Ultramafic Complex Research Articles

Magnesite hosted by the Neoarchean ultramafic rocks in Attappadi, southern India: Insights from spectral and stable isotope investigation

Magnesite is an economically important mineral commonly found in ultramafic complexes worldwide, primarily in Archean to Proterozoic ultramafic complexes. This study focuses on the chemical and spectral characterization of magnesite found in the Neoarchean ultramafic rocks in the Attappadi region in the Southern Granulite Terrane of southern India. The research utilizes x‐ray diffraction analysis, hyperspectral, laser Raman, Fourier Transform Infrared, and Isotope Ratio Mass Spectrometry. The studied ultramafic rocks are part of a well‐exposed ophiolitic suite known as the Agali ophiolitic complex. Magnesite primarily occurs as veins, veinlets, and lenses within weathered ultramafic rocks. The hyperspectral analysis of the magnesite samples shows absorption bands in the shortwave infrared region, particularly around 2.3 and 2.5 μm, which correspond to the stretching and bending of the CO bond in the (CO3)2− ion in MgCO3. The laser Raman spectra show intensity peaks at 1095, 738, and 330 cm−1, which may be attributed to the translational and librational vibrations. The Fourier transform infrared data reveal transmittance at 1434, 880, and 747 cm−1, corresponding to MgO bond stretching and asymmetrical CO stretching. The x‐ray powder diffraction spectra exhibit diffraction peaks at 32°, 35°, 42°, 46° and 53°, characteristic of pure magnesite. The spectroscopic parameters derived from various analyses indicate that the magnesite is high quality and free from gangue minerals. Stable isotope analysis of the magnesite samples yielded δ13C values ranging from −5‰ to −9‰ and δ18O values in the range of 21‰–25‰. The estimated water temperature from which the magnesite has been precipitated is ~59 ± 3.9°C. Based on the field relations, mode of occurrence and isotopic signatures, the mineralization is considered to have been formed by the low‐temperature alteration of ultramafic rocks facilitated by CO2‐rich fluids in the near‐surface environment. This study compares the characteristics of magnesite from the study area with a few Neoproterozoic serpentinite‐hosted magnesite veins in the ophiolitic sequence of the Egyptian Eastern Desert, which is part of the Arabian Nubian shield. The research aims to contribute to understanding magnesite formation in Archaean to Proterozoic mafic–ultramafic rocks on the Earth's crust. It also provides insights into the geological processes that govern the genesis of ultramafic‐hosted magnesite globally, particularly in East Gondwana fragments. This information can enhance mineral exploration and resource evaluation in these regions, helping to identify economic prospects and assess the feasibility of magnesite resource extraction and utilization in East Gondwana fragments.

Natural hydrogen exploration within western European and eastern Mediterranean ophiolites and ultramafic complexes

Natural hydrogen exploration within western European and eastern Mediterranean ophiolites and ultramafic complexes

Asbestos: Communicating the Health Issues Derived from Fibrous Minerals to Society

Asbestos, also known by its commercial name “amianthus”, has been widely used in various industries due to its unique properties. However, the extensive use of asbestos has had serious consequences for human health, most notably asbestosis, an irreversible chronic lung disease. Asbestosis increases the risk of lung cancer and malignant mesothelioma, both of which are fatal. Applied sciences such as microscopy (optical and scanning electron microscopy) and geochemistry have been fundamental in characterizing the mineral fibers of asbestos to understand its role in human health. We previously used these techniques to characterize these fibers; in this study, we explored the issues associated with asbestos and asbestosis, as well as the challenges facing science communication strategies in effectively informing society and workers about these risks. The lack of scientific culture, in general, has led to a lack of public awareness of the risks of asbestos. As such, effective communication and outreach plans and strategies, including the visualization of the fibers to demonstrate why problems arise if inhaled, must be implemented to address these challenges. Educational campaigns, guidelines, and plans that are informative and actionable, teaching workers, communities, and the public about the risks of asbestos are crucial. A general knowledge of mineralogy and geochemistry is needed, and providing and disseminating proper scientific communication may help to close the knowledge gap. We use examples and experience from Spain and Italy to illustrate this matter, as we have been working on the characterization of ultramafic complexes in these countries for more than ten years. Additionally, because these countries have strict laws for asbestos-containing materials, they are currently involved in retiring and demolishing buildings and infrastructure that contain asbestos.

