Medium-grained Biotite Granite Research Articles

Late mesozoic magmatism in the Gucheng district: Implications for REE metallogenesis in South China

Regolith-hosted rare earth element (REE) deposits are common in South China. The newly-discovered Gucheng REE deposit in the western part of Guangdong Province, is characterized by HREE enrichment (with ∑HREE oxides of 55%). Three types of granites have been identified in the Gucheng ore district, a REE-fertile coarse-grained biotite granite (CGBG), a weakly REE-fertile fine-grained biotite granite (FGBG) and the barren medium-grained biotite granite (MGBG). New LA-ICP-MS zircon U-Pb dating reveals that the MGBG (107.7 ± 0.4 Ma), CGBG (103.2 ± 0.6 Ma) and the FGBG (98.9 ± 0.7 Ma) were all formed in the Late Cretaceous.Mineralogical and geochemical data indicate that the CGBG is an unfractionated I-type granite, whereas the FGBG and MGBG are fractionated I-type granites. The CGBG and FGBG have (87Sr/86Sr)i and εNd(t) ranging from 0.7121 to 0.7140 and −8.6 to −8.0, and 0.7125 to 0.7131 and −8.2, respectively. The source of these granites was mainly composed of two end-members: one having 90% Paleoproterozoic basement and another 10% enriched mantle metasomatized by subduction-related melts. The barren MGBG is also derived from partial melting of a Paleoproterozoic source with a minor contribution of enriched mantle. The involvement of enriched mantle can provide REE into the magmas, which plays an important role in REE enrichment. Geochemical data show that allanite have been crystallized during magma evolution process of all the three types of granites. However, no allanite has been discovered in the MGBG, and the FGBG contains lower abundance of allanite than that of the CGBG, which is due to different degrees of fractionation. The crystallization and separation of allanite has greatly affected the LREE of the three types of granites, which further influences their potential for LREE mineralization. Lower K/Rb and Nb/Ta ratios of the CGBG, FGBG and MGBG indicate that these three types of granites were affected by hydrothermal events after their crystallization. Zircon geochemical data show that the MGBG was formed in a lower oxygen fugacity environment than the CGBG and FGBG. Above all, involvement of enriched mantle, a relatively high oxygen fugacity, crystallization and separation of allanite as well as involvement of hydrothermal events after magmatic crystallization are important factors controlling REE mineralization at Gucheng, of which the hydrothermal events may play the most important role.

Geological and Hydrogeophysical Investigation of Angwan Zakara, Keffi Sheet 208N.E of North Central Nigeria

The geological and hydrogeophysical assessment of the groundwater prospect/potential in Angwan Zakara and its environs, Karu Local Government, Nasarawa State, North-Central, Nigeria has been carried out in this study. The study area covers 25km2.The area is underlain by the Basement Complex of the North-Central Nigeria consisting of Medium grained biotite granite, biotite gneiss, phyllite and un-mappable muscovite schist with structural features such as joints, veins, foliation, faults, and xenoliths trending NW-SE direction. Forty Nine (49) Vertical Electrical Sounding were carried out in the study area using Omega Resistivity Terrameter, GPS12 Garmix with a maximum cable spread of AB/2=100m and MN/2=5m. The results obtained from the field data were interpreted using IXID Software for quantitative analysis. True resistivity map, piezometric map, basement resistivity map and depth to basement map were prepared and interpreted using computer software for qualitative analysis (SURFER 8). From the IXID interpreted results, five (5) curve types were obtained from the acquired data namely A, H, KH, AH, and HK curve types are the dominant. The study area showed depth to basement ranges from 20-90m. That revealed good groundwater potential. The study area revealed 4-7 lithologic sequences consisting of top soil, laterite, clay, weathered/ fractured basement however the host rocks in the study area are biotite granite, quartzite and schistose-gneiss. The results obtained shows that the direction of water flows revealed five ridges R1-R5 and four depressions D1-D4 with receptacles trends of the ridges are R1 and R2:NW-SE; R3 N-S, R4 : NE-SW and R5; E-W. The geoelectric sections were produced and correlated with the geology of the study area and it was found to be in conformity with the each other. Based on this, the study area is zoned into three namely good, moderate and poor groundwater potential zones.

Geochronology and geochemical properties of the large-scale graphite mineralization associated with the Huangyangshan alkaline pluton, Eastern Junggar, Xinjiang, NW China

