695

The CanadinnM ineralo gi st Vol. 31,pp. 695-710(1993)

PYROSMALITEIN CANADIANPRECAMBRIAN SULFIDE DEPOSITS: MINERALCHEMISTRY, PETROGENESIS AND SIGNIFICANCE

YLIANMING PAN, MICHAEL E. FLEET, ROBERT L. BARNER E-llPYUAN CIIEN Depanmentof Geology,University of WesternOntario, Lnilon, OntarioN6A 587

ABSTRACT

Pyrosmalite-seriesminerals [(Fe,Mn)sSi6Or5(OH,Cl)10]are reportedfrom metamorphosedsulfide depositsin three Canidian Precambrianmining camps: Matagami, Quebec (Archean, Zn-Cu-Ag-Au), Manitouwadge, Ontario (Archean' Cu-Zn-Ag-Au) and ThompsonNickel Belt, Manitoba (hoterozoic, Ni-Au-PGE). As a result of electron-nricroprobedata, pyrosmaliteis found to form a continuoussolid-solution series from a value of Mn/(Fe + Mn) of 0.08 to 0.85, and is n sink for bi. texturat characteristicsand elementpartitioning indicatetlat pyrosmalitecrystallized during both regional metamorphism and late-stagehyttrothermal activity. However, the initial Cl-emichment in the host lithologies may have occurred during seafloorhy&othermal alterationas an integral part of the syngeneticore-forming processes for the associatedbase-metal nin- eralization.Identification of pyrosmalitein volcanogenicmassive sulfide flfMS) depositsprovides further supaortfor a brine- pool model for ore genesisind suggeststhat the precious-metalmineralization commonly associatedwith these sulfide depositsmay havebeen related to Cl-rich fluids.

Keywords:pyrosmalite-series minerals, (Fe,I\4n) solid solution, Cl-enrichment,Canadian hecambrian suLfrdedeposits, brine- pool model,precious-metal rnineralization.

Solwtenn

Nous avonsd6couvert des membres de la s6rie de la pyrosmalite[(Fe,Mn)3Si6O15(OH,Cl)10] dans des gisementsm6tamor- phis6s de sulfures dans trois campsminiers pr6cambrienscanadiens: Matagami, Qu6bec(arch6en, Zn-Cu-Ag-Au)' Manitouwadge,Ontario (arch6en,Cu-Zn-Ag-Au), et la ceinturenickelilbre de Thompson,Manitoba (protfrozolque,Ni - Au - 6l6mentsdu groupedu platine). A la lumibre desdonn6es obtenues par microsonde6lectronique, la pyrosmaliteest une solu- tion solide continueMn(Fe + Mn) entre 0.08 et 0.851et concenre le Cl pr6sentdans ces toches. l,es texturescaractfristiques et la r6partition des 6l6mentsmonffent que la pyrosmalitea cristallis6i la fois au cours d'un m6tamorphismer6gional et pen- dant une activit6 hydrothermaletardive. Toutefois,l'enrichissement initial des lithologies h6tesen Cl aurait pu se produire au cours d'une alt€rationhydrothermale lors de la mindralisationsyng6n6tique en m6taux de base,sur les fonds ocdaniques.La prdsencede la pyrosmalitedans des gisements volcanog6niques de sulfuresmassifs 6taye l'hypothbse d'un bassinde saumures impliqu6 dansia mindralisation;la pr6senced'une accumulationdes m€taux pr6cieux couramment associ6e i ce gemede gise- ment de sulfurest6moignerait de f implication d'une phasefluide riche en chlore. (Iraduit par la R6daction)

Mots-cl6s: min6rauxdu groupede la pyrosmalite,solution solide (Fe, Mn), ernichissementen Cl, gtsementsde sulfurespr6- cambrienscanadiens, modble de bassinde saumures,min6ralisation en m6tauxpr6cieux.

INTRODUCI]ON upward- and downward-facingin six-membered Si6O15rings (Kashaev1968, Tak6ucht et al. L969, Pyrosmalite was originally establishedas a single Kato & Tak6uchi 1983),with Cl preferentiallylocated mineralspecies (Zambonini 1901, DanaL920, Frondel at OH(l) positions(Kato & Tak6uchi1983). Similar & Bauer 1953, and referencestherein), but presently sheetsilicates include "brokenhillite" (Czank 1987, refers to minerals within the solid-solution series questionablestatus in Nickel & Nichols 1991), (Mn,Fe)sSi6O15(OH,Cl)10,including the end-members friedelite (cf, Bauer & Berrnan1928, Frondel & Bauer manganpyrosmaliteand ferropyrosmalite(vaughan 1953),mcgillite @onnay et al. 1980),nelenite (Dunn 1987).In tlis paper, "pyrosmalite" will be used to & Peacor 1984) and schallerite(c/ Bauer & Berman refer to the sclid-solution series.The structure of 1928, Frondel & Bauer 1953), and are collectively pyrosmaliteconsists of brucite-typelayers of octa- referred to as minerals of the friedelite group. Peacor hedra alternatingwith sheetsof tetrahedra,both & Essene(1980) suggestedthat caryopilite has a gen- 696 THE CANADIAN MINERALOGIST

