Biotite Content Research Articles

In-situ and experimental investigations of the failure characteristics of surrounding rock through granites with biotite interlayers in a tunnel

Significant differences in the failure characteristics of surrounding rocks caused by complex lithologies and geological conditions have been observed in deep tunnels. In this work, a failure involving rockburst and collapse observed in a deep tunnel excavated by a tunnel boring machine (TBM) was introduced. The in-situ failure characteristics of granite with biotite interlayers with different biotite contents and particle sizes were studied via field investigations and mineral composition analysis. The microseismic activity characteristics and fracture mechanisms at different failure zones were analyzed. The strength, failure, acoustic emission (AE) and brittleness characteristics of these types of granites were studied via true triaxial compression tests. The results showed that the biotite granite with biotite interlayers is prone to rockburst and that high-intensity rockburst may occur with less energy than in the intact biotite granite area. The rock fractures are mainly tensile failures, even in the biotite interlayer area. In contrast, the feldspar biotite schist surrounding rock is prone to collapse regardless of whether it contains biotite interlayers. The number of microseismic events during this collapse is relatively small, but the energy is relatively high compared with that of the rockburst at the biotite granite with biotite interlayers. The true triaxial strength and brittleness of the granite samples gradually decrease with increasing biotite content. The biotite granite exhibits very high AE activity, so it is prone to rockburst. The AE activity of medium-coarse grained monzogranite is relatively low; thus, both rockburst and collapse may occur. The strength, brittleness, and AE activity of feldspar biotite schist are very low, and its failure mode is mainly collapse. This study elucidates the typical failure modes and characteristics of different granites with biotite interlayers and can provide a basis and guidance for targeted failure warning and mitigation in tunnels with similar lithologies and geological conditions.

Change in the qualitative composition of non-metallic mineral raw materials as a result of blasting operations

Purpose. The research purpose is to study the change in the qualitative composition of granite before and after blasting operations to determine its compliance with the criteria of marketable products. Methods. X-ray phase and X-ray structural research methods are used to study changes in the mineral composition of granites before and after blasting operations. To separate magnetic and non-magnetic fractions of the selected granite samples, a three-roller RST magnetic separator is used. X-ray phase research is conducted using a DRON-3 diffractometer. Additionally, an analysis of the unit cell dimensions of the quartz crystal lattice was conducted, and the dislocation density along the corresponding crystallographic planes was studied. Findings. It has been determined that after blasting operations, granite mass is redistributed from coarse fractions of 1-20 mm to small fractions of 0-1 mm with an increase in the latter by 4.2%. It has been found that the biotite content decrea-ses naturally and consistently, and the quartz content increases correspondingly in products in the following series: magnetic separator drum (90%, 2%) → lower roller (72%, 14%) → upper roller (55%, 31%) → non-magnetic product (48%, 34%) before blasting operations. Therefore, despite significant differences in the magnetic favorability of these two mineral phases, they are present in all magnetic separation products (with the exception of quartz in the non-magnetic product): magnetic separator drum → lower roller → upper roller. Originality. It has been established that along the crystallographic directions 101 and 211, the maximum gradient of dislocation density increase in the quartz crystal lattice in granite samples before blasting operations is observed during the transition from the lower roller product to the upper roller product, amounting to 1.55·1010 and 6.63·1010 cm-2, respectively. After blasting operations, in granite samples along the same directions, the maximum gradient of dislocation density increase is observed between the upper roller product and the non-magnetic product, amounting to 3.01·1010 and 4.67·1010cm-2. As a result of the thermodynamic impact of blasting operations, the weighted average dislocation density value along crystallographic planes 101 and 211 in the quartz crystal lattice increases by 47.21 and 25.72%, respectively. Practical implications. Understanding the quality characteristics of marketable products after blasting operations will contribute to optimizing the stages of further processing of non-metallic mineral raw materials (two-, three- or four-stage crushing) and expanding the scope of granite applications. This increases its competitiveness in the building materials market by reducing the costs for additional processing with a reduction in the labor intensity of the process.

A new approach for improving the properties of tailings sand autoclaved aerated concrete - From a mineralogical perspective

This study proposed a new method to improve the performance of tailings sand autoclaved aerated concrete (SAAC). Firstly, high silicon iron tailings from the Anqian area and low silicon molybdenum tailings from the Weinan area were selected, and the mineral composition of these two tailings was analyzed. Then, the single mineral in the two tailings were used instead of siliceous raw materials to prepare mineral autoclaved concrete (MAC). The autoclaved reactivities of these minerals were analyzed through compressive strength, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM), and which minerals were beneficial for the preparation of SAAC were determined. On this basis, magnetic separation and gravity-magnetic separation processes were used to pretreat Anqian iron tailings and Weinan molybdenum tailings, respectively. Finally, the effectiveness of this method was verified by preparing SAAC made with tailings before and after pretreated. The tested results showed that the autoclaved activities of siliceous minerals were in the following order: quartz hornblende, feldspar, chlorite, while the montmorillonite and biotite, and the metal mine (hematite and pyrite) did not have autoclaved reactivities. The main crystalline phase of hydration products in MAC made with single mineral without autoclaved reactivities were C-S-H, Ca(OH)2, CaCO3, and hibschite, and that in MAC made with quartz, hornblende, feldspar, and chlorite were C-S-H, tobermorite, Ca(OH)2, CaCO3, and hibschite (except quartz). After 1.3 T strong magnetic separation treatment, the content of Fe2O3 in iron tailings decreased from 11.11 % to 4.16 %, and the compressive strength of SAAC made with iron tailings with magnetic separation pretreated increased by 11.43 % comparted to that of SAAC made with original iron tailings. After gravity separation and 1.1 T strong magnetic separation pretreated, the content of SiO2 in molybdenum tailings increased from 63.97 % to 84.03 %, and the mineral content of biotite decreased from 40.5 % to 11.2 %. The compressive strength of SAAC made with molybdenum tailings with gravity-magnetic separation pretreated increased by 24.09 % comparted to that of SAAC made with original molybdenum tailings.

