rare-earth-element mineralogy of granitic pegmatites in the trout creek pass district, chaffee...

673

Canadian MineralogistVol. 30, pp.673-686 (1992)

RARE-EARTH-ELEMENT MINERALOGY OF GRANITIC PEGMATITES IN THE TROUTCREEK PASS DISTRICT, CHAFFEE COUNTY, COLORADO

SARAH L. HANSONI, WILLIAM B. SIMMONS, KAREN L. WEBBERAND ALEXANDER U. FALSTER

Department of Geology and Geophysics, University of New Orleans, New Orleons, Louisiana 70148, U.S.A.

ABSTRACT

Numerous bodies of granitic pegmatite are associated with the 1.7 Ga Denny Creek Granodiorite in the TroutCreek Pass pegmatite district in Chaffee County, Colorado. They range in size from several meters to approximately85 meters in maximum dimension. Four of the larger pegmatites are well zoned and notably enriched in REE, Nb,and Ti, and depleted in fluorine. All exhibit a distinct spatial as well as a chemical separation of the REE into LREE-and H&EE-ewiched mineral phases. In the absence of abundant fluorine as a potential complexing agent, we suggestthal crystallochemical constraints and mineral fractionation are primarily responsible for the observed LREE-HREEseparation. The proposed three-stage crystallization sequence for REE-mineral formation is: 1) during crystallizationof the wall zone and early stages of core crystallization, all of the R.EE, Y, Nb, and Ti were selectively partitionedinto the residual melt; 2) during the later stages of core crystallization l, REE and P were incorporated into allanite-(Ce)and monazite-(Ce), selectively removing these elements from the residual melt; 3) the remaining HREE-, M-, andTienriched fluid eventually corroded and replaced earlier-formed core minerals and ultimately formed albite-richreplacement units containing polycrase-(Y) or aeschynite-(Y). The formation of polycrase-(Y) or aeschynite-(Y) as alate-stage pegmatite mineral requires the r,rre combination of Ti, Nb, Y, and HREE enrichment coupled with lowconcentration of fluorine in the final stages of pegmatite formation.

Keywords: pegmatite, rare-earth element, polycrase-(Y), aeschynite-(Y), allanite-(Ce), monazite-(Ce), Trout CreekPass, Colorado.

SoMMAIRE

De nombreuses venues de pegmatite granitique sont associ6es avec la granodiorite de Denny Creek (1.7 Ga), dans; le district pegmatitique de Trout Creek Pass, dans le comt6 de Chaffee, au Colorado, Elles vont de quelques mbtres[. i environ 85 mbtres en dimensions maximales. Quatre des massifs les plus puissants sont zonds et definitivementfenrichis en terres rares, Nb et Ti, et appauvris en fluor. Tous font preuve d'une forte zonation spatiale et chimiquet des terres rares, log6es dans des min€raux enrichis en terres rares, soit l6g0res, soit lourdes. En I'absence du fluor qui

aurait pu effectuer la complexation n€cessaire, nous pensons que ce sont les contraintes cristallochimiques et lefractionnement des mindraux qui etaient surtout responsables de la sdparation efficace des terres rares. Nous proposonsune sequence de cristallisation en trois stades: l) au cours de la cristallisation de la paroi externe et au stade precoce

ide la formation du coeur, toutes les terres rares, ainsi que Y, Nb et Ti, ont prefer€ le liquide silicat6 r6siduel; 2) lorsdes stades plus avancds de la cristallisation du coeur, les terres rares l6gbres et le P ont servi ir la cristallisation de

i I'allanite-(Ce) et de la monazite-(Ce), ce qui les a appauvris dans le bain fondu r6siduel; 3) une phase fluide, dansI laquelle les terres rares lourdes qui restaient, ainsi que le Nb et le Ti, ont 6t6 concentrds, a 6ventuellement attaqud etfl remplac6 les min6raux pr6coces du coeur pour former des zones de remplacement riches en albite et contenantI polycrase-(Y) ou aeschynite-(Y). La formation de ces phases accessoires au stade ultime de cristallisation d'une

pegmatite granitique requien la combinaison assez rare d'un enrichissement en Ti, Nb, Y et terres rares lourdes, etd'une faible teneur en fluor.

(Traduit par la R6daction)

Mots-clds: pegmatite granitique, terres rares, polycrase-(Y), aeschynite-(Y), allanite-(Ce), monazite-(Ce), Trout CreekPass, Colorado.

rPresent address: Department of Geology and Geophysics, University of Utah, 717 WBB, Salt Lake City, Utah84102-1183, U.S.A.

674 THE CANADIAN MINERALOGIST

Ftc. l. Location map of the Trout Creek Pass pegmatite bodies showing the location of the Yard, Crystal No. 8,Clora May and Tie Gulch pegmatites.

INTRoDUcTIoN

The Trout Creek Pass pegmatite district islocated in the Mosquito Range near Buena Vista,in Chaffee County, Colorado (Frg. l). Numerousbodies of granitic pegmatite are associated with theDenny Creek Granodiorite. These pegmatites rangein size from several meters to approximately 85meters in m,u(imum dimension, are poorly exposed,and have not been extensively quarried. Only fourof the larger pegmatites, the Yard, the Clora May,the Crystal No. 8, and one informally named theTie Gulch pegmatite, exhibit well-developed inter-nal zonation consisting of a thin, discontinuousborder zor.le, a wall zone, and a compositequartz-microcline core with superimposed albite-rich replacement units. These four also arecharacterized by strong R.EE-mineral enrichmentsand are the only pegmatites investigated in thisstudy.

The Trout Creek Pass pegmatites containnotable concentrations of .R.EE, Nb, and Ti, andare conspicuously fluorine-poor. There are distinctspatial and chemical separations of the REE intolight-REE-enriched and heavy-REE-enrichedmineral phases. Alanite-(Ce) and monazite-(Ce),the dominant LREE-enriched phases, are found inassociation with the core, whereas polycrase-(Y) oraeschynite-(Y), the dominant .Ir'REE-enrichedphase, is restricted in its occurrence to late-stagereplacement units. A similar separation of .REEintodistinct HREE- and LREE-mineral suites in thefluorine-enriched pegmatites of the South Plattepegmatite district, Jefferson County, Colorado,has been attributed 1o fluorine complexing (Sim-mons el al. 1987, Simmons & Hanson 1988, l99l).The Trout Creek Pass pegmatites provide anopportunity to examine .REE behavior in afluorine-depleted, R.EE-enriched pegmatite $uite.