SABIA 1. OCCI'ERBNCE5 OI ISE PYROATAI]IIE SENTEE

tletoeDces Oorut@a c6tDsttion ta€t@rttbic Or.d€

t&boatrl 1901, Xoadnut, atGden Ir- 0.41-0.49 aDpbt"bollt€ fscLeg Drs 1920 (F€r ha!o6i,c, cl - 3.79-4.a8 Zrabolr.al 1tol, D!@, g€da :&r O.81 epblboUte trct€E D&. 1920 (te, Prstaro6lo) CI - 3.52-3.?0 B!u* & Bs!.nr! 1928, At6ruag Eill, :bo 0.76 gttlullts flclea Fsnda:, I Baus 1t53 tra at€rrry, UBA cl. . 3.80 (t!-tFltt, PloteFrolcl

guit6 1956, B!o!.€n Etlt, au3tral.h gtaault!. g'tttlcU Au- O.42-O.85 facl€. e !.cAndr* {PF !-Ag, Prteruol.s) cl - 3.78-3.9O 1957, rl1@ 1984

l'tt.ltbe & lGto 1958, tluaatg Dias, X&E O.53-O.82 (mtarcr!|hor€d) tlatuab€ et !1. 1961 !€bl.gi, Jat[! Cl r 5.00-5.63 (F*La, Pal@@l.cl

AatrotEa 1964 Itrhuaat eat Ogblatlm tsE 0.60 (@lqrcr!tro6ad) dstpslta, Xaeatbatu - (FFlln) cl 3.62 ga€bs Ott€dal & 1965 Doldearkito dnss, ao tnfomtto! ? Crond, OElo, loll,ay audius gtll€tors, 6l 11. 1966 s€deD no tnforutloa allrhi"bo:.tta frolea (Ag-tFtaa, [email protected]

fsacbaroLo et al. Pr!@r!E, tluEsl. Sh€ (mt@rfftosed) t9?9 (Pb--Ua-lo-Ag, 0.55-0.64 cl E CrsEac€asl 5.35 vrugbe 1986 P€guolt, Austlalir Xe- O.OS &tth$ollt€ facl€s (Pb-ZD, Ploteercj,c) cl . 4.O0-4.2s ru €t !1. 1992 nafalgz!, X*- 0.65 coatasE LLaolbg, chlla ct- @t6m4'bsd (tln-ls, hotatorclc) :.ag

cost! at al. 1983, bttlgatlt ta&e obs, grsEcbisi froleE tbia study :&! 0.33-0.85 liBtage!', Qu€b€c a ( 8a-Gr-eg-es, Arab€m) Cl 0.79-5.42 Pe i tleat 1992, Geso & tatltroy elEs, this Btudt ltaaltoMdg€, ODtulo (Chr-h-ag-etr, lrobest lr'.';.'J,i;.'i ff.:ff::T":i* tbla rtudy llbffitEo! nl'm, lb6ten, t{an!,,lo5b! o;.1,11;.1'" (rl-eu-F$, PtltaEaola) Iri P.3ffi*T#.'

&& - l{!./(t€ + u!) at@lc ratlo. eral formula of (Mn,Fe,Mg)8Si6O15(OH)tsand also is recently, we have identified pyrosmalite-seriesminer- a memberof the friedelite groirp. als in two other Canadian Precambriansulfide Although pyrosmalite was originally consideredto deposits:the Willroy Cu-Zn-Ag-Au massivesulfide be exceedinglyrare, it has since been observedwith deposit of the Manitouwadgemining camp, Ontario, increasingfrequency in metamorphosedpolymetallic and the Thompsonnickel sulfide deposit of the sulfide depositsand Fe-Mn depositsworldwide (Table ThompsonNickel Belt, Manitoba. I). However, identification of pyrosmalite-seriesmin- In this paper,we report on the texturesand chemi- erals has undoubtedlybeen obscuredby its optical cal compositionsof pyrosmalite-seriesminerals in the resemblanceto white @an & Fleet 1992).The above three CanadianPrecambrian mining camps. discovery of the pyrosmalite-seriesminerals in Resultsof electron-microprobeanalyses establish a the Geco Cu-Zn-Ag-Au massive sulfide deposit of continuoussolid-solution between ferropyrosmalite the Manitouwadgemining samp,Ontario @an& Fleet sld manganpy'osmalite.Textural characteristicsand 1992,8.U. Petersen,pers. courmun.l9g2) was made element partitioning are used to elucidate the para- only through a combinationof electron-microprobe genesisand origin of pyrosmalitein thesemeta- analysisand X-ray powder diffraction. Similarly, man- morphosedsulfide deposits;assemblages of coexisting ganFl'rosmalitein the MattagamiLake Zn{u-Ag-Au minerals and available fluid-inclusion data are ana- massivesulfide deposit,Matagami, Quebec(Costa lyzed to consfrainits conditionsof fonnation. In addi- 1980, Costa et al. 1,983)was recognizedby partial tion, we discussthe significance of pyrosmaliie, and electron-microprobeanalysis (without a determination particularly its high Cl content,in metamorphosed of Cl) and single-crystal X-ray diffraction. More rnassivesulfide depositsin the light of syngeneticmod- PYROSMALIIE IN CANADIAN STJLFIDEDEPOSITS 697

