45 research outputs found
Chromite Grain Diameter (CGD) from the ore-hosting dunite of the Xerolivado-Skoumtsa chrome mine (Vourinos,Western Macedonia, Greece): implications for chrome ore exploration
No full textThe largest chrome-ore bearing dunite of the Vourinos Complex occurs within the Xerolivado-Skoumtsa Mine District. The host dunite body has a surface exposure of 3 km2 and extends at least 400m into the subsurface.
The dunite body is hosted by harzburgite tectonite interfolded with the dunite body during ductile phases of deformation.
The Xerolivado-Skoumtsa mine is one of the world’s largest ophiolite-hosted chrome deposits with a potential of 6 million tons of ore assaying at 22 wt.% Cr2O3. Even so, chrome ore bodies compose less than 1% of the volume of the dunite body. Exploration consisted chiefly of expensive drilling programs.
A well-documented suite of chrome ores from the south sector of the mine were collected during the final years of its operation (1987-1988). Samples include twenty-seven (27) samples of serpentinite altered from primary olivine that originally coexisted with the chromite. Two types of serpentinised dunite were distinguished: Type A samples are from serpentinised dunite 1m from the ore bodies, and Type B samples are silicates infolded with the ores during original high-temperature mantle deformation.
Thin-polished sections were studied via optical microscopes (transmitted and reflected light). All chromite grains (2,776 total measurements) were photographed and measured in eight directions at angular resolution of 22.5o, starting from the maximum diameter. The average and median chromite grain diameter (CGD) was calculated for each sample.
These geometric analyses indicate that CGD decreases depending on the position (Type A or Type B) of the samples: the average and the median of the CGD were smaller in the serpentinites next to the chromite ore bodies (Type A) than those within consecutive chromite ore bodies (Type B).
A decrease of the average and median CGD was found in (today’s) vertical ore dimension: samples from mine level 717m have larger average and median CGD than samples from over-lying mine level 738m and from the underlying mine level 692m. This concurs with the position of the thickest size of the ore bodies, decreasing towards the overlying levels and underlying levels.
The grain size of chromite in these dunites is due to a combination processes of original Cr-spinel crystallization and grain break-up and deformation concurrent to original dunite thinning around the ore layers. With the lack of preserved olivine morphology, these structures are the only “fingerprints” of the type of deformation undergone on grain scale. These results could provide a “petrographic tool” useful for the exploration of schlieren-type chrome ores: host dunite (serpentinite) samples present lower average and median CGD when they are found closer to the ore bodies. Future research on this subject should focus on the verification of the results in other similar ore-hosting dunites and mineralogical and/or metallogenetic interpretation of the numeric results
