Biotite Content Research Articles

Petrography and Mineral Chemistry of Magmatic and Hydrothermal Biotite in Porphyry Copper-Gold Deposits: A Tool for Understanding Mineralizing Fluid Compositional Changes During Alteration Processes

DOI: 10.17014/ijog.5.1.47-64This study aims to understand the petrography and chemistry of both magmatic and hydrothermal biotites in porphyry copper-gold deposits, and to evaluate the fluid compositional changes during alteration processes. A total of 206 biotite grains from selected rock samples taken from the Batu Hijau porphyry Cu-Au deposit was analyzed. Detailed petrography and biotite chemistry analysis were performed on thin sections and polished thin sections, respectively, representing various rocks and alteration types. A JEOL JXA-8900R electron microprobe analyzer (EMPA) was used for the chemistry analysis. The biotite is texturally divided into magmatic and hydrothermal types. Ti, Fe, and F contents can be used to distinguish the two biotite types chemically. Some oxide and halogen contents of biotite from various rocks and alteration types demonstrate a systematic variation in chemical composition. Biotite halogen chemistry shows a systematic increase in log (XCl/XOH) and decrease in log (XF/XOH) values from biotite (potassic) through chlorite-sericite (intermediate argillic) to actinolite (inner propylitic) zones. The y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from potassic and intermediate argillic zones are similar or slightly different. In contrast, the y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from inner propylitic zone display different values in comparison to the two alteration zones. Halogen (F,Cl) fugacity ratios in biotite show a similar pattern: in the potassic and intermediate argillic zones they show little variation, whereas in the inner propylitic zone they are distinctly different. These features suggest the hydrothermal fluid composition remained fairly constant in the inner part of the deposit during the potassic and intermediate argillic alteration events, but changed significantly towards the outer part affected by inner propylitic alteration. High halogen content, particularly Cl, in hydrothermal biotite may portray that copper and gold were transported in mineralizing fluids in the form of chloride complexes CuCl2- and AuCl2-, respectively.

Effects of Mineral Compositions on Matrix Diffusion and Sorption of 75Se(IV) in Granite.

Exploring the migration behaviors of selenium in granite is critical for the safe disposal of radioactive waste. The matrix diffusion and sorption of 75Se(IV) (analogue for 79Se) in granite were systematically studied to set reliable parameters in this work. Through-diffusion and batch sorption experiments were conduct with four types of Beishan granite. The magnitudes of the obtained apparent diffusion coefficient (Da) values are of the following order: monzogranite > granodiorite-2 > granodiorite-1, which is opposite to the sequence of the Kd values obtained from both the diffusion model and batch sorption experiments. The EPMA results of the granitic flakes showed that there was no obvious enrichment of Se(IV) on quartz, microcline and albite. Only biotite showed a weak affinity for Se(IV). Macroscopic sorption behaviors of Se(IV) on the four types of granite were identical with the sequence of the granitic biotite contents. Quantitative fitting results were also provided. XPS and XANES spectroscopy data revealed that bidentate inner-sphere complexes were formed between Se(IV) and Fe(III). Our results indicate that biotite can be representative of the Se(IV) sorption in complex mineral assemblages such as granite, and the biotite contents are critically important to evaluate Se(IV) transport in granite.

Biotitická plagioklasová rula z Koutů nad Desnou a Rejhotic (vrbenská skupina v zóně Červenohorského sedla): nové mineralogické údaje

The paper deals with metamorphic rocks of the Vrbno Group in the Červenohorské sedlo Zone near the Kouty nad Desnou village (north-eastern part of the Bohemian Massif). The studied rocks are named simply as biotite plagioclase gneiss in geological maps. Research has shown that most of the rocks in the area correspond to the graphite-bearing staurolite-biotite plagioclase gneiss. This gneiss merges into mica schist with the same mineral association but with a higher content of biotite. Plagioclase is a major and sometimes even dominant constituent of the rocks. Its composition varies from An39 to An84. Accessory minerals include ilmenite, apatite-(CaF), less often zircon, tourmaline (dravite), garnet (almandine), pyrite, and chalcopyrite. In the mentioned rocks, thin graphite-bearing chlorite plagioclase gneiss intercalations were found. Plagioclase has an extremely high basicity (An88-91). It is obvious from the chemical and mineral composition of the studied rocks that their protolith had to be rich in iron, aluminum and calcium. Clay rocks can be assumed as protolith. The origin of clay sediments or clay residue was possibly linked to the weathering of basic volcanism products.