Acoustic emission features of granite from different rockburst areas in Sangzhuling Railway Tunnel

In order to investigate the acoustic emission (AE) features of rocks in different (medium and strong) rockburst areas, the Sangzhuling Railway Tunnel granite in China was taken as an example, the mineral composition of rocks in different rockburst areas was analyzed by using XRD (X-ray diffraction) method. The Original rock cores of different rockburst areas were processed into standard rock specimens (diameter 50 mm, height 100 mm) in different directions (transverse, oblique and longitudinal). AE feature parameters (event number, ringing count and energy) of standard rock specimens during indoor uniaxial compression test were obtained by using AE technique. The variation law of AE feature parameters of rocks in different rockburst grade areas was then analyzed. The AE features of failure precursor of rocks in different rockburst areas were therefore discussed. It shows that compared with rocks in medium rockburst area, the content of quartz and feldspar of rocks in strong rockburst area is high, while the content of biotite is low; the rock in the strong rock burst area released more energy during the failure process with about 2–3 times that of the rock in the medium rock burst area; the cumulative ringing curve of rock in medium burst area is a stepped type, while the cumulative ringing curve of rock in strong burst area is the smoothed type; the end of the second and first AE quiet period may be regarded as the failure precursor of rocks in medium and strong rockburst area, respectively. The results presented herein are important for understanding the mechanisms of rockburst.

Influence of Biotite Content on the Mechanical Response of Granite Using a Novel Three-Dimensional Grain-Based Model and Force Chain Analysis.

In this study, a three-dimensional grain-based model based on the discrete element method is utilized to replicate the heterogeneous structure of crystalline granite, and corresponding laboratory tests are conducted to validate the numerical conclusions. A novel model and an analytical method involving a multilevel force chain network are employed to quantitatively investigate the influence of mineral content on the mechanical behavior of granites. First, a set of granite specimens with varying biotite contents is constructed, and then, uniaxial compression tests are conducted. The effects of the mineral content on the mechanical behavior, force chain network characteristics, and fracture resistance of granite specimens are quantitatively analyzed. The results indicate an inverse relationship between the biotite (VB) content and the load-bearing capacity of granite under uniaxial compression conditions. As VB increases, the number of contacts within the biotite structure increases, as does the force chain distribution density within the biotite structure, while the force chain distribution density in other intragranular structures correspondingly decreases. The average values and sum values of all of the force chains in the whole specimen decrease with increasing VB. Among the various structures, intragranular structures exhibit the highest fracture resistance, whereas intergranular structures exhibit lower resistance.

Red-green-bleached redox interfaces in the proximal Permian Cutler red beds: implications for regional fluid alteration

Siliciclastic strata of the Colorado Plateau attract attention for their striking red, green, bleached, and variegated colors that potentially record both early depositional and later diagenetic events. We investigated the proximal-most strata of the Paradox Basin, from their onlap contact with the Precambrian basement of the Uncompahgre Plateau to the younger Cutler strata exposed within 10 km of the Uncompahgre Plateau to attempt to understand the significance of the striking colors that occur here. These strata preserve a complex geology associated with buried paleorelief and sediment-related permeability variations at a major basin-uplift interface. Strata exposed within ∼1.5 km of the onlap contact exhibit a pervasive drab color in contrast to the generally red colors that predominate farther from this front. In-between, strata commonly host variegated red/green/bleached intercalations. Thin-section petrography, SEM, XRD, Raman spectroscopy, Mössbauer spectroscopy, and whole-rock geochemistry of samples representing different color variations from demonstrate that water–rock interactions charged the rocks with Fe(II) that persists primarily in the phyllosilicate fraction. Color variations reflect grain-size differences that allowed the reduction of fluids from regional fault and basement/fill contacts to permeate coarser-grained Cutler sediments. Hematite and chlorite occur in both red and green sediments but are absent in the bleached sediments. Pervasive hematite in both red and green layers suggests that sediments were hematite-rich before later alteration. Chlorite and smectite are elevated in green samples and inversely correlated with biotite content. Green coloration is generally associated with 1) coarser grain sizes, 2) spatial association with basement contacts, 3) elevated smectite and/or chlorite, 4) less total Fe but greater Fe(II)/Fe(III) primarily in the phyllosilicate fraction, and 5) uranium enrichment. The bleached coloration reflects the removal of pigmentary Fe(III) oxide, while the green coloration is due to the removal of pigmentary hematite and the abundance of Fe(II)-bearing phyllosilicates. Abundant mixed-layer and swelling clays such as smectite, illite/smectite, and chlorite/smectite (including tosudite) dominate the mineralogy of the clay fraction. These results are consistent with other studies demonstrating fault-associated fluid alteration in the Paradox Basin region. However, the pervasive greening was not observed in many of these studies and appears to reflect the unique aspects of the paleovalley system and the importance of biotite alteration to Fe(II)-bearing phyllosilicates.