Textural and chemical variations in peridotite induced by hydrous melt migration in mantle under the back-arc spreading

This study presents the structural and petrological characteristics of mantle peridotites in relation to the rock-hydrous melt reaction found in the Hayachine ultramafic complex, NE Japan. We conducted sampling, microstructural observations, crystal-orientation analyses, and major element composition analyses of the major constituent minerals in the peridotites. We used 17 serpentinized peridotites that preserved better mantle textures. The peridotites are composed of lherzolite to harzburgite, consisting of olivine, orthopyroxene, clinopyroxene, amphibole, and spinel. The peridotites were classified into two textures according to olivine grain size: coarse-grained (ca. 2–3 mm) and fine-grained (ca. 0.3–0.5 mm). Fine-grained peridotites were newly found in this study and were characterized by aggregates of orthopyroxene and amphibole with a large number of spinel inclusions. Based on olivine crystal-preferred orientation (CPO), we found that the coarse-grained peridotites were further classified into Group 1 (A type CPO) and 2 (AG type CPO) and the fine-grained peridotites were accordingly classified into Group 3 (weak CPO). The systematic continuity in the chemical compositions of the minerals suggests that Group 1 peridotites partially melted to form Group 2 peridotites, followed by Group 3 peridotites, due to further reaction of Group 2 peridotites with hydrous melts. These textural and chemical variations in the peridotites could have resulted from rock-hydrous melt reactions under back-arc spreading and subsequent processes.

Tectonic Geomorphology of Ultramafic Complex in Asera, North Konawe Regency

Ultramafic complex in Sulawesi have many potential from mining to environmental aspects. The process of weathering and tectonic is a key factor in understanding how to utilize these potential. Tectonic geomorphology by using morphometric indices and field observation has proven to be a beneficial method in distinguishing the topography and morphogenetic development of a region due to the complex interaction between erosional processes and tectonic movements. IAT measurement of 71 sub-basins shows that tectonic activity in the research area are divided into 4 classes with values ranging from 1,5 – 2,6. Field observation shows that morphologically the research area are faulted hills consist of peridotite, dunite and pyroxenite with various degree of weathering. The effect of weathering also reveal on the shape of sub-basins and drainage density in the research area. Tectonic activity present in the form of intensive joint on some parts, with no clear correlation with IAT Class. keyword: tectonic geomorphology, carbon capture storage, ultramafic, east Sulawesi ophiolite, morphometric indices

Characteristics and Deep Mineralization Prediction of the Langmuri Copper–Nickel Sulfide Deposit in the Eastern Kunlun Orogenic Belt, China

The discovery of a Cu-Ni sulfide deposit in Langmuri of the Eastern Kunlun Orogenic Belt holds significant geological implications. This study, based on the examination of the metallogenic geological body, metallogenic structure, and metallogenic process characteristics, suggests that the deposit is a magmatic Cu-Ni sulfide deposit formed in the collision of orogenic and post-extension processes of the Late Ordovician. The early mineralization of the deposit was primarily derived from the differentiation of sulfides in the mafic–ultramafic rock (450–439 Ma) of the Late Ordovician, while the late-stage mineralization underwent significant superimposed modification by the magmatic–hydrothermal activity of crustal-contaminated biotite granite (415 Ma). In addition, this article analyzes the measurements of the geochemical studies of sediments, and the magnetic and gravity measurements carried out in the area, focusing on the geochemical and geophysical anomaly characteristics in the study area, and selects favorable exploration areas, which have been confirmed to have multiple mineral bodies. By integrating comprehensive gravity, magnetic, induced polarization, and audio-frequency magnetotelluric profile measurements, this study analyzes delineated mineralized zones and the deep extensions of surface mineral bodies to assess deep mineralization potential and identify deep ore-finding targets. It suggests that diverse and scattered mafic–ultramafic complexes in the Langmuri mining area have a large-scale distribution of ore-bearing rocks in the deep. Through the analysis and inverse of the geophysical data, a deep mineralization predictive model was established in the basic–ultrabasic rock mass. The study presents prospects for the delineation of the deep-seated mineralization in the Langmuri deposit.