B u e n a V i s t a

I Trout Greek \\

, l Paes

)t--\

a - '

)3---

O 1 2 3km--

Legend

Quarry

Prospect

C o l o r a d o

REE MINERALOGY, TROUT CREEK PASS PEGMATITES 675

GSNTRAI- GEoLocY

Host pluton

The Trout Creek Pass pegmatite district islocated within the Denny Creek Granodiorite, amember of the synorogenic Routt Plutonic Suite.Plutons of this suite are foliated to various degreesand concordant with their metamorphic country-rocks (Tweto 1987). The Denny Creek Granodioriteis a cluster of intrusive bodies ranging in composi-tion from quartz monzonite to quartz diorite(Tweto 1987). In the Trout Creek Pass pegmatitedistrict, the dominant rock-type is a foliated biotitegranite, close to quartz monzonite in composition.

The name Trout Creek Augen Gneiss wasoriginally applied to the Denny Creek Granodioritein the Mosquito Range by Hutchinson & Hedge(1967) and Hutchinson OnD, However, as theserocks are no more foliated than other units of theRoutt Plutonic Suite, Tweto (1977, Table l) revisedthe name Trout Creek Augen Gneiss to the DennyCreek Granodiorite. The Trout Creek Augen Gneissof Hutchinson & Hedge (1967, Fig. 8) is ap-proximately 1.7 Ga based on Rb-Sr age determina-tions. Thus, the host Denny Creek Granodiorite isrelated to the Boulder Creek orogenic event.

Pegmotites

The four REE-enriched pegmatites investigatedin this study are internally zoned, ellipsoidal bodiesconsisting of a thin discontinuous border zone, agraphic granite wall zone, and a compositequartz-microcline core with superimposed albite-rich replacement units. Pegmatites typically haveelliptical horizontal cross-sections. Dips of thepegmatite - host rock contacts, as well as contactsbetween the internal zones of the pegmatite, rangefrom either gently outward or steeply outward inthe upper portion of the pegmatite, to steeplyinward in the lower portion. Replacement units(pods) are larger and more abundant in the upperportions of the pegmatites. Although the true"replacement pods" are generally restricted to theouter core, secondary albitization occurs in boththe core and wall zones.

Wall zones of the pegmatite bodies lange inthickness from I to 15 m, with an average thicknessof 3 to 4 m, and completely enclose the compositecore. Wall-zone rocks are composed primarily ofa graphic intergrowth of pink microcline perthiteand quartz. In general, graphic granite in the wallzone gradually increases in grain size toward thecore. In some places, microcline perthite of thegraphic granite has been partiaily or completelycorroded and replaced by white albite, which wassubsequently sericitized.

The composite quartz-microcline core isvolumetrically the largest portion of the pegmatites.The core consists primarily of microcline perthiteand quartz, with lesser amounts of both primaryand secondary, highly sericitized plagioclase, andminor amounts of biotite. Microcline, either pinkor white in color, has an ayerage grain-size ofapproximately 0.6 m. The plagioclase is generallyonly slightly smaller in size. Electron-microprobeanalyses reveal that the primary plagioclase isoligoclase ranging from Anp.r to An2e.5. Thesecondary plagioclase is nearly pure albite. Quartzoccurs as masses of "bull" quartz that range insize from several cm to several meters across. Largebooks of biotite, up to one meter in maximumdimension, are generally restricted to thin discon-tinuous zones, which are located along the core -wall-zone boundary near the top of the pegmatitebodies. Biotite also occurs in minor amounts alongthe core - wall-zone boundary as smaller grains Ito 2 cm across. Muscovite, I to 2 cm across, occursas a fracture-related phase in the core. trn additionto these principal minerals, lesser amounts ofmonazite-(Ce) and allanite-(Ce) are associated withthe core. A single gadolinite-(Y) crystal was foundon the mine dump from the Clora May pegmatite(P. Modreski, pers. comm.). From the associatedminerals, it appears most likely that the gadolinite-(Y) also formed in the quartz-microcline core.

Replacement units are typically located along thecore - wall-zone margin. They range in size from0.5 to 2 m in diameter and are characterized byaggregates of anhedral quartz grains, from 0.5 to2 cm in maximum dimension, which are eitherpartly or completely surrounded by a secondary,highly sericitized, white albite. In some instances,the quartz in these aggregates is smoky. Otherminerals occurring in replacement units are rnag-netite and polycrase-(Y) or aeschynite-(Y). Mag-netite occurs as subhedral to euhedral masses upto 2 cm across. Polycrase-(Y) or aeschynite-(Y)typically occur as anhedral masses up to five cmacross and as rare, crudely formed crystals in theYard and Clora May pegmatites and as I to 2 mmgrains in the Crystal No. 8 and Tie Gulchpegmatites.

ANer-vltel METHoDs

All REE-bearing minerals were analyzed in thewavelength-dispersion (WD) mode on the ARLelectron microprobe at the University of NewOrleans, with an accelerating voltage of 15 kV, asample current of 22 nA measured on brass, anda beam diameter of I pm. Data were collected at150,000 preset beam counts (approximately 31-second counting times). La peak positions wereused for all REE delerminations. For each mineral.


background positions were carefully selected fromWD scans in order to avoid interfering peaks. R.EEpeak-overlap interferences were corrected for byapplying spectrometer and crystal-specific empiri-cal correction-factors determined by Wayne (1986).The R.EE corrections were calculated and appliedto the raw data using REECOR, a programdeveloped at the University of New Orleans.Corrected data were reduced using PDQ, amodified 30-element, IBM-PC version of EM-PADR (Rucklidge 1967). The following standardswere used for the R.EE: synthetic R.EE-bearingglasses (Drake & Weill 1972), synthetic REEfluorides (Wayne 1986), and slmthetic REE-Gagarnets (J. S. National Museum numbers: 5-65,5-67, 5-69, S-87, S-90, S-92, and 5-529). Thelimits of detectability for rhe REE are between 0.1to 0.05 oxide fi.90, with the exception of Pr, Tb,Dy, Ho, Er, and Yb, which have large correctionsdue to overlap and are essentially eliminated asconcentration levels fall below about 1.0 to 0.1oxide fi.90, depending on the concentration of theinterfering element. Other standards used weretanzanite, albite, thorianite, rutile, pyrope,uraninite, fluorapatite, synthetic Ba-Cl-bearingapatite, ferrosilite, manganotantalite, and synthetic Yniobate, Y-Al garnet, andZr oxide (Hanson 1990).

X-ray-diffraction analyses of polycrase-(Y) andaeschynite-(Y) were carried out using a ScintagXDS-2000 X-ray diffractometer, and analyses ofallanite-(Ce) and monazite-(Ce) were conductedusing a Norelco XRG-5000 X-ray diffractometer.Samples were run with an operating voltage of 35kV and a current of 15 mA, using CuKcv radiation

(graphite-monochromated for the Norelco instru-ment), and a scan rate of 2 20 per minute.Synthetic corundum and quartz were used asstandards for instrument calibration. Unit-celldimensions were calculated from X-ray powder-dif-fraction data using lt to 23 reflections between l0oand 60o 20 and CELL, a modified IBM-PC versionof the least squares unit cell refinement programof Appleman & Evans (1973).

Polycnesn-(Y) alro AnscnvNrrr-(Y)

Strongly radioactive, black, vitreous, anhedralmassgs and euhedral crystal fragments a few mmto ten cm across occur with quartz-albite ag-gregates in replacement units from the Yard, CloraMay, Tie Gulch and Crystal No. 8 pegmatites.Samples are optically isotropic in thin section andshow no X-ray-diffraction peaks, indicating com-plete metamictization of this material. Materialfrom the Yard pegmatite was previously identifiedas "euxenite" by Hanley et al. (1950).

The general formula for minerals of the euxenitegroup of complex orthorhombic Nb-Ta-Ti oxidesis 48206, in which .4 represents Y, REE, Fe{ ,Mn, Ca, Th, U, Pb, and Sc, and B represents Nb,Ta, Ti, Fe3+, W, Sn, and Zr (Ewing 1976). Thedominant cation in the B site is Nb in euxenite, Tain tanteuxenite, and Ti in polycrase-(Y) @ig. 2a).These minerals are almost always metamict andgenerally altered; thus their crystal structure ispoorly understood.

Further complicating the classification ofeuxenite-group minerals is their close chemical and

U+ThTonteuxenite Polycrose-(Y)Fto. 2. Triangular plots of Trout Creek Pass M-Ta-Ti oxides: (a) major B-site cations (Nb, Ta and Ti) with

euxenite-group mineral names; and (b) major,4-site cations (REE + Y, U + Th, and Ca). The fields of "polyc.rase"(within the dark outlined area), "priorite" (stippled area), and "blomstrandine" (horizontal-ruled area), ofdernf& Ercit (1989) are shown for comparison. Symbols for pegmatite samples are as follows: squares: Yard, triangles:Crystal No. 8, diamonds: Clora May.

CoTiTo

REE+Y

REE MINERALOGY. TROUT CREEK PASS PECMATITES 677

structural relationship to aeschynite-group minerals(Cernf & Ercit 1989). Aeschynite-group minerals[including aeschynite-(Ce), aeschynite-(Y),"priorite", and "blomstrandine"l have the samegeneral 4B206 formula as euxenite-group minerals.In most aeschynite-group minerals, Ti is thedominant B-site cation and LREE are the dominant/-site cations. Thus, in older literature "aes-chynite" typically refers to aeschynite-(Ce)."Priorite" and "blomstrandine" are the namespreviously applied to the HREE-Ti-dominantaeschynite-group minerals and are now bothconsidered equivalent to aeschynite-(Y)."Blomstrandine" was considered to be a Ti-richvariety of "priorite" (Komkov 1963). Thus,aeschynite-(Y), "blomstrandine" and "priorite"are all chemical/y equivalent to the euxenite-groupmineral polycrase-(Y).

The difficulty of chemically differentiatingNb-Ta-Ti oxides was addressed by Ewing (1976),who employed a method of canonical discriminantanalysis to distinguish between euxenite- andaeschynite-group minerals. He suggested that thesum of uranium oxides ("EU") and ThO2 contentmay be critical in discriminating between"euxenite" [euxenite-(Y)] and "priorite" [aes-chynite-(Y)1. By inference, as polycrase-(Y) is aeuxenite-group mineral, the abundance of U andTh could possibly be used to discriminate betweenpolycrase-(Y) and aeschynite-(Y). For example, aTi-dominant.48206 oxide with the sum of uranium

oxides ("XU") greater than ThO2 should be calledpolycrase-(Y). Alternatively, if the sum of uraniumoxides is less than ThOr, the nomenclature isambiguous (Ewing 1976).

Analytical results

Tables I and 2 show the electron-microprobeanalytical results and calculated phemical formulasfor the Trout Creek Pass pegmatite districtNb-Ta-Ti oxides. Formulas were calculated ou thebasis of three cations total. Iron is reported as allFqO3 with the exception of Clora May samples,where 5090 of the iron was converted to FeO tocompensate for high totals in the B site and lowtotals in the z4 site. Although the valence state ofuranium is unknown, all uranium is reported asUrOs, which yields better analytical totals thanUO2. UO3 would yield even higher totals, but it isconsidered unlikely that all of the uranium ispresent as U6*. All of the microprobe analyses yieldlow analytical totals. As the ratio of the sum of.A-site cations to the sum of B-site cations is closeto the stoichiometric ratio of .1:2, the low analyticaltotals are believed to be attributable to absorbedmolecular water, a common,feature of metamictminerals (Ewing 1975).

The dominant B-site cation in Trout Creek Passpegmatite district Nb-Ta-Ti oxides is Ti. Y andREE are the dominant.,4-site cations (Figs. 2a, b).The overlap of the "polycrasel', "priorite", and

lQOs 18la, l65t 178/t 1535 165t t0r0 19./9 l93a t738 9.73 gt6 lo€ loiETa&; 2.s1 2.9 2.a 2.s) 6s7 6.66 8.s o.to e03 6.El 3.el 6Jg 0.64rE ap as 26.00 zs.r3 2t&, uaag zl:e 2/r.55 2539 zraS ELlr clgl Q&Ttd, g5 2.41 2'! Er2 Z8 2r9 2fi 217 2.11 O!2 4J8 O't3 4t6lr3oS rgrg 'tE49 1634 rA6 98 7.q 4{6 8,/t4 ctg 3.S L@ 438 4ltlt-ieQ 0,@ nn. n.d. 0.f, 0.6 0r!4 o.G o.ot 06 0.@ 0.0 0!4 o.clC.2Og nd. n.d. n.d. n.d. n.d. n.d. [d. n.d. n.d. 0.@ O04 Oto n.d.NdZOr 035 O41 o49 o./g olo O.A oZ 0.e o5 0.@ O?4 0.03 o'll!sm2o3 0s o./to o84 ot3 036 o39 olo o.a 0.,|8 o7i2 0.08 0.8 0.@Eu2O3 0,6 n d. nd. O.G ni. n.d. n d. n.d. 0.a7 n d. 0.6 lI@ n.d.Gd2% lA l.l5 La l.l3 036 OJg 1.17 1.11 l.t6 1t0 2fr t'gl 1.60I!?O3 O.lo otg 033 o,a o24 Ol4 O30 o.3s o,A 0,$ 0.{4 o.4r O.eDttq L14 ito 2.12 z1a 2.& 22 2,76 28 znt 2.n &13 33 3.14t{%O3 OJ3 OA O.8 O.€ Ortg A',? 0.& OtO Oe 0.6 0.12 OA 022Er2q ri8 l.4r 1.05 1J5 l.m r.lo te l.8l lr2 1.7i2 131 l.ol ljormzos o2r ol8 o2!l o{8 039 010 031 0.4 o€ ol9 o14 lutr 030v!t% i.$ rr0 7,gt i.B5 1.03 t,ao t.45 19 1gl ojo o@ l.l0 ll9Lltq oJg o.zt o.Jr oja oJ3 oe o49 oJo ooil o.a o11 024 0r0Y2q lo.@ gJ4 llSO 9.68 i4ja $.12 t?./O lal? 10.10 lo78 1474 t6.6 lO.'19rno o./t0 0a un 0.l]' o/o o{s 0./g o/o o'14 0t8 0.€ 039 0.'14z.ro2 &'' 0,6 nd. n.d. n.d. nd. nd. nd. o.Oa nd. nd. nd. nd.cro 2.9 357 33S En 29' L78 222 2:n lr0 l.s ota t!8 0.ssqq 0.16 olo 0.6 0,6 olo 0.@ o'12 ot! o14 nd. oE 0.(E 0!53t62 0.6 0.04 0,0f O.B o2l O,' Ol7 0.72 0.16 LA 05 0.S o.Otplo r.84 03t O/|8 Otll 038 0.:l9 Oe Ofl 18 ML ntL OA o04WO3 OJ6 Glo o.of o.!0 2.6 11!2 l.8o 2&. 2.49 4Al 431 639 /LGFo&s 3.0 28 3.& 2.n 4n 4.45 AU 4.S 2,9,2 lto t,, 0.76 1.05F€o 1.4 1.13 ilgl 038

aEscltYNTE{Y)

Clli Ctfi2 CU.3 CNr-6

TOTA! g?,til gg 84.01 05J48 nfi 18'L1g 0217 gatt gd.:n 84.S g30 9433 93.12

TABLE 1. CHEUTCA! COUFOS|TTON OF TROT'T CREE( PASS FOLVCFASE{Y) AND AE9CHYNITE.(Y)

Pr mt .€d ior hd nol dde.lodi D d. € rd dsleclod


AESctmSTF(ncst cI-2 cF3 cF3

o0a6 0.@ 0.6lt 0.0,91 0-CF OO|o 0.@ OdI9 0.Gl4 OG 0.m O@ 0.@0266 Ol88 o.zft 0"2|6 Ot2. 0.G8 O@ o.El O@ O05-, 0.03/t oltt o.rEl0.0r olFt 0.01 0.01 o.Dt oot 0.01 o0r 0.m

0&r oot [email protected] oG o.ott olto 0.@t 0.G 0.G 0.o7 0.@ 0.ot4 03!6 o.ot4 0.GoJl2 0.0tt oor4 0.o!3 0.67 0.G 0,@ 0.@ oot0 0.0t7 0J't8 0,018 0tt30&a o.ot 0.0t o.ot oat ul}tocff oca o.cri ooa 0.0e0 0.@ 0.@4 lMl aM o04,t 0.010 0!{0 oBaoG oG Ed, 0.6 0.05 0.@ 0.G 0.6 0.6 0.@ 0G, otto o.o8ool2 0.040 oo{a 0,0{a ooli 0.0at 0-056 0.060 0.064 oct o6t o.@ o.Gr0.6 o.ot 0.G 0.G ooto 0@ 00ti 0,@ oot2 oat o-@t 0.6 o.0{o.CA OCA o,|El l|..}'! 0.(}3 OtE9 0.44 O(B/t Oogt o.dF O.OA OtBt OGo.Gl oGl 0.G 0G o.st 0.o7 o.mo .0.@ o@ o.o4 0.G oot oGo.Gn o(t}t oc6 0.@ 0.Gn olEI o.@ 06 0.61 0.ot8 0.ot3 o.ca 0.04i0.m 0.ol 0.o7 o.o!t ooto 0'ot1 0.@ 0.o!0 oltr oG oot 0.o4 0.040.32 0334 05tl 0317 0r''6 OaEt Ott! 0Jt5 0J3t 0388 OJ{3 OtS o.B2ooa 0..n6 0.0t0 0.0a 0-0tl \@ oez. oca o.ul o@ 0-06 o'@t uBOt97 orft UEU o24t 0.10t Oltt Ot/8 Gt?o Ola Oilg Or.o O.@ otF{

ThuLAC6NdSrtrEUGdIbDtHoETTmYbL!vUnCrScPbFe2r

0.@ 0.c o.oE 0-B 0.G 0.G 0.8 oot 0.o7qqlt ool{ oo oot2 0.@ 0.@ 0J'l0 o.Gt oo2r

o.Gr 0.@ o,G0.G 0.0t

slfuA l,gt r.@ .t.@ '.tn 7.gt lo|t r.o{t 1.or .t.@ r,G o.sr ost o..g

llb O'ltg O{S OrEo O(! 0.'6t Oat 0J{8 o.Ett O.ra o.A AA U&, UATa 0!€ OgF o.G'8 oltt O..Ba o.Gt Ot.t2 o.t0t o.OS Oi2r Oi6o Ot13 OitOn, lr88 l.l'tg irl6 t.O l.lcl t.lgt t.lal t.106 l.l&! tJaot 1.'t88 t.a$ r.,gtFo3. otlo ot2o o.t?t ot30 orG n26 o.t2a 0206 ots6 o.ci 0.@ o.Bi oo{0w 0.|n act otrt 0.6 oc!| 0,02r o6t o-otB o0rt0 tt.0s or,3 oct o.caSn O|m Oml Oqn o.Ot O@ .t.|n Oma 0"l|!l O.@a OJ!! O@ O@

sfJH g t.E}o l.gt 1.812 t-Oll r.8l 1380 1188 1Jt8 r.$4 l.Sa 2.U12 2.gB ,,,n1

Fo@habagt o0rFtobt 6tb6

"blomstrandine" fields of ternf & Ercit (1989) forB-site cations in M-Ta-Ti oxides is shown inFigure 2a. The Trout Creek Pass samples overlapthe "polycrase" and "blomstrandine,' fields. Thediagram showing l-site occupancy @ig. 2b)suggests that samples from the yard are"polycrase", whereas samples from the Clora Mayand Crystal No. 8 fall within the area of overlapbetween the "blomstrandine" and,,polycrase',fields. Thus they are not clearly either ,.polycrase',

[polycrase-(Y)] or "blomstrandine,' [aeschynite-(Y)1. However, samples from the yard and theCrystal No. 8 pegmatites have U3O6 in excess ofThO2, suggesting that they are polycrase-(y),whereas those from the Clora May pegmatite haveUrO6 less than ThO2, which does not unambiguous-ly categorize them as either polycrase-(y) oraeschynite-(Y).

A plot of the major ,4-site cations (DLREE,DHREE * Y, and Ca) shows the extreme LREEdepletion of the M-Ta-Ti oxides (Fig. 3c).Chondrite-normalized plots (Fig. 4) for these oxidesshow that the HREE and Y are enriched over theLREE by almost two orders of magnitude.

X-ray difiractometry

Heating experiments of metamict, complexNb-Ta-Ti oxides by Ewing & Ehlmann (1925) showthat upon heating, an aeschynite-type phase forms

first at low temperatures and then is converted roa euxenite-type structure at high temperatures.They reported the transition to occur between 550and 750oC for Y-rich compositions, and between900 and l000oc for Ce-rich compositions.

Only the Yard and Clora May pegmatites yieldedsufficient material for recrystallization experi-ments. Samples were heated in air at 400, 500, 600,700, 900, 1000, and llOOoc for 24 hours (Fre. 5).All samples recrystallized between 500 and 600.C.Samples from the Yard pegmatite recrystallized toa euxenite-type structure, and diffraction patternscorrespond closely with that of a heated euxenite-(Y) (PDF 9-442); the Yard samples have slightlysmaller d-values (Hanson 1990). These samplesretained the euxenite-type structure from 600 to1000"C (Fig. 5a). Samples from the Clora Maypegmatite recrystallized first with anraeschynite-type structure, with a diffraction pattern cor-responding closely to that of a synthetic aeschynite-Cn (PDF 20-1401) (Hanson 1990). This strucrurewas retained up to 1000'C and then converted tothe euxenite-type structure between 1000 andll@"C (Fig. 5b).

Thus, based on the heating experiments, bothpolycrase-(Y) and aeschynite-(Y) are present withinthe Trout Creek Pass pegmatite district. However,the annealing results are different from thosereported by Ewing & Ehlmann (1975) in that theYard polycrase-(Y) recrystallizes directly to a

TABLE 2. C}ItrICAL FOFMULAS OFTBOUT CFEEK PAS€I PTOLYCFASE{Y) ANI, AESCHVT$TE{Y)

euxenite-type structure with no intermediate aes-chynite-type structure. Furthermore, the transitionfrom an aeschynite-type structure to a euxenite-typestructure for Clora May samples occurs between1000 to I l00oc, which is higher than the transitionsreported by Ewing & Ehlmann (1975).

679

Cell parameters calculated for recrystallizedpolycrase-(Y) from the Yard pegmatite. are: a5.534(li b 14.424(5), and c 5.178(l) A. cellparameters calculated for recrystallized aeschynite-(Y) from the Clora May pegmatite are:. o 5.181(3),b lO.9Ol(7), and c 7.382(3) A.

REE MINERALOCY, TROUT CREEK PASS PEGMATITES

LREE HREE+YFtc. 3. Triangular plot of major z4-site cations for Trout Creek Pass minerals: (a)

monazite-(Ce), O) aUanite-(Ce), and (c) polycrase-(Y) and aeschynite-(Y).Symbols for pegmatite samples are as follows: squares: Yard, triangles: CrystalNo. 8, diamonds: Clora May, stars: Tie Gulch.

C oCoTh

q)

c

-c

Io-

U)

1 000000

1 00000

I 0000

'1000

100Lo Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y

Ftc. 4. Chondrite-normalized REE plot for Trout Creek Pass polycrase-(Y) andaeschynite-(Y). Symbols as in Figure 2.

/e/*{

^cS " /

&eY--"

,/re-s

{js

Polycrose-(Y) Aeschynite-(Y)


FIc. 5. X-ray-diffraction patterns showing the recrystallization history of metamict Nb-Ta-Ti oxides: (a) Yard samplesrecrystallized with a "euxenite" structure, which was retained through 1000'C; (b) Clora May samples recrystallizedfirst with an "aeschynite" structure, which was relained up to 1000'C before conversion to a "euxenite" structureabove l000oC.

Ananrrr-(Ce)

Allanite-group minerals are members of theepidote group, represented by the general formulaA2M3S\O$H, where z4 represents large, high-coor-dination-number cations such as Ca, Sr, REE, etc.,and M represents octahedrally coordinated Al,Fd+, Mn3+, Fd*, Mg, elc. (Dollase l97l).

Allanite-group minerals are related to epidotethrough the coupled substitution: REE+ + Fd+= Ca2+ + Fe3* (Dollase 1971, Deer et ol. 1962,Exley 1980).

Allanite-(Ce) occurs as anhedral, black massesup to 2 cm in size in the Yard and the Tie Gulchpegmatites. Although no allanite-(Ce) was foundin the Clora May or the Crystal No. 8 pegmatites

4 . 2 . 2. . 1 . 5 4 1

Euxqnl , tc st ructur6YlFtl Polycrllr- (Yl

hrltrrl foa la hr!. rt:

tooo o c.1.^ ^

rl ---

hJrr\rflt.J 'rA

g o o o c

rl ,l . i

6000 c

Sooo c

.l0O o C

Clors l lay A€achyntt!- (Y,

he l tcd fo r t? h r6 . a t :Euronl t6 structure

A6achyn l t ! s t ruq tuF!


in this study, it is reported to occur in both ofthesepegmatites, with allanite-(Ce) from the Crystal No.8 occurring as long straight crystals up to one cmacross and fifteen cm long (Hanley et ol. 1950).Allanite-(Ce) is always associated with microclineperthite of the core rather than with quartz-albiteaggregates of replacement units.

Analytical results

Representative results of electron-microprobeanalyses and calculated formulas are given inTables 3 and 4. Formulas were calculated on thebasis of three Si cations, as the epidote-groupminerals characteristically show little replacementof Si by Al in the tetrahedral sites (Deer et ql. 1962\.The sum of the M sites is slightly high, and thesum of the.4 sites is somewhat low. Total iron waspartitioned into ferrous and ferric iron on the basisof 25 total charges. OH was calculated bystoichiometry on the basis of one (OH, Cl, F).

Allanite-(Ce) from the Trout Creek Pass peg-matite district is LREE-enriched, with Ce as thedominant REE (Table 3). Allanite-(Ce) from theYard pegmatite has higher total REE than thatfrom the Tie Gulch pegmatite. Figure 3b shows theLREE enrichment of allanite-(Ce) on a triangularplot of major.4-site cations. Ce is approximatelytwice as abundant as either La or Nd on a weightbasis. The relative proportions of Ce, La and Ndare shown in Figure 6b. Allanite-(Ce) samples fromthe Yard are somewhat enriched in Nd comparedto Tie Gulch samples. Chondrite-normalized plots(Fig. 7) of allanite-(Ce) show the extreme IREEenrichment relative to Y.

CREEK PASALIANTF{Co)

OIDE YD€ YD{ TCd IGB

TAALE lr. CHEUICAL FORUUI.AS OF TBOUTCREEK PAggAIANIF(CO)

YD€ Yl'€ TG.A TEB

3.@ Em 3.@ 3.m

6 1.08E l.@ 1.t447Ca 038 03Ol OZUlr 0J64 0139 0114l{d 0.1431 (L156 0,@gr 0!40 o.Oall 0Jl0Gd oMl ogB 0.011Yb 0.o4 0.04Lu 0.o7 0.64 0s4Y 0.@ 0!ll 0010un 0019 ol}tl 0010

1r0o.zaol13o@[email protected]'l

0.o80.o16

s0.?2 103{ rr39 sjo

Elm'Iaana|ladtorblt trotd6bct€d ldude:N& U, F, Pt, Eu, ID, Dr, Ho, Errnal TmlLAsDdddlc!!.li

g.lll a 1.8! t30l 1gtt2 1t80

$JilU 3.U El6l 3.14'l S.A

0.04:1 0.0{r 0.6-t o.g7

o'95, 035, 034t otal

Oll dolsmhod bt stodddt|gl'Y

X-ray diffractometry

X-ray-diffraction analysis reveals that TroutCreek Pass allanite-(Ce) is only partially metamict,as XRD patterns yield most of the rnajorcharacteristic peaks of allanite-(Ce), yet show noneof the smaller peaks (Hanson 1990). Cellparameters were calculated for samples from boththe Yard and the Tie Gulch pegmatite. Celldimensions for Yard material are: a 8.892(l), b5.706(4), and c 10.136(2) A, with B l l5.27".TheTie Gulch allanite-(Ce) yielded thg cell dimensionso8.955(2), b 5.701(4), c 10.187(2) A, and B I15.48".These values are slightly different from values givenby Cernf et al. (1972) (PDF 25-169) for a non-4getamict allanite-(Ce): a 8.932, b 5.770, c 10.1575A, and I114.69'. The slight differences in thesevalues are likely related to slight differences incomposition and the partially metamict nature ofallanite-(Ce) from the Yard and Tie Gulchpegmatites.

MoNeztrr-(Ce)

Monazite-(Ce) is the least abundant R.EEmineralin Trout Creek Pass pegmatites. In this study' itwas found only in the Yard pegmatite, where itoccurs sporadically as brick-red euhedral to sub-hedral crystals up to 20 cm across. Like allanite-(Ce), monazite-(Ce) occurs in the core and is notassociated with the albite-rich replacement units.

The general formula for monazite-(Ce) is,48On,where .4 represents REE, Th, U, and Ca, and Brepresents P and Si. Monazite-(Ce), (Ce,La,Nd,Th)POa, is a member of an isostructural series of

Af ?.350 23Al z.fin 221liFe2r o?s u7:,! oloi 0.89663+ o.ct4 o.18 oiFTt 0.@ o-Gl o.cd o.oD

3.O 374 3331 34J.32ft9 2,8 6&2 ZL1611.t5 1r.63 1&13 r5.O'f0.t6 932 8S 734489 421 Un 3]5t4A'l /r.s L't7 2nra r38 031 0300r8 039 039 0lgOla O14 n.t|.. nnoZ O13 Ol4 rAo.1? o,2, 05 o.110.r3 0,05 032 030o.a ot8 u2, o.2,nrd. nd. 0.81 Og70lI Un 0.00 n.LloJt g:tf 1078 12.80.o 051 r.8t oanon n.8 oia n9

slo2al2o3Croqo3teAO3ilqo3S!t2O3C.l2O!vQo3Lr2O3Y2oErqilnoI|'qrrgoF60Fe2%clsullOsCN

99.18 lmil

0.6 0.tt,

c7.a 657

0.G| 0r,

682

1 000000

1 00000

1 0000

J 000

'100

monoclinic minerals including cheralite, (Ca,Ce,ThXP,Si)O4, and huttonite, ThSiO4 (Bowles et al.1980, Fleischer 1987).

Anolytical results

Tables 5 and 6 show representative results of

THE CANADIAN MINERALOGIST

C o

Lo NdFtc. 6. Triangular plot of major rare-earth elements, Ce, La and Nd, for Trout

Creek Pass minerals: (a) monazite-(Ce) from the Yard pegrnatite (squares), and(b) allanite-(Ce) from the Yard (squares) and Tie Gulch (stars) pegmatites.

o

o(.,

Eoa

Al lon i te- (Ce)

\ \-- l L-- --- -- --\--

\

Lo Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y

Ftc. 7. Chondrite-normalized R.EE plot for Trout Creek Pass allanite-(Ce) from theYard (squares) and Tie Gulch (stars) pegmatiles. The dashed lines areextrapolated across the HREE to Y as the .F/R.E'E abundances in allanite-(Ce)are at or below the limits of detection.

electron-microprobe analyses and calculated chemi-cal formulas for monazite-(Ce) from the Yardpegmatite. The formulas were calculated on thebasis of four oxygen atoms. The sum of ,4-sitecations is slightly low, and the sum of 8-site cations issomewhat high. Monazite-(Ce) is ZR.EFenriched,with Ce as the dominant .r4-site cation (Fig. 3a).

/e/f'

^\s"


TABLE6. CIIEflICAL AMLYSES OF TBOUT CREEKPAStOl{,aTE(Ce)

Pfsslo2t82O3CE2O3n2oatld2O3$n2O3Er43Gd293Dy2o3Y2oinqCaO

30JO ,g.Jg274 Ut|9.c| &482459 UA3t.04 154

11.&r 11.1033t 351o.8o 0.sg0 3.o10.s 0312J8 1gr&a{t to57o74 tg7

29t6 3r.1028r UA8r5 8tlafi agtot t.€!71,a i1.993,{O 3tB050 0r92.9 3.O0.!0 0.€2S UAro32 8.180J0 0r8

ub gol8.8t 8.7:lzlgt asl1t0 tno1?J5, 11,o354 3310r0 0{93.@ Z7r2051 0,49271 2Sf8.17 tt.3|o?t o.gt

FIB U3 lrFaA ll€A U6B t€

TAaLET. Utlr-CELL DATA FOB IOI{A;ATE (@) Al{D SOIrESYNT}ETF ENDGIBEN PH@TIATES

a(A) D(Al c(A B(')

Yatlr a788{11 7-ql) 0.'116(r) 18.7i

u.sdcoF. a796 7fi a{06 '10(195

f-eFO4- C& 78 6./A 1045t

CoFOI- &7n O"Gl 6n'|t lBJ

caTqFodt2* 0.69 o.sr e3a 104n

' (5rq|arrr.(t0t0);(PDFStt€)- sor.ts08|l

Bcrlsletar (1@lEdb&HfrrD(rga)

The relative proportions of Ce, La and Nd areshown in Figure 6a. The monazite-(Ce) in the TroutCreek Pass pegmatites is enriched in Nd relative toLa. It is interesting to note that the relativeproportions of La, Ce and Nd in monazite{Ce) arevery similar to those of allanite-(Ce) (Fig. 6b).Chondrite-normalized plots of monazite-(Ce) showthe strong and relatively uniform enrichment ofZR"EE (Fig. 8).

X-ray diffractometry

X-ray-diffraction patterns of Trout Creek Passmonazite-(Ce) correspond almost perfectly to thatof Carron et ol. (1958; PDF ll-556) and can befound in Hanson (1990). Calculated unit-celldimensions for monazite-(Ce) from the Yardpegmatite are shown in Table 7. The table showsthe relationship between the cell dimensions ofmonazite-(Ce) from the Yard pegmatite, that inPDF ll-556, and other synthetic monazite-struc-ture phosphates.

suu 1001 10!1 to5 ro.l2 $.&l 10.12

Ebm.ftr mF ior hn rd dsbd lEldo: Fq U, Ib,Ho, E, Trir Yb ard L!; it d. s rd.l6!scLd

TABLE A CHETICAL FORiN.,I.A9 OF TROUT CMETPA$UOl|laIE{Col

slB U-i rr4A t€A t{B f{

0.94 0.9@ 0te5 otgl 0388 0356

9UU B r,07t !.on 1.G5 r.cro 1.o?! 1JJn2

@PItLlSnE{C.lDtYThC8Pi

[email protected],[email protected]!to.ono.tlll

u12a038o.El0.163OM0.G0.Gt50.60.04110.0090.qr

0341 034it0.023 0,@ot00 016:lo.oa3 0.0{7o.@ 0.o7O$B O.GF0.0it 0.6t0.052 0.04,1ortz 0€0oJtr 0.G15o.G ooto

o"jva o34aofrB [email protected] GlOl0.015 034ro.rt 0.Go.gb 0r!!0.G 0.G0.042 0.0450.098 0Jrt00.qr6 o.cno-dto o.trt o-m d-m

slrf A 0.m 09t9 ogn 0.198 09t4 0.'t0

Fombs bsd on iour orygon eloma

()!

0,

a

1 000000

1 00000

1 0000

1 000

1 0 0Lo Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y

Ftc. 8. Chondrite-normalized REE plot for Trout Creek Pass monazite-(Ce) fromthe Yard pegmatite (squares). The dashed lines are extrapolated across the F/REEto Y as the HREE abundances in monazite-(Ce) are at or below the limits ofdetection.

Monozi te- (C")

= = = = _ E E


DIScUSSIoN

The Trout Creek Pass pegmatites display adistinct chemical, as well as a spatial separation ofthe light versus the heavy rare-earths. Chemically,polycrase-(Y) or aeschynite-(Y) is the only HREE-enriched phase present, and allanite-(Ce) andmonazite-(Ce) are the only LREE-enriched phases.Within the pegmatites, the lREEminerals, allanite-(Ce) and monazite-(Ce), are spatially restricted tothe core or core margin, whereas the HREEmineral, polycrase-(Y) or aeschynite-(Y), is alwaysassociated with late-stage, albite-rich replacementunits.

Similar separations between early-formingLREE minerals and late-stage IIREE minerals havebeen reported by Mineyev (1963). Two argumentshave been suggested to explain the separation oflight from heavy rare-earths. One view holds thatREE separation can be achieved by crystalchemistry alone. According to the other view, REEseparation can be explained by geochemical factors,in particular the stronger tendency for the HREEto form complexes.

According to the crystallochemical model, RE'Eseparation is a direct result of crystal-structurerequirements such as ionic radius and coordination.Semenov (1958) suggested that lanthanide selec-tivity is related to coordination number (CN).Minerals with high-CN elements are ZR.6E-selec-tive, those with low-CN elements are -FIREE-selec-tive, and those with intermediate-CN elements arenonselective. Semenov classified "euxenite" asbeing Y-selective, "allanite" as nonselective, and"monazite" as Ce-selective.

On the other hand, Mineyev (1963) suggestedthat HREE-LR.EE separation may be explained interms of geochemical differences. He suggested thatthe HREEhave a tendency to form complexes morereadily than the LREE, particularly with fluorineand chlorine, thus allowing the HREE to undergomore pronounced differentiation.

In pegmatites of the South Platte district,Colorado, Simmons et al, (1987) observed achemical zonation of F, Nb, Th, U, and REEbetween groups of pegmatites. They reported adirect correlation between high concentrations offluorine and HREE mineralization. Pegmatitescontaining abundant fluorite are enriched in theHREE and yttrian phases, samarskite-(Y), HREE-enriched zircon and yttrian fluorite. Pegmatiteswith sparse or no fluorite are characterized by theLREE phase allanite-(Ce). They suggested thatfluoride complexing was primarily responsible forthe REE separation in South Platte pegmatites.

However, in the Trout Creek Pass pegmatites,no fluorine- or chlorine-bearing minerals arepresent in the late-stage replacement units. As

fluoride or chloride ions were unavailable for theformation of HREE complexes, the observedHREE-LREE separation must be the result ofsome process other than fluoride or chloridecomplexing. It appears likely that in the TroutCreek Pass pegmatite district, the sequence ofmineral formation and crystallochemical factorsare responsible for the observed HREE-LREEseparation. The separation of the IREE occurredfirst, with the crystallization of monazite-(Ce) andallanite-(Ce) along the core - wall-zone margin. Theeuhedral to subhedral nature of the monazite-(Ce)crystals is further evidence that they are primaryand not the result of the later replacement phaseof crystallization. The HREE were consequentlypartitioned into the residual fluid, which sub-sequently formed the late-stage replacement unitscontaining polycrase-(Y) or aeschynite-(Y).

Several questions arise related to the mineralogyof the replacement units. First, why does polycrase-(Y), a rare mineral, form as the Nb-Ta-Ti oxide,and second, why does rutile not crystallize fromthis titanium-rich residual fluid. Burt (1989)suggested that simple combinations of ,4-B oxidesmay be used to define oxide reactions. For theTrout Creek Pass pegmatites, we propose thefollowing reactions:

B O 2 + A B O 4 - 4 8 | 0 6TiO2 + YMO4 - Y(Ti,Nb)r2O6Rutile + Fergusonite-(Y) -

Polycrase-(Y) or Aeschynite-(Y).This reaction suggests that the association rutile

+ fergusonite is unstable if polycrase-(\) oraeschynite-(Y) is stable. Polycrase-(Y) or aes-chynite-(Y) may coexist with either rutile orfergusonite-(Y), but not both. In addition, thefollowing relation:

A8|06+ AF - A2B2O6FY(Ti,Nb)r2O6 + NaF - (Y,Na)g2(Ti,Nb)r2O6F.Polycrase-(Y) + Fluoride species *

Pyrochlore-group mineraldemonstrates that an ABrOu oxide such aspolycrase-(Y) or aeschynite-(Y) is stable only in afluorine-depleted environment. Hence, the absenceof fluorine in the Trout Creek Pass pegmatites is,at least in part, responsible for the formation of theseminerals. However, in the presence of fluorine, thefollowing relation:

ABO4+ 248206- 438506YNbO4 + 2FeNb2O6 - (Fe2Y)sNb5O16Fergusonite-(Y) + Ferrocolumbite -

Samarskite-(Y)may explain the presence of samarskite-(Y) in theSouth Platte pegmatites (Simmons et al. 1990,Simmons & Hanson 1991).

Thus, the formation of polycrase-(Y) or aes-chynite-(Y) as a late-stage mineral in the pegmatitebodies requires the rare combination of fluorine

REE MINERALOCY. TROUT CREEK PASS PECMATITES 685

depletion, coupled with Ti, Nb, Y, and HREEenrichment in the residual fluid, a relationship thataccounts for the scarcity of the mineral.

AcKNowLEDcEMENTS

We thank the Department of Geology andGeophysics of the University of New Orleans forthe financial support for the field and laboratorystudies. We thank Kim Montague for her help inpreparation of the figures. We are grateful to PetrCernf, Robert F. Martin, and Donald D. Hogarthfor helpful comments and suggestions that sig-nificantly improved the manuscript.

RSFERENcSS

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BoATNER, L.A., BEALL, G.W., AnnaneM, M.M., FrNcH,C.8., HuRAy, P.G. & Reeeaz, M. (1980): Monaziteand other lanthanide orthophosphates as alternateactinide waste forms. /r Scientific Basis for NuclearWaste Management 2 (C.J.M. Northrup, Jr., ed.).Plenum Press. New York.

Bowre, S.H.U. & HonNE, J.E.T. (1953): Cheralite, a newmineral of the monazite group. Mineral. Mag, 30,93-99.

BowLES, J.F.W., JoBBrNs, E,A. & YouNc, B.R. (1980):A re-examination of cheralite, Mineral. Mas. 43,885-888.

BuRr, D.M. (1989): Compositional and phase relationsamong rare eafih element minerals. .Ir Geochemistryand Mineralogy of Rare Earth Elements (B.R. Lipin& G.A. McKay, eds.). Rev. Mineral. 21,259-307.

CARRoN, M.K., NAESER, C,R., Rosr, H.J., Jn. &HrroraneNo, F.A. (1958): Fractional precipitation ofrare earths with phosphoric acid. U.S. Geol. Sun,,Bal/. 1036-N, 253-275.

dpcH, F.,.VnANa, S. & PovoNone, P. (19?2): Anon-metamict allanite from Zambia. Neues Jahrb.Minerol. Ab h. 116, 208-223.

dsnltf, P. & Encrr, T.S. (1989): Mineralogy of niobiumand tantalum: crystal chemical relationships,paragenetic aspects and their economic implications..In Lanthanides, Tantalum, and Niobium (P. Mdller,P. Cernf & F. Saup€, eds.). Springer-Verlag, Berlin(27-79).

Drrn, W.A., HowrE, R.A. & ZussueN, J. (1962):Rock-Forming Minerols. l. Ortho- and Ring Silicates.Longmans, London.

Dorlesr, W.A. (1971): Refinement of the crystalstructures of epidote, allanite and hancockite, Am,Mineral. 56,447-464.

DRAKE, M.J. & Wrrll, D.F. (1972): New rare earthelement standards for electron microprobe analysis.Chem. Geol. 10, 179-181.

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Exlrv, R.A. (1980): Microprobe studies of R.E'E-richaccessory minerals: implications for Skye granitepetrogenesis and REE mobility in hydrothermalsystems. Earth Planet. Sci. Lett.48,97-110.

FLETSCHER, M. (1987): Glossary of Mineral Species (fifthed.). The Mineralogical Record, Tucson, Arizona.

HANLEv, J.B,, HErNmcH, E.W. & Pecr, L.R. (1950):Pegmatite investigations in Colorado, Wyoming, andUtah, 1942-19M. U.S. Geol. Surv., Prof. Pop. 227.

HANsoN, S. (1990): Mineralogy, Petrology, andGeochemistry of the Trout Creek Pass PegmotiteDistrict, Colorodo. M.Sc. thesis, Univ. New Orleans,New Orleans, Louisiana.

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KoMKov, A.I. (1963): Euxenite and priorite - polymor-phous varieties of YNbTiO6. Dokl. Acad. Scj. USSR1218, 103-104.

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Rucrrrocr, J. (1967): A computer program for process-ing microprobe data. J. Geol,75,126.

Sruerov, E.I. (1958): Relationship between compositionof rare earths and composition and structures ofminerals. Geochemistry, 57 4586.

(1963): Mineralogy of the Rare Earl&s. USSRAcademy of Sciences, Moscow (in Russ.).


SIMMoNS, W.B., & HANsoN, S.L. (1988): Fluorineabundance arrd HREE/LR.EE separation in lowphosphate melts in the Pikes Peak batholith,Colorado. Geol. Soc. Am., Abstr, Programs 20,A251.

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& FNsrER, A. U. (190): Heavy rareearth element-niobium mineralogy in fluorine-en-riched and fluorine-depleted pegmatite districts inColorado, USA. /n lsth Cen. Meet., Int. Mineral.Assoc., Abstr., 956-958.

-, LEE, M.T. & BREwsrER, R.H. (1987):

Geochemistry and evolution of the South Plattegranite-pegmatite system, Jefferson Counly,Colorado. Geochem. Cosmochim. Acta 51, 45547 1.

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Received lanuary 16, 1991, revised manuscript acceptedMay 28, 1991.

rare-earth-element mineralogy of granitic pegmatites in the trout creek pass district, chaffee...

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