n27 CanadianMineralogist Vol. 30,pp. 1127-1142 (1992) HYDROTHERMALAND METAMORPHICBERTHIERINE FROM THE KIDD CREEK VOLCANOGENICMASSTVE SULFIDE DEPOSIT. TIMMINS, ONTARIO JOHNF.SLACK U.S.Geological Survey, Nationnl Center, Mail Stop954, Reston, Virginia 22092, U.S.A. WEI-TEH JIANG ANDDONALD R. PEACOR Depamnent of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, U.S.A. PATRICKM. OKITA* U.S.Geological Survey, National Center,Mail Stop954, Reston,Virginia 22092,U.S.A. ABSTRACT Berthierine,a 7 A pe-Al memberof the serpentinegroup, occursin the footwall stringerzone of the ArcheanKidd Creek massivesulfide deposit, Ontario, associated with quartz,muscovite, chlorite, pyrite, sphalerite,chalcopyrite, and local tourmaline' cassiterite,and halloysite. Berthierine has been identified by the lack of 14A basalreflections on X-ray powderdiffractionpattems, by its composition (electron-microprobedata), and by transmissionelectron microscopy (TEM). Peoogaphic and scanning eiectronmicroscopic (SEM) studiesreveal different types of berthierineocculrences, including interlayerswithin and rims on deformedchlorite, intergrowthswith muscoviteand halloysite,and discretecoarse grains. TEM imagesshow thick packetsof berthierineand chlorite that are parallel or relatedby low-angle boundaries,and layer terminationsof chlorite by berthierine; mixedJayer chlorite-berthierinealso is observed,intergrown with Fe-rich chlorite and berthierine.End-member (Mg-free) berthierineis presentin small domainsin two samples.The Kidd Creekberthierine is chemicallysimilar to berthierinefrom other localities, and to Fe-rich chlorite from a variety of geologicalsettings. This is the first reportedoccurence of berthierinefrom volcanogenicmassive sulfide deposits.Textural relations suggestthat most of the Kidd Creekberthierine formed as a primary hydrothermalmineral at relatively high temperatures(*350"C) in the footwall stringerzone, probably by the replacementof a pie-existingaluminous phase such as muscovite or chlorite.However, the intergrowth textures observed by SEM andTEM suggest thatsome oftheberthierine originatedby syn- orpost-metamorphic replacement ofchlorite. The difficulty ofidentifying berthierine by routinepetrographic, X-ray, andelecfon-microprobe methods suggests that muchofthe Fe-richchlorite described from modem and ancientmassive sulfide depositsmay insteadbe berthierine. Keywords:berthierine, chlorite, volcanogenicsulfide deposit,fiansmission electron microscopy, electron-microprobe data X-raY powderdiffraction, Kidd Creekmine, Timmins, Ontario. SonaN.lans On trouve la berthierine,membre Fe-Al I 7 A du groupede la serpentine,dans la zone de minerai en veinulesde la paroi infdrieuredu glte archdende sulfuresmassifs de Kidd Creek,en Ontario,en associationavec quartz, muscovite, chlorite, pyrite, sphal6rite,et chalcopyrite,avec prdsence locale de tourmaline,cassitdrite et halloysite.On reconnaitla berthierinepar I'absence d^'uneraie ayant une valeur d de-14 A surle clich6de diffractionX, par sacomposition (donn6es i la microsonde6lectronique), et par 6tudei au microscopedlectronique par transmission.Des 6tudespdrographiques et au microscope6lectronique i balayage montrentque la berthierinese pr6sente sous plus d'un aspect:elle forme une interstratificationavec et une gaine sur la chlorite d6form6e,une intercroissance avec muscovite et halloysite,et desgrains individuels relativement grossiers. Les imagesobtenues par transmissionmontrent d'6pais amas de berthierineet de chlorite parallblesou I faible angle d'incidence,et des feuillets de chloriteayantuneterminaison deberthierine. Desassemblages mixtes dechlorite-berthierine sont aussiprdsents, enintercroissance avec chlorite fenifbre et berthierine.Le p6le ferrifdre de la berthierine (sansMg) est signald en petits domainesdans deux 6chantillons.Du point de vue composition,la berthierinede Kidd Creekressemble a celle d'autresendroits, et d la chlorite riche en Fe de plusieurimilieux g€ologiques.Nous signalons ici pour la premibrefois la pr6sencede berthierinedans un gisementde sulfuresmassifs volcanog6niques. D'ap€s lesrelations texturales, la plupartde la berthierinei Kidd Creeks'est form6e comme minfral primaireI unetempdrature relativement 6lev6e (*350"C) dansla zonetr veinulesde la paroi inf6rieure,pmbablement par remplacementd'un pr&urseur alumineuxtel la muscoviteou la chlorite. Toutefois,les texturesd'intercroissances observ6es par microscopie6lectronique d balayageet par transmissionfont penserqu'une partie de la berthierinea uneorigine par remplacement syn- ou post-m6tamolphiquede la chlorite.la difficult6 quenous avons 6prouv6e d identifier la berthierinepar mdthodescourantes dL Ftrograptrie, de diffraction X et d'analysei la microsonde6lectronique nous incite i penserque