Mica Granite Research Articles

Molybdenum fertility indicators, granite zircon chemistry, and U-Pb geochronology of the Manjo pluton, southwestern Cameroon

Due to an increasing interest in mineral prospection, Manjo granites which are orogenic have been studied in terms of the geochemistry of whole rock and isotopes of interest found in the associated zircons. This was done to define and situate these rock unit within the context of the regional belt that is Pan African in age, establish the source of Manjo granites and their evolution during the Pan-African orogeny. More so, this study sheds more light on the controversy around the orogenic statues of granites in this section of the geological region, examines their potential for hosting molybdenum, establishes their link with other rocks within this part of the region and how they relate to the Mo-U-bearing biotite-granite in its Ekomedion neighborhood. Sixty-six zircon grains gotten from the granites and their trace elements and Lu-Hf isotopic signatures were examined. The zircon grains' ages were gotten by mass spectrometric method using the U-Pb systematics by laser ablation.The zircons ratios of U to Th varry between 0.2–2.3 relating to sources that are originally magmatic and totally different from those related to souces related to hydrothermalism and metamorphism. The granites were emplaced within the 585±17–616±12 Ma age bracket. Zircons in this study similar to the nearby Ekomedion U-Mo-bearing two mica granites and other felsic massifs found within the shear zones of central Africa (CASC)point to the fact that the Manjo granites were formed at low oxygen fugacity (log ƒO2; -15.848 to -4.515, and log ƒO2@FMQ; -17.409 to -3.677). More so, samples plot mainly outside the defined fertile fields on plots of Eu/Eu* Vs (Ce/Nd)/Y, 10000 × (Eu/Eu*)/Y Vs (Ce/Nd)/Y and Eu/Eu* Vs Dy/Yb. The above points support dominantly plagioclase fractionation in a reduced and less hydrous melt system pointing to a low Mo fertility potential of this pluton emplaced at an average Ti-in-zircon temperature of 861± 56°C. The apparent εHf(t) values for CMR-01 zircon grains range between -15.84 and -1.45 and apparent εHf(t) values for CMR-02 zircon grains vary from -25.02 to -12.39. On spidergraphs, the grainites are depleted in HREE and enriched in LREE . These plots together with εHf(t) values and other indications point to the fact that the granites were derived through partial melting of quartzo-feldspathic crustal magmatic sources. More so, the data showing a new age here show clear signs of post collisional Pan-African magmatism at ∼ 585±17 Ma in the context of a pre-drift Gondwana evolution.

The Permian Cornubian granite batholith, SW England; Part 1: Field, structural, and petrological constraints

The Permian Cornubian granite batholith (295−275 Ma) in SW England includes seven major plutons and numerous smaller stocks extending for ∼250 km from the Isles of Scilly in the WSW to Dartmoor in the ENE. The granites are peraluminous and classified as crustal melt S-type, predominantly two-mica granites, and biotite or tourmaline monzo- and syenogranites, with subordinate minor topaz granite and lithium mica granite. The granites and their host rocks are pervasively mineralized with tin (cassiterite), tungsten (wolframite, ferberite), copper (chalcopyrite, chalcocite, bornite), arsenic (arsenopyrite), and zinc (sphalerite) mineralized lodes. Quartz-muscovite selvedges (greisen-bordered) also contain enrichment of lithophile elements such as boron (tourmaline), fluorine (fluorite), and lithium (lithium-micas such as lepidolite and zinnwaldite). They are derived from both muscovite and biotite dehydration melting of pelitic-psammitic rocks and intruded from a common source along the length of the batholith. Pressure estimates from andalusite and cordierite-bearing hornfels in the contact metamorphic aureole (150 ± 100 MPa) show that the granites intruded to 3 km depth. Cupolas around the Land’s End and Tregonning granites show aplite-pegmatite dikes and tourmaline + quartz + muscovite veins (greisen) that are frequently mineralized. Synchronous intrusions of lamprophyre dikes suggest an additional heat source for crustal melting may have been from underplating of alkaline magmas. The lack of significant erosion means that the source region is not exposed. In an accompanying paper (Part 2; Watts et al., 2024), gravity modeling reveals possible solutions for the shape and depth of the granite and the structure of the lower crust. We present a new model for the Land’s End, Tregonning, and Carnmenellis granites showing a mid-crustal source composed of amphibolite facies migmatites bounded by prominent seismic reflectors, with upward expanding dikes feeding inter-connected granite laccoliths that show inflated cupolas with shallow contact metamorphism. The Cornubian granites intruded >90 m.y. after obduction of the Lizard ophiolite complex, and after Upper Devonian−Carboniferous Variscan compressional, and later extensional, deformation of the surrounding Devonian country rocks. Comparisons are made between the Cornubian batholith and the Patagonian batholith in Chile, the Himalayan leucogranites, and the Baltoro granite batholith along the Karakoram range in northern Pakistan.

