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Minerals
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In-Situ Microanalytical Techniques in Geological and Geochronological Research
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In-Situ Microanalytical Techniques in Geological and Geochronological Research

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

Deadline for manuscript submissions: closed (9 August 2024) | Viewed by 5078

Special Issue Editor

Prof. Dr. Basem Zoheir

E-Mail Website
Guest Editor
Institute of Geosciences, University of Kiel, 24118 Kiel, Germany
Interests: mineralogy, economic geology; mineral exploration; remote sensing; structural geology, geochronology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

For decades, we have witnessed the fast-progressing use of in situ microanalytical techniques in geological research that significantly contribute to revealing the details of the mantle and crustal processes. These techniques, including X-ray energy dispersive and wavelength dispersive spectrometry, X-ray fluorescence, electron backscatter diffraction, Raman spectroscopy, secondary ion mass spectroscopy, and laser ablation inductively-coupled mass spectrometry, are common. These highly flexible techniques enable single-point(spot) analysis/ablation for inclusions, line or raster sampling for bulk analysis or imaging, and precise time-depth profiling studies. 

This Special Issue intends to publish a wide spectrum of interdisciplinary studies and new findings. Investigations that integrate microscopic and microanalytical data quantitatively and forensically to answer novel scientific questions and studies that attempt to advance understanding of terrestrial and extra-terrestrial igneous, metamorphic, and sedimentary processes, as well as mining and ore petrology, are highly welcomed.

Prof. Dr. Basem Zoheir
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • microchemical analysis
  • mineral deposits
  • petrogenesis
  • trace elements
  • microtextures

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Published Papers (4 papers)

