Characteristics of tourmalines from Nanping granitic pegmatites in Fujian Province
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Tourmaline is a kind of accessory mineral widely distributed in acidic igneous rocks and metasomatites,and the most widely distributed Fe-Mg-Li tourmaline includes several end members like dravite,schorl and elbaite as well as a series of transitional minerals.In the same area,the same rock is often characterized by the development of the same type of tourmaline.Nevertheless,the end members and transitional minerals are well developed in Nanping pegmatite and altered wall rocks,except for elbaite.Such a phenomenon is very rarely observed in the same type of granitic pegmatites both in China and abroad.In Nanping,tourmalines with different components are distributed in different types of granitic pegmatites and different differentiation evolution stage of the pegmatite.The schorl (Fe tourmaline) is widely distributed in the four types of pegmatites as well as their altered wall rocks.In the rare metal mineralized pegmatite,the tourmaline can be divided into two types,i.e.,the middle member of the Fe-Li series (Li-Fe tourmaline) and the members of the Mg-Fe series comprising dravite and Mg-Fe tourmaline.The two types of tourmalines are apparently different in the formation age and the paragenetic association of minerals.Based on detailed descriptions of physical-optical characteristics,chemical components,X-ray powder diffractions,infrared absorption spectra and thermal spectra of tourmalines from Nanping pegmatites,this paper discusses the evolution regularity and formation environment of these tourmalines.The schorl in Type Ⅰ pegmatite was formed under the conditions of upper hydraulic pressure,low content of rare elements and absolute domination of crystallization.In contrast,the schorl in Type Ⅱ-Ⅲ pegmatites was formed in a relatively low depth suggesting the beginning of the transformation to the open system,with rare elements concentrated in the pegmatite melt-solution in such an environment.The Li-Fe tourmaline in Type Ⅳ pegmatite was formed in a relatively open system with wide metasomatism,with its formation depth apparently shallower than that of Type Ⅰ-Ⅲ pegmatites.In such a formation environment,elements such as Li,Rb,Cs,Nb,Ta and Sn are highly concentrated in the pegmatite melt-solution.The formation environment of dravite in Type Ⅳ pegmatite was no longer belonging to endogenic pegmatite mineralization,but this mineral inherited some characteristics of Li-Fe tourmalines in Type Ⅳ pegmatite in content of elements such as Li.Its modes of occurrence are very rarely seen in pegmatite areas both in China and abroad.The formation sequence of tourmalines in Nanping pegmatites and wall rocks is on the whole in order of black Fe-tourmaline→yellowish green Li-Fe tourmaline→yellowish brown Mg-Fe tourmaline→grayish blue dravite.This sequence will surely play an important indicating role in researches on the formation environment and evolution of the Nanping pegmatiteKeywords:
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Abstract The alteration zone around pegmatites can be used as a direct tool to trace the property of pegmatite-derived fluids. In the present study, EPMA, LA-ICP-MS, and MC-ICP-MS were used to analyze major elements, trace elements and boron isotope compositions of tourmaline from Qinghe barren pegmatite, NW China. Most tourmalines from the pegmatite are schorl, while the remaining tourmalines from the pegmatite, the contact zone, the altered wall rock and the unaltered wall rock are dravite. All tourmalines follow the exchange vector (Fe + Mg) (Al + X vac ) −1 , indicating enriched Fe and Mg. The Fe 3+ Al −1 exchange vector and increase of V/Sc in the late stage suggest sudden destruction of the pegmatite system. The δ 11 B indicates that a small scale fluid exsolution occurred in the late stage. Compared with other fertile pegmatites around the world, Qinghe pegmatite has the most negative δ 11 B and lower Li content, indicating that both the source and evolution process have an impact thereon.