Slab break-off of the Kalamaili oceanic slab revealed by the latest Carboniferous mafic–ultramafic rocks in eastern North Tianshan (NW China)

Identifying the tectonic transition from oceanic subduction to collision is crucial for tracking the final stage evolution of ancient orogenic belts. In this study, we present new geochronological and geochemical data for the Mozbaysay mafic–ultramafic complex in the Balikun area, eastern North Tianshan of the southern Central Asian Orogenic Belt. This complex had intruded into the late Carboniferous volcano-sedimentary rocks and is comprised mainly of hornblende gabbro and lherzolite. Zircon U-Pb ages of the hornblende-gabbros reveal that this complex was emplaced at ca. 305 Ma. Geochemical analyses suggest these mafic–ultramafic rocks are characterized by slight enrichment of light rare earth elements (LREEs) and relatively depleted heavy rare earth elements (HREEs), resembling enriched mid-ocean ridge basalt (E-MORB). They also exhibit restricted (87Sr/86Sr)i ratios (0.702396–0.704295) and εNd(t) values (+7.0 to +9.1), indicative of a depleted mantle source with minimal crustal contamination. Incompatible element ratios (i.e., Nb/Ta, Zr/Hf, Rb/Nb, and Ba/Nb) suggest the involvement of subducted slab-derived aqueous fluids in their mantle source. These collectively indicate that the parental magmas of the Mozbaysay mafic–ultramafic rocks may have been generated by a mixed mantle source consisting of the E-MORB-like asthenospheric mantle, subcontinental lithospheric mantle (SCLM), and hydrous fluids from subducted slab. Furthermore, a slab break-off model is proposed to explain the generation of these latest Carboniferous mafic–ultramafic rocks. Integrating these findings with regional geological data, we propose that the tectonic transition from subduction (slab roll-back) to collision (slab break-off) along the Kalamaili suture zone occurred at ca. 305–300 Ma.

Co-Ni distribution and Re-Os isotopic age of the Wuxing complex in the Central Asian orogenic Belt: Implications for sulfide mineralization in Alaskan-type complexes

Alaskan-type mafic–ultramafic complexes have been recognized as potential hosts of magmatic Ni-Cu sulfide deposits. However, the distribution and controlling factors of ore-forming metal elements like Co and Ni within these complexes remain poorly understood. This study offers comprehensive petrological observations and quantifies the Co and Ni contents of silicate minerals and sulfides in the Wuxing complex, the oldest Alaskan-type complex hosting a distinctive PGE-rich Ni-Cu sulfide deposit in the Central Asian Orogenic Belt. The Co-rich minerals, including cobaltite and pentlandite, occur as inclusions or interstitial grains in other mineral phases. Among the sulfide assemblages (pyrrhotite, pentlandite and chalcopyrite), pentlandite exhibits the highest 3.59 ∼ 5.98 wt.% of Co and 28.7 ∼ 32.7 wt.% of Ni contents, with the Co contents being 2 to 10 times higher than those in magmatic Ni-Cu sulfide deposits. Clinopyroxene and hornblende in the Wuxing complex display lower Co and Ni contents compared to those in sulfide-free rocks of typical Alaskan-type complexes. This could be ascribed to the reduction in Co and Ni contents in evolved magmas following sulfide segregation. Additionally, lack of olivine and chromite crystallization would elevate Co and Ni contents in silicate magma and promote the sulfide mineralization in the Wuxing complex. The Re-Os isotopic dating in ore samples at 596 Ma, combined with previously zircon U-Pb ages of 510 ∼ 517 Ma, reveals that long-term magmatism would facilitate mineralization in the Wuxing complex. Our investigations provide a new insight of mineral crystallization for understanding of magmatic Ni-Cu-PGE sulfide mineralization in Alaskan-type complexes.