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Research

25 pages, 10774 KiB  
Article
Recycling of Au during Serpentinization of Ultramafic Rocks: A Case Study from Neoproterozoic Forearc Ophiolites, Egypt
by Basem Zoheir, Astrid Holzheid, Aliaa Diab, Azza Ragab, Fatma Deshesh and Amr Abdelnasser
Minerals 2024, 14(9), 916; https://doi.org/10.3390/min14090916 - 6 Sep 2024
Viewed by 573
Abstract
Gold, along with other highly siderophile elements, is hosted by Fe-Ni sulfide phases within peridotites and mantle melts. In this context, the lithospheric mantle emerges as a principal reservoir, providing materials crucial for the inception, augmentation, conveyance, and genesis of auriferous CO2 [...] Read more.
Gold, along with other highly siderophile elements, is hosted by Fe-Ni sulfide phases within peridotites and mantle melts. In this context, the lithospheric mantle emerges as a principal reservoir, providing materials crucial for the inception, augmentation, conveyance, and genesis of auriferous CO2-rich mantle fluids. EPMA and laser ablation ICP-MS data, integrated with petrographic and SEM studies, were used to assess the transfer of base and precious metals into the Earth’s crust, discerning between inputs from subduction-related processes and post-formation metasomatism. The study focuses on sulfide minerals in serpentinized peridotites of the Abu Dahr ophiolite in the Eastern Desert of Egypt. Originating in a supra-subduction setting during the Neoproterozoic era, the Abu Dahr peridotites underwent serpentinization and contain discrete sulfide minerals, including pentlandite, nickeloan pyrrhotite, millerite, chalcopyrite, and violarite. The uneven distribution of calcite ± magnesite ± serpentine veins throughout the host ophiolitic rocks reflects the intricate interplay of serpentinization and carbonation, as fO2 and fCO2 conditions fluctuated. Geochemical data of the host rocks reveal a progressive geochemical evolution marked by concurrent silicification and carbonate alteration, driven by the interaction of ultramafic rocks with hydrothermal fluids, ultimately leading to the extensive silicification and formation of birbirite. The ICP-MS data show that pentlandite contains up to 6.11 ppm of Au, pyrrhotite up to 0.41 ppm, millerite 0.34 ppm, and violarite 0.12 ppm. The gold concentration in pentlandite is significantly higher than in pyrrhotite, millerite, and violarite, which exhibit lower but detectable levels of Au. Desulfurization reactions of sulfide minerals during progressive serpentinization triggered the release and redistribution of Au as well as base metals and highly siderophile elements. Published thermodynamic modeling at temperatures below 300 °C and pressures of 50 MPa closely replicates the mineral assemblage observed in the Abu Dahr ophiolites, including sulfide assemblages and variations in major elements such as Mg and Fe. This suggests that the serpentinization process, along with associated hydrothermal fluids, played a crucial role in the mobilization and redistribution of gold, particularly affecting its incorporation into secondary sulfides. The mobilization of Au and other highly siderophile elements during serpentinization occurred in an environment marked by strong oxidation, as indicated by the presence of acicular antigorite, magnetite, millerite, and goethite intergrowths. Full article
(This article belongs to the Special Issue In-Situ Microanalytical Techniques in Geological and Geochronological Research)
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22 pages, 5061 KiB  
Article
A Protocol for Electron Probe Microanalysis (EPMA) of Monazite for Chemical Th-U-Pb Age Dating
by Bernhard Schulz, Joachim Krause and Wolfgang Dörr
Minerals 2024, 14(8), 817; https://doi.org/10.3390/min14080817 - 12 Aug 2024
Viewed by 650
Abstract
A protocol for the monazite (LREE,Y,Th,U,Si,Ca)PO4 in situ Th-U-Pb dating by electron probe microanalyser (EPMA) involves a suitable reference monazite. Ages of several potential reference monazites were determined by TIMS-U-Pb isotope analysis. The EPMA protocol is based on calibration with REE-orthophosphates and [...] Read more.
A protocol for the monazite (LREE,Y,Th,U,Si,Ca)PO4 in situ Th-U-Pb dating by electron probe microanalyser (EPMA) involves a suitable reference monazite. Ages of several potential reference monazites were determined by TIMS-U-Pb isotope analysis. The EPMA protocol is based on calibration with REE-orthophosphates and a homogeneous Th-rich reference monazite at beam conditions of 20 kV, 50 nA, and 5 µm for best possible matrix matches and avoidance of dead time bias. EPMA measurement of samples and repeated analysis of the reference monazite are performed at beam conditions of 20 kV, 100 nA, and 5 µm. Analysis of Pb and U on a PETL crystal requires YLg-on-PbMa and ThMz-on-UMb interference corrections. Offline re-calibration of the Th calibration on the Th-rich reference monazite, to match its nominal age, is an essential part of the protocol. EPMA-Th-U-Pb data are checked in ThO2*-PbO coordinates for matching isochrones along regressions forced through zero. Error calculations of monazite age populations are performed by weighted average routines. Depending on the number of analyses and spread in ThO2*-PbO coordinates, minimum errors <10 Ma are possible and realistic for Paleozoic monazite ages. A test of the protocol was performed on two garnet metapelite samples from the Paleozoic metamorphic Zone of Erbendorf-Vohenstrauß (NE-Bavaria, western Bohemian Massif). Full article
(This article belongs to the Special Issue In-Situ Microanalytical Techniques in Geological and Geochronological Research)
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20 pages, 9384 KiB  
Article
Petrogenetic Implications of the Lithium-Rich Tongtianmiao Granite Pluton, South China: Evidence from Geochemistry and Geochronology