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Research Article| September 30, 2019 Titanium in tourmalines from granitic pegmatites and their exocontacts Petr Gadas; Petr Gadas Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Search for other works by this author on: GSW Google Scholar Milan Novák; Milan Novák Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Search for other works by this author on: GSW Google Scholar Radek Škoda; Radek Škoda Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Search for other works by this author on: GSW Google Scholar Jan Cempírek; Jan Cempírek Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Search for other works by this author on: GSW Google Scholar Adam Zachař; Adam Zachař Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Search for other works by this author on: GSW Google Scholar Tomáš Flégr; Tomáš Flégr Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Search for other works by this author on: GSW Google Scholar Federico Pezzotta Federico Pezzotta Mineralogy Department, Museo di storia Naturale, Corso Venezia 55, Milan I-20121, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Petr Gadas Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Milan Novák Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Radek Škoda Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Jan Cempírek Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Adam Zachař Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Tomáš Flégr Department of Geological Sciences, Masaryk University Brno, Kotlářská 2, Brno ZIP 61137, Czech Republic Federico Pezzotta Mineralogy Department, Museo di storia Naturale, Corso Venezia 55, Milan I-20121, Italy Publisher: Mineralogical Association of Canada First Online: 07 Oct 2019 Online Issn: 1499-1276 Print Issn: 0008-4476 © 2019 Mineralogical Association of Canada The Canadian Mineralogist (2019) 57 (5): 745–747. https://doi.org/10.3749/canmin.AB00011 Article history First Online: 07 Oct 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Petr Gadas, Milan Novák, Radek Škoda, Jan Cempírek, Adam Zachař, Tomáš Flégr, Federico Pezzotta; Titanium in tourmalines from granitic pegmatites and their exocontacts. The Canadian Mineralogist 2019;; 57 (5): 745–747. doi: https://doi.org/10.3749/canmin.AB00011 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Mineralogist Search Advanced Search Titanium is a typical trace to minor cation in tourmalines from granitic pegmatites. Concentrations up to 2 wt.% TiO2 (∼0.25 apfu Ti) were locally found in tourmalines from primitive pegmatites and in black tourmalines from outer pegmatite units of more evolved pegmatites, whereas Fe-poor and Li-enriched tourmalines from inner units of complex (Li) pegmatites are typically Ti-free (Selway et al. 1999). We found Ti-rich tourmalines in three distinct paragenetic types: (i) Ca-enriched schorl-dravite associated with Kfs + Pl/Ab + Qz ± Ttn, Bt from several localities of intragranitic NYF pegmatites of the Třebíč Pluton, Moldanubian Zone,... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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The Xuebaoding W-Sn-Be deposit located in the Songpan-Ganze Orogenic Belt (Sichuan Province, China) is a hydrothermal deposit with less developed pegmatite stage. The deposit is famous for the coarse-grained crystals of beryl, scheelite, cassiterite, apatite, fluorite, muscovite, and others. The orebody is spatially associated with the Pankou and Pukouling granites hosted in Triassic marbles and schists. The highly fractionated granites are peraluminous, Li-Rb-Cs-rich, and related to W-Sn-Be mineralization. The mineralization can chiefly be classified based on the wallrock and mineral assemblages as muscovite and beryl in granite (Zone I), then beryl, cassiterite and muscovite at the transition from granite to triassic strata (Zone II), and the main mineralized veins composed of an assemblage of beryl, cassiterite, scheelite, fluorite, and apatite hosted in metasedimentary rock units of marble and schist (Zone III). Due to the stability of tourmaline over a wide range of temperature and pressure conditions, its compositional variability can reflect the evolution of the ore-forming fluids. Tourmaline is an important gangue mineral in the Xuebaoding deposit and occurs in the late-magmatic to early-hydrothermal stage, and can thus be used as a proxy for the fluid evolution. Three types of tourmalines can be distinguished: tourmaline disseminations within the granite (type I), tourmaline clusters at the margin of the granite (type II), and tourmalines occurring in the mineralized veins (type III). Based on their chemical composition, both type I and II tourmalines belong to the alkali group and to the dravite-schorl solid solution. Type III tourmaline which is higher in X-site vacancy corresponds to foitite and schorl. It is proposed that the weakly zoned type I tourmalines result from an immiscible boron-rich aqueous fluid in the latest stage of granite crystallization, that the type II tourmalines showing skeletal texture directly formed from the undercooled melts, and that type III tourmalines occurring in the mineralized veins formed directly from the magmatic hydrothermal fluids. Both type I and type II tourmalines show similar compositional variations reflecting the highly fractionated Pankou and Pukouling granites. The higher Ca, Mg, and Fe contents of type III tourmaline are buffered by the composition of the metasedimentary host rocks. The decreasing Na content (<0.8 atoms per formula unit (apfu)) and increasing Fe3+/Fe2+ ratios of all tourmaline samples suggest that they precipitated from oxidized, low-salinity fluids. The decreasing trend of Al content from type I (5.60–6.36 apfu) and type II (6.01–6.43 apfu) to type III (5.58–5.87 apfu) tourmalines, and associated decrease in Na, may be caused by the crystallization of albite and muscovite. The combined petrographic, mineralogical, and chemical characteristics of the three types of tourmalines thus reflect the late-magmatic to early-hydrothermal evolution of the ore-forming fluids, and could be used as a geochemical fingerprint for prospecting W-Sn-Be mineralization in the Xuebaoding district.
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Various species of the tourmaline-group are common accessory minerals in the Boqueirao, Capoeira and Quintos Li–Be–Ta–Nb-bearing, LCT-family, rare-element-class granitic pegmatites from the Borborema Pegmatite Province (BPP), northeastern Brazil. Tourmaline from the border and wall zones of the pegmatites is enriched in Mg and Fe, crystallizing as Mg-rich members of the dravite–schorl solid-solution series. Tourmaline from the intermediate zone is richer in Fe and Al+Li, crystallizing as schorl. The Fe–Mg-free and Li–Al-rich elbaite is typical of the transition between the intermediate zone and the quartz core, and of replacement pockets. The bright turquoise blue elbaite known as “Paraiba tourmaline” is produced in the Capoeira 2 and Quintos pegmatites and is distinguished by high Cu contents, up to 1.07 wt.% CuO. In other occurrences of the “Paraiba tourmaline” in the BPP, up to 2.37 wt.% CuO were reported. Differences in the geochemical evolution trend of tourmalines among the pegmatite bodies investigated (vacancy at the X site, Fe, Mg, Zn, Li and F contents), suggest that they reached variable degrees of fractionation. This observation agrees with chemical data on white mica, feldspar, garnet and gahnite, and therefore permits the use of tourmaline composition as an indicator of the degree of evolution of the hosting pegmatite. According to these data,”Paraiba tourmaline”-producing pegmatites share the following characteristics: 1) they are the most evolved pegmatites so far known in the BPP; 2) they are hosted by quartzites or metaconglomerates (iron-poor host rocks); 3) they exhibit comb-textured dravite in the border zone (early saturation in tourmaline) and 4) the elbaitic “Paraiba tourmaline” is found in the most evolved parts of the pegmatites.
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In the Larsemann Hills, Prydz Bay, East Antarctica, granulite-facies metasedimentary units containing tourmaline, prismatine and grandidierite are cut by three generations (D 2 , D 3 and D 4 ) of granitic pegmatites, several of which are also unusually enriched in B-rich phases, including tourmaline (schorl – dravite – foitite solid solutions), prismatine, grandidierite, werdingite, boralsilite and dumortierite. Tourmaline can be used to gain information about the crystallization history of the pegmatites. Six microstructural varieties of tourmaline have been recognized: 1) primary tourmaline in a graphic intergrowth with quartz, 2) tourmaline overgrowths on tourmaline in the graphic intergrowth, 3) prisms of tourmaline with oscillatory zoning, 4) tourmaline that has replaced boralsilite, 5) tourmaline that has replaced prismatine, and 6) chaotically zoned tourmaline. Tourmaline compositions evolved as crystallization proceeded in the D 2 and D 3 pegmatites (considered together) and in the D 4 pegmatites, resulting in an increase in X -site vacancy, a decrease in Ti and F contents, an increase in Al at the ( Y + Z ) sites, and a decrease in the ratio Mg/(Mg + Fe). The first three changes are consistent with decreasing temperature. However, oscillatory zoning is characteristic of open systems, where there had been a mixing from different chemical sources; we consider it more likely that X -site vacancy and F content varied as a function of fluid composition rather than temperature per se. On the basis of the compositional variation and microstructural relations and comparison with the retrograde path inferred for the host rocks, we suggest that the pegmatites evolved as temperatures decreased from 700–750°C, 3–4.5 kbar when the graphic tourmaline + quartz crystallized, through 600–700°C, 3–4 kbar, the stability range considered appropriate for boralsilite, to below 600°C at~3 kbar for secondary tourmaline and dumortierite, conditions consistent with the presence of secondary andalusite.
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Dominant primary solidus and minor subsolidus tourmalines from
a variety of granitic pegmatites enclosed in serpentinites of
the Moldanubian Zone, Czech Republic were examined, mainly by
electron probe micro-analyser, to reveal the degree of external
Mg(Ca)-contamination from their host rocks. The rocks include:
(i) homogeneous to slightly hetero- geneous nests of
plagioclase-tourmaline rocks (group A) of anatectic or
metasomatic origin, (ii) subhomogeneous to simply zoned barren
pegmatite dikes (group B), and (iii) Li-bear- ing zoned
pegmatite dikes of rare-element class (group C). The
plagioclase-tourmaline rocks (group A) show spatial relation to
pegmatites of the group B. Mostly black primary tourmalines
(dravite, oxy-dravite, uvite, schorl, oxy-schorl, fluor-schorl)
show extensive Mg- and Ca-contamination (group A), moder- ate
Mg- and locally minor Ca-contamination (group B plus the
locality Věžna I of the group C) and weak Mg-contamination of
the tourmaline solely from outermost pegmatite units (group C);
tourmalines from internal units of the pegmatites are typically
Mg-free.
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Tourmaline can be found as an accessory mineral in a variety of rocks including leucogranite, pegmatite, quartz veins, and metamorphiccountry rocks in Hajiabad-Dehgah area in SE of Boroujerd city. Tourmaline in pegmatites is coarse-grained, subhedral to euhedral, anddisplays strong to moderate pleochroic blue rimmed by olive green. In contrast, tourmalines from leucogranite, quartz-veins, and hornfelsschist are very fine- to medium-grained, mainly subhedral to euhedral and in some cases zoned. They are strongly pleochroic withgenerally bluish green to brownish olive colors. The replacement of some feldspar grains by tourmaline forming skeletal texture is alsocommon in leucogranite. The tourmaline in pegmatite is Fe-rich schorl (Fe/Fe + Mg = 0.86–0.95), whereas those in leucogranite, quartzveins and hornfels schist are of schorl-dravite composition (Fe/(Fe +Mg) = 0.31–0.61). Tourmalines in all these rock types are aluminous,alkali-rich, with Na being the dominant alkali element present, and they have small amounts of X-site vacancy. However, the distinctdissimilarity is the Zn contents of pegmatite schorl tourmaline (on average 0.02 apfu), which are noticeably lower than those of tourmalinesof schorl-dravite composition (on average 0.13 apfu). The dominant variability in composition of the studied tourmalines seems to becontrolled mainly by the alkali-deficient AlOMg-1(OH)-1 and proton-deficient □AlNa-1Mg-1 exchange substitutions. Tourmaline grains frompegmatite have the chemical features of tourmalines from Li-poor granitoids and associated pegmatites and aplites, whereas those fromleucogranite, quartz-veins and hornfels schist possess the chemical characteristics of tourmalines from Ca-poor metapelites, metapsammites,and quartz-tourmaline rocks.
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The Koktokay No. 3 pegmatite, Altai, northwestern China, is a spodumene-subtype granitic pegmatite. In this study, we report textural and chemical features of tourmaline from the altered country-rock, the contact zone, and the pegmatite. The tourmaline ill the altered country-rock, Ca- and Fe-rich dravite, shows an obvious chemical heterogeneity within individual grains. Tourmaline in the contact zone consists of two generations: zoned Ca- and Fe-rich dravite and in interstitial foitite-schorl solid solution. Tourmaline from the altered country-rock and the contact zone reflects interaction between the country rock (metagabbro) and the pegmatite-forming melt or fluids derived from it. The chemical variation of these tourmalines depends on various contributions of components from the country rock and the pegmatite. The tourmaline in the outer zones (zones I to IV) of the pegmatite is elbaite-schorl solid solution with all intermediate composition between the end members; it is generally homogeneous within individual grains. In the inner zones (zones V, VI, and VIII), the tourmaline is dominantly elbaite with rare rossmanite in zone V. Elbaite is either abruptly zoned within individual grains, or has a replacement texture. Chemically, elbaite in the inner zones has a higher proportion of X-site vacancy than elbaite-schorl in the outer zones. Chemical trends of tourmaline compositions in the spodumene-subtype Koktokay No. 3 pegmatite are generally similar to those in other pegmatite subtypes (lepidolite, petalite, and elbaite subtype). Systematic variations in the internal textures of tourmaline from the outer zones to the inner zones suggest that exsolution of fluids occurred between zone IV and zone V. The outer zones crystallized from a volatile-unsaturated pegmatite-forming magma, whereas the inner zones crystallized from a hydrothermal system. This evolution process is consistent with the London model of internal evolution of granitic pegmatites.
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Tourmaline
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Muscovite
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Pegmatite
Muscovite
Tourmaline
Spodumene
Dike
Topaz
Petrogenesis
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