Petrography and chemistry of chromite phases from the Mesoarchean chromitite bodies of the Boula-Nuasahi ultramafic complex, India: Indicators of magmatic evolution and hydrothermal alteration

Petrography and chemistry of chromite phases from the Mesoarchean chromitite bodies of the Boula-Nuasahi ultramafic complex, India: Indicators of magmatic evolution and hydrothermal alteration

Genesis of the Devonian Habaqin ultramafic arc complex and associated low-grade Fe–Ti oxide mineralization in the northern North China Craton

In the northern North China Craton (NCC), abundant non-layered ultramafic complexes and associated low-grade Fe–Ti oxide ores (over 1000 million tons) were uncovered. However, their petrogenesis and metallogeny have remained unclear. The Habaqin complex is one of the larger intrusions of the region and hosts the largest low-grade magnetite occurrence. Here we present petrography, zircon U–Pb geochronology, mineral and whole-rock major and trace element compositions, and whole-rock Sr–Nd and zircon Lu–Hf isotopes of the complex to constrain its genesis. The complex includes early pyroxenite (∼75% clinopyroxene, ∼15% amphibole, ∼10% magnetite) and late hornblendite (∼80% amphibole, 15–20% magnetite, 0–5% apatite). Zircon grains from the hornblendite yielded a weighted mean 206Pb/238U age of 395 ± 2 Ma. The increasing whole-rock FeOtot and TiO2 contents from pyroxenite (FeOtot = 18.9 wt%, TiO2 = 1.31 wt%) to hornblendite (FeOtot = 19.1–30.4 wt%, TiO2 = 2.63–3.12 wt%) correlate with higher modal proportions of amphibole and magnetite. The pyroxenite and hornblendite display similar arc-like trace element characteristics of enrichment in LILEs and LREEs, and depletion in HFSEs. The complex formed by fractional crystallization of clinopyroxene, amphibole, magnetite, and apatite from a hydrous parent magma. Early removal of clinopyroxene caused H2O enrichment in evolved residual magmas and crystallization of magnetite and amphibole, forming low-grade mineralization with Ti-V-poor magnetite in hornblendite. The complex displays high initial 87Sr/86Sr ratios of 0.706413–0.707341, negative εNd(t) values of −16.0 to −14.2 and negative εHf(t) value of −30.6 to −12.0, suggesting a parent magma derived from an enriched lithospheric mantle, with possible existence of amphibole-bearing pyroxenite veins within the source. During the Early Devonian, the retreat of the subducted Paleo-Asian oceanic slab as well as arc-continental collision along the northern NCC induced partial melting of the veins and eventually formation of the complex.

The Architecture of a Root Zone of a Large Magmatic Conduit System From High Resolution Magnetic, Gravity and Petrophysical Data: The Reinfjord Ultramafic Complex

AbstractThe Seiland Igneous Province (SIP) is a large province of mafic and ultramafic (UM) complexes interpreted to be relics of a giant plumbing system feeding the Ediacaran Central Iapetus Magmatic Province. The Reinfjord Ultramafic Complex (RUC) is one of the four major ultramafic complexes of the SIP. The RUC has a younger dunite core surrounded by wehrlite and lherzolite embedded in country rocks consisting of layered gabbros with sub‐horizontal layering and metamorphosed sedimentary rocks. Here, we develop a 3D subsurface model for the RUC using high‐resolution magnetic and gravity data and extensive petrophysical measurements from oriented surface samples and drill core samples. Our model indicates that the RUC narrows in depth, extending a minimum of 1.4 km below sea level, and plunges eastwards below the country rock. This model allows us to decipher the lithologic heterogeneities, and the depth and lateral extent of ultramafic rocks, which we interpret in the context of the geologic history of the area. The RUC is spatially separated from other UM complexes of the SIP and the result of this study indicates a smaller depth extent. Combining these findings with the previously reported distribution of the SIP rocks based on the regional gravity data, we propose that the uplift of the crustal block hosting the RUC is larger than for ultramafic complexes in the northwestern part of the SIP.