Geochemical Conditions and Factors Controlling the Distribution of Major, Trace, and Rare Elements in Sul Hamed Granitic Rocks, Southeastern Desert, Egypt

Egypt is mainly covered by ophiolitic rocks, muscovite, and two mica granites, in addition to different types of acidic and basic dikes. Our field observations indicated that El Sela granites were subjected to alteration types such as silicification, kaolinization, and hematitization, which is associated with uranium mineralization. Petrographic investigations clarified that these rocks were affected by saussiritization, muscovitization, and silicifications as the main alteration types associated with uranium mineralization (uranophane and autunite). We carried out chemical analyses of our samples for major oxides and trace and rare earth elements using ICP-OES and ICP-MS. The studied altered granites had high silica, titanium, and phosphorous as major components, with enhanced amounts of trace elements such as Nb, Ta, Zn, Mo, Pb, and Re, in addition to REE, especially light ones. The average REE content was higher than that of worldwide granites with LREE enrichment. One sample had a strong M-type tetrad effect in the fourth type; other samples had weak W-type in the third type, indicating the effect of hydrothermal alteration processes in the altered granites. This was confirmed by calculating the ratios of most isovalents that deviated from the chondritic ratio in many values. Variation diagrams of U and some trace elements illustrated that U had a weak positive correlation with Y and a strong positive correlation with gold, while it had weak to moderate negative correlation with Hf and Zr/U. In addition, uranium had a weakly defined correlation with the other trace elements, indicating a weak to moderate effect of magmatic processes, while the post-magmatic processes surficial or underground water greatly influenced the redistribution of uranium and other elements.

Uranium and rare metal mineralization in the El Sela and Qash Amir granitic intrusions, south Eastern Desert, Egypt

The Gabal El Sela and Gabal Qash Amir younger granites in the Arabian Nubian Shield (ANS) occurred within the Onib- Sol Hamed suture zone in the southern Eastern Desert of Egypt. In the study area, a pluton composed of biotite granites, muscovite granites and two mica granites is crosscut by altered dibase, microgranitic and bostonite dykes with a distinctive distribution of mineralization with high concentrations of rare metals. Silicification, hematitization, kaolinitization, episyenitization and sericitization are the main hydrothermal alteration processes in these younger granites. Gabal El Sela fractured younger granite shows highly alteration, uranium enrichment and a strong enrichment in some rare elements (such as; Zr = 2287 ppm, Y = 1123 ppm and Nb = 269 ppm) whereas, the bostonite dyke (such as; Zr = 1604 ppm, Y = 709 ppm and Nb = 292 ppm). Gabal Qash Amir muscovite granite shows a favorable enrichment in some rare elements (such as; Zr = 1898 ppm, Y = 181 ppm and Nb = 966 ppm) while, the bostonite dyke (such as; Zr = 1500 ppm, Y = 711 ppm and Nb = 286 ppm).Mineral characterization of the highly radioactive zones shows enrichment in autunite, uranophane, uranothorite, zircon, xenotime, monazite, fergusonite, samarskite and columbite. Field radiometric measurements of the studied El Sela fractured granite revealed that eU reaches up to 459.5 ppm, bostonite dyke eU reaches up to 58 ppm and altered basic dyke eU reaches up to 1625 ppm, while Qash Amir muscovite granite eU reaches up to 51 ppm and the bostonite dyke eU reaches up to 34 ppm.Geological, mineralogical, radiometrical and geochemical studies indicated that Gabal El Sela fractured younger granite is the most promising area characterized by strong enrichment in both uranium and some rare metals mineralization than Gabal Qash Amir muscovite granite.

Multistage magmatism recorded in a single gneiss dome: Insights from the Lhagoi Kangri leucogranites, Himalayan orogen