els @riesenet aL L982,Costa 1980,Costa et al. L983, and overlain by the Key Tufflte (Fig. 1; Costa 1980, I-arye 1992).Finally, the occurrenceof pyrosmalitewith Costaet al. 1983,and referencestherein). associatedCl-rich fluids is related to precious-metal Pyrosmaliteat the Mattagami Lake mine is res- mineralizationcommonly associatedwith hecamb'rian tricted to the uppermostportion of the pyrite-spha- sulfide deposits(cf Friesenet al. 1982,Costa 1980, lerite unit, just below the hanging-wall Key Tuffite Costaet aL 1983,Hanninglon & ScotrL989,1-arge et al. (Fig. l). The pyrosmalite-bearingrocks are composed 1989,&en et al. 1993,LargeL992). of pyrite, sphalerite,pyrrhotite, magnetite,chalcopy- rite, carbonates(, dolomite, ankerite and OccunnsNcEsam Pgrnocnapnv siderite),, cummingtonite-dannemorite,actino- lite-tremolite, chloriteo , pyrosmalite, Matagami,Quebec and caryopilite (Costa1980, Costa et al. 1983). Pyrosmalite locally makestp 3040Vo by volume The MattagamiLake mine exploits an Archeanvol- of the pyrite - sphaleriteore, commonly occurring canic rock-hosted Zn-Cu-Ag-Au massive sulfide as large grains or flakes (up to 0.5 X 0.3 mm) deposit located in the Matagami mining camp of with well-developedbasal cleavageoin close asso- northweslernQuebec, within the Abitibi subprovince ciation with carbonatesand disseminatedwithin of the SuperiorProvince (Costa 1980, Costa et al. the ore minerals (Fig. 2a). Mutual contactswith 1983,and referencestherein). It consistsof two ore amphiboles(1.e., cummingtonite-dannemorite zones (a pyrite - sphalerite unit and a pyrite - and -tremolite) and other silicate minerals pyrrhotite - magnetiteuoit) and is underlainby vino- are common,but no replacementtexture involving clastic rhyolite and basalt of the Watson Lake Group pyrosmalite after any other mineral phases

s450w Outlineof Main Gross-Cut A (Section39)

v cD5-9 Ps3-1::::::::::oP2-1 cos-t !iii!i!i!!'i5l'-r

cDs-13 3-1:.i'ln-::t. ''!9. .!t !:::::: I

{*' l\( i 5i$u:: :==l:,:,:,:':'.gji,i 4 I Keyruffire | fiffi ovrire-sPhaleriteore I A €:=::

==9it==::= @ pyrite-pyrrholito-magnetits

Fro. 1. Geologicaloutline of section39 of the MattagamiLake Zn{u-Ag-Au orebody,with samplelocations (after Costaet al. 1983).Only numbersfor the pyrosmalite-bearingsamples (filled circles) and thosecited in Tables2 and 3 aregiven. 698 THECANADTANMINERALOGIST

has been observed.Instead, individual grains of and Willroy mines, two of the four Archean pyrosmalite are commonly rimmed by caryopilite Cu-Zn-Ag-Au massive sulfide deposits at the @ig.2b). Manitouwadgemining camp of northwestemOntario, which is located at the northernedge of the Wawa Manitoawadge,Ontario subprovinceof the SuperiorProvince (Fiesen et al. 1982,Petersen 1986, Pan & Fleet 1992).These Pyrosmalitehas been observedin the Geco depositsare stratigraphicallyunderlain by garneti-

Ilc. 2. Hectronback-scafiered images (a and b) andphoromicrographs (c, 4 e and f) itlustraring@currences and texu:res ofpyms- malite @s):a) as a majorphase (grey) associated with ore minerals(white: including pyrite, sphalerite,pyrrhotite and magnetite) from the Mafiagamil-ake mine; note severalcrystals of pyrosmaliteshowing a hexagonaloutline (scale bm 100Um); b) partly replacedby caryopilite(Car), from tle Mattagamir akemine (scale bm 10Um; c) in associarionwith gamet(Grt), actinolite (Act), pynte (Py),and qphalerite (Sp) as characteristicradiating clusters, Aom the Gecomine (from Pan& Fleet 1992);d) in association with actinolite(Act), calcits(Cal) and quafiz (Qtz) as an aggregarereplacing (Cpx) in chdcopynte(Ccp)-richore from the Willroy mine; e) in associationwith grunerite(Gnr), quartz and pyrrhotite@o) as aggregatesreplacing ferrosilite (Fs) fromthe Thomp'sonmine,ard f) in associationwithpynhotite as cross-cutting vein from theThompson mine. PYROSMALITEIN CANADIAN SULFIDE DEPOSITS 699 ferous cordierite - orthoamphibolegneisses that are ThompsonNickel Belt, Manitoba interpreted as altered mafic to intermediatevolcanic rocks, and are overlain by quartz - - feldspar The ThompsonNickel Belt is locatedat the bound- gneisses,interpreted as metasedimentswith inter- ary befweenthe Superiorand Churchill provinces.The calatedvolcanic rocks (Friesenet al. 1982).The mas- zoneof nickel mineralizationat the Thompsonmine is sive sulfide deposits and supracrustalcountry-rocks associatedwith sequencesof metasedimentaryrocks, have undergonemultiple periods of deformation ald including metapelite (biotite schist) and related have been subjectedto a regional metamorphismof granitic pegmatite,quartzite, skarn and iron formation. upper amphibolite to granulite facies @etersen1986, Serpentinitesoccur in the pelitic member as small Pan& Fleetl1992). lenses(Peredery et al. 1982). The main Ni-sulfide Pyrosmalip in the Gecomine appearsto be restrict- mineralizationis found in metapelite,and minor disse- ed to the lowgr, smaller 412 Copper Zone (for metal minations of sulfides are presentin ultramafic lenses. zonation, see Friesen et al. L982). It occurs both as Regionalmetamorphism of the ThompsonNickel Belt extremelyliaslgained inclusions(<15 pm in maxi- includes an earlier granulite-faciesevent, followed by mum dimension) within spessartine-richgarnet an amphibolite-faciesevent of the HudsonianOrogeny porphyroblastsand as radiating clustersassociated and a late-stagehydrothermal alteration @erederyel with actinolite (Fig. 2c), epidote,chlorite, plagioclase, al. 1982). K-feldspar,biotite, calcite, sphalerite,and pyrite in Pyrosmalitewas observedat the Thompsonmine in skarn-likecalc-silicates (Pan & Fleet 1992). only one sampleof bandediron formation (BIF) that In the Willroy mins, pyrosmalite was observedin was collected within the footwall and about 3 to 15 severalsamples of chalcopyrite-richore. It is com- metersbelow the nickel sulfide orebodies;the footwall monly present in associationwith actinolite, qvulz, is characterizedby altemating layers rich in iron sili- calcite, epidote, and chlorite as aggregatesreplacing cates+ magnetiteand rich in quartz.The layersrich in clinopyroxene(Frg. 2d) and garnet. iron silicates+ magnetiteconsist of mainly garnet'