The Utilization of LiCSBAS for Deformation Monitoring in Geresa Segment of Matano Fault, Central Sulawesi, Indonesia

Sulawesi is situated between the confluence of three plates, resulting in a very complex tectonic setting on the island. This has an impact on the occurrence of geological structures, including faults. One of them is the Matano Fault which consists of 6 segments (Kuleana Segment, Pewusai Segment, Matano Segment, Pamsoa Segment, Ballawai Segment, and Geresa Segment). The research area is located in Morowali Regency, covering the Geresa Segment. Morowali Regency recorded an earthquake with a magnitude of 5.7 in 2012. This indicates that deformation has occurred. Therefore, this study aims to identify the deformation velocity around the Geresa Segment area. The methods used are geological observation and satellite image data processing to obtain information on deformation rates. The geological field study includes aspects of geomorphology, geological structure, and the rock types distribution. Meanwhile, the processing of satellite image data in the form of InSAR is carried out through the LiCSBAS package tools that has been integrated with LiCSAR. The analysis results illustrate the difference in deformation velocity around the Geresa Segment area. The area which is composed of Tolaka formation and Ultramafic complex tends to uplift with a deformation rate of up to 17 mm/year. In addition, alluvium that covers the southeastarn part has a land subsidence of up to 7 mm/year.

Neoproterozoic Lysan Alkaline–Ultramafic Complex in the Eastern Sayan, Southern Siberia, Russia: Mineralogical Constraints of Carbonate Rocks and Albitite for Petrogenesis

The Lysan alkaline–ultramafic complex is located in the Sisim shear zone at the contact of the two largest tectonic structures of the accretion–collisional belt in the southwestern frame of the Siberian craton. Intrusions of the complex consist of ore-bearing olivinites, kaersutite clinopyroxenites, and banded kaersutite gabbro, which have been «cut» by albitite dykes and veins. The veins and veinlets of the carbonate rocks are mainly associated with the albitites. The present paper represents the first detailed mineralogical study of carbonate rocks and albitites in the Podlysansky Massif of the Neoproterozoic Lysan alkaline–ultramafic complex. The mineral composition was determined in situ in a polished section by scanning electron microscopy, energy dispersive spectrometry, and electron probe microanalysis. The carbonate rocks of the Podlysan Massif have been found to contain minerals that are typical of siderite–carbonatites (senso stricto), including calcite, siderite, phengitic muscovite, apatite, monazite, REE fluorocarbonates, pyrite, and sphalerite. These rocks are enriched in light rare earth elements due to the presence of monazite-(Ce), bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce). The albitites were formed as a result of the fenitization of leucocratic gabbro by alkali-rich carbo-hydrothermal fluids in zones of intense development of tectonic fractures. Infiltration was the dominant mechanism of fenitization. The obtained data significantly enhance the current understanding of the geochemical and ore specialization of rocks in the Lysan Complex.

Application of spectral signature study and geochemical analysis in the characterization of Bhavani Mettupalayam Ultramafic Complex in the Southern Granulite Terrane, India

The Bhavani Suture Zone, a region in the Southern Granulite Terrane (SGT), is where the Neoarchean Madurai Block and the Southern Madurai Block in western Tamil Nadu have been joined. The Mettupalayam Mafic-Ultramafic Complex, located in the eastern section of the BSZ, is made up of metagabbros, metadiorites, amphibolites and mafic granulites. The mafic-ultramafic outcrops are viewed and mafic-ultramafic rocks collected from Nellimalai, Togamalai, Sakkitiyan Karadu, Karudamalai, Karattur, Odhimalai, Tenkalmalai, Ramakavundanur hills. This study methodology is composed of three perspectives such as remote sensing study, laboratory spectral signature study and geochemical study. Firstly this study applied on Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) and Sentinel-2A used as a tool for mapping mafic-ultramafic rocks and applied the remote sensing techniques like color composites, BR (band ratio), PCA (Principal Component Analysis), MNF (Minimum Noise Fraction), SAM (Spectral Angle Mapper) and SVM (Support Vector Machine). Secondly laboratory spectral signature study is conducted for the 19 samples with ASD FieldSpec Pro® spectroradiometer was used to get the reflectance spectra in the 350–2500 nm spectral region. For different host rocks, the continuum-removed reflectance spectra offer diagnostic absorption features. Critical analysis was done on how the rock samples' elemental composition and related important minerals affected the absorption bands. The major and minor elements geochemical compositions of the BMUC rock samples identified by XRF method. The aim of this research is to characterize the BMUC using remote sensing studies, spectral signature study and geochemical analysis. The Sentinel-2A showing discriminating the lithology well than ASTER data and the spectral signatures absorptions are indicating presence of Fe and Mg contents. The rock samples are falling the series of tholeiitic to calc alkaline characteristics in geochemistry.