Determining the geochronological framework and geochemical nature of magmatism associated with orogenic processes is crucial to decipher the evolution of orogenic belts. The Himalayan orogen has recorded considerable information regarding deformation, metamorphism, and magmatism related to orogenic processes. Here, we identify four stages of granitic magmatism on the basis of monazite U–Th–Pb dating of rocks from the Lhagoi Kangri dome, north Himalayan antiform, southern Tibet: middle Eocene (42–40 Ma), late Eocene (ca. 36 Ma), Oligocene (ca. 26 Ma), and Miocene (16–13 Ma). The middle Eocene tourmaline-bearing leucogranite is characterized by (1) relatively high SiO2 (78.7 wt%), Al2O3 (12.6 wt%), and Na2O (6.3 wt%) contents; (2) enrichment in light rare earth elements (LREEs), depletion in heavy REEs, high abundances of REEs, and pronounced negative Eu anomalies; and (3) relatively low values of whole-rock SrNd isotope compositions (87Sr/86Sr(t) = 0.72101 and εNd(t) = −9.8). And the coeval garnet–bearing two–mica granite has a pronounced negative Eu anomaly (Eu/Eu* = 0.07) and a significate lanthanide tetrad effect (TE1,3 = 1.46). These geochemical data suggest that these leucogranites underwent fractional crystallization. They provide a robust evidence for that anatexis of the lower crust of Indian plate began at 42–40 Ma in the central Himalayan orogen. The Oligocene and Miocene two–mica granites share broadly similar geochemical characteristics, such as moderate REE contents and weak negative Eu anomalies, and are distinct from the garnet-bearing muscovite leucogranite. Whole-rock SrNd isotope compositions of the Oligocene and Miocene leucogranites differ from those of the middle Eocene leucogranites, with higher 87Sr/86Sr(t) ratios (0.73524–0.74188) and lower εNd(t) values (−14.7 to −13.7). These geochemical data indicate that the Oligocene and Miocene leucogranites are products of muscovite-dehydration melting of metasedimentary rocks. The garnet-bearing muscovite leucogranite shows the REE tetrad effect, which suggests that it is more evolved than the coeval two–mica granite. We therefore infer that the variations in age and isotopic characteristics of the studied leucogranites were caused by a change in melt source resulting from the compression–extension evolution of the Himalayan collisional orogenic system.

Investigação da relação chuva-deslizamentos no município de Mauá – SP para obtenção de limiares críticos deflagradores de deslizamentos

The Mauá city, Region of Grande ABC Paulista, is among the five municipalities of the São Paulo state with the most critical situation in relation to the number of records of geological accidents, which makes it vulnerable to intense and persistent rainfall. This study investigates the relationship between precipitation events and landslide occurrence in this municipality from the geological-geotechnical characterization of samples representative of the horizons most susceptible to the region's geodynamic processes, precipitation patterns and the frequency of landslides. It was found that rains of different intensities and durations can increase the number of landslides. In addition, the geological and geotechnical characteristics of the region's pedological horizons (residual soil from mica schist and granite) and anthropic interventions contribute to the magnitude of susceptibility to geodynamic and related processes. The curves of landslides obtained, for different criteria of daily and accumulated precipitation before the occurrence, showed that the greater the accumulated value of precipitation, the lower the intensity of daily precipitation necessary to trigger the landslides. The criteria indicated the daily total of 35 mm as the most restrictive, regardless of the value accumulated in days prior to the occurrences, which was validated with the cases of recent landslides occurred in the region, not considered in the calibration of the adjustment equation. In addition, in periods without rain in the previous days, the landslides will tend to occur with rainfall greater than 70 mm on the day of the event, an increase of this value may be observed with the increase in the number of previous dry days.

Spectral characterization of the Batuga granite pluton, South Eastern Desert, Egypt: influence of lithological and mineralogical variation on ASD Terraspec data

The paper concerns with potential utilization of Landsat-8 data combined with TerraSpec spectro-radiometer and field studies for mapping and discriminating the different granitic varieties of Batuga pluton in the South Eastern Desert of Egypt. Integrated data of band combination, principal component analysis (PCA), band rationing, fusion technique, and TerraSpec measurements substantially improve visual interpretation to differentiate between granite varieties as well as basalt dikes traversing the pluton. Compilation of field, petrographic, and spectral data enables to distinguish three varieties of granite, namely alkali feldspar granite, garnet-bearing leucogranite, and two-mica granite (monzogranite). False color composite (FCC) image PC1, PC3, and PC4 in R, G, and B, respectively, is successful to discriminate the western part of Batuga pluton as mica granite (monzogranite) but it failed to discriminate the other two granite types. On the other hand, the band ratio combination 6/7, 5/6, and 2/4 successfully used to discriminate the three varieties of granite. Also, the image fusion technique of false color composite (7, 5, & 2) and band ratio (6/7, 5/6, & 2/4) combinations with the high spatial resolution band 2 of Sentinel-2 is applied using the Gram-Schmidt method. Regarding with TerraSpec measurements, the alkali feldspar granite displays two absorption features around 1.4 and 2.25 μm. Moreover, the garnet-bearing leucogranite shows four little absorption features at 1.4, 2.21, 2.25, and 2.33 μm, while the mica granite shows low reflectance values throughout the VNIR and SWIR regions compared to the other two varieties, and low four absorption features at 1.4, 2.21, 2.25, and 2.33 μm wavelengths. The basalt dikes show a low, nearly flat spectral profile in the VNIR and SWIR wavelength regions and small four absorption features also observed around the 0.65, 1.0, 1.2, and 2.32 μm wavelengths. Data materialized in the paper suggests the usefulness of Landsat-8 and TerraSpec spectroradiometer data as a powerful combination to discriminate the granitic rocks and the traversing basalt dikes as well.