by Xinhui Yu, Yongzhang Zhou, Wei Cao, Hanyu Wang, Can Zhang, Lifeng Zhong, Wu Wei, Zhiqiang Wang, Jianying Yao, Zhiqiang Chen and Qinghe Xu
Minerals 2024, 14(7), 637; https://doi.org/10.3390/min14070637 - 21 Jun 2024
Viewed by 728
Abstract
The South China Block, a region renowned for its extensive granite distribution and rich metal deposits, serves as a natural laboratory for the study of granite-related mineralization. This research focuses on the Tongtianmiao granite pluton, which is located at the intersection of the [...] Read more.
The South China Block, a region renowned for its extensive granite distribution and rich metal deposits, serves as a natural laboratory for the study of granite-related mineralization. This research focuses on the Tongtianmiao granite pluton, which is located at the intersection of the Qin-Hang and Nanling metallogenic belts and has been confirmed as a significant lithium mineral resource. Despite its discovery and ongoing development, the lithium-rich Tongtianmiao pluton has been understudied, particularly concerning its petrogenesis, which has only recently come to the forefront of scientific inquiry. By integrating an array of petrogeochemical data with geochronological studies derived from zircon and monazite dating, this study provides insights into the magmatic processes related to lithium enrichment in the Tongtianmiao granites. The Tongtianmiao granites are classified as A-type granites characterized by high SiO2 contents (69.18–78.20 wt.%, average = 74.08 wt.%), K2O + Na2O contents (4.59–8.34 wt.%, average = 6.86 wt.%), A/CNK > 1.2, and low concentrations of Ca, Mg, and Fe. These granites are enriched in alkali metals such as Li, Rb, and Cs but are significantly depleted in Ba, Sr, and Eu. They show no significant fractionation of light or heavy rare-earth elements but present characteristic tetrad effects. A finding of this study is the identification of multiple ages from in situ zircon U–Pb dating, which implies a prolonged history of magmatic activity. However, given the high uranium content in zircons, which could render U–Pb ages unreliable, emphasis is placed on the monazite U–Pb ages. These ages cluster at approximately 172.1 ± 1.1 Ma and 167.9 ± 1.6 Ma, indicating a Middle Jurassic period of granite formation. This timing correlates with the retreat of the Pacific subduction plate and the associated NE-trending extensional fault activity, which likely provided favorable conditions for lithium enrichment. The study concluded that the Tongtianmiao granites were formed through partial melting of crustal materials and subsequent underplating by mantle-derived materials, and were contaminated by strata materials. This process resulted in the formation of highly differentiated granite through magmatic differentiation and external forces. These findings have significant implications for understanding the petrogenesis of lithium-rich granites and are expected to inform future exploration endeavors in the Tongtianmiao pluton. Full article
(This article belongs to the Special Issue In-Situ Microanalytical Techniques in Geological and Geochronological Research)
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28 pages, 6429 KiB  
Article
Polymetallic Sulfide–Quartz Vein System in the Koudiat Aïcha Massive Sulfide Deposit, Jebilet Massif, Morocco: Microanalytical and Fluid Inclusion Approaches
by Samira Essarraj, Basem Zoheir, Matthew Steele-MacInnis, Matthias Frische, Abdelali Khalifa and Abdelmalek Ouadjou
Minerals 2022, 12(11), 1396; https://doi.org/10.3390/min12111396 - 31 Oct 2022
Cited by 1 | Viewed by 2269
Abstract
The Koudiat Aïcha Zn-Cu-Pb deposit (3–Mt ore @ 3 wt.% Zn, 1 wt.% Pb, 0.6 wt.% Cu) in the Jebilet massif (Morocco) comprises stratabound lenticular orebodies and crosscutting sulfide-bearing quartz ± carbonate veins in the lower Carboniferous Sarhlef volcano sedimentary succession. The veins [...] Read more.
The Koudiat Aïcha Zn-Cu-Pb deposit (3–Mt ore @ 3 wt.% Zn, 1 wt.% Pb, 0.6 wt.% Cu) in the Jebilet massif (Morocco) comprises stratabound lenticular orebodies and crosscutting sulfide-bearing quartz ± carbonate veins in the lower Carboniferous Sarhlef volcano sedimentary succession. The veins are characterized by abundant pyrrhotite, sphalerite, subordinate chalcopyrite and galena and rare Ag and Au minerals. The stratabound massive sulfide ores are attributed to a “VMS” type, whereas the origin of the sulfide–quartz ± carbonate veins remains poorly understood. New mineralogical and microanalytical data (SEM, EPMA and LA-ICP-MS) combined with fluid inclusion results point to two-stage vein formation. The early stage involved C–H–O–N Variscan metamorphic fluids which percolated through fractures and shear zones and deposited pyrite at >400 °C, followed by the formation of pyrrhotite and sphalerite (300 ± 20 °C) in quartz veins and in banded and breccia ores. The pyrrhotite–sphalerite mineralization was overprinted by aqueous brines (34 to 38 wt% eq. NaCl + CaCl2) that precipitated carbonate and Cu-Pb sulfides (±Ag-Au) at ~180–210 °C through mixing with low-salinity fluids during tectonic reworking of early-formed structures and in late extension fractures. The latter ore fluids were similar to widspread post-Variscan evaporitic brines that circulated in the Central Jebilet. Overlapping or successive pulses of different ore fluids, i.e., metamorphic fluids and basinal brines, led to metal enrichment in the quartz–carbonate veins compared to the massive sulfide ores. These results underscore that even a single deposit may record several distinct mineralizing styles, such that the ultimate metal endowment may be cumulative over multiple stages. Full article
(This article belongs to the Special Issue In-Situ Microanalytical Techniques in Geological and Geochronological Research)
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