Metamorphic P–T paths of Archean granulite facies metasedimentary lithologies from the eastern Beartooth Mountains of the northern Wyoming Province, Montana, USA: constraints from quartz-in-garnet (QuiG) Raman elastic barometry, geothermobarometry, and thermodynamic modeling

Abstract. Metamorphic pressure and temperature (P–T) paths in late-Archean high-grade rocks of the eastern Beartooth Mountains of Montana (USA), a portion of the Wyoming Province, are established by a combination of imaging, analytical, and modeling approaches. Garnet inclusion mechanical and chemical thermobarometry, applied to several granulite-facies migmatites and an iron formation, is particularly useful in constraining the prograde P–T conditions. Quartz-in-garnet (QuiG) elastic Raman barometry was used on quartz inclusions in garnet for all samples studied. For a smaller subset of four representative samples, QuiG constraints were used in conjunction with Ti-in-quartz (TitaniQ) and Ti-in-biotite (TiB) thermometry to establish unique prograde inclusion entrapment P–T conditions. Ti measurements of garnet hosts and cathodoluminescence (CL) imagery of inclusion and matrix quartz grains were employed to check for Ti loss/diffusion. Lastly, inclusion studies were supplemented with thermodynamic modeling and matrix chemical thermobarometry to examine garnet nucleation temperatures and peak metamorphic conditions. Disagreement between the volume strain and elastic tensor methods used to calculate quartz inclusion pressures implies that quartz inclusions studied are under strong differential strain. Prograde entrapment results from the two inclusion thermobarometry pairs used are distinct: 0.55–0.70 GPa and 475–580 ∘C (QuiG–TitaniQ) versus 0.85–1.10 GPa and 665–780 ∘C (QuiG–TiB). Garnet modal isopleth modeling indicates that the majority of garnet growth occurred at ∼ 450–600 ∘C, implying that P–T conditions of garnet growth are interpreted to be most reliably represented by QuiG–TitaniQ inclusion thermobarometry. Normal distributions of calculated QuiG inclusion pressures and the concentration of mineral inclusions in garnet cores suggest that the majority of garnet inclusions were entrapped during a single stage of porphyroblast growth. A general lack of evidence from CL imagery for post-entrapment mechanical or chemical modifications to quartz inclusions suggests that quartz inclusions used to calculate entrapment P–T largely preserve their initial entrapment conditions. Biotite inclusions preserve higher temperatures than quartz inclusions in the same garnets, likely due to Fe–Mg exchange with garnet hosts that allowed Ti content of biotite to change after entrapment. Pseudosection modeling and matrix chemical thermobarometry of multiple, independent lithologies examined during inclusion studies suggest a range of peak granulite facies conditions of ∼ 0.50–0.70 GPa and 730–800 ∘C. Peak metamorphic P–T modeling work from this study, together with evidence of regional amphibolite facies overprinting in immediately adjacent samples, indicates an overall clockwise metamorphic P–T path with nearly isobaric prograde heating to peak temperatures. Interpreted P–T path reconstructions are consistent with metamorphism developed in a more modern-style continental arc subduction zone and are observed in portions of the northern Wyoming Province as exemplified by metasupracrustal lithologies of the eastern Beartooth Mountains.

Geochemical variation in biotite from the Devonian South Mountain Batholith, Nova Scotia: Constraints on emplacement pressure, temperature, magma redox state and the development of a magmatic vapor phase (MVP)