Melting of subducted continental crust during collision and exhumation: Insights from granitic rocks from the North Qaidam UHP metamorphic belt, NW China

The formation and reworking of continental crust have close connections with orogeny. Syn- and post-collisional magmatism is key to understanding crustal growth and reworking during continental collision and post-collisional extension. Here we report a series of syn-collisional felsic magmatic rocks intruded into migmatized gneiss and amphibolite/eclogite in the North Qaidam ultrahigh-pressure (UHP) metamorphic belt, to provide insights into melting/reworking of UHP metamorphosed continental crust during continental collision and exhumation. The syn-collisional magmas are mainly tonalite-trondhjemite and mica granite that occur as plutons and dykes, and high potassium granite veins in migmatites. They were formed by decompression melting of subducted oceanic and continental crust at different levels during exhumation, without any discernible mantle contribution. The tonalite-trondhjemites show adakitic signatures of both oceanic crust and mafic continental crust with varying Nd isotopic compositions. The mica granite plutons have high silica and alkali contents, are weakly to strongly peraluminous, and have crustal SrNd isotope compositions. These mica granites were formed by partial melting of previously subducted continental crust, and formed mostly in high-pressure conditions, in the garnet stability field. The protolith is predominantly granitic gneiss, with minor meta-sediment and metabasite. A compilation of published ages and our results show that these syn-collisional magmatic rocks formed between 437 and 397 Ma, overlapping with UHP metamorphic ages (440–420 Ma), and suggests that exhumation occurred synchronously with continental subduction. Individual zircon grains show metamorphic cores and magmatic rims with a ≤ 20 Myr time interval, interpreted as the time between peak UHP metamorphism and melting during exhumation. Such long-lived and episodic melting of UHP metamorphic continental crust should result from periodic processes, involving melt weakening and decompression by upward movement within the subduction channel, rather than coherent motion of the entire UHP belt. This process represents crustal reworking during collision and exhumation, without input of mantle melts.

Combined zircon U-Pb dating and chemical Th–U–total Pb chronology of monazite and thorite, Abu Diab A-type granite, Central Eastern Desert of Egypt: Constraints on the timing and magmatic-hydrothermal evolution of rare metal granitic magmatism in the Arabian Nubian Shield

We present the first chemical age determination of monazite from a geochemically-specialized rare metal granite of the Central Eastern Desert (CED), Egypt. The Abu Diab composite A-type granite of the CED divides into three co-magmatic phases: two mica granite (TG), garnet-bearing muscovite granite (GMG), and muscovite granite (MG). The GMG granitic phase is a typical example of a rare metal, volatile-rich aqueous silicate magma. Its zircon has extremely high U-concentration (up to 45,000 ppm) and intense metamictization, resulting in significant radiogenic Pb-loss, as well as common Pb contamination, along fractures and other imperfections. Laser ablation (LA-ICP-MS) zircon U-Pb results yield imprecise to meaningless dates. On the other hand, the GMG exhibits two texturally and chemically distinct varieties of monazite, pristine (Mnz1) and altered (Mnz2), that yield similar electron microprobe (EMP) chemical ages of 587 ± 8 Ma (2σ) for Mnz1 and 587 ± 9 Ma (2σ) for Mnz2. These ages, combined with the inferred alteration temperature (T > 400 °C), indicate monazite alteration/replacement occurred during or soon after crystallization of the pluton, in response to expelled magmatic-hydrothermal fluids inferred to be F-rich, late-staged deuteric fluids. The alteration and elemental substitution of zircon and monazite reflect coupled dissolution-recrystallization processes during late-staged deuteric alteration when zircon and thorite were relatively vulnerable to post-magmatic hydrothermal effects because of their extremely metamict state. The ca. 587 Ma age is typical of A-type granite intrusion across the CED and the post-collisional stage of the Arabian Nubian Shield (ANS; 610 – 560 Ma), and is within analytical error of associated magmatic thorite (592 ± 8 Ma). These two ages agree with the timing of rare metal-rich intrusions (0.6−0.4 Ga) related to the Pan-African orogeny. Future research using the monazite chronometer may better constrain the timing of rare metal granitic magmatism of the ANS.