The Huangyangshan alkaline pluton is located within the southern part of the Eastern Junggar orogenic belt in Xinjiang Province, and forms part of the Kalamaili alkaline granite belt. The pluton hosts the Huangyangshan super-large graphite deposit, which develops unique spherical structure and coexists with metal sulfides. This study examines the genetic relationship between the alkaline magmatism that formed the pluton and the graphite mineralization using zircon LA–ICP–MS U–Pb dating, geochemical analysis for representative rock types in the Huangyangshan pluton, and new Re–Os isotope dating for the graphite in the Huangyangshan graphite deposit. Zircons from medium-grained arfvedsonite granite, medium–fine-grained amphibole granite, medium-grained biotite granite, and fine-grained biotite granite phases of the Huangyangshan pluton yield weighted mean U–Pb ages of 322.7 ± 4.5, 318.3 ± 4.0, 303.9 ± 2.1, and 301.1 ± 3.6 Ma, respectively, indicating that all of the granite phases were emplaced during the Late Carboniferous over a period of around 20 Myr. Six graphite samples from the deposit yield a Re–Os isochron age of 332 ± 53 Ma. Combining these ages with the genetic relationship between the graphite mineralization and magmatism in the study area and the relatively large uncertainty on the Re–Os isochron age for the graphite suggests that the mineralization formed at ca. 320 Ma. The graphite samples yield an initial 187Os/188Os value of 0.38 ± 0.2, indicative of carbon derived from a mixture of organic and mantle-derived sources. The different granite phases in the Huangyangshan pluton are geochemically similar with relatively high SiO2 (75.6–78.2 wt%) and Na2O + K2O (8.01–9.04 wt%) and relatively low CaO (0.18–0.7 wt%), MgO (0.06%–0.13 wt%) and Fe2O3 (TFe2O3 = 1.08–2.06 wt%) contents. The granites are enriched in light rare earth elements (LREE), large-ion lithophile elements (LILEs) (e.g. Rb, Th, and K), and high field strength elements (HFSEs) (e.g. Zr and Hf), depleted in heavy rare earth elements (HREEs), and have negative Ba, Sr, P, Ti, and Eu anomalies. These geochemical characteristics are indicative of derivation from juvenile basaltic oceanic crustal materials in the lower crust. This suggests that the Huangyangshan pluton formed from magmas generated by partial melting caused by mantle-derived magma underplating, with the magmas then undergoing mixing, separation, and significant fractional crystallization. Diorite enclaves within the granites have weaker trace element anomalies that are indicative of magma mixing. In addition, the mantle-derived intermediate–basic end-member involved in the magma mixing is likely one of the important carriers of carbon and metal. In summary, the Late Carboniferous Huangyangshan pluton and its associated graphite mineralization formed in a post-collision extensional tectonic setting in the Kalamaili area.

Petrographical, petrochemical characteristics of Hòn Rồng massif granitoids, Cam Ranh, Khánh Hòa

Hòn Rồng massif granitoid has a high mountainous terrain, with an absolute height of 728 m, relatively equal, slightly extended in the Northwest-Southeast direction, occupying an area of ​​about 29 km2. Petrographical composition is mainly medium - grained biotite granite (phase 2), minor is fine- grained biotite granite (phase 3), vein rocks are aplite granite and pegmatite and a little of xenolith of granodiorite in medium - grained biotite granite. Medium-grained biotite granite: major mineral composition (%): plagioclase (oligoclase) 25–35, quartz 30, orthoclas 25, biotite 5 - 8 and few hornblend; fine-grained granite (%): plagioclase (oligoclase) 30 - 35; quartz 30 - 35; feldspar kali (orthoclase, and microclin) 30, biotite 3 - 5; accessory mineral is zircon, orthite, apatite, sphen, and very little ore minerals (about ​​2%); epimagmatic minerals including: chlorite, epidot, kaolinite, sericite, carbonate, sausorite-replaced association. Rocks are altered alkalization strongly (albitization and microlinization), and minor are chloritization, epidotization and sericitization. Averaged chemical compositions (%)SiO2: 69.07–72.07; total alkali(K2O+Na2O) 7.35–7.96. Ratio of K2O/Na2O 1.04, low TiO2 (0.24–0.37). Ratios of A/CNK 1.02–1.09, Rb/Sr: 0.27–1.62; Ba/Sr: 1.82–2.56, Ba/Rb: 1.58–7.13; K/Rb: 0.42–0.62; Ca/Sr: 0.21–0.47; the value of Eu anomalies is low. Granite belongs to calc-alkaline, aluminum content is from medium to high; K-Na alkaline series, I-granite type. Granitoid had been formed in plutonic - volcanic arc of subduction-zone. Compared with the granitoid formations in South Vietnam territory, Hòn Rồng massif granitoid belongs to phase 2 (main) and phase 3 (minor) of Đèo Cả complex with late Kreta age.

Physico-chemical conditions of crystallization and ore-bearing of granitoids of the border zone of the Southern and Middle Urals

