Chemical Composition Of Biotite Research Articles

Two-mica rhyolitic tephra in the East Pisco Basin (Peru): new age and dispersion constraints for the eruptions of the Eastern Cordillera of Central Andes

Two-mica—biotite and muscovite—volcanics are particularly rare in the geological record. One of the several dozen volcanic ash layers from Central Andes volcanoes found in the upper Miocene marine succession of the Pisco Formation (Ica Desert, Peru) contains juvenile biotite and muscovite, sillimanite/andalusite, feldspars, and rhyolitic glass. 39Ar–40Ar dating on biotite and muscovite concordantly constrain an age of 7.96 Ma for this two-mica ash layer. A second tephra in the Pisco Formation has a similar biotite composition and an age between 7.45 and 6.93 Ma. The peculiar mineral assemblage and the chemical composition of biotite indicate a strongly peraluminous composition of the erupted magmas and, together with the 39Ar–40Ar ages, suggest to consider a correlation of these ash layers to the eruptions of the Miocene Macusani (Peru) or Morococala (Bolivia) volcanic complexes in the Eastern Cordillera of Central Andes. The major and trace element composition of glass supports the correlation with Macusani. A provenance from Morococala seems less likely given the large distances involved. These results provide new data on the volcanic activity of the Eastern Cordillera revealing ash that dispersed to over 500 km to the west, in the forearc marine basins. This finding highlights that the exhumed forearc East Pisco Basin is highly promising as an archive of distal ash for the reconstruction of the volcanic activity of Central Andes during the Miocene silicic flare-ups.

A Late Variscan tin province associated to the ilmenite-series granites of the Sardinian Batholith (Italy): The Sn and Mo mineralisation around the Monte Linas ferroan granite

The characterisation of the late Variscan intrusion of Monte Linas (southern Sardinia) allowed to firstly study some Sn-bearing ores of this area and their relationships with the surrounding intrusives. The Monte Linas pluton was emplaced at ca. 290Ma at a shallow crustal level between allochthonous units and the foreland of the Sardinian Variscan belt. The pluton emplaced in a post-collisional regime into a previously exhumed low-grade basement, forming a coarse-grained monzogranite that is capped by an almost continuous sub-horizontal sheet of fine-grained rocks. The rocks within the pluton are ferroan F-bearing granites, belonging to the ilmenite-series. They have alumina saturation index values indicative of sub-aluminous to slightly peraluminous granitoids, as also indicated by the chemical composition of biotite within the pluton. The new data of this study indicate that the Monte Linas pluton formed from water-undersaturated magmas under low-fO2 conditions at temperatures >850°C. The later stages of magmatism were characterised by boiling and fluid expulsion at confining pressures of <1kbar, producing fayalite-bearing pegmatites, miarolitic facies and greisening.A wide variety of mineral deposits are associated with the Monte Linas pluton, including different types of Sn-bearing and Mo-bearing ores. Sn-bearing ores are represented by 1) Sn–As and Sn–Pb–Zn–Cu veins, and 2) “wrigglite” skarn Fe-Zn-Sn ores. Field and analytical studies, including fluid inclusion analyses, EMPA and SEM-EDS, allow to refer these deposits to the evolution of initial highly saline, hypothermal magmatic fluids, as confirmed by parageneses and fluid inclusion analyses of cassiterite in veins, which provide evidence of polyphase processes that started at temperatures close to 400°C. The hydrothermal systems were initially characterised by low-fO2 and high-chlorine solutions that mobilised Sn and underwent rapid changes in physicochemical conditions that led to the deposition of cassiterite. In the “wrigglite” F-rich genetic environment, a role of fluoride as complexing agent for Sn can be inferred. The Monte Linas pluton is also characterised by Mo deposits, not typical in ilmenite series granites; they occur both as greisens and veins. Mo was mobilized as a result of rapid increases in fO2 within the magmatic system, and precipitated in a fS2-rich environment nearby the contact between the intrusion and the surrounding country rocks.The variety of Sn mineralising events around the Monte Linas pluton confirms the role of physicochemical characters of magmas and of magmatic processes in the genesis of tin deposits. The occurrence in southern Sardinia of a wide suite of ilmenite-series ferroan granites emplaced in similar geological contexts allows to consider the idea of a low-grade tin province and opens the way to further explorations.