Autunite-Group Minerals and Their Paragenesis from the Sheared Granite of Gabal El Sela, South Eastern Desert, Egypt

G. El Sela is located in the Southern Eastern Desert of Egypt cropping as two parts, occupied by monzogranites that were categorized as biotite granite, muscovite granite and two mica granites. The northern part is more significant according its high concentrations of uranium that controlled by complicated structure regime; faulting, infrastructures and shearing are the most common structural criteria of this part. The Egyptian Nuclear Materials Authority (NMA) mined this part to produce the uranium ore. The previous mineralogical studies indicated that this granite was dominated by primary uranium minerals (pitchblende and coffinite) and secondary minerals belong to the autunite group (autunite, metautunite, phurcalite) in addition to uranophane. In the present work, petrographic and mineralogical studies are applied for the granites using the polarized and stereo microscopes and followed by electron microscope and XRD. The result of the microscopic examinations revealed the tectonic regime controlling the radioactivity and recognized the sodic autunite (meta-natroautunite) beside the pre-mentioned autunite group minerals completing the paragenetic sequrnce of these minerals. In this study, it is concluded that the sheared biotite granite is monzogranite originated during the episode of the continental plate collision (syncollision). The study finished to presence of two main types of the alteration corresponding to the two high levels of radioactivity (moderate and anomalous). The first is the thermal alteration (saussiritization, sericitization, kaolinization, silicification and hematization) and the second is the chemical transformation (oxidation, dehydration, ion substitutions and confusion) responsible for formation of the secondary uranium minerals. The temperature needed for the thermal alteration is sourced by the hydrothermal solutions, while the temperature needed for the uranium minerals transformation may be generated during the episode of the continental plate collision (syncollision). Paragenesis of these minerals indicates that they represent a series of uranyl phosphate minerals (autunite group) with paragenetic sequence starting by autunite (calcic uranyl phosphate) and ends by meta-natroautunite (sodic uranyl phosphate). An advanced process of dehydration accompanies the process of mineral transformation from autunite to meta-natroautunite leading to formation of the anhydrous uranyl mineral (phurcalite) formed by oxidation and dehydration of autunite. Meta-autunite is recorded as a transitional mineral composed of sodic-calcic uranyl phosphate. Uranophane is created by thermal confusion of autunite with the silica.

U-Pb zircon age of the pegmatoid of the Muong Lat complex

Muong Lat granitoid complex located in Thanh Hoa province. It is composed of two mica granite, aplite and pegmatoid. Rock forming minerals include mainly K-feldspar, quartz biotite and muscovite. Crystallization age of pegmatite in Muong Lat body is determined by U-Pb zircon LA-ICP-MS method. Most of the analytical results 206Pb age / 238U ranged from 217–238 Ma, average 230 ± 7 Ma. Age results indicate, the existence magma activity in the study area. Three inherited zircon core gaves age of ~2.8Ga, ~2.4Ga, ~1.8Ga, ~400Ma and ~750 Ma, suggesting that the continental crust of the study area including material composition of the Neoarchean, Paleoproterozoic, Paleozoic and Neoproterozoic

U-Pb geochronology and petrogenesis of peraluminous granitoids from northern Indian plate in NW Pakistan: Andean type orogenic signatures from the early Paleozoic along the northern Gondwana

The pre-Himalayan peraluminous magmatic event along the northern margin of Indian plate in north-western Pakistan has been investigated leading to a correlation with the magmatic evolution in other Himalayan and northern Gondwana regions. The two mica granites from Utla and Mansehra regions of NW Pakistan are dominantly megacrystic, strongly peraluminous (A/CNK > 1.1) and intruded by aplitic dykes and quartz rich veins. U-Pb zircon dating by SIMS reveals their emplacement during the early Paleozoic, ranging from 476 Ma to 480 Ma. These granites are enriched in light rare-earth elements (LREEs) and show similar REE patterns with negative Eu anomalies. Geochemical modelling indicates that these granites were derived mainly from the partial melting of pelitic sources followed by the evolution of melt via fractional crystallization of feldspars, biotite, muscovite, apatite, and/or zircon, with the aplite dykes representing the very last fractionation product. Based on their compositions, source rock characteristics and U-Pb geochronology, we assign these to the regional association of other Cambro-Ordovician granitoids from the Himalayas and northern Gondwana terranes. Due to these similarities alongside other metamorphic, stratigraphic and geochemical evidence, an early Paleozoic Andean-type orogenic event is proposed for the genesis of these granitoids where the process could have been initiated by the subduction of the Proto-Tethys oceanic lithosphere beneath the northern Gondwana continental margin.