la plupart desexemples de chlorite riche en fer citds dansla litldraturesur les gites de sulfuresmassifs modemes ou ancientsseraient plut6t de la berthierine. (Traduit par la R6daction) Mots-clds:berthierine, chlorite, gite volcanog6niquede sulfuresmassifs, microscopie 6lectronique par transmission,donn6es d la microsonde6lectronique, diffraction X, m6thodedes poudres, mine de Kidd Creek,Timmins, Ontario. *hesent address:BHP-Utah htemational Inc.,200 Fairbrook Drive, Hemdon, Virginia 22070, U.S.A. 1128 TI{E CANADIAN MINERALOGIST II.ITRODUC"noN Chlorite is one of the most abundantminerals in the alterationzones of volcanogenicmassive sulfide depos- its (e.9.,Franklin et al. l98l); it typicallyoccurs in veins with quartz,sulfides" and other minerals, and as replace- mentsof sedimentaryand volcanichost-rocks. In an- cient metamorphoseddeposits, chlorite may be the most commonlayer silicate,together with variableamounts of phengitic muscovite 1 paragonite;talc, stilp- nomelane,and biotite generallyare rare. In the pristine, unmetamorphosedalteration zones of the Miocene KC-813 Kurokodeposits ofJapan, layer-silicate assemblages are complexand include chlorite, illite, smectite,local talc, celadonite,and vermiculite,and rare chrysotile (Iijima 1974,Shirozu 1974, Utada et al. 1974,Shlrozu et al. 1975). The alterationpipes of Cretaceousmassive sulfide depositson Cyprus, also unmetamorphosed, containillite, chlorite,smectite, and rectorite (Lydon & Galley 1986,Richards et aL.1989).In this paper,we describethe occurrence of berthierine.an Fe-Al semen- tine-type mineral, and berthierine--chloritemixtures from the metamorphosedKidd Creekmassive sulfide deposit,ofArchean age, and discuss the implications of thesemixtures for interpretingthe paragenesisof Fe-Al layer silicatesin modern and ancient volcanogenic sulfideenvironments. KC-3231 IDEN'TFICATONAND OCCURRENCE 24 '20(CuKal Geologicalsetting Fro. l. X-ray powder-diffractionpattems (CuKcr radiation) for The large Kidd CreekCu-Zn-Pb-Ag deposit,north mineral separatesof layer silicates from the footwall of Timmins,Ontario, consists of massivepyrite" chalco- stringer zone (north orebody) of the Kidd Creek mine. pyrite,sphalerite, pynhotite, and galena locally under- Pattemsfor samplesKC-813, KC-2505, and KC-3421 -14 lain by a chalcopyrite-richstringer zone(Walker et al. lackthe diagnostic A (63'2e) and4.7 A (ts.s"zo) 1975,Coad 1985).The ores are hostedby Archean peaksof truechlorite (chl) andconsist mainly (or wholly) volcanicrocks dated by U-Pb zirconmethods at2711 of berthierine(ber) mixed wilh muscovite(mus) 1 quartz (qtz); Ma (Nunes& Pyke 1981,Banie & Davis 1990)and are small peaksat 7.V7.5"20 axeinstrumental artifacts. pattem^for sample KC-3231 (bottom) that believed to have formed Compare on or near the sea floor containsonly 14A chlorite.All patternswere acquired on synchronouslywith localvolcanism and sedimentation. air-driedand untreated samples. Multiple events related to postore deformation are evidencedby mine-scalefaults and shearzones, strain fabrics in hand specimenand thin section,and U-Pb geochronologicaldata (Walker et al. 1975,Bisbinet al. fied (by JFS) on the basis of optical featuresand results 1990,Banie & Davis 1990).Regional metamorphism, of electron-microprobe analyses. Identification of the which only reachedlower greenschistgrade, took place Fe-rich chlorite is in error, however, as shown by X-ray at approximately2685 Ma (Percival& Krogh 1983)and powder-diffraction Q(RD) patterns of mineral separates was followed by a local metasomaticevent in the mine of layer silicates from Several samples^(Fig. 1). The areaat about2576Ma(Maas et al. 1986). Fe-rich silicate lacks the diagnostic 14 A reflection of chlorite, and therefore is berthierine" an Fe-Al member X-ray powder dffiaction of the serpentine group (a.9., Brindley 1982, Bailey 1988). The Fe-rich chlorite ("daphnite") described by Slack& Coad(1989) recently described the textures Slack & Coad ( I 989, Table 2, Fig. 12) consists largely and chemistry of Mg- and Fe-rich chlorite from the or wholly of berthierine, including that in samples footwall stringerzone at Kidd Creekand suggestedthat KC-8 I 3, KC-2505, KC-3421 , and KC-3482. An XRD thesetwo compositionaltypes of chloriteformed during study of layer silicate separates from the other Kidd separatehydrothermal events. The chlorite was identi- Creek samples(e.g.,KC-3231, Fig. l) showsprominent BERTHIERINEFROM TI{E KIDD CREEK DEPOSIT tt29 mn-Drlmgld DAIA mR Bmlmlm TM 1. X-W grain-sizesare 10-50!rm, althoughsome large crystals ' thatappear prismatic in crosssection (normal to {001}) h](l h&l AlEsb@ otr1l rc-au Kc-342r (@no) (h*) al-ca1c d-calc d-oalc d-calc in samplesKC-3421 and KC-3482 are as much as 100-200 pm long. Bertlierine grains