Magnesite Deposits Research Articles

Sepiolite from Serbian deposits as an industrial mineral

Long-termed geological exploration of sepiolite in Serbia has proved that there exist two structuralmorphological types of sepiolite deposits: the vein type - in ultrabasic rocks, associated with vein magnesite deposits (of Goles, Trnava, Milicevci, Cavlovac, Masnica, Kive Strane and Slovici) and the stratiform type - in sedimentary series of Miocene basns (represented by deposits of Andrici, Tolica Kosa, Stanici and Silopaj). The deposits of both types contain considerable concentrations of sepiolite which possess favourable adsorptive and other properties (before all: rheologic and catalytic ones). On the basis of these properties the sepiolite from the deposits has been treated as a potential industrial mineral which could be used, like in the world, in various industrial branches, mainly as an sorbent. However, this usage was proved recently (in 2012), only for the sepiolite (i.e. sepiolite clay) from the Tolica Kosa deposit, by industrial technological testing of a technological sample. This testing, guided by the InterCer Company d.o.o. from Belgrade, demonstrated that, in appropriate industrial facilities and by using an appropriate technological treatment, it is feasible to get quality products (in the first place sorbents, additives for animal food and the others) from the sepiolite clay of the Tolica Kosa deposit which have application in Serbian industry.

Boron-polymetallic metallogeny of the north and northeast of the Sino-Korean Craton

Based on published data and original investigations, it has been shown that the combination of widely known Ag, Fe, and Fe-Mn ore deposits, as well as boron and Pb-Zn world-class deposits, is typical for metallogenic zones in the north and northeast of the Sino-Korean Craton. The ore genesis was spatially inherited and lasted from the Archean to Mesozoic. The Archean metallogenic zones are related to the protocontinental margin terranes of the craton basement and they comprise banded iron ore and Cu-Zn sulfide deposits. The proterozoic-Early Paleozoic metallogenic zones are related to rift basins, where the ore-bearing Archean folded basement is overlain by volcanic and sedimentary complexes. The Proterozoic metallogenic zones host quartz veins and schistosity zone-related Au deposits, banded iron and Cu-Zn ore deposits, large sedimentary-metamorphogenic borate and magnesite deposits, Cu-W deposits in tourmalinites, exhalation-sedimentary Pb-Zn ore deposits, and large polygenic REE-Fe-Nb ore deposits. The Riphean-Cambrian terrigenous-carbonate strata are represented by stratiform Pb-Zn and fluorite deposits. Mesozoic metallogenic zones related to volcano-plutonic complexes of intraplate series coincide with zones where the folded basement is made of Precambrian ore-bearing series. Gold deposits are typical of all the metallogenic zones, but most of them are related to Mesozoic volcano-plutonic complexes.

Sm–Nd dating of hydrothermal carbonate formation: An example from the Breitenau magnesite deposit (Styria, Austria)

The geochemical evolution and chronology of the Breitenau sparry magnesite deposit has been investigated by means of major and trace element abundances, stable C–O isotope, and Sm–Nd isotope analysis. Chemically separated magnesite fractions (leachates) show consistent light-REE depleted REY patterns (marine carbonate normalized) and nearly constant normalized values for the middle and heavy REE without significant Ce, Eu or Y anomalies. Non-carbonate residues (composed of dark matrix material) are high in Al2O3 and show variably light to middle REE enriched REY patterns similar to shales. Leachates of limestone from nearby country rocks have normalized REY patterns similar to marine carbonates. Only Ce and Y are slightly fractionated. Based on their trace element chemistry and normalized REY patterns, leachates of dolomite from the margin of the deposit closely resemble either limestone (Type A) or magnesite (Type B). With one exception, δ18OVPDB for both dolomite types is within the range of the respective magnesite values (δ18OVPDB c. −14.2 to −15.7‰). Leachates of dolomite from druses within the deposit (Type C) show low REY abundances with normalized patterns similar to those of magnesite. Sm–Nd isotope data for magnesite leachates yield a well-defined isochron age of 222.5±9.8Ma (MSWD 3.1). Isochron calculations for leachate(s) and residue(s) from individual magnesite samples (“internal isochrons”) yield ages between 236±16Ma and 193.5±8.6Ma with a low degree of scatter (MSWD<1.3). The most precise estimate for the time of Sm–Nd isotopic equilibration between carbonates and their host assemblages, both on hand specimen and deposit scale, is obtained from the mean of internal isochron calculations for eight samples (229.3±2.4Ma; MSWD 0.65) and is interpreted to date hydrothermal formation of the magnesite deposit. The scatter in initial Nd isotopic composition of the eight internal isochrons (0.511891±0.000014; MSWD 7.7) indicates geologically based heterogeneities in isotopic composition on the deposit scale. Sm–Nd isotope data for Type C dolomite scatter off the upper right of the magnesite isochron. In combination with the respective O isotopic composition, the Sm–Nd isotope data of Type C dolomite can be modeled in terms of three distinct age groups: 1) 130±20Ma (δ18OVPDB c. −15‰), 2) 37.9±5.4Ma (δ18OVPDB c. −12.5‰), and 3) −1.7±6.8Ma (δ18OVPDB c. −11‰). Type C dolomite data indicate that druses were formed by open-system fluid flow throughout the deposit.

Influence of the nitrogen concentration on the electrical characteristic of hydrogenated amorphous silicon nitride (a-SiNx:H) based Schottky diodes

The Eskisehir magnesite deposits (Suleymaniye, Margi, and Tutluca) are located in the western part of the Izmir-Ankara Suture Zone, northwestern Turkey. These vein and stockwork type magnesite deposits, which occur along major and minor fault systems, are hosted by Alpine-type ultramafic rocks. The purpose of this study was to understand the origin of the hydrothermal waters responsible and the source of carbon dioxide, and to compare these deposits with similar magnesite occurrences in Turkey and elsewhere. Petrographic and XRD analyses indicate that magnesite was the major carbonate mineral formed. Deposits are predominantly micritic and locally microsparitic, but some also contain secondary calcite and dolomite. The delta13C (V-PDB) values of the Suleymaniye magnesites (-2.7%o to -7.7%o), the Margi magnesites (-7.6%o to -11.2%o), and the Tutluca magnesites (-8.7%o to -10.4%o) indicate that sources of carbon may include atmospheric carbon, dissolved inorganic carbon, freshwater carbonate, and mantle derived CO2. The delta18O (SMOW) compositions of the magnesite range from 27.4%o to 30.8%o and show that the oxygen was derived from marine limestone and metamorphic rocks. The Suleymaniye magnesites have heavier carbon isotopic values than the others because of the greater contribution of mantle sourced CO2, while oxygen isotopic values were similar to those of other altered ultramafic related magnesites in Europe (Former Yugoslavia, Greece). The Margi and the Tutluca magnesite deposits have carbon and oxygen isotopic values similar to those of other ultramafic-related magnesite deposits. Based on isotopic data, we argue that the magnesite deposits in the Eskisehir area formed in a near surface environment at low pressure and temperature. The estimated temperature, using average delta18O values, suggests that magnesite was precipitated from water at 37 °C.

Mathematical testing the edges of subsidence in undermined areas

In order to protect the environment, in particular the protection of human life and property, it is necessary to examine mining subsidence on the surface, i.e. subsidence, which is created over undermined spaces as a natural continuation of tectonic processes in the rock massif. It is necessary primarily in the abandoned old undermined regions, where in a case of not protected entrance of persons there is increased danger of personal accidents and human lives threat and damage or destruction of properties. The limits of undermined regions in many cases equal to isolines connected so called breakpoints occurred in the front of the subsidence borders. The theory for the estimation of polynomial breakpoints in the case of subsidence analysis is presented. The theory was developed as a part of the kinematics analysis procedures for the evaluation of the magnesite deposit in the city suburb of Kosice-Bankov on the northern outskirts of the city of Kosice in the eastern Slovakia. The subsurface abandoned mine Kosice-Bankov is located in the immediate vicinity of the recreational and tourist zone in the northern suburb of the city of Kosice. Some numerical and graphical results from the breakpoints estimation in the magnesite deposit Kosice-Bankov are presented. The obtained results are transformed into GIS for the needs of local governments.

Physicochemical model of the formation of Satka sparry magnesite deposits

Physicochemical model of the formation of Satka sparry magnesite deposits

Sequestration of atmospheric CO2 in chrysotile mine tailings of the Woodsreef Asbestos Mine, Australia: Quantitative mineralogy, isotopic fingerprinting and carbonation rates

Since closure of the Woodsreef Asbestos Mine, located in the Great Serpentinite Belt (GSB), New South Wales, Australia, extensive carbonate-rich crusts have formed by recessive weathering of fine-grained material on the surface of the tailings pile. A relationship exists between the mode of carbonate occurrence, the mineralogy and the isotopic fingerprint of carbonates from the tailings pile. Vertical carbonate crusts, covering most of the tailings, predominantly consist of the hydrated Mg-carbonate hydromagnesite (Mg5(CO3)4(OH)2·4H2O), which has precipitated from evaporating meteoric waters incorporating atmospheric CO2, as reflected in high δ18O, δ13C and F14C signatures, respectively. Low and variable concentrations of magnesite, dolomite and calcite represent bedrock carbonate, which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high δ18O, low δ13C and F14C, a signature typical for ‘weathering-derived’ magnesite deposits in the GSB. The carbonate fraction of deep cement samples, collected from 70 to 120cm below the surface, representing the bulk tailings material at depth, predominantly consists of pyroaurite (Mg6Fe2(CO3)(OH)16·4H2O) and, despite stable isotope signatures similar to bedrock, contains significant radiocarbon. This indicates that pyroaurite, forming under different conditions as hydromagnesite, may represent an additional trap for atmospheric CO2 in the Woodsreef mine tailings. The distribution of carbonates and quartz, together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric-derived carbonate, strongly indicates that dissolution and re-precipitation of bedrock carbonate is not a dominant process in the Woodsreef tailings. The cations for carbonate formation are instead derived from the dissolution of serpentine minerals (lizardite and chrysotile) and brucite.The internal standard method and the reference intensity method have been used with X-ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite, respectively. Considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that, between 1400 and 70,000t of atmospheric CO2 have been sequestered in the mine tailings since closure of the mine 29a ago. Carbonation rates of 27gCm−2y−1 and 1330gCm−2y−1 are significantly higher than background rates of CO2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of CO2 in carbonate minerals.

Sequestration of atmospheric CO2 in a weathering-derived, serpentinite-hosted magnesite deposit: 14C tracing of carbon sources and age constraints for a refined genetic model

The Attunga magnesite deposit is texturally and geochemically distinct from other spatially associated, serpentinite-hosted magnesite deposits in the Great Serpentinite Belt, New South Wales, Australia, such as the hydrothermal Piedmont magnesite deposit or widespread silica–carbonate alteration zones. Cryptocrystalline magnesite at Attunga predominantly occurs in nodular masses and irregular, desiccated veins that occupy pre-existing cracks and pore spaces resulting from fracturing and weathering of the host rock. Incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of MgO and CaO from the serpentinite. Pore spaces and permeability created during weathering and fracturing of the host rock provide access for CO2-, MgO- and CaO-bearing meteoric waters which led to an increase of volume during carbonation. SiO2 is only mobilised during more advanced stages of weathering and late stage infiltration of SiO2-bearing waters and precipitation of opal-A lead to local silicification of the serpentinite.Stable carbon and oxygen isotope signatures show that nodular magnesite at Attunga has formed under near-surface conditions incorporating carbon from C3-photosynthetic plants and oxygen from meteoric waters. Radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and, together with distinct stable carbon and oxygen isotope signatures, indicate that magnesite at Attunga precipitated from low temperature, supergene fluids. Even though there is no direct geochemical and isotopic evidence, some textural observations and field relationships for weathering-derived magnesite deposits suggest the prior existence of a possibly Early Triassic, hydrothermal magnesite deposit at Attunga. The presence of a pre-existing magnesite deposit may entail the localised formation of the weathering-derived magnesite at Attunga, but the predominance of weathering-related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at Attunga. Conventional radiocarbon ages of about 50ka represent a maximum age constraint for the formation of the magnesite deposit during Quaternary weathering. A significant amount of atmospheric CO2 has been sequestered via the biosphere and carbonation of serpentinite at Attunga.

C–O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis

The worldwide 2.33−2.06 Ga unique positive δ13Ccarbexcursion has been correlated with the Great Oxidation Event (GOE). The Dashiqiao Formation in the Liaohe Group of the northeastern North China Craton formed at 2.2−2.174 Ga and hosts one of the world‐class magnesite deposits. Here we present major element and C and O isotope analyses of 22 samples from the Dashiqiao Formation and use the data to evaluate the impact of the GOE in the North China Craton, as well as the genesis of the Dashiqiao giant magnesite deposits. Six dolomitic marble samples from a ~600 m thick interval with 1.10 ± 0.04 of MgO/CaO (mol) ratios show higher δ13CPDBvalues of 0.6−1.4‰ (average 1.2 ± 0.3‰) than those of normal marine carbonates over the globe. However, they display lower δ18OSMOWof 16.4−19.5‰ (average 18.2 ± 1.1‰) as compared to their contemporaneous counterparts, suggesting that the primary carbonates in the Dashiqiao Formation should possess a positive δ13C anomaly (possibly 4.2‰) reflecting the impact of the GOE, and that the δ13C and δ18O values have been depleted in post‐sedimentation diagenesis and/or regional metamorphism. The &gt;550 m thick magnesite layer in the studied section has MgO/CaO ratios ranging from 4.45−200.00. These rocks show δ13C and δ18O values of 0.1−0.9‰ and 9.2−16.9‰, with average values of 0.4 ± 0.2‰ and 13.3 ± 2.5‰, respectively, obviously lower than those of the underlying dolomites. The depletions of13C and18O in magnesites relative to dolomitic marbles are interpreted to be the result of hydrothermal alteration related to regional metamorphism leading to rock recrystallization and mass exchange. This interpretation is further confirmed from the hanging‐wall dolomitic marble and the veinlet‐filled magnesite from the ore layer. The former contains mega‐crystals of cylindrical talc and has δ13C of −2.6‰ and δ18O of 14.1‰, indicating that a local fluid–rock interaction between (argillaceous) dolomite and (siliceous) hydrothermal fluids poor in13C and18O resulted in the formation of talc and further depletion both in δ13C and in δ18O. The veinlet‐filled magnesite yields δ13C and δ18O values of −2.7‰ and 16.2‰, respectively, showing lower δ13C but higher δ18O than those of massive magnesite in the adjacent strata. Our observation thus strongly supports the interpretation that the massive magnesite interacted with low‐δ13C fluids which were possibly sourced from meteoric water at low temperature during post‐ore time. Thus, the formation of the Dashiqiao magnesite deposits involved primary sedimentation, diagenesis, regional metamorphism, hydrothermal replacement and local post‐ore fluid–rock interaction. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Genesis of sedimentary- and vein-type magnesite deposits at Kop Mountain, NE Turkey

Sedimentary- and vein-type magnesites were deposited within and on ultramafic rocks of the Kop Mountain region in Bayburt province. In the field, magnesites are exposed along NE-SW trending normal faults and in fractures in the ultramafic rocks. Petrographic studies reveal that magnesite is predominantly micrite, but also occurs as microsparite formed by recrystallization of micrite. The ultramafic rocks hosting the magnesites consist of serpentinized olivine, hypersthene and diopside. Ni, Co and Ti contents of magnesites suggest precipitation from percolating water through the serpentinized ultramafic rocks. The sedimentary- and vein-type magnesites have different \delta^{18}O and \delta^{13}C values, characterizing formation under different conditions. Temperature estimates using the average \delta^{18}O values reveal precipitation from water at ~24.5°C for sedimentary magnesite and ~37.0°C for vein-type magnesite. The \delta^{13}C values of vein-type magnesites are distinctly more negative than those of sedimentary magnesites, indicating carbon isotopes derived from predominantly decarboxylation of organic sediments in shales and carbonate dissolution. Less negative \delta^{13}C values in the sedimentary magnesite are mainly due to outgassing of mineralizing water. Our data suggest a petrogenetic model in which the surface water percolates through the ultramafic and sedimentary rocks becoming heated by volcanics at depth and enriched in Mg^{+2} and light carbon isotopes, followed by migration upward to form magnesite near the surface in ultramafic rocks as fracture-fill and as sediment at the surface.

Stable isotope geochemistry of magnesite from Holocene salt lake deposits, Taoudenni, Mali

Stable isotope data (δ18O, δ13C) were obtained for magnesite (MgCO3) from Holocene salt lake deposits of the Taoudenni–Agorgott basin, Mali, in which it is the only carbonate mineral present. The deposits have a high glauberite content (Na2Ca(SO4)2), representing a type of continental evaporite formation that is commonly magnesite‐bearing. Samples from seven different levels in a 5 m long sequence were analysed. δ18OV‐PDB values are between +3.17 and +5.91‰, which is lower than might be expected for evaporitic environments, recording reduced 18O enrichment at high salinity. δ13CV‐PDB values are between −1.32‰ and −4.79‰, showing an influence of carbon derived from the decomposition of organic matter rather than from exchange with atmospheric CO2. Covariance between δ18O and δ13C is strong for the lower part of the sequence, recording coupled 18O and 13C enrichment as commonly observed for closed basins. Covariance is lacking for the upper part of the sequence, with only periodic massive magnesite deposition in a more shallow lake. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Formation of magnesite and siderite deposits in the Southern Urals—evidence of inclusion fluid chemistry

World-class deposits of magnesite and siderite occur in Riphean strata of the Southern Urals, Russia. Field evidence, inclusion fluid chemistry, and stable isotope data presented in this study clearly proof that the replacement and precipitation processes leading to the formation of the epigenetic dolomite, magnesite and hydrothermal siderite were genetically related to evaporitic fluids affecting already lithified rocks. There is, however, a systematic succession of events leading to the formation of magnesite in a first stage. After burial and diagenesis the same brines were modified to hot and reducing hydrothermal fluids and were the source for the formation of hydrothermal siderite. The magnesites of the Satka Formation as well as the magnesites and the siderites of the Bakal Formation exhibit low Na/Br (106 to 222) and Cl/Br (162 to 280) ratios plotting on the seawater evaporation trend, indicating that the fluids acquired their salinity by evaporation processes of seawater. Temperature calculations based on cation exchange thermometers indicate a formation temperature of the magnesites of ~ 130 °C. Considering the fractionation at this temperature stable isotope evidence shows that the magnesite forming brines had δ18OSMOW values of ~ +1 ‰ thus indicating a seawater origin of the original fluid. Furthermore it proves that these fluids were not yet affected by appreciable fluid-rock interaction, which again implies magnesite formation in relatively high crustal levels. In contrast to the magnesites, the siderite mineralization was caused by hydrothermal fluids that underwent more intense reactions with their host rocks in deeper crustal levels compared to the magnesite. The values of 87Sr /86Sr in the siderites are substantially higher compared to the host rock slates. They also exceed the 87Sr /86Sr ratios of the magnesites and the host rock limestones indicating these slates as the source of iron as a consequence of water-rock interaction. The siderites were formed at temperatures of ~ 250 °C indicating a relatively heavy fluid in equilibrium with siderite of 13 ‰ δ18OSMOW, which is in the range of diagenetic/metamorphic fluids and reflects the ± complete equilibration with the host rocks. Carbon isotope evidence shows that the fluid forming the siderites underwent a much higher interaction with the host rocks resulting in a lowering of the δ13C numbers (−3,3 to −3,7 ‰). The light carbon was most probably derived from decaying hydrocarbons in the Riphean sediments. In a very early stage after sedimentation of the Satka Formation (~1,550 Ma) magnesite was formed by seepage reflux of evaporitic bittern brines at the stage of riftogenic activity in the region (1,380–1,350 Ma). Sedimentation of the Bakal Formation (~1,430 Ma) and intrusion of diabase dykes (1,386 ± 1,4 Ma) followed. Diagenetic/epigenetic mobilization of these buried fluids at ~ 1,100 Ma resulted in the formation of hydrothermal siderite bodies.

Ore mineral discrimination using hyperspectral remote sensing—a field-based spectral analysis

Advanced Spaceborne Thermal Emission and Reflection Radiometer data of Salem District and field-based spectral observations using SVC HR 1024 spectral radiometer is used to make a clear discrimination of ore mineral deposits in parts of Salem District of Tamil Nadu. Spectral analyses, one of the most advanced techniques, are used to discriminate the magnesite deposits in the central northern part of Salem District. Different spectral processes were used in ore discrimination, which include the following: (1) atmospheric correction (FLAASH), (2) minimum noise fraction and (3) pixel purity index preparation which helps in discrimination by matching these purest pixels with field spectral observations. Spectral angle mapper method is used to produce score between 0 and 1, where the value of 1 makes a perfect match showing the exact ore deposit in the study area. Using these techniques, we were able to find two ore deposits in the study area, i.e. magnesite and lateritic bauxite, recording different scores related to their abundance.

Formation of weathering-derived magnesite deposits in the New England Orogen, New South Wales, Australia: Implications from mineralogy, geochemistry and genesis of the Attunga magnesite deposit

Nodular, cryptocrystalline, weathering-derived magnesite deposits in the New England Orogen, Australia, provide a significant source of high-purity magnesite. Common textural features and related isotopic fingerprints indicate a close genetic relationship between weathering-derived magnesite deposits hosted by ultramafic rocks at Attunga and by sediments at Kunwarara while silica-carbonate rock alteration and rare hydrothermal magnesite vein deposits reflect contrasting conditions of formation. Localised weathering of carbonates in a soil environment shifts stable isotopic composition towards low δ13C and high δ18O typical for weathering-derived magnesites while intrusion-related fluids do not significantly change the isotopic composition of affected carbonates. At Attunga, magnesite consists of irregular, nodular veins and masses filling faults and cracks in the weathered serpentinite host rock as well as soft powdery magnesite in pervasive serpentinite alteration zones. The high-grade magnesite at Attunga can be contaminated by amorphous silica and serpentine relicts but does not contain dolomite or ferroan magnesite as observed for its hydrothermal equivalent, the Piedmont magnesite deposit, or other widespread deposits of silica-carbonate rock in the Great Serpentinite Belt. Heavy δ18O values are compatible with a supergene formation from meteoric waters while low δ13C suggests C3-photosynthetic plants as the predominant source of carbon for the Attunga magnesites. We infer that weathering-derived, nodular magnesite deposits hosted in ultramafic rocks like the Attunga magnesite deposit have formed in a two-step process involving the hypogene formation of a pre-cursor magnesite deposit and complete supergene overprinting by meteoric waters that acquired carbon from percolation through soil.

An epigenetic magnesite deposit in the Bergslagen area, central Sweden

A Palaeoproterozoic magnesite deposit in the Bergslagen ore province in Sweden is characterized in terms of petrography and major element, trace element and stable isotope compositions. The magnesite horizons are situated at the contact between a metamorphosed gabbro intrusion and felsic metavolcanic rocks, in association with iron-oxide mineralizations and intense Mg-metasomatism. The alteration of the surrounding rocks is used to explain the formation of the magnesite, and chemical dating of hydrothermal monazite constrains the timing of Mg-alteration to a pre-metamorphic age of 1911 ± 16 Ma (2σ). High Y contents in hydrothermal monazite in both metavolcanic and magnesite samples indicate a temperature of>400°C for the hydrothermal alteration. C and O isotopic composition of the magnesite points to interaction with seawater at 200–250°C. We conclude that the magnesite was formed by replacement of a carbonate precursor through hydrothermal alteration, induced by the emplacement of the gabbro intrusion.

Serpentinite-hosted talc–magnesite deposits of Wadi Barramiya area, Eastern Desert, Egypt: Characteristics, petrogenesis and evolution

Enormous quantities of practically untapped talc–magnesite rocks are distributed in the Wadi Barramiya area in intimate spatial and genetic association with the ophiolitic serpentinites. These deposits are an important potential source of magnesia, which is used in a broad spectrum of strategic industries. Barramiya ophiolitic serpentinites represent obducted oceanic slices onto island-arc successions. They occur as elongated mountainous ranges in the form of anticlinal–synclinal sheets demarcating the general ENE-WSW brittle–ductile shear zones of the area. The serpentinite-hosted talc–magnesite deposits of Barramiya area are located: (a) along major faults that cut the serpentinite slices, or (b) at thrust contacts between obducted serpentinites and other mélange components (more siliceous country rocks of island-arc affinity). The latter were regionally metamorphosed at greenschist up to middle amphibolite facies conditions. The talc–magnesite rocks represent in situ fissure-fed metasomatic products of serpentinite precursors via extensive rock–fluid interactions. The main fluids involved in the transformation processes of serpentinites to talc–magnesite were SiO2aqueous solutions and CO2. The deposits located along the fault systems cutting the serpentinite-host are magnesite-rich, whereas those located at the contacts between serpentinites and the more siliceous country rocks are typically talc-rich. Based on the proportional distribution of talc and magnesite in conjunction with other accessories, the rocks have been distinguished into assemblages. Their characteristics, petrogenesis and evolution from serpentinite precursors are elaborated in the light of their petrography, XRD, EDAX, and XRF data. Constraints on the conditions of their formation include temperature of about 490°C and a maximum XCO2 of about 0.13. New mapping was undertaken for the area using remote sensing and GIS techniques. Accordingly, the Barramiya talc–carbonate rocks were more precisely mapped as separate layers and their reserve estimation was accomplished.

Fluid inclusion and stable C-O isotope constraints on the origin of metasomatic magnesite deposits of the Western Carpathians, Slovakia

Primary fluid inclusions in metasomatic magnesite deposits hosted in Palaeozoic basement of the Western Carpathians are filled with of low-to-moderately saline aqueous solutions, with locally increased CO 2 concentrations (up to 34 mol.%). Brine inclusions with up to 42 wt.% of dissolved salts are less frequent. K/Na ratios in the fluid inclusion leachates indicate formation temperatures between 180–310 °C in the Gemeric unit and 230–300 °C in the Veporic tectonic unit. Carbon isotopes in metasomatic magnesite and dolomite show larger spread than those of oxygen. In some deposits, the δ 18O values are almost fixed in various generations of the metasomatic Mg-carbonates, while δ 13C values vary within several ‰. The C, O-isotope covariation reflects low concentrations of CO 2 (less than several mol.%) in the aqueous fluid precipitating the Mg-carbonates in an open hydrothermal system and high fluid/rock ratios ( w/r >5). Calculated δ 18O fluid values between 2 and 10‰ (V-SMOW) indicate isotopic exchange of the carbonate-precipitating fluid with crustal silicate rocks and/or marine carbonates at increased temperatures. Calculated δ 13C fluid values between –5 and 3‰ are thought to reflect dissolution of the metasomatised carbonate as well as the escape of lighter carbon isotope during the CO 2 degassing. Mg-carbonate-precipitating fluids typically contain increased Br-concentrations resembling the halite-fractionated residual brines originated by seawater evaporation. However, extent of the Br-enrichment substantially exceeds the buffering capacity of the seawater evaporation and it is even greater than that in the spatially associated siderite vein- and replacement-type deposits. Apart from the seawater evaporation, superimposed leaching of the organic matter from marine sediments probably played important role. This mechanism has, however, little effect in open hydrothermal systems. Hence, mechanism of the aditional Br-enrichment of the magnesite-forming fluids remains unknown. The observed stable isotope record is a result of Alpine hydrothermal processes as evidenced by coarse-grained dolomite with alpine-type mineral assemblage (rutile, apatite, zircon, muscovite-phengite) identified also in the spatially associated siderite vein- and replacement-type deposits. Another evidence for the Alpine origin are frequently observed primary CO 2-rich aqueous inclusions, up to 50 μm in diameter, which could not survive the Early Cretaceous Alpine metamorphic overprint, as well as different covariation of stable isotopes in siderite deposits, where larger oxygen isotope fluctuations are accompanied by less extensive carbon isotope fractionation. This indicates different precipitation mechanisms, i.e., CO 2-devolatilization in open system during Mg-metasomatism and devolatilization-absent precipitation of the siderite in a closed system triggered by rising temperature. The associated magnesite and siderite deposits may be co-sanguineous with respect to the presence of the evaporated seawater component in the ore-forming fluid, but they cannot be coeval owing to different composition of primary fluid inclusions, hydrologic regimes (open versus closed hydrothermal system) and precipitation mechanisms. The fluid inclusion and stable isotope evidence does not definitely discard genetic models, linking the Mg-metasomatism with infiltration of bitter brines along faults during Permo-Triassic rifting, but this process must have been entirely obliterated by the late Alpine (Cretaceous) hydrothermal activity along shear zones formed during middle-to-late Cretaceous transtension-extension of the orogenic wedge. The Permo-Triassic rift-related origin of the magnesite must cope with the problem of complete loss of pristine isotopic signature of the metasomatic Mg-carbonates during the superimposed Alpine hydrothermal activity, contrasting with none or negligible Alpine metamorphic/hydrothermal overprint of the spatially associated Fe-carbonate vein- and replacement-type deposits.

Stable isotopes of carbon and oxygen as indicators of magnesia metasomatosis in the Lower Riphean deposits of the Southern Urals

The comparative study of the isotopic–geochemi� cal properties of sparry magnesites and carbonate rocks hosting them makes it possible to clarify the problem of genesis of deposits of this type magnesite [13, 14] and to identify the magnesium sources and the time and the mechanisms of its formation. In this case, it is important to study stable isotopes of carbon and oxygen in carbonate rocks and ores. Previously, iso� lated data about the values δ 13 С and δ 13 С in magnes� ites of the Satka and Bakal deposits were used to prove their sedimentary genesis [1]. Our study of stable iso� topes of carbon and oxygen from a sequence of etalon deposits in the Southern Ural province localized in the Lower Riphean deposits enabled us to establish differ� ent trends of changes in the isotope ratios depending on the mechanism of metasomatic transformations and to confirm the possibility of the evaporite brine origin of magnesia fluids. The magnesite occurrence in the Lower Riphean deposits of the Southern–Ural province in the struc� ture of the Bashkir meganticlinorium (Fig. 1) refers to two subtypes under the above type in terms of the geo� logical–geochemical features [4]. The deposits of the first subtype are represented by sheetlike formations of

Hyperspectral Radiometry to Characterise Dunite Alteration and Magnesite Deposits of Salem, South India

This work reports the results of insitu surveys, hyperspectral-radiometry and geochemistry for dunite-alteration and magnesite mapping in the Salem, southern India. Spectral parameters such as the strength of absorption in the 865 nm and 2,300 nm range for Fe2+ and CO32- respectively, and the position of absorption trough were derived from the laboratory spectra for 13 samples. It is observed that dunite alteration and conversion to magnesite produce measurable changes in the VIS-NIR-SWIR spectra due to a transition from the silicate-dominated rocky composition to carbonate-dominated industrial mineral composition. Relationship between the spectra and mineralogy suggests that we can identify the varieties of magnesite using hyperspectral radiometry.

Magnesite-bearing fracture zones of the Zlatibor ultrabasic massif (Serbia) as a discrete structural-morphological type of magnesite deposits in ultrabasites

In this paper, a discrete structural-morphological type of magnesite deposits in ultrabasites, i.e., in magnesite-bearing fracture zones, is presented. The most prominent occurrences of such zones in Serbia are in the Zlatibor ultrabasic massif and they are economically very significant because they contain large reserves of high-quality magnesite, as well as of the accompanying sepiolite.