Geochemistry, Zircon U–Pb Dating and Hf Isotopic Characteristics of Neoproterozoic Granitoids in the Yaganbuyang Area, Altyn Tagh, NW China

AbstractThe South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions: (1) Yaganbuyang granitoids mainly consist of two‐mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high‐K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ∼954 Ma for granitoids, respectively. (2) The εHf(t) values of two–mica granite and granodiorite are in the range of –3.93 to +5.30 and –8.64 to +5.19, respectively. The Hf model ages (TDM2) of two‐mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust. (3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.

Petrology, geochemistry, radioactivity, and M–W type rare earth element tetrads of El Sela altered granites, south eastern desert, Egypt

The southern part of the Eastern Desert of Egypt—about 30 km southwest of Abu-Ramad city—is mainly covered by ophiolitic rocks (Sul Hamed), island arc assemblage, younger granites (muscovite granites of Qash Amer and two mica granites of El Sela), and various acidic and basic dikes. Field, petrological, and geochemical studies indicate that the El Sela shear zone has been subject to hydrothermal and supergene alteration such as kaolinization, albitization, sericitization, and hematitization. It is invaded by quartz ENE–WSW veins associated with hydrothermal alteration accompanied by radioactive mineralization. The investigated younger granitic rocks had very low contents of compatible elements, such as Cr, Ni, and Co; and high contents of incompatible elements, such as Zr, and large ion lithophiles, such as Sr, especially in the El Sela shear zone. Major oxide and trace element analyses revealed calc-alkaline affinity and peraluminous character. These highly differentiated granitic rocks’ lower Zr/Hf and higher Y/Ho than the normal ratio are consistent with hydrothermal alteration. Most samples had rare earth element (REE)-patterns with an M-type tetrad effect in the first and fourth segments and a W-type tetrad in the third segment. The average ∑REE in the studied granites was lower than the world granite average; the ratio of light to heavy REEs greater. The main radioactive, uranium-bearing, and uraniferous Fe and Mn minerals are uranothorite, autunite, uranophane and autunite as compounds, kasolite, columbite, xenotime, uranophane-bearing zircon and jarosite, silver-bearing pyrite, hematite, and autunite-bearing pyrolusite.

In situ boron isotopic analyses of tourmalines from Neogene magmatic rocks in the northern and southern margins of Tibet: Evidence for melting of continental crust and sediment recycling

Sediment recycling has important impacts on the differentiation of the continental crust, and is considered to mainly occur in arc settings. In collisional orogenic belts, however, sediment recycling processes are comparatively less well understood. In general, sedimentary rocks or tourmaline with continental affinities have boron (B) isotope compositions that differ from marine sedimentary rocks, magmatic rocks undergoing seawater alteration or tourmaline originating from these rocks or fluids. This study uses laser-ablation multi-collector, inductively coupled plasma-mass spectrometry (LA-MC-ICPMS) for in-situ B isotope analyses of tourmaline from the northern and southern margins of Tibet. Tourmalines from the Hudongliang Pliocene two mica rhyolites in the Songpan-Gangzi block and the Cuonadong Miocene two mica granites in the Himalayan Block have δ11B values of −10.47 ± 0.54‰ and −12.48 ± 1.04‰, respectively. Combined with petrological and Nd–Sr isotope data, we suggest that these strongly peraluminous magmatic rocks from the northern and southern margins of Tibet were mainly generated by partial melting of subducted or overridden metasedimentary rocks with continental affinities due to the contraction caused by the collision between the Indian and Asian plates. Given the widespread occurrences of strongly peraluminous Neogene magmatic rocks in the southern and northern margin of Tibet, we suggest that the recycling of sediments with continental affinity played an important role in the evolution of continental crust during the collisional orogenic process.

Analysis of Geological and Geophysical Datasets for Radioelement Exploration in Kab Amiri Area, Central Eastern Desert, Egypt

