745

The Canadian Mineralo gist Vol. 34, pp.745-768 (1996)

GEOCHEMISTRYOF CASSITERITEAND ITS INCLUSIONS AND EXSOLUTIONPRODUCTS FROMTIN AND TUNGSTENDEPOSITS IN PORTUGAL

ANA M.R. NEIVA Departmentof EarthSciences, University of Coimbra,3000 Coimbra, Portugal

AxSTRACT

Euhedral cassiteritefrom Sn-bearinggranitic pegmatitesand stanniferousquartz veins in Portugal shows sequencesof altematingparallel darker and lighter zones.The darkerzones are strongly pleochroic,oscillatorily zoned,and have more Nb, Ta and Fe than the lighter zones,which are nearly pure SnO2.Darker zonesmainly show exsolvedcolumbite- and ixiolite, rarely ferrotapiolite, and locally, ilmenite, which are less abundantin lighter zones. Columbite-tantalite inclusions were infrequently found; they generally have combined Ti, Sn and W contents lower than those of exsolved columbite-tantalite.Compositional features differentiate the columbite-tantaliteminerals and varietiesof ixiolite. from W-Sn-bearing quartz veins is generally zoned; darker zones are commonly homogeneousand slightly pleochroic,but chemically similar to lighter zones.This cassiteritehas mainly inclusionsof rutile and locally of ilmenite. Exsolvedrutile has similar or higher combinedM, Ta, Sn, W, Fe, Mn contentsthan included rutile. Euhedralto subhedralgrains of massive cassiteritefrom a volcanogenicdeposit are slightly pleochroic, and their color deepensfrom yellow to dark brown with increasingFe content;such cassiterite is devoidof inclusionsand products of exsolution.

Keyvords: cassiterite,columbite-tantalite minerals, , ixiolite, rutile, inclusions,exsolution, Portugal.

: SolwtanB

Des cristaux de cassit6riteidiomorphes provenant de massifsde pegmatitegranitique et de veinesde quartz stannifbresau Pornrgalmontrent une alternancede zonesde croissanceparalldles claires et plus sombres.Les zonessombres sont fortement plfochroiques,zon6es de fagon oscillatoire,et contiennentplus de Nb, Ta et Fe que les zonesclaires, qui ont une composition voisine du p61eSnO2. f€s zonessombres contiennent des produits d'exsolution, surtout columbite-tantalite et ixiolite, rarement ferrotapiolite et rutile, et, localementseulement, ilm6nite, qui sont moins abondantsdans les zonesclaires. l,es inclusionsde columbite-tantalitene sont pas courantesien g6n6ral,elles contiennentdes teneursen Ti + Sn + W plus faibles que dansles domainesde columbite-tantaliteexsolv6e. Des critbresgdochimiques diff6rencient les min6rauxdu groupecolumbite-tantalite desvari6tds d'ixiolite. Les cristauxde cassit6riteprovenant de veinesde quartzrnin6ralis6es en W et en Sn sonten g6n6ralzon6s. l,es zonesplus sombressont homogdnes et ldgbrementpl6ochroiques, mais leur compositionressemble i celle deszones claires. Ce type de cassit6ritecontient surtout desinclusions de rutile et, localement,d'ilm6nite. Le rutile exsolv6contient desniveaux comparablesouplus6lev6sdeNb+Ta+Sn+W+Fe+Mnquelerutileeninclusion.Lacassit6ritemassive,encristaux idiomorphesi sub-idiomorpheset provenantd'un gisementvolcanogdnique, est ldgdrementpl6ochroique; sa couleurpasse du jaune au brun fonc6 avec une augmentationde sa teneuren fer. Ce type de cassit6ritene contient aucuneinclusion ou lamelle d'exsolution. (Traduit par la R6daction)

Mots-cl6s: cassit6rite,mindraux du groupede la columbite-untalite, tapiolite, ixiolite, rutile, inclusions,exsolution, Portugal.

INrRoDUcrroN 1993).The veinsof graniticpegmatite cut gmnitesand surrounding country-rocks,which consist of pre- There are many occurences of cassiterite and Ordovician,Ordovician and Silurianmetapelites. The wolframite in northem and cenhal Pormgal,and most quartzveins cut thesecountry rocks at a distanceaway ofthem havebeen exploited. Cassiterite occurs in veins from the granites, and rarely cut the granites of granitic , and wolframite, in veins of themselves(Cotelo Neiva 1944). Cassiterite also quartz. These veins are related to Hercynian S-type occursin tle massivevolcanogenic sulnde deposit at granites(Neiva 1983, 1984, 1987), except for the Neves{orvo, in southernPortugal, which is related W-Sn-bearing quartz veins flil > Sn) from Carris to olderHercynian felsic rocks. (Gerez),which are relatedto an l-type granite (Neiva Compositional studies of cassiterite are rather 746 TIIE CANADIAN MINERALOGIST numerous(e.9., Grice et al, 1972,Moore & Howie columbite-tantalite" rutile. ilmenite inclusions and 1979,Foord 1982,Cem! & Ercit 1989,(em! et al. products of exsolution (including ixioli@ also are 1985,Izoret et al. L985,Giuliani 1987.Gonzalez & presented.The element partitioning among Nb- and Revuelta 1989, Ogunbajo 1993, Gomes 1994). Ta-bearingphases also is discussed.Twenty-one Sn However,papers dealing with inclusionsand products and W depositswere selectedfor this study @g, l). of exsolutionin cassiteriteare scarce(Murciego er a/. 1987,Spilde & Shearer1992, Fuente & Izard 1994, PARAGENETTcRsr-arroNsHrps Suwinonprechaet al. L995),as are thoseon coexisting oF PoRTUGT]ESECAssnER[E columbite-tantalite and cassiterite (Cernf & Ercit 1985, eernj et at. 1986u b, Suwinonprechaet al. In Sn-bearingveins of gfanitic pegmatite of the 1995). Hercynianbelt in Portugal,euhedral cassiterite occurs This paper concerns the phase composition and mainly interstitially in associationwith albite - geochemistry of Portuguesecassiteriie on a broad muscovite - quartz, or replaces mainly quartz regional and parageneticbasis. The compositionsof and muscovite (Fig. 2a). The crystals, generally between2 and 10 mm across,rarely host microscopic (360 x 40 pm) inclusions of quartz, muscovite and columbite-tantalite.On the otherhand, they common-ly show exsolved Nb- and Ta-bearing oxide minerals (<350 x 150 pm), exsolvedrutile (3100 x 40 pm) is rarer, and only occasionallyare exsolvedferrotapiolite (<3 x 2 pm) and ilrnenite (<4 x 2 pm) found. Rutile inclusions (<20 x 20 pm) were found only in the cassiterite from Bessa, which does not show any Droductsof exsolution.

+.4 +JI+ + a h I FIG. 1. Location of the twenty-oneSn and W depositschosen g for study. a: he-Ordovician metamorphic complexes, Paleozoic,some igneous and ultrabasicrocks and igneous A complexesfrom Alentejo; b: Marine Carboniferous metasedimentaryand metavolcanicrocks; c: Hercynian f granitic rocks; d: Mesozoic and Cenozoic stiilimentary rocks. Ore deposits: e: volcanogenic sulfrdes and Sn A deposits [2]: Neves Corvo (Sta B6rbara dos Padr6es, e Castro Verde)l; f: Sn-bearinggranitic pegmatitic veins [1: Cabragdo(Cabragdo, Ponte dr Lima); 2: Bessa (Morgade, Montalegre), 3: Fental (Sto. Aleixo do mnTdmega Ribeira de Pena), 4: Revel (Tr0s Mnas, Vila d Pouca de Aguiar), 5: Vieiros @ebordelo, Amarante)l; g: stanniferous quartz veins [6: Montezinho (Franqa [5 Braganga),7:Argozelo (Argozelo, Vimioso)l; h: W-Sn- bearing quartz veins [8: Carris (Cabril, Montalegre), c 9: Lombo de Boi (-amalonga, Macedo de Cavaleiros, 10: Linhares @rmelo, Mondim de Basto), 11: Fonte = Figueira (Aboadela, Amarante),12: Vale das Gatas b (S. Lourengo de Ribapinhdo e Souto Maior, Sabrosa;, 13: Muralha flilar de Magada Alij6), 14: Carvalhal tl (Cheires, Alij6), 15: Soutelinho (Favaios, Alij6), a 16: Filharoso (Presand6es,Alij6), 17: S. Domingos (Alij6, A1ij6), 18: Folgar (S. Mamedede Ribatua Alij6), 19: Bougo (S. Mamede de Ribatua, Alij6), 20: Panasqueira(Aldeia de S. Franciscoe S. Jorge da Beira, Covilhd e FundSo)1.Parish and boroughare given for the locality information. CASSITERITEAND ITS INCLUSIONS, PORTUGAL 747

Flc. 2. a Cassiterite (c) from the Vieiros pegmatite replacing quartz (q) and muscovite (m) (x55); b. euhedral grain of cassiterite(c) from the quartz veins from Argozelo, associatedwith a muscovite-richselvage (m) and qu*,rtz(q) (x27).

In quartz veins, euhedralcassiterite occurs among SaMpLes.ANatYlcar METHoDS quartz crystals, mainly along the vein-schist contact, ANDTREAI'N{ENT OF DATA associatedwith a muscovite-rich selvage (Ftg. 2b). Cassiteritecrystals from the stanniferousquartz veins A total of 1738 compositions were obtained by from Argozelo are generally more than 1 cm across electronmicroprobe, 1100 on cassiteritein 63 selected and locally cut by -filling veinlets of quartz, crystals,203 on their inclusions(82 of columbite- arsenopyriteand sphalerite.crystals of cassiteritefrom tantalite.108 of rutile, and 13 of ilmenite)and 435 of stanniferous quartz veins generally show exsolved their products of exsolution (293 of columbite- Nb- and Ta-bearing oxide minerals (<80 x 50 p-), tantalite,72 of.iJ{iohte, 15 of ferrotapiolite,43 of rutile, whereas tlose from W-Sn-bearing quafiz veins and 12 of ilmenite). commonlyhost inclusionsof rutile (<70 x 50 Fm) and The oxide minerals were analyzedfor major and rare inclusions of ilrnenite (<8 x 3 pm). However, minor elements on a Cameca Camebax electron exsolvedNb- andTa-bearing oxide mineralsand rutile, microprobe at Instituto Geol6gico e Mineiro, S. or rutile alone(<30 x 20 lrm), were locally found. Mamede de Infesta, Portugal. Analyses were In the volcanogenic deposit from Neves-Corvo, conductedat an acceleratingvoltage of 15 kV and a meter-thick massive lenses of euhedral to subhedral beam current of 20 nA. Standardsused include SnO2 cassiterite with interstitial quartz, carbonates and (Sn o), FqO, (FeKcr),MnTiO, (Mn-I(a and TiKcl), sulfideslocally overlie the massivecopper ore (Gaspar pure Ta (fo), Nb (Lo) and W (I{x) metals. Each 1991).This cassiteriteis intergrownwith or cut by elementwas countedfor 20 seconds.ZAF corrections veinletsof chalcopyrite,pyrite and carbonates.Neither were applied. inclusionsnor productsof exsolutionwere found. Included and exsolved Nb- and Ta-bearing oxide

CASSITERITEAND ITS INCLUSIONS. PORTUGAL 749

Ftc. 3. a. Part of a crystal of cassiteritefrom the Revel pegmatite(x53); b. cassiferitefrom the Vieiros pegmatite(x214); c. distribution of Ta in b; d. cassiteritefrom the volcanogenicSn depositfrorn NevesCorvo (x21l). (-

mineralsin cassiteriteshow a variety of compositions. crystals of cassiterite from the pegmatite bodies at Owing to their small size, it was impossible to get Vieiros are zoned in this way, whereas others are inforrnation on their sftucturalstate and, consequently, unzoned (Frg. 3b) and strongly pleochroic. In the in somecases, to identify them completely.Chemical darker zones of some crystals from the Sn-bearing criteria weretherefore used to distinguishthe relatively pegmatitebodies at Fental and Revel, the pleochroism pure minerals of t}re columbite-tantalite group is lessintense: e reddishbrown, crlbeige. In crystalsof (whatevertheir structural state) from minerals of the cassiteritefrom the pegmatitebodies at Bessa,some ixiolite- series, arbitrarily called here crystals from the stanniferous quartz veins from ixiolite. Both columbite-tantalite and ixiolite phases Argozelo,and most crystals from W-Sn-bearingquartz were comparedon a uniform basis of six atoms of veins, the darker zones are only slightly pleochroic: oxygen, despite the differencesin unit-cell contents. e brown to o light brown. Howeveroin other crystals The review of andtantalum minerals by dernf from W-Sn-bearing quartz veins from Carvalhal,the & Ercit (1989)provided the terminologyused in this pleochroism of the darker zones is strong: € red, paper. o translucentcolorless. Crystals of cassiteritefrom pegmatite bodies and CassrrsR[EZoN${c, INclustoits stanniferousquartz veins commonly show productsof ANDPRoDUc"rs oF ExsoLUTroN exsolution,whereas accidental inclusions are common in crystalsof cassiteritefrom the W-Sn-bearingquartz The cassiteritefrom most of the granitic veins (Table 1). Products of exsolution were and quartz veins exhibits narrow parallel alternating commonly found in the strongly pleochroic darker lighter and darker growth-zones(Fig. 3a). The lighter zonesof cassiterite,but they were also found in lighter zones are translucent.colorless to tan. whereasthe zones,mainly in contactwith darkerzones. Inclusions darker zones are pleochroic. The darker zones occur in both lighter and darker zonesof the crystals. generallyexhibit strongpleochroism (e red or deepred The distinction befween accidental inclusions and and even black co translucentand colorless). Some products of exsolution was based on textural

TABLE 1. INCLUSIONSAND PRODUCTSOF EXSOLUTIONIN CASSITERIIEFROM GRANMC PEGMATTTESAND QUARTZVEINS FROM NORTHERNAND CENTRALPORTUGAL

GRANIIIC PEGMATTIES Inolusions ProductsofExsolution Fenotmioliie Ixiolite Rutile

Cabraqeo Cabrageo Fental Fenal Fmtal Fental Rwel - Revel Rwel

STANNIFEROUSQUARTZ VEINS W.Sn.BEARINGQUARTZ VEINS

Produdsofexsolution lnclusions Productsofexsolution Columbite-tantalite Ixiolho kiolite Rrfile Montezinho Montezinho Canis Argozelo Argozelo lombo deBoi TinhAres Fonte Figueira Vale das Gatas Carvalhal Soutelinho Filharoso S. Domingos Folgar Bougo 750 THE CANADIAN MINERAIOGIST

observationsand on electron-microprobetraverses of TABi.E 3. SELECIED ELECTRONMICROPROBE DATA ON CASSITERJTEFROM STANNIFEROUSQUAR'\Z VEINS FROMNORTHERNPORTUGAL the host cassiteritenear the inclusionsand products of exsolution.Inclusions occur within the crvstalsof ffi cassiterite,whereas products of exsolutionoccur Nb205 0.33 l.l3 r.22 0.&7 0.01 1.06 t.12 0.85 0.06 0.16 throughouttfie cassiterite.Chemical composition is Ta2OS 0.9 0.29 t.1S 3.19 0.04 1.71 2,31 2.81 1.66 2.U Ti 02 0.09 0.29 0.23 0.24 0.13 0.13 0.23 0,25 0.24 0.3r necessaryto distinguishbetween accidental inclusions Sn02 9.54 98.33 96.15 94.42 99.58 96.65 95.50 95.33 97.?6 .92 and products o.05 0.01 of exsolution.In the caseof accidental MDO 0.01 - 0.03 o.tt 0.08 0.01 0.oJ inclusions,the compositionof the darkerzone of the FeO 0.13 0.52 0.71 0.8t 0.03 0.19 0.89 0.98 0.3J 0.4E Tel 100.I9 1m.56 [email protected] 99.70 99.?9 100.34 [email protected] [email protected] 100.08 99.96 host cassiteriteis homogeneous,whereas appropriate Nb 0.00.{ 0.013 0.014 0.010 - 0.012 0.013 0.010 0.@1 0.@2 compositionalgradients in the hostphase are found in Ta 0.002 0.012 0.022 - 0.012 0.016 0.019 0.011 0.014 the caseof productsof exsolution. Ti 0.m2 0.005 0.004 0.005 0.002 0.@2 0.004 0.00i 0.005 0.006 Sn 0.991 0.971 0.956 0.9.16 0.97 0.960 0.950 0.949 0.97? 0.969 Subhedral to euhedral cassiterite from the Mn 0.001 0.m2 0,002 0.002 Neves-Corvovolcanogenic deposit (Fig. 3d) exhibits 0.003 0.01t 0.015 0.01t 0.001 0.016 0.019 0.020 0.007 0.010 yellow,brown and deep brown components, which are T@l 1.000 1.002 1.002 r.003 1.0@ l.@2 1.004 1.003 l.mt 1.003 only slightlypleochroic, do not definezonal sequences, 8: Mont@irho (a: lighter anq b1:red anq b2: deepred zone, b3: rery d@p r€d are devoidof inclusionsand exsolutionproducts, and zone):9: Aryozelo (a: lighter ang bq bq bp, br, bs: reddishbrcm ane with are extensivelvfractured. incroing distae &om @lumbite-tmtalite0r! b!, bp) ad timim ixiolite witb sbordimte W > Sn 0r, bs) wlution products).Oxids in wt.%t - not det*ted. Calionfomula bas€don two atomsofoxygs. Analyst:A. Neiva. GEocHEMrsrRyor CessrrsR[E

In the zonedcrystals from Sn-enrichedbodies of Table 3, anal. 8, 9). The red zonesbecome progres- granitic pegmatitefrom Cabragdo,Fental and Revel sively deeperred with increasingTa and Fe contents (Table 2) and stanniferous quartz veins from (Table 3, anal. 8bl, b2, b3). The darker zonesare Montezinhoand Argozelo (Table 3), the chemical heterogeneous,and their Tal(Ta + M) valuesvary with compositionsofthe lighterzones and darker zones are increasingdistance from exsolvedNb- andTa-bearing well distinguished.The lighter zones are nearly pure oxide minerals(Fig. 4a); the zoning in each darker SnO2,whereas the darkerzones have generally higher zone is oscillatory.The Ta and Fe contentsof the Nb, Ta and Fe contents(Table 2" anal. 1. 3. and darker zones decreasenear exsolved columbite-

TABLE 2. SELECTED ELECTRON MICROPROBE DATA ON CASSITEzuTE FROM .ENRICI]ED ORANITIC PEGMATITES FROM NORTHERN PORTUCAL

2.3 aba,bab ab

ItbeOS 0 0J L 19 0.13 0.14 l.El 0.15 0.43 0.03 0.E2 0.01 0.t'7 0.14 0.14 - 0.25 0.60 0.4 r.29 1.48 Ta2O5 0.04 1.66 0.09 0.06 t.60 0.04 0.16 0.04 0.14 - 0.33 0.25 0.39 0.J3 2.06 4.93 6.28 8.66 11.89 TiO2 0.07 0.17 0.56 0.01 0.05 0.53 0.81 0.29 0.84 0.39 0.44 0.67 0.97 0.0E 0.01 0.13 0.19 0.16 0.30 SnO2 99.77 95.% 99.39 99.13 95.40 98.65 97.9t 99.07 97.70 98.58 98.92 99.J1 98.m 99.26 97.6a %!9 9t.34 87.57 43.s4 WOJ 0.03 0.| 7 0.09 0.08 0.08 0.03 0.15 0.25 MnO 0.01 0.03 0.02 0.04 0.01 0.01 0.01 0.03 - 0.07 0.06 0.09 FeO 0.04 0.61 0.06 0.t7 0.61 0.M 0.19 0.03 0.26 0.08 o.tt o33 0.ll 0.43 0.8? t.52 2.08 2.58 Tokl 100.00 99.79 100.i4 99.59 99.62 99.4t 99.t0 99.50 99.77 99.22 [email protected] 100.6E 99.43 99.98100.43 100.02 [email protected] 99.82 99.t8

Nb - 0.013 0.001 OT'0.021 0.q)2 0.005 - 0.009 - 0.@2 0.002 0.002 - 0.003 0.007 0.007 0.015 0.01? - 0.011 0.001 0.011 - 0.002 - 0.00r - 0.002 0.002 0.003 0.004 0.014 0.034 0.043 0.059 0.082 Ti 0.001 0.003 0.010 0.@l 0.010 0.015 0.005 0.016 0.@7 0.008 0.012 0.018 0.002 - 0.002 0.004 0.003 0.006 Sn 0.997 0.957 0.985 0-994 0.952 0.9a7 0.974 0.993 0.969 0.990 0.983 0.982 0.973 0.993 0.974 0.938 0.917 0.882 0.843 w - 0.001 0.001 0.001 0.001 0.001 0.002 Mn - 0.001 0.001 - 0.@t 0.001 o.mt 0.002 0.001 0.013 0.00r 0.00i 0.013 0.@l 0.004 o.ml 0-005 0.002 0.@2 0.007 0.002 0.009 0.018 0.032 0.044 0.055 ToGl 0.999 0.999 0.999 t.00I 1.000 1.000 1.000 0.999 1.000 1.000 0.996 1.000 1.003 l.@l 1.0@ 0.999 1.004 1.004 1.005

I : Cabragao, 2: B*s4 3 and 4: Fental 5 and 6: Revel 7: Vieiros. a: Iighter zonq b: darko zone; 4b: averageof zon* a md b; 6 (b[ bh bl-red zone witb incr%ing distm@ Iiom rutile inclusion);7 (bl-light red zong b2 md b3-red rcng b4, b5 and b6 dep red zone). Oxids inwt.o/o. - not detected. CatioD iomula basedon two atoms of oxygm. Analyst: A. Neiva.

FIc. 4. a. Variationin compositionof thehost dark zone of cassiteriteat progressivelyincreasing distances from differentgrains of exsolvedNb- and Ta-bearingoxide minerals.O: exsolutionproducts of: 1,2: ferrocolumbite,3: titanianixiolite with subordinateW > Sn,4: stannianixiolite; X: hostdark zoneofcassiterite at - 10pm; -- 20 prm,-- 30 pm from the rim of the exsolutionproduct. b, c, d. Variationsin chemicalcomposition of darkzones of a singlecrystal of cassiteritedeter- mineda1 l0 pm from the rim of the exsolutionproduct, consisting of: b: columbite-tantalite(I), c: titanianixiolite with subordinateW > Sn (/\), d: columbite-tantalite(V) andSn-rich titanian ixiolite (A); b. Vieiros;c. Argozelo;d. Monrezinho; e. Correlationbetween Ta andNb ofcassiteritefrom Sn-enrichedpegmatites (O Cabragio,+ Fental,Z Revel,tr Vieiros) andstanniferous quartz veins (V Montezinho,A Argozelo),1: cassiteritewith Nb > Ta, and2: cassiteritewith Ta > Nb. CASSITERITEAND ITS INCLUSIONS.PORTUGAL

z-o + o c) o o F

t0 30 t0 30 r0 30 50 Mn100/(Mn +Fe ) Mnl00/(Mn+Fe) Mn100/(Mn * Fe ) -.+ .-)

A A A A .az + (l + F AA o t o 40 V o F Y

VtV EV

Mn100/(Mn+Fel Ta5'atom. --+ 752 THE CANADIAN MINERALOGIST

tantalite(Table 3, anal. 9bm, bn, bp) and exsolved Cassiteritefrom the pegmatitebodies at Bessaand ixiolite (Table 3, anal. 9br, bs) and increasewiti from W-Sn-bearing quartz veins from Carris, Lombo distancefrom these exsolveddomains. There is no de Boi, Linhares, Fonte Figueira, Vale das Gatas, significantchemical distinction among closely spaced Muralha, Carvalhal, Soutelinho, Filharoso, S. dark zones.However, in the samecrystal, significant Domingos,Folgar, Bougo and Panasqueira (Fig. 1) are differencesin the Tal(Ta + M) valuescan exist in dark zoned. However, in general, no significant chemical zonesthat are far apart Gigs. 4b, c), althoughthese distinction was found between the darker, slightly show the same product of exsolution (either pleochroic zones and the lighter zones, and average columbite-tantaliteor ixiolite). For example,in a compositionsare given in Table2 (aaal.2)andTable 4 singlecrystal from Montezinho,deep to very deepred (anal.10, 11,12,13,14,15,16, l8). Thesamples of zones containing Ta > Nb and showing mainly cassiteritefrom the quartz veins from Carvalhal, exsolvedSn-rich titanian ixiolite generallyhave higher Soutelinho, Filharoso, S. Domingos, Folgar and Ta/(Ta + Nb) values(Fig. d) and Ta, Fe conrenrs Bougo, all occuring close to each other (Fig. l) (Table3, anal.8b2, b3) thanred zones characterized by andrelated to the sameS-type granite, have a similar Nb > Ta and showingcolumbite-tantalite exsolution chemical composition (representedcollectively by products(Table 3" anal.8bl). anal. 16 in Table 4). However, some crystals of In the pegmatitebodies at Fental and Revel, there cassiterite from Carvalhal have strongly pleochroic alsoare crystals whose darker zones show less intense darkerzones, with Ti contenthigher than in the lighter pleochroismand have more Nb, Ta, Ti and Fe than in zones(Table 4, anal.17a,bl,b2). thelighter zones (Table 2, anal.4a,b and5a, b), but the In crystals that host accidental rutile or ilrnenite chemicaldifference between darker and lishter zones inclusions,but lack any productsof exsolution,the hereis more subtle,because the lighter zoies are less cassiteriteis fairly homogeneousnear the inclusions, pure than usual. These crystals show generally which seemto be uniformly distributed in the lighter exsolvedtitanian ixiolite with subordinateW > Sn, and darker zones.Furthermore. there is no chemical rutile t ilmenite mainly, but not exclusivelyin the distinction in successivedarker zonesin each crystal. darkerzones. The Ti contentofthe darkerzones nexr However, in crystals of cassiterite from Muralha, to domainsof exsolvedrutile increaseswith increasing which contain exsolved rutile and ixiolite, there is a distance away from the exsolved blebs (Table 2, progressiveincrease in the Ti content of dark zones anal.6h, k, 1). with increasingdistance from theseblebs (Table 4, Cassiteritefrom the pegmatitebodies at Vieiros is anal. 15bh,bk, bl and br, bs, bt respectively).The mainly unzonedand stronglypleochroic. The red and chemicalcomposition of successiveclosely spaced red deep red cassiteritehas higher contentsof Ta and Fe zonesgenerally does not changesignificantly, except than the pale red cassiterire(Table 2, anal. 7bl-b6). if there is an increase in intensity of color that is It is heterogeneous,exhibiting a wide rangeofcompo- accompaniedby an increasein Ti content(Table 4, sitions (Fig. 3c); it containsinclusions of quartzand anal. l7bl,b2). muscovite,and many small (<2 x 1 pm) grains of The brown componentsof cassiteritefrom the exsolvedcolumbite-tantalite and stannian ixiolite. Neves-Corvovolcanogenic deposit have higher Fe

TABLE4 SELECTED E ECTRONMCROPROBE DATA ON CASSITERITE FROM W > So-BEARINC QUAR]Z VEINS FROM NORTIIERN AND CENTRALXIRTUcAL AND A VOLCANOGEMCDEPOSIT FROM SOUT}IERN PORTUGAL

8,b - --;-- -eb - r"b a,b 4b 4b qom 4b- bt b2- d ,l e, Nb205 0.03 0.09 o.0t o.m 0.01 0.1? o.l5 o.l9 0.17 0.r0 0.24 o.1l 0.24 o.0l 0.20 0.36 o.ol - Ta2Oj 0.03 0.07 0.01 0.0E o.t2 0.05 0.22 0.39 O.2g 0.39 o.zE 0.3i 0.34 0.19 o.O2 o.zg 0.12 0.06 0.ll 0.05 0.40 TiO2 0.42 0.16 0.12 0.60 0.87 0.41 0.55 O.i2 O.t6 0.2E 0.42 0.i2 O.S2 0.3i 0.67 0.92 0.5E sno2 0.04 9.13 9t.ru 99.26 98.t5 99.00 99.05 9E?3 9E.?E 98.209E.96 98.68 98.5t 99.m 99.6t 98.59 9E43 99.32 WO3 99.85 98.t7 91.72 0.10 0.06 0.M 0.04 O.O1 0.08 O.t2 _ - 0.ll 0.05 0.04 0.01 0.23 0.14 0.06 0.95 MrO 0.01 0.02 O.O2 O.0l 0.02 O.0l 0.02 0.01 O.Ol _ 0.0i 0.01 O.O2 0.03 - 0.0r 0.02 0.02 0.01 FeO 0.13 0.05 0.04 0.05 0.06 0.06 0.16 0.0? o.l9 0.10 0.13 0.09 0.09 0.02 0.06 0.09 0.03 o.lt 0.90 1.93 Tobl 99.89 99.74 l(n.I? 9.?5 loo.os [email protected] 100.00100.06 99.94s9.72 9g.E7 99.76 ro0.l8 l00.lJ [email protected] 100.16 100.26l00.ll 1m.0J - - Nb 0.@l 0.001 . 0.002 0.002 0.002 0.002 0.0010.003 0.@l 0.003 - 0.@2 0.()ol la - - 0.001 0.001 0.@3 0.002 o.@3 0.@2 0.003 0.@2 0.00I - 0.002 0.@l - 0.001 0.003 0.@8 0.014 0.013 0.01t 0.016 0.009 0.010 0.013 0.016 0.005 o.oot 0.010 0.010 0.@7 0.013 0.017 0.01r 0.00r so 0.9E8 0.9E3 0.9t5 0.985 0.981 0.965 0.932 0.9Et 0.t5 0.990 0.9E40.9E3 0.983 0.992 0.9il 0.973 0.9t6 0.995 o.yn 0.n6 o.()0l w - O.mt o.ool 0.001 0.@l - 0.@6 Mn 0.001 0.001 Fe 0.003 0.001 0.00t 0.001 o.oot 0.001 0.001 0.@l 0.004 0.0020.003 0.002 0.002 - 0.00t 0.002 0.001 0.004 0.019 0.0,t0 loa 1.0@ 0.999 0.999 0.99 0.998 0.99S 1.000 0.999 l.ool Looo 1.0020.999 0.999 1.000 0.999 0.99t 0.999 1.001 1.002 1.019

l0: Canis; 1l: Iombo de Boi; 12: Linhres; 13: Fonte Figueiq 14: Vale das Gatas; 15: Muralha (bl, blg bl: withinceasing distme fiom exsolvedrutile md br, bs, bt: &om exslved titmim ixiolite with subordinate W > Sn); 16: Carvalhal, Soutelinhq Filharoso, S. Domingos, Folgar, Bougo; 17: Canalhal @l: red rcne, b2:.dep red zone); a: Iightc zong b: drker zone; 4 b: averageofzones a and b; 18: Panasquein; 19: Neves CoFo (d: yellow, el: browq e2: dep brc*;. Oxidc in wt.%. - no! det6ted. Cation formula basedon two atoms of orygm. Analyst: A Neiw. CASSITERITEAND ITS INCLUSIONS.PORTUGAL 753 content than the yellow components(Table 4, anal. granitic pegmatites and stanniferous quartz veins 19d, el, e2). The brown componentsbecome deep generallycontain more Nb than Ta" but somedeep red brown with increasingFe content. zones and also deep red unzoned crystals contain significantly more Ta than Nb. As a result,two distinct GsocuEr"flsrR.yor Cassnpnng: trends with different slopes were defined in the A Srlvntanv diagram showing Ta versus Nb for dark cassiterite (Fig. 4e). In general,these crystals contain exsolved Most of the cassiteritecrystals analyzed tend to be columbite-tantaliteor ixiolite (or both), preferentially richer in Fe than Mn. Dark zones of crvstals from in the dark zones. Note that the cassiterite from

Fe,MnXNb,Ia)z

,MnXNb,Ta)

I/ "/r

.l00 0 Fe,Mn (FqMnXSn,W,Ti) Sn,Ti

t.6 @

./ Fe,Mn)(Nb,Ta)z FW :' ,/. ? 2_"

,00 r00 99 Sn,Ti

Rc. 5. a. A (I.{b,Ta)- Ge,Mn) - (Sn,Ti,W) diagramshowing the location of triangular plots for Portuguesecassiterite (CsQ, rutile (Rr), columbite-tantalite (C0, ixiolite (lxt). b. Compositionsof the cassiteriterichest in Nb + Ta of Portuguese Sn-enrichedpegmatites and stanniferousquartz veins, plus the locations of cassiteritediagrams (c) and (d), expanded in the following figures. c. Compositionsof cassiteritefrom PortugueseSn-enriched pegmatites and stanniferousquartz veins. d. Compositionsof cassiteritefrom PortugueseW > Sn-bearing qtJartzveins. Symbols: Sn-enrichedpeg-atites (O CabragSo,O Bessa, + Fental, Z Revel, tr Vieiros); stanniferousquartz veins (t Montezinho, A Argozelo); W > Sn-bearingquartz veins (* Carris, Vlombo de Boi, O Lfuhares,O Fonte Figueira, O Vale das Gatas,A Muralha, I Carvalhal,Soutelinho, Filharoso, S. Domingos,Folgar, Bougo, A Panasqueira);volcanogenic deposit ( X Neves-Corvo). 754 THE CANADIAN MINERALOGIST

,/-i-''. OL 0 r00 I Sn Flc. 6. a. A (Nb,Ta)- Ti - Sn diagramshowing the location ofdiagram (b). b. Compositionofthe cassiteriterichest in Nb + Ta from bodiesof Sn-enrichedpegmatite mainly from Vieiros, but also from Cabragio and Fental and showing the location of cassiteritediagram (c) and of its area (d), which are expandedin the following figure to avoid data superposition. c. Compositionsof cassiteritefrom PortugueseSn-enriched pegmatites, stanniferous quartz veins and W-Sn-bearingquartz veins.Cassiterite hosting rutile t ilmenite inclusionsor rutile + iknenite t ixiolite i columbite-tantaliteexsolution produfis fall in area(d). Symbolsas in Fig. 5.

pegmatite bodies and stanniferous quartz veins is The dataon Portuguesecassiterite (Tables 2,3,4) generally richer in Nb, Ta and Fe, particularly suggest that the pleochroism of cassiterite can be concentratedin dark zones, than cassiteritefrom relatedto tlle presenceof Ta andM, which agreeswitb W-Sn-bearingquartz veins. findings of Hall & Ribbe (1971),but it can also be The crystals of cassiteriteanalyzed contain up to attributedeither to Ti or to Fe. 2A2wNVoMrO, (frompegmatite bodies at CabragdoT, 2.84 wtVo TarO5 and 0.98 wt-VoFeO (both from pegmatitebodies at Fental). However, higher values are found in cassiterite from pegmatite bodies at Vieiros (up to 3.26 wLToM2O5, 11..89wLVo Ta2O5 and 2.58 v,t Vo FeO). Niobium, Ta and Fe may be TABIT 5. REPRESEN"TATryECOMPOSITTONS OT INCIIJDED M EXSOLVED incorporated in submicroscopic inclusions and COLUMBITE.TMALM AND DGOLVED TAPIOM N CASSITERITEFROM TIIE products of exsolution indistinguishablewith the WC PECMIITITFSTROM VIEROS NORTHERNPORTUCAL electron microprobe. Furthermore, the (Ta + Nb)/ Incl6i06 EsldioaPmd6 56789r (Fe + Mn) values are less than 2, rangng between Nb2O5 39.9 39.57 26.54 2t,n 41.31 4t.05 36.17 30.62 5.71 1.5 and 1.7 for cassiteritecontaining from 6.28 to Ta?OJ 42.22 4t,54 ,J.87 61.30 31. 37.03 4t.60 46,q nsg TiO2 0.52 0.J6 0.63 0.38 1.9? 2.1t 2.27 2.19 0.16 11.89wt;Vo TarOr, indicatingthan the Ta + Nb content Str02 0.37 0.73 0.17 0.33 1.23 l.s r.62, 3.48 1.00 in cassiterite wo3 !.aL ad. Ld. tuL 0.20 0.19 0.04 0.ll 0.41 is not exclusivelycontrolled by included MnO 4.53 tL37 4.AS U.73 1.36 4.59 l.l3 2.q 1.03 particles and exsolved blebs of columbite-tantalite FeO \2.74 3.t2 12.30 1.96 16.10 12.56 13.6J 13.0 13.73 Tod 9.q 99-93 9.57 1m.49 [email protected] s.69 99.28 9.68 100.23 (Miiller et al.1988). Nb 1.20J l.2s 0.a70 0.721 1.22t r.2r7 t.t29 0.961 0.209 The concentrationof Ti doesnot exceed,0.40wLTo 0.r5 0.761 1.101 r.23r 0.619 0.6 0,764 0.886 1.712 Ti 0.026 0.028 0.034 0.021 0.097 0.134 o.ilJ 0.114 0.046 TiO, in the dark zonesof cassiteritefrom pegmatite Sn 0.010 0.020 0.@5 0.010 0.012 0.041 0.044 0.096 0.032 bodies and stanniferousquartz veins, 0.m3 0.003 0.@l 0.002 0.009 where free of Mn 0.259 0.705 0,219 0.923 0.076 0.255 0.06J 0.t75 0.071 exsolvedor includedrutile. However,in dark zonesin 0.19 0.288 0.146 0.12t 0.885 0.689 0.884 0.??8 0.933 Iokl 2.99.t 3.006 3.m5 3.033 3.000 199 3.002 3.012 3.012 the cassiteritefrom pegmatitebodies at Revel, which l00Mn 71 z7 containsexsolved rutile, it reaches0.97 wLVoTiO" M+Fe away from theseblebs (Table 2, anal. 5 and 6). Th; l00Ta Ti content of cassiteritefrom W-Sn-bearing quartz TatM

veins attains 1.82 wtVo TiO2 (Vale das Gatas),but l: fwmlumbite, 2: matrgo@olumbite, 3: niobian fenotamalitq 4: m€motatalite uniformly distributed in both lighter and darker inclu6io6; 5, 6: ter@lutrtbitg 7: tmtalie fw@lubitq 8: totalim ffr@l@bhe gnding to ixiolite, 9: f@otapiolite wlution peducti Oxid6 in wt.%. rd. - not zones. det*ted. Cation fomula bsed on 6 aroG of oxygo. Analys: A Neiva. ,:F CASSITERITEAND ITS INCLUSIONS. PORTUGAL /JJ

TABLE6. REPRESENTATIVECOMPOSMONS OF EXSOLVEDCOLTJMBITE.TANTALTTE AND TAPIOUTE(t) FROMCASSITENTE FROM GRANITICPEGMA'I'JTES AND STANNIFEROUSQUARTZ VEINS FROM NORTHERN PORTUGAL

i0 ll Lzt 13 14 l5 16 l7t 18 19 20 21 22 23 24 NbZOs 50.23 21.88 10.18 42.56 37.07 60.E0 26.69 5.65 62.23 69.E0 36.65 26.15 2r.U 52.3',163.91 TAOS 29.91 55.62 73.64 31.11 42.53 t9.47 55.28 77.28 12.80 6.48 42.88 s2s2 56.02 26.A6 10.22 TlO2 0.41 0,23 0.21 1.28 1.53 0.33 0.47 0.57 3.06 1.63 t.8r 2.10 2.E0 1.46 2.69 SnO2 0.38 0.18 l.0l 0.59 0.48 0.20 0.34 1.04 1.07 0.62 0.76 0.89 1.52 0.77 0.91 WOr 0.23 0.04 0.33 0.28 0.15 0.20 0.13 4.26 1.02 0.56 0.26 0.35 0.26 o.42 3.00 MnO 4.Oz 3.41 0.42 3.67 0.97 13.,16 4.22 0.69 3.26 1.28 2.39 3.12 10.52 3.40 tt.42 FeO 14.50 13.0E 14.37 r4.2t 16.61 5.t7 t2.56 14.09 15.99 19.35 15.03 t3.47 5.49 14.98 7.45 Total 99.6E 100.44 100.16 99.70 99.34 9.63 99.69 99.58 99.43 99.72 99.7E 99.60 99.45 99.46 99.60

Nb 1.453 0.904 0.366 1.268 1.138 t.674 0.873 0.209 1.660 1.819 1.120 0.860 0.746 1.487 1.697 Ta 0.520 1.0E5 1.593 0.665 0.785 0.322 1.08E r.72r 0.205 0.102 0.78E 1.024 1.1@ 0.u5 0.163 Ti 0.020 0.012 0.013 0.063 0.078 0.015 0.026 0.035 0.136 0.071 0.092 0.112 0.152 0.069 0.119 Sn 0.010 0.@5 0.032 0.016 0.013 0.005 0.010 0.034 0.025 0.014 0.020 0.025 0.044 0.019 0.021 w 0.@t - 0.00? 0.005 0.003 0.003 0.002 0.@6 0.016 0.008 0.005 0.006 0.005 0.007 0.046 Mn 0.218 0.207 0.028 0.205 0.056 0.694 0.259 0.048 0.163 0.062 0.t37 0.1EE 0.643 0.lEI 0.568 Fe 4.776 0.785 0.956 0.783 0943 0.263 0.760 0.965 0.7E9 0.933 0.850 0.801 0.332 0.187 0.366 Total 3.@1 2.99E 2.995 3.005 3.016 2.976 3.018 3.018 2.994 3.009 3.012 3.016 3.022 2.995 2.980

100Mn 2l I'7 L4 l9 Mn+Fe

100Ta 26 55 81 34 4L 16 55 89 11 5 4l 54 60 Ta+Nb 10: ferrocolumbitg1l: niobianfemotantalitg 12: ferrotapiolitefrom Cabrag6o;13: fenocolumbitg14: tantalianferrooolumbitq 15: manganocolumbitg16: niobianGnotantalitg 17: ferrotapiolitefrom Fental;18: fenocolumbitefrom Revel; 19: fenocolumbitq20: tantalian fenocolumbite,21: niobian ferrotantalitg 22: niobian manganotantalitegrading to ixiolite from Montezinlo; 23: fenocolumbitg24: manganocolumbitefrom Argozelo.Oides in wt.%. Cationformula based on 6 atomsof orygen. Analyst:A Neiva.

The compositionof the Sn, Nb, Ta oxide minerals triangular diagram (Nb,Ta) - Sn - Ti (Fie. 6). wasplotted in termsof Q.{b,Ta)- @e,Mn)- (Sn,Ti,W) Cassiteritehosting inclusions of rutile or ilaenite and diagram (Fig. 5a), in which triangular areas for cassiteritewith exsolved rutile, ilmenite and ixiolite cassiterite(Cst), rutile (Rt) and columbite-tantaliteand plots in the aread of Figures6b and 6c. This category ixiolite (Ct-tO are shown.All the compositionsof the of cassiterite is richer in Ti than that which has cassiteritefrom these bodies of pegmatiteand quartz exsolvedcolumbite-tantalite and ixiolite only and that veins plot close to the trend defined by the ideal contains local inclusions of columbite-tantalite"and substitution(Fe,Mn)2* + 2(Nb,Ta)s++ 3(Sn,Ti)4 which plotsoutside area d. (Cern! et at. 1985) or close to the (Sn,Ti) corner of the (sn,Ti) - (Ta,M) - (Fe,Mn) diagram @gs. 5b, GsoclDMIsrRvoF THECoLIJMBnE-TAI.I-IAI-rrE c, d), as found by Spilde& Shearer(1992). To avoid INcr-ustotrsAND PRoDUcrs oF ExsoLUTroN superposition,compositions of cassiteritefrom the pegmatite occwrencesand stanniferousquartz veins Representativecompositions of columbite-tantalite are plotted in Figures 5b and c. Cassiterite from inclusionsand productsof exsolution,as well as of W-Sn-bearing quartz veins shows a more restricted exsolved fenotapiolite, are given in Tables 5 and 6. substitution(Fig. 5d). The accidental inclusions, recognized in crystals The dominant mechanismof incorporation of Nb, of cassiterite from Sn-enrichedpegmatite bodies at Ta, Fe, Mn and Ti in cassiterite from Sn-enriched Vieiros, have compositions ranging from ferro- grainitic pegmatite, stanniferous quartz veins and columbite to manganocolumbite, occasionally W-Sn-bearing quartz veins clearly is 2(Nb,Ta)5++ extendinginto the maqganotantaliteand ferrotantalite (Fe,Mn)z+- 3(Sn,Ti)4. The (M,Ta) - (Fe,Mn) - quadrants (Fig. 7a) (Cem! et al. 1989b). The Tal (Sn,Ti) diagram(Figs. 5b, c, d) does not suggesta (Ta + Nb) values tend to increase with increasing significant role for any other substitution. Mn/(Mn t Fe) from ferrocolumbite to mangano- Cassiterite from the volcanogenic deposit at tantalite. Neves-Corvois poor in Nb t Ta, but rich in Fe, and Both oscillatoryand smoothlyprogressive zoning plotsclose to the (Sn,Ti)- Ge,Mn)join Gig. 5c). have been reported in columbite-tantalite (Barsanov The cassiterite compositions were plotted in the et al. 1971,Sahama 1980, von Knorring & Condliffe 756 THE CANADIAN MINERALOGIST

MnIa2 0 '.'- tl I /

;$n#* @ FeNb2 06 ffit Mn Nb2O6 FeNb205 MnNb205 Rc. 7. Compositionsof includedand exsolvedPortuguese columbite-tantalite and ferrotapiolitein the columbite quadrilateral: a. from Sn-enrichedpegmatites from Vieiros andRevel and stanniferousquartz veins from Montezinho;b. from Sn-enriched legmatiles from Cabragdoand Fental, and sranniferousquartz veins from Argozelo. Bands of coexisting or associated ferotapiolite and tantalite compositionsand the gap (dashed)befween individual compositionsin ferrotapiolite and ferro- tantalite are taken from Cern! et al. (1992a). Symbols: columbite-tantalite inclusions (I Vieiros); columbite-tantalite productsof exsolution(tr-Vieiros, (O Revel, V Montezhho, O Cabragio,+ Fental, A Argozelo); exsolvedferrotapiolite (fr Vieiros, X Cabragio, e Fentall.

1984,Lahti 1987,Spilde & Shearer1992,tem! et at. trend of increasingMn(Mn + Fe) and Tal(Ia + M) 1992b).Oscillatory zoning is mainly controlledby the values from ferrocolumbite to manganocolumbiteis growth dynamicsof the crystalsand the concentration defined for products of exsolution in the cassiterite anddiffusion of the main elements,particularly M and from Montezinho. Ta (Lahti 1987). In primary columbite-rantalite Some of the individual blebs of exsolved crystals, the oscillatory zoning representsa state of columbite-tantaliteare homogeneous@g. 8a), but in high free energy even at the late-magmatic stage general they display several types of zoning. of theircrystallization (Cernf et aI.'I992b).Oscillatory Oscillatory zoning is tle most common,and probably zoning was observed in single inclusions of is the result of the concentrationand diffirsion of manganocolumbitewithin cassiteritefrom a pegmatite M and Ta, and also of the growth dynamicsof the at Vieiros, showing more restricted range in Tal crystals.Some single blebs of ferrocolumbiteshow an (Ta + Nb) than in Mr/(Mn + Fe) (Table 7, A), and is increasein Nb and Mn, and a decreasein Ta and Fe" attributedto a stateof high free energy.A decreasein from coreto rim (Table8), but Ta andMn decreaseand Nb, Mn, Mn/(Mn + Fe) and an increasein Ta, Fe, Nb and Fe increasefrom core to rim in other blebs of Tal(Ta t Nb) from core to rim was found in sinele ferrocolumbite@gs. 8b, c). inclusions of ferrocolumbite in cassiterite from ire Compositionaldata also were obtained on exsolved samepegmatite (Table 7, B). ferrotapiolite and niobian ferrotantalitefrom the same Most of the exsolvedorthorhombic phases have crystals of cassiteritefound in the pegmatite bodies compositionsof [email protected], b). However, from Cabrag6oand Fental (Table 6), but the products rare niobian ferrotantalite was exsolved from of exsolution are not in mutual contact.The tie-lines cassiteritefrom pegmatiteoccurrences at Cabragdoand linking thesecoexisting minerals run acrossthe length Fental and from stanniferous quartz veins of of a two phase-region(Fig. 7b) and are slightly Monteziaho.Very rarely, cassiteritefrom thesequartz convergent,suggesting equilibrium. The compositions veins also contains exsolved manganotantalite. fall within the boundariesdefined by Aem! et al. Cassiteritefrom Fentaland stanniferousquafiz veins at (1992a),as is characteristicof coexistingferrotapiolite Argozelo also exsolvedmanganocolumbite. A clear + tantalite. Crystals of cassiterite from the Vieiros CASSITERITEAND ITS INCLUSIONS,PORTUGAL 757 pegmatite bodies commonly exsolved ferro- The proportion of Nb and Ta of the included columbite, but very rarely exsolved ferrotapiolite columbite-tantalite and exsolved columbite-tantalite, (Table 5, Fig. 7a), found only in cassiteritecrystals fenotapiolite and ixiolite in the cassiterite studied that do not show any other product of exsolution. here is plotted in Figures lOa and b. Most of the The ferrocolumbite and ferrotapiolite exsolved from compositionsfall within the columbit*tantalite field, the Vieiros cassiteritecarry moreTi, Sn andW than the but those containing substantialcontents of combined columbite-tantaliteinclusions hosted by this cassiterite Ti" W and Sn or of Sn alone fall below the lower (Table 5), which agrees with the findings of boundaryand are arbiuarily consideredto be ixiolite. Suwinonprechaet al. (L995). Thosefrom the pegmatitebodies at Vieiros and some from the stanniferousquartz veins from Montezinho GsocHENflsrRYoF ExsoLvEDlxolrrB are stannian ixiolite (Ta,Sn,M,Fe?Mn,Ti).Or, and others from Montezinho are Sn-rich titanian ixiolite The chemical compositions of exsolved ixiolite (Ta,M,TbSn,Mn>Fe)oOs. However, others from the from cassiteritefrom bodies of granitic pegmatiteand pegmatite bodies at Fental and Revel, stanniferous quartzveins arepresented in Table 9. The ixiolite is not quartz veins from Argozelo and the W-Sn-bearing in contact with the exsolved columbite-tantalitein a quartz veins from Muralha are titanian ixiolite with given crystal of cassiterite. subordinateW ) Sn (Nb,Ta,Ti,Fe?Mn,W,Sn)aOg The findings of severalauthors were used here to (Table 9). Sn-rich titanian ixiolite and stannian define two paratlel boundariesin the diagramof Tas* ixiolite have Ta > Nb, whereastitanian ixiolite with yersas Nb5+ @gs. 9a, b) to distinguish chemically subordinateW ) Sn hasTa < Nb. between minerals of the columbite-tantalite group The data of severalauthors plotted in Figure 9 also and those of the ixiolite-wodginite family. The were plotted in the (Sn,Ti,W) - (Nb,Ta) - @e,Mn) columbite-tantalite compositions plot between diagram@gs. 1la, b, an enlargementof the triangular the boundaries.Compositions grading to ixiolite fall area Ct-Ixt shown in Fig. 5a). It is possible to ort the lower boundary, ixiolite and wodginite plot distinguishbefween columbite-tantalite (field Ct) and below that boundary, but wodginite with 0.35 wLTo ixiolite (field lxt) in Figure 11, becausethe data on Li2O falls on the upper boundary,and lithiowodginite theseminerals fall within the respectivefields (except lies above this boundary Gig. 9a). Columbite for lithiowodginite, which was not plofted here). containing7-18 wt VoWO3, <1.90 wt % Sc2O3and The data on columbite-tantalite (included and 34.7 wu%oTiO2 (Beddoe-Stephens& Fortey 1981) exsolved)in Portuguesecassiterite studied here plot in (Fig. 9b) and 9.8-11.3 tttLVoWO3 (Suwinonprecha the corresponding field in Figures L2a, b, c. et al. 1995) (Fig. 9a) plots below the lower boundary Columbite-tantalite has higher levels of Nb + Ta and is probablyixiolite. than ixiolite and lower Sn + Ti + W than stannian

TABLE 7. ELECIRON MICROPROBEDATAONZONEDCOLUMBITEINCLUSIONS INCASSITERITE FROM GRANITICPEO\,fATTIESFROM VIEIROS

B 1 Rim Core -_''------.----Rim I 3 I 2345

Nb205 42.64 33.08 40.83 27.09 40.47 50.12 48.90 48.08 45.11 U.24 Ta2Oj 49.45 40. 55.85 4r.45 29.61 30.97 32.51 35.43 36.99 TiO2 0.39 o.27 0.35 0.20 0.36 0.77 0.79 0.81 0.52 0.71 SnO2 026 0.16 0.20 0.25 0.28 o.t1 0.23 o.2l 0.ll o.lt MnO 15.63 8.92 16.80 8.16 16.52 6.12 5.43 4.07 4.n 2.43 F€O 1.86 8.03 0.64 1.93 0.64 t2.42 8.42 t4.26 14.04 15.28 Total 100.70 99.91 99.38 99.49 99.72 [email protected] 99.74 99.94 1m.08 99.83

Nb 1.046 1.242 0.889 1.230 1.453 1.418 1.399 1.348 1.316 TA 0.716 0.940 0.142 1.103 0.758 0.510 0.5ilo 0.569 0.629 0.62 Ti 0.019 0.014 0.018 0.011 0.018 0.037 0.038 0.039 0.026 0.035 Str 0.007 0.004 0.005 0.007 0.008 0.004 0.006 0.005 0.003 0.005 Mn 0.874 0.528 0.951 0.J02 0.941 0329 0.295 0222 0.236 0.135 Fe 0.103 0.470 0.036 0.482 0.036 0.680 0.720 0.768 0.76 0.841 Total 2,991 3.@2 3.0S 2.94 3.013 3.017 3.@2 3.008 2.994

100Mn 89 53 96 FerMtr

100Ta 38 Ta+M A: complexoscillatory zoned manganocolumbite;B: regularlyzoned ferrocolumbite.Orides in wt.%. Cationformula based on 6 atomsoforygen. Analyst:A Neiva. THE CANADIAN MINERALOGIST CASSITERITE AND ITS INCLUSIONS. PORTUGAL 759

Frc. 8. Distribution of elementsin productsof exsolutionfrom cassiterite.a. Homogeneousdistribution of Ta in ferrocolumbite from Argozelo. b. Decreasein Ta from core to rim of ferrocolumbitefrom Montezhho. c. Increasein Fe from core to rim of the samegrain of ferrocolumbite.d. Distribution of Ta in rutile from Muralha but this grain hastwo small inclusionsof cassiterite.

ixiolite and Sn-rich titanian ixiolite. The exsolved TABLE 8, ELECTRON MCROPROBE DATA ON EXSOLVED ZONED FERR@OLUMBM FROM columbite-tantalitein the Vieiros cassiteritegenerally CASSITERITEFROM STANNIFEROUSQUARIZ has higher Sn + Ti + W contentsand, consequently, VEINS FROM ARGOALO lower Nb + Ta contentsthan the columbite-tantalite Core Rim inclusions in cassiterite from the same deposit t2 @g. 12a).Tapiolite falls in the field Ct @gs. l2a, c). MZOS Ms1 46.94 6196 6SJ3 Stannianixiolite has higher levels of Ta, Sn and Ta2O5 35.09 32.37 11.95 9.61 TiQz 0.61 1.06 l.lt 0.61 lower levels of Nb" Ti than Sn-rich titanian ixiotte SnO2 0.57 0.66 0.83 0.42 (Table9). Both havehigher levels of Ta, Sn andlower WO3 0.22 0.07 1.08 0.30 ixiolite with subordinate MnO 2.& 2.31 3.13 3.27 levels of Nb. W than titanian FeO 15.05 15.10 16.14 t6.21 W 2 Sn. Stannianixiolite and Sn-rich titanian ixiolite Toral 98.7? 98.51 100.20 99.15 fall within the ixiolite field of eem! & Ercit (1989) Nb 1.333 1.386 1.754 1.a26 and have greater Tal(Ta + Nb) values than titanian Ta 0.632 0.575 0.191 0.r54 ixiolite with subordinateW > Sn, which falls outside Ti 0.030 0.052 0.049 0.027 13a). Sn 0.015 0.017 0.019 0.010 that field @g. w 0.@4 0.001 0.017 0.005 The stannian ixiolite and Sn-rich titanian ixiolite Mn 0.149 0.128 0.156 0.163 havemore Sn, Ta, a greaterTal(Ta + Nb), and lessNb Fe 0.833 0.825 0.794 0.7n Total 2.996 2.9U 2.940 2.942 than the columbite-tantalite. The Sn-rich titanian ixiolite also has more Ti than columbite-tantaliteand l@tvln 15 13 stannianixiolite. These ixiolite compositionshave a FefMn greaterTal(Ta + Nb) valuethan the columbite*tantaliie 100Ta 32 29 10 I of correspondingMr/-(Mn + Fe) ratio, which agrees Ta+M with the findingsof Cernf & Ercit (1985, 1989)and (em! et al. (198tu} 1, 2, 3 and 4-fenocolumbite. Oxides in wt.%. On an atomic basis, the titanian ixiolite with Cation formula based on 6 atoms orygen. subordinateW > Sn from Fental,Revel, Atgozelo and Analyst: A Neiva Muralha has Ti > W, whereasthat from the Lake District ofEngland (Beddoe-Stephens& Foriey 1981) has W ? Ti, but generally W > Ti, and the phase probably correspondsto "wolframo-ixiolite". Both

TABLE 9. CO]VTPOSINONSOF NSOL!'ED D(OIJIE FROM CASSITER.IIE FROM CRANINC PEO\4ATMC VEINS AND QUARTZ VEINS FROM NOXTHERN PORTUGAL

Stmim ixiotite Titnim ixiolito 1234567 -Irt@ -M@ -i,f@- -M* -; M@ r lriii- Mod- s !6trt-=.F !l*---;--- Mrt---Mad-- Mhi- r,[dd- lr(@- s !.fii:-G

Nb2Oj 7.12 l.&4 4.13 9.51 9.24 11.E3 0.58 u.09 13.03 J5.38 10.65 40.t6 6735 60.tE 39.n 1.9 6.43 12.43 48.61 4,14 41.E3 55.76 Ta2O5 e.m 3.tt 61.0E69.58 63.17 61.04 t.6l s8.5463.69 rt.39 11.45 4.62 35.14 12.31 9.t? E.(X 0.26 2.r.72 23.12 4.t1 16.09 3125 Ti02 0.2t o.n 0 0.76 3.37 6.21 0,76 4.45 1.19 3.n 0.64 2.82 4.11 4.18 129 0.9 1.79 J.98 4.16 0J6 2.y7 5.19 SnO2 14.94 1.30 13.21 16.15 11.6 7.08 1.55 4.r7 10.23 0.95 0.33 0.55 0.43 1.33 0.95 0.52 027 1.95 1.10 0.29 0.74 1.6 wol 0.22 0.15 0 0.43 0.24 0.34 0.23 0 o.tl 2.23 0.63 t.X 3,23 2.2X 6.A 2.s3 3.ll 13.09 3.(o 1.38 2.29 6.51 MtrO 8.72 t.25 1.43 10.76 4.01 6.x o.22 6.5t 7.3t 4.9r l.E4 2.M 6.32 3.u 6.10 2.54 l.4l 11.47 tt.29 2.20 7.41 r4.8 FeO 4.0t t.32 2.t4 5,2s 4.26 6.31 0.24 5.94 6.84 14.24 0.t7 13.3515.15 16.14 r2.& 2.vt 7.46 lE.lo 6.61 2,36 3.3E 10.t6 Tobl 99.49 99.75 99.73 99.94 99.48 99.45 99.21

8 3 6 3 l2

Nb 0.343 0.0t4 0.204 o.4y 0.4r4 0.526 0.0x 0.494 0.J7J 2.015 0.300 t.s59 2.325 2.142 2.r4r 0.2tt t.712 2.464 1.8290.144 l.@9 2.016 Ta 1.t63 0.ut 1.750 2.W 1.758 1,.6320.U3 1.554 1.703 0.&2 0.214 0.096 0.t20 0,2& 0.1910.183 0.m5 0.614 0.J36 0.101 0.351 0.713 Ti 0.022 0.021 0.060 0.259 0.4@ 0.055 0.331 0.531 0.r8 0.049 0.161 0.301 o,u7 0.1960.060 0.104 0.340 0.2600.04t 0.1t5 0.32t Sn 0.645 0.M9 0.572 0.683 0.,168 0.2?E0.061 0.19t 0.40t 0.030 0.011 0.016 0.049 0.M2 0.030 0.017 0.008 0.062 0.036 0.010 0.024 0.053 w 0.006 0.004 0.012 0.006 0.009 o.ffi - o.o2t 0.046 0.012 0.031 0.@l 0.045 0.1360.053 0.M5 0.m 0.0770.030 0.048 0.136 Mr 0.788 0.125 0.663 0.947 0.34E 0.5730.01E 0. 0.614 0.3i!0 0.114 0.149 0.4m 0.201 0.4,t9 0.173 0.093 0.786 0.795 0.156 0.i03 0.969 0.358 0.113 0.194 0.,163 0.101 0.519 0.020 0.4E9 0.565 0.959 0.092 0.916 Lon 1.063 0.846 0.193 0.48E 1Jl4 0.e O.l7l 0.236 0.728 4-015

l, 2: stamian ixiolite; 3: Sn-rich titanim ixiolite; 4 5, 6, ?: 6t$ian ixiolite with ubordinate W > Sq l: Vieiros; 2, 3: Mortainho; 4: Fqtal; 5: Rwel; 6:Argozelo; 7: Muralha" Oxictesin wt.%. s-standarddwi1tioll n- number ofanalyses. Cation formula basedon 8 aioms oforygro. Analy*: A Neiva. 760 TIIE CANADIAN MINERALOGIST

2.0

El. Et.2 o o (! (o t a ln rt o0. g 0.8

0.8 1.2 0.4 0.8 1.2 Nb5' atom. Nb5'atom.

Fro. 9. Diagram of M5+ varsasTa5+ of columbite-tantaliteminerals located between the two parallel boundaries;minerals of the ixiolite-wodginite family plot below the lower boundary, except lithio-wodginite. Columbite-tantalite, Ct (open symbol);ixiolite, lxt (half-closedsymbol); wodginite, Wdg (closedsymbol). Symbols: a. CoteloNeiva (1954)(O, Ct); von Knorringar al. (1969a)(O lxt); von Knoning & Condliffe(1984) ( x Ct); Wise& Cemt (1984)(tr Ct I wdg); demf et al. [(1,986b)(V Ct,V IxL VWdg);(r992a) (O Ct); (1992b(+ Ct)]; Cemg& Lenton(1995) (9Ct); Lahti (1937)(OCt); Wengeret al. (1991)(OCt), ftcit et aL (1992a,b,c) (OWdg); Spilde& Shearer(1992) (A Cr);Suwinonprecha er al. (1995) (E Ct, I kt). b. Nickel et al. (1963) (O Ixt); von Knorring et al. (1969b) (A Wdg); crice et al. (1972) (E Ct, I Wdg); Zelt (1975)(+ Ct); Fergusonet al. (1976)(O Wdg); Sahama(1980) ( x Ct); Beddoe-Stephens& Fortey (1981) (O probably k0; Cem! et al. [(1985)(tr ct, I Wdg); (1989a)(O C0; (1989b)(9 Cr); (1989c)(A C0]; Foord(1982) (OCt O wdg); Gomes(1991) (O C0; Wenger& Ambruster(1991) (V C0.

Et.2 o o + tt f o.e

0 0.4 0.8 1.2 1.6 2.0 0A 0.8 1.2 t.6 2.0 Nb5'atom. Nb5'atom. FIc. 10. Diagram of Nb5+ versus TaJ+of Portuguesecolumbite-tantatite and ixiolite minerals. a. lncluded and exsolved columbite-tantaliteand ferrotapiolite from Vieiros, Revel and Montezinho(symbols as in Fig. 7), exsolvedstannian ixiolite ([l Vieiros, V Montezinho), Sn-rich titanian ixiolite C7 Montezinho) and titanian ixiolite with subordinateW > Sn (O Revel). b. Exsolvedcolumbite-tantalite and ferrotapiolite from Cabragdo,Fental and Argozelo (symbolsas in Fig. 7) and exsolvedtitanian ixiolite with subordinateW > Sn (* Fental, A Argozelo, O Muralha). CASSITERITEAND ITS INCLUSIONS.PORTUGAT 76r haveTa < Nb, but the ratio Tal00/(Ta + Nb) ranges stannianixiolite. between 0 and 34 in this Portugueseixiolite and Titanian ixiolite with subordinateW > Sn plots between2 and 4 in the Enelish ixiolite. Furthermore. betweenthe (Sn,Ti) - Ge,Mn) (M,Ta)2 and Ge,Mn) theranges of Mnl00/(Mn iFe) are7-80 and61J2 n (M,Ta)2 - (Fe,Mn)(Sn,W,Ti) joins (Figs. l2b, c, d) the former and latter, respectively,both falling outside and below the datafor columbite-tantalite.The higher the ixiolite field in Figure 13a.This Portuguesetitanian the W content,tle more pronouncedis the shift to the ixiolite has a heterogeneouscomposition, whereas that latter join Gig. 12d), probably drifting toward a from the Lake District is homogeneous.The highest (Fe,Mn)WOacomposition, which agreeswith findings values of Ti and W in ixiolite were found in the of Suwinonprechaet al. (1995),although wollramite stanniferousquartz veins from Argozelo (Table 9). was not found as an exsolutionproduct of cassiterite. The small blebs of exsolvedixiolite generallyshow oscillatory y6ning, which is probably due to the GEoclnt"trsrRvor INcl-tloso concenfiation and diffusion of Ta and Nb and ANDEXSOLVED RI.rru-S the growth dynamics of the crystals. hogressive zoning also occurs,as documentedin Table 10. An Rutile inclusionswere 6ainly found in cassiterite increasein Nb, Sn anda decreasein Ta, Ta/(Ta+ Nb), from W-Sn-bearing quartz veins and also from the and Ti from core to rim of single crystals of Sn-rich pegmatitebodies at Bessa(Table l1). Rutile included titanian ixiolite Clable 10, A) were found. In single in cassiterite from quartz veins from Carvalhal, crystalsof titanianixiolite with subordinateW > Sn, an Soutelinho, Filharoso, S. Domingos, Folgar and increasein Nb and a decreasein Ta, Tal(Ta + Nb), Bougo has a similar composition.These systems of Ti, and W from core to rim also were observed veins all arerelated to the sameS-type granite (Ftg. 1). (Table10, B). Thus, an averagecomposition for the rutile in these In the Sn-rich titanian ixiolite and stannianixiotte. veins is given in Table 11 (anal.7). However,rutile the substitution(Fe,Mn)2+ + 2(M,Ta)5++ 3(Sn,Ti)a from BouEo containsup to 11.37 wt.7o Nb2O5, dominates,as suggestedby their alignment along the 5.78wt%o Ta2O5 and 4.15 wtVoFeO. The rutile richest (Sn,Ti)- Ge,Mn) Q.[b,Ta),join (Fig. 12d),extending in W (4.95wtVo WO) is includedin cassiteritefrom from columbite-tantalite data (Cem! et al. 1986b). the W-Sn-bearingquartz veins from Panasqueira. These compositionsmay contain some Fe3+obecause Rutile was interpretedas a product of exsolutionin some of them deviate slightly from that join in the the cassiterite from pegmatite bodies at Fental and direction(Sn,Ti) - (Fe,Mn)(M,Ta) (Figs. 12a,b, d). Revel and the W-Sn-beaing qtartz veins from However, tJreirFe3+ content is probably low, as their Muralha. Some of these crystals of cassiterite also cation totals normalizedto 8 atoms of oxygen do not show the presenceof exsolved columbite-tantalite, generally exceed 4.00, except in some grains of titanian ixiolite with subordinateW > Sn and, locally,

,f{1)(Nb,Ta)2

/- - -b< . o.,to /.oT ^"-: 17' o ,xr t /o o e l, /.8 E1 T

25 20 15 t0 o2520 SnJiW (Fe,MnXSn,W,Ti) Sn.Ti.W (FeMn)(5n,w,Ii)

Flc. 11. Compositionsof columbite-tantaliteminerals and ixiolite-wodginite minerals in the (Sn,Ti,W) - (Nb,Ta) - (Fe,Mn) diagram.a. and b. The compositionsplotted in the Figures 9a, b respectively.Enlargements of the triangular areaCt-kt shownin Figure 5a. 762

,41 75 r'/

,Mn)(Nb,Ta)z gMn)(Nb,Ta)2

5n,Ti,W (Fe,MnXSn,W,Ti) {--

75

r -/ /^ffi ,fiio'./ct .zt it,l Cr l.z -/ffi**r- i/ ./l.f ,/ ooo i I I txt i'' / I I 25 20 iq in R 60 10 200 Sn.Ti,W (Fe,Mn)(5n,\ry,T11 (Fe,MnXSn,VV,Ti) +- Sn,Ti,W Fe,Mn

ftc. 12. Compositionsof included and exsolved Portuguesecolumbite-tantalite; exsolved ferrotapiolite, stannian ixiolite, Sn-rich titanian ixiolite and titanian ixiolite with subordinateW > Sn in the (Sn,Ti,W) - (I.{b,Ta)- (Fe,Mn) diagram. a. Vieiros; b. Revel, Argozelo,Montezfuho; c. Cabrag6o,Fental, Muralha; a, b, c. Enlargementsof the triangulararea Ct-Ixt shown in Figure 5a. Slrnbols as in Figures 7 and 10. d. Selectedrepresentative data of a b, c on the whole diagram; + columbite-tantalite, X stannianixiolite, O Sn-rich titanian ixiolite. a titanian ixiolite with subordinateW > Sn.

iknenite, but thesephases are never in mutual contact. rutile, therefore,probably contain Fe3+, which is also The rutile richestin Sn, M and Fe (4.24'ut%oSnOr, supportedby the clusterof rutile compositionsbetween 21.39 wt%o MzOs, 7.22 wt%o FeO) was exsolved the (Sn,Ti,W) - (Fe,Mn) (M,Ta)z and (Sn,Ti,W) - from cassiteriteat Revel"whereas the rutile richest in (Fe,Mn)(M,Ta) joins (Fig. l3b). Ta (20.90wLVo Ta2O) was exsolvedfrom cassiterite In rutile, Nb usually predominates over Ta at Muralha. In the exsolvedrutile, X(Nb + Ta r Sn + (Table 1l), and the crystals are heterogeneous W t Fe + Mn) is similar to or exceedsthat in the (inegularly zoned), but homogeneouscrystals were includedrutile. found. Only rutile exsolvedfrom cassiteritefrom the In general,the cationtotals norrnalizedto two atoms W-Sn-bearing quartz veins from Muralha shows a of oxygenexceed tlre ideal value of 1.00,except in the generaltendency for Ta > Nb; mostbut not all of these rutile poorest in Nb and Ta. Most of the crystals of crystalsseem homogeneous (Fig. 8d). h rutile, Sn CASSITERITE AND ITS INCLUSIONS. PORTUGAL 763

FeTa2O5, Mn Ta206,

t\e\d r*o\Yl- ,r/K ,(\ .*#.t' o : ^^o o * o a xlP* nng q^l* q.^ a A A*AAAA A 96 Fe Nb2O5 MnNb2 O5 SnJi,W

>:a ,(\ \x:\-\\=:-'- @ Y i-_=t_lr-_-\v I I .o "t.. I z I + 6 F o x I N..; e d :$" o N 10 60 20 /+0 60 80 t00 Mn100/(Mn+Fe) Mn 100/(Mn+Fe) Frc. 13. a. Pornrguesestannian ixiolite, Sn-rich titanian ixiolite and titanian ixiotte with subordinateW 2 Sn in the columbite quadrilateral.Symbols as in Figure 10.[emFositional gap separatingcolumbite-tantalite from tapiolite and the ixiolite field from Cernf & Ercit (1989).b. Compositionsof includedand exsolvedrutjle in the (Sn,Ti,W) - (I.[b,Ta)- (Fe-Mn) diagram. Symbols:O Bess4 * Carris,V Lombo de Boi, O Linhares,gFonte Figueir4 O Vale dasGatas, I Carvalhal,Soutelinho, Filharoso, S. Domingos,Folgar, Bougo, A Panasquehainclusions; + Fental, Z Revel, A Muralha exsolutionproducts. c, d. Selectedexamples ofdark zonesof cassiteritehost andtheir exsolutionproducts. Symbols: as in Figures7 and 10,rutile from I Revel, * Fental, O Muralha x dark zone of cassiteritehost at 10 pm from the rim of exsolved mineral; c. -- Cabragao,-- Fental,- 4ttozelo, -. - . - Muralha; d. - \'rigi165,-- Revel, -- Montezinho.

normally predominatesover W, but locally, at Vale das The ratio Fe/@e+ Mn) is extremelyhigh, generally Gatasand Panasqueira(Table 11), rutile inclusions 1 or close to it. The ratio (Fe + Mn)/(Nb + Ta) with W ) Sn were found. However.W concentrations generallyvaries from 0.5to 1.1,but highervalues were can vary significantly in a single crystal, with between found in the rutile richest in W, included in cassiterite 0 up to 3.70vtt.VoWO3. from the W-Sn-bearing quartz veins from Vale das 764 THE CANADIAN MINERALOGIST

TABLE IO. ELECTRON MCROPROBE DATA ON EXSOLI/ED ZONED DCOLITE FROM The exchange 2(M,Ta)5+ + (Fe,Mn)2+ = 3Ti4+ CASSITENTE FROM STANNIFEROUS VEINS QUARIZ may well be a mechanism of incorporation of Nb, B Ta, Fe2+, and Mn in rutile, whereas Wfi Fe2+= 2Ti4+ Core =-- J Rim Core + Rim 1234 may explain the rutile enriched in W that is very deficient in Nb and Ta. The substitution Sne = Ti4 Nb2O5 Il.rr 11.20 1t.85 12.17 13.03 5t.49 60.8t 62.27 6.t7 Tr205 63.69 62.22 @.12 59.14 58.54 9.43 5.96 5.57 4,61 explains the incorporation of Sn in rutile. Tio2 7.O2 7.09 6.94 5.11 5.63 3.33 2.82 2.69 2.75 SBO2 4.47 5.69 6.22 8.89 8.83 t.27 0.61 0.73 0.75 wo3 o.09 0.45 0.48 0.81 0.61 13.09 8.49 7.6 J.?E GrocnsvtrsrRyoF INcLUDED MnO 6.79 6.65 1.26 6,U 7.10 4.35 8.13 6.87 5.63 F€O 6.23 6.32 6.27 6.68 6.28 16.06 11.90 13.14 14.08 ANDEXSOLVED II-MENIE Tolal 99.E2 99.62 9t.14 9.64 100.02 99.02 98.79 98.88 99.77 Nb 0.494 0.491 0.525 0.544 0.575 1.902 2.lm 2.2t9 236 Accidentallyincluded and exsolvedilmenite are 1.703 1.660 r.6lE 1.589 t.J54 0.209 0.128 0.118 0.096 Ti 0.519 0.J23 0.496 0.380 0.413 0.205 0.16E 0.160 0.159 scarce and without contact with other inclusions or S! o.r91 0223 0.243 0.3fi 03U 0.041 0.019 0.023 0.023 w 0.002 0.011 0.012 0.021 0.015 0,277 0,t74 0.156 0.115 productsof exsolution.Chemical compositions, given Mn 0.565 0.553 0.602 0.573 0.587 0.301 0.545 0.458 0.368 in Table 11.show M > Ta. The exsolvedilmenite has 0.514 0.519 0.514 0.552 0.513 1.097 0.?88 0.866 0.909 Toal 3.988 3-986 4.010 4.009 4.00r 4.032 4.N2 4.000 3.9?8 higher contentsof Nb, Ta and Sn than the included

100 Mr ilmenite. which is richer in Mn. Exsolvedilrnenite F*MN containsup to 0.70 wLTo SnO2,0.66 wtTo M2O5 t*t l00Ta 18 71 16 74 73 tO 6 5 4 and 0.06 VoTa2O5, and includedilmenite contains T*Nb up to 4.70 wt,VoMnO. The contentsof Nb and Ta A: Sn-dch titanian ixiolite ftom Mortsinho, B: titaniu ixiotite with are too low to indicate any specific mechanismof subordinateW > Sn &om A'goalo. Oxide in wt.%. Cation fomula bsed on substitution. However, a mechanism such as 8 atomsofoxygm. AnalJ6X:A Neiva. (Nb,Ta)5* + Fe3+ = 2Ti4+ is suggestedby the progressivedecrease in Ti with increasing(Fe + Mn + Nb + Ta).

Er-sMEr.lrPARTmoNIlrc Auolc Nb- Gatas and Panasqueira(3.2-9.0 and 2.6-12, ANDTa-BEARING PHASES respectively).Such rutile has a low Fe + Mn content and is amongthe most deficientin Ta + Nb. These In veins of granitic pegmatite,a single crystal of W-enriched rutile crystals do not fit the expected cassiteritemay show isolated exsolved grains of correlationsbetween Olb + Ta) and Fe2+,nor between different compositions,e.9., some of columbite- (Ta + Nb) and Ti. The ratio Tal(Ta + M) varies tantalite,others of ixiolite and rutile. and noneof them between0 and 0.69,but Ti/(R2++ Rs+)varies widely, in mutual contact.Grains of the samespecies may have befween3.L alld994. variouscompositions, which suggestthat they arenot

TABLE 11.AVERAGE COMPOSITIONSOF INCLLDED AND EXSOL!€D RLl'flLE AND ILMENTE (D IN CASSITERIIEFROM GRANITIC PECTi4ATIIES AND QUARTZ WINS FROM NORTMRN AND CENTRAI PORTUCAL

Inclusions Exsolutionproduots l0nt2tn TiO2 88.61 71.55 89.14 95.98 78.55 9t.25 .11 94.98 53.52 u.92 69.0E 6E.2E 5t.5E Srlo2 2.06 r.71 2.15 2.34 1.93 1.78 1.43 1.14 0.04 1.84 2.30 1.65 0.60 Nb2O5 5.07 8.64 5.39 0.83 10.10 2.54 3.09 0.30 0.32 t2.26 t4.33 7.74 0.45 Ta2O5 2.0? 1.65 0.05 0.10 4.81 0.08 1.63 0.04 n.d. 1.ll 8.44 16.3E 0.04 WO3 0.21 0.08 0.61 0.13 0.25 2.11 0.18 2.34 0.01 0.16 0.10 0.14 0.02 F(o 2.30 4.01 t.17 0.30 4.30 t.l5 t.42 0.79 42.84 4.04 5.91 S.1E 45.36 MnO 0.01 0.03 0.01 0.01 0.01 0.08 0.01 n.d. 3.63 0.01 0.03 0.04 t.67 Tota.l 100.33 99.67 99.78 99.69 99.95 99.59 99.87 99.59 [email protected] 100.34 100.19 [email protected] 99.72

! l0 l3 lt 2 l8

Ti o.gu 0.855 0.927 0.978 0.855 0.944 0.951 0.970 2.0t6 0.861 0.783 0.797 t.973 Nb 0.032 0.057 0.034 0.005 0.066 0.016 0.019 0.002 0.007 0.078 0.098 0.054 0.010 Ta 0.008 0.030 0.019 - 0.006 0.004 0.035 0.069 0.@l Sn 0.011 0.010 0.015 0.013 0.011 0.010 0.008 0.006 0.001 0.010 0.014 0.010 0.012 w 0.001 0.002 - 0.001 0.010 0.001 0.008 0.@l - 0.001 0.027 0.049 0.020 0.003 0.052 0.013 0.016 0.009 t.194 0.048 0.074 0.07J 1.929 Mr - 0.@1 0.154 0.001 0.072 Toral l.@3 1.001 0.998 0.999 1.004 0.994 1.001 0.995 3.912 l.@2 1.004 1.007 3.997 1: Bessa,2: Canis, 3: Lombo de Boi, 4: Linhares,5: Fonte Figueira,6: Vale dasGatas, 7: Carvalhal,Soutelinho, I'ilharoso, S. Domingos,Folgar, Bougo, 8: Panasqueir49: Carris, l0: Fental, 11: Revel, 12: Muralha, 13: Fental.Oxides in wt.o/o.n.d. - not deteoted.n-number ofanalyses of rutile andnumber ofanalyzed grains ofilmenite. Cationformula ofrutile anditnenite basedon 2 and 6 atomsoforygen respectively.Analyst: A Neiva. CASSITERITE AND ITS INCLUSIONS. PORTUGAL 76s in equilibrium. However, both ferrotapiolite and rarely to a Hercynian I-type granite, has Fe > Mn ferrotantalite are homogeneous,and probably in andNb > Ta andis usually zoned.The darkerzones are equilibrium (Fig. 7b). The former is enrichedin Ta and generallyslightly pleochroic and chemicallyindistinct Fe in comparisonwith the lat[er. from the alternatingparallel lighter zones.Both types Exsolved Sn-rich titanian ixiolite and stannian of zonemay containrutile t ilmenite inclusions.If the ixiolite are enriched in Ta and Mn compared to darker zones are strongly pleochroic, they host coexisting columbite and tantalite. Exsolved titanian exsolved rutile t titanian ixiolite with subordinate ixiolite with subordinateW > Sn, however,may have W > Sn, and havemore Ti than the lighter zones. greater or smaller values of Tal(Ta + Nb) and (3) The darker zonesof cassiteritefrom pegmatites Mn/(Mn + Fe) than coexist'ng columbite-tantalite. and stanniferousquartz veins havea much larger range Exsolved rutile is norrnally enriched in Ta and Fe of Nb + Ta and Fe than cassiteritefrom W-Sn-bearing relative to coexisting columbite-tantaliteand titanian quartz veins, which is normally the richest in Ti. ixiolite with subordinateW > Sn.This is in asreement The main mechanismresponsible for Nb, Ta, Fe, Mn with the dataof dernf et at. (1981,1986b)aid demf and Ti incorporation in cassiterite is probably & Ercit (1989); however,at Fental,the rutile phase 2(M,Ta)5++ (Fe,Mn)2+i= 3(Sn,Ti)+. shows preferencefor M and Fe. Exsolved ilrnenite (4) Euhedral to subhedral cassiterite crystals of occurstoo infrequently to be comparedwith others. Sn-oreoverlying cupriferousores from a volcanogenic As the compositionof the dark zonesof the host depositare related to older Hercynianfelsic rocks.This cassiteritevaries with the distancefrom the productsof cassiteriteis only very slightlypleochroic, with brown exsolution(Fig. 4a), the compositionof the cassiterite to deep brown componentsricher in Fe than yellow 10 p.rnfrom exsolvedparticles was arbitrarily takenfor components.It is Fe-enrichedand devoid of inclusions purposesof comparison.The compositionof selected andproducts of exsolution. pairs(host cassiterite - exsolutionproduct) are shown (5) The exsolved columbite-tantaliteis mostly in Figures 13c, d. In general, all the products of composedof ferrocolumbite.Cassiterite from the exsolution are enrichedin M and Mn in comparison pegmatitesat Vieiros hosts accidental inclusions with the host cassiterite"in asreementwith data of ranging from ferrocolumbite to manganocolumbite. Wise& dernf (1984),(em! d at. (1985,1986b) and Theseinclusions generally carry less Ti + Sn + W than Suwinonprechaet al. (1995).Equilibrium is suggested exsolved columbite-tantalite. Exsolved ferrotapiolite between cassiterite and some of its products of is rare in cassiteritefrom pegmatiteoccurrences and is exsolution,as shown by paralleltielines. probably in equilibrium with coexistingferrotantalite. Columbite-tantalite inclusions have greater or (6) The diagramTa5+ versas Nb5+ and the triangular smaller Tal(Ta + M) and Mr/(Mn + Fe) valuesthan diagram(Nb,Ta) - (Sn,Ti,W)- (Fe,Mn) distinguish the host cassiterite.Rutile inclusions and host between minerals of the columbite-tantalite group cassiteriteusually have Mn/(Mn + Fe) = Q, fg1 (whatever their structural state) and minerals of Tal(Ta + M) is either greater or smaller in the the ixiolite-wodginite family, in this work arbitrarily inclusion. called ixiolite. Furthermore, these diagrams differ- entiate stannian ixiolite and Sn-rich titanian ixiolite CoNcr-usroNs from titanian ixiolite with subordinateW > Sn. The mdn mechanismof incorporationof elementsin these (1) Euhedralcassiterite from bodiesof Sn-bearing compositionalvarieties of ixiolite is probablythe same granitic pegmatite and stanniferousquartz veins, asthat found in cassiterite. relatedto HercynianS-type granites,generally has Fe (7) Complexoscillatory zoning in commonin the > Mn and Nb > Ta and is zoned, with alternating includedand exsolvedcolumbite-tantalite and ixiolite, parallel darker pleochroic zones richer in Fe, Ta but smoothlyprogressive zoning also was found, as and Nb than the lighter zones,which are nearly pure well as occasionalhomogeneous crystals. SnO2.Some deep red, stronglypleochroic cassiterite (8) Inclusions of rutile are conmon in cassiterite hasTa > M. The darkerzones are oscillatorily zoned from the W-Sn-bearingquartz veins, whereas exsolved and show exsolution blebs of columbite-tantalite or rutile is scarcein cassiteritefrom theseveins and from ixiolite or both. but where thesezones also contain pegmatites. Both the inclusions and exsolution exsolvedrutile + ilmenite, they arericher in Ti than the productsare generallyheterogeneous; tlte former have lighter zones. Successivevery closely spaced,red lessNb + Ta + Sn + W + Fe + Mn than the lafter. Rutile zoneshave a similar composition,but in any single usually has M > Ta and Sn > W, but included crystal, a large range of Ta/(Ta+Nb) values can be rutile with W 2 Sn and exsolvedrutile with Ta > M found throughout the red zones. Occasionally, were found. The mechanismresponsible for incor- columbite-tantaliteinclusions were found in both poration of Nb, Ta, Fe2+and Mn in rutile is probably lighter and darkerzones. 2(M,Ta)5* + (Fe,Mn)2+= 3Tia; w6rFe2+= 2Ti4+ (2) Euhedralcassiterite from W-Sn-bearingquartz is tle mechanismresponsible for incorporationof veins, relatedmainly to HercynianS-type granites and W and Fe in rutile deficient in Nb and Ta, and 766

Sn+ = Ti4 explainsthe incorporationof Sn in rutile. & - (1989):Mineralogy of niobium and (9) Ilmenite inclusions were rarely found in : crystal chemical relationships, paragenetic cassiteritefrom W-Sn-bearingquartz veins, containing aspectsand their economicimplications. /n Lanthanides, Tantalum Niobium (P. MOller, P. demf F. Saup6, in addition,inclusions of rutile. Ilmenite and & exsolvedfrom eds).Springer-Verlag, Heidelberg, Germany -79). cassiteritewas only found in a granitic pegmatite.It has Q7 low Nb > Ta contents.The inclusionshave lessMo & Wsq M.A. (1986a):Mineralogy, Ta and Sn and more Mn than the products of paragenesisand geochemicalevolution of Nb, Ta-oxide exsolution. There is a regular decreasein Ti as mineralsin granitic pegmatites..lnLMinzral. Assoc.,14th, Fe + Mn + Nb + Ta increases,suggesting that the Abstr.Programs,Tl. mechanism (Nb,Ta)s++ Fe3+= 2Ti4+ might have operated. & - (1992a): The tantalite- (10) The host cassiteriteshows preference for Ta tapiolite gap: natural assemblagesversus experimental data.Can. Mineral.30. 587-596. and Fe relative to M and Mn with respectto all the products of exsolution,but no distinct preferencewas GoAD, 8.E., HAwrHoRr.[E,F.C. & CHAPMAN,R. found with respectto its columbite-tantaliteinclusions. (1986b):Fractionation trends of the Nb- and Ta-bearing oxide mineralsin the GreerLake pegmatiticgranite and its AcK].{owLEDGEIVIEI.{TS pegmatiteaureole, soutleastern Manitoba. Am. Mineral. 7L. 501-517. Thanksare due to Prof. J.M. Cotelo Neiva and Eng. Alrneida Correia for their help in collecting many of - & Lrvror, P.G.(1995): The Buck and Pegli lithium the samples.hof. M.R. Machadokite, Drs. J.M.F. deposits, southeastemManitoba: the problem of updip Ramos, M.M. Sim6es and Mr. F.A.P. Santos are fractionation in subhorizontal pegmatite sheen. Ecor. Geol.90, 658-675. thankedfor allowing the useof the electronmicroprobe and photographicequipment facilities at the tnsiiruto N6var, M. & CHApMAN,R. (1992b):Effects of Geol6gicoe Mineiro, S. Mamedede Infesta,Pornrgal. sillimanite-grademetamorphism and shearingon Nb-Ta Drs. J.M.F.Ramos and J.F.W. Bowles are thanked for oxide mineralsin granitic pegmatites:Mar5lkov, northern writing the programto processthe electron-microprobe Moravia" Czechoslovakia.Can. Mineral. 30, 699-718. data. This paper benefitted-greatlyfrom the very helpfulcomments of Prof.P. Cernf andDr. M.A. Wise Peul, B.J., HawruonNe,F.C. & CuanuaN,R. and the subsequentreview of the Editor, Prof. R.F. (1981): A niobian rutile - disordered columbite Martin. intergrowth from the Huron Claim pegmatite, south- easternManitoba. Can. Mineral. 19.541-548.

RSFERENCES RoBERrs,W.L., ERcn, T.S. & CHapuar, R. (1985):Wodeinite and associated oxide minerals from the Peerlesspegmatite, Pennington County, South Dakota. BARsANov,G.P., YSREI N, N.I. & SsncsyEva, (1971): N.Y. Am. M ineral. 70. 1044-1049. Columbite-tantalite zoning as revealed by electron-probe microanalysis. Dokl. Acad. USSR, Eanh Sci. Sect.20l, r74-176. Ucaxuwr,'N,E.K. & Crurver, R. (1989c): A ferrotantalite-ferrotapioliteexsolution from Uganda. NeuesJahrb. Mineral., Monatsh., L09-120. BEDDoE-S'rEeHENs,B. & FoRrEy, N.Y. (1981): Columbite from the Carrock Fell nrngsten deposit. Mineral. Mag.44, Corplo Nntve, J.M. (1944):Jazigos porrugueses de cassi- 217-223. terite e de volframite. Comun.Serv. Geol. Portugal2S.

(1954): Pegmatitos com cassiterite e CrnNl, P., CHawraN,R., Cnecrowsrv, L.E. & ERcn, T.S. tantalite-columbiteda Cabragdo(Ponte do Lima - Serra (1989a): A ferrotantalite-fenotapioliteintergrowth from de Arga). Mem. Not. Mus. Inb. Mineral. Geol., Univ. Spittal a.d. Drau, Carinthia, Austria.Mineral. Petol.4l, Coimbra36.1-61. 53-63. Encrr, T.S., Crrur*, p. & HewrHonNs,F.C. (1992b):The GOD,R., NTEDERMAYR,G. & WrsE,M.A. wodginite group.III. Classificationand new species.Can. (1989b): Exsolution intergrowths of titanian ferro- Mineral.30.633-638. columbite and niobian rutile from the Weinebene spodumenepegmatites, Carinthia, Austria. Mineral. - & McCAMMoN,C.A. (1992c): Petrol. 40. 197-206. The wodginite group. II. Crystal chemistry.Can Mineral. 30.613-631.

& ERcr, T.S. (1985):Some recent advances in the Hewruonrrre,F.C. & CERN'f,P. (1992a):The mineralogy and geochemistry of Nb and Ta in rare- wodginite group. I. Structural crystallography.Caz. elementgranitic pegmatites.Bull. Mindral. 108, 499-532. Mineral. 30. 597-611. CASSITERITEAND ITS INCLUSIONS. PORTUGAL 767

FERcusoN,R.8., HawrsonNE,F.C. & GrucB,J.D. (1976): The MrRcrEco,A., SeNGnz, G.A. & Pozes, J.M.M. (1987): crystal structues of tantalite, ixiolite and wodginite from Microinclusionesen casiteritasde distintos tipos de Bernic l,ake, Manitoba. II. Wodginite. Can. Mineral. 14, yacimientosdel centro-oestede Espanha.Cualemo Inb. ss0-560. Xeol6xicode laxe 12, n3-287.

FooRD,E.E. (1982):Minerals of tin, ,niobium and Nswa, A.M.R. (19g3):The petrogeneticimporrance of trace granitic tantalumin pegmatites.In Grmitrc Pegmatitesin elemenrsof Hercynian granitil-Trace rocks from portugal. 1z Scienceand Industry @. eernf. ed,.).Mineral. Assoc. The Significance of Elements in S-olving Can.,Short-Course HandbookS, 187-238. petrogenetic problems and Controversies (S.S. Augustithis,ed.). Theophrastus Publications S.A., Athens, FuENfE,M.F. & kano, A.M. (1994):El campopegmatftico Greece(331-351). de Forcarey y las mineralizacionesde Sn, Ta y Nb associadas(Pontevedra, Galicia, Espafla).Bol. Soc. (19g4):Geochemistryoftin-bearinggraniticrocks. Espan.Mineral.l7,5l-63. ChernGeo1.43.241-256. Gaspan, O.C. (1991): Paragenesisof the Neves-Corvo (1987):Geochemistry of greisenizedgranites and volcanogenic massive sulphides. Comun. Serv. Geol. metasomaticschist of -tindeposits in Pornrgal./zl Porlugal 77, n-52. Chemical Transport in Metasomatichocesses (H.C. Helgeson,ed.). NATO ASISer. 2L8,681-699. Gruliau, G. (1987): La cassitdritezon6e du gisementde Sokhret Allal (granite des Z,aEr,Maroccentral): compo- sition chimique et phases fluides associ6es.Mineral. - (1993): Geochemistryof granitesand their minerals Deposita22,253-261. from Gerezmountain, northem Portugal.Chem. Erde 53, 227-258. Goms, C.L. (1991):CaracterizagAo d4s niobites-tantalites do campoaplito-pegmatftico de Arga-Minho (l.{ de Porrugal.l. Nrcrpr-, E.H., Rowlem, J.F. & MCADAM,R.C. (1963): Geoci?ncias,Rev. Univ. Aveiro 6,173-191. Ixiolite - a columbite substructure.Am- Mineral. 48, 96r-979. (1994): Estudo estrutural e paragendtico de utn sistema pegmat4ide gran{tico - o campo aplito- OcuNBAJo,M.I. (1993):Jhs minsralegyand geochemistry of pegnntttico de Arga, Minhn - Portugal. Ph.D. thesis, somecassiterite from the YoungerGranite province of the Minho University, Minho, Pormgal. Josplateau, Nigeria. J. \fr. Earth Sci.16,465-472.

GoNzalnz,R.F. & Rrvuslrn, M.B. (1989):Elementos traza SeHava,T.G. (1980):Minerals of the tantalite-niobiteseries y parametroscristalinos em cassiteritascomo indicadores from Mozambique.Bull. Mindral. L03, 190-197. de procedencia;aplicacion a la zona de Golpejas (Salamanca).B ol. Soc.Espan. Mineral. 12, 341-349. Spnor, M.N. & Snrenrn, C.K. (1992): A comparisonof tantalum-niobiumoxide assemblagesin two mineralogi GnrcE,J.D., dewf, P. & FrncusoN,R.B. (1972): The Tanco cally distinct rare-element granitic pegmatites, Black pegmatite at Bernic lake, Manitoba. II. Wodginite, Hills, SouthDakota. Can.Mineral. 30, 7 l9-7 37. tantalite, pseudo-ixiolite and related minerals. Can. Mineral. LL,609-642. SrvruoNpnncre,P., Crmi, P. & FREDRICH,G. (1995):Rare metal mineralization related to gralites and pegmatites, HALL,M.R & Rmse, P.H. (1971):An electronmicroprobe Phuket,Thailand. GeoI.90, 603-615. studyof luminescencecent€rs in cassiterite.Arn. Mineral. .Econ. 56.3t-45. Vol.l KNonnwc, O. & CoNolrrr, E. (1984): On the IzoREr, L., MARNTER,G. & Dusausov, Y. (1985): occurrenceof niobium-tantalumand otler rare-element Caract6risationcristallochimique de la cassit6rite des mineralsin the Meldon aplite, Devonshire.Mineral. Mag. gisementsd'6tain et de tungsGnede Galice,Espagne. Car. 48,443448. Mineral.23.22l-231. Sanava, T.G. & LnFrNsN,M. (1969a):Scandian Letm, S. (1987): Zorungin columbite-tantalitecrystals from ixiolite from Mozambique and Madagascar.BUII. Geol. the ganitic pegmatitesof the Erdjiirvi area, southern Soc.Finland 41.75-77. Finland.Geochim. Cosmochim. Acta 51. 509-517. & - (1969b):Ferroan wodginite MOLLER,P., DL'r-sKr,P., SzAcKr,W., Malow, G. & RrEom,E. from Ankole, soutl-west Uganda. Geol. Soc. Finlan4 (1988): Substitutionof tin in cassiteriteby tantalum, BuIL 4l.65-69. niobium, tungsten,' and manganese.Geochim. Cosmn c him. Acta 52, 1497- 1503. WENGER,M. & AnMsnusrER,T. (1991): Columbite (Fe,Mn)(M,Ta)2O6in the pegmatitesof the calc-alkaline MooRE,F. & Hown, R.A. (1979):Geochemistry of some Bergell intrusion (southeastcentral Alps). Schweiz. Comubiancassiterites. M ineral. Deposita14, 103-107. Mineral. Petrogr. Mitt. 71, 349-369. 768 THE CANADIAN MINERALOGIST

& GEIGER,C.A. (1991):Cation distri- ZEt-'t,G.A.(1975):DataforsomeAfricancolumbite-tantalite bution in partialy orderedcolumbite from the Kings specimens.Geol.Soc.Finland,Bull.47,ll7-125. Mountain pegmatite, North Carolina. Am- Mineral. 76, 1897-1904.

WISE,M.A. & eERN'f,P. (1984):First U.S. occurrenceof wodginite from PowhatanCounty,Yirginta. Am. Mineral. 69. 807-809.

unit cell dimensionsfor orderedcolumbite-tantalite end- Received August 6, 1995, revised manuscript accepted members.Neues Jahrb. Mineral., Morntsh.,372-378. Februnry24, 1996.