The sorption and diffusion of 133Ba in crushed and intact granitic rocks from the Olkiluoto and Grimsel in-situ test sites

The distribution coefficients of barium on Olkiluoto pegmatitic granite and veined gneiss, Grimsel granodiorite and their main minerals (quartz, plagioclase, potassium feldspar and biotite) were obtained by batch sorption experiments carried out as a function of the concentration of barium. The distribution coefficients on biotite and veined gneiss were modelled with the PHREEQC computing program. In addition, the diffusion of barium into rock cubes was also studied both experimentally and computationally and the rock cubes from the diffusion experiments were studied with autoradiography and scanning electron microscopy. The results showed that the distribution coefficients of barium were largest on biotite and the sorption as a function of barium concentration on all the minerals followed a similar trend. The distribution coefficients of barium on veined gneiss, pegmatitic granite and granodiorite followed the distribution coefficient trend of their main minerals and the distribution coefficients were largest on granodiorite due to the low salinity of the groundwater simulant. The distribution coefficients of barium on veined gneiss were of the same magnitude as on granodiorite because of the high biotite content of veined gneiss and those on pegmatitic granite were a magnitude smaller. It was also discovered that the distribution coefficients in saline water were considerably smaller than the results obtained in low salinity water, which suggests that competing ions play a significant role in the sorption of barium. Finally, the concentration decrease of barium in the solution in the diffusion experiments was largest in granodiorite which can be explained with both the porous structure of all the minerals of granodiorite leading to high accessible surface area and with the sorption properties of barium. It was discovered with autoradiography that the barium was mainly sorbed on the dark minerals of the rocks, but, additionally, barium sorption on plagioclase was also concluded to be significant. In addition, the sorbed barium could be seen with scanning electron microscopy on the biotite and calcite veins in the fissures of the rock in granodiorite and veined gneiss.

Surfactant Effects on Structure and Mechanical Properties of Ultrahigh-Molecular-Weight Polyethylene/Layered Silicate Composites.

In this study, the reinforcement of ultrahigh-molecular-weight polyethylene (UHMWPE) with biotite was investigated. The biotite filler was mechanically activated with different dry surfactants to improve its compatibility with UHMWPE and decrease agglomeration among biotite particles. Alkyldimethylbenzylammonium chloride (ADBAC) and cetyltrimethylammonium bromide (CTAB) were selected as cationic surfactants. The tensile strength of composites containing 1 wt % of CTAB-treated biotite was increased by 30% relative to those with untreated biotite, but was unchanged with ADBAC treatment of the same biotite content. The stereochemistry of the surfactant may be critical to the composite structure and mechanical properties of the material. The stereochemistry of CTAB was preferable to that of ADBAC in enhancing mechanical properties because the stereochemistry of ADBAC impedes favorable interactions with the biotite surface during mechanical activation.

Applications of biotite inclusion composition to zircon provenance determination

Detrital zircons are the only confirmed surviving remnants of >4.03 Ga crust while younger detrital zircons provide a parallel record of more recent crustal evolution to that preserved in crystalline rocks. Zircons often preserve inclusions that may provide clues as to the origins of out-of-context grains in the sedimentary record. Previous studies have established that inclusions of biotite in magmatic zircon are compositionally well-matched to biotite in the source rock matrix, although a direct application to ancient detrital zircons has not been made. A number of studies have documented variations in the Fe, Mg, and Al contents of magmatic biotite from different source rocks and tectonic settings, suggesting that biotite inclusions may indeed serve as provenance indicators for detrital zircons. Consistent with earlier studies, we find that the FeO⁎/MgO ratio of magmatic biotite from continental arcs, collisional, and within-plate settings varies with relative oxidation state as well as whole-rock FeO⁎/MgO, while its Al2O3/(FeO⁎ + MgO) varies with whole-rock A/CNK (molar Al/(2⋅Ca + Na + K)). Biotite from oxidized metaluminous and reduced S-type granitoids can be readily distinguished from each other using FeO⁎/MgO and Al2O3/(FeO⁎ + MgO), while biotite from reduced I-type and oxidized peraluminous granites may in some cases be more ambiguous. Biotite from peralkaline and reduced A-type granites are also distinguishable from all other categories by Al2O3/(FeO⁎ + MgO) and FeO⁎/MgO, respectively. Biotite inclusions in Hadean zircons from Jack Hills, Western Australia indicate a mixture of metaluminous and reduced S-type host rocks, while inclusions in 3.6–3.8 Ga detrital zircons from the Nuvvuagittuq Supracrustal Belt indicate more oxidized peraluminous magmas. These results highlight the diversity of felsic materials on the early Earth and suggest that biotite inclusions are applicable to zircon provenance throughout the sedimentary record.

