Introduction The composition of skarn's mineralizing fluids is closely related to the physicochemical conditions prevailing during the cooling and crystallization of magma. Biotite is an effective indicator for determining the physio-chemical conditions prevailing during the cooling and crystallization of magma. In this study, the Biotite composition of Sarvian Biotite quartz diorite from Urmia-Dokhtar magmatic arc was investigated to estimate the magma crystallization conditions and also to determine the petrological and metallogenic characteristics of the granitoid rocks. Materials and methods The study area is located 15 km northeast of Delijan city and in Markazi province (Figure 1). Miocene Sarvian quartzdiorite rocks are classified into three subgroups: quartzdiorite, micro quartzdiorite and Biotite quartzdiorite. In this study, 21 spots of Sarvian Biotite quartzdiorite were analyzed at the Iran Mineral Processing Research Center (Table 1). Results and discussion The Biotites of Sarvian granitoid are crystallized at a temperature of about 750 ° C, oxygen fugacity is between 10-11 and 10-13 and the pressure is about 0. 6-1. 1 kbar. The mentioned crystallization conditions indicate that the Biotite quartzdiorite rocks of Sarvian crystallized at high temperature, shallowly and under high oxygen fugacity conditions. In addition, it shows that Sarvian Biotite quartzdiorite has a high chance of mineral exploration. Placement of Sarvian Biotite quartzdiorite rocks in Cretaceous limestones and Eocene pyroclastics, crystallization at a pressure of about 1 kbar and the mentioned crystallization conditions, indicate the formation of skarns in the region. The formation of skarn iron ores in the area is a confirmatory examination that has been performed on the studies. Conclusion Emplacement of Sarvian Biotite quartzdiorite rocks are at shallow depth and crystallization at high temperature conditions. High magnesium calc-alkaline magmatic series, high oxygen fugacity and type I orogenic granites from subduction of the oceanic crust below the continental plate leads to magma which is the result of melting and mixing of crust and mantle. So it has created suitable conditions for the formation of metal skarns.

Major cations, Fe, Mg and AI, in Biotite are sensitive to magmatic processes and Biotite chemistry could be used for petrogenetic investigation of granitioids. In this research composition of Biotite from Boroujerd granitoids in Sanandaj-Sirjan Zone has been investigated in order to study its geochemical nature and petrogenesis. Separated Biotites were analyzed by WDXRF and Biotites in polished thin section were analyzed by EPMA. Samples were selected from Older granites (120 Ma) and Younger granites (60-70 Ma) after intensive petrographic examinations. Data from both techniques are in good agreement and discriminate two generation of granites clearly. Based on Mg, Mn, Fe3+, Fe2+, Ti and Al Biotites in Younger granite incorporated more Mg than those in Older granites. The main differences between Biotites in two generation of granites are amount of total Al and Fe/Fe+Mg ratio. Biotites in granodiorite and quartz diorite of Younger age are annite-phlogopite with 2.48-2.74 Al per formula unit, and Fe/Fe+Mg ratio of 0.375-0.600. Biotites from Older granites are annite-sidrophyllite with 2.76-3.69 and Fe/Fe+Mg ratio of 0.597-0.720. Composition of Biotites indicates that two generation of granites formed under different oxygen fugacity and both are calcalkaline and shows I and S characteristics respectively.

Biotite is usually formed as a rock-forming mineral in a wide range of felsic to intermediate intrusive rocks. Due to complex crystal structure of Biotite, different elements can substitute in this rock-forming mineral,therefore can record the physicochemical conditions of the source magma. Based on the chemical classification of mica, the Biotites of the igneous rocks, investigated in the Hararan area, can be placed between the poles of phlogopite and annite, and are magnesium type, which indicates their formation in high oxygen fugacity, and according to the amounts of Mg, TiO2 and FeO oxides, these Biotites are primary type. These Biotites belong to the calc-alkaline magmatic series formed in the subduction environment. Based on the chemistry of Biotites, oxygen fugacity in the source magma of Hararan granitoid is in the range of iron oxide. Geothermometry of Biotites shows that these Biotites formed at temperature ranging between 680 to 780 degrees Celsius and pressure of 2 (1-2) Kbars.

Touyeh-Darvar granitoid pluton is situated in the south of eastern Alborz zone (45Km SW of Damghan in Semnan province). This pluton has intruded into the late Paleozoic formations (including Barut and Lalun). Based on the field observations and petrographic studies, the pluton is composed of monzonites, quartz monzonite and monzodiorite. In terms of mineralogy, the Touyeh-Darvar granitoid consists of plagioclase, orthoclase, quartz, ± hornblende and ± Biotite. Accessory minerals consists of ilmenite, magnetite, zircon, apatite, titanite and pyrite. Sericite, epidote, calcite, and chlorite are considered as secondary phases. The iron-rich Biotite is the most significant mafic mineral which are situated in the alkaline and anorogenic Biotite fields. The total Al content of Biotite in granitic rocks can be a useful indicator for distinguishing between mineralized and non-mineralized granitic rocks. The presence of mineral veins from oxides and hydroxides of iron and manganese, fluorite, barite, lead and zinc in the host rock of this pluton also confirms that the Biotite composition is useful for mineralization potential study of this pluton. Applying the thermometry based on the Ti content of Biotite and barometery based on total Al content of Biotite resulted in calculating temperature ranges of 650– 730° C and pressures lower than 1Kb for stopping the exchange and final equilibrium of this mineral in the pluton.

Content of iron cations in three Biotite specimens of true trioctahedral mica were determined by Mossbauer spectroscopy, electron microprobe and wet-chemistry methods. International certified reference materials were analyzed simultaneously with micas to evaluate the accuracy of the wet-chemistry method. High precision Mossbauer spectroscopic Fe3+/Fe2+ ratios coupled with the electron microprobe iron determinations were compared with the wetchemical data. Comparisons of data show that in wet-chemistry method powdered micas dissolve more readily during acid attack than the granular micas and thus yield higher precision and accuracy.

Biotite samples from different units of Boroujerd Granitoid Complex (BGC) of the Sanandaj-Sirjan Zone, western Iran, have been analyzed by electron microprobe for major elements. Biotite analyses from three units of quartzdiorite, granodiorite and monzogranite of BGC have their own distinct non-overlapping compositional fields in the annite – siderophyllite – phlogopite – eastonite quadrilateral (ASPE), reflecting their host rock compositions. Biotite from each rock unit has an increasing trend of Al contents at almost fixed Fe/(Fe+Mg) values. In quartzdiorite it shows an approximately constant range of Fe/(Fe+Mg) with a low to moderate Al content from 2.5 to 3 atoms per formula unit (apfu). Biotite from granodiorite exhibits a fairly wide range of Al values reaching up to 3.32 apfu, at Fe/(Fe+Mg) from 0.6 to 0.7, whereas Biotite from monzogranite have a relatively narrow range of Fe/(Fe+Mg) and total Al values of limited range of 3.1 to 3.3 apfu. Biotite compositions from these two latter units considered to be derived entirely from crustal material, characterized by a remarkable increase in total Al at relatively high Fe contents. Biotite samples of quartzdiorites define a distinct and non-overlapping trend from those of granidiorites and monzogranites and hence interpreted to be derived from a parental magma with different composition. Calculation of log (XMg/XFe) ranges from -0.09 to -0.02 and most of samples from quartzdiorite fall within weakly and moderately contaminated I-type field of log (XF/XOH) versus log(XMg/XFe) diagram, whereas the other two units, containing Biotites with log(XMg/ XFe)< -0.21, classified as strongly contaminated reduced I-type. Oxygen fugacity (log ƒO2) of -15.4 to -17.5 bars and ƒH2O of 200 to 560 bars were calculated for quartzdiorite. Likewise, log (ƒO2) of –17.66 bars and water fugacity (ƒH2O) of 400 and 700 bars were also calculated for granodiorite and monzogranites respectively. In the FeO*–MgO–Al2O3 Biotite discrimination diagram, Biotite compositions from BGC are distributed between the calc-alkaline and peraluminous fields, i.e., Biotite from the qaurtzdioritic rocks fall principally in the calc-alkaline field, whereas those from the granodioritic and monzogranitic units plot almost exclusively in the peraluminous field consistent with their host rock nature.

The Youseflo pluton, a part of Ahar-Arasbaran magmatic belt, is located in south east of Ahar city, north-east of East Azarbaiejan Province of Iran. The constituents of this pluton are mainly quartz monzonite, granodiorite and granite, nevertheless, the major studied rock is granodiorite. The pluton mineralogically includes quartz, plagioclase, Biotite, amphibole, K-feldspar, chlorite, zircon, sphene, apatite and opaque minerals. Biotites, as a significant ferromagnesian mineral in Youseflo pluton, are Mg-rich, Cl-poor all of which are primary type. Considering Fe/ (Fe+Mg) (from 0. 37 to 0. 43) and Al IV (average 2. 32 apfu), minerals are classified as Biotite between Annite-siderophyllit endmembers. The study of Biotites’ mineral chemistry indicates that the calculated pressure based on total Al content in Biotites varies from 0. 19 to 0. 89 kb which is indicative of a shallow depth emplacement. Crystallization temperature of Biotites based on Ti content and Ti/Fe+2 ratio suggests an average temperature of 749 oC. According to MgO, Al2O3, FeO in Biotites, magmatic series of the host rocks display calc-alkaline orogenic nature. The study of Biotites shows fairly high oxygen fugacities (ranged from10-10 to 10-12 bars) and oxidizing conditions. Consequently, the Youseflo pluton is classified as the magnetite series granitoids. The Yousflo pluton is an I-type granite, originated from a mixed mantle-crust source.

Several studies have been conducted to investigate the composition of micas (especially Biotite) with the magmatic suites of the host rock (especially granitoid), thus to understand the tectonic environment of the host rock. This study deals with the issue of what compositional trends or elemental correlations exist in igneous micas when a large dataset with a given tectonic environment is used. In this regard, variations in the chemical composition of Biotite, phlogopite, and muscovite from three tectonic environments were investigated, regardless of the composition of their host rock. Enrichment of Fe or Mg in micas, such as Mg-rich Biotite or Fe-rich phlogopite, can make us wrong in determining whether a mineral is primary or secondary based solely on chemical composition. The negative and good correlation between FeO and MgO caused Biotites and phlogopites of all three tectonic environments to follow the trend of the calc-alkaline orogenic suites of Abdel-Rahman's classification. Considering the excellent and negative correlation between Al and Mg in muscovite, the substitution of 2Mg2+ = 3Al3+ is significant in this mineral. The data distribution shows that Biotites and phlogopites belonging to rift and convergent environments can be divided into Al-rich and Al-poor groups or Mg-rich and Mg-poor groups.

Compositions of Biotite from three different rock types of Mashhad granitoids, i. e., granodiorite, monzogranite and leucogranite in NE of Iran have been documented by electron microprobe and wet chemistry for Fe3+ and Fe2+ Mashhad granitoids have been geochronologically and petrologically grouped into G1 and G2 phases. Microprobe data show that the total Fe contents in Biotite from G2 leucogranite are higher than those in Biotite from G1 granites. In addition, the oxidation state of iron determined by wet chemistry shows that Fe3+/(Fe2+ + Fe3+) ratio in Biotite from G2 leucogranite is 0.10 indicating relatively reducing whereas, in G1 ones is 0.18 and 0.23 suggesting more oxidizing conditions. The most outstanding compositional characteristics of Mashhad Biotite are differences in total Al contents and Fe/(Fe+Mg) ratios. In the annite-siderophylite-phlogopiteeastonite (ASPE) quadrilateral, represented based on the above parameters, Biotite samples from G1 and G2 granites define two distinct and non-overlapping trends. Each trend is characterized by a pronounced trend of increasing total Al at relatively narrow Fe/(Fe+Mg) values. The total Al contents of G1 Biotite are in the range of 2.8 to 3.1, whereas, in G2, 3.3 to 3.6 (apfu). Fe/(Fe+Mg) values of G1 Biotite are in the range of 0.52 to 0.59 which is considerably lower than those from G2 Biotite, 0.67 to 0.72. The trend of increasing Al contents at constant Fe/(Fe+Mg) is relatively common and observed in Biotite from several locations worldwide and attributed to considerable contributions from aluminous supracrustal material, either by assimilation or anatexis.