Detailed geological mapping description of the different granitic types of Kab Amiri pluton were integrated with geophysical (ground gamma ray spectrometry and aeromagnetic) data to identify and map the distribution of radioelement concentrations as well as delineate structural trends that control the mineralized zones in the study area. The geologic studies revealed the existence of four granite varieties namely; biotite granite, garnet two mica granite, muscovite granite, and episyenite. The structural interpretation of geological and geophysical data revealed two intersecting sets of NW and NE-trending faults. The NW-trending set of faults is younger than the NE-trending set where the latter is dissected and displaced by the former. Interpretations of radiometric data revealed the presence of radioactive anomalies southwards that indicate an original increase in uranium contents in the same direction. It could be related to the prevailing NE and ENE fault trends. The southern anomalous zone is related to a very high episyenitization and uranium mobilization. It exhibits a sharp increase in the eU concentrations reaching 370 ppm resulting in a high eU/eTh ratio, approaching 4.5 and, characterized by oval shape trending in the NE direction. Some areas along the peripheral part of Kab Amiri pluton are episyenitized and show a remobilization of uranium. These areas are mostly controlled by faults mainly trending ENE. In the case of the episyenite zone, strong mobilization of uranium is expected to host epigenetic uranium occurrences because more uranium is available. It is obvious that the episyenite rocks of high permeability have higher levels of uranium and their ratios. Thus, these rocks act as an important reservoir for U- mineralization bearing solutions.

태백산지역과 인근에 분포하는 우백질 화강암체의 존재

태백산지역과 주변의 선캠브리아기 고기 화강편마암류 및 고생대 퇴적변성암류 분포지역에 산포되는 소규모 암주상 우백질(알카리) 화강암류는 기존 연구에서 다소 기재가 등한시되어왔다. 그 구분을 위하여 야외노두의 육안상 차이, 광물조성 및 지화학적 특성 등을 파악하였다. 고기 화강편마암(고기 화강암질암)류는 미그마타이트조직을 나타내거나, 유색광물류에 의한 편마구조가 뚜렷한 편이다. 그리고, 부분적으로는 석영과 장석류의 녹회색화로 어두운 암색을 나타내거나, 복운모화강암이나 우백질화강암의 특성을 나타내기도 한다. 이에 비하여 후기 우백질화강암류는 훨씬 밝은 암색을 나타내며 구성광물은 석영, 장석류, 백운모 외에 각섬석류, 견운모, 전기석류 및 레피도라이트(lepidolite) 등을 소량 포함하기도 한다. 모든 우백질 화강암류는 칼크-알카리계열이며, 과알루미나형으로서 S-형에 속한다. 또한, 이들은 분화를 거치면서 알바이트화(albitization) 등에 의하여 CaO와 철함량이 상대적으로 감소하였으며, 영운암화(greisenization) 작용으로 인하여 <TEX>$K_2O$</TEX>와 <TEX>$Na_2O$</TEX>는 부화되었다. The Taebaegsan region and its vicinities mainly consist of Precambrian granitic gneisses and Cambrian meta-sedimentary rocks. And lots of leucocratic(alkali) granites smaller than the stocks are found here and there. Therefore the presence of leuco-granites is not properly described yet in the former studies. For the effective distinction of several granitic rocks, outcrop characteristics, mineral identification, and petro-chemical properties were studied. Some part of granitc gneisses could be classified into typical metamorphic rocks such as migmatites and banded gneisses. And some shows rather dark appearance with gray quartz and feldspars, and others two mica granites, leucocratic ones etc. But all of leucocratic granites of the region usually show bright milky white to beige color. Since they mainly consist of quartz, feldspars, muscovite, and small amounts of sericites, amphiboles, tourmaline and lepidolite. And all of alkali granites belong to the calc-alkalic, peraluminous and S-type in character. During magmatic differentiation of leucocratic granites, CaO and total Fe contents are clearly decreased than those of the older granitic rocks. On the other hand, magmatic evolution also had induced the greisenization and albitization which enriched the relative amounts of alkali elements such as <TEX>$K_2O$</TEX> and <TEX>$Na_2O$</TEX>.

Tow Mica Granites, Southeastern Desert, Egypt: Geochemistry and Spectrometric Prospecting

Tow Mica Granites, Southeastern Desert, Egypt: Geochemistry and Spectrometric Prospecting