tAar.E 2. @ttPoolllola oF ltsB FrnoSltALllE sBlEs

loc.tlo! urtttgali I*s Etna uultowadga fhqleon

8.!ple PS4-1 P32-1 0?1-7 0P1-7 8383. 83631 9350 A81A lsl.s 8rq (gt. r, 34.42 3s.19 34.84 35.44 35.29 3L.t2 34.86 t4.L2 34.43 ttq 0.o3 0.00 0.o0 0.00 o.oo 0.03 0.00 o.o0 0.11 ar:o! o.13 0.02 0.08 0.06 0.06 2.43 0.40 0.24 0.24 c!:o3 o.oo 0.02 0.03 0.00 o.o0 0.oo o.o3 o.o4 0.05 ulo 2A.O4 43.66 23.2A 17.39 20.36 31.?0 12.85 ?.O4 5.76 l€O. 24.61 a.07 28-8a 36.09 34.47 21.18 40.23 46.77 46.73 s@ 1.01 1.78 0.81 1.40 o.25 0.42 o.o2 0.64 o.58 tDO o.oo 0.02 0.46 1.o3 O.OO O.O0 0.oo 0.00 ad c!0 o.o4 0.02 0.oo o.oo o.o4 o.2t o.29 0.03 o.09 t{rp o.o5 0.ol 0.oo o.00 o.oo 0.04 O.O1 0.O2 0.03 &ro o.o2 0.@ o.oo o.o1 o.oo o.o4 o.oo o.o1 0.12 ct 5.14 4.5.1 4.O0 0.79 o.92 3.70 4,19 4.87 3.17 BPr. 7.32 7.59 7.58 8.51 a.51 7.99 7.49 7.35 7.77 orcl 1.16 1.02 0.90 0.18 0.2L 0.86 0.94 1.10 0.71 Total 99.65 99.90 99.03 99.64 99.69 97.90 99.13 99.93 9A.42 cbdloal fotnulae calculatad on th€ basLs of, 14 catlons s1 5.98 6.03 6.0? 6.02 6.04 5.52 6.05 5.95 6.02 rAl 0.02 0.0{, 0.00 0.oo 0.00 o.48 o.oo 0.o5 o.o0 uer o.01 0.o0 0.ol 0.01 o.01 o.o2 0.o8 o.ot 0.06 Cr o.oo o.oo 0.o0 0.00 o.oo o.oo 0.00 0.00 0.02 F9 4.08 1.16 4.21 4.95 4.92 3.10 5.89 6.91 6.42 !69 o.2€ 0.45 0.21 0.35 o.05 0.11 0.o5 0.14 0.16 l,la 3.62 6.34 3.43 2.47 2.94 4.?L 1.91 1.O4 0.46 ,u o.oo o.oo 0.06 0.13 o.oo o.04 0.oo 0.00 Ce o.o1 0.00 0.00 o.oo 0.01 o.oo o.o5 0.00 o.ot !a 0.o1 0.oo 0.00 o.o0 o.oo o.o1 0.o0 0.oo o.ot K o.00 0.oo 0.oo o.o0 o.oo o.oo o.o0 0.oo o.o2

c1 1.51 r.32 1.14 O.23 o.27 1.10 1,.24 1.44 0.94 ot 8.49 8.68 8.82 9.77 9.73 6.90 4.76 4.56 9.06

B€ Fig. 1 fos aasttla il&b€rs aad t@aiLom of tb€ Urttagel' taL€ t4.!st aga3 a;d 9360 trE slspla6 ol tb€ G€oo and tftllroy ltn€sr-raP€sBl€lt, ta18 iE a bladd Im foa.tlo! sepla o! tbo ,ftlmtrcn ELaet a, t! radiat!.lq clustct b, rs lsl'urlo I'a garnet tprttbtrcblaot, c, ln crd- atthg wUl a, repllolDg fcaoaLllte, wt. t, f€tgbt IErent, t, totit l:oa aontmt aa i'eo, rr, gp .alelated f,r@ ol - (10 - Cf). 700 TI{E CANADIAN MINERALOGIST