Mineral Surface Science and Nanogeoscience: The Case of Mineral Nanoparticles, Nanominerals and Natural Nanoporous Oxide Materials
No full textInvestigation of Trace and Critical Elements (Including Actinides) in Flotation Sulphide Concentrates of Kassandra Mines (Chalkidiki, Greece)
No full textPyrite/arsenopyrite (Py-AsPy), galena (PbS), and sphalerite (ZnS) concentrates from the flotation plants of Olympias and Stratoni (Kassandra mines, Chalkidiki, N. Greece) were investigated for their major, trace, minor, and critical element contents, including actinides associated to natural radioactivity. It is revealed that in addition to the Pb, Zn, Ag, and Au being exploited by Hellas Gold S.A., there are also significant concentrations of Sb and Ga (Sb: >0.2 wt.% in PbS concentrate; Ga:25 ppm in ZnS concentrate), but no considerable contents of Bi, Co, V, or REE. Concerning other elements, As was found in elevated concentrations (>1 wt.% in Py-(As)Py-AsPy Olympias concentrate and almost 1 wt.% in Stratoni PbS and ZnS concentrates) together with Cd (specifically in ZnS concentrate). However, actinides occurred in very low concentrations (U < 2 ppm and Th < 0.5 ppm in all examined concentrates), limiting the possibility of natural radioactivity in the Hellas Gold S.A. products. The concentrations of the natural radionuclides (238U, 232Th, and 40K) are much lower than those of commercial granitic rocks, and thus the associated radioactive dose is insignificant
SYNTHESIS AND STUDY OF COMPLEX COMPOUNDS SUPPORTED ON NATURAL ZEOLITES
No full textTRANSITION METAL COMPLEX COMPOUNDS SUPPORTED ON NATURAL ZEOLITE CRYSTALS (OF THE HEU - TYPE/HEULANDITE) WERE SYNTHESIZED AND CHARACTERIZED. THE STUDY INCLUDED CU - AND CO - COMPLEXES WITH DIETHYLDITHIOCARBAMATE LIGANDS AS WELL AS NI - COMPLEXES WITH PYRIDINE. THE SYNTHESIS WAS ACHIEVED BY MEANS OF GRADUAL CHEMICAL MODIFICATIONS OF THE INITIAL (RAW) ZEOLITE CRYSTALS. IN THE CASE OF CU AND CO, SURFACE COMPLEXES "ANCHORED" ONTO THE ZEOLITE WERE IDENTIFIED. IN THECASE OF NI, BOTH INTRAZEOLITE AND SURFACE COMPLEXES WERE DEFECTED USING IN -SITU SPECTROSCOPIC TECHNIQUES. THE RESULTS OF THIS STUDY COULD LEAD TO THE DEVELOPMENT OF NEW MATERIALS AND CONTRIBUTE TO THE SOLUTION OF PROBLEMS RELATED TO THE GEOCHEMISTRY OF THE MICROPOROUS ALUMINOSILICATE MINERALS.ΣΥΜΠΛΟΚΕΣ ΕΝΩΣΕΙΣ ΜΕΤΑΒΑΤΙΚΩΝ ΣΤΟΙΧΕΙΩΝ ΚΑΘΗΛΩΜΕΝΕΣ ΣΕ ΚΡΥΣΤΑΛΛΟΥΣ ΦΥΣΙΚΟΥ ΖΕΟΛΙΘΟΥ (ΤΥΠΟΥ - HEU/ΧΙΟΥΛΑΝΔΙΤΗ) ΣΥΝΤΕΘΗΚΑΝ ΚΑΙ ΧΑΡΑΚΤΗΡΙΣΘΗΚΑΝ. Η ΜΕΛΕΤΗ ΠΕΡΙΕΛΑΒΕ ΣΥΜΠΛΟΚΑ CU ΚΑΙ CO ΜΕ ΔΙΑΙΘΥΛΟΔΙΘΕΙΟΚΑΡΒΑΜΙΔΙΚΑ LIGANDS ΚΑΘΩΣ ΚΑΙ ΣΥΜΠΛΟΚΑ NI ΜΕ ΠΥΡΙΔΙΝΗ. Η ΣΥΝΘΕΣΗ ΕΠΙΤΕΥΧΘΗΚΕ ΜΕΣΩ ΣΤΑΔΙΑΚΩΝ ΧΗΜΙΚΩΝ ΤΡΟΠΟΠΟΙΗΣΕΩΝ ΤΩΝ ΑΡΧΙΚΩΝ (ΑΥΤΟΥΣΙΩΝ) ΖΕΟΛΙΘΙΚΩΝ ΚΡΥΣΤΑΛΛΩΝ. ΣΤΗΝ ΠΕΡΙΠΤΩΣΗ ΤΟΥ CU ΚΑΙ ΤΟΥ CO ΕΞΑΚΡΙΒΩΘΗΚΑΝ ΣΥΜΠΛΟΚΑ "ΑΓΚΥΡΩΜΕΝΑ" ΣΤΗΝ ΕΠΙΦΑΝΕΙΑ ΤΟΥ ΖΕΟΛΙΘΟΥ. ΣΤΗΝ ΠΕΡΙΠΤΩΣΗΤΩΝ NI, ΕΝΤΟΠΙΣΘΗΚΑΝ ΤΟΣΟ ΕΝΔΟΖΕΟΛΙΘΙΚΑ ΟΣΟ ΚΑΙ ΣΥΜΠΛΟΚΑ ΕΠΙΦΑΝΕΙΑΣ ΧΡΗΣΙΜΟΠΟΙΩΝΤΑΣ IN - SITU ΦΑΣΜΑΤΟΣΚΟΠΙΚΕΣ ΤΕΧΝΙΚΕΣ. ΤΑ ΑΠΟΤΕΛΕΣΜΑΤΑ ΤΗΣ ΕΡΕΥΝΑΣ ΑΥΤΗΣ ΘΑ ΜΠΟΡΟΥΣΑΝ ΝΑ ΣΥΜΒΑΛΛΟΥΝ ΣΤΗΝ ΑΝΤΙΠΤΥΞΗ ΝΕΩΝ ΥΛΙΚΩΝ ΚΑΙ ΝΑ ΣΥΝΕΙΣΦΕΡΟΥΝ ΣΤΗΝΕΠΙΛΥΣΗ ΠΡΟΒΛΗΜΑΤΩΝ ΠΟΥ ΣΧΕΤΙΖΟΝΤΑΙ ΜΕ ΤΗΝ ΓΕΩΧΗΜΕΙΑ ΤΩΝ ΜΙΚΡΟΠΟΡΩΔΩΝ ΑΡΓΙΛΟΠΥΡΙΤΙΚΩΝ ΟΡΥΚΤΩΝ