영광-나주지역에 분포하는 화강암류의 광물성분에 대한 연구

이 연구의 주목적은 영광-나주지역에 분포하는 송림-대보화강암류를 지질시대, 광물조성, 화학성분과 조직에 따라 각섬석-흑운모화강섬록암, 흑운모화강암, 반상화강암과 복운모화강암의 네가지 암상으로 구분하였다. 이들 화강암류는 동원마그마로부터 분화된 일련의 분화산물로 이루어진 화성암 복합체이며, 페름기말에서 트라이아스기 사이에 옥천습곡대와 영남육괴 사이에서 지괴들의 충돌운동으로 유발된 응력장하에서 형성되었고, 그리고 이 변형대의 형성기에 전후하여 정치된 화강암류가 대보운동을 받아 엽리상화강암류와 비변형화강암류를 형성하였다. 이들 영광-나주지역에 분포하는 화강암질암류의 구성광물 성분은 사장석, 흑운모. 백운모와 각섬석으로 구성되어있다. 사장석은 오리고클레스(<TEX>$An_{19.3-27.7}$</TEX>)와 안데신(<TEX>$An_{28.4-31}$</TEX>)성분에 해당하며 누대구조의 성분변화도 좁은영역에 치우치면 이는 느린 결정작용과 이들 결정들의 성장이 최종고결작용 이전에 일어났음을 보여준다. 흑운모의 Mg 함량은 산소의 압력과 분화도의 증가에 따른다(프로고파이트에서 시데로피라이트로 변함). <TEX>$Al^{iv}$</TEX>/<TEX>$Al^{total}$</TEX> 관계는 전체 알루미나양에 따라 증가한다. 백운모는 일차기원이며 높은 <TEX>$TiO_2$</TEX>함량을 보이는 세라도나이트이다. 각섬석은 회각섬석류에 속하며 지질압력계로 계산한 화강암질암의 고결심도는 11.3-17.2 Km이다. Main aspect of this study are to clarify mineral compositions on granites in Youngkwang-Naju area. These granites are is divided into four rock facies based on the geologic ages, mineralogical composition and chemical constituents, and texture : hornblende-biotite granodiorite, biotite granite, porphyritic granite and two mica granite. These granites constitude an igneous complex formed by a series of differentiation from cogenetic magma. In compressive stress field between the Ogcheon folded belt and the Youngnam massif, the foliated and undeformed granites had formed owing to heterogeneous distribution of stress. The geochemical data of study area indicate magma of these rocks would had been generated by melting in lower and middle crust. The major minerals of granitic rocks in study area are plagioclase, biotite, muscovite and hornblende. Plagioclase range in composition from oligoclase (<TEX>$An_{19.3-27.7}$</TEX>) to andesine (<TEX>$An_{28.4-31}$</TEX>), and shows normal zoning patterns, This uniformed composition indicated slow crystallization, and it is obvious that the growth of these crystal occurred before final consolidation of the magma. The Mg content of biotite are increases with increasing of <TEX>$f_{O2}$</TEX> and grade of differentiation, changing from phlogopite to siderophyllite. Its <TEX>$Al^{iv}$</TEX>/<TEX>$Al^{total}$</TEX> ratios are propertional to bulk rock alumina content. Muscovite is primary in origin with high content of <TEX>$TiO_2$</TEX>, and Its composition correspond to celadonitic muscovite. Hornblende indicated calc amphibole group (<TEX>$(Ca+Na)_{M4}{\geq}1.43$</TEX>, <TEX>$Na_{M4}</TEX><TEX><</TEX><TEX>0.67$</TEX>). and consolidation pressure of granitic body by geobarometer of Hammerstrume and Zen show 11.3~17.2 Km.

Petrophysical and geochemical characteristics of late Variscan granites in the Karlovy Vary Massif (Czech Republic) - implications for gravity and magnetic interpretation in shallow depths

* �Correspondingauthor The Karlovy Vary Massif (KVM) in northern Bohemia is a composite granite body built up of Late Variscan biotite, two-mica and lithium mica granites. We summarize the available whole-rock geochemical and petrological data and correlate them with similar information from three boreholes in the northern and southwestern parts of the Massif. The aim of the study was to determine whether various types of granites differ in their physical and chemical properties, and whether any differences in physical characteristics affect the accuracy of geophysical interpretation. In accord with the earlier studies, we distinguish two geochemically and petrophysically contrasting granite suites - the Older Intrusive Complex (OIC) and Younger Intrusive Complex (YIC). The geochemical data show that the OIC and YIC granites differ significantly in the content of most major-element oxides (like SiO 2 , TiO 2 , FeO, Fe 2 O 3 tot , MgO and CaO). As to physi- cal parameters, the granites differ markedly in magnetic susceptibilities and in the contents of radioactive elements (U and Th). From gravity and magnetic data we compiled a 22 km long geophysical profile, which crosses two of the three studied boreholes. For the construction of geological model along this profile, we used the data on the petrophysical properties measured on samples from the boreholes. Densities of the individual granite types are very similar to each other and thus the distinction of the OIC and YIC granites based on gravity data is not possible. Magnetic susceptibility differs markedly for the OIC and YIC granites in the drill logs, but absolute values of magnetic susceptibilities are very low. Modelling showed that neither gravimetry nor magnetometry are suitable methods for distinguishing between the different types of granites. On the other hand, it proved that the spatial distribution of individual granite intrusions does not affect the overall interpretation of the shape, size and depth of the whole granite body.