Petrological and geochemical studies of ultramafic–mafic rocks from the North Puruliya Shear Zone (eastern India)

Ultramafic and mafic rocks occur within a linear belt, trending nearly E–W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbro-norite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic–ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47–81) and Al 2 O 3 (5.5–17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic–ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic–ultramafic rocks of high grade terrain, Alaskan type ultramafic–mafic complex and ophiolites. It is observed that the ultramafic–mafic rocks of present study have similarity with Alaskan type complex.

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.

Chemical composition of biotite from the Kuh-e Dom pluton, Central Iran: implication for granitoid magmatism and related Cu–Au mineralization

The composition of the Kuh-e Dom intrusion (NE Ardestan, Iran), in the Urumieh-Dokhtar magmatic belt, ranges from gabbro to granite. Several diabase dikes and numerous enclaves are common in the studied rocks. The intrusive rocks contain biotite as major or minor minerals (1–19 %). The biotites are Mg-rich typical for I-type calc-alkaline rocks related to subduction setting. The biotite chemistry in the acidic rocks suggests crystallization temperatures in the range of 720–750 °C. Oxygen fugacity of biotite has been buffered by the Ni-NiO buffer and the intrusion crystallized under high oxygen fugacity of −15.16 bars in the acidic rocks and –13.6 bars in the intermediate–basic rocks. The average calculated H2O fugacity of these rocks is about 3 bars. The average values of the calculated log (ƒH2O/ƒHF) of fluid in equilibrium with the chemical composition of biotite are 4.65 for the acidic and 4.2 for the intermediate–basic rocks. The average values of the calculated log (ƒH2O/ƒHCl) of fluids in equilibrium with the chemical composition of biotite are 3.81 in the acidic and 3.36 in the intermediate–basic rocks. These F and Cl values for biotites in the Kuh-e Dom intrusion are similar to those of high-Cl igneous rocks and porphyry Cu ore deposits. As the Kuh-e Dom biotites are primary, their crystallization from Cl-high magma is suggested. It seems that in the subduction zone, the release of Cl-bearing fluid from a subducted slab into the mantle, causing mantle metasomatism, plays an important role in the mineralization of the Kuh-e Dom.

Mineralogy and geochemistry of biotites from Proterozoic granitoids of western Arunachal Himalaya: Evidence of bimodal granitogeny and tectonic affinity

Felsic magmatic rocks in Kameng corridor of western Arunachal Himalaya are represented by extensively exposed Palaeoproterozoic porphyritic muscovite-biotite granite (GGn) of the Bomdila Group and small stock-like Mesoproterozoic hornblende-biotite granite (HBG) of the Salari Group. Mineralogy and chemical composition of biotites from GGn and HBG have been utilized to understand the nature and tectonic environment of their parental felsic melts. Biotites in GGn (FeOt/MgO=3.1–4.6) are Fe-biotites and have shown affinity with primary biotites co-precipitating with muscovite in a peraluminous (S-type) felsic melt of syn-collisional tectonic environment. Biotites in HBG (FeOt/MgO=1.3–2.2) are transitional between Fe and Mg biotites evolved from Fayalite-Magnetite-Quartz (FMQ) to Nickel-Nickel Oxide (NNO) buffers and are related to primary biotites co-existing with amphibole and other ferromagnesian minerals in a calc-alkaline metaluminous (I-type) felsic melt mostly formed in a subduction setting. Both GGn and HBG biotites exhibit Mg⇌Fe substitution, which is more pronounced in HBG biotites. GGn biotites exhibit 2Al⇌3Fe2+ substitution as expected in peraluminous melt, whereas 3Mg⇌2Al substitution normally expected to operate in metaluminous melt is less pronounced in HBG biotites. GGn biotites are markedly enriched in siderophyllite, and depleted in phlogopite components as compared to HBG biotites, which point to diverse genetic conditions. HBG biotites indicate oxidizing environment of the felsic melt unlike the reducing nature of the porphyritic granite (GGn).