Mineral Surface Science and Nanogeoscience
No full textIn the last decades technological developments have revitalized a new area of research in Mineralogy with respect of the structure and reactivity of mineral surfaces. Mineral Surface Science is closely associated to the fields of Molecular Geochemistry and Biogeochemistry, concerning the investigation of geochemical processes at the molecular level. The expansion of both scientific subjects is based on the combined utilization of advanced microscopic and -surface- spectroscopic techniques, such as AFM, STM, TEM, SIMS, LIBS, and XPS. Nowadays, it is possible to study, by means of in situ AFM, crystal growth and dissolution processes occurring at mineral-fluid interfaces, in real time, also on a molecular scale (nanoscale). Moreover, accelerator-/Synchrotron-based techniques, including PIXE, NRRA, RBS, SR-(µ)XRF, SR-(µ)XRD and (µ)XANES/EXAFS, present new opportunities for Nanogeoscience and, in general, to Earth and Environmental Sciences. Mineral Surface Science and molecular Geochemistry have contributed to the establishment of Nanogeoscience with regard to the study of nanoparticles in nature and the investigation of geological processes in the nanoscale (1 nm–100 nm). As an example, a part of the research currently elaborated concerns the surface chemical behavior of calcite. This common carbonate mineral plays a major role in the global CO2 cycle, participates in key biomineralization processes, and shows high reactivity in fluids controlling the geoavailability and bioavailability of certain contaminants. On the other hand, nanoporous minerals, such as zeolites, clays, and Fe-Mn-oxides/oxyhydroxides, are important natural materials when studying the Earth and developing relevant Environmental Technology. Additionally, Mineral Surface Science and Nanogeoscience are crucial in ore systems research. This Special Issue focuses on recent advances in Mineral Surface Science and Nanogeoscience, including, but not limited to, topics such as crystal growth; mineral dissolution; nanominerals; mineral nanoparticles; nanoporous minerals; nanoscale ore mineralogy; environmental mineralogy; environmental nanoparticles; atmospheric particles; biominerals; medical mineralogy; nanofossils; and nanoscopic methods
Dissolution, sorption/(re)precipitation, formation of solid solutions and crystal growth phenomena on mineral surfaces
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Mineral chemistry of sulphide minerals in concentrates of the Kassandra mines (Chalkidiki, Greece)
No full textThe Kassandra mining district contains porphyry Au-Cu and Au-Ag-Pb-Zn-Cu carbonate replacement deposits that are associated with Oligocene-Miocene intrusions emplaced into polydeformed metamorphic basement rocks belonging to the Permo-Carboniferous to Late Jurassic Kerdilion unit and the Ordovician-Silurian Vertiskos unit. Regional extensional tectonics active since the middle Eocene resulted in the development of widespread normal and transtensional faults, including the Stratoni fault zone that hosts carbonate replacement sulfide ore bodies (Siron et al., 2018).