Abstract Here we report the composition of biotite from the peraluminous Devonian South Mountain Batholith (SMB) of southwestern Nova Scotia (Canada), the largest intrusive body within the Appalachian orogen. The batholith was emplaced in two phases: an early (379–375 Ma) granodiorite-monzogranite suite (Stage 1) and a later (375–372 Ma) more-evolved monzogranite-leucogranite suite (Stage 2). Biotite analyses (major and minor elements) were obtained on 55 unmineralized samples representing 11 plutons. Regardless of the stage of pluton emplacement, biotite is commonly interstitial to alkali feldspar, quartz and plagioclase, indicating similar timing of biotite saturation. This suggests that biotite chemistry records conditions at similar extents of magma evolution for the chosen suite of samples. Biotite compositions are Fe-rich, with Fe/(Fe+Mg) ranging from 0.6 to 0.98, and Al-rich, with IVAl ranging from 2.2 to 2.9 atoms per formula unit (apfu; 22 oxygen basis), the latter reflecting the coexistence of other Al-rich phases, such as muscovite, garnet, aluminosilicates, and cordierite. Biotite anion sites are dominated by OH (>3 apfu), followed by F (~0.3 apfu) and Cl (≤0.02 apfu), with a general trend of decreasing OH, increasing F and a marked decrease in Cl, with increasing differentiation. Pressure (P) is estimated from the Al content of biotite to be between 280–430 MPa, consistent with a range of 240 to <470 MPa derived from phase equilibria and fluid inclusion microthermometry combined with mineral thermobarometry. Temperature (T) calculated from the Ti content of biotite ranges from 603–722 °C. Comparison of P-T estimates with water-saturated granite phase relations suggest minimum water contents of 6–7 wt% for the SMB magmas. The redox state of the SMB was estimated by comparing biotite Fe#-Ti relations with compositions calculated using the MELTS thermodynamic model, as experiments have shown that biotite Fe# increases with decreasing fO2 at a given extent of crystallization. Results of MELTS modeling for the most primitive magmas of the SMB sample suite indicate that the observed biotite Fe#-Ti variation is consistent with crystallization at FMQ to FMQ-1, with more oxidizing conditions suggested for the most strongly differentiated samples. To constrain the origin of the biotite anion site variation, a quantitative model using biotite-melt exchange coefficients (KD) derived from existing experimental data was used to track the change in biotite OH-F-Cl abundances as a function of crystallization, with or without an extant magmatic vapor phase (MVP). The model reproduces the relative OH, F, and Cl abundances in biotite, and suggests that SMB crystallization occurred in the presence of a MVP. The relatively reduced redox state of the SMB, similar to other peraluminous granitoid occurrences worldwide, aligns with other measures of fO2 for the SMB, including the occurrence of primary ilmenite. The observed correspondence between the estimated fO2 and that imposed by graphite-gas equilibrium suggests a role for reduced carbon in the generation and evolution of the SMB. This is consistent with evidence for SMB interaction with graphite-bearing felsic granulites of the underthrust Avalon terrane, and assimilation of carbonaceous and sulfidic metasediments during pluton ascent and emplacement. Reducing conditions and development of a MVP have implications for granophile element concentration processes in the SMB magmatic system. Low fO2 during crystallization affects the mineral/melt partitioning and solubility of the redox-sensitive elements Sn, W, U, and Mo, serving to suppress early SnO2 precipitation, and cause both an increase in W/Mo and an overall buildup of all four elements in evolving SMB liquids. Available experimental data indicate that reducing conditions also shifts DMVP/melt to favor partitioning into the melt phase. Therefore, early vapor exsolution under reducing conditions also lessens the extraction efficiency of these redox-sensitive elements to the MVP, further underscoring the role of extensive crystallization as an important metal enrichment process.

Improving mechanical properties of manufactured sand concrete with high biotite content: Application of magnetic separation process and equipment optimization

• Degradation mechanism of biotite in manufactured sand on concrete performance was presented. • An empirical formula of compressive strength for different biotite content was presented. • FEM-DEM coupling program was developed to optimize biotite separation process. Harmful components such as biotite in fine aggregates formed by natural rock crushing need to be rigorously assessed and effectively separated to reduce their potential damage to concrete structures. In this study, magnetic separation was used to remove excess biotite from manufactured sand and to realize the upgrade of manufactured sand, and a series of laboratory tests were carried out to study the influences of biotite content on the compressive strength and splitting strength of concrete. Experimental results show that the magnetic separation method can effectively reduce the biotite content in concrete from 10 % to 2 %, thus improving the mechanical properties of concrete. Through microscopic characterization, we found that the surface layer of biotite had a strong bonding effect with the early hydration product. This bonding effect contributes to the early strength of concrete, leading to a small difference in the strength values of manufactured sand concrete with different biotite contents. With increasing curing age, the strength contribution caused by this bonding effect gradually decreases. In addition, FEM-DEM coupling simulation was used to optimize the operation parameters and magnetic system structure of the magnetic separator to further achieve efficient separation of biotite from manufactured sand. Numerical prediction indicates that the dry magnetic separator has an extrusion magnetic system structure, which makes the magnetic induction and magnetic induction gradient at the guide disk higher and provides a much greater magnetic force than other competitive forces for biotite particles. To efficiently recover low-grade manufactured sand (low biotite content) from manufactured sand, the feed rate t , conveyor belt speed V and magnet-to-steel disk thickness ratio μ should be kept at 0.8 kg/s, 0.85 m/s and 3, respectively. This study can provide potential solutions and broad application value for the problem of manufactured sand with high biotite content in practical engineering.

An assessment of the relationship between the petrographic, physical, and morphological properties of aggregates used for railway ballast

• Qualitative petrographic variables affect aggregate degradation resistance. • Mineralogy defines the physical and morphological behavior of aggregates. • Rocks with a higher concentration of felsic have undergone greater degradation. • Rocks with higher concentrations of mafic and biotite showed angularity gain. The performance of the ballasted permanent track is linked to the quality of the aggregates that make up the ballast layer. This layer is the only one that allows the regularization and leveling of the rail pavement. Evaluating the relationships between the properties of rocks and aggregates helps in predicting the behavior of rail ballast and in reducing wear and premature failures in the permanent way. The objective of this study is to evaluate the relationship between the petrographic, physical and morphological properties of the aggregates. The materials were selected from the literature with application of rocks for different areas. The petrographic properties of the rocks were filtered or identified through photomicrographs. The physical and/or morphological tests of the rocks were verified. Based on the database of 21 rocks, the results show the strong influence of grain shape, granulation, texture, contact between minerals and, mainly, mineralogy on the physical and morphological behavior of the aggregates. Rocks with higher mafic content provide greater resistance to aggregate degradation. Rocks with higher mafic and biotite contents contribute to increase the angularity value of aggregates after Micro-Deval (MD) wear tests. Medium/coarse grained rocks induce a higher value of unfilled intergrain microcracks between minerals and, consequently, higher porosity and water absorption and higher compression degradation. Furthermore, the results show that it is possible to predict the morphological behavior of aggregates after degradation from the morphological variables before their degradation.