Chemical composition of biotite from the Casino porphyry Cu–Au–Mo mineralization, Yukon, Canada: evaluation of magmatic and hydrothermal fluid chemistry

The chemical composition of biotite has been determined for the Dawson Range batholith and the Casino, porphyry-style Cu–Au–Mo occurrence, Yukon Territory, Canada. Biotite from the propylitic, phyllic and potassic alteration zones of the Casino occurrence possesses higher X Mg, Al 2O 3, SiO 2, F and Cl, and lower TiO 2, BaO and MnO concentrations than biotite outside these alteration zones. This phenomenon is similar to that recorded for biotite of other porphyry Cu deposits. However, the absolute concentrations of the oxides and halogens vary significantly among deposits. Calculated log ( fH 2O)/( fHF), ( fH 2O)/( fHCl), ( fHCl)/( fHF) ratios, determined from biotite microprobe data, indicate that hydrothermal fluids associated with potassic alteration at Casino were similar to those associated with phyllic alteration. In contrast, fluids responsible for propylitic alteration had higher log ( fH 2O)/( fHF) and less negative log ( fHF)/( fHCl) values. The log ( fH 2O)/( fHCl) and ( fHF)/( fHCl) ratios established for Casino are similar to those for other porphyry Cu deposits. However, log ( fH 2O)/( fHF) values vary greatly among porphyry deposits. This variation in log ( fH 2O)/( fHF) values may be related to the source of the magmas and/or magmatic processes (assimilation/fractional crystallization) associated with melt on its ascent through the crust prior to the exsolution of magmatic fluids that are responsible for porphyry mineralization. The biotite compositions from the Dawson Range batholith are either not consistent with the Fe–F and Mg–Cl avoidance principles or record changes in the F/Cl ratio of the fluid during crystallization of the granitic body.

Post-peak re-equilibration in a mafic gneiss from the KTB main hole: implications for the metamorphic evolution

Detailed microprobe investigations were carried out on mineral phases of a mafic garnet–biotite–hornblende and garnet–biotite gneiss from the KTB main hole. The results indicate that the complex zonation patterns of garnet porphyroblasts are mainly due to post-growth diffusional exchange, as constrained by theoretical modelling. Moreover, the chemical composition of biotite and hornblende enclosed in garnet were also changed by later diffusion and retrograde net-transfer reactions. Therefore, the garnet zonation in combination with mineral inclusions cannot be used to reconstruct the prograde metamorphic evolution or to estimate the maximum temperatures attained. However, by applying the GRISP geobarometer, minimum pressures of 8.5 kbar (at 700 °C) can be derived for the metamorphic peak, well conforming to previous estimates on the amphibolite-facies metamorphic stage of the KTB metamorphics. Mineral assemblages formed during the retrograde evolution allow to estimate P–T–X conditions of approximately 3 kbar, 450 °C and X(H2O)=0.9.

Chemical variability of Al-Ti-Fe-Mg minerals in peraluminous granitoid rocks from Central Spain

Two broad series of peraluminous granite types can be distinguished in the Central System of Spain. The first group consists of cordierite-bearing granites that are moderately peraluminous in composition (peraluminous S-type granites, PS). The second is composed of amphibole/allanite-bearing granites, weakly peraluminous in composition (peraluminous I-type, PI). These granite types evolved through complex igneous fractionation processes. Both peraluminous granite types show differences in the chemical composition of biotite and cordierite; cordierite is common in PS granites but restricted to some highly fractionated PI granites. Garnet and ilmenite cannot be used as chemical criteria for distinguishing the two series. The Al and Na content of biotite and cordierite correlate well with the granite type (PS and PI). The higher Na content in biotite (and cordierite) of PS granites is noteworthy. When plotted in a Na vs. [VI1A1 diagram biotites are located in different fields according to the peraluminosity degree of the granite type. The estimated Fe3+/(Fe3++Fe2+) ratio of biotite is higher in PI than in PS granites, although this value is very pluton-dependent. Several compositional variations of Al-Ti-Fe-Mg (ATFM) minerals are functions of the degree of fractionation or evolution of the magma, irrespectively of its peraluminosity. Other chemical features of ATFM phases, such as XFe or XMΠ, can be used as fractionation indices. Thus, the more acid the magma, the higher XFe and XMΠ in ATFM minerals. This correlation is not linear showing a rapid increase for silica values of SiO2 ≥ 74 %. Usually, XFe garnet > XFe biotite > XFe cordierite, and XMΠ ilmenite = XMΠ garnet > XMΠ cordierite > XMΠ biotite, while XFe and XMΠ of whole rock are very close to biotite values. The high increase in Mn content, more marked than in Fe, in all AFM phases in the silica-rich granites (SiO2 = 74 %), can be interpreted as a consequence of the incompatible behaviour of this element in highly evolved granites, that are sufficiently poor in Ti, Mg and Fe to prevent or diminish crystallization of ore-minerals, such as ilmenite.