An Iapetus origin for a layered eclogite complex in the northern Western Gneiss Region, Scandinavian Caledonides

AbstractThe Western Gneiss Region (WGR) is a Precambrian basement domain in the Scandinavian Caledonides and one of the world's largest high‐ and ultrahigh‐pressure terranes. The south–central WGR underwent regional eclogite facies metamorphism 415–400 Ma ago when Baltica subducted beneath Laurentia, during the Scandian orogeny. Eclogites in the WGR group into two traditional types: (1) Precambrian mafic intrusions metamorphosed in situ during Scandian continental subduction and (2) eclogites, garnet peridotites and garnet pyroxenites within ultramafic complexes derived from the subcontinental mantle beneath Laurentia. We document, using field relations, petrography, whole‐rock geochemistry and secondary ion mass spectrometry (SIMS) zircon geochronology, a hitherto unrecognized third type of eclogite in the WGR that places new constraints on its tectonic architecture: an eclogitized fragment of oceanic crust from the Iapetus Ocean. The Kråkfjord eclogite complex is a km2‐sized body with an interior consisting of kyanite eclogite (meta‐troctolite) and subordinate layers and lenses of garnet peridotite, garnet websterite and kyanite–garnet leucotonalite. This interior is capped by Fe–Ti‐rich eclogite, which locally contains subordinate pockets of migmatitic aluminous gneiss. The elemental abundances and isotopic compositions of the Fe–Ti‐rich eclogites resemble those of mid‐ocean ridge basalt (MORB). In contrast, the interior kyanite eclogites, peridotites and pyroxenites have compositions similar to the gabbroic cumulates in the lower oceanic crust of slow‐spreading ridges. U–Pb SIMS dating of igneous zircon cores from a leucotonalite pod in the interior of the Kråkfjord complex yields Cambro‐Ordovician igneous ages of 500–440 Ma, with the ~500 Ma age interpreted as the isotopically undisturbed age. This age matches those of Iapetan oceanic rocks exposed elsewhere in the mountain belt. Metamorphic zircon from an Fe–Ti‐rich eclogite in the carapace of the Kråkfjord complex dates the eclogite facies metamorphism at 421.9 ± 2.2 Ma, synchronous with the continental collision. Zircon from a leucosome in Fe–Ti‐rich retro‐eclogite indicates an age of 408.5 ± 2 Ma for the crystallization of partial melt following the decompression. Detrital zircon core ages from a pocket of aluminous migmatitic gneiss in the carapace indicate derivation of sediment from the Baltic crust. Collectively, the data show that the eclogite complex (1) originated at an Iapetus spreading centre near the continent Baltica, (2) subducted to eclogite conditions during Scandian continental collision and (3) was tectonically intercalated with the Precambrian Baltica basement of the WGR.

Wrapping a Craton: A Review of Neoproterozoic Fold Belts Surrounding the São Francisco Craton, Eastern Brazil