Mineralogy of the Neoproterozoic epidote-bearing TTG suite, Mons Claudianus batholith (Egypt) and implications for synorogenic magmatism

AbstractThe Neoproterozoic, epidote-bearing Mons Claudianus Batholith (MCB), Egypt, consists of tonalite-trondhjemite-granodiorite (TTG) lithologies, containing variable contents of quartz, feldspars, amphiboles, biotite, and magmatic epidote, with accessory titanite, zircon, allanite, apatite, opaque magnetite and ilmenite. Plagioclase varies from An49to An19, and K-feldspars possess near end-member compositions (Or97to Or91). Amphiboles are calcic (Ca = 1.88–1.92 atoms per formula unit (apfu)), Al-rich (average AlT= 1.84 apfu), having an average Fe/(Fe + Mg) ratio of 0.50, and are edenite, ferro-edenite and ferropargasite. The Al-in-Hb barometer produced an average crystallization pressure of 5.5 kbar, consistent with the presence of magmatic epidote; the association epidote – Al-rich-Hb suggests mesozonal crustal levels, and thus a possible average rate of regional uplift for the Nubian Shield would have been in the order of 0.03 mm/yr. Calculated temperatures (using the Hb-Plag geothermometer) range from 729 to 754°C (average 747°C). The calculatedP / Tvalues of epidote-bearing MCB rocks fall within the experimentally-determinedP-Trange of stability of magmatic epidote withfO2buffered from NNO to HM. Biotites in the MCB are moderately Mg-rich (Fe/(Fe + Mg) = 0.42 to 0.50), and are type 'C'-biotite, typical of calcalkaline orogenic suites, which are distinct from types 'A' and 'P' biotites occurring in anorogenic alkaline, and peraluminous lithologies, respectively. The minor secondary chlorite phases, with their Fe/(Fe + Mg) ratios of 0.37–0.52, are pycnochlorite and ripidolites, and belong to group 'c' chlorites. Minerals of the MCB reflect a petrogenetic history involving a wet, subsolvus, typically orogenic magmatic system. Results of this study could have wide implications for mineralogical characterization, level of emplacement and evolution of magmatic systems of TTG suites occurring in other orogenic belts.

Halogen-Bearing Minerals From the Tamazeght Complex (Morocco): Constraints On Halogen Distribution and Evolution In Alkaline To Peralkaline Magmatic Systems

Abstract Halogen abundances in apatite, biotite, amphibole, titanite, and other halogen-rich minerals (sodalite and eudialyte) from ultramafic pyroxenites and glimmerites, shonkinites, and gabbroic, monzonitic, and syenitic rocks of the alkaline to peralkaline Tamazeght complex (Morocco) are presented. Apatite, biotite, and amphibole show the highest F contents in the most evolved rocks, which also contain interstitial fluorite (restricted in syenites). The Cl contents of apatite, biotite, and amphibole are highest in the intermediate rocks. Sodalite (Cl-rich) is equally common in the evolved rocks, although Cl contents of apatite, biotite, and amphibole are low. We suggest that the early magmatic crystallization of sodalite causes a strong depletion of Cl in the remaining melt, resulting in the subsequent crystallization of Cl-poor apatite, biotite, and amphibole. Late-magmatic eudialyte in some of the rocks may indicate a late-stage re-enrichment of Cl. The Br contents of biotite, amphibole, eudialyte, and sodalite reveal that Cl-rich minerals generally contain high Br. The Cl/Br ratios of individual minerals are, however, highly variable. This suggests that besides melt composition, other factors, such as crystal-melt partitioning and fluid mobility, may influence Cl/Br ratios in igneous minerals, resulting in potentially strong fractionation of Cl from Br in minerals. Estimation of F and Cl contents in alkaline melts suggests that primitive ultramafic melts are poorer in Cl than evolved melts, whereas their F contents are relatively similar. The low apparent Cl contents of the syenitic melts, calculated based on apatite compositions, may reflect the halogen abundance during late-magmatic conditions, as the presence of early magmatic sodalite indicates Cl-rich syenitic melt compositions.