The importance of mineralogical composition for the cytotoxic and pro-inflammatory effects of mineral dust

BackgroundRespirable mineral particles represent a potential health hazard in occupational settings and ambient air. Previous studies show that mineral particles may induce cytotoxicity and inflammatory reactions in vitro and in vivo and that the potency varies between samples of different composition. However, the reason for these differences is largely unknown and the impact of mineralogical composition on the biological effects of mineral dust remains to be determined.MethodsWe have assessed the cytotoxic and pro-inflammatory effects of ten mineral particle samples of different composition in human bronchial epithelial cells (HBEC3-KT) and THP-1-derived macrophages, as well as their membranolytic properties in erythrocytes. Moreover, the results were compiled with the results of recently published experiments on the effects of stone particle exposure and analysed using linear regression models to elucidate which mineral components contribute most to the toxicity of mineral dust.ResultsWhile all mineral particle samples were more cytotoxic to HBEC3-KT cells than THP-1 macrophages, biotite and quartz were among the most cytotoxic in both cell models. In HBEC3-KT cells, biotite and quartz also appeared to be the most potent inducers of pro-inflammatory cytokines, while the quartz, Ca-feldspar, Na-feldspar and biotite samples were the most potent in THP-1 macrophages. All particle samples except quartz induced low levels of membranolysis. The regression analyses revealed associations between particle bioactivity and the content of quartz, muscovite, plagioclase, biotite, anorthite, albite, microcline, calcite, chlorite, orthopyroxene, actinolite and epidote, depending on the cell model and endpoint. However, muscovite was the only mineral consistently associated with increased cytotoxicity and cytokine release in both cell models.ConclusionsThe present study provides further evidence that mineral particles may induce cytotoxicity and inflammation in cells of the human airways and that particle samples of different mineralogical composition differ in potency. The results show that quartz, while being among the most potent samples, does not fully predict the toxicity of mineral dust, highlighting the importance of other particle constituents. Moreover, the results indicate that the phyllosilicates muscovite and biotite may be more potent than other minerals assessed in the study, suggesting that this group of sheet-like minerals may warrant further attention.

Differences in Properties between Pebbles and Raw Ore from a SAG Mill at a Zinc, Tin-Bearing Mine

Semi-autogenous (SAG) mills are widely used grinding equipment, but some ore with critical particle sizes cannot be effectively processed by SAG mills and turned into pebbles. This research aims to analyze and compare the properties of raw ore and pebbles from a zinc- and tin-bearing ore. The results show that the contents of sphalerite, cassiterite, biotite, antigorite, pyroxferroite, ferroactinolite, and ilvaite in the raw ore are higher than those in the pebbles, and that the pebbles have higher contents of hedenbergite, chlorite, epidote, actinolite, etc. Meanwhile, the abrasion and impact resistance of pebbles is greater than that of the raw ore. In addition, the sphalerite is evenly embedded, and the grinding process is regular. Fine cassiterite associated with harder minerals is difficult to dissociate; it is often found in softer or brittle minerals which may be easily ground into ore mud. The cassiterite in the pebbles is associated with hard and brittle hedenbergite and soft chlorite, making it difficult to recover. This research provides a good foundation for evaluating the recovery value of pebbles and improving the productivity of the SAG process.

Significance of Granulometric Composition and Physicochemical Properties for Interpreting the Lake Grand Sedimentation

Abstract —The paper is concerned with a study of the slope deposits being weathering products of rhyolites and their tuffs in the vicinity of Lake Grand (northern Okhotsk area). The samples were divided into grain size fractions of 2500, 250, 140, 100, 63, 40, 20, and 1 μm. Analysis for major and trace elements and mineralogical and petrophysical studies were performed for each fraction. It is shown that a decrease in the fraction size is accompanied by the enrichment of the sediments with Al2O3, Fe2O3, TiO2, MgO, Y, Rb, Ni, and paramagnetic minerals and by an increase in LOI. The fine fractions are characterized by low contents of SiO2 and Na2O and high values of CIA, PIA, and Rb/Sr. The maximum magnetic susceptibility, saturation magnetization, and contents of CaO, Sr, and Zr are established in the fractions of 40 μm. The values of magnetic susceptibility, Js, and Jrs decrease in passing from the fractions of 40 μm to the fractions of 1 μm, whereas the values of Bc and Bcr increase. A specific feature of these fractions is high paramagnetic susceptibility and the presence of lepidocrocite. The qualitative composition of ferrimagnetic minerals is the same for the slope deposits and lacustrine sediments. In passing from coarse fractions to fine ones, the contents of quartz and K-feldspar decrease, and the contents of muscovite, biotite, chlorite, and kaolinite increase. The distribution of petromagnetic and geochemical characteristics in the Lake Grand sediments of varying grain size is similar to that in the slope deposits. The complex characteristics of the lacustrine sediments that formed in cold and warm periods are consistent with the distribution of these parameters in various fractions of deluvium and colluvium. Moreover, the fine-grained material acquired specific geochemical, mineralogical, and petrophysical properties when being on the slopes. Comparison of the SiO2/TiO2 and Fe2O3/TiO2 ratios of the slope deposits and lacustrine sediments makes it possible to identify the intervals of biogenic and chemogenic sedimentation in water basins.