A synthesis of the evolution of the Neoproterozoic belts or orogens surrounding the São Francisco craton (SFC) in northeastern and southeastern Brazil is presented. Emphasis is placed on recognizing the superposition of sedimentary basins, from rift to passive margin to retroarc and foreland, as well as identifying three diachronic continental collisions in the formation of the SFC. The Tonian passive margin occurs in the southern Brasília Belt with the Vazante, Canastra, and Araxá Groups. During the Tonian, island magmatic arcs and basins developed in front and behind these arcs (fore- and back-arcs). Subsequently, in the Cryogenian–Ediacaran, a retroarc foreland basin developed with part of the Araxá Group and the Ibiá Group, and finally, a foreland basin developed, which was filled by the Bambuí Group. A tectonic structure of superimposed nappes, with subhorizontal S1–2 foliation, formed between 650 and 610 Ma, is striking. In the northern Brasília Belt, there is the Stenian passive margin of the Paranoá Group, the Tonian intrusion of the Mafic–Ultramafic Complexes, and the Mara Rosa Island magmatic arc, active since the Tonian, with limited volcanic–sedimentary basins associated with the arc. A thrust–fold belt structure is prominent, with S1 foliation and late transcurrent, transpressive tectonics characterized by the Transbrasiliano (TB) lineament. The Cryogenian–Ediacaran collision between the Paranapanema and São Francisco cratons is the first collisional orogenic event to the west. In the Rio Preto belt, on the northwestern margin of the São Francisco craton, the Cryogenian–Ediacaran Canabravinha rift basin is prominent, with gravitational sediments that represent the intracontinental termination of the passive margin that occurs further northeast. The rift basin was intensely deformed at the Ediacaran–Cambrian boundary, as was the Bambuí Group. On the northern and northeastern margins of the São Francisco craton, the Riacho do Pontal and Sergipano orogens stand out, showing a comparable evolution with Tonian and Cryogenian rifts (Brejo Seco, Miaba, and Canindé); Cryogenian–Ediacaran passive margin, where the Monte Orebe ophiolite is located; and Cordilleran magmatic arcs, which developed between 620 and 610 Ma. In the Sergipano fold belt, with a better-preserved outer domain, gravitational sedimentation occurs with glacial influence. A continental collision between the SFC and the PEAL (Pernambuco-Alagoas Massif) occurred between 610 and 540 Ma, with intense deformation of nappes and thrusts, with vergence to the south and accommodation by dextral transcurrent shear zones, such as the Pernambuco Lineament (PE). The Araçuaí belt or orogen was formed at the southeastern limit of the SFC by a Tonian intracontinental rift, later superimposed by a Cryogenian–Ediacaran rift–passive margin of the Macaúbas Group, with gravitational sedimentation and glacial influence, and distally by oceanic crust. It is overlain by a retroarc basin with syn-orogenic sedimentation of the Salinas Formation, partly derived from the Rio Doce cordilleran magmatic arc and associated basins, such as the Rio Doce and Nova Venécia Groups. A third continental collision event (SF and Congo cratons), at the end of the Ediacaran (580–530 Ma), developed a thrust–fold belt that deforms the sediments of the Araçuaí Belt and penetrates the Paramirim Corridor, transitioning to the south to a dextral strike-slip shear zone that characterizes the Ribeira Belt.

Emplacement and ore potential of the Permian Pobei mafic–ultramafic complex, NE Tarim, NW China

A number of mafic–ultramafic intrusions with variable degrees of Ni-Cu sulfide mineralization occur in the northeastern Tarim Block and East Tianshan Orogenic Belt (NW China). Among them, the Pobei complex is composed of a gabbro body intruded by several ultramafic bodies including Poyi and Poshi. These bodies have similar mineralogy and chemical compositions and were derived from a common magma. Olivine crystals from the Poyi and Poshi bodies generally have high Fo contents with the highest Fo value of 89.5 and Ni up to 3300 ppm Ni, indicative of crystallizing from Ni-undepleted, high-Mg basaltic magmas. Sr-Nd-Pb isotopic compositions show that more mafic rocks show relatively low degrees of crustal contamination, whereas more evolved rocks experienced higher degrees of contamination, especially in the upper part of the complex. Olivine crystals from both the Poyi and Poshi bodies show sharp decrease of Ni with decreasing Fo values, indicating sulfide segregation in these two bodies. Gabbros may have potential of reef-type chromite mineralization at the deep level, and V-bearing magnetite mineralization at higher stratigraphic level corresponding to the current surface level, but the potential of PGE mineralization is low. We propose that the ultramafic bodies of the Pobei complex may have been formed from the injection of olivine- and sulfide-laden crystal slurry from the bottom of a large magma chamber. The Ni-Cu mineralization was triggered by the crustal contamination. The Pobei complex was formed by the multiple intrusions of magmas to form the current complex.

Characterization and imaging magnetic minerals from ultramafic roots of a LIP: implication for deep crustal magnetic sources

SUMMARY Satellite magnetic surveys have revealed features consistent with magnetization at depth in the lithosphere. Previous studies have reported magnetic minerals preserved in mantle nodules and in some eclogite facies rocks. Deep crustal rocks are another possible source for these deep lithospheric signals, but have not been extensively studied, in many cases due to the difficulty in obtaining samples unaffected by later near-surface alteration processes. Here, we used a combined approach involving petrophysical, rock magnetic and scanning magnetic microscopy (SMM) analyses on unaltered pristine ultramafic samples from the Reinfjord Ultramafic Complex in northern Norway. The focus was to identify the magnetic carriers using SMM and link the magnetic anomalies mapped in thin section to distinct rock magnetic measurements. The dominant magnetic carriers are Cr-magnetite exsolved from grains of Al-chromite, and magnetite exsolution lamellae from clinopyroxene. In addition, some samples have exsolved magnetite from Al-Cr-spinel and Fe-rich exsolution from Cr-spinel as carriers. Rock magnetic measurements suggest that these primary magnetic carriers, could retain magnetization to considerable crustal depths.

Characterization of Talcose Rocks Derived from Serpentinite—Pilot Study in the Ultramafic Complex of Cabo Ortegal (Spain) for Potential Use and Commercialization

Cabo Ortegal, in Spain, was declared a UNESCO Global Geopark in 2023. An ultramafic complex makes it a geologically exciting unit, where many research works have been carried out. Serpentinites, formed by the weathering of peridotites, dunites, and other ultramafic rocks, have been described in detail in previous works. Their role as a construction material has been elucidated, although due to their complexity and heterogeneity, the results of using these materials for construction are not always successful. Talcose rocks, related to serpentinites, can also be found in the complex, although it is difficult to distinguish them. Talcose rocks may be a resource to be explored and exploited in an unpopulated area. The use of talc in pharmaceuticals, cosmetics, and handicrafts makes it a material of growing importance. However, the asbestos and heavy metal content should be severely limited to prevent health issues. The goal of this work is to start the characterization of these talcose rocks before promoting their potential use in different contexts to support the economy of an underpopulated area of Spain.

Geochemistry of Rocks at the Neskevara Rare-Metal Deposit of the Vuoriyarvi Alkaline–Ultramafic Complex, Kola Peninsula

The Vuoriyarvi Paleozoic alkaline–ultramafic complex with carbonatites is made up of a great diversity of rocks with various ore mineralization. The paper presents data on the geochemistry of pyroxenites, phoscorites, and carbonatites from the Neskevara deposit of rare metals. The pyroxenites of the rare-metal deposit are significantly enriched in Nb, Ta, and Th relative to the primitive mantle and the primary alkaline–ultramafic melt composition calculated for the Kola alkaline province and are characterized by high Nb/Ta, Zr/Hf, and Th/U ratios of 29, 35, and 14, respectively. HFSE are maximally enriched in the phoscorites and carbonatites of stages II and III, with the highest concentrations of Nb (16 000 ppm), Th (2800 ppm), and Zr (4000 ppm) found in the calcite–tetraferriphlogopite phoscorites, in which pyrochlore crystallization on the liquidus was identified. The rocks of the carbonatite series are strongly enriched in LREE relative to carbonaceous chondrite. The calcite–dolomite carbonatites of the late magmatic–carbothermal stage show REE enrichment up to 25 800 ppm. The chondrite-normalized REE patterns and (La/Yb)N ratio indicate that REE were systematically more strongly fractionated in the sequence pyroxenite (70)—phoscorite (90)—calcite (540) and dolomite (3790) carbonatites The crystallization sequence of minerals in the rare-metal phoscorites and carbonatites of intermediate stages indicates that magnetite and pyrochlore crystallized nearly simultaneously. The crystallization temperatures of such associations are, according to data of the magnetite–ilmenite thermometer, lower than 500–600°C, at ∆NNO = –0.3 and + 1.5 and corresponded to the temperature at which the rare-metal ore mineralization of the main stage was formed.