Microstructures, deformation mechanisms and seismic properties of a Palaeoproterozoic shear zone: The Mertz shear zone, East-Antarctica

The Mertz shear zone (MSZ) is a lithospheric scale structure that recorded mid-crustal deformation during the 1.7Ga orogeny. We performed a microstructural and crystallographic preferred orientation (CPO) study of samples from both mylonites and tectonic boudins that constitute relics of the Terre Adélie Craton (TAC). The deformation is highly accommodated in the MSZ by anastomosed shear bands, which become more scattered elsewhere in the TAC. Most of the MSZ amphibolite-facies mylonites display similar CPO, thermal conditions, intensity of deformation and dominant shear strain. Preserved granulite-facies boudins show both coaxial and non-coaxial strains related to the previous 2.45Ga event. This former deformation is more penetrative and less localized and shows a deformation gradient, later affected by a major phase of recrystallization during retrogression at 2.42Ga. Both MSZ samples and granulite-facies tectonic boudins present microstructures that reflect a variety of deformation mechanisms associated with the rock creep that induce contrasted CPO of minerals (quartz, feldspar, biotite, amphibole and orthopyroxene). In particular, we highlight the development of an “uncommon” CPO in orthopyroxene from weakly deformed samples characterized by (010)-planes oriented parallel to the foliation plane, [001]-axes parallel to the stretching lineation and clustering of [100]-axes near the Y structural direction.Lastly, we computed the seismic properties of the amphibolite and granulite facies rocks in the MSZ area in order to evaluate the contribution of the deformed intermediate and lower continental crust to the seismic anisotropy recorded above the MSZ. Our results reveal that (i) the low content of amphibole and biotite in the rock formations of the TAC, and (ii) the interactions between the CPO of the different mineralogical phases, generate a seismically isotropic crust. Thus, the seismic anisotropy recorded by the seismic stations of the TAC, including the MSZ, must be due to mantle rather than crustal structures.

Biotite weathering by Aspergillus niger and its potential utilisation

Biotite, as a type of associated mineral, is normally applied as a filling material for buildings, or is discarded as tailings. However, as a potassium-bearing phyllosilicate mineral, biotite can be easily weathered by fungi, which leads to its internal potassium being released for agricultural production (1), and the mineral residues being weathered by the fungus may be applied for adsorption of heavy metal ions (2). This work investigates the weathering of biotite by Aspergillus niger through the analysis of the differences in ion dissolution from biotite, producing of organic acids, the change of mineral morphology and composition by inductively coupled plasma optical emission spectrometry (ICP-OES), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Besides, the mineral residues were applied for adsorption of heavy metal ions. Results showed that the mycelia envelope the mineral and form fungal–mineral aggregates. The fungus can secrete a variety of organic acids including citric acid and oxalic acid; these attacked the surface and cleavage of biotite to release ions (Al3+, Fe3+, Mg2+, and K+). During incubation with A. niger, biotite weathered as shown by the relative decrease in biotite content and increase in interlayer spacing. Moreover, a certain concentration of phytic acid and tween-80 could promote the release of K+, and the fermentation liquid of rice bran has the same effect. Biotite residues showed a good adsorption for Cd2+, Pb2+, Zn2+, and Cu2+. The results indicate that biotite can be biotransformed and release K+, of which the production can be acted as heavy metal ion adsorbent. It provides a reference for application of biotite in agriculture and control of heavy metal ion pollution in soil.

Mineralogy and Beneficiation of Lamujärvi Syenites

The Lamujarvi syenites intrusions occur within Svecofennian (ca. 1.92 Ga) gneisses, ca. 70 km west of the Otanmaki alkaline area in central Finland. Previous studies have revealed zones in the syenites that display strong enrichment in Zr (1587 ppm), Nb (up to 685 ppm), Ta (up to 82 ppm), and REE (up to 5350 ppm). The major REE-bearing minerals in the Lamujarvi syenites are allanite and monazite. A sample of the Lamujarvi syenites with the REE content of 4700 ppm was studied on the mineralogy and beneficiation at GTK Mintec. The mineralogical analysis was conducted by MLA. The REE-bearing minerals allanite, parisite, zircon, and apatite were identified at significant concentrations and high contents of titanite (15.4%), biotite (30.9%) and magnetite (8.2%) were displayed in the sample. The beneficiation experiments by flotation, wet low and high gradient magnetic separations and gravity separation with a shaking table were carried out. A composite REE-Ti concentrate with REE 23,000 ppm, Zr 5000 ppm, Nb 3400 ppm and TiO2 25.5% at REE and Ti recoveries of 57% and 54% was obtained. In addition, biotite and magnetite concentrates were gained as by-products.

