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Home , Childrenite, Eosphorite, Scorzalite

WYLLIEITE REACTION CORONAS ON SCORZALITE IN DYKES - SERRA DE ARGA (PORTUGAL)

P. A. DIAS 1, C. LEAL GOMES 1, F. GUIMARÃES 2, F. HATERT 3

1 CIG-R, Univ. Minho, Portugal; [email protected]; [email protected]

2 LNEG, S. Mamede de Infesta, Portugal; [email protected]

3 Laboratory of , Univ. Liège, Belgium; [email protected] Poster Session: , and pegmatite mineralogy

ABSTRACT In the region of Serra de Arga (Northern Portugal) pegmatite dykes with approximately 50 cm thick and 2 m long, affected by Variscan deformation, contain scorzalite that is partially replaced by wyllieite reaction coronas. composition of the dykes consists of , , potassium and . Accessory include andalusite, Mn-rich , -(Fe), gahnite, uraninite, montebrasite and (Dias, 2012). Scorzalite occur as disseminated bluish to greenish single crystals up to 3 mm in size. Inclusions of muscovite, gahnite and montebrasite (?) were identified. Scorzalite often displays complex alteration patterns corresponding to the development of brownish to black Al-Fe-Mn rich products (gormanite or -?). Other breakdown products include associations of crandallite-goyazite and . Scorzalite electron-microprobe analysis showed the following average 2+ composition: (Fe 0.90Mg0.05-0.07Mn0.02Zn0.0-0.01)=0.95-1.01Al 2.0-2.1(PO4)2(OH)2. Wyllieite forms light blue corona-like overgrowths around primary scorzalite and also penetrate along fillings of the scorzalite crystals, as revealed by transmitted light microscopy and EMP study. Electron-microprobe analysis provided 2+ P2O5 = 45.5-47.2; Al2O3 = 8-8.6, MnO = 15.2-16.3, FeO = 23.5-24.6, MgO = 0.44-0.54; Na2O = 4.2-5.3 wt. %. The resulting formula, calculated on the basis of 12 O, is (Na0.64-0.79Ca0.02-0.03Mn0.30-0.39)=1.01-1.22 (Mn0.60-0.71 Fe 0.29- 2+ 3+ 3+ 0.40)=1(Fe 0.27-0.61Fe 0.34-0.67Mg0.05-0.06)=1(Al0.72-0.77Fe 0.23-0.28)=1(PO4)3. Some of these compositions correspond to wyllieite, while oxidized grains correspond to rosemaryite (Hatertet al. , 2006). Such unusual previously undescribed scorzalite breakdown was caused by post-magmatic, Na bearing fluids interacting with the pegmatite. Na could have become available by feldspar breakdown. Both albite and K-feldspar occur in the matrix and reflect distinct high phosphorous contents. K-feldspar contains up to 3.6 wt% of P2O5 and coexisting albite up to 1.98 wt%. Distribution of P between Fk and Ab (PFk/Ab ) is 1.8. Textural relationships indicate albitization of the K-feldspar. According to (Hatertet al. , 2006), wyllieite could have formed at temperatures lower than 400ºC, considering a pressure of 0.1Kbar. These estimates are within the considered field for scorzalite collapse (475-560ºC, 1-3Kbar) (Schmid-Beurmann et al., 2000).

1. GEOLOGICAL SETTING OF SERRA DE ARGA PEGMATITES 3. SCORZALITE-WYLLIEITE INTERGROWTHS

The Serra de Arga pegmatite field consists of a swarm of granite-related aplite-pegmatite sills and dykes (Leal Gomes, 1994) and earlier highly peraluminous anatectic pegmatites (Dias, 2012), mostly emplaced in metassedimentary and metavolcanosedimentary-exhalative Silurian series (Minho Central and Domo de Covas Units). The Sta. first group, developed around the Arga granite plutonite (S-type peraluminous granite, ± 318 Ma), comprises evolved Li-bearing pegmatites with a layered structure, 3 Cristina belonging to the , petalite, lepidolite and elbaite subtypes of the rare-element class; the pegmatites are mineralized with cassiterite and Nb-Ta oxides. The anatectic pegmatites consist of thin stroma and vein-like irregular bodies, derived from low-degree hydrated partial melts in conditions of intermediate P-T (2.9-4.2 kbar, 650-710 º A C). The composition is significantly enriched in muscovite and andalusite (or albite) and depleted in potassium feldspar. They are characterized by a more or less simple structure although an internal zonation is commonly observed and inward fractionation is noticeable. A classification as abyssal or muscovite types is proposed, although a remarkable feature is the occurrence of tantalian rutile, ferrocolumbite and in some of the vein deposits. Scz g g Qz g Scz

UMC SPAIN VM g g g Domo de g UMC Covas ATLANTIC OCEAN ATLANTIC Wyl a PORTUGAL VM FDC 2 Serro UMC 0.5 cm 100 μm 100μ m UMC g 1 Abr . Qz - quartz; Scz - scorzalite; Wyl - wyllieite. g UMC

Arga UMC The polished specimen is of a fine-grained portion of a pegmatite dyke from Santa Crisitina type locality (see Fig.2), consisting essentially of quartz, plagioclase, potassium feldspar and muscovite in a subhedral granular texture. granite g Scorzalite crystals ranging in size from 0.1-3mm are scattered throughout the rock and may be recognized by their deep blue color. The photomicrographs show PPL views of one scorzalite crystal surrounded by a 0.02-0.05 mm g wide rim of wyllieite. a Sto. Ovídeo granite The photomicrographs were made from a thin ATLANTIC OCEAN ATLANTIC Fk Qz Ms A B Gm/Ch C Ms D Scz section of the sample illustrated above and show G11 UMC g hole PPL, XPL and BSE views of scorzalite crystals. FDC Fk Ms Pl Qz Ms S17 Qz Ghn A-C: a section of irregularly shaped scorzalite g Pl Fk which has been replaced by gormanite or Pl(I) g a UMC Ros childrenite-eosphorite (brownish to black in PPL) Gm/Ch SERRA Mbr? Qz W12 Scz show inclusions of muscovite, gahnite (Zn0.85 Fe 0.08 DE ARGA Ms (OH) Ms Pl Qz Mn0.002 ) =0.94 Al 2.04 O 4) and montebrasite (?). The Ms Qz g Qz brownish yellow color around the margin of 200m m PPL BSE BSE PPL 200m m Bragança scorzalite is a narrow mantle of rosemaryite which is also clearly identified in the BSE view.D : another GTMZ S I M P L I F I E D G E O L O G I C A L M A P scorzalite crystal less altered to gormanite showing Wyl a Recent sedimentary deposits - Pliocenic to Quaternary Cambrian and Ordovician Autocthonous Formations E F G a deep blue absorption color and a corona of Ros wyllieite and rosemaryite (developed Porto Morais g Variscan syn- to late-tectonic granitoids Ros Ros R9 Intrusive dykes: pegmatites and hydrothermal quartz Wyl indiscriminately between scorzalite and the various CIZ Silurian Parautochthonous Formations R4 groundmass minerals). Geotectonic Units: VM Vilar de Mouros Major thrusts GTMZ Minho Central Unit (W of the Vigo-Régua shear) Orbacém Thrust Galiza-Trás-os-Montes Zone (Parautocthonous and UMC 1 S´8 Gm/Ch E-G: High magnification views of parts of the field Allochthonous Terrains). Continuous shear structures UMC Minho Central Unit (E of the Vigo-Régua shear) Ros of view shown in fig. D. In the first view (E) the CIZ Polygenic Silurian Allochthonous (?) Formations 2 Vigo-Régua Shear Zone S6 brownish yellow color of rosemaryite serve to Central Iberian Zone (Autocthonous Terrain). Scz FDC Domo de Covas Unit Dias & Leal Gomes (2013) G1 distinguish it from the wyllieite which shows a light m PPL100 m XPL blue absorption color and high relief. In the second m PPL200m m PPL 200 m BSE view (F) wyllieite appears to form an inner mantle 525000 526000 527000 528000 529000 530000 531000 D E T A I L E D G E O L O G I C A L M A P surrounded by rosemaryite. Photopgraph G shows Coura 1C sheet - revision proposal (CIG-R, 2008; Dias, 2012) Var Cra/Goy scorzalite relics and a predominant slightly more Qz Ms H I J K VARISCAN GRANITOIDS C25 hydrated and Mn-rich scorzalite blue to greenish in 63 Var 100 75 Syn- to late-tectonic biotite granites color (Scz-OH). The dark patches which are lighter

g 70 ´´1 porphyritic granodiorite Scz in the BSE view are mainly of gormanite/childrenite- 200 S23 COUTO DE OURO Syn-tectonic two mica granites 4636000 eosphorite. The narrow brown rim is of rosemaryite, gg coarse grained granite (Covas W) Qz with anomalous interference colors in the XPL view. gm 74 medium grained granite (Covas E) Qz 30 Ghn 76 g 66 2 mz medium to fine grained gneissic granite (Romarigães - Sabariz) Fk H-K: scorzalite crystals altered to aggregates of gg coarse grained granite (Arga) 70 variscite and crandallite. Scorzalite relics can be 52 80 84 PARAUTOCHTHONOUS AND ALLOCHTHONOUS UNITS 4635000 Ms m recognized and wyllieite-rosemaryite coronas are 30 200m m 100 m

3 0 Minho Central Unit - Silurian (Wenlock, Landovery) 0 62 absent. 300 PPL XPL BSE BSE 86 81 3 UMC Formigoso - metapsammopelites interstratified with black-shists, lidites, quartzites and tourmalinites Abr. Scz - scorzalite; Wyl - wyllieite; Ros - Rosemaryite, Gm/Ch - gormanite or childrenite-eosphorite; Scz (OH) - more hydrated and Mn-rich scorzalite; Cra/Goy - 82 Var Qz Ab Ms Fk Mbr Ghn CABEÇO DO MEIO DIA crandallite- goyazite; - variscite; - quartz; - albite; - muscovite; - potassium feldspar; - montebrasite; - gahnite. 30 56 UMC Sapardos a Gandrachão - metapsammopelites interstratified with 80 ampelites, quartzites and lidites

4634000 70 Domo de Covas Unit - Silurian (Landovery) 35 5 00 polygenic metapsammopelites (mica-schists and quartzphyllites) 12 84 AC 18 interstratified with quartzites, black-schists, lidites and exotic psammitic 24 60 26 18 26 400 lithologies with volcanogenic-exhalative affiliation (+), volcanogenic- 80 4. SELECTED COMPOSITIONS - ELECTRON MICROPROBE ANALYSIS 30 30 70 63 46 80 carbonated-exhalative affinity (++) and metassomatic derived products 28 (+++). 68 21 80 82 40 30 22 38 70 4633000 82 76 +++ Rib. Pombas ++ Cerdeirinha + Cumieira 38 72 20 32 70 5476 74 SCORZALITE OTHER 70 28 INTRUSIVE DYKES WYLLIEITE - ROSEMARYITE 36 20 18 84 45 60 12 51 30 56 74 10 Hydrothermal quartz veins and breccias

0 0 30 6 70 28 20 62 ANALYTICAL PROCEDURES 50 80 Peraluminous anatectic pegmatites (abyssal and rare-element Wyl Wyl Wyl Ros Ros Scz Scz Scz(OH) Grm/Ch Cra/Goy

80 400 600 50 44 72 muscovite classes?) and metamorphic segregation veins

0 (seeDias, 2012 ) 0 Arga de Cima 78 2 wt.% W7 W12 W13 R9 R4 S6 S23 S´8 G11 C25 Mineral chemical analyses were performed on 4632000 Rare-element aplite-pegmatites and pegmatites - REL-Li LCT types CUMIEIRA - 28 predominate: beryl, spodumene (after petalite), petalite, lepidolite and TiO2 0,02 - - - 0,02 - 0,008 0,0057 - representative sections using a five-channel 50 70 74 elbaite subtypes (seeLeal Gomes, 1994 ).

100 26 Al O 8,07 8,59 8,41 8,29 8,43 30,61 30,63 28,10 25,72 31,99 wavelength JEOL JXA 8500F 10 30 45 70 2 3 74 15 50 60 4484 Scorzalite bearing Sta. 10 48 78 38 microprobe, routinely operated at an accelerating 700 1 2 3 62 42 35 pegmatites Fisga Lousado Cristina FeO 24,64 23,88 23,49 23,81 24,12 19,38 19,04 21,51 22,86 1,11 1 78 84 voltage of 15 kV and a beam current intensity of 10 MnO 16,16 16,43 16,27 15,92 15,20 0,43 0,37 2,80 5,42 0,15 nA. MgO 0,52 0,47 0,51 0,54 0,44 0,57 0,80 0,42 0,24 0,008 The standards used were (K lines): Orthoclase CaO 0,22 0,28 0,34 0,28 0,35 - 0,03 0,07 0,09 7,99 (Al, K), Albite (Na), MgO (Mg), (P, Ca), 2. SCORZALITE-BEARING PEGMATITES Volastonite (Ca, Si), Fe2O3 (Fe), MnTiO3 (Mn, Ti), Na2O 4,98 5,20 5,31 4,69 4,24 0,008 - 0,04 0,21 0,01 Barite (Ba), Fluorite (F), Cr2O3 (Cr), SrTi O3 (Sr), K2O 0,02 0,02 0,00 0,01 0,03 0,061 - 0,01 0,03 0,06 Sphalerite (Zn), FeS2 (S), AsGa (As), Vanadinite Three types of scorzalite bearing pegmatites were identified: BaO 0,08 0,12 0,01 0,11 - 0,061 0,13- 0,02 0,77 (Cl), Yttrium Al Garnet (Y). ZnO - - - - 0,09 0,04 0,33 0,06 0,06 - FORMULAS N Fisga type - Thin, highly F 0,15 0,08 - 0,15 0,07 - - 0,04 - 0,35 1 deformed, fine-grained pegmatite Cl 0,01 0,00 - - - - 0,01 0,00 0,01 0,01 Wyllieite-rosemaryite veins hosted in metaquartzphyllite Cr O 0,07 - 0,02 0,06 - - 0,01 0,04 0,08 0,01 (Na0.64-0.79 Ca 0.02-0.03 Mn 0.30-0.39 ) =1.01-1.22 (Mn 0.60- and lidite layers, possibly anatectic 2 3 2+ 2+ 3+ 0.71Fe 0.29-0.40 ) =1 (Fe 0.27-0.61 Fe 0.34-0.67 Mg 0.05- 10 cm in origin. Although scorzalite is P2O5 46,56 46,30 45,93 47,18 45,46 41,16 41,7 39,15 33,4 30,26 3+ 0.06) =1 (Al 0.72-0.77 Fe 0.23-0.28 ) =1 (PO 4) 3 ; N=5. quartzphyllite disseminated across the veins, is Y2O3 - - - 0,04 0,02 -- - - more persistent along a 3 cm thick SrO 0,10 - - 0,04 0,03 - 0,006 0,03 0,03 6,97 Scorzalite border zone. Sillimanite is a 2+ widespread mineral mostly SO3 - 0,04 0,05 - - - 0,05 0,06 0,002 - (Fe0.90 Mg 0.05-0.07 Mn 0.02 Zn 0.0-0.01 ) =0.95-1.01 Al =2.0-2.1 Legend replacing scorzalite, and is related As2O5 - 0,04 - 0,04 - - -- 0,01 - (PO 42) (OH) 2 ;N=5 . Pegmatite contour 2.5 cm 1cm S2 to a late-tectonic increase of Sorzalite salband Total 101,59 101,44 100,35 101,17 98,47 92,33 93,11 92,32 88,18 79,53 Fisga Metamorphic foliation regional P conditions. (*1) - Below detection limit. BSE images in Fig. 3 (B, C, G, J and K) indicate the spots chosen to perform the analyses.

Legend Peg. contour 2 S2, S3 , L2, L3 Lousado type - Thicker (up to 1 m), 5. CO-EXISTENT - TEXTURES AND COMPOSITIONS S2 S3 Metamorphic foliations and deformed, fine-grained pegmatite 43º lineations L3 40º 53º lenses with simple structure hosted c/s The photomicrographs show the equigranular Shear structures 39 D3 in a poly-deformed micaschist. The groundmass consisting of quartz, plagioclase, Qz lenses are subconcordant and the potassium feldspar and muscovite (A ). Plagioclase Qz Fk A B C D S3 70º contact with the host rock is not Ab L2 feldspar and potassium feldspar are mostly subhedral 50º easily traced. Scorzalite occur as Qz and have slightly interdigitating boundaries. It D3/D´3 50º Qz Qz Ab N L2 millimeter disseminated grains. S3 appears that two generations of plagioclase are D2 49º 20cm Ap 53º Ms S2 (*2) 2 mm Pl1 present: small subhedral to euhedral crystals showing 50º Fk Qz Ab micaschist S3 multiple twinning (Pl1) and large subhedral crystals Fk L3 S2 30 cm most easily identified by a turbid brownish Lousado 35º 28º Ms Fk Ab Ab appearance (Ab) resulting from very small inclusions Fk Qz of mica. The strong alteration of the plagioclase (B ) is Ab the first characteristic that enables to distinguish it Sta. Cristina type - Dikes up to 50 200m m XPL 200m m XPL 200m m XPL 10m m BSE A N from potassium feldspar, recognized here by the lack cm thick, ranging from aplite (A) to A B 50 cm 3 of alteration and sometimes the presence of simple pegmatite (B), concordant to the S3 SiO2 Na2OAl2O3 K2OP2O5 MnO SrO CaO BaO Total twins (A ). Evidence for potassium feldspar dissolution 80 Sta. metamorphic foliation of the B 61,36 0,58 21,29 12,48 3,60 0,02 0,23 - 0,07 99,64 and replacement by albite + muscovite is shown inC . andalusite Cristina andalusite micaschist host. The Fk micaschist Ab 67,07 8,43 21,68 0,08 1,98 0,01 0,30 0,13 0,09 99,77 Apatite microinclusions are widely distributed within pegmatitic part display a muscovite the albite and are clearly seen in the BSE view (D ). The AB B enriched border zone followed compositions of both albite and potassium feldspar Electron microprobe analysis; Rb2 O not quantified; - below detection limit. inward by an intermediate zone are exceptionally rich in phosphorous. composed of quartz, potassium 20cm 1cm Aplitic facies feldspar, muscovite, albite and Legend scorzalite. In the core zone 1 Scorzalite Pegmatitic REFERENCES 2 Muscovite fraction facies potassium feldspar exhibits thin 3 Potassium feldspar with fractures filled with scorzalite 1 2 3 fractures filled with scorzalite. (*3) CIG-R (2008).Minutas de revisão da folha 1C – Caminha. Carta Geológica de Portugal 1/50 000. Dias, P.A.; Leal Gomes, C. (2013). Considerações sobre a natureza vulcanogénica a exalativa de algumas formações metamórficas da Serra de Arga – Minho – Portugal – consequências para a cartografia. In: Actas da 9ª Conferência anual do GGET: Geodinâmica e Tectónica global; a Importância da Cartografia Geológica, pp. 117-121. *1 and 2 - The composition of the veins is 45% quartz, 26% muscovite, 13% andalusite+sillimanite, 6% albite, accessory minerals (scorzalite, apatite, , Dias, P. A. (2012). Análise estrutural e paragenética de produtos litológicos e mineralizações de segregação metamórfica – Estudo de veios hiperaluminosos e protólitos poligénicos Silúricos da região da Serra de Arga chrysoberyl, columbite- (?) and gahnite). (Minho). Ph.D Thesis, Univ. Minho, 464 p. 3+ *3 - The composition of the aplitic facies is: 41% quartz, 7.5% muscovite, 15.2% potassium feldspar, 29.6% albite, accessory minerals (scorzalite, wyllieite, Hatert, F.; Hermann, R.; Fransolet, A.; Long, G.; Grandjean, F. (2006). A structural, infrared, and Mossbauer spectral study of rosemaryite, NaMnFe Al(PO 43) . Eur. J. Mineral., 18, 775-785. rosemaryite, crandallite group phosphates, variscite, Mn-rich fluorapatite, montebrasite, brasilianite, andalusite, columbite-Fe, gahnite, uraninite). Leal Gomes, C. (1994). Estudo estrutural e paragenético de um sistema pegmatóide granítico - O campo filoniano de Arga - Minho (Portugal). Ph.D Thesis, Univ. Minho, 695 p.