M 3r. Mtttm 0t trc:@a, W@Erc m a!OIE biotite, and magnetite,with variable amountsof pyroxene, grunerite, pyrosmalite, ilmenite, and re{ l't@3 olr:qlllE bldlto pyrrhotite. Two distinct textural varietiesof pyros- 8.dltrd 9350 sl8 P32-2 6{-1 ru-t @}9 OS-13 S1O malite are present.More commonly,pyrosmalite 910, (c.4, r9.9! a7.10 31.21 37.39 !?.O9 36.?' 3a.Oa 33.29-i.ei occurs as aggregateswith grunerite, quartz and Itq 9.99 9.9s o.m o.oo o.o2 1.74 o.ii uA g.?g 0.39 o.o3 l.tl o.tt 14.?o 13,4! :,6.39 pyrrhotite (Frg. 6& g.gg g.gl o.oo 0.03 o.04 o.oo o.o2 o.oo after ferrosilite 2e). Although replace- rc -{.1! .1.9! 6.eB l0.4o 4.1: o,28 o.tr a.t F {.91 aq.{8 41.5. t?.?0 a3.rd r?.s3 rg.i: ri.3t ment along or parallel to the cleavageof ferrosilite is rlo g.!! 4.27 3.48 a.87 4.61 n,62 7a.23 3.?3 b -9.99 !4 0.r,0 d o.o7 d ad d observedlocally (Fig. 2e), most aggregatesoccur @ 23.4! 0.26 O.@ o.tl 0.02 o.il o.e o.m h 9ddddd0.GO.O2O.tg around grain boundariesand show no prefened s.1o g.?l o.ot o.ot o.0o o.00 o.oa 0.06 o.o? rp 9.99 0.0! 0.oo 0.0! 0.02 9.ao e.go a.ir crystallographicorientation to the host ferrosilite, indi- t 9.99 0.o0 o.o0 0.00 o.m 2.os 2.8 a.i€ c1 o.oo o.@ o.6t 0.i6 o.B4 o.!.3 0.06 o.i cating the absenceof any epitaxic relationship @rgt 0.s 0.00 o.t4 0.1? 0.12 o.gs L2e 0.26 betweenthese two minerals(see also Hutton 1956). T4d [email protected] [email protected] 69.99 91,22 90.50 94.?? 96.73 97.28 Secondly,pyrosmalite also is presentin association 6 ortt@ (8t r At, ! 6.r 22 6!E@ with pynhotite in cross-cuttingveins (Fig. 2f). a1 1.99 :..99 8.99 C.ao rtt t.9a 5.69 5.79 5.36 0.or 0.01 0.01 0,20 0.o2 2.3t 2.2t 2.64 MrweRALCnurnsrny ! 0.o0 0.01 0.00 0,00 o.oo 0.37 0.20 0.46 0.00 0.@ 0.oo o.@ o.oo 0.t0. o.02 0.20 6 o.@ o.@ o.oo o.o0 0.s 0.00 0.00 0.@ t€ o.€ 1.65 5.89 4.23 9.92 2.41 2.31 3.?a The chemicalcomposition of pyrosmalileand asso- !9 o.ao 0.2? o.as 2.OA 1.11 2.91 t.46 0.09 b o.14 0.07 0.08 1.36 0.56 0.0,1 O.O2 0.O3 ciated minerals from the h O.OO _- O.O3 O.O1 three Canadianhecambrian e o.m 0.o1 0.00 0.o2 0,@ o.o1 0.o1, 0.01 presented E o,@ o.00 0.o1 mining camps is in Tables 2 and 3. All tu o.02 o.@ 0.00 0.@ 0.oo o,01 0.ol 0.o2 I 0.00 0.oo 0.@ 0.@ 0.00 1.93 1.90 1.&t chemicalanalyses were madewith a JEOL IXA-8600 P o.oo o.@ 0.00 0.m o.@ 1.02 1.36 0.24 ql 0.00 o.@ o.t7 0.20 o.la o.o3 0.0: o.o8 electronmicroprobe fitted with four automatedwave- length-dispersionspectrometers, at the University of a. 36 ?dle 2 d rlg. 1r *. t, Etgh M, r, Ual l.fu @ G F€t .., dc b a Ess€@ (19a0). WesternOntario. Operatingconditions included an

leBla 3b. couFostlloNs oa N,tpstBoLES

l6catl'o! Uatttgadl' t,ate Elne Nffiltoumdge Th@trEoa

8ep1€r PA{-l 0PL-7 pS4-1 0p1-? cD3-9 cD3-9 8383 9360 t51A

lrberal D& Dan Act Act Edn par Act Aal Gn 8tq (sr. c) 54.01 53.37 54.06 51.75 44.89 39.?7 49.63 5!1.33 50.16 tl(L 0.00 0.00 0.00 0.oo 0.28 0.04 0.00 o.00 0.00 arri 0.04 0.15 1.15 1.33 10.?8 16.69 o.o4 0.06 1.12 crd O,Oo o.o2 0.oo o.o0 0.o1 0.00 0.06 o.0o 0.01 ur6- 10.54 11.14 4.33 3.1'l 1.24 1.38 7.t2 2.OL 1.50 Fao. 17.68 20.29 11.O? 20.57 16.23 19.13 2e.69 15.07 36.29 r&o 15.30 12.53 15.56 8.66 10.93 7.80 0.78 13.18 7.42 ZaO nd O.57 Bd 1.20 nd nd O.O0 o.o0 o.0o cao 0.67 O.39 11.96 11.37 10.33 10.87 LL.47 t2.44 0.O3 na.p o.ot 0.o5 o.12 0.t4 2.05 2.25 0.O5 o.o? 0.45 x"rt o.01 0. o0 o.o0 0.13 0.19 0.36 0.O7 0.01 0.10 ci o.o0 0.o0 o.00 0.02 0.69 1.50 o.OO 0.oo a.20 oscl 0.00 0.oo o.o0 0.00 0.16 0.34 0.00 o.oo 0.05 94.26 98.55 98.26 98.51 97.46 99.45 97.9I 97.2L 97.23

Cbsll.ca1 f,otmula€ calculatad oa ttrs ba6is of 23 eatlong s1 a.oo ?.81 7.83 rAl a.oz 6.?5 6.02 7.9A 7.99 7.93 o.00 0.00 0.19 0.1? 1.25 1.98 0.01 0.O1 0.07 utl o.oo 0.o3 o.o1 0.07 0.64 t.oo o.oo 0.o0 0.14 Tl, o.oo 0.oo 0.oo 0.00 0.o3 0.00 o.oo 0.00 0.oo cr o.o0 0.oo o.oo o.00 0.oo 0.oo o.oo 0.oo 0.o0 8€ 2.t9 2.55 1.34 2.60 2.O3 2.42 3.A6 1.85 4.79 xs 3.38 2.81 3.35 1.95 2.44 t.76 0.19 2.A9 l.?5 lla 1.32 L.42 0.53 0.40 0.16 0.18 0.97 0.25 0.20 Za 0.06 0.13 0.00 0.o0 0.0o ca 0.11 0.06 1.8s 1.85 1.66 L.77 1.98 L.97 0.00 llr o.oo 0.01 o.03 0.10 0.60 0.66 0.01 o.o2 0.14 a 0.00 o.o0 0.00 0.or o.o4 0.07 0.01 o.00 0.o2 cl o.o0 o.o0 0.o0 0.00 0.1? 0.38 0.00 0.00 o.os