Correlation between magnetic fabrics, strain and biotite microstructure with increasing mylonitisation in the pretectonic Wyangala Granite, Australia

The Wyangala Granite is a foliated, porphyritic Silurian granite from the Palaeozoic Circum-Pacific type Eastern Lachlan Orogen (ELO) of Australia. It is a paramagnetic ilmenite-bearing, S/marginal I type two-mica- to mainly biotite–granite with different biotite contents and local chlorite alteration. Very highly strained quartz–epidote bands are present. In this contribution, anisotropy of magnetic susceptibility (AMS) is compared with independently measured intensity and 3D style of strain, biotite microstructure and degree of mylonitisation for low-strain granites with weak S-foliations, through medium-strain protomylonitic granites with moderate S- and C-foliations to a high-strain altered granite with a strong single foliation. The samples are further analysed for possible contributions from sample heterogeneity, magmatic flow and ‘sub-magmatic’ deformation.A good correlation, P′AMS ~1.02+0.04ln P′(e)Qtz, is obtained between site-average degree of AMS (P′AMS) in the granite and degree of finite-strain anisotropy (P′(e)Qtz) from aspect ratios of quartz aggregates in S-foliations in hand specimen and outcrop (P′AMS 1.03–1.14, P′(e)Qtz 1.4–19). The magnetic fabric ellipsoids agree with a kinematic regime between neutral and pure oblate predicted by the March model. The observed quartz strains, however, exceed the AMS March strains and are near neutral, plano-linear character. The geological factors that may have contributed to these differences include intra- and inter-crystalline deformation of biotite and bimodality in S and C.Magmatic fabric is not clearly evident in either the AMS or the biotite data. New data for synkinematic oligoclase, low-titanium biotite and low-sodium K-feldspar show that conditions during deformation were approximately transitional greenschist–amphibolite facies: i.e., well below solidus. This agrees with published age data that put the granite emplacement in an extensional, back-arc setting in already deformed country rocks, and before later convergent regional deformation in Middle Devonian (Tabberabberan event) to Early Carboniferous (Kanimblan event) time.

Zn and Pb mobility during metamorphism of sedimentary rocks and potential implications for some base metal deposits

Comprehension of the genesis of Pb-Zn ore systems is currently limited by a poor understanding of where these metals are sourced from. Our study of metal mobility during regional metamorphism in the Mt. Lofty Ranges, South Australia, demonstrates that in staurolite-absent siliciclastic metasedimentary rocks, biotite contains >80 % of the bulk rock Zn, as well as a considerable proportion of the total Pb. Fluid flow through these metasedimentary rocks led to a continuous depletion of Pb and Zn on a mineral and bulk rock scale during prograde regional metamorphism. We calculate that ∼80 % of the bulk rock Zn and ∼50 % of the bulk rock Pb were mobilised, mainly through reactions involving biotite. These reactions led to a calculated Pb and Zn “loss” of ∼2.7 and 27 Mt, respectively, in the high-grade metamorphic zone. Halogen contents of apatite and biotite and bulk rock Zn isotope data provide evidence that Cl-rich metamorphic fluids were important for metal transport. Hence, fluid flow accompanying prograde metamorphism of typical sedimentary rocks can mobilise base metals to the degree required to potentially supply significant Pb-Zn ore systems.

Petrography, Geochemistry and Rb-Sr Geochronology of the Basement Granitoids from Umthongkut Area, West Khasi Hills District, Meghalaya, India: Implications on Petrogenesis and Uranium Mineralization

Abstract The basement granitoids from Umthongkut, West Khasi Hills district, Meghalaya is exposed in a very small area (1.5 km x 0.5 km) and unconformably overlain by Mahadek sandstone of upper Cretaceous age and successively followed by rocks of Tertiary age. Megascopically, granitoids are leucocratic, mesocratic to mild melanocratic and differ in texture and mineral abundance without any definite contact relation in field. The leucocratic granitoid is medium-grained, designated as granite (syenogranite and monzogranite) with appreciable content of biotite and garnet and has peraluminous to mild metaluminous character (mol. Al2O3/mol. CaO+Na2O+K2O= 0.9-1.17). However, mesocratic granitoid is relatively fine-grained, identified as quartz monzonite with abundant biotite, minor hornblende and opaque like magnetite, ilmenite, anatase, pyrite and chalcopyrite and metaluminous to mild peraluminous (mol. A/CNK=0.76-1.02) in nature. The presence of characteristic minerals and textural replacement features point towards S-type signature for granite and I –type for quartz monzonite. On the other hand, mixed S and I-type characters are observed in geochemical plot of SiO2 vs. A/CNK. The coexistence of granite and quartz monzonite with former being more evolved, S-type signature and presence of garnet with biotite suggests that the granite appears to be generated from melting of lower crustal source of monzonitic composition. The Rb-Sr dating is also attempted and the errorchron age of 1130±53 with low initial 87Sr/86Sr ratio of 0.7063±0.0011Ma appears to be the emplacement age for these coexisting phases of granitoid. Considering the Meghalaya plateau being northeastern extension of Chhotanagpur granite-gneiss complex (CGGC), the calculated age for the studied samples corresponds to the 1200-1000 Ma. which is defined as fourth tectono-magmatic thermal event of CGGC. Interestingly, these granitoids are considered as the probable source for uranium in the sandstones of Mahadek Formation of Cretaceous age hosting ore grade uranium mineralization at Umthongkut,

Evaluating physicochemical conditions of Miocene–Pliocene volcanic rocks in the middle part of the Urumieh-Dokhtar Magmatic Arc

Urumieh-Dokhtar Magmatic Arc (UDMA) resulted from subduction of the Arabian plate beneath the Eurasian plate. Miocene–Pliocene volcanic rocks in the middle part of UDMA located in the north of Isfahan (Central Iran) are mainly dacite. They are chiefly composed of phenocrysts of plagioclase, amphibole, and biotite lying in a matrix made of feldspar, quartz, opaque, glass, and microlite. Having a relatively invariable composition, plagioclases are all andesine. Amphiboles are calcic and tschermakite type. The chemical composition of biotites hardly varies. All of them are Mg-biotite. On average, they are composed of 55.3 % phlogopite, 15.7 % talc, 12.8 % Ti-phlogopite, 11.6 % eastonite, 3.7 % Ferri-eastonite, and 0.9 % muscovite. The chemical composition of biotite indicates the nature of calcalkaline for magmatic series of magma generating biotites. An estimation of the temperature and pressure of crystallization resulted from integrating amphibole and amphibole-plagioclase thermobarometry equations indicates that amphibole-plagioclase phenocrysts were crystalised in the temperature range of 763–823 °C with average of 797 °C and in the pressure range of 2.2–4.5 kbar with the average of 3.4 kbar. An estimation of the oxygen fugacity of the magma, based on chemical composition and Fe3+ content of biotite, shows the oxygen fugacity was equal to that of the FMQ buffer. Quantifying oxygen fugacity shows that logfO2 was about −15.

The Ni–Cr–Cu content of biotite as pathfinder elements for magmatic sulfide exploration associated with mafic units of the Sudbury Igneous Complex, Ontario, Canada

Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) was used to evaluate the dissolved Ni–Cr–Cu content of biotite as an exploration pathfinder for magmatic Ni–Cu–platinum-group element (PGE) sulfide deposits associated with mafic igneous units of the Worthington quartz diorite offset dyke and their host rocks at the Totten Mine (Vale Canada Ltd), Sudbury Igneous Complex (SIC), Ontario, Canada. Enrichment in Cu in biotite (up to two orders of magnitude higher than background) occurs within barren to weakly mineralized, sublayer quartz diorite and adjacent Huronian metasediments within ~200m of massive sulfide. With respect to Ni and Cr, three distinct populations of biotite were distinguished based on textural and chemical criteria: (i) type I — isolated, euhedral laths within only inclusion-rich sublayer quartz diorite (IQD; the main mineralized host lithology), and high Ni (~1400ppm<[Ni]Bt<~2700ppm), low to moderate Cr (~50ppm<[Cr]Bt<~2450ppm) and variable Ni/Cr ratios (always >2). (ii) Type II — coarse-grained poikiloblasts (enclosing amphibole, chlorite, and type III biotite) within country rocks, and having moderate to high Ni (~500ppm<[Ni]Bt<~1400ppm), moderate to very high Cr (~1750ppm<[Cr]Bt<~6000ppm) but consistently low Ni/Cr ratios (always <0.5); and (iii) type III — subhedral to euhedral laths, intergrown with amphibole in dense, foliated aggregates and having low Ni ([Ni]Bt<~300ppm), very low to moderate Cr (~4ppm<[Cr]Bt<~1200ppm), and variable Ni/Cr ratios (<20), found within Huronian country rocks, sublayer quartz diorite (QD), and cross-cutting diabase dykes (Sudbury dyke swarm). Type I biotite within IQD is compositionally distinct from those observed in all other lithologies associated with the Sudbury Igneous Complex and its footwall rocks, and can be most readily discriminated in a Ni/Cr vs. Ni binary diagram or in a Ni–Cr–Cu ternary diagram by anomalously high Ni content and Ni/Cr ratio >2.Application of biotite chemistry to routine exploration requires establishing local “background” metal-in-biotite concentrations for each potential host lithology, and scrutiny of anomalous or heterogeneous metal contents in biotite resulting from discrete sulfide microinclusions that contaminate the analytical volume, and chloritization or coeval sulfide minerals in direct contact with biotite causing localized modifications to primary biotite metal abundance.In the Sudbury environment, the Ni–Cr–Cu chemistry of biotite can be used (i) in drill core to identify proximity to mineralization, and to differentiate QD (hosting minimal sulfides) from IQD (primary host to sulfide ore bodies), rock types for which bulk textural and compositional discrimination is problematic; and (ii) in soils and tills through the analysis of biotite and its weathering products to locate buried or surface-exposed IQD. The results may be extended to other mafic–ultramafic systems where sulfide-saturated or metal-enriched intrusive phases grew metal-enriched biotite during primary crystallization, or through secondary processes of metasomatic enrichment involving remobilization of base metals by magmatic-hydrothermal fluids.

Influence of mineralogy on granite decay induced by temperature increase: Experimental observations and stress simulation

Rocks can be subjected to high temperatures in several instances as for example in geothermal processes or if affected by fires. Temperature variations lead to a complex stress distribution in crystalline rocks due to mineral thermal expansion. In polymineralic such as granites, these stresses depend on fabric parameters such as mineral proportion, grain size and their related thermal properties.Eight granitic rocks were heated to less than 400°C and their decay patterns were observed and quantified by means of scanning electron microscopy. Heating was also modeled by finite-element simulations (OOF software) with polymineralic microstructures. Quartz, feldspar and biotite contents were used as a variable in the model in order to elucidate the influence of mineralogy on the thermal-elastic response of granites.Real and modeled heating showed similar trends of microcracking in microstructures and of thermal expansion coefficients. Microscopic observations of real samples revealed mainly intragranular microcracks in quartz, opening of cleavage plains and deformation in mica. Simulations confirmed that in spite of the high thermal and anisotropic expansion of quartz, the microstructure of rocks with large amounts of quartz does not necessarily experience large stresses. Biotite produces a concentration of stresses along their grain boundaries. As a result, OOF models with 10% biotite showed higher stresses than monomineral ones. Thermal expansion coefficients of real granites fitted within the limits of the simulated ones proving once more the success of using finite element modeling applied to polymineralic rocks.

Petrography of Miocene Siwalik Group sandstones, Karnali River section, Nepal Himalaya: Implications for source lithology and tectonic setting

The Siwalik Group constitutes an important archive of Himalayan uplift and related climate changes. Compositional and textural properties of Siwalik sandstones are important parameters for the reconstruction of source lithology, uplift, and the unroofing history of the Himalaya. This study examines fluvial sandstones of the Siwalik Group along the Karnali River, where the large paleo-Kamali River is expected to have flow ed. Modal QFL analysis shows that the sandstones are mainly sub-litharenites or litharenites. Multivariate statistical analysis using Principal Component Analysis (PCA)and the Weltje method shows light variations in sediment composition occur between the Chisapani and Baka Formations. These variatio ns are mainly linked to the source area and tectonics rather than to facies, grain size, or climate. The detrital modes of the sandstones indicate recycled orogen provenance. Comparison of the detrital modes with previous studies indicates that the Higher Himalaya and Lesser Himalaya zones were a common source area throughout the time of deposition. However, subtle changes in feldspar and biotite contents indicate significant supply of detritus derived from the Higher Himalaya after 9.6 Ma.

The metasedimentary rocks from the eastern margin of the Tarim Craton: Petrology, geochemistry, zircon U–Pb dating, Hf isotopes and tectonic implications

The Dunhuang Block, located in the eastern Tarim Craton, widely exposes Precambrian TTG gneisses and metamorphosed supracrustal rocks. A suite of metasedimentary rocks of the Dunhuang Group in the Hongliuxia area on the eastern margin of the Tarim Craton are characterized by moderate contents of quartz, plagioclase, and biotite, with minor amounts of garnet or kyanite, most of which have experienced strong deformation, resulting in well-developed amphibolite-facies foliations. The examined samples are characterized by moderate Fe2O3+MgO and TiO2 contents, and Al2O3/SiO2 and K2O/Na2O ratios with low Chemical Index of Alteration (CIA) and high Index of Compositional Variability (ICV) values, suggesting that the protolith sediments originated from continental island arc environment. The U–Pb ages of magmatic-type detrital zircons from the Hongliuxia metasedimentary rocks range between 2476Ma and 1950Ma, with a peak at 2417Ma. Detrital zircons of metamorphic origin yielded an age peak at 1832Ma, which may represent a tectono-thermal event in the Paleoproterozoic. Considering that the main age populations of the analyzed samples are consistent with the tectono-thermal events in the Tarim Craton during the early Paleoproterozoic, we propose that the Tarim Craton was possibly the major source for the protolith sediments of the metasedimentary rocks in the Hongliuxia area. Zircon Hf isotopic compositions (εHf(t)=−5.8 to +2.9) suggest voluminous addition of juvenile materials to the crust and minor reworking of old materials in the eastern Tarim Craton during the Mesoarchean (TDMC=2.8–2.9Ga). The metasedimentary rocks of the Hongliuxia area provide clear constraints to the evolution of the Tarim Craton. A possible tectonic model is that multiple thermal events (~2.4Ga, 2.2Ga, 2.0Ga and 1.8Ga) occurred in the study area, and the time period of Mesoarchean was important for crustal growth in the eastern Tarim Craton, whereas the ~1.83Ga metamorphism might represent a thermal event associated with the Tarim Craton within the supercontinent Columbia.

The role of provenance in the diagenesis of siliciclastic reservoirs in the Upper Triassic Yanchang Formation, Ordos Basin, China

A better understanding of the controls on reservoir quality has become essential in the petroleum exploration in recent years. Determining the original composition of the sediment framework is important not only for paleogeographic reconstructions, but it is also vital for predicting the nature of physical and chemical diagenesis of the potential reservoirs. Depositional setting and diagenesis are important factors in controlling the type and quality of most siliciclastic reservoirs. We studied the Upper Triassic Chang 8 and 6 members, where the relationship between sediment provenance and diagenesis was examined. The study attempts to clarify sediment provenance and post-depositional diagenetic modifications of the sandstones through systematic analytical methods including petrographie macro- and microscopic analysis of grain and heavy mineral types, and measurements of the palaeocurrent direction of the Yanchang Formation sediments in the outcrops in order to determine the provenance of the studied sediments. Furthermore, the relationship between framework grains, pore types and diagenesis of the sediments was analyzed by thin section petrographic characterization using a polarizing microscope. Additionally, a JEOL JSM-T 330 scanning electron microscope (SEM) equipped with a digital imaging system was used to investigate the habits and textural relationships of diagenetic minerals. On the basis of our results, we believe that sediment provenance is a significant factor which controls the type and degree of diagenesis which may be expected in sandstones. In the Chang 8 and 6 members, the formation of chlorite rims and laumontite cement was observed where volcanic rock fragments constitute a large part of the framework grains. Furthermore, high biotite content provides abundant iron and magnesium and enables the formation of chlorite rims due to biotite hydrolysis. In addition, ductile deformation of biotite leads to strong mechanical compaction of the sediments. Conversely, high feldspar content diminishes the degree of mechanical compaction, however the dissolution of feldspar minerals in sandstones is commonly observed. Apart from feldspars, quartz and other rigid framework grains highly control the degree of mechanical compaction during the initial stage of burial (0–2 km).