The geological structure of the border zone of the Southern and Middle Urals (Kunashak area), as well as the composition and conditions for the formation of granitoid complexes developed here, whose age varies from Devonian to Triassic, is briefly considered. Thermobarometric studies of quartz of medium-grained biotite granites showed that in the age range ― Poletaev (D3), Shalkar (P1), Sultayev (P1), and Yugokonev (P1T2) complexes ― water pressure during the formation of melt inclusions was 2.22.7, 2.53.0, 3.94.4 and 3.64.5 kbar, and the crystallization temperature of rocks ― 800840, 900940, 840900 and 940980С. This indicates a consistent increase in the crystallization depth of the granite massifs in this series from the hypabyssal-subsurface to the hypabyssal-abyssal facies. At the same time, in the melt-fluid inclusions, a decrease in fluid volume is noted ― 14.216.8, 8.114.3, 6.27.9 and 4.36.8 vol.%, Water concentrations ― 3.74.8, 2.13.9, 1.82.3 and 1.31.9 wt.% as well as chlorine ― 0.040.08, 0.030.07, 0.030.06 and 0.020.05 wt.%.
 It is shown that the granitoids of the Sultayev and Yugokonev complexes are very promising for tantalum, niobium, tungsten, molybdenum and beryllium. Of the greatest interest in rare-metal mineralization are the leucocratic aplitic and greisen granites of the final phases of the formation of intrusions. The level of erosional slice of various structural and formation zones of the Kunashak area relative to each other has been established.

Physico-Chemical Conditions of Crystallization and Ore Potential of Granitoids from the Boundary Zone of the Southern and Middle Urals

Abstract—The paper briefly considers the geological structure of the boundary zone between the Southern and Middle Urals (Kunashak area), as well as the composition and conditions of formation of Devonian–Triassic granitoid complexes developed here. Thermobarometric studies of quartz from medium-grained biotite granites showed that the Poletaev (D3), Shalkar (P1), Sultayev (P1), and Yugokonev (P1–T2) complexes were formed at water pressure of 2.2–2.7, 2.5 –3.0, 3.9–4.4 and 3.6–4.5 kbar and crystallization temperature of 800–840, 900–940, 840–900 and 940–980°С, respectively. This indicates a systematic increase in the crystallization depth of the granite massifs in this series from the hypabyssal–subsurface to the hypabyssal-abyssal facies. At the same time, the melt–fluid inclusion study revealed a decrease in fluid volume (–14.2–16.8, 8.1–14.3, 6.2–7.9 and 4.3–6.8 vol %), and concentrations of water (–3.7–4.8, 2.1–3.9, 1.8–2.3 and 1.3–1.9 wt %) and chlorine (–0.04–0.08, 0.03–0.07, 0.03–0.06 and 0.02–0.05 wt %) in this series. It has been shown that the granitoids of the Sultayev and Yugokonev complexes are very promising for tantalum, niobium, tungsten, molybdenum, and beryllium. The leucocratic aplitic and greisen granites of the final phases of the intrusions are most promising for the rare-metal mineralization. The erosion level of different structural and formation zones of the Kunashak area relative to each other has been established.

Late Paleozoic and Early Mesozoic rare-metal granites in Central Mongolia and Baikal region: review of geochemistry, possible magma sources and related mineralization

The Central Asian Orogenic Belt (CAOB) was a scene of intense granitoid magmatism during the Phanerozoic with formation of vast batholiths: Angara-Vitim and Daurian-Khentei. In the Late Paleozoic and Early Mesozoic times, the peripheral zones of batholiths underwent granitic magmatism associated with rare-metal mineralization. Petrological and geochemical studies show that the rare-metal Li–F granites formed, with a gap about 100 My, large igneous provinces of the Mongol-Okhotsk Belt. Late Paleozoic rare-metal granites build a series of multiphase plutons in the Baikal region (e.g. Kharagul 318 ± 7 Ma, Bitu-Dzhida 311 ± 10 Ma and Urugudei 321 ± 5 Ma). The early medium-grained biotite granites and leucogranites were followed by topaz-bearing microclineand amazonite–albite granites and a series of dikes. The Early Mesozoic epoch was marked by the formation of the Daurian-Khentei Batholith (230–190 Ma) in the center of area and rifting zones with alkaline and rare-metal granite plutons on the peripheries. In contrast to the Late Paleozoic, small Early Mesozoic intrusions (e.g., Avdar Pluton ~10 km2, 212–209 Ma) of rare-metal Li–F granites within the Avdar-Khoshutul series of granitoids coexisted with sizable plutons (e.g., Janchivlan Pluton ~70 km2, 227–195.3 Ma). Rare-metal Li–F granites of the Janchivlan Pluton produced small domal intrusions composed of microcline–albite, amazonite–albite and albite–lepidolite granites. The Sn–Ta–Nb mineralization is associated with albite–lepidolite granites. The rare-metal granites of the Baikal region and Central Mongolia of contrasting ages show an identical geochemical signature of Li–F granites. It is expressed by increase in F, Li, Rb, Cs, Sn, Be, Ta and Pb and decrease in Sr, Ba, Zn, Zr, Th and U contents in course of multiphase intrusions formation. The geochemical data confirm the magmatic model for genesis of the studied rare-metal Li–F granites. However, this process of magma differentiation was terminated with formation of albitites, microclinites and muscovite greisens. The whole-rock geochemistry and isotopic composition of the granites points to the Precambrian crust of the Baikal region (T2DМ = 1.0–1.3 Ga) as the most likely source. We propose the formation of the initial granitic melts due to anatexis of the higher levels of the continental crust, with fluids released during granulite-facies metamorphism in the lower crust. The rare-metal Li–F granites of the studied provinces are intraplate formations geochemically different from the Early Paleozoic collisional granitoids. This could be caused by the influence of deep-seated source on the occurrence of rare-metal magmatism.