Mineralogy of a rare Ediacaran epidote‐bearing trondhjemitic complex from the Nubian Shield: Insights into P‐T conditions of magma emplacement

Igneous epidote occurring in tonalite–trondhjemite–granodiorite (TTG) rocks provides valuable insight into the physiochemical parameters of their magmatic system. Epidote has been identified within a newly discovered, rare, Ediacaran, high‐Al TTG‐suite at the Fannani Igneous Complex (FIC), Nubian Shield. The objective is to assess P–T conditions of magma emplacement using petrographic‐, mineral chemical data, and thermobarometry methods. The TTG‐suite is made up of ubiquitous oligoclase, variable contents of quartz, K‐feldspar, amphibole, biotite, epidote, accessory titanite, zircon, apatite and magnetite. Feldspars vary from An14 to An26 in plagioclase, with K‐feldspar having near‐end‐member compositions (Or91–Or95). Amphiboles are Al‐rich (AlT = 1.65–2.04 atoms per formula unit [apfu]), calcic (Ca = 1.83–1.93, apfu), with average Mg/(Fe + Mg) of 0.44, and are ferroedenite–edenite–ferropargasite. Biotites are moderately Fe‐rich (Fe/(Fe + Mg) = 0.50–0.58) characteristic of type ‘C’–biotite of calc–alkaline orogenic rocks. Epidote exhibits pistacite components [Ps = Fe3+/(Fe3++Al)] of Ps24–Ps33, typical of magmatic epidote. The average crystallization pressure of 5.41 kbar (calculated using the Al‐in‐Hb barometer) is consistent with the presence of magmatic epidote and reflects the mesozonal crustal levels of emplacement. The Hb–Plag–geothermometer produced an average crystallization temperature of 721°C. These values fall within experimentally‐determined P–T ranges of stability of magmatic epidote with fO2 buffered from nickel‐nickel‐oxide (NNO) to hematite (HM). The FIC rocks were developed from a wet, subsolvus, orogenic, Al‐rich magmatic system. Findings reported here could have implications for conditions of magma emplacement and mineralogical characterization of TTGs occurring within various continental masses.

Crustal anisotropy and deformation of the southeastern Tibetan Plateau revealed by seismic anisotropy of mylonitic amphibolites

The composition and deformation patterns in the deep crust of southeastern Tibet are remain controversial. In this study, we present microstructures, fabric and seismic properties of amphibolites from the Ailao Shan-Red River shear zone, western Yunnan, China. The amphibolites display a distinct mylonitic foliation, and the amphibole grains show low intracrystalline deformation, slight compositional zoning but strong crystallographic preferred orientations (CPOs). We explain these CPOs could have formed by rigid body rotation during deformation accommodated by diffusion creep and grain boundary sliding. The amphibolites show strong seismic anisotropies (AVp = 4.6–9.3% and Max. AVs = 3.2–9.0%). Rock recipe modelling results indicate the seismic anisotropies of the mylonitic amphibolites are dominated by the content of biotite and amphibole. The delay time (0.28–1.01 s, average of 0.58 s) calculated for a 40 km-thick amphibolite layer is consistent with the observed delay time (0.52 s) of Pms wave splitting in this region, which indicates a thick amphibolitic layer in the crust of the southeastern Tibetan Plateau. The observed Pms wave splitting, extensive fold deformation and low velocity zones (LVZs) in the Diancang Shan (DCS) massif indicate two anisotropic layers in the crust. The upper layer related to frozen fabrics of amphibolites, which deformed during compressional folding and strike-slip shear. The lower layer related to the alignment of amphibole and melt pocket induced by present-day channel flow. The observed Pms wave splitting in the Ailao Shan (ALS) massif is attributed to amphibolites with vertical foliation and horizontal lineation which are generated by compressional folding and strike-slip shearing.