More particularly, Stratoni (Madem Lakkos, Mavres Petres) and Olympias are the two main carbonate-replacement massive sulphide Pb-Zn (Ag-Au) deposits of the district; they are located on the footwall of the Tertiary Stratoni-Varvara fault. Both deposits are interpreted to form the proximal and distal part of a fault-controlled exoskarn-type ore system triggered by nearby small-scale intrusions close to the fault system (Hahn et al., 2012).
The mineral chemistry of basic sulfide minerals (major phases) into concentrates from the flotation plants of Stratoni and Olympias mines was investigated by EPMA using a JEOL 8200 SEM equipped with WDS.
The chemical formulae of the minerals in their relevant concentrates were calculated as following:
Galena (Stratoni Mine): Pb0.975-0.990Zn0.000-0.004Mn0.000-0.002As0.000-0.001S
Sphalerite (Stratoni Mine): Zn0.788-0.845Fe0.118-0.167Mn0.006-0.010Pb0.000-0.001S
Pyrite (Olympias Mine): Fe1.019-1.051As0.000-0.033Pb0.000-0.001Zn0.000-0.001S2
Arsenopyrite (Olympias Mine): FeAs0.848-0.878S1.065-1.131
In addition, the presence of boulangerite was detected in the pyrite/arsenopyrite concentrate, with microprobe analyses revealing the following chemical formula:
Pb5.182-5.253Sb4.214-4.449As0.058-0.154Fe0.040-0.154Zn0.000-0.063Mn0.010-0.020S11
All sulphide minerals studied were found having typical/expected chemical compositions in major elements. Ongoing research on these samples is also targeting the determination of their trace element concentrations, focusing on noble metals (Godelitsas et al., 2015; Kasama et al., 2018) and elements considered as Critical Raw Materials (CRM) for the EU.
Aknowledgments. This research is implemented through IKY scholarships programme and co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the action entitled ”Reinforcement of Postdoctoral Researchers”, in the framework of the Operational Programme ”Human Resources Development Program, Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) 2014 – 2020
The Rare Earth Elements Potential of Greek Bauxite Active Mines in the Light of a Sustainable REE Demand
No full textMore recent data of Greek bauxites from the Parnassos-Ghiona active mines prove that rare earth elements (REEs) occur mainly in the form of authigenic/diagenetic LREE3+ carbonate and phosphate minerals (bastnäsite/parisite group and florencite). Bulk geochemistry of representative samples, from underground mines and open pits, showed an increased content in LREE (ΣLREE—from La to Gd—varying between 106 and 913 ppm; avg. ΣLREE = 321 ppm; n = 17), and lower HREE (ΣHREE—from Tb to Lu including Y—varying between 45 and 179 ppm; avg. ΣHREE = 95; n = 17). The overall REE concentration (ΣREE + Y+Sc) varies from 192 to 1109 ppm (avg. 463 ppm; n = 17). The most abundant REE is Ce (min: 67 ppm; max: 655 ppm; avg. 193 ppm; n = 17), exhibiting in general a positive geochemical anomaly (avg. Ce/Ce* -CeA-: 2.6), identical to the case of marine Fe–Mn-crust and terrestrial desert vanish, implying also that Ce4+ may exist either in REE-oxides and/or epigenetically sorbed in Fe-oxides. On the other hand, Nd content, which is more interesting for the industry, is lower (avg. 41 ppm; n = 17). The concentration of REEs is much higher in Fe-rich (red) bauxite, compared to Fe-depleted (white) bauxite (avg. ΣREE + Y+Sc = 569 ppm and 268 ppm, respectively). The new data presented herein show a rather lower REE potential of Parnassos-Ghiona bauxites, compared to previous literature, but similar values compared to karst-type bauxites of the globe. Although their REE concentration is higher compared to that of various geochemical reference materials (i.e., positive REE geochemical anomalies in comparison with chondrites, UCC, PAAS, NASC, and ES), it is vitally lower compared to