Petrography and Mineral Chemistry of Tourmaline in Molla Taleb Ganitoid, Northeast of Aligudarz (Lorestan Province)
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Abstract:
Molla Taleb pegmatites (northeast of Aligudarz) are located in the western part of the metamorphic-igneous Sanandaj-Sirjan Zone (SSZ). Slates and schists along with siliceous veins and veinlet and black Hornfels, as well as metamorphic sandstones are among the oldest deposits of this area. The most important geological event in this area is the development and intrusion of granitoid masses into schists of the Molla Taleb area during the Middle Jurassic. The rocks of the study area are in the range of gabbro, diorite, granodiorite, and granite. Granites are in the range of type-I granites. Most specimens are calc-alkaline and mainly contain peraluminous. Microprobe electron analysis of tourmalines present in pegmatites, tourmaline- aplite-pegmatite veins, nodular tourmalines, and quartz-tourmaline veins shows that all tourmalines are in the Schorl region and the range of alkaline tourmalines. These tourmalines with FeO / FeO + MgO ratios between 0.6 and 0.8 are in the range of magmatic-hydrothermal tourmalines and more than 0.8 in the magmatic range. Therefore, the studied tourmalines are dependent on granite environments and are formed by a hydrothermal fluid of magmatic origin.Keywords:
Pegmatite
Tourmaline
Hornfels
Diorite
SLATES
Petrogenesis
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Tourmaline minerals are a main petrogenetic tool because of their refractory nature, chemical variability, and extensive occurrence in various geological settings. The Middle-Jurassic Boroujerd igneous rocks are one of the largest bodies that located in the middle part in the Sanandaj-Sirjan Magmatic Arc (SSMA) that introduced into regional metamorphic rocks. They are mostly composed of granitoids (granodiorite, quartz-diorite, and monzogranite) and contain apatite, zircon and tourmaline as abounadant accessory minerals. Tourmalines occur in varying types of mineral assemblages, chemical compositions and individual forms including tourmalinite, quartz-tourmaline vein, as accessory mineral in the more evolved granitoids, and schists. Tourmaline crystal sizes in these rocks varies from very fine to coarse-grained. The colour is brown to black and some crystals displaying a finescale chemical zonation. Tourmaline crystals commonly exhibit cellular features. Based on electron probe microanalysis (EPMA) analyses, schorl is the most abundant type of tourmaline in granitoids but foitite and dravite are common compositions in the pegmatite and schist, respectively. Presence of several tourmaline generations and their compositional trend may indicate time-varying relatively acidic boron-bearing fluids and reflects an anatexic melts influence in their crystallization.
Tourmaline
Pegmatite
Diorite
Metasomatism
Electron probe microanalysis
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Hornfels
Actinolite
Pyroxene
Grossular
Metasomatism
Titanite
Almandine
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Leucogranite
Tourmaline
Pegmatite
Muscovite
Diorite
Greisen
Titanite
Alkali feldspar
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The granitoids of the Dipilto Batholith in northern Nicaragua range in composition from amphibole-biotite tonalite to cordierite-biotite and biotite granite.The petrographic and geochemical features indicate hybrid origin for the metaluminous granodiorite and tonalite (El Paraiso Suite).Dominant peraluminous granites (leucogranite dykes, Yumpali and La Piedra suites) represent a typical product of fractional crystallization of crust-derived melts.Tourmaline occurs as rare mineral in peraluminous granites of the Yumpali Suite (randomly distributed grains and quartztourmaline nodules), but is common in the younger leucogranite, pegmatite dykes and hydrothermal veins.Chemical variations (mainly X Fe and F) in tourmaline as well as in biotite are consistent with magmatic differentiation processes in granites and pegmatites.The presence of quartz-tourmaline hydrothermal veins indicates involvement of B-rich post--magmatic hydrothermal fluids at the final stage of the Dipilto Batholith evolution.Tourmaline chemistry evolved from Mg-rich schorl in peraluminous granites, to F-rich schorl-foitite in the hydrothermal veins.This evolutionary trend is typical of F-poor granite-pegmatite systems.
Batholith
Tourmaline
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Pegmatite
Hornblende
Quartz monzonite
Allanite
Alkali feldspar
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The Mata Azul pegmatitic field, Tocantins/Goiás, central Brazil: geology, genesis and mineralization
In Goiás and Tocantins States, Central Brazil, several granitic pegmatites were characterized and grouped for the first time. These pegmatites had been intensely explored by hand in the past, producing mainly gemstone varieties of tourmaline and beryl. Barren, beryl- and tourmaline-bearing pegmatites occur across an area of 2,000 km2 where they intrude regional metasedimentary rocks and peraluminous granites. K-feldspar (mostly altered to kaolin), quartz and mica (mainly muscovite) are the major minerals. The main accessory minerals are beryl, tourmaline, garnet, albite, Fe-Mn phosphate aggregates, and trilithionite. The paragneiss surrounding the barren pegmatites was affected by thermal metamorphism and later hydrothermal alteration, producing Ca-silicates, Ti-Nb-Y oxides and sulfides. Leucogranites of the Mata Azul Suite are peraluminous and syn- to post-orogenic with geochemical characteristics of the LCT granite-pegmatite group. LA-ICP-MS U-Pb geochronology in monazite yields an age of 519 ± 2.8 Ma. Additionally, U-Th-Pb chemical dating of uraninite reveals a maximum age between 500 and 560 Ma. These ages, the field relationships, the mineralogy and the geochemical data suggest that the granites of the Mata Azul Suite are the probable sources of the studied pegmatites. The mineral associations and the mineral chemistry are used to define the degree of fractionation of the pegmatites. We propose that the group of studied pegmatites represents a pegmatitic field, called the Mata Azul Suite Pegmatitic Field.
Pegmatite
Tourmaline
Muscovite
Uraninite
Geochronology
Columbite
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Tourmaline
Pegmatite
Stockwork
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The Seixoso-Vieiros Rare Element Pegmatite fined by Farias et al (1987). The Seixoso-Vieiros pegmatite field is known for containing numerous granitic pegmatite-aplite veins (Seixoso and Vieiros pegmatites). The area is bounded at the north by the Variscan Celorico de Basto granite massif. On the SE it is bounded by the syn-tectonic Felgueiras granodiorite. Several pegmatites outcrop within cordierite-andalusite isograde Silurian schists. The field is also known for mining of cassiterite and columbite-tantalite in the last century (Maijer, 1965). In the Seixoso area, an unusual heterogeneous granitic intrusion outcrops as two main apices in Seixoso and Outeiro as granites cupolas (Lima et al., 2009). These rocks show a typical granitic mineral assemblage and exhibit a textural variation from biotite-bearing, at depth, to two mica, or muscovite tourmaline, near the apex roof (Helal et al., 1993). The Seixoso granite is described as a fine to medium-grain leucogranite, with biotite and muscovite, strongly altered with albitization and greisenization close to the contact zones. The Outeiro granite is layered and shows pegmatitic segregations. In the latter, Li-bearing minerals, such as petalite and spodumene, have been observed. In addition, minerals from the amblygonite-montebrasite series have also been noted within the granitic mineral assemblage (Lima et al., 2009). Other notable accessory minerals include: beryl, chrysoberyl, tourmaline and sekaninaite, and others. In the Vieiros area, the granitic aplite-pegmatite veins mainly cross-cut schists of Silurian age within the andalusite isograde. A dozen N-S to NE-SW-trending Sn-bearing granitic aplite-pegmatite veins outcrop in the area. They present a rich mineralogy: quartz, K-feldspar, albite, muscovite, petalite, spodumene, amblygonite-montebrasite, cassiterite, columbite-tantalite, tourmaline, and many different sulfides. An albite type pegmatite is exposed in the Vieiros mine and measures 300 meters in length, an average 5 meters in width, and is subvertical, striking E-W, and dips N25°. During this study (Melleton et al., submitted), columbite and tantalite grains were dated by the U-Pb method, using the LA-SF-ICP-MS technique, from the Outeiro mine granite and the Vieiros mine albite type pegmatite. Results of dating (figure 1) from the Vieiros pegmatite yield an age of emplacement of 301 ± 4 Ma (12 analyses). Ages obtained from the Outeiro granite yield 301 ± 5 Ma (9 analyses) and 316 ± 9 Ma (from two analyses located in cores of two different single grains, and with significantly low concentrations of U). This latter age is interpreted as age of crystallization of the Outeiro granite, and the younger age corresponds to post-emplacement disturbance related to the Vieiros-Seixoso pegmatite emplacement, located in the surrounding area. Located hundred meters from the Outeiro mine granite, the Seixoso pegmatite shows similar structural and mineralogical features as the Vieiros pegmatite. Therefore, emplacement of these pegmatites and associated fluids could have been the cause of the Outeiro Mine columbite-tantalite rim age. The Celorico de Basto late-D3 granite in the north and the Felgueiras syn-D3 granodiorite in the south had not been directly dated. However, Dias et al. (1998) dated equivalent granitoids and obtained ages around 305-308 Ma for the late D3 granite and early ages ranging between 310 and 320 Ma for the syn-D3 granites. Thus, there is not a temporal link between the Vieiros pegmatite emplacement and the surrounding granites of this field. New samples are being collected in order to understand the different mineralizing events and relationships between other pegmatites and surrounding granitic cupolas of the studied area.
Pegmatite
Andalusite
Tourmaline
Cassiterite
Muscovite
Leucogranite
Sillimanite
Columbite
Massif
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Hornfels
Tourmaline
Pegmatite
EMPA
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Abstract Pegmatites of the Fregeneda area, Salamanca, Spain, show a zonal distribution, from barren to enrichment in Li, Sn, Rb, Nb>Ta, B and P. They intrude pre-Ordovician metasediments which were metamorphosed to sillimanite-zone conditions near the Lumbrales granite. Field, mineralogical and petrographic data show the following zonal sequence from the granite outward: (1) barren pegmatites (pegmatites T1, T2, T3 and T4) with quartz, K-feldspar > albite, muscovite, tourmaline ± andalusite ± garnet; (2) intermediate pegmatites (types T5 and T6), characterized by the occurrence of beryl and Fe-Mn-Li phosphates; and (3) fertile pegmatites (dykes T7 and T8), with lepidolite, cassiterite, columbite, albite > K-feldspar, montebrasite and spodumene. Tourmaline from different pegmatites shows significant compositional variations. Trace element variations in mica and K-feldspar suggest that the origin of the different pegmatitic bodies may be explained by three different paths of fractional crystallization of melts generated by partial melting of quartzo-feldspathic rocks.
Pegmatite
Tourmaline
Cassiterite
Spodumene
Muscovite
Sillimanite
Andalusite
Petrogenesis
Topaz
Anatexis
Fractional crystallization (geology)
Columbite
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Citations (89)