Biotite chemistry and mineral association as an indicator of redox conditions in the iron oxide Cu-Au (IOCG) system: Constraints from the Khetri Copper Belt, western India

Key constraints related to the nature of alteration and mineralization in geologically complex and economically important iron oxide copper–gold (IOCG) systems remain highly speculative, especially, the physicochemical characteristics of the hydrothermal fluids. This study was conducted on samples from the Khetri Copper Belt (KCB) in western India that hosts several IOCG-type deposits. The study aims to constrain qualitative oxygen fugacity conditions during alteration-mineralization events using biotite and uraninite chemistry. The inferred redox conditions are backed up by the presence or absence of redox-sensitive minerals including magnetite, ilmenite, and graphite. Biotite is present in association with REE ± Th ± U and Cu-Co-U-REE mineralization, which has a genetic connection with IOCG-style K-Fe-Mg alteration. The first type of mineralization is mostly sulfide-free and is characterized by the presence of REE-silicate, REE-phosphate, U-Th-silicate, and U-oxides with minor ilmenite, magnetite, and pyrite. The other type is characterized by the presence of Cu-Co-Fe sulfides, U-oxides, REE-silicates and -phosphates with significant volume of graphite. The Fe3+ in biotite was calculated from electron probe data by two different methods, and U and Th concentrations in uraninite were measured by an electron probe microanalyzer (EPMA). Stability of redox-sensitive phases (magnetite, ilmenite, and graphite), Fe3+-Fe2+-Mg content of biotite, and U/Th ratio of uraninite collectively suggest redox conditions essentially below the haematite-magnetite buffer often reaching the fayalite-quartz-magnetite buffer. We conclude that the studied alteration-mineralization assemblages represent the deeper and reduced facies of the Khetri IOCG system. We suggest that biotite and uraninite chemistry can be used as an indicator of redox conditions for alteration/mineralization assemblages in IOCG systems where redox-sensitive minerals particularly magnetite is absent.

Sediment Sources and Dispersion on the Western Sunda Shelf, Malay Peninsula, Southern South China Sea

Thirty-nine surface sediment samples collected from the western Sunda Shelf off the Malay Peninsula (WSSMP) in the southern South China Sea (SCS) were analysed for grain size, major and trace elemental compositions, and light/heavy mineral contents to trace the sediment sources and their transport mechanisms in the study area. In the WSSMP, the surface sediments are relatively poorly sorted but transportable. A principal component analysis of 37 elements and grain size fractions indicates that the surface sediments can be grouped into four major assemblages in the study area. Integrating with the light/heavy minerals data in the 63–125 μm fractions of the surface sediment samples, to better trace the sediment sources of the coarse-grained components in the marine environment, the study area can be further divided into four sediment provinces. Province I is located in the northwestern part of the study area. The concentrations of TiO2, Na2O, garnet, siderite, and glauconite in Province I were higher than in the other provinces. The main sediment source for this province originated from the Kelantan River and the Gulf of Thailand transported by the northeastern monsoon current. Province II is located offshore of the Pahang and Endau Rivers. The percentages of TiO2, rare earth elements, Al2O3, quartz, plagioclase, hypersthene, and magnetite in the surface sediments were typically higher in this province than in the other provinces. The Pahang and Endau rivers provide most of the sediments to this province, which are transported by southward coastal currents. Province III is located in the northeastern and eastern parts of the study area, where the coarse-grained sediment fraction had relatively high hornblende and biotite contents. Sediments in this province are mostly transported from the Mekong River during the northeastern monsoon. The other parts of the study area belong to Province IV, where the surface sediment elemental and mineral concentrations were mostly between those of the other three provinces. Therefore, we suggest that Province IV has a mixed source due to inputs from the surrounding rivers.

Numerical shear experiments of quartz-biotite aggregates: Insights on strain weakening and two-phase flow laws

For progressively deforming multi-phase aggregates, it is unclear to what extent the change in geometry and orientation of the involved phases leads to textural strain weakening and thus may control strain localization. Consequently, the question arises how the ductile flow of multi-phase rocks can be described or determined. To contribute to the understanding of these knowledge gaps, two-dimensional numerical shear experiments of quartz-biotite aggregates were conducted at variable conditions. Textural variations after a shear strain of γ ≈ 10 appear to be dependent on the viscosity contrast between the minerals involved. To estimate whether a numerical experiment is undergoing strain weakening or hardening, the temporal evolution of the mean second invariant of the deviatoric stress tensor was tracked. The results suggest that strain weakening occurs if biotite is distinctly isolated in form of strong or weak inclusions and that it is more effective under conditions with larger viscosity contrasts between matrix and inclusions. However, observed stress drops in experiments purely based on textural strain weakening are low compared to other strain weakening processes. Numerical results from experiments with variable strain rate, temperature and biotite content were combined to determine two-phase flow law parameters for quartz-biotite aggregates, which are in broad agreement with existing analytical mixed-aggregate flow laws.

Pegmatitic granite fluid compositions and thermochronometry in the Seridó Belt, Borborema Province, Brazil: Insights from trace element advection-diffusion-partitioning halos in host schist and gneiss

At the Seridó Belt pegmatitic province, fluid advection from dykes and sills led to trace element diffusion and partitioning in biotite, producing sub metric concentration halos in host mica schist and gneiss. We analyzed trace element concentration vs. distance profiles in the host rock of pegmatitic granite intrusions showing enrichments in Li, F, Cl, Zn, Rb, Nb, Sn, Cs, Ta, U and depletions in Sr and Ba. We estimated fluid temperatures in the range 600 to 700 °C using methods of Ti in biotite, F-OH in biotite-apatite and Tschermak component in biotite-muscovite. We analytically modeled thermal profiles around pegmatitic planar intrusions and found that cooling by thermal flats in the first meters into the host rock is reached in 100 years for a 10 m thick sill. The model constraints sustained heat flow during pegmatitic melt emplacement into a colder host rock. The measured trace element profiles were fitted with solutions of differential equations modeling advection-diffusion-partitioning in porous media under isothermal and cooling conditions. Each trace element profile is equally fitted by values of pegmatitic fluid concentration vs. fluid flux duration plotting as a straight line. We obtained a theorical framework combining pegmatitic fluid trace element composition, fluid flux duration and velocity, rock/fluid trace element partition coefficient, and cooling rate. Using published fluid inclusion trace element composition, we obtained fluid flux duration between tens of years to several centuries for the studied profiles. In the case of low temperature fluid flux at 450 °C the modeled flux duration is increased by less than one order of magnitude. The results allow us to interpret the trace element halos as sub millennial hot isothermal fluid influx from the pegmatites into their host rock. Trace element partitioning from the fluid into host rock falls mostly within the range of 0.01 to 25 and decreases in the order Nb, Cu, Rb, Zn-Li, Cs-Sn. The model constraints fluid advection velocity between 1 × 10−11 m/s and 1 × 10−9 m/s, typical of regional metamorphism to shear focused fluid flow regimes. The trace element enrichment of biotite along the profiles reproduces the observed pattern for whole rock, indicating that biotite is their main sink during pegmatitic fluid influx. Using experimental F in biotite diffusivity we obtained a minimal planar diffusion distance, or the effective porosity, between 7 and 15 μm for the total F re-homogenization of metamorphic biotite by pegmatitic fluid. As shown from others fluid-present petrogenetic systems, the trace element contents of biotite in host rock at the contact with pegmatitic intrusions can be a potential tool for the assessment of their rare metal potential.

A new activity model for Fe\u2013Mg\u2013Al biotites: II\u2014Applications in the K2O\u2013FeO\u2013MgO\u2013Al2O3\u2013SiO2\u2013H2O (KFMASH) system

The new biotite activity model and standard-state thermodynamic properties of Ann, Phl, and Eas presented in part-I were used to make pseudosections of bulk compositions representing experimental Fe–Mg exchange equilibria and (model) pelitic bulk rock compositions in the system K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH), using mainly the software Perple_X. These pseudosection calculations (termed ‘our calculation(s)’ in the following) were compared to analogous ones performed with the solution model of biotite and thermodynamic data cited in White et al. (J Metamorph Geol 32:261–286, 2014, 10.1111/jmg.12071), termed ‘W14 calculation’. Our calculations with the experimental bulk composition used by Zhou (Ti–Mg–Fe biotites: formation, substitution, and thermodynamic properties at 650 to 900 °C and 1.1 Kb with fO2 defined by the CH4–graphite buffer. PhD thesis, State University of New York, 1994) in his experimental study of the Fe–Mg exchange between biotite (Bt) and olivine (Ol) confirm that biotite had no or only minimal octahedral Al (AlVI) in these experiments. The experimental data of Ferry and Spear (—FS78, Contrib Mineral Petrol 66:113–117, 1978, 10.1007/BF00372150) on the Fe–Mg distribution between biotite and garnet (Grt) are well reproduced by our calculations. The computed composition of biotite (XFe) in equilibrium with garnet of Alm90Py10 composition and the resulting lnKD values as a function of temperature are in good agreement with the experimental brackets. An analogous W14 calculation on the same Fe-rich bulk composition predicts too high XFeBt in order of 0.1 mol fraction. The AlVI contents of biotite of about 0.3–0.45 apfu, as measured by Gessman et al. (Am Mineral 82:1225–1240, 1997, 10.2138/am-1997-11-1218) in similar biotite–garnet exchange experiments performed with Alm80Py20 and Alm70Py30 garnets, are well reproduced by our, as well as by W14 calculations. The extent of Tschermak substitution in biotite in the FS78 experiments, which had Fe-richer bulk compositions, has not been measured. Comparing the FS78 biotites with the ones from Gessman et al. (Am Mineral 82:1225–1240, 1997, 10.2138/am-1997-11-1218), it is very likely that the biotites reported in FS78 contained AlVI in the same order of ca. 0.3–0.4 apfu. A T–XFe (= molar FeO/(FeO + MgO) pseudosection demonstrates the bulk composition dependence of lnKD of the Mg/FeGrt/Bt exchange reaction in high-variance fields. Further comparisons, demonstrating the application of the new biotite solution model in the KFMASH system, are presented in pseudosections constructed for an average model pelite, as well as for a natural high-T/low-P and a natural high-P metapelite. The pseudosections show that biotite according to our biotite model breaks down at lower temperatures and pressures than predicted from the W14 biotite model in the KFMASH system. This means that KFMASH biotite can break down before the wet solidus is reached, which can explain the existence of dry high-T/low-P metapelites. At higher pressures, biotite according to our calculations breaks down at lower pressures than computed with the W14 biotite model. Before biotite breaks down, however, its AlVI content based on our calculations could potentially be used for pseudosection barometry, similarly as the Si-in-phengite barometer. These trends need to be confirmed by a future extension of our model which incorporates Ti, Fe3+ and a di–tri-octahedral substitution.