Act, actlnoJ,ltot Da[, 4a'r!r!nnrLte, Ealn, €d6ntte, O!u, gnnelLlE, Ptr, p!r9aEl't6, a, a€ 1abl€ 2 ald ttg. It sC. t, ml.git p€lc€nt, i, total tro! cotrtent as t€O. PYROSMALITEIN CANADIAN SULFIDB DEPOSTTS 701 acceleratingvoltage of 15 kV, beamcurrent of 10 nA, beam diameterof 2-3 lr:'mo2O-second counting time, and minerals and synthetic glassesas standards. Matrix correctionswere performed using the Tracor- NorthernZAF prograrn.

Pyrosmalite tr Although pyrosmalite from the Mattagami Lake, =+ Geco, and Willroy mines is extremely heterogeneous in chemical compositionfrom sampleto sample,it is generally homogeneouswithin individual grains, and exhibits only minor grain-to-grain variations within most samplesin all three Precambrianmining camps examinedin this study. P):rosmalitein only one sam- ple (OP1-7) of the MattagamiLake mine showswide variationsin both Cl contetrtand Mn(Fe + Mn) ratio, 46 which are positively correlated(Fig. 3). A similar correlation befieen Cl and Mn/(Fe + Mn) ratio was Fe reportedfor pyrosmalitein skarn-like calc-silicates from the Gecomine (Pan& Fleet 1992). Frc. 4. Plot of Mn versasFe showinga completesolid solu- Most compositionsof pyrosmalite-seriesminerals tion in thepyrosmalite series from a Mn/@e+ Mn) value in the literature have an Mn/(Fe + Mn) atomic ratio of 0.08to 0.85.Crosses represent data from the literatue, rangrngfrom 0.41to 0.85(Table 1, Fig. 4). An Fe-rich opencircles, from theMattagami Lake mine, Quebec' end-memberwith Mr(Fe + Mn) = 0.08 was described filled circles,from theGeco and Willroy mines,Ontario' circles,from the Thompsonmine' only recently from the Pegmontdeposit, Australia andhalf-filled Manitoba.The solid line indicatesthe ideal correlation. (Vaughan 1986). The two texturally distinct varieties of pyrosmalitein the bandediron formation of the Thompsonmine @igs. 2e,f) show n6 s6mFesitional difference and have an Mn/(Fe + Mn) ratio ranging Fe-rich end-memberfrom the Pegmont deposit from 0.10 to 0.15 (Table 1), consistentwith the high (Vaughan 1986).Fyrosmalite from the Geco,Willroy whole-rockFe/Mn ratio and similar to that of the most and MattagamiLake minesvaries widely in Mn/(Fe + Mn) ratio (TablesL,2) andencompasses both fenopy- rosmalite and manganpyrosmalite.Of particular inter- est are the intermediate compositions of ferropyros- malite from the Geco and Willroy mines, indicating a continuous solid-solution seriesfrom 0.08 to 0.85 (Frg. 4). However, pure end-membercompositions of either ferropyrosmalite or manganpyrosmalitehave not yet beenfound (Iable l, Fig. 4). Chlorine is present in all pyrosmalite grains ana- s lyzed to date (Tables1, 2). Althoueh most pyrosmalite .j i compositionsestablished in the presentstudy have a Cl content within the range in the literature (3'58 to 5.63 wt.VoCl; cl Vaughan1986), chlorine-depleted o compositions(ess than 3.58 wt.VoCl) also have been obtained for some pyrosmalite grains from all three Canadianhecambrian mining campsClable 2). oo Significant amountsof Zn and Mg have been detectedin pyrosmalite from the Mattagami Lake ol- mine (Table 2; cf. Frotdel & Bauer 1953, Hutton 0.3 0.4 0.5 1956, Stillwell & McAndrew 1957).Znc is typically below detectionlimit in ferropyrosmalitefrom the Mn/(Fe + Mnl Thompson mine. Although sphalerite is abundantin all pyrosmalite-bearingsamples from both the Geco Ftc. 3. Plot of Cl versus Mnl@e + Mn) showing composi- and Willroy minss, and gahniteis presentin the skarn- tional variation of pyrosmalite in sample OPl-7 from like calc-silicatesof the Gecomine, zinc has not been the Matagami Lake mine, Quebec(see Fig. 1). detectedin pyrosmalitefrom thesetwo deposits. 702 TIIE CANADIAN MINERALOGIST

