A STUDYOF PYROCHLOREAND BETAFITE D. D. HOGARTH Unhsersityof Ottawo, Ottowa' Canad'a
ASSIRACT several types canadian occur- Pvrochlore and betafrte were investigated from 9f eleven analyses for eight con- ,*iJ"""1it* ;;;G; f;t*;;ty ;nstituents and oH)18(F' oH)s is proposedfor stituenta are presented.2i;;;il;l*;lu-i*-"n'u(o' sites in the unit cell. Differen- the pyrochlore-betafite serie"switlr r representing vaLnt two states of water' Betafite and tial thermal and thermogravimetric curves indicate can begin w-ell the exo' thorian pyrochlore tt" t"l,i-i.i, id"i recrrs4li'ation .below edge of ignitea minerals tends to thermic reaction indicateiln b.r.n. ."*o. The cell *"ig-ttt" dirived from densitv-cell decrease as titanium i;;i;;;;;. Molec'lar ""i irom analyses. Observed r-ray edee data correspond q""fiilii""i' a. ii,o"e .al"ul"ted role of iron is uncertain. Frequency il1;#;;";;irh;d;;J;.iues, but the and betafite at 15 per cent uranium. dragrams suggesr u ,ru.ur;l*Jio-i;io" Jpyro"hloru
Iutnoouctton long been disputed' The relationship of pyrochlore and betafite has betafite are very X-ray powder patterns of pyrochlore and ignited quite different. Pertinent ,i*if", tut chemical compositions are usually (1932), who showed chemical work has U""" i"ported by Machatschki flom stoichio- that membersof the;yro"hlo." seriesdepart considerably that vacant cationic ;"ary, and Ros6n &'W""tg'"" (1938), who showed structure' Borodin & sites are common it with the pyrochlore "o*pJt"ds structure occurs in Nazarenko (1957) mainiain that this type of defect the pyrochlore series natural pyrochlore. Ci.rf"tg et at' (1958) extended formula Az-,BzXz'The to include betafite rJ a3A-iite wiih the general last two publications writer's research*., n"utty complete before these substantiates becameavailable. A new .t"""s'ne"t of data independently the main conclusionsof the Russian authors' been known for some The symmetry and structure of pyrochl'orehave - Gaertner (1930); time. The spacegroup was determined as OI Fd'\mby (1941), using- morphological using rc-ray diffraction and by Donnay is describedas the type data. Gaertner also determined the structure. It -E8rin the Struhturberi,cht. a state which has All betafite and some pyrochlore are metamict' to take place with frindered ,-ruy irr',r"Jig"tit"' Crystallization is known The exothermic pheno- evolution of heat whei the minerals are ignited. curves (Kurath, mena are -.rrirot"J,s f"arc on differential thermal mineral do not always igfD. Peaks that are typical for th9 -specific appear (Kulp, Volchock, & Holland, 1952)' 610
Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 P]TROCELORE AND BETAFITE 611 x-ray diffraction patterns of pyrochlore and ignited betafite are similar although not identical. A structural relatioriship between the two mineralswas proposedby Bilrlykke (1981)and Reuning (1988),but contested by Machatschki (1982). Rutile and pyrochlore lines were identified in the x-ray patterns of ignited betafite by Takubo, ueda, & Nishimura (1951).A uraninite structure may arsoappear as was shown by Gasperin(1957). Furthermore, Sfrum (195b)ignited metamicr pyro- chlore and obtained, besidespyrochlore, r-ray rinesof columbite, loparite, and a new phaseof uncertain composition.
DnscnrptroNs oF Seupr,Bs ewn OccunRENcES
Mineral, Separation samples of pyrochlore and betafite were separated in ottawa at the Geological survey of canada and at the Mines Branch, Department of Mines and rechnical surveys. Most sampleswere concentrated by hand under the binocularmicroscope but some(Hg-1-1, Hg-1-4, and H9-1-HS) were concentrated on the Frantz isodynamic separator, upgraded on the Haultain superpanner, and finally handpicked under the binocular microscope. sample H8A was passed through the Frantz isodynamic separator, and a heavy liquid concentrate (sink from diluted clerici solution) was made by Dr. E. H. Nickel of the Division of Mineral Dressing and ProcessMetallurgy, Mines Branch. Mineral association, purity, and zoning of pyrochrore and betafite grains were studied by means of thin sections, polished sections, and autoradiographs. Autoradiographs were taken on Kodak, ff-ray, no- screenfilm. Most sample concentrates weighed from 2 to b grams although five samples weighed about L gram and one sample (Hg4B) weighed only 0.3 gram. Lack of material limited the number and type of tests for many samples. sample data are listed in Table 1. Data are not included for samples Hlc and HZ which had been separated previously by Dr. R. J. Tiaill and were given to the writer in powder form. sampre Hrc is a rare thorian variety of pyrochlore from Blue River, British columbia, while H7 is the "betafite" from the Manny zone, Molybdenum corporation of America, Oka, Quebec(Rowe, lgbb, p. 5, ,,betafite"). Occurrence The geological occurrenceof most deposits from which samples were taken has been previously described and only a few generalizationswill be given in this paper. occurrencesare summarized and referenceslisted
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it tr | N 3ap$ F=r)< Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 614 THE CANADIAN MINERALOGIST Ph'D' thesis (Hogarth' in Table 1. Further details are given in the writer's 195e). British Columbia' and Well-crystallized pyrochlore at Blue River' rock' The Blue River pyrochlore is Oka, Quebec, o""rrr.'in carbonate appears to have been found in both aoto*it" and calcite' Dolomite At Oka pyrochlore was granulated. Pyrochlore often contains columbite' The larger grains contain observed in calcite- and diopside-rich rocks' pyrochlore both localities is frequently abundant gangue -i"Jr. from exterior of the crystal. zoned with the -ort,Jouctive zone at the The pegmatites Betafite was studied from several types of occurrence' Ontario' contain unzoned of Viking Uf.u, Su"'Lt"hu*t", and-Hybla' veins and ellipsoidal and usually u.rf,"arrif"iJt". detafite fiom calcite near Bancroft, Ontario' calcite bodiesof the Hofan and Basin occurrences ,,cubo-octahedral" in habit. Betafite in the is unzoned u,rt "o--ffi is octahedral and some- amphibole-ri.t, ,r"it"l,t--fi"ll to*""hip' Quebec' The associatedbreccias also times zonedwith a J;;i;;"Jioactive iim. zoned' contain betafrte but here ihe mineral is rarely pyrochlore and betafite Apatite i, tfonauniiv ttsociut"d with all the Magnetite is common ,u-it"" except those wirich came from pegmatite'- River' It occurs in small with samplesfrom Of.t, vifti"g Lake' andglue Hull township betafite' and amounts in the uoga,, ietant; is rare in the was not detected in betafite from the Basin occurrence' AND BerepnB Tsn CnBurcar- CoruposITIoNor PvnocnloRE Methodsof AnalYsis principally by the The choice of analytical methods was determined quantityofsampleavailable.Inmostcasesthesmallamountofmaterial limited-the number of wet chemical determinations' and were analysed Nine sample, *"ru for detailed examination ""i""t"d in the following steps: to 20 : 87o with a (1) Samples *",J?t""" d' by cc-rayfluorescence were made bv R' J' General Electric ,-*y 'p""t'o-"t"t'-5"*"v Analyses and the writer at McGill Traill at the c"orogiJuf of Canada UniversitY. carried out in both (2) r'ray fluorescentanalyses were Quantitative were read directly helium and air puth; by the writer. Peak'intensities subtracted from each reading. from a binary was "".iur.-g."kground employed as standards along Specimensto bu lnalysed were "f,"*ically synthetic ThOr and SrO with previot"ly .tuly""Jtt*pt""' In addition' standards were PrePared' by drying a portion (3) Moisture i" fg_tA *as measuredby tjre writer with Pzor as desiccant' with an infra_redl;;;r; sbring in a desiccator Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCELORE AND BETASITE 615 (4) Samples HLA,_ H2, HB, H6A, HZ, HgA, Hg_1_4,Hg_BA, and H9-4A were sent to. Ledoux arrA Comp.ny, Teaneck, New Jersey, for the determinationof major constituenti. (q) portion of sampre . 4 was dehvdrated bv s. Abbev at the gical Survey {z Georo- of Canada and total ..tu, *u, determined. (6) Portions of sampres were sent lo s. courv're of the Georogical survey of canada for the determination of Nazo (in sampre H9-BA), HzO, and F. (7) Qualitative spectrographic analyseswere made bv W. H. Champ at the Geologicarsurvey. particurar attention was paid to sio2, and MgO. 41203, (8) MgO in sample H2 ^ was determined spectrographically by W. O. Taylor, Ontario Department of Mines. Analyti.cal, Data Detailed analysesare presented in Tabre 2. Theoxide percentagesare based on moisture-free sampres. Totar iron is given * F;o,-;;;nium as UaOr.The symbols XCezOgand EyrO, ,ufur ao the sums of cerium and Tasr,s 2. ANanvsrs or Cewa,oraw pynocsloRp e.ND BETAr.rrE HlA H2 H5 H6A H7 H8A H9.I..4 H9-3A H94A NarO 6.80 0.42 0.64 0.p3 2.88 r.!6 0.31 KrO 0.1 n.d.t n.d. 4.M 0.58 CaO r3.76 4.M 10.64 MnO 'g* ,?:i,,g.?e Tr,* 0.26 0.62 ,l$nli- tiq FeO 0.47 /. d8 3.15 gL, Mgo j,:6 Tr. 0.5 0.32 +! 9:i!,i?? ICero' 0.2 0.2 Tr. i8H IYzOs n.d. 2.4 Tr. ThOz 0.07 0.5 0.2 t; aizd'?' $;i fi fi UsOs 3.51 2L,LO22.24 ,??.s Pbo Tr. 4.75 r.4g i:$ i:33,g:1, ,g:i, ,g::* SrO 0.83 o.2t 0,42 BaO Tr. 2.77 Tr. NbOo 60.90 18.99 32.44 'j*S TazOs o. oo 3.64 0.26 ftg r* srioa +ii.q, ZrOz Tr. Tr. Tr. 4:iy 4 Ti02 2.07 20.66 16.93 y:; SnO, n.d. n.d. Tr. ,f- ,i,tE!:,#,i# ,yi; F 3.76 0.46 1.2A lHrO+j 0.10 4,70 3.47 SiOz 4.04 iias'ii, a.?s ift ?h;,k Al:Oa 0.72 99.1 94.6 93.9 99.3 100.3 99.9 O-F 1.6 0.2 98.9 99.8 100.7 0.5 0.6 0.9 1.0 0.8 0.9 1.3 Total 97.5 94.4 93.4 98.7 99.4 98.9 98.1 98.9 99.4 Moisture 0.26 2.99 5.2L 1.61 0.4t 0.18 HO 0.35 7.55 1.16 0.61 2.28 8.50 7.30 7.9 1.05 6.70 2.20 8.00 *Tr. trace. tn.d. sought but not detected. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 616 THE CANADIAN MINERALOGIST was found yttrium group oxides respectively' Structural water [HzO*] (H'gO)and correcting for by subtracting moisture irom thl total water of. fluorine the weight of the dried sample' The oxygen equivalent" oxides SiOz and (O - F) was subtracted for each sample analysed' The probably account for much AlzOswere only determined in sampleUZ and of 1ne remaining percentagein other samples' a featurecharacter- The analyse"rho* ubilevariation of cor.nponents, abnormally rich in istic of pyrochlore and betafite' Sample H2 is of titanium and urra burirrrn. With respect to a high content vi"i"- from the Tangen iron, ttt" mineral is similar to iyrochlore and betafite p' 804' analyses quuity, Norway (Palache, Ber-an, & Frondel' 1944' 6,-'samplertTurrasimilarmaterialfromOkahasbeencalledbetafite' 7, and 8). analysis B-)and those Rowe,s analyses(Rowe, 1955,p. 5, and 1958,p. 80, per cent), of the writer stow thut the mineral is highln thorium_()5. but low in uranium sodium ()2 per und fluorine ()2 per cent) ""nli, who namddbetafite' ( lz p"r'""ntj. A".oriiog to Lacroix (1922,p' 378)' 'idoit-e,'" ) cbt6 de celui the betafite group: plac6 dans la systdmatique en urane et pyrothtor" dont ii se distingue surtout par sa grande rich-esse fluor.'' 1 i'.brurr"" de rproportions notables d'alkalis et de be re- It therefore ^Sa-plesthat the oka "betafite",should """-"-rppropriate and H8A were also named thorian pyro"hlor". HlA, HlC' H3' other 'samples were .i"t"in"a as pyrlchlore in this study, while the tentatively classifiedas betafite' of betafite' Sample H9-3A contains an amount of uranium typical- a-ndhigh percen- However, the low percentageof water (2'20 pet celt) t.geofNarO(a.0ap"r"",'t;aremorecharacteristicofalow-uranium analyses in py?o"tttor".-Sodium is not recorded in any of the betafite Hybla ellsworthite F'alache,Berman, & Frondel (lg44,p'804)' nor in the high density,4'60' is or hatchettolite(.i,Uid., p.75d, no.7 and 9). The perhaps the result of a low titanium and water content' TesLB 3. Penrrar- CnsMrcar- ANar'vsesE H9-r- H9'1-1 HS H9'38 H9'48 HlC II3 II4A H4B H4C H6B H6C o 2 3.4 3.5 3.8 4.1 3.6 4.4 2.9 FeO 2.5 Low 0.1 0.1 0.1 0.2 0.1 0.1 Low ThOz 3.9 0.5 0.1 23 18.7 20.0 22.7 23.2 23.0 22 UaOe 1.7 t4.6 18.7 18.7 , 0.3 1.4 1.4 2.1 2 Pbo Tr 1.0 0.5 0.6 1.0 o.2 0.7 0.3 1.3 o.7 0.6 SrO 0.6 0.3 o.6 o.7 o.5 28.6 3l .l 38.6 32.0 tu a7 NtNOo 46 33.0 39.0 41.1 40.7 4.O 3.7 1.6 1.2 <0.5 <0.5 TaOr 2.4 t2 4.4 4.O 17.r 17.E 17.4 18.7 6 13 Tlo: 10.1 11.8 13.5 t4.a t4.o 0.80 9.30 8.70 7.95 HO 3.20 12.80 10.4t) 8.tfO Lp.2 7.2 8.4 24 27 >100 >74 NbrOr:Ta0o 18.7 2,8 9.0 9.8 S' C' Couwille' *X-ray Fluorescence bv D. D. Ilogarth' Total HzO bv Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCELORE AND BETAFTTE 6t7 Table 3 presentspartial analysesof other samples.The anarysesmust be consideredas approximate only, becausedata were derived by x_ray fluorescenceon undried samples. The Relationshi.pof pyroclttroreand, Betafite The main difficurty in crassifying b"tunt" with pyrochrore has been chemicalcomposition. I-deallVin pyrochlore, g(A2B2OsF),.4 represents sodium and carciumand B niobium and tantalut- (a;;;; r9B0). on the other hand Madagascarbetafite has a formura {i- inror.otlro, yjt\ A mainly "ios" uranium and carcium and B niobium and titanium (Palache,Berman, & Frondel, 1g44,p. g0B). If the formula of betafite g(Ar,rBrOaHzO).nHzO, is written as one can consider betafite as a hydrous, uranian pyrochlore witi OZ p", cent of the ,4 ions missing. other pyrochlore structures with vacant sites in the '4 position* have pabst been-described by (1989), Fu;i & cavarca (rg4), and Mason & vitaliano (rgsa). If pyrochror" ur,J-b"tufite are isostructural the general formula could be written as A6--"816(0,'H)4E(F, oH)r, -4 representingions with typicar radii 0.g to 1.1 A and B ions with radii 0'65 to 0.75A. p6+, Ttre ions Alii, and Si+aappear to be too small for the 3 position. As a checkon thesespeculations sixty-three analysesfrom the literature and the nine analyses in Table 2 are plotted on a triang;; diagram accordingto their atomic contents (rig. r). The prots t;;J; ,"presenr the formulas lroBrooag and Ad.saBr6olsrespectively. The calcurations were based on the following premises: .4 : -\a, K, Ca,I\{n. toIg:1"^*i-ECe, Iy, Th, U, pb,Sr, Ba, Bi l^: \F,Tu, Ti, Zr,'Sn,-Fe*',W- SiOz, AhOs, P2O6were excluded. Atomic weight of rce assumed to be rrt0.6,t that of gg.g2, were recorded ry assumed valencies as reported.in the-li.-terature *rr".Jr-#J;;;is by the letters rollowed "a" and "b'.in which-c;;;; t;#r""ii"pi included / (as in ihe structural positions Fs+z; and B (as Fe+s) respectiv;t. i;;;;"w calculated analvsesin Table 2, uranium was as uaor. however, iir_"r-prl,'H;r"d H.oe-"-vg"" from *."-iliiJiea orectty thermobalance data as'outlined'ber... eii""r*btions in the B position. were based on 16.00 ions The compositionsp]gJt"d on Fig. 1 are in formula accord with the proposed An*"'rc(o,oH)4s(F, oHlJ rn" -J"J;;il ro, ,r,upoints to lie to the right of the 1}ne An_rBroOascan be explainedly u., o""r, of oxygen due to substitution (OH)- of ior F-. This line S""";f" agrees with the plotted compositions with'Fe+2 in the .4 position. However, if all iron is regarded as Fe+s in the B position one must ,"rr;;';;; B areused to denoteboth chemical groups and their J?igi i:ffi1*:"0 respective tCe:La:Nd:Pr - 5:1:1:1 from r_ray fluorescentanalysis of sampleHgA. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 618 TITE CANADIAN MINERALOGIST r Ploited cornPosiiion . Alfarnative comPosition ^o( l\o \ -lO .*#. i3. .? ^o \e '\ '\ '\ 25 2O Afomic Per Cent B 63 previous analyses and I new Frc. 1. Diagram shoriling the atomic compositions of analyses of pyrochlore and betafite' substitutionof(oH)_foro-2sinceitisnecessarytobalancethereduced positive charge of the B ions. ' good agreementwith High titanian pyrochlore and betafite afe not in all iron is assumd to be in the the froposed pyiochlore formula when but agree better when g pJ"fd bloited as H2b, lb, 2b, 3b, and 4b) and 4a)' it"-" ir assumedin the -4 position (as H2a, La, 2a, 3a' - but most The series ArsB$OnrAs.aa'BtO$appears to be complete Ambatofotsikely compositions are cl;; io-- irr4ruOn6.-Samples from of anoma- and Ambatolampikelv (No' 6), claimed to be iN;:;t lolmerlv (LgM' p' 805' Notes 8 tou" -*porition by puft"n", Bu"nu", & Frondel and 9), 6t satisfactorily into this scheme' Combtned,ond, Ercess Water Theroleofwaterinpyrochloreandbetafiteisnotclear.Hydroxylis bestcalculatedbyuuru.""ingpositivechargesandisassurnodtofillthe negative sites normally occupiedby Q-r and F-' Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 P]TROCELORE AND BETAFITE 619 There appears to be little relation between water determined by analysis (after subtraction of "moisture") and water necessaq/ to balance the positive charge. Generally there is more water in the sampre as [Hzo*] than required in the formula. This may be due to failure to liberate all loosely bound water when the sampre was dried. - lxtra water (water not substituting for oxygen and fluorine as hydroxyl) does not appear to be related to the number of vacant sites in the ,4 position of.betafite-A*_,B'(O, OH)48(F,OH)r. Madagascar betafite is particularly deficient in ,4 cations yet the canadian mineral often contains more water by analysis. often there is too much water to be accommodatedin the structure even if we assumeall iron to be in the B position. consider sampreH7. The quoted anarysissuggests 18.7 molecules of water per unit ceil. only r..g4 water morecures(or B.gg hydroxyl ions) can be located in the positions normalry occupied by fluorine. The remaining 11.8Hzo moleculescannot possibiyreside in the 0.5 vacant sites of the ,4 position. That there are two types of water is, however, suggestedby difierential a F J o t lo F ''l J ,ol F I .l ; 3 .I z UJ "L u. "l rd L loo 2OO 3OO 4OO 5OO 600 7oo gOO gOOcC TEM PERATURE Frc. 2. Reconstructed D.T.A. and T.G.A. curves of betafite (H4A) from Hybla, Ontario. The sampleswere fired in uigon. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 620 THE CANADIAN MINERA.LOGIST analysis (T'G'A') thermal analysis (D.T.A.) and thermogravimetric curyes.Figure2isanexamplefor..ellsworthite''-rtr4A.Theendothernlic and com- peaks at iOO" C and 425"C -.y correspondto loosely bound withr a Lined water respectively. The 421ioC peak can be correlated The difference in thermobalance indication occurring above 340oC' (J'2deg' C/min' temperature can be explained by different heating rates curve (air- for D.T.A. and 6 deg. C/min. ior T'G'A')' The equilibrium and shows ignition) of Walker d Purron, (1923a,p' 15) is quite different no correspondinginflection. appears It is interesting to note that most of tlte water in ellsworthite loss of 8'9 per cent to be loosely bound. The T.G.A' curve indicates a is 12'80 per cent water at th; 340'C inflection point. If the total water bound' (data from analysis) at least 69.5 per cent of the water is loosely Thesignificanceoftheexcesswaterisstillimperfectlyunderstood. inclusions but canadian betafite contains numerous microscopic lfluid?] water. one may tjrose observedcould probably not account for sufficient loosely held bv theorize that water is adsorbed in open spacesa1d ls bondsthathavebeendisruptedthroughradioactivebombardment. Stnucrunan CnvstanocRAPHY Crystal,l,i'zati,on Sample H7 Pyrochlore exhibited varying degrees of crystallinity' powder photograph showed no rc-ray reflections u"a Hge gave an r-ray British Colum- *itf, o"fv 14 broad lines. Some samplesfrom Blue River' al reflections clearly ti", g* excellent po*a"t patterns with ar and resolved at high angles. were metamict i-nuy photlgraphs indicated that all betafite samples lines and samples utthough ,arnpt" HOi-US showed 6 weak pyrochlore H5 anl H6A each showed 5 weak pyrochlore lines' CrystallizationtemperatureswereinvestigatedatMcGillUniversity evaluate oxidation .r"irrg n.f.e. (air-ignition) apparatus' In order to (argon ignition) ancl T'G'A' effects some sampluJon"r" i""t"i by D.T.A. Mines Branch' *con ignition, Stanton t-hermobalance)at the a;ir-;e not be attributed to It was found that rigrin.u"t exothermic peakscould oxidation.---cr-p"riron pyrochlore of the exothermic peaks on D.T.A. charts of andbetafiteshowsthattheyareusuallyquitedifierent.Typically'at? shows a broad h"",G rate of 12oc per minute,.pyrochlore-microlite & Holland' 1952' e>rothermicpeak at SbO-SfO"C (Kulp, Volchock' gives a Soboleva& Pudovkina, L957,pp' 287-288, p' 294) -whiletetafite orcel & L6vy, 1953). narrow peakat 670_t0d"c (*",, & Holland, 1951, Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCHLORE AND BETAFITE 'renr-a 621 4' Exornnnlrrc psArs oN D.T.A. cunvas or pvnocslonn aNo BsrA'ris Air igniliel*12,6 deg. C/min. Argon lgdtlon.-l2 deg. C/mi\. Other tlltlmate Other lntlmate peaks temp. Sample peaks 6ZO-62coC660-Z00oC fc) temp fc) 52G6700C 65G0900c (oc) ec) HIB W 435 -S 1000 HIC 425.-5 1050 465 -W 890 H2 w 720 -s 860 /710 -s l .[aeo-w/ roes H3 w 466 -w 850 H41A S H4B 860 s 1006 H4C s H5 850 ws* 850 Isso -s l w -s 1076 H64. Ws laao-s \ \CIs / t715-W,r 900 s 1060 II6B s 850 H6C s r080 s 860 H8A s 1030 900 615 -S 1070 H0-t-1 H9-t-4 850 850 H9-1-HS /+eo-wi \zoo -w/ 860 H9-3A H9€B s 585 -W Hg-8C 860 s 425 -S 860 H9€D s 900 H9.3E w H9.4A 870 s 850 xDouble pea&. S, Strong or Drominent peali W' Weak or'questlonable peak. The present data are summarized .. in Table 4. It will be noted that the "pyrochlore p*k" (52a-520" c) is prominent for several betafite speci- mens while the "betafi^tepeak" (664I-200"c) appears i" ti"-pvr"chrore curves of HlB and HgA.-Furthermore, sampresfrom the same occur- rence may display very different thermal behaviour. S;;;i;; H,_BA, H9-3B, H9-3D, and Hg-BE were all tut fro- within 2 feet, yet each gave a distinctive D.T.A. "., ou,rve. Samples from the MacDonald mine show typical betafite peats (Fig. zjii-"or,trast to the corresponding "ellsworthite" curves of Kerr'&"H"riu"a irggr) and Kurath (19b2). x-ray diffraction tests before and after the exotherrrri" mdicate a crystallization phenomena f"ur." at- the peak temperature. For crystatine pvrochlore the cooring curve did ,,oi :;;ililiig i;nu"tior,, and heating above the exother-i" "how-. p"ut merely sharpened the x-rav Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 THE CANADIAN MINERALOGIST (l) phasesof a betafite illustrating "dark"-(d) and "light" Frc. 3. Polishedsection 6ns-giainedhematite (h) (type H6A) f'"'"'#;;;;'il'"61t'':-J;'pulti"";; Surv' sample PhotbmicrographNo' 109727Geol' and an unidentified-"oiril'*i"*;i i*l' 116A'from pto.og'.ph of the "light phase"of betafite.'tvpe "?*1.oi1i"r"rJ$51' Contactprint irom filmNo Bancroft,ontario. ctlN'i'"b;*;;; ;il::82's;-' io.os3-C*ot. Surv. of Canada' the pyrochlore phase below and reflections. Similarly, betafite shows the exothermic peak pyrochlore above the 660_700"i;;;. Abor."- but not necessarily sharper' and reflections become ,^'"tt "oo"ger phasesare synthesized' usually small amou,ti" of uttia"ttlin"d may be recrystallized well below It is interesting to note that betafite show r-ray reflections of pyrochlore the exothermic peak. So*" samples minutes' The "light" or most highly after ignition in air at-500" C foi f H6A (Fig' 3) gave a distinct r-ray reflecting phaseof ttt" pJlh"a section Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCELOREAND BETAFITE 628 diffraction pattern with 16 broad pyrochrore lines (Fig. 4). The ,,dark ph.u"9" gave only 4 indistinct r-iay ,efle"tion, coieipo"air,g to the principal pyrochlore reflections. Becausethe sampre*u, t to 1B5oc in mounting, and perhaps localry to higher temperatures"utui in porishing, the tight_-phasemight have been synthiized i" ;r;.;i;; tie potished section' unmounted specimens entirely of tn" a?rr. prru.". The uppermost "onri"t"d limit to which pyrochlore can be heated in vacuum withoutconverting to a new phaseappears to be about 1000oc. samples of py:ochlore (HlA) an9_beta6te lHto-r-+ywere held at rhis temperarure for about 20 hours. In HlA an unidentified ,rew phase was formed, but H9-1-4 was not affected. on tJreotier hand pyro&lo"u (HsA) and beta- fite (H9-3A) were not changed on heating at g00" c for 20 hours. Cel,l,Parameters patterns -{-rav nowaer were used to determine the size of the unit cell of the pyrochlore photographs phase. were taken with a philips 57'3-mm. diameter camera using coplei Ke radiation. Films were cor- rected for shrinkage and the cell parameterswere extrapolated to d : g0o according to tre method of rayror & sincrair (1g4s), *rto protiua appar- ent cell edgesagainst the function | (cos'o +-t', 2\sind' "o"'o\o /' only values corresponding to hz + kz + p > 64 were used for the extrapolations. - cubic cell edges varied from 10.347 to 10.485+ 0.005A for pyro- chlore and 10.27 to r.0.89+ 0.02 A for betafite. The size of the unit ceil may depend on the ignition temperature. The ceil edgeof betafite (H6A) is 0.7 per cent shorter after ignition in vacuum at 700oc than after ignition at 135oc. Another sample (H9-BA) showed a corresponding shrinkage of per 0.3 cent for betafiie ignited at temperaturesbetween 500 and 900oc. These shrinkages are lerhaps due to reorganization of crystallites, and further expulsionof water. It is uncertain wlhetheroxida- tion causes a decreasein cell size, discrepanciesbeing beyond the limits of accuracy. rn agreement with the observations of Ginzburg et ar,. (rg5g) the cefl size appears to decreaseas the number of titanium and iron ions in the B position of the structure increase. Fig. b illustrates this relationship with iron alternately accommodatedin each of the two structurar posi- tions, '4 and B. spectrographic analyses did not indicate a reration be- tween cell size and aluminum and iron content. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 624 TEE CANADIAN' MINERALOGIST t2 oHZ il LEGEN D . lron ln A t0 o lron In E '9 8 @l 7 7 +. i,b ?' + \, rl \ . 'rHge i:+ -34 QH9 u) z gr 'aH9-3A ta, \ '' \'\ OHIA.osra t0.28 ro.30 to.t2 10.34 10.36 1o.38 1o.40 lo,az to.44 10.46A CELL EDGE Frc.S.Graphillustratingthevariationoftbecellsize'ofpyrochloreandbetafitewith position o-f-pyrochlore structure' The the number of Tia+."a if.ii"oiio""l; th" B not pbsitioned mathematically' broken line indicates a."ia ir, bui.was " "o*po.itio" in vacuum for 30 minutes at tem- c;ji;**;;t; detet*i"Jlio* *Inpl"* ignited oeratur6sfrom 700 to 750'C. Molecalar Weight using the relationship A molecular weight was calculated after ignition y - (DV)/(1.6602), where M is the molecularweight for the.contents and V of the'unii cell, D is the density (grams per cubic centimeter)' the cell volume (A). Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCHLORE AND BETAFITE 625 The following data were used: H6A-Density of sample ignited in air at Z00o C for 15 minutes : 4.51. Cell edge of sample ignited in air at 200" C for 15 minutes : 10.28A. " 4.51x 10.283 M: : 2950. 1.6602 Molecular weight was also calculated from the chemical analysis. i Calculations q/ere based on the following premises: I (1) All water driven off but fluorine retained; ' (2) Uranium present as U6+; i (3)ThegeneialformuIaA$nB$oag_EFg*"...... ,. The followingvalues were obtained: , r ,i.1,. i All iron as Fe+2in the .4 position; M : BZ02;All iron as FeJ{ in the B position;M :2908. Agreement with the value calculated from density-cell size data is surprisingly good and does not invalidate the proposed formula Ata-,Bn(O, OH)48(F,OH)r. However, uncertainties in both types of, calculation preclude any generalization of the role of iron. t X-ray Difraction Pattern The r-ray powder pattern of the Blue River pyrochlore (HlA) is i similar to that of pyrochlore and microlite from other districts. The r pattern of ignited Blue River pyrochlore includes all the reflections listed r by Arnott (1950'Table 3) for microlite from Amelia, Virginia, with the exceptionof.244,842, and 10.8.4-12.6.0; the latter is not in accord with the pyrochlore structure of Gaertner (1980). The *-ray patteins of ignited betafite and pyrochlore from other rocalities were nol as sharp and showed fewer lines. systematic extinctio's agreed with the sym- metry otr and the structure -E81,and no justification could be found for relegating pyrochlore to the spacegroups O, - Frn\m, Os - F4BZor Tf; - F43rn as recommendedtry Ginzburg et al. (Lglg). Besides pyrochlore, other phases were identified in the patterns of ignited betafite. Anatase and rutile were only identified in specimens from viking Lake, saskatchewan (H2), but r-ray diffraction photo- graphs indicated that the titania was not distributed homogeneously throughout the sample. The r-ray difiraction patterns of ignited betafite from other localities showed b weak lines designated as a, b, c, d, and,e (Fig. 6). These lines were sometimesmarkedly broader than those of the accompanying pyrochlore and were therefore thought to represent an additional phase or phases.The relative intensities greatly 'typical varied but data are as shown in Table b. ;i Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 SAMPLE HIA ( unheated) l6 27 32 SAMPLE H8A (argon 44 [ ignifion) t6 27 ? 'i ll J[-'ooT /l ll .l ,e '2 SAMPLE H5 (vacuum ignilion) l6 go 7F 'b'll /\"q' '1" / \". *-.'a go 70 60 40 2oo 29 Frc. 6. X-ray difrractometer charte of pyrochlore and beta6te. Intensities are recorded on a logarithmic scale. Cu/Ni. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCHLORE AND BETAFTTE 627 Taslr 5 Possible r" d(A) phase 10 3.28 Rutile b 8 2.35 c 2 2.00 o 2 L.72 Rutile e I 1.38 Anatase X-ray diffraction patterns of pyrochlore and betafite show marked differencesin intensities (Fig. 6). The fact that odd-numbered planes of betafite are greatly suppressedmay, in an extreme case, produce an apparent half-sized primitive cell. This may explain why Bjlrlykke (1931)gave a cell edgeof betafite from Krager6, Norway, as b.t48 instead of 10.30A. Gasperin (personal communication, 1958) has pointed out that this feature can probably be explainedby compensatingterms in the structure factor equation. For planes with even-numberedMiller indices the con- tribution of the A and B ions reinforce each other. Conversely,in planes with odd-numbered Miller indices the contributions of tiese ions oppose each other and when the respective scattering factors become almost equal (as in betafite) extinction occurs.To test this hypothesiscalculated and observedintensities were compared. For calculating intensities un-ionized atomic scattering factors were taken from Cullity (1956, Appendix 8) and corrected for dispersion by the K electrons using the method of James (1950, Appendix B). For each structural position scattering factors were prorated according to the degreeof filling of the respective ionic sites and the total scattering factor was a sum of all the fractional values. Intensities were calculated with iron alternately in each of tJre two structural positions A and B. The A and B positions were adjusted to 16.00 ions each in sample H8A. Other calculations were based on 16.00 ions in the 3 position and ions in other sites according to their respective atomic proportions. All water was assumeddriven ofi, all fluorine retained in the ignited specimens.For specimensignited in air all iron was assumedconverted to FezOaand uranium converted to UOg. An r-ray pattern showing the first twenty lines of pyrochlore (HlA) is compared with a pattern of ignited betafite in Table 6. Intensities were recorded at McGill university using a General Electric spectrometer operated at 35 kilovolts and 10 milliamps, and driven at the rate of 2 degreesper minute. Peak areas were derived by multiplying height by width at half height. The lines 3, tI, 27,and bl (hzI pz f P) are quite Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 628' TrrE cANADTAN MINERALocIST Tasr.p 6. Spectwcseno InrnNsrtrns or PYnocm.oREAND Bnrerrte usrNc CorpBnKa RaorerroN HlA;d=10.42A HOA (isrited in Argon); a : 10.29 A Spacings (A) I!tensities Spacings (A) Intemities Calc. CaIc. Calc. Calc. h2 + kz + 12 d calc. d obs. (Fe ln ,4) Obs. (Fe in B) d calc. d obs. (Fe in 4) Obs. (F'e in B) 3 6.016 5.98 31.9 25 35.3 6.94r 3.4 t3.7 8 3 .684 3 .72 0. I strong for pyrochlore but are greatly reduced for betafite. It is evident that the principal planes affected have h2 + k2 + F (and hkl') odd. A pyrochlore (H8A), with an *-ray pdttern intermediate between normal pyrochlore and betafite, and two betafite specimens(H9-4A and H5) were selectedfor further study. Intensities were measuredat the Geological Survey of Canada with a Geneial Electric spectrometer set at 50 kilovolts and 16 milliamps, and rirn. at 0.2 degreesper minute. Tenr,s 7. INturrsrtres or Prnocm.ono er.rb Brtarrip usrNc CoPPERKrz RanrerroN 1194A: a: 10.30A H8Ai @- 10.3s3A H5; a : 10.285A Ignited in alr Ignlted in argon Igrrited in cuum h2+ NaCaNbOeF h2+ t2 a - 10.38i! A Calc. obs. Calc. Calc. Obs. Calc. Calc. Obs. Calc. ' Calc. (Fe in A) I , (Fe tn E) (Fe in 4) (Feiu.B) (Fein4) (FeinB) 3 37.8 5.3 6 10.6 112.6 16 14.9 t, ?* ot 11 29.9 5.1 7.6 8 9.6 1.7 2 2.3 t2 100.0 100.0 100 100.0 100.0 100 100.0 100.0 1@ 100.0 '2.6 T7 8.5 2.3 , 3.0 5 3.6 2.O 41 2.4 to 5.6 o.2 0.6 1.4 7 t.7 o.01 *ftqgion of hlgh background. flncludes da and line "c". Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCHLORE AND BETAFITE .629 The area under the curve was measuredwith a pranimeter. carcurated and observed intensity data of the six strongest odd-numbered pranes are presented in Table 7. The calculated intensities of NaecaeNbrsooaF, are included for comparison.* The calculated intensities comparefavourabry with those derived from spectrometer measurements.one may conclude that pyrochlore and betafite are indeed isostructural and lhat diadochy has i great affect on the intensities of.r-ray reflections. Cr,assrr.rcetroN oF rrts pynocnlonB SBnrBs GeneralStatement The pyrochlore seriesis characterizedby a wide range of substitution in the two cation sites. Maximum percentagesof sixteJn oxides, usualry considered non-essentialin pyrochlore, are reported by palache, Berman, & Frondel (1944, p.74g). Eleven of these*id"" exceedb per cent. It is therelore not surprising that many varieties and species have been proposed. To-day the most_widely accepted classification is that of palache, Berman, & Frondel (LgM, pp. Z 45-74Z), who defined pyrochlore_microlite and betafite as two distinct series. other niobium and tantalum oxides with the pyrochlore phase were classifiedas variants of one or other of these series, although individual variants were not given speciesstatus. A novel classification was proposed by Ginzburg-et al. (tgtSA).These authors separate the pyrochlore titanium-tantalum-niobaies primarily according to the type of B cations (minerar groups), then according to the type qf ,4 cations (mineral species),a.rd irruliy'iy the J;il];d ;; l.cations (mineral varieties)- For exampre,the haich"ttolitu group con- tains the species hatchettolite which in turn comprises the y,4rieties mendelejevite, ellsworthite, hatchettolite, blomstraniite, and betafite: Ginzburg's classification fails to accommodate the new sodium-rich betafite H9-3A. The main objection to this classification, however, is not its lack of scope (which could easily be extended) but its impractical neture. In order to find the lack of cations in the L position a detailed analysis would be required. A classification based entirely on elemental composition would appear to be more useful. l The P yr ochl,ore-Betafi,te Series It is well known that pyrochlore and microlite contain varying amounts of uranium but the extent of this substitution has received bcint atten* ECalculated intensitiis fo.lrTr compound differ from those of Gaertner (1980); who used a different trigonometiic factor and difierent atomic scattering r""t"r!. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 630 THE CANADIAN MINERALOGIST 9"o !J f, $ro t L lo o.5 l.o 1.5 Z.O 2.5 3. o S.5 URANIUM IONS PER UNIT CELL SAMP LES zso u f g Hzo |! lo 5lo t5 20 \^,EIGHT PER CENT URANIUM of pyrochlore and Frc. 7. Frequencyhistogram showing the uranium content betafite. tion.FigureTisafrequencyhistogramofseventy.twomineralsofthe pyrochlore-betafi te series. of a pyrochlore struc* Atoms of uranium were calculated on the basis in the literature except ture. Valencies of iron were resolved as reported assumed to be divalent for tJre iron-rich titanian betafites where iron was as divalent in the and located in the -4 position. Iron was also taken new Canadian analYses peaks occur at com- A bimodal distribution is apparent: frequency atoms of uranium positioo" with 0 to 0.5 atoms of uranium ar'd2'5 to 3'0 listing approxi- pe, uoit cell. These two peaks correspond to analyses mately0toSandlsto20percenturaniumrespectively.Rareinter- Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCELORE AND BETAFITE 63I mediate membersindicate that, in nature, a complete seriesmay extend from pyrochlore to betafite. The writer would define betafite as a mineral with the pyrochlore structure and high uranium and niobium content. As pyrochlore analyses with L0 to 15 weight per cent uranium or 1.b to 2 atoms of uranium seem to be relatively uncommon, it seemslogical to restrict the name betafite to a mineral with more than 15 per cent uranium metal. Ellsworthite and hatchettolite are intermediate membersand need.not be retained in the mineralogical nomenclature. Parallel serieswould extend from titanian pyrochlore to titanian betafite and from microlite to tantalian betafite. Groupedtogetherall could be classedas the pyrochlore group, anisodesmic by virtue of the linked 3206 groups which are the essential units of the structure (Machatschki, 1932 and Bystr6m, 1g4b). Acrctowr,pocMENTs professor This research was conducted under the direction of J. s. Stevensonat McGill university and Dr. R. J. Traill at the Geological survey of canada. The writer is greatly indebted for their encourage- ment and assistance. Thermogravimetric analyses and some of the differential thermal analyses were carried out at the Mines Branch, Department of Mines and Technical surveys, under the supervision of hr N. F. H. Bright. specirnensfor r-ray difiraction study were ignited in vacuum in the laboratory of Dr. D. H. Heyding, Division of Applied chemistry, National Researchcouncil, ottawa. Dr. Madeleine Gasperin of the Laboratoire de Min6ralogie-Cristallographie,universit6 de paris, suggestedthat the differencesin x-ray patterns of pyrochlore and betafite could be reconciled on structural grounds. Intensities were calculated accordingto methods recommendedby Dr. w. H. Barnes of the Division of Physics, National ResearchCouncil. Grateful acknowledgmentis made to the National Advisory committee on Research in the Geological sciences for a grant which in part de- frayed the cost of chemical analyses.The writer acknowledgesfinancial assistancegiven during the summer of 1gb6 by Frobisher Ltd., which made possible the initial field work in the Meach Lake (Hull township) area of Quebec. Dr. R. J. Traill of the Geological Survey of Canada and Dr. E. H. Nickel of the Mines Branch, kindly read the manuscript. Rspgnpnces Anro:T, R. J. (1950): X-ray difiraction data on some radioactive oxide minerals, ,4zra. MLneral.35. 38H00. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 632 TEE CANADIAN MINERALOGIST B1lnrvrrc, H. (1931): Ein Betafitmineral von Tangen bei Krager6, Norsk Geol. T,id.sskr.,12, 73-88. Bonoorw,- L.5., & NAzAnnrro, L I. (1957): The chemical composition of.pyrochlor-e and isomorphic substitution in the molecule AtBrXr Geochem'istry,No. 4 For 19671' zzs-zst. [English translation: can. Dept. Mines and Tech. Surveys, 46502 Russian BVPl. Bvsrndu, A. (1S45): X-ray analysis of Ca:SbsOzand compounds of similar composition, Arhfu Kerni, Mineral,. Geol'.A 18, No' 21. Cur.Lr:ry, B. D. i19S6): El,ementsof x-ray d.i,fraction. Reading, Mass.: Addison-Wesley Publishing Co. Roy.Soc. Can., DorNiv, J. D:H. (1941): Morphologie crystalline de la microlite, Trons. 35, Sect. IV, 51-56. Er_r_swonTn,H.'V. (1932): Rare element minerals in canada, Geol,.suru. canaila, Econ. GeoI,.Ser., ll. FrnnAnr, A., & Cevelce, L. (1944): La struttura del clorocadmiato di bario e le sue relazioni con i minerali deigrupo del pirochloro, Gazz.ch,i.m.'i.ta1,.,74, tl7-126. GesnrNpn, H. R. (1930): Die Kriitallstrukturen von Loparite und Pyrochlore, Neoles Jahrb. Mi'neral,.Geol,, Beil'age Bil', 61, abt. A' 1-30. Gesrenrn, M. (1957): Identification aux rayons X des produits.obtenus lors de la recrisiallizaiion de La bdtafite, Bull. soc.franE. minbro.l,.et cr'i,st.,8A, 2BZ-2?4, GlBlrN, P. E. (1955): The geology and mineralogy of the Basin property, Faraday town- ship, M,A.SI. thesis, Unio. of Toronto. Grxzrunc, A. I., Gonzuevsreve,, S' A., EnororvA, E. A., & Stoor'rgo, G' A' (1958): The chemical composition of isometric titanium-tantalum niobates, Geochemistry, No. 5 For 19681, 486-500. Bnglish translation: The Geochemical society, Geo- chem.i,stry,No. 5, L958, 61ffi361. Hocenru, o.'o. (rsbs): A mineralogical study of pyrochlore and betafite, Pk.D. thesi's, M cG,i,Il Uni;t., M ontreal'. r-rays, The crystall'ine Jeuns, R. W. (1{iE0): The optiral, pri,nciples o! the d.ifracti,on of state,2. London: G. Bell and Sons. KBnn, P. F., & Hor-r.eNo, H. D. (1951): Difierential thermal analysis of. davidite, Am. Mineral.,36, 563-572. f*", j. L., Vorcuocr, H. L., & Holr-Aro, H. D. (1952): Age from metamict minerals, Am. 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Mi,neral.,-24,566-576. Perecur, b., gt*MAN, H., & Fnoronr,, C. (1944): Dana's systemof mineral'ogy,ed' 7, 1, New York: Joho Wiley and Sons. precu, p. A. (1960): Some pegmatites from Eastern Ontario and their geological environment, Pk.D. thesis, Un'i'o.Toronto. REUNTNG,E. (19i3): Microlith varietiiten von Donkerhuk, Stidwestafrika, Chem.Erile, E, 186-217. nosnisoN, s. c. (1956): Mineralogy of uranium deposits, Goldfields, Saskatchewan, Geol.Suns. Cana.d'a,Bul'L.,31. Downloaded from http://pubs.geoscienceworld.org/canmin/article-pdf/6/5/610/3458092/610.pdf by guest on 24 September 2021 PYROCELORE AND BETAFITE 633 Ros6n, o., & wesrenon, a (1g3g): Minerals of the varutriisk pegmatite. XII on the structure and composition of minerals belonging to the pyiochlore-atopite group r"_ ?19. j-p{ analysis of disintegrated stibtm-icrolite, daol,. Fttren. i' &o&hol,rn Fdrh., 60, 229-235. Rowu, R' B.,(1955): Notes on columbian mineralization, oka district, Two Mountains county, Quebec,Geol.. Sura. 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