Hydrogeochemical appraisal of fluoride in groundwater of Langtang area, Plateau State, Nigeria

Consumption of high fluoride in groundwater of Langtang area, manifest in the inhabitants of the area in form of dental fluorosis and skeletal fluorosis in older group. The aim of this study was to appraise the hydrogeochemistry of fluoride in the groundwaters of Langtang area. Thirty seven surface and groundwater samples and nine rock samples were collected in Langtang area for geochemical analysis. The Inductively Coupled Plasma Emission Spectrometry (ICPOES) was used to detect cations. The anions (Cl - , SO 4 = and Br - ) were determine by Ion Chromatography method. Fluoride was determined by the Specific Ion Electrode and bicarbonate was determined by titration. Major oxides, trace elements and rare earth elements for the rock samples were determined by the XRF method and fluorine by the Fusion method. Polished thin sections for rocks were prepared and studied. Geochemical results from analysis of the samples (rock and water) show that four major rock units make up the geology of the area; coarse porphyritic biotite granite, migmatite, rhyolite and riebeckite granites, the minor ones are pegmatite, trachyte, aplite and fine to medium grained biotite granites. The rhyolite, the riebeckite granites and trachyte have the highest level of fluorine content in the area (1,470, 1000, 900 and 800 ppm) respectively. The fluorine mineral (Fluorite) crystallized in the late stage of the magma as replacement of Fe/Mg mineral probably hornblende or biotite. Fluorine is leached into the groundwater from the rhyolite under the slightly alkaline (Ca-Mg-HCO 3 evolving Na-HCO 3 ) water in the area. The two major groundwater types (Ca-Mg-HCO 3 and Na-HCO 3 ) in the area have good relationship with content of fluoride in water. Although, the riebeckite granites have high fluorine content, contribution of fluoride from them is towards the southern portion of the map, owing to the groundwater flow direction. The different water sources in the area do not show variation in content of fluoride in water. However, groundwater barriers (dykes) may be responsible for some area having low fluoride (<1.5 mg/l) content. The consumption of high content of fluoride in the area has resulted in severe dental fluorosis in both children and youths and bowing of legs ( Genu Valgum ) in children with no discrimination between the sexes. Keywords: Fluoride, Fluorite, Fluorine, Fluorosis, Riebeckite Granite, Groundwater

Building up of a nested granite intrusion: magnetic fabric, gravity modelling and fluid inclusion planes studies in Santa Eulália Plutonic Complex (Ossa Morena Zone, Portugal)

AbstractThe Santa Eulália Plutonic Complex (SEPC), located in the Ossa Morena Zone (south Portugal), is composed of a medium- to coarse-grained pink granite (G0-type) and a central grey medium-grained biotite granite (G1-type). Available Rb–Sr data indicates an age of 290 Ma. An emplacement model for the SEPC is proposed, taking into account magnetic fabric, 2D gravity modelling and fluid inclusion planes studies. The G0 and G1 types demonstrate different magnetic behaviour: G0 is considered a magnetite-type granite and G1 is an ilmenite-type granite. The formation of G0 required oxidized conditions related to the interaction of mafic rocks with a felsic magma. The 2D gravity modelling and subvertical magnetic lineations show that the feeder zone of the SEPC is located in the eastern part of the pluton, confirming the role of the Assumar and Messejana Variscan faults in the process of ascent and emplacement. The magma emplacement was controlled by ENE–WSW planar anisotropies related to the final brittle stages of the Variscan Orogeny. The emplacement of the two granites was almost synchronous as shown by their gradational contacts in the field. The magnetic fabric however suggests emplacement of the G0-type first, closely followed by emplacement of the G1-type, pushing the G0 laterally which becomes more anisotropic towards the margin. The G1-type became flattened, acquiring a dome-like structure. The SEPC is a nested pluton with G0-type granite assuming a tabular flat shape and G1-type forming a rooted dome-like structure. After emplacement, SEPC recorded increments of the late Variscan stress field documented by fluid inclusion planes in quartz.