Biotite from rapakivi

This paper deals with the chemical composition of biotites from rapakivi granites. For this purpose, 61 chemical analyses of biotites from composite anorthosite-rapakivi plutons in the Fennoscandian and Ukranian shields were used. Figurative points of the biotite composition were plotted on diagrams designed for biotites byFoster (1960),Winchell (1949) andVelikoslavinsky (1972). Consideration of the diagrams shows that a) the biotites from rapakivi granites have exotic composition not characteristic of other biotites from other igneous rocks, b) that they belong to the annite-siderophyllite series and c) that they crystallized at low pressures and high temperatures. Model crystallization temperatures range from 760° (early intrusive phases) down to less than 435° (late intrusive phase).

The chemical composition of biotites from anatexites and their metabasitic inclusions, Bayerischer Wald, Eastern Bavaria

The chemical composition of biotites from anatexites and their metabasitic inclusions, Bayerischer Wald, Eastern Bavaria

Chemical composition of biotite in the metamorphic and granitic rocks of Richughuta, district Palamau, Bihar (India)

Partial chemical analyses of eighteen biotite samples along with complete analyses of the respective host rocks were carried out on some metamorphic and granitic rocks of the area around Richughuta in the Palamau district of Bihar. Chemical changes in the biotites show an increase of Ti, Fe, Mn and alkali contents with decrease of Al, Mg and MgO/FeO ratio from schist to granite. The ratio MgO/FeO increases with increase in the oxidation ratio of the host rock.

Trace elements in biotites from granites and gneisses

91 biotites (53 from granites, 35 from highly metamorphic gneisses, 3 from redwitzites) were separated and analyzed for Fe, Mn, Zn, Cl, Sn, Ni, Co, Or, Cu, V, Mo, Pb. Biotites from gneisses contain much more Ni, Co, Cr, V but less Fe, Mn, Zn than those from granites. However, the distinction between biotites from gneisses and from granites on the basis of these elements is not certain. If a gneiss undergoes anatexis, the contents of Ni, Co, Cr, V, Zn and Sn of the preexistent biotite fractionate: Zn, Sn and Pe enter the anatectic melt readily while Ni, Co, Cr and V concentrate in the remaining matter (restite). Ni, Co, Cr and V are strongly positively correlated with one another but negatively with Fe and Zn, the latter being positively correlated with Pe. The chemical composition of biotites from granites depends not only on a potential degree of secondary decomposition into chlorite and muscovite but much more on the percentage of biotite in the rock: The more biotite, the higher the content of Ni, Co, Cr, V and the lower Fe, Zn and Sn in the biotite. Thus, it is possible to distinguish between normal and abnormal concentrations of an element in a biotite and in a rock. This might be useful in geochemical prospecting. Abnormal high concentrations of Sn and Zn were found in biotites from some granites which are connected with mineralizations of these elements. It is impossible hitherto to gain informations about the history and the parental material of a granitic magma from the minor elements in the rock or the biotite because their concentrations depend on how much biotite could be incorporated by the melt. The distribution coefficient of Cl between the lattice of 4 biotites and their fluid inclusions was determined to be 0,08.

Chemical composition of biotites as a guide to ascertain the origin of granites

Biotites occurring in igneous and metamorphic-metasomatic rocks have been critically studied. The study reveals a marked difference between the chemical composition of biotites from igneous rocks on one hand and those from metamorphic-metasomatic ones on the other. It is concluded that the chemical composition of a biotite reflects the environment of its formation as well as that of the rock containing it. The most frequently occurring ferromagnesian mineral in granites is biotite. As such it is thought that by processing the chemical data as suggested in this paper it should be possible to distinguish between granites formed by more than one mode of origin.

Geochemistry of Minerals from Granite. II. Chemical Composition of Biotite from Granite and Granite Adjacent to Pegmatite

Geochemistry of Minerals from Granite. II. Chemical Composition of Biotite from Granite and Granite Adjacent to Pegmatite