Ass ociate d silicate minerals of Cl, are presentin both varieties. However, neither phlogopitenor biotite has beenobserved in the pyros- Most silicates,oxides, carbonates and sulfidesasso- malite-bearingsamples of the MattagamiLake mine. ciated with pyrosmalite in all three mining camps According to the classificationof Leake (1978), the studied have been analyzedin some detail (Costa Fe-Mg-Mn amphibole associatedwith ferropyros- 1980, Costaet al. L983,Pan & Fleet 1992, Chen malite in the bandediron formation of the Thompson 1993).Additional compositionaldata on pyroxenes, mine is grunerite (Table 3b). The Fe-Mg-Mn amphi- caryopilite, biotite and amphibolesare presentedhere bole at the MattagamiLake mine belongsto the cum- (Tables3a b). mingtonite-dannemoriteseries (Table 3b; see also The pyroxene that is replacedby ferropyrosmalite Costa et al. 1983).It is noteworthythat both cum- in the bandedhon formation from the Thompsonmine mingtonite and dannemoritefrom the pyrosmalite- is ferrosilite, with an Fe/(Fe + Mg + Mn) ratio of bearing samplesof the Mattagami Lake mine contain about 0.83 (Table 3a). The clinopyroxenein the measurableZn contents(up to 1.8 wt.VoZnO; c/ Klein Willroy mine varies significantly within the diop- & Ito 1968). side-hedenbergiteseries and has a variable content of Calcic amphibolesassociated with pyrosmalite at the johannsenitecomponent (Table 3a). The man- the Geco and Willroy mines vary from actinolite to ganesecontent of pyrosmaliteis directly relatedto that ferroactinolite(c/ kake 1978),with variableamounts of the host clinopyroxeneat the Willroy mine @g. 5). of Mn. The highestMn content(up to 7.1 MnO wt.Vo: Caryopilite from the Mattagami Lake mine has an Table 3b) was found in grains in direct association Fd(Fe + Mn + Mg) ratio greaterthan 0.55 (table 3a), with manganoanferropyrosmalite at the Geco mine. and representsa ne\il Fe-rich member (work in Calcic amphibole in pyrosmalite-bearingsamples progress).These compositions of Fe-rich caryopilite from the MattagamiLake mine invariably belongsto alsocontain minor amountsof Zn and Cl (Table3a). the actinolite-tremolite series.and contains variable The biotite associatedwith Cl-depletedferropyros- amountsof Mn (Table 3b). Similar to their Ca-poor malite from the Geco mine is F-rich but doesnot con- counterparts,both actinolite and tremolite from the tain detectableCl @an& Fleet I992).T\e biotite from Mattagami Lake mine contain significant contentsof the ThomFsonmine containsminor arnountsof both F Zn (up to 1.2 wt.VoZnO: Table 3b; cl, Klein & Ito and Cl Qable 3a). Costaet al. (L983) recognizedtwo 1968). varieties of the -biotite series(Ti-rich and In this study,large grainsof calcic amphibole(up to Tipoor) in ttre footwall rhyolite and basalt of the 2 mm in diameter)also have beenobserved in several Mattagami Lake mine. The presentstudy shows that samplesfrom the pynte - pyrrhotite - magnetiteore significant amountsof F, but only backgroundvalues unit and the alteredfootwall rhyolite of the Mattagami Lake mine. Thesegrains of calcic amphibolecom- monly contain a Cl,Al,Na-rich core (up to 1.5 wt. Vo Cl; Table 3b) rimmed by Cl-absentactinolite. The Cl- o.5 rich core is extremelyheterogeneous with respectnot o only to Cl contentbut also to Fe/IVIgratio and contents (Table o.4 of Al and Si 3b), and rangesfrom edenite to Etr pargasite.galsls amFhibolesrich in Cl and K that are a o a not associatedwith pyrosmalitehave beenobserved o o.3 also in skarn-likecalc-silicaies from the main orebodv .s a of the Gecomine @an &F"leetl992). c a o = o.2 OO DrscussroN + o o' In addition to the occurrencesof pyrosmalitein the tlr o.1 three CanadianPrecambrian mining campsconsidered : here, the Sullivan mine, Kimberley, British Columbia E (a Proterozoic,sediment-hosted Zn-Pb-Ag sulfide 0.0 deposit)is the type locality of mcgillite, a polytype of o.0 o.1 o.2 o.3 o.4 o.5 manganpyrosmalite(Donnay et al. 1980).We have examinedsamples from many other well-known Mn/(Fe + Mn) in PYroxenes Canadiansulfide mining camps (e.9., Bathurst, New Brunswick; Kidd Creek and SturgeonLake, Ontario; Flc. 5. Mn(Fe + Mn) distribution betweenpyrosmalite and Noranda, Quebec;and Snow Lake, Manitoba) but host clinopyroxenefrom the Willroy nine (filled circles); have failed to detectpyrosmalite or any other member data for pyrosmalite and ferrosilite from tle Thompson of the friedelite group. However, glven the dfficulty mine (half-filled circles) are shownfor comparison. in identification of theseminerals by optical means PYROSMALITEIN CANADIAN SULFIDE DEPOSfIS 703 and limited numberof samplesexamined (ess than 10 1.0 each),the presentstudy is by no meansexhaustive. q, a g o.B o_o Partitioning of Fe and Mn betweenpyrosmalite and o E oo coexistingsilicate minerals o g 0.6 The most important criteria used to interpret the CL ,a paragenesisand origin of pyrosmalitein the metamor- .s phosedhecambrian sulfide depositsof this study are o.4 textural characteristics(see below). Elementpartition- tl. c ing also providesinvaluable information on coexisti.g o.2 E o minerals during the crystallization of pyrosmalite (cf o Mueller 1961,Pan & Fleet 1989).Figure 6a shows that the Mn/Fe ratios in pyrosmalite and Fe-Mg-Mn 0.0 0.0 0.2 0.4 0.6 0.8 am.Fhibolesat the MattagamiLake mine correlatepos- grving (K) itively, a distribution coefficient of l.M Mn/Fe in Fe-Mg-Mn amphiboles with a standarddeviation of 0.12; hence Mn is only slightly enrichedin pyrosmaliterelative to coexisting Fe-Mg-Mn amphiboles.$imilafly, systematicdistrib- utions of Fe and Mn betweenpyrosmalite and calcic o b amphibolesoccur at both the Mattagami Lake mine .: E 0.8 a (Frg. 6b) and the Geco and Willroy mines (Fig. 6c). tr However,the calculateddistribution coefficientsof 6 0 oo 2.6 for the MattagamiLake mine and2.4 for the Geco and Wilhoy mines are considerablyhigher than that ir 0.6 for pyrosmalite and Fe-Mg-Mn amphiboles at the .g o oo Mattagami Lake mine. Although biotite and chlorite lt from the Geco and Willroy mines are much less : o.4 emichedin Mn than the coexistingamphiboles (Pan & = Fleet 1992),the pattemsof distribution of Fe and Mn betweenpyrosmalite and eachof thesetwo former o.2 minerals are also alrnost linear (not presentedhere). 0.0 4.2 0.4 0.6 From textural evidenceand thesedata on elementpar- titioning, we tentatively concludethat pyrosmalite Mn/Fe in calcic amphiboles crystallized in chemical equilibrium with calcic amphibole,Fe-Mg-Mn amphibole,biotite, and chlo- o.8 (e.9., rite, albeit on a very local scale within aggre- o G gates of grains). The distribution of Fe and Mn .g betweenpyrosmalite and host pyroxenesalso is sys- !: v.o at E tematic (Frg. 5) and is interpretedto reflect cation pro- v, 0 portions inherited during replacementprocesses @igs. a" x,e). o o.4 .; jO