Garnet geochemistry of tungsten-mineralized Xihuashan granites in South China

The Xihuashan complex intrusion in South China, which is emplaced at ca. 154Ma, mainly comprises medium-grained porphyritic biotite granite, medium-grained biotite granite, and fine-grained two-mica granite. Medium-grained biotite and fine-grained two-mica granites are important tungsten-bearing granites and contain an unusual amount of garnet. Garnets from this intrusion are dominated by almandine and spessartine, which constitute 94% to 99% of the total molecular composition of the garnet. These garnets display unusual compositional zoning. The cores of these garnets are rich in heavy rare earth element (HREE), Y, Ca, and contain abundant HREE- and Y-rich mineral inclusions. Their rims are free of mineral inclusions and have low of these elements. Two types of fluorite inclusions exist in garnet: Y fluorite and Y-poor fluorite. Garnet exhibits specific Mn zoning with a relatively Mn-poor core but a relatively Mn-rich rim, thus constituting a specific “spessartine inverse bell-shaped profile” that belongs to typical magmatic garnets. All analyzed garnets have high REE content and exhibit HREE-enriched and LREE-depleted patterns with strong negative Eu anomalies. The incorporation of REE into garnet is in part controlled by its crystal chemistry, with REE3+ following a coupled substitution of the type [Fe2+,Mn2+]−1VIII[REE3+]+1VIII[Si4+]−1IV[Z3+]+1IV. The texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure–temperature–composition condition of magmatic evolution, internal crystal-chemical parameters, and kinetics during mineral growth. The garnet core grows in near equilibrium with magmatic melt under a relatively high pressure–temperature (P–T) condition. By contrast, the garnet rim grows rapidly by the coexisting melt-fluid phase and CO2-rich volatile environment under a relatively low P–T condition, which is virtually unfavorable for the incorporation of REE into the magmatic garnet structure. Garnet fingerprints the magmatic-hydrothermal transition during crystallization of these granites.

Variscan granitoid plutonism in the Strzelin Massif (SW Poland): petrology and age of the composite Strzelin granite intrusion

Petrological data and recently published U/Pb zircon SHRIMP ages reveal a protracted Variscan magmatic evolution in the Strzelin Massif (SW Poland), with three main stages of granitoid plutonism: 1 – tonalitic I, 2 – granodioritic and 3 – tonalitic II/granitic. The granitoids of the second and third stages form the Strzelin intrusion that is composed of three varieties: medium-grained biotite granite, fine-grained biotite granite and fine-grained biotite-muscovite granite. New SHRIMP data show that the medium-grained and fine-grained biotite granites comprise different zircon populations that reflect complex and prolonged plutonic processes. Two distinct magmatic events seem to be represented by well-defined zircon populations with apparent 206 Pb/ 238 U ages of 303 ± 2 Ma in the medium-grained biotite granite, and 283 ± 8 Ma in the fine-grained biotite granite. These dates, however, do not necessarily reflect the true magmatic ages, possibly being “rejuvenated” by radiogenic lead loss in zircons (impossible to resolve based on routine SHRIMP data). Based on field evidence, the third variety, the biotite-muscovite granite, postdates both types of biotite granites. The petrographic and geochemical features, including Nd isotope signature, along with various zircon inheritance patterns and ages, suggest that the parental magmas of the three granites originated from different crustal sources and were emplaced during three successive magmatic pulses.

Sequential granite emplacement: a structural study of the late Variscan Strzelin intrusion, SW Poland

The Strzelin Massif in SW Poland (Central European Variscides) records a protracted igneous evolution, with three main magmatic stages: (1) tonalitic I, (2) granodioritic and (3) tonalitic II/granitic. In the northern part of this Massif, the Strzelin intrusion proper comprises three successively emplaced rock types: a medium-grained biotite granite (303 ± 2 Ma), a fine-grained biotite granite (283 ± 8 Ma) and a fine-grained biotite-muscovite granite; based on field evidence, the third variety postdates both types of the biotite granites. The structural data from the three granites, including their parallel, approximately E–W striking and steeply dipping lithological contacts and ENE–WSW trending subhorizontal magmatic lineations, suggest that the emplacement of all three successive granite varieties was controlled by an active, long-lived strike-slip fault, striking ESE–WNW, with a dextral sense of movement. After the emplacement of the youngest biotite-muscovite granite, the intrusion underwent brittle extension which produced “Q joints” striking NNW–SSE to N–S and dipping at 55–70° WSW to W, and showing evidence of broadly N–S directed sinistral displacements. The structural observations, supported by new geochronological data, indicate that the internal structure of the composite granitoid intrusion, including the faint magmatic foliation and lineation, formed in a long-lived strike-slip setting, different from the subsequent, post-emplacement extensional tectonics that controlled the development of brittle structures.

Petrogenesis of the Xihuashan Granite in Southern Jiangxi Province, South China: Constraints from Zircon U‐Pb Geochronology, Geochemistry and Nd Isotopes

Abstract:Mesozoic granitic intrusions are widely distributed in the Nanling region, South China, Yanshanian granites are closely connected with the formation of tungsten deposits. The Xihuashan granite is a typical representative of tungsten‐bearing granite. The Xihuashan granite consists mainly of medium‐grained porphyritic biotite granite, medium‐grained biotite granite and fine‐grained two‐mica granite, which correspond to LA‐ICP‐MS zircon U‐Pb ages of 155.5±0.4 Ma, 153.0±0.6 Ma and 152.8±0.9 Ma, respectively. Rocks from the Xihuashan mining area displays high SiO2 (73.85% to 76.49%) and Na2O+K2O contents (8.09% to 9.43%), belonging to high‐K calc‐alkaline series. They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 1.06. All granites in this study area are rich in Rb, Th, U and Pb, and depleted in Ba, Sr, P, Ti, Nb and Eu, especially depleted in medium‐grained biotite granite and fine‐grained two‐mica granite. The medium‐grained porphyritic biotite granites usually have high LREE concentrations, whereas medium‐grained biotite granite and fine‐grained two‐mica granite displays high HREE contents. Our geochemical data reveal that the studied rocks are highly fractionated I‐type granite. The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity, which may explain the formation of three types of distinct granites. Variations of Rb, Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar. Fractional crystallization of monazite, allanite and apatite resulted in LREE changes in granite, and formation of garnet mainly caused HREE changes. Granites from the Xihuashan mining area have relatively high εNd(t) values (–9.77 to –11.46), indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantle‐derived magmas.

U-Pb isotopic age, composition, and sources of the plagiogranites of the Kalba range, Eastern Kazakhstan

Of special importance in the evolution of the Paleoasian ocean is the Carboniferous‐Permian stage, which reflects the closure of the oceanic basin and formation of the structure of the Central Asian fold belt (CAFB) in its present-day form [1]. This is also the time (320‐280 Ma) when the largest Angara‐Vitim granitoid batholith and conjugate synplutonic basite dikes in Transbaikalia, granitoid intrusions and bimodal basalt‐rhyolite series of the Gobi‐Tien Shan zone of South Mongolia, and the Kalba‐Narym and ZharmaSaur batholithic bodies and preceding subalkaline gabbroids, picritoids, high-Al plagiogranitoids, and paleovolcanic structures of the central type in Eastern Kazakhstan were formed. Unlike the Permian‐Triassic stage, which was proved to be related to the Siberian superplume [2], the geodynamic nature of the Carboniferous‐Permian magmatism of the CAFB remains controversial. The plume model was proposed for the Angara‐Vitim batholith [3], and break-off of lithospheric plates in the collision zone between the Kazakhstan and Siberian paleocontinents was suggested for the batholithic belts of Eastern Kazakhstan [4]. These models believe that the collision-related mantle was supplied either with autonomous plumes or with asthenospheric fingers produced by mantle extinction at the divergent margins of lithospheric plates. The solution of this problem consists in studying key magmatic complexes (composition, structure, age), with a special emphasis on the sources of magmatic melts. One such key complex is the plagiogranite of the Kalba Range traditionally distinguished in the Kunush Complex. One group of researchers suggested an Early Carboniferous age and island arc affinity [5], while others consider them as collision-related Late Carboniferous rocks [6, 7], or as products of the Tarim plume [8]. The analysis of the tectonic position of the magmatic complexes of Great Altai (according to N.A. Eliseev) and their correlation with sources [8, 9] sheds no light on this controversary. This article is aimed at accurate dating of the plagiogranites of the Kalba‐Narym zone for refining their position in the magmatic scheme, as well as for estimating the formation conditions and sources of plagiogranite magmas based on their composition and geochemical modeling of the protolith‐melt system. We studied the plagiogranites from the Zhilandy and Tochka massifs (Fig. 1). The Zhilandy Massif forms an isometric body, with medium-grained biotite granites in the central part and fine-grained porphyritic varieties and plagiogranite porphyry dikes in the marginal parts. The plagiogranites consist of large biotite, short-prismatic zoned andesine‐oligoclase, and single grains of orthoclase‐microperthite and green hornblende. The Tochka Massif is made up of NW-extended minor bodies and dikes of fine-grained porphyritic biotite plagiogranites and plagiogranite porphyries. The plagiogranites of the Tochka Massif differ macroscopically from the Zhilandy rocks owing to superimposed processes of mylonitization; however, microscopically, they have similar petrographic and mineral composition. The dikes of plagiogranite porphyries of both the massifs contain phenocrysts of short-prismatic zoned plagioclase, quartz, and biotite embedded in the microcrystalline groundmass. In both cases, the plagiogranites intrude black shales of the Takyr Formation ( D 3 –C 1 ) and are cut by the Early Permian granitoids of the Kalba batholithic belt [5‐7, 10].

Geochemical characteristics of surface efflorescence on the seventh century stone pagoda in Republic of Korea

This study presents detailed description and geochemical characteristics of the efflorescence caused by interaction of water and the concrete on the surface of the seventh granitic stone pagoda in Republic of Korea. The pagoda comprised light gray medium-grained biotite granite with partial porphyritic texture, and it has been repaired for the destroyed parts using concrete in the 1910s. The surface of the pagoda was found to be contaminated by efflorescence at present. As a result of the study, the efflorescence is more concentrated within the areas of water pathway and the northern faces, and in the time of winter season. The efflorescent pollutants were mainly composed of carbonates. Through the extraction experiment, inorganic components of the efflorescence were quantitatively analyzed and discussed for an application with regard to the surface cleaning. The cleaning solvent with pH 6.2 is more effective than pH 5.0 to remove the efflorescent pollutants in general, however, the pH 5.0 solvent showed better results only for anions. Cleaning using chemical agents should be conducted only for small spots with sufficient water washing. And the cleaning effectiveness shows the maximum with the duration of 1 h in which soluble elements dissolve in the solvent the most.

Anorogenic Gross Spitzkoppe granite stock in central western Namibia: Part I. Petrology and geochemistry

The Gross Spitzkoppe is a small (~30 km 2 ) anorogenic granite stock that was emplaced into the Damara Orogenic Belt of central western Namibia in response to mantle plume activity and early Cretaceous rifting of western Gondwanaland. The epizonal Gross Spitzkoppe stock (GSS), penecontemporaneous mafic and felsic dikes in the country rocks, and synplutonic mafic dikes and mafic magmatic inclusions within the GSS indicate bimodal magmatism. The GSS consists of three zonally arranged granitic units: medium-grained biotite granite at the margins, coarse-grained biotite granite, and porphyritic granite at the center of the stock. Late-stage silicic dikes and pegmatites cut the granites of the stock. All the granites are mildly peraluminous, topaz-bearing, high-silica monzogranites that contain extremely Fe-rich biotite (siderophyllite-annite) as the only primary mafic silicate. Common accessory minerals include: topaz, fluorite, magnetite, zircon, monazite, thorite, ilmenite, columbite, and niobian rutile. Miarolitic cavities and pegmatite pockets within the stock suggest that fluid saturation was attained. Rectilinear structures of biotite-rich schlieren along the marginal parts of the stock suggest that magma flow was parallel to the walls of the chamber, whereas turbulent or plume-like flows are indicated by curved, circular, and ladder-dike schlieren. Geochemical variation among the granites can be attributed to fractional crystallization of major and accessory minerals and by accumulation of halogen complexes with rare-earth and high-field-strength elements. The negative, partially irregular, correlation between whole-rock contents of F and Cl suggests that Cl was partially lost to a vapor phase during magmatic degassing. The granites of the Gross Spitzkoppe show clear A-type and within-plate granite characteristics, corresponding to the actual tectonic setting. The granites are interpreted to have formed by partial crustal remelting related to mafic underplating in a continental rift environment

Petrography and geochemistry of the Singo granite, Uganda, and implications for its origin

The Singo granite in western central Uganda intrudes metasedimentary rocks that have experienced low-grade regional and contact metamorphism. Rocks of the main body are pink and coarse-grained with a porphyritic texture. Marginal gray medium-grained biotite granite (BG) and several other varieties with intermediate composition occur with limited extent. The Singo granite is generally massive, contains mainly plagioclase, K-feldspar, quartz, biotite, muscovite and opaques. The BG has higher Al 2O 3, MgO, CaO, Fe 2O 3, TiO 2, Ba, Zr, and V, but lower SiO 2, Th, U, and rare earth elements (REE) and alkali totals than the pink porphyritic granite (PPG). Spider diagrams (chondrite-normalized) show negative Eu, Sr, and Nb anomalies, and unfractionated heavy-REE (HREE). The Eu and Sr anomalies and unfractionated HREE suggest the presence of plagioclase and absence of garnet in the source, whereas the Nb anomaly implies a crustal component. Singo granite has both S- and I-type characteristics, and was emplaced in a syn- to post-collision tectonic setting in several magma pulses within relatively short time intervals. The pluton, in general, shows zonation in texture, mineralogy, and geochemistry from the margin to the center. The BG is relatively old and less felsic, whereas the PPG represents a younger and more felsic part of the pluton. There is continuity between the BG and the PPG through the intermediate granite, suggesting a common origin. Field, petrographic, and geochemical characteristics support a magmatic origin from a water-undersaturated, heterogeneous crustal source rock under low pressure conditions. Petrographic and chemical variations were mainly the result of fractional crystallization and source heterogeneity. Late- and post-magmatic stages were dominated by strong hydrothermal activity.

P-T path fluid evolution in the Gross Spitzkoppe granite stock, Namibia

FRINDT, STEPHEN and POUTIAINEN, MATTI 2002. P-T path fluid evolution in the Gross Spitzkoppe granite stock, Namibia. Bulletin of the Geological Society of Finland 74, Parts 1–2, 103–114. The Gross Spitzkoppe granite stock (GSS) is a zoned 30 km2 epizonal intrusion that consists of three main granites: 1) medium-grained biotite granite (marginal), 2) a coarse-grained biotite granite, and 3) a central, porphyritic granite. The stock contains pegmatites as banded marginal stockscheiders and isolated pockets composed of large alkali feldspar and quartz, dark mica, interstitial fluorite, and euhedral topaz and beryl crystals. In the porphyritic granite there are local wolframite-bearing greisens and hydrothermal fluorite and topaz-rich veins. Fluid inclusion studies were conducted on: 1) topaz and quartz crystals from the marginal stockscheider; 2) quartz, topaz, fluorite and beryl crystals from isolated pegmatites; 3) topaz from a miarolitic pegmatite; 4) beryl and quartz veins from greisenized porphyritic granite; and 5) fluorite from a late fluorite vein in the coarse-grained biotite granite. Preliminary data indicate the presence of three compositionally distinct primary and pseudosecondary inclusion types that are of late magmatic-hydrothermal origin. Type 1. Low salinity (0–10 eq. wt% NaCl) H2O (± CO2) inclusions that homogenize to the liquid phase in the temperature range of 300 to 550 C. These inclusions are from quartz, topaz and beryl. Inclusions in fluorite from the fluorite vein homogenize at ~170 C and have a salinity of ca. 1–2 eq. wt% NaCl. Type 2. Saline (25–30 eq. wt% NaCl) halite-bearing H2O (± CO2) inclusions that homogenize to the liquid phase in the temperature range of 300 to 400 C. These inclusions are from quartz. Type 3. Low salinity (0–3 eq. wt% NaCl) H2O-CO2 inclusions that homogenize to vapor phase in the temperature range of 330 to 550 C. These inclusions are from quartz and topaz. Hydrothermal fluids from greisen minerals are represented by type 1 and type 2 H2O inclusions. They are predominantly of low salinity (~8 eq. wt% NaCl) and homogenize to the liquid phase in the temperature range of 300 to 500 C. Isochores for contemporaneous type 2 and type 3 inclusions with homogenization temperature range of 330 to 400 C indicate a maximum trapping pressure of about 900 bar for the marginal stockscheider.

Petrogenetic and mineralization processes in Paleo- to Mesoproterozoic rapakivi granites: examples from Pitinga and Goiás, Brazil

The 1.8 Ga Pitinga granites—Água Boa and Madeira massifs—in Amazonas (northern Brazil) are within-plate, shallow-level rapakivi granites associated with an extensional fracture system. They comprise an early facies of pyterlitic to wiborgitic rapakivi granite, a fine- to medium-grained biotite granite, as well as topaz granite (Água Boa massif) and albite granite (Madeira massif). The granites are usually metaluminous to peraluminous, the albite granite, however, is peralkaline. They are enriched in SiO 2, K 2O, Na 2O, F, Rb, Th, Nb, Y, Zr and the rare-earth element (REE) and impoverished in MgO, TiO 2, P 2O 5 and Sr, as the majority of Sn-mineralized granites. Sn contents range from ∼1 ppm in the rapakivi facies to ∼3400 ppm in the albite granite. ε Nd (at 1.8 Ga) values vary from −2.2 to +0.4 and Nd model ages lie between 2.4 and 2.1 Ga. Mineralization in the Madeira massif includes disseminated magmatic cryolite, zircon, cassiterite, pyrochlore, columbite-tantalite and xenotime and massive cryolite bodies in the F-rich peralkaline albite granite. In the Água Boa massif, Sn mineralization is associated with greisens and episyenite. The 1.77 Ga (g1) and 1.58–1.57 Ga (g2) rapakivi granites of Goiás (central Brazil) are coeval with the Araı́ rift basin. Granites of the g1 suite are metaluminous and alkaline, while the g2 suite is metaluminous to peraluminous. Both are enriched in F, Sn, Rb, Y, Th, Nb, Ga and the REE. Primary micas range from Fe-rich biotite to zinnwaldite. The micas of the more evolved granites and the metasomatic micas are strongly enriched in F, with F/Li between 2 and 10. The initial ε Nd values of both suites show a considerable range (∼−14 to 0) and indicate substantial compositional variation in source. Sn deposits in Goiás are hosted mainly by greisens. Indium is concentrated in quartz–topaz rock and albitized g2d granite of the Mangabeira massif and is always related to a cassiterite-sulfide association. This quartz–topaz rock is of metasomatic origin, probably generated by a hydrothermal fluid derived from the topaz–albite granite. Mineralization in the studied deposits was essentially associated with F enrichment. In the peralkaline Madeira albite granite, extremely high F contents favored disseminated mineralization, while in the Goiás Tin Province (GTP) and Água Boa massif greisenization was related to early fluid saturation. The GTP and Pitinga granites display tectonic, petrogenetic, geochemical, isotopic and metallogenic similarities that can be applied in search of Sn and rare-metal deposits.

Geology and Geochemistry of Granites Around Jaswantpura, Jalore District, Southwestern Rajasthan, India

The Neoproterozoic granite plutons around Jaswantpura, western India, form a large complex of granitic rocks and, at least, four distinct granite types, based on cross-cutting relationships, have been found: coarse- to medium-grained biotite granites; medium- to fine-grained two- mica granites; coarse- to medium-grained porphyritic hornblende granites and fine-grained biotite granites with accessory hornblende. Younger acidic and basic dykes cut these granites. The Jaswantpura granites show a narrow range of variation in terms of their chemistry. The hornblende granites are hypersolvus with mild peralkaline character as reflected by the enrichment in incompatible trace elements including Zr, Nb, La and REE but are characterized by relatively low Sr and Al 2O 3. The biotite granites are subsolvus, mildly to moderately peraluminous and are characterized by relatively high SiO 2, Al 2O 3, Rb and low Zr, Nb and REE contents compared to the hornblende granites. The mineralogical and chemical characteristics of the different granite types exposed in the Jaswantpura area point to a continental crust source.