REE resources being mined, such as REE–Fe–Nb–Th deposits. A trend similar to REE geochemical trend also stands for most of the trace elements that are present in Greek bauxites—mainly HFSE—except for LILE. Besides, Greek bauxite metallurgical residue’s (red mud) REE content seems to be remarkably increased by almost two times compared to that of the Parnassos-Ghiona bauxite parent material. Scandium is another critical element. In the studied bauxites, it varies from 29 to 73 ppm (avg. 47 ppm; n = 17); it is typical for the Mediterranean and EU bauxites and laterites, but much lower compared to the exploitable Australian laterites. The Fe-rich samples contain higher concentrations of Sc compared to Fe-depleted (avg. 54 and 33 ppm, respectively). This means that common red Greek bauxite is rather more exploitable, with regard to Sc (and the rest REE), but not the white one (which is of high quality in terms of Al). Bulk geochemistry indicates that Sc is correlated to Fe but not to Zr, while microscale observations demonstrated the presence of fine-grained scandian-zircons. This is in line with a very recent study proving that Sc is mainly present in Fe-oxide minerals (mainly hematite and goethite) and zircons. Bulk geochemical Fe–Pb and Fe–As positive correlations are also verified among the associated trace elements. Finally, the investigation of the REE vertical distribution in a characteristic deposit of the B3 horizon (i.e., Pera Lakkos mine case study), showed that the REE concentration is increased in the Fe-rich domain (lying above the footwall limestone), as well as in the coal layer interstratified between the Fe-depleted domain and the hanging wall limestone. However, it is revealed that the Ce/Ce* (CeA) is increased in the coal layer and is raised to the uppermost Fe-depleted domain, but not the lowermost Fe-rich bauxite domain. This might be attributed to the Ce3+ ↔ Ce4+ and the LREE re-mobilization during the supergene/epigenetic processes
New insights into nanomineralogy and geochemistry of Ni-laterite ores from central Greece (Larymna and Evia deposits)
No full textNickeliferous laterite ores from two typical central Greece deposits (Larymna and Evia), currently used in the LARCO GMMSA smelting plant to produce ferronickel, were characterized using a combination of diffraction, microscopic, and analytical techniques. X-ray diffraction patterns of various fractions, with emphasis to the clayey material (< 2 μm), after glycolation and heating at 550 °C, indicated that both materials contain crystalline Fe3+ oxide (hematite) and chlorite-group phyllosilicates, whereas the Evia sample contains additional illite. Transmission electron microscopy investigations revealed that the LARCO laterite ores consist of complex nanoscale aggregates of the above-mentioned phases. Different Ni-bearing Mg-Fe-phyllosilicates (mainly chlorite-group minerals), occur in mixture with hematite. Nickel is present in all examined phases, and therefore the separation of pure Ni-phases, by physical or chemical methods, is practically unfeasible. Trace element bulk analyses showed that there no significant differences, with regarding to Ni content concentrations (ca. 0.6–0.7 wt.%), between the initial ore and the clay fraction, for both the Larymna and Evia laterites (ca. 30% and 26% wt.% enrichment respectively). However, the Larymna ore contains double quantities of Co and it is enriched in rare earths compared to Evia (ΣREE = 774 ppm and 76 ppm respectively), while Sc concentrations are comparable in both mining areas (64 ppm and 42 ppm respectively). Discrimination diagrams (e.g. Th/Sc vs. Zr/Sc and Ce/Ce* vs. Eu/Eu*) showed that LARCO laterite Ni-ores do not exclusively originate in ultrabasic -ophiolitic- rocks as previously considered
