RARE-EARTH ELEMENT GEOCHEMISTRY OF SELECTED S.4MPLES FROM THE SULLIVAN Pb-Zn SEDEX DEPOSIT THE ROLE: OF AL1,ANITIE IN MOBILIZING RARE-EARTH ELEMENTS IN THE CHLORITE-RICH FOOTWALL (82Gh2) By Eva S. Schandl, University of Toronto and Michael, P. Gorton, Royal Ontario Museum (Contribution No. 4, SulIivan-Aldfidge project)
-I" -I" -.-,
KEYWORDS: Economicgeology, Sullivan mine, Metamorphic monazitehas bem reported in the dark grey lithogeochemistry, rare-earth elements. carbonaceous bands of siltite in the Aldridge Formation b) Huebschman (1973). Fine-graincd monazite ' gas descri tjec. as aggregates within the bands. The mode of lccurrencc 01 INTRODUCTION allanite in the chloritized and mineralized fc xwall in thi!; This is a prelimintary reconnaissance survey of rdre-earth study is significantly different : n the cilorit zed footu ;ill, element (REE) geochemistry(supported by major and trace allaniteovergrows or is intin1al:ely intergro vn with pyr.. element geochemistry) of selected rock samples represent- rhotite and galena, and the wide IJleochr83ic h; lo around ).he ing various alteraticmn types at the sediment-hosted Sullivan grains suggests a high uranium content in the nineral (Plate: lead-zinc sedex deposit, British Columbia. 2-5-1). We report the ocl:urrence of very fine grained (<30pm) allanite (REE-rich ,epidote group mineral) in thechlorite- ANALYTICAL TECHRIQUES alteredmineralized footwall, and in the albite-chlorite Rare-earth element geochemistry of select ed rocks ${a:; alterationzone at theSullivan mine. The presence of determined by instrumental n1:1 tron acivatil sn analysi j at allanite (Plate 2-5-1) identified in the mineralized, chlorite- the SLOWPOKE reactor at the University of' bronto. Sam altered footwall and the albite-chlorite altered hangingwall plepreparation and analytical procedures followed the: of the deposit is accompanied by an apparent increase in guidelines setout by Bames md Gorton ( 1984). h4 3jor rare-earth element concentration in the footwall. The close textural relationship between chlorite, allanite, titanite, pyr- rhotite, sphalerite and galena suggests that the crystalliza- tion of this assemblage was more or less contemporaneous. Thus, allanite formation was either contemporaneous with mineralization, or with post-ore alteration that was associ- ated with some rernobilization of the ore.The selective crystallization of the REE-rich epidote in the mineralized chlorite(ibiotite) alteration zones implies one of two things: a rare-earth element gradient was superimposed on the rocks duringalteration and mineralization, or less likely, the present rare-earth element concentration predated min- eralization, andallanite may have formed after thelight REE-rich phosphate, "metamorphic monazite", that report- edly occurs in the carbonaceoussediments of the Lower AldridgeFormation. In eithercase, as the abundance of allanite is accompaniedby elevated rare-earth element values or significant rare-earth element fluctuation, combin- ingdetailed petrography with rare-earth element geo- chemistrycould se:rve as apotential tool for identifying target areas that ho,,t mineralization. Allanite has been pre- viouslyidentified in thetourmalinitized footwall of the western part of theSullivan ore zone by Campbell and Ethier (1984). in a biotite and garnet alteration zone within quartzite at North Star Hill by Delaney (1975).and in the granophyric part csf thePurcell (Moyie) sills by Bishop (1974). Allanite grains in thisstudy can be identified by their wide pleochroic halo which is the result of radiation damage to the host mineral by the decay of uranium (Plate 2-51), Because of the pleochroic halo around the grains, Plate 2-5-1. Allanite with plerlchroic halo, i 1 chlorite they may be mistaken for zircon. Field 2.3 mm. Plane polarized ligh .
Geological Fieldwork 1991, Paper 1992-1 2 73 TABLE 2-5-1 PETROGRAPHIC SUMMARY OF ANALYSED SAMPLES FROM AND AROUND THE SULLIVAN DEPOSIT
# and Lw. Rock Type Mineral Assemblage Description s-I Pebble congl. qtr-carb-bio-ep-murc- Garnrtixd, fine-gr. siltstone G~13-30 (argillite) gnt-po-sph-cp S~2 Moyir sill amph-plag-m-mag-ilm- Epidutewmph. altered. cuarre gr. G~13-30 gabbro rp-qtz-carh-p-cp gahhro s-3 tourn. breccia qtl-toum-musc-biu-ru- Fine-gr. siltstme repl. by G-13-30 mag-po toumalinc s-4 chlorite rack Chlorilized, carhonati,ed sdtrtmc' P-10-4 CTOSSCUtS ore S-5 chlorite rock^ Med.-gr. chlorltixd, loliatcd K-I0-3(1 footwall utanite-rich siltstonelwacke S-6 chlorite rock^ Med.-gr., foliated chloritixd footwall titanite-rich siltstonriwacke
TABLE 2-5-2 MAJOR, TRACE AND REE GEOCHEMISTRY OF SELECTED ROCKS FROM THE SULLIVAN MINE AND ITS AREA
# SI sz s3 s4 S6 S8 SI0 SI1 S14e SI40 sio; 61.7 51.466. I 311.5 26.2 59.8 68.I 65.9 50.5 62.0 TiO, 1.15 0.20 0.55 0.63 0.80 0.72 0.65 0.58 0.72 0.44 5.22 13.0 11.3 15.0 17.8 17.8 16.5 13.0 14.6 13.8 3.68 13.4 12.7 20.4 20.2 4.67 3.25 7.30 10.3 5.75 1.00 0.32 0.02 I .ox 0.72 0.07 0.04 0.16 0.15 0.09 1.63 6.01 1.76 17.4 18.4 2.68 I .20 I .34 8.36 3.99 13.4 8.52 0.21 2.45 0.60 0.68 0.19 0.06 10.0 7.88 0.06 I .34 0.72 0.02 0.03 9.24 1.01 0.07 1.59 3.09 1.3Y 0.49 0.08 I .49 0.02 0.10 4.88 4.51 0.45 0.52 0.09 0.1 I 0.1 I 0.I I 0.08 0.09 0.13 0.08 0.07 0.M 9.5J 2.31 2.93 8.23 10.05 2.70 2.62 6.23 2.70 1.77 98.0 98.1 96.6 97.4 95.4 98.7 98.8 99.4 99.5 99.5
19 106 41 50 78 62 47 42 276 72 6 37 21 2 0 3 7 13 37 22 3 44 8 10 16 16 13 10 38 20 174 91 328 343 362 338 266 350 50 243 0.50 0 I .40 1.10 I .40 I .so 0.30 1.80 0.20 0.20 I .8 0.8 2.2 1.1 I .7 I .5 I .7 2.7 I .3 2.7 72 14 I 90 3 7 I 70 155 18 I2 100 44 10 60 0 35 820 600 I MI I15 4.40 I ,912 10.90 11.40 17.70 15.40 13.00 11.00 I.50 7.30 1.10 0.33 2.90 3.20 4.50 4.10 3.60 3.00 0.10 1.30 23.00 8.10 22.40 10.20 67.70 17.90 36.20 62.40 5.60 19.70 51 .KO 20.60 50.40 21.90 147.10 45.30 76.40 143.60 11.00 ?6.10 20.90 9.40 20.80 10.00 57.70 24.10 27.M 53.WJ 5.40 I9 70 5.15 3.22 5.00 2.80 12.80 9.00 6.30 11.90 1.84 5.47 0.82 I .08 1.12 0.99 3.85 I .3n 11.84 2.48 0.55 0.99 0.94 0.83 0.83 0.48 1.68 1.30 0.87 1.10 0.36 I .MI
3.00 2.30~~ 3.50~ ~~ 2.50 4.65 3.94 4.10 1.55 1.45 L" 0.44 0.54 0.39 11.. 44. . 1.000.62 0.60 0.74 -0.24 0.58 -Total re expressed a Fe,O,. g=gabbro, p=scdimcnl c/o1 in gabbro
2 74 Columhiu British Geological Surwy Brunch elementanalysis was obtained on fused disks by x-ray fluorescence (X-RayAssay Laboratory, Toronto). The rocks analyzed were collected during a visit to the mine in the fall of IYYO. Samples were selected from alteration types that would most likely contain dateable hydrothermal accessory minerals such as rutile and titanite (Hamilton et a/., 1982; Leitch, 1991). Detailedpetrographic study preceded anal- ysis in order to determine the mineralogy and the textural relationships between alteration assemblages. Allanite was identified by electron microprobe. A summary of mineral- ogy, textureand the sample locations is given in Table 2-5- I, whole-rock g~x~chemistryin Table 2-5-2 and micro- probe analysis of selectedallanite grains in Table 2-5-3.
REE GEOCHEMISTRY OF ALTERED la Ce S" E"-.-i_- it) "- Ib L" ROCKS Figure 2-5-1. Rare-earth elemtmt pattern of ga jbros from Various rock types were selected for analysis in order to the Moyit: !:ills. identify alteration type(s) associated with REE mobility and subsequently with the abundance of allanite. The samples included gabbro from the Moyie sills in the mine, pebble conglomerate in thc footwall of thelaminated ore, tour- malinized breccia, albitized sediment and chloritized sedi- ment from the footv?all. In addition. gabbro with a 'grano- phyric' inclusion was collected from the Lumberton sill at Moyie Lake, south rlf Cranbrook as well as Lower Aldridge siltstone from North Star Hill immediatelysouth of the deposit,and siltstone from the lowerMiddle Aldridge markerunit (Hiawtha marker). The rare-earth element composition of the ;analyzed rocks is discussed below. The two samples of Moyie sill gabbro have a flat rare- earthelement pattern typical of rocks of tholeiiticbasalt composition and it is in agreement with the tholeiitic basalt composition determined by trace and major element chem- I i istry formust Moyiesills in southem British Columbia l (Hoy, 1989; Figurc. 2-51). However, there is a distinct - La cs N(1 & EL.- Tb "b LY chemical differencebetween the gabbro fromthe mine (S-2) andthe gabbrofrom the Moyie Lake area (S-I4g, Table Figure 2-5-2. Rare-eanh element pattern of Iebble con 2-5-2); the former has higher rare-earth element concentra- glomerate (SI), chloritized footwall (Sf,) and chloritirl:rl rock in a fault (S4). tion, it is higher in scandium and lnwer in chromium, rubidium and barium, which indicates that it is either a more fractionated equivalent of the gabbro from Moyie Lake, or ~ that the two areunrc:lated. The comparable1anthanum:ytter- T t TABLE 2-5-3 MICROPROBE AVALYSES* OP MINERALS FROM THE SULLIVAN MINEt ALLANITE APATITE SO, ...... 32.16 31.19 0.0 AI,O, 17.92...... 17.53 0.0 CaO ...... 10.80 9.61 54.61 FeO ...... 14.7213.94 0.46 P,O, ...... [I.O (1.n 42.41 La,O, ...... s.09 4.58 0.0 Ce,O, ...... 12.35 11.36 0.0 Nd,O , ...... 3.54 4.32 0.0 SO, ...... 0.56 0.0 0.0 TOTAL ...... 94.7295.97 97.55
Geolofiicul Fieldw~rk1991, Puper 1992-1 2iT Plate 2-5-2a. Sedimentinclusion ('granophyre') in Plate 2-5-3. Alldnite grains in chlorite-rich albitite, the Lumbertonsill gabbro. Both fields 5.8 mm.Crossed Field: 0.8 mm. Plane polarized light. polars.
Plate 2-54, Allanite and pyrrhotite in chlofite. Plate 2-5-2b. Gabbro from the Lumbertun sill, Field: 0.8 mm. Plane polarized light.
276 British Columhiu Genlogical Survey Brunch bium ratios suggest that the rare-earth element abundances Based on relative REE concentrations, Ril hards (1989: have not beendisturbed in theserocks during extensive reported some correlation in cc ncentral ions of indivlcual epidotization, and that the difference in their concentration stratigraphic horizons in the Pritchard Formati )n (USA) md is aprimary feature. The'granophyre' pod or inclusion those in the Aldridge Formation, suggesting that the :;ul- (S-14~)0.5 by 0.5 metre in size, in theLumberton sill livanhorizon is also recogniza':~lein t1e B, It Basin. !le represents a fragment of fine-grainedsediment (Plate concludedthat the similarily between Pitchard :md 2-5-2a).Textural evidence and rare-earthelement con- Aldridge tourrnalinite rare-eanh concentratic 1 indicalerl a centrations (Table 2-i-2) suggest a sedimentary precursor to similar origin and that rare-earth I:lemen!s cou d he used for this inclusion in the gabbro (Plate 2-5-2b). The low REE stratigraphiccorrelation. Our work indicat, s signifi1;m concentration in the gabbros, coupled with the absence of rare-earth variation between tourmalinized 2nd chlorite- allanite, suggest that rare-earthmobility was insignificant altered rocks and hence we maintain that alte ration typ: i:, within the gabbrosduring their emplacement and during the main variable that influencer, rare-earth II obilizatinrl ir subsequent hydrothmnal alteration. Sullivan mine rocks. Thesediments in the mine have been overprinted by A siltstone with comparably high rare-earth :oncentralior various types of akration, including tourmaline, chlorite, (S-l 1, Figure 2-5-3) was collecl ed from the lpper par of albite, garnet and pyrite (Hamilton et a/., 1982: Leitch and altered Lower Aldridge Forma1:ion on North : tar Hill. 7"1is, Turner, 1991; Leitch t'f ul., 1991). Although the mineralogy fine-grained rock is characteri2,et:l by a high p irrhotite con. of some sedimentsmay be distinctly different, the similarity tent and biotite alteration. Allarlite grains generally 111i:ur in REE concentrations implies that the REE were 'fixed' in either in the biotite, or are intagrown with p irrhotite. the rocks prior to alteration and were not disturbed subse- quently. For exampl?, S-l (pebble conglomerate), S-3 (tour- DISCUSSION AND CommIorIS malinized breccia), S-8 (albitized sediment with only minor chlorite) and S-14p (sediment fragment in gabbro) all dis- This preliminary study is a p:cursor 10a c mprehenwve playcomparable .rawearth element trends (negative geochemical investigation of RE E conccntrat on and mobi.. europium anomaly) and concentrations (Figures 2-5-2 and lity associated with alteration and mineralizat on in various 3). hut their mineralogy is significantlydifferent (Table rock types at the Sullivan deposil: and th: sun mnding area, 2-5-1). This sugge:,ts thattourmalinitization, albitization, and an investigation concerning the role of tl e Moyie :;ill:; garnetizationand epidotjration of the rockswere not in mineralization (Hamilton et &/., 1982; Ho: , 1989). accompanied by sig:niticant mobilization of rare earths. It Thesignificance of the F'resence of allanite in l.he should be noted here that in the albitized sample, S-8, REE chlorite-alteredmineralized foxwall, and nthe altite- concentrations are not particularly high, and allanite grains chlorite alteration zone at the mine is twofold by recogciz- are sparse,whereas in samples in which albite is accom- ing a high REE gradient (accilmpanied by allanite <'on. panied by extensivechlorite alteration, the number of centration) or significant REE fluctuation, we may define a allanite grains increases five to tenfold (Plate 2-53), possible zone of mineralization. distinguishil g it from thr: The major element concentration in S4 and S6 basically 'barren' alteration zones; and pclssible dating of allmitt: by reflects the extensive chloritealteration observed in the U-Pb geochronology may definc the age of r lineralization. rocks, thus the original nature of the rock is difficult to infer The reported occurrence of allanlte in the gran lphyric mne!; (Table 2-5-1). Looking at the elements least likely to have of the Purcell (Moyie) sills (Bishop, 1974) is lot surpnsing, heen disturbed by rhloritization (Zr, Th), S4 and S6 are as rare earths are common corsituents (ofter as mnna,:tte) distinct in havingunusually high zirconium and thorium of some carbonaceous sediment:. Therefore, he meltin? or concentrations. Furthermore,the zirconium and thorium partial melting of included sediments in the g Ibbro, and the concentrations in these samples cover the range of similarly contemporaneous ('?) crystalliz.3tion of alk nile with th,: highconcentrationlr in theAldridge sediments (Table emplacement and subsequent deuteric a terati In (epidotiza- 2-5-1). Thus we infer that S4 and S6 are chloritized sedi- tion of feldspars) of the sills sug,;:ests the: scav mging of rare ments. S4 and S6 have significantlydifferent rare-earth earths fromremelted sedimm ts. The cry! tallizatiol of concentrations. However, as there is evidence for significant allanite under such specific conditions (does tot negate the rare-earth mobility in the chlorite alteration zones, localized importance of itsassociation \with ni.neral zatiort. hlor,: concentration anddepletion associated with the chlorite significant is theallanite vein reported by 3arnpbell ;mi alteration is expected. Either (1984). who recogni;!ed large (301 mpm) allanit,: The chlorite-rich sample (S-6) which was collected from grains crosscutting tourmalini;!ed Aldridge SI diments. 'This the mineralized footwall of the orebody is distinguished by is in agreement with our observations with respect to th: its elevated rare-earth concentration (Figure 2-5-2) and its hydrothermal origin of the minerals around th ! ore. Bec.lus: lack of a negative europium anomaly. The high REE values REE tend to favor precipitation under .educ ng conditions are accompanied by the presence of allanite in the chlorite (Schandl and Gorton, 1991), IN,:would expi:t a RET: gra- (Plates 2-5-4 and 5). The close textural association of chlo- dient(enrichment and/or fluctuation) arc und sulplide rite, allanite, titanit<: and pyrrhotite (Plates 2-56, 7 and 8) orehodies. Rare-earth element (enrichment i round sew:rzd and galena (Plate 2-59) in the mineralized rock suggests Archean massive sulphide depjsits hasbeen reported by that thecrystallization of these phases was more or less Campbell et al. (1984) and Schr.ndl and Gort )n (1991) and contemporaneous. Although it should he noted that while a current study funded by thc Ontario Geo ogical Survey pyrrhotite is oftenovergrown by allanite,galena is often Research GrantProgram is under way to~nvestigate the intergrown with the! allanite grains. impactof this rare-earth element halo 01 exploration
Geological Fieldwork Geological 1991. Paper 1992-1 277 .I I
e %
Plate 2-5-5. Allanite and pyrrhotite in chlorite. Plate 2-5-1. Allanite rims pyrrhotite. Field 0.8 mm. Field 0.8 mm.Plane polarized light. Plane polarized light.
Plate 2-5-6. Titanite(large centre grain) and small allanite grains(with pleochroic halos) in chlorite.Field: Plate 2-5-X. Allanite intergrown with pyrrhotite in 0.8 mm. Plane polarized light. chlorite. Field: 0.8 mm. Plane polarized light.
2 78 British Columbia Gro/o,qicu/ Survey Brunch posium, Volume 2; Univer:;ifyof Idah< and IdaFo Bureau of Mines and Gro1ofi.y.page!; 15-( 6. Campbell. F.A. and Ethier, V,G(1984): Coinpositiorl of Allanite in the Footwall of tkSullivan 0 ebody, bit- ish Columbia: Canadian i2.rineralogist. Volume :!2, pages 507-51 1. Campbell, I.H.,Lesher, C.M., 'Goad, €I, Fr Inklin, J.b[., Gorton, M.P. and Thurston, P.C. (1984) Rare Earth Element Mobility in Alteration Pipm Be ow Mass ve Sulphide Cu-Zn Sulphide Deposits; Chem CUI Gcdo$y, Volume 45, pages 18 1-202. Delaney, G. (1975): Internal Rcprt to Comir:o Ltd. Hamilton, J.M, Bishop, D.T., Morris, H.C. and Owens, O.E. (1982): Geology of the Sull van Orebod), Kimberl:y, B.C., Canada: in Precambrian Sulphil ,e Depos 3, Hutchinson, R.W., Spence, C.D.and Frinklin, J.I% Editors, Geoloxical Asso&rion ($ Can Ida. Special Paper 25, pages 598-665. Heubschman, R.P. (1973):tC:)rrelation 0' Fine Car- bonaceous Bands acrossa Prxamhrian St @ant Ba:,in: Journal of Sedimentat-y P,!trvlogy. Volu~le 43, pa.F 688-699. HOy, T.O. (1989): The Age, Che~nistryand Te :tonic Setling I- of the Middle Proterozoic h'loyie Sills, I urcell Sul!':i- Plate 2-5-9. Allanltc intergrown with galena, in chlorite. group, Southeast British Columbia; Cum dian Jo~~trlal Field: 0.3 mm. Plane polarized light. ($Earth Sciences, Volume :!6, pages 23(5-231'7. Leitch,C.H.B. (1991): Prelir2inary Fluid I~clusionand (Schandl et a/.. 1991 ). In this preliminary study, the textural Petrographic Studies of Part; of the Sulli! an Stratifom relationship between allanite, sphalerite, galena and chlorite Sediment-hosted Pb-Zn Deposit, Southe Hem Bri :ish suggests that mineralization was contemporaneous with the Columbia; in Current Research, Fart i, Geo/o,q'l.ui mobilization of rare-earth elements and with the crystalliza- Surwy ofCanada, Paper 91-lA, pages "1-101, I!.'Ol tion of allanite in thc2 localities studied. The source of rdre- Leitch, C.H.B. and Tumer, R.J.W. (I99 I):TI e Vent Cum- earth elementsmay have been the "metamorphic monazite" plex of the Sullivan Stratiiorm Sediment-hosted Zn-PI-, (Heubschman, 1973) or other rare-earth element-rich min- Deposit,British Columbir: Preliminary Petrogrqthic erals in the carhon-rich horizons of the Lower and Middle and Fluid Inclusion Studies in Current I esearch, Pan. Aldridge. Work is in progress for detailed rare-earth element E, Geological Survey of Cc'nada, Paper 91-IE, pages; studies of the Moyie sills and the altered zones in the Lower 33-44. and Middle Aldridge sediments, and the U-Pb geochronol- Leitch, C.H.B., Turner, R.J.W. and Hiiy, T (1991): I'hc ogy of hydrothermal alteration around the Sullivan orebody. District-scaleSullivan-North Star Altl ration %(,?e. Sullivan Mine Area, Britiit Columbia: . L Prelmil w) ACKNOWLEDGMENTS PetrographicStudy: in Current Rese; rch,Part E, We thank Cominco Ltd. for its permission to collect GeoloXical Survey of Cunodu, Pxper )I-lE,. page!; samples from the Sullivan mine. Special thanks 10 Dr. John 4557. Lydon of the Geological Survey of Canada for his helpful Richards, B.D. (1989): RareEarth Element Gc achemislry OF suggestions concerning this project and to Dr. Trygve Hey Proterozoic Prichard/Aldrid;;:e Formation as an Indica. for his help in collecting samples outside the mine. Funding tor for Occurrences of Stratiform Mmsivl Sulfide hlin- of the project by theDepartment of Energy. Mines and eralization; Program with ,4l-6tracts, 85th Annual Meet- Resources (Canada) and National Science and Engineering ing,Cordilleran Section, .42nd AnnuiI meetin&.of Research Council 10 M.P. Gorton is gratefully acknowl- Rocky Mountains Section; TIIP CeoloRi .a1 Socierb of edged. America. Volume 21, No. 5. page 3383. Schandl, E.S. and Gorton, M.P. (1991): Post-are Mobiliza- REFERENCES tion of Rare Earth Elementi; at Kicd Cr, ek and Other Barnes, S.J. and Gorton, M.P. (19x4): Trace Element Anal- Archean Massive Sulfide Deposits; Econ Pmic Geol jg), ysis by Neutron Activation with a Low Flux Reactor Volume 26, No.7. (SLOWPOKE 11): Results for International Reference Schandl. EX, Davis, D.W., Gcrton, M.P. a] d Wasten:ys, Rocks; GeosmndurdNewsleffer, Volume 8, No. 1, H.A. (1991): Geochrono1og.y of Hydrotl ermal Akra- pages 17-23. tionAround Volcanic-h:)sted Mass veSulphid~: Bishop, D.T. (1974.): Petrologyand Geochemistry of the Deposits in the Superior Pnlvince: Ontar io Geoscilwe Purcell Sills in Boundary County, Idaho; in Belt Sym- Grant Program, Summar!/ :)f Rese,xch.
Geological Fieldwork 1991. Paper 1992-1 ,279 NOTES