic affinity of the depleted mantle source. The arc-related metasediments are represented mainly by schists and slate. Many samples of metasediments are relatively low in alumina (Al₂O₃ < 15%), suggesting a low clay content and formation in an island arc setting. In contrast, protoliths of island-arc metabasalts and meta-andesites crystallized from calc-alkaline magmas in the immature oceanic arcs. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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25 pages, 20567 KiB

Open AccessArticle

Tectonometamorphic Evolution of the Migmatitic Paragneisses of the Filali Unit (Internal Rif, Morocco)

by Abdelkhaleq Afiri, Abderrahim Essaifi, Ali Charroud, Mourad Aqnouy, Kamal Abdelrahman, Amar Alali and Mohamed Abioui

Minerals 2023, 13(4), 484; https://doi.org/10.3390/min13040484 - 30 Mar 2023

Viewed by 1716

Abstract

A lithosphere-scale extensional shear zone juxtaposes an underlying sub-continental peridotite body and overlying migmatitic paragneisses of the Filali unit in the Beni Bousera massif (Internal Rif, Morocco). Three stages are recognized in the metamorphic evolution of the aluminous paragneiss, marked by the chemical zoning of garnet porphyroblasts and the evolution of associated mineral assemblages characterized by the presence of kyanite and rutile (M1), sillimanite, k-feldspar and melt (M2), and cordierite (M3). Phase-equilibrium modeling (pseudosections) and multi-equilibrium thermobarometry point to P-T conditions of 7 kbar 750 °C and 3.5 kbar 685 °C for the M2 and M3 stages, respectively. M1 conditions of 9.3 kbar 660 °C were inferred using modeling after the reintegration of melt lost during M2 into the bulk composition. Published geochronological data suggest a Variscan age (250–340 Ma) for the M1 event, whereas M2 and M3 are Oligo-Miocene and related to the Alpine orogeny. The recorded sub-isothermal decompression is related to significant crustal attenuation in the Oligo-Miocene and is responsible for the juxtaposition of the hot asthenospheric mantle and the crustal units, causing the melting of the paragneiss. The exhumation of the gneisses by crustal extension is associated with the westward retreat of an Alpine subduction (slab rollback). Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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20 pages, 9894 KiB

Open AccessArticle

Neoproterozoic Aksu Diabase Dyke, Chinese South Tianshan: Magma Sources and Implications for Regional Gold Metallogeny

by Guoxiong Ma, Xiaobo Zhao, Chunji Xue and Renke Wang

Minerals 2023, 13(3), 326; https://doi.org/10.3390/min13030326 - 25 Feb 2023

Viewed by 1607

Abstract

Tianshan is one of the world’s largest gold provinces; however, the relationship between gold mineralization and metasomatized subcontinental lithospheric mantle (SCLM) remains poorly understood. To improve our understanding, we present new bulk-rock geochemistry and platinum group element (PGE) concentrations of the SCLM-sourced Aksu Neoproterozoic diabase dykes in Chinese South Tianshan. These data, combined with in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of hydrothermal pyrite grains in the diabase dykes, are used to discuss the SCLM source characteristics in the region and their potential links to formation of gold deposits. The diabase dykes exhibit high Th/Yb (0.47–0.62) and low Nb/U (13.4–16.3) ratios, indicating that magma evolution involves subduction-related fluid metasomatism and limited contamination of the continental crust. This is consistent with little variation in whole-rock Pd/Zr, Cu/Zr, and Ni/MgO ratios, suggesting that no sulfide segregation was caused by crustal contamination and magma mixing. In addition, the diabase dykes show low PGE and Au contents, with high Cu/Pd (>10⁵) and low Cu/Zr (<0.5) ratios, indicating that magmas were derived from low-degree partial melting of the SCLM under S-saturated conditions. Such source characteristics indicate residual sulfides and chalcophile elements (e.g., PGEs, Au, and Cu) were concentrated at the SCLM reservoir in South Tianshan. Hydrothermal pyrite in the studied dykes has similar Au/Ag ratios and trace element distribution patterns to gold-bearing pyrite of lode gold deposits in Chinese South Tianshan, indicating that metasomatized SCLM may have contributed ore metals during the formation of these gold deposits. Adding to the available data, our study highlights that the SCLM may be a potential metal source reservoir, and it may have contributed to formation of the lode gold deposits in Chinese South Tianshan. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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33 pages, 7382 KiB

Open AccessFeature PaperArticle

Geochemistry of Waziristan Ophiolite Complex, Pakistan: Implications for Petrogenesis and Tectonic Setting

by Raham Jalil, Olivier Alard, Bruce Schaefer, Liaqat Ali, Muhammad Sajid, Mohamed Zaki Khedr, Mohammad Tahir Shah and Muhammad Naveed Anjum

Minerals 2023, 13(3), 311; https://doi.org/10.3390/min13030311 - 23 Feb 2023

Cited by 4 | Viewed by 3634

Abstract

The Waziristan ophiolite complex (WOC), a segment of paleo-suture zone between the Indo-Pakistan plate to the south-east and the Afghan microplate to the north-west, is primarily composed of serpentinized dunites and serpentinites after harzburgites, crosscut by pyroxenites. The crustal portion dominantly comprises basalts and dolerites, with less abundant plagiogranites. Whole-rock XRF and trace element ICP-MS analyses were undertaken to determine the degree of melt extraction and subsequent geochemical depletion or enrichment of peridotite protoliths. The investigated peridotites are extremely refractory and show high Mg# values (0.88–0.92), low Al₂O₃ (0.19–0.96 wt%), total alkali values (0.02 < Na₂O + K₂O ≤ 0.20 wt%), CaO (0.04–0.73 wt%), and TiO₂ (0.001–0.017 wt%), but are rich in Cr (up to 3550 ppm) and Ni (up to 2340 ppm). Bulk REE modelling suggests that Waziristan peridotites underwent a high degree (15%–25% melting) of melt extraction in the closed system of spinel-bearing peridotite facies at shallow depths above a subduction zone and, in their chemistry (Sc, REE, Al₂O₃, and MgO), resemble Izu-Bonin-Mariana (IBM) forearc peridotites. Their U-shaped REE patterns and trace elements resemble peridotites derived from supra-subduction zone (SSZ) settings, especially a forearc setting, and also reflect metasomatism by slab-derived fluids. The ultramafic rocks preserve depletion in REE content (0.03 < ΣREE_CN < 0.60), indicating the highly depleted nature of refractory peridotites. The basalts (Mg#, 0.48-0.68) are similar in composition to typical boninite and show low to moderate MgO (6.2–13.0 wt%), low total alkali content (0.01–4.45 wt%) and TiO₂ (0.13–0.17 wt%), but are higher in Al₂O₃ (≈11.9 wt%). They show a sub-alkaline affinity and possess geochemical signatures that are transitional from island arc basalt (IAB) magmas to boninitic magmas due to the changes from an extensional to a compressional regime during the initiation of subduction. These geochemical signatures suggest the formation of basalts from melts, resulting from the re-melting of the depleted mantle during intra-oceanic subduction initiation. The higher Th/Nb and V/Ti ratios of the studied basalts further confirm their generation in an SSZ setting characterized by subduction-derived fluids under higher oxidizing conditions. The mafic-ultramafic rocks of the WOC were, therefore, likely formed during intra-oceanic subduction initiation (forearc spreading) in the SSZ setting; they were exhumed along a thrust fault, and obducted onto the forearc region as result of the collision between the Indian plate and the Afghan microplate. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Mafic-Ultramafic Assemblages and Associated Ore Deposits)

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