Paragenesisand ortgin of pyrosmalite l'|. c O,2 a A1l examplesof pyrosmalitein the literature, with E O the possible exception of the Norwegian occrurence (oftedal & saebo 1965),which is without eirher nn chemical or X-ray data"arc found in metamorphosed 0.0 4.2 0.3 o.4 Fe-Mn and massivesulfide deposits(Table l). The MattagamiLake, Geco and Willroy mines of the pres- Mn/Fe in calcic amphiboles ent study also have been interpretedto be volcano- genic massivesulfide (VMS) deposits(Fiesen et al. Ftc. 6. Mn/Fe distribution between pyrosmalite and: 1982,Costa 1980,Costa et al. 1983,Pan & Fleet a) Fe-Mg-Mn amphibolesof the Mattagami l*ke mine 1992, and referencestherein). There is no general (open circles) and the Thompsonmine (half-filled agreementconcerning the origin of the Thompson circles); b) calcic amphibolesof the Mattagami Lake nickel sulfide deposit,for which the "volcanogenic mine (opencircles), and c) calcic amphibolesof the Geco exhalative" model is only one ,unongmany proposed andWillroy mines (filled circles). 704 TIIE CANADIAN MINERALOGIST

geneticmodels (e.9., volcanogenicor Kambaldatype, hydrothermal replacementand massive sulfide flow; c/. Peredery et aI. L982). Howeverothe ferropyros- malite at the Thompson mine is restricted to the I . sgv{zo bandediron formation (i.e., metamorphosedchemical sediments).Despite its exclusiveoccrurence in Fe-Mn i *,*"Yffi and massivesulfide deposits,there is no evidencefor 6 the direct precipitationof pyrosmalitefrom hydrother- o mal fluids on the seafloor. Pyrosmalitehas not been o@ observedin modern sulfide deposits or Fe-Mn : depositson the 6 seafloor, and the ancient Fe-Mn and b ezo massivesulfide depositshave all beenmetamorphosed tt E (Table1). o It is peculiar therefore that talc, carbonates,Mn- F4@ bearing serpentine,Mn-bearing amFhiboles and the sulfide ore mineralsat the MattagamiLake mine were consideredbyCostaet al. (1983)to be directlyprecip- 'K'*o itated during hydrottrermal activity on the seafloor. Talc, an important ganguemineral at the Mattagami Lake mine, is indeed presentas a primary mineral in some presently active seafloor hydrothermal systems 0.006 0.010 0.015 0.020 0.02t o.o3 (seeRona 1988for a review), and the presentdescrip- tions and discussionindicate that pyrosmalite was X(COrlat P = 3000 bars most likely part of the main silicate assemblagein the Mattagami Lake mine. Howeveroa greenschist-facies Ftc. 7. IsobaricT-X(CO) diagramfor the systemK2O - regional metamorphismhas been documentedin the CaO-MgO - FeO- A12O3- SiO2 - H2O-CO2 calculat- Mattagami[,ake areaby Jolly (1978), and the silicate ed usingthe GE@{ALC softwarepackage of Brown et (1988) internally mineral assemblageswithin the MattagamiLake mine al, and consistentthermodynamic (Costa dataof Berman(1988) at a total pressureof 3 kbar for 1980, Costa et al. 1,983,see above) are not assemblagesof alteration minerals in skam-likecalc-sili- inconsistentwith it (cf Gole 1980, Miyauo & Klein caGsat the Gecomine (mineral data from Pan& Fleet 1989). More importantly, silicate minerals such as 1,992):An, anorthite;Cal, calcite;Chl, clinochlore;Kfs, talc, chlorite, am.Fhibolesand pyrosmalite in the ore K-feldspar;Phl, phlogopite;Qtz, quartz,and Tr, tremo- units and chlorite in the alteredrhyolite of the footwall lite. Forreactions (3), ( ) and(6) seetext. do exhibit a degreeofpreferred orientation.It is possi- ble, therefore,that pyrosmalitein the Mattagamit ake mine rilas a product of the greenschist-faciesregional metamorphism,and not a direct precipitate from the et al.1961, this study).Reactions involving metaso- hydrothermalfluids responsiblefor the ore deposit.A matic replacementmay be quantified by mass-balance prograde metamorphic origin has been proposedby calculationsusing mineral compositionsand data on Vaughan (1986) for the ferropyrosmalite in the specific gravