Granitic Composition Research Articles

Enrichment of REE and HFSE during the magmatic-hydrothermal evolution of the Baerzhe alkaline granite, NE China: Implications for rare metal mineralization

The Baerzhe Cretaceous (123.7 ± 0.9 Ma) peralkaline pluton underwent extensive fractional crystallization and extreme enrichment in incompatible elements including rare earth elements (REE) and the high field strength elements (HFSE). It is one of the largest resources of rare metals in China, containing approximately 100 million tons of ore with an average grade of 1.84 wt% ZrO2, 1.00 wt% REE2O3 (34% heavy rare-earth oxides), and 0.26 wt% Nb2O5. Zr, REE and Nb are mainly hosted by hydrothermal minerals, such as zircon, hingganite-(Y), monazite-(Ce), polycrase, pyrochlore, fergusonite and columbite. An integrated investigation of field geology, mineral textures and compositions of minerals and host granites was carried out to examine the evolution of the Baerzhe pluton and the roles of magmatic and hydrothermal processes in concentrating REE and HFSE. Most minerals in the intensively altered subsolvus granite show secondary textures or replaced pseudomorphs, such as the replacement of arfvedsonite by aegirine, zircon dissolution and reprecipitation, and the replacement of monazite-(Ce) and polycrase-(Y) by hingganite-(Y). Compositions of the key economic minerals and changes with respect to these alteration stages reveal evidence that hydrothermal alteration played a role in the mineralization of the pluton. In-situ analyses and element mappings suggest that large volume of metals were remobilized and redistributed during hydrothermal replacement, such as the replacing of monazite-(Ce) and polycrase by hingganite-(Y). It is suggested that subsolidus re-equilibration and hydrothermal alteration, in addition to magmatic fractionation, is critical for further concentrating REE and HSFE in peralkaline granitic systems.

Zircon U–Pb Geochronology, Whole-Rock Geochemistry and Petrogenesis of Biotite Granites in the Gaudeanmus Area, Namibia

The Gaudeanmus area is located at the southern Central Zone of the Damara orogenic belt in south-western Africa. In this paper, we investigate the whole rock major and trace element compositions and Sr–Nd–Pb isotopic compositions of the biotite granite, and determine the age of the samples utilising U–Pb zircon dating methods. Our results provide an LA–collector inductively plasma mass spectrometer (ICP–MS) zircon U–Pb age for the biotite granite of 540 ± 4 Ma (i.e., earliest Cambrian). The biotite granites show the characteristics of metaluminous compositions belonging to high-K calc–alkaline to shoshonite series. The granites contain high alkali and rare earth elements (REE), are enriched in large-ion lithophile elements (Rb, K, Pb), and depleted in high field-strength elements (Nb, Ta, Ti). The REE patterns are characterised by enrichment of LREEs relative to HREEs and medium negative Eu anomalies in the chondrite-normalised REE diagram. These rocks have high initial 87Sr/86Sr ratios (0.71400–0.71768); low εNd(t) value (−12.0 to −7.1); Sm–Nd isotope crust model ages ranging from 1711 to 2235 Ma; and large variations in 206Pb/204Pb (18.0851–19.2757), 207Pb/204Pb (15.6258–15.7269), and 208Pb/204Pb ratios (38.7437–40.5607). Such geochemical signatures indicate that the biotite granite rocks derive mainly from partial melting of ancient crustal rocks resembling the local basement meta-sedimentary rocks. However, minor mantle-derived materials may have also been involved in the formation of these rocks. Combining with regional tectonic evolution, we consider that the biotite granite intrusions in the Gaudeanmus area formed in a transitional tectonic regime that went from compressional to extensional tectonics.

Research on the Permeability Characteristics of Granite with Different Weathering Degrees before and after the Influence of Mining Method Construction

The influence of mining method tunnel construction on the groundwater environment is a very important and complex engineering environment problem, and the strong differential weathering of water-rich granite strata increases the difficulty of this problem. In this paper, the mineral composition and microstructure characteristics of granite with different weathering degrees before and after the influence of mining method were studied by in-situ and indoor seepage tests and theoretical calculation, and the impact of mining method tunneling on granite permeability was also analyzed. Calculation results revealed that the permeability coefficient of surrounding rock at 1.1 m away from excavation face increased 41.6 times as much as the original. The permeability coefficient of moderately and strongly weathered granite increased by 6.12 and 3.33 times, respectively and the permeability also increased. The variation of the permeability coefficient of fully weathered granite was the smallest, increasing by 1.67 times, which is due to mechanical excavation of a fully weathered layer on-site, and the disturbance was far less than that caused by blasting. The scale of the excavation damaged zone (EDZ) induced by mining method was determined by wave velocity test, which provides a basis for subsequent seepage field calculation and research.

Geochronology, geochemistry and Hf isotopic composition of Late Cretaceous Laojunshan granites in the western Cathaysia block of South China and their metallogenic and tectonic implications

Sn-, In- and W-rich granites are identified in Laojunshan area in the western Cathaysia block, South China, including coarse-grained two-mica monzogranite (CMG) and fine-grained two-mica monzogranite (FMG). Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U–Pb dating of CMG and FMG are from 85.6 ± 0.8 Ma to 90.37 ± 0.7 Ma and 89.9 ± 1.4 Ma, respectively. All samples have relatively high total alkalis contents (5.74 wt% to 9.73 wt%) and Al saturation indices (0.95 to 1.79), indicating that most of granites belong to the strongly peraluminous granites. The granites are enriched in P, Rb, Cs, Sn, Li, Be, and U, and are depleted in Ti, Mg, Co, Ni, Sr, Ba, Zr, and Hf. The fractional crystallization of plagioclase and K-feldspar was the principal process of magmatic differentiation that controlled Rb, Sr, Ba and Eu concentrations. While rare earth elements were fractionated by accessory minerals such as apatite, monazite or ilmenite. These geochemical features suggest that most of rocks are highly fractionated S-type granites. The εHf(t) values of the zircon samples from CMG and FMG range from −12.88 to −1.19, with the two-stage Hf model ages ranging from 1.2 Ga to 1.9 Ga. The geochemical and isotopic data show that the Laojunshan granites are derived from a crystalline basement that has metamorphosed pelitic rocks from the Mes-paleoproterozoic continental crust. The upwelling of the asthenosphere caused by a strong lithospheric extension led to the partial melting of the metamorphosed pelitic rocks to form widespread Late Cretaceous S-type granites in the Laojunshan area. Lithospheric extension and Cretaceous magma in SE Yunnan are probably related to the Palaeo-tethys ocean crustal delamination, which subducted beneath the Indochina block.

Early to late Neoproterozoic subduction-accretion episodes in the Cariris Velhos Belt of the Borborema Province, Brazil: Insights from isotope and whole-rock geochemical data of supracrustal and granitic rocks

The Cariris Velhos Belt is an unique domain of the Borborema Province, Brazil, because it presents magmatic and metamorphic lithotectonic associations spanning all the Neoproterozoic. In this study, we investigate the main sources of its major supracrustal sequence (i.e. São Caetano Complex) as well as genetic aspects of a later intrusive granitic body, the São Pedro Stock. Detrital U-Pb zircon determinations for the supracrustal rocks are characterized by a major peak in the range of 1.0-0.9 Ga, with maximum deposition age at around 0.86 Ga. Minor components are aged at 1.8-1.6 Ga and 2.5 Ga. The Nd isotopic composition for this unit suggest crustal reworking of Meso-to Paleoproterozoic sources as well as inheritance of juvenile mantle material. Whole-rock geochemical data points out to derivation from magmatic arc-related andesites and rhyolites as well as foreland material, and we interpret this sequence as remnant of the Cariris Velhos (1.0-0.9 Ga) post-orogenic basin. The São Pedro Stock corresponds to a mostly isotropic intrusion of dominantly granitic composition. U-Pb zircon data from a monzogranitic and a tonalitic samples suggest crystallization ages of ca. 615 ± 02 Ma and 596 ± 22 Ma, respectively. Zircon crystals with ages of ca. 981 ± 29 Ma are interpreted as inherited crystals. Sm-Nd isotopic behavior is similar from samples of the São Caetano Complex, whereas overall geochemistry suggests crystallization from high-K calc-alkaline and peraluminous magmas, in addition to trace-element distribution compatible with Cordilleran granites. It is proposed that the São Pedro stock were formed in a modern-style subduction zone in later stages of the Brasiliano-Pan African orogeny (0.6-0.5 Ga). Accordingly, we conclude that systematic subduction-accretion episodes took place in this part of West Gondwana from early to late Neoproterozoic times.

Mineral Composition, Pore Structure, and Mechanical Characteristics of Pyroxene Granite Exposed to Heat Treatments

In deep geoengineering, including geothermal development, deep mining, and nuclear waste geological disposal, high temperature significantly affects the mineral properties of rocks, thereby changing their porous and mechanical characteristics. This paper experimentally studied the changes in mineral composition, pore structure, and mechanical characteristics of pyroxene granite heated to high temperature (from 25 °C to 1200 °C). The results concluded that (1) the high-temperature effect can be roughly identified as three stages: 25–500 °C, 500–800 °C, 800–1200 °C. (2) Below 500 °C, the maximum diffracted intensities of the essential minerals are comparatively stable and the porous and mechanical characteristics of granite samples change slightly, mainly due to mineral dehydration and uncoordinated thermal expansion; additionally, the failure mechanism of granite is brittle. (3) In 500–800 °C, the diffraction angles of the minerals become wider, pyroxene and quartz undergo phase transitions, and the difference in thermal expansion among minerals reaches a peak; the rock porosity increases rapidly by 1.95 times, and the newly created pores caused by high heat treatment are mainly medium ones with radii between 1 μm and 10 μm; the P-wave velocity and the elastic modulus decrease by 62.5% and 34.6%, respectively, and the peak strain increases greatly by 105.7%, indicating the failure mode changes from brittle to quasi-brittle. (4) In 800–1200 °C, illite and quartz react chemically to produce mullite and the crystal state of the minerals deteriorate dramatically; the porous and mechanical parameters of granite samples all change significantly and the P-wave, the uniaxial compressive strength (UCS), and the elastic modulus decrease by 81.30%, 81.20%, and 92.52%, while the rock porosity and the shear-slip strain increase by 4.10 times and 11.37 times, respectively; the failure mechanism of granite samples transforms from quasi-brittle to plastic, which also was confirmed with scanning electron microscopy (SEM).

Albian–Cenomanian A-type granite-related Ag–Pb–Zn veins in the central Yidun Terrane, SW China: constraints from the Xiasai deposit

The Xiasai–Lianlong metallogenic belt in the central Yidun Terrane (China) hosts several Sn–Ag and (Sn–) Ag–Pb–Zn deposits, which are spatially associated with Cretaceous granites. The Xiasai Ag–Pb–Zn deposit (about 0.27 Mt Pb+Zn, 1028 t Ag, and 20,000 t Sn) is the largest deposit in the belt and is related to a monzogranite intrusion. The deposit consists of sulfides in hydrothermal veins, resulting from three successive mineralization stages (I–III). A Rb–Sr isochron of sphalerite samples yielded an age of 99 ± 3 Ma, and zircon U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating of the Xiasai monzogranite gave ages between 102 ± 1 and 101 ± 1 Ma. The Xiasai monzogranite has a weakly peraluminous A-type granite composition, with high SiO2, alkali, and FeOt contents and low CaO, MgO, and TiO2 contents. It is marked by enrichments in Rb, Th, and U, with depletions in Ba, Nb, Sr, P, and Ti relative to the primitive mantle. The REE patterns show a negative slope due to LREE enrichment with negative Eu anomalies (Eu/Eu* = 0.1–0.3). The Xiasai monzogranite, with variable eHf(t) values (− 2.7 to 0.6) and Meso- to Neoproterozoic two-stages Hf model ages (TDM2 = 925–1095 Ma), was probably derived from mixing of melts derived from partial melting of the Paleoproterozoic crustal basement and the Early Cretaceous mantle in an extensional tectonic setting. Hydrothermal fluids are characterized by high temperatures (423–481 °C) and salinities (14.9–19.0 wt% NaCl) for Sn mineralization (stage I), moderate temperatures (285–386 °C) and salinities (3.5–8.0 wt% NaCl) for the Cu–Zn mineralization (substage II-2), and low temperatures (158–242 °C) and salinities (3.4–5.7 wt% NaCl) for the Ag–Pb mineralization (substage II-3). The H–O isotopes indicate that the hydrothermal fluid likely has a magmatic component that mixed over time with infiltrating meteoric water and organic matter during fluid–rock interactions. The δ34S values of sphalerite range from − 9.7 to − 3.1‰ and those from galena from − 10.5 to − 4.9‰. The estimated δ34S value of the hydrothermal fluid is − 8.5‰, using the sulfur isotopic fractionation of sphalerite–galena pairs that are interpreted to be in equilibrium. Sulfides from substages II-2 and II-3 have relatively homogeneous Pb isotopic compositions, which are similar with those of K-feldspars from the Xiasai monzogranite. Geochronological and isotope data support a magmatic–hydrothermal origin for the Xiasai Ag–Pb–Zn deposit.

Partial resetting of U–Pb ages during experimental fluid-induced re-equilibration of xenotime

Experimentally metasomatized xenotime was investigated in terms of preservation of U–Pb ages during fluid-induced alterations at 250, 450, 550 and 650 °C. Starting materials for experiments included xenotime (38.4 ± 0.6 Ma), albite, K-feldspar, biotite, muscovite, garnet, SiO2, CaF2, Na2Si2O5 and H2O that roughly replicated metapelitic to granitic composition with high Na, Ca, Si and F activities in the fluid. Despite partial replacement of xenotime by secondary phases including (Y,REE)-rich fluorapatite to Y-rich fluorcalciobritholite in all runs, and an unnamed (Y,HREE)-rich silicate in 250 °C experiment, only two experiments at 550 °C, 800 MPa and 650 °C, 600 MPa resulted in development of faint to moderate patchy zoning in the xenotime. Experimental results indicate higher chemical-stability of xenotime at lower P-T conditions compared to those corresponding to amphibolite facies conditions. The xenotime domains metasomatized via coupled dissolution-reprecipitation reactions are characterized by depletion of U and Pb and younger 206Pb/238U dates of ca. 15–34 Ma, demonstrating preferential removal of Pb and thus the partial resetting of the age record. The U–Pb data for the first time experimentally confirm that xenotime may be affected by re-equilibration induced by fluid or melt with high Na, Ca and F activities via coupled dissolution-reprecipitation reactions that result in removal of radiogenic Pb under temperature conditions of 550–650 °C. These findings have important implications for U–Pb geochronology of igneous (particularly in pegmatites) and metamorphic processes in terms of preservation of U–Pb ages of xenotime that was affected by multiple thermal events in the presence of alkali-rich fluid and/or melt.

Influence of heterogeneity on thermo-mechanical behaviour of rocks

A new methodology combining Weibull functions and the real mineral composition of granite is proposed, which overcomes the shortcomings of using existing methods for the heterogeneity characterization of rocks at the crystal-size or grain-size level. The proposed Weibull-mineral based model can simulate thermal cracking of rocks in a more realistic way compared with previous methods such as the mineral-based model. The study also reveals the importance of thermo-mechanical property distributions at the crystal-size level for the overall thermo-mechanical behaviours at larger scale. Supported by lab tests, the new model can reproduce the mechanical behaviour of heterogeneous materials. The thermal cracking of granite at elevated temperatures is also possible to be predicted.

THERMOCHRONOLOGY AND MATHEMATICAL MODELING OF THE FORMATION DYNAMICS OF RARE‐METAL‐GRANITE DEPOSITS OF THE ALTAI COLLISION SYSTEM

The article presents an event correlation of the Permian‐Triassic granites of the Altai collision system, which are associated with industrial ore deposits and occurrences (Mo‐W, Sn‐W, Li‐Ta‐Be). The multi‐system and multi‐mineral isotope datings of igneous rocks and ore bodies (U/Pb, Re/Os, Rb/Sr, Ar/Ar‐methods) suggest the postcollisional (intraplate) formation of ore‐magmatic systems (OMS), the duration of which depended on the crustmantle interaction and the rates of tectonic exposure of geoblocks to the upper crustal levels.Two cases of the OMS thermal history are described: (1) Kalguty Mo‐W deposit associated with rare‐metal granite‐leucogranites and ongonite‐ elvan dykes, and (2) Novo‐Akhmirov Li‐Ta deposit represented by topaz‐zinnwaldite granites and the contemporary lamprophyre and ongonit‐elvan dykes. For these geological objects, numerical modeling was carried out. The proposed models show thermal cooling of the deep magmatic chambers of granite composition, resulting in the residual foci of rare‐metal‐granite melts, which are known as the petrological indicators of industrial ore deposits (Mo‐W, Sn‐W, Li‐Ta‐Be). According to the simulation results concerning the framework of a closed magmatic system with a complex multistage development history, the magmatic chamber has a lower underlying observable massif and a reservoir associated with it. A long‐term magmatic differentiation of the parental melt (a source of rare‐metal‐granite melts and ore hydrothermal fluids) takes place in this reservoir.

Geology and mineralogy of the Novo-Akhmirovskoe deposit of lithium topaz-zinnwaldite granites (East Kazakhstan)

Research subject. The Novo-Akhmirovskoe lithium-bearing deposit in the East Kazakhstan region, which is represented by an intrusive layer of topaz-zinnwaldite granites, is located within of the Kalba-Narym-Koktogai lithium-tantalum raremetal-granite belt. Being part of the Altai collision system, this belt is considered unique in terms of its length (more than 1000 km). Ores in the Novo-Akhmirovskoe deposit are represented by massive to low porphyry leucocratic granites composed of quartz (30–40%), albite (25–40%), microcline (15–35%), lithium mica varying in composition from zinnwal dite to lepidolite (up to 10%) and topaz (up to 5%). According preliminary estimates, the Novo-Akhmirov deposit is factually a poor lithium deposit with the Li2O content of 0.2–0.4 wt % and the estimated Li2O reserves of 110 thousand tones. Despite the favourable infrastructure and close proximity of this stock to Ust-Kamenogorsk mining and chemical-metallurgical enterprises, its ore-generating potential has not been sufficiently studied.Materials and Methods. In this research, we obtained new data on the geological structure, age, mineral composition and formation conditions of topaz-zinnwaldite granites in the Novo-Akhmirovskoe deposit. In addition, a comparative analysis of these ores with the topaz-biotite granites of the Black Sopka massif (0.6–0.7 wt % Li2O in protolitionite) and spodumene granite porphyries of the Alakha stock (Li2O = 0.9–1.1 wt %) was conducted. Results and Discussion. It is concluded that the development of this unique nonpegmatite lithium-bearing deposit requires deep exploratory drilling, mineralogical and technological research of core samples and reconsideration of economic efficiency parameters.

Poly-Orogenic Melting of Metasedimentary Crust From a Granite Geochemistry and Inherited Zircon Perspective (Southern Calabria-Peloritani Orogen, Italy)

Inherited zircon ages and geochemical features of late Cadomian and late Variscan granitoids from the north-eastern Peloritani Mountains (NE Sicily) and the western Aspromonte Massif (SW Calabria) shed new light on the sources and processes involved in poly-orogenic granitoid magmatism. The two groups of strongly peraluminous granitoids have similarities in trace element abundance patterns and Sr and Nd isotopic compositions consistent with both being derived from crustal sources, possibly with a minor contribution from mantle-related components. Comparison of the granite compositions with those of experimental melts derived from various metaigneous and metasedimentary sources indicates that both groups of granitoids originated exclusively from different degrees of melting of similar greywacke-dominated turbidite. Abundant inherited zircon cores from representative samples of metamorphosed late Cadomian (545 ± 5 Ma) granite and late Variscan (300 ± 4 Ma) leucogranodiorite have the same range of U-Pb ages, from Early Paleoproterozoic to latest Neoproterozoic, with main age clusters at ~ 0.55 and ~ 0.63 Ga, and minor age clusters at ~ 0.95 and ~ 2.5 Ga. The pattern of detrital zircon ages from a paragneiss, host rock to the late Cadomian granite, is the same, indicating, in conjunction with the geochemistry, that both granites originated by partial melting of deeper crustal equivalents of those paragneisses. The same crustal sequence melted during successive orogenies under different thermal regimes and in different post-collisional tectonic settings, giving rise to granitoid associations with different ages and geochemical features largely reflecting the melting conditions. On the other hand, the zircon inheritance patterns and specific chemical features of S-type granitoids reflect the nature of their crustal magma sources, independently from the effects of the thermal regime or tectonic setting at the time of magmatism.

250 Ma metagranitoid from Drangovo Village: a new discovery of Permo-Triassic magmatism in the Eastern Rhodopes, Bulgaria

This short communication reports a 251.4 ± 6.8 Ma age of a Permo-Triassic metagranitoid (augen gneiss) in the Bulgarian part of the Eastern Rhodopes. The rock is intruded by the early Eocene Drangovo pluton and represents part of the upper metamorphic unit of the Kessebir dome. The analyzed sample has slightly peraluminous (ASI = 1.11) granitic composition with SiO2 = 70.6 wt.%. It is enriched in LILE and LREE and depleted in HREE, with a deep Eu (Eu/Eu* = 0.49) anomaly consistent with garnet and plagioclase fractionation. The large number of xenocrystic zircons, along with the low (780 °C) crystallization temperature and petrochemical data, suggests significant assimilation of basement rocks by the granitic magma. The rock has a subduction-related signature.

РАДИОЭКОЛОГИЧЕСКАЯ ОПАСНОСТЬ ДЛЯ НАСЕЛЕНИЯ В РАЙОНАХ РАСПРОСТРАНЕНИЯ ВЫСОКОРАДИОАКТИВНЫХ ГРАНИТОВ

Актуальность исследования обусловлена необходимостью объяснения высокой заболеваемости населения в районах распространения радиоактивных пород и почв. Исследование выполнено в рамках нового научного направления – медицинской геологии. Целью работы является изучение масштабов радоновыделений в районах выхода на поверхность высокорадиоактивных гранитов, оценка их радиоэкологической опасности и медико-биологических последствий. Объекты: геохимический и минералогический состав образцов гранитов, кор выветривания и почв, масштабы радоновыделений и частота заболеваемости в различных областях мира (г. Чжухай в китайской провинции Гуандун; г. Эшасьер во французском регионе Овернь) и Сибирского региона (г. Белокуриха Алтайского края; пгт. Колывань Новосибирской области). Методы. В рамках исследования применялся широкий комплекс методов, включающий инструментальный нейтронно-активационный, рентгенофазовый анализы, гамма-спектрометрию, осколочную радиографию, электронную микроскопию, экспрессное измерение объёмной активности радона, расчет потока плотности радона, эквивалентной эффективной дозы и частоты вновь выявленных заболеваний (incidence). Результаты. Проведено обобщение данных по воздействию ионизирующего излучения на организм человека. По результатам геохимических, минералогических, радиоэкологических и медико- статистических исследований выявлено, что в процессах коро- и почвообразования радионуклиды высвобождаются из структурных решеток акцессорных минералов и сорбируются на глинистых минералах. Данный процесс способствует повышению радоновыделений и радиационного фона. Дано объяснение возможных связей повышенных концентраций радионуклидов в подстилающих породах, почвах и высокой активности газа радона с показателями заболеваемости населения. При сопоставлении первичных показателей онкозаболеваемости у всех групп населения с общероссийскими и мировыми показателями отмечаются превышения уровня во всех исследуемых районах. К территориям «риска» по частоте заболеваемости раком легкого можно отнести Белокуриху в Алтайском крае и Колывань в Новосибирской области; раком носоглотки – провинцию Гуандун; раком кроветворной ткани – Колывань; анемиями – Гуандун; по врожденным порокам развития – Гуандун и Колывань.

The tectonic domains of southern and western Madagascar

Southern and western Madagascar is comprised of five tectonic provinces that, from northeast to southwest, are defined by the: (i) Ikalamavony, (ii) Anosyen, (iii) Androyen, (iv) Graphite and (v) Vohibory Domains. The Ikalamavony, Graphite and Vohibory Domains all have intermediate and felsic igneous protoliths of tonalite-trondhjemite-granodiorite-granite composition, with positive εNd, and low Sr and Pb isotopic ratios. All three domains are interpreted to be the products of intra-oceanic island arc magmatism. The protoliths of the Ikalamavony and Graphite Domains formed repectively between c. 1080–980 Ma and 1000–920 Ma, whereas those of the Vohibory Domain are younger and date to between c. 670–630 Ma. Different post-formation geologic histories tie the Vohibory-Graphite and Ikalamavony Domains to opposite sides of the pre-Gondwana Mozambique Ocean.By contrast, the Androyen and Anosyen Domains record long crustal histories. Intermediate to felsic igneous protoliths in the Androyen Domain are of Palaeoproterozoic age (c. 2200–1800 Ma), of tonalite-trondhjemite-granodiorite-granite composition, and show negative εNd, moderate to high 87Sr/86Sr and variable Pb isotopic compositions. The felsic igneous protoliths of the Anosyen Domain are of granitic composition and, when compared to felsic gneisses of the Androyen Domain, show consistently lower Sr/Y and markedly higher Sr and Pb isotope ratios. Like the Vohibory and Graphite Domains, the Androyen Domain can be linked to the western side of the Mozambique Ocean, while the Anosyen Domain shares magmatic and detrital zircon commonalities with the Ikalamavony Domain. It is consequently linked to the opposing eastern side of this ocean. The first common event observed in all domains dates to c. 580–520 Ma and marks the closure of the Mozambique Ocean. The trace of this suture lies along the boundary between the Androyen and Anosyen Domains and is defined by the Beraketa high-strain zone.

Multi-attribute optimization of end milling epoxy granite composites using TOPSIS

ABSTRACTEpoxy granite composites are identified and recognized as better materials for machine tool applications due to inherent damping properties. However, end milling of these composites has not been explored much. Milling of epoxy granite composites presents a number of problems, namely, cutting forces and surface roughness appear during machining. This research work focuses on end milling of epoxy granite composite specimens using high-speed steel end mill cutter by varying the cutting conditions such as spindle speed and feed with a uniform depth of cut and selection of optimal machining parameters. The experimental runs of 27 different trials were carried out and three different attributes such as thrust force, tangential force, and surface roughness were analyzed. This research work presents a sequential procedure for machining parameters selection. Selection of optimal machining parameters is done on the basis of Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method.

Rare earth element distribution in main lithologies of the Atibaia and Jaguari rivers’ subbasins (Southeast Brazil)

In this study, we investigated the mineral and geochemical compositions of the main lithotypes constituting the Atibaia and Jaguari rivers’ subbasins (Southeast Brazil), with the aims of characterizing the distribution of rare earth elements (REE) in that diversified geological framework and identifying their source bearing minerals to the environment at the catchment scale. Samples from six geological units comprising granitoids of monzogabbroic to granitic compositions, orthogneisses (dioritic to granitic compositions), paragneisses and local occurrences of quartzites were studied. In estimates of mineral proportions in each analyzed lithotype, we identified plagioclase, K-feldspar, and Ca-amphibole followed by minor amounts of apatite, titanite, allanite and rarely monazite as the potential light REE hosting phases, while the dominant heavy REE carriers were Na-amphibole, garnet, and zircon. The ∑REE contents in the rocks ranged between 59 and 791 mg kg−1, with a significant surplus of light over heavy REE [(La/Yb)CN = 11–197]. The whole-rock negative Eu anomalies of most samples result from the combined Eu budget of the individual minerals. Metamorphic lithotypes dominate at the Atibaia subbasin, whereas the main lithology of the Jaguari subbasin are granitoids. Comparatively, the first rocks contain slightly more ∑REE and are more enriched in light REE. These features and the relative weathering susceptibility of the REE hosting minerals constitute the initial step to explain the behavior of these elements in the environment.

Evaluation of the contributions of possible sources to the leucosome of the diatexite of Socorro-Guaxupé Nappe, in the Alfenas Region, MG, Brazil

The Socorro-Guaxupé Nappe crops out in southern Minas Gerais and it has an intermediate unit called Metaxite Unit, dominated by diatexites at its base, with large volumes of leucosome and schollen of stromatic garnet-biotite metatexite. Leucosome within the schollen crystallized via fractional crystallization and is dominated by plagioclase and quartz, although K-feldspar might be present. However, the larger volume of the coarse-grained leucosome, that dominates the unit, has granite, sometimes close to minimum granite composition. So, its formation, after partial melting, involved, segregation, fractional crystallization and accumulation. Proportions of leucosome / residue and leucosome / residue / peritectic phases indicate that the leucosome crystallized from more melt than a pelite source could produce, and probably diatexite worked as a pre-magmatic chamber and stocked melt produced from the granulites sitting at its bottom. Large proportion of biotite crystallized in the residue was formed due to equalization of water chemical potential between residue and leucosome.

Geochemical signatures and weathering rates in soils derived from different granites in contrasting climatic locations

We studied the mineralogical properties and chemical composition of different granites using energy dispersive X-ray spectroscopy coupled with scanning electron microscopy to understand the relationship between granite signatures and soil characteristics, including weathering patterns and soil fertility status. The discriminant analysis (DA) was based on soil physical and chemical properties and was used to differentiate soils developed from I- and S-type granites across contrasting climatic conditions in northeast Brazil. The DA identified the highest values of organic carbon, clay and plant nutrients as key variables to recognize soil profiles derived from I-type granites. In contrast, the greater sand contents and Al saturation distinguished soils developed from S-type granites. These results were related to the mineralogical characteristics of each granite type, such as a high percentage of silica-bearing minerals in the S-type granites. The highest concentrations of K, Ca, Mg, and P in I-type granites were found in feldspars, amphiboles, and apatite. These elements account for the majority of nutrients derived in their soil profiles. However, it seems that the harsh conditions of the humid tropical environment equalized the effect of the rocks on weathering rates-the difference in chemical index of alteration is more extreme in the dry region.

Petrology and geochemistry of the Yoro-Yangben Pan-African granitoid intrusion in the archaean Adamawa-Yade crust (Sw-Bafia, Cameroon)

Abstract: South of Bafia (Cameroon), the Pan-African Yoro-Yangben massif is emplaced in the Adamawa-Yade block, an archaean-paleoprotrozoic micro-continent that detached from the Congo craton during the early Neoproterozoic. This emplacement within a micro-continent raises the problematic of its (i) origin either by the melting of a subducted slab and the mantle wedge, or by the melting of the base of a thick crust or both, and (ii) bearing on the evolution of the Pan-African orogeny in Cameroon. Granodiorites, quartz monzonites, quartz diorites and adamellites occur as massive bodies crosscut by dykes of gabbros and granites. The texture varies progressively from granular bands at the core of the massif to foliated texture towards the border. Mineralogical composition is constant in all the rock types (Am+Bt+Pl+Kfs+Qtz+Op+Sph+Zrn+Ap), except the adamellites which are amphibole-free. Chemically, these potassic rocks are either magnesian and metaluminous, or ferroan and peraluminous. Quartz diorites, granodiorites and granites are High-K calc-alkaline whereas quartz monzonites, adamellites and gabbros are shoshonitic. Most incompatible elements (e.g. Nb, Zr) show an erratic variation with increasing silica contents. Granites rare earth elements (REE) patterns are highly fractionated with a positive Eu anomaly (Eu/Eu* = 2.50–2.04) compared to less fractionated REE patterns of adamellites, quartz monzonites, and granodiorites. The negative anomalies in U, Nb, Ta and Ti shown by gabbros, quartz diorites, quartz monzonites and granodiorites spider diagrams as Th, K, Pb, Zr and Hf positive anomalies for the adamellites and granites patterns are consistent with magmas derived from a subduction setting. The low 87Sr/86Sr(600) initial ratio (0.697–0.706) and eNdi values (−0.82706- 1.03707) of the rocks plot in the mantle array. However, a wide variation of the 87Sr/86Sr ratio values with constant eNdi suggests an enrichment in radiogenic 87Sr likely from an old crust displaying high Rb/Sr ratio. The variations of the La/Yb, Y/Nb and Zr/Nb ratios preclude the fractional crystallization process. Moreover, these characteristics, combined with the erratic (Zr, Nb) suggest particular magmatic sources and complex fusion processes to the Yoro-Yangben heterogeneous granitoids. The lower range of Ba/Nb values (130–135) and the occurrence of shoshonitic magmas likely point to the melting of an oceanic slab; while the higher range (225–230) indicates a blend of melts from oceanic slab and the associated sediments. Granite compositions are similar to melting liquids of metagreywackes. La/Sm and Sm/Yb ratios in gabbros, quartz monzonites and quartz diorite indicate an origin by a batch melting of phlogopite-amphibole-garnet lherzolite, whereas granodiorites and adamellites parent magmas may have originated from a batch melting of a metasomatized spinel lherzolite. Whole rock Sm-Nd and Rb-Sr results yield a unique age of 600 Ma, assigned to the collision time between the West-African and the Congo cratons. Thus, the Yoro-Yangben intrusion is part of the numerous Pan-African granitoids in Cameroon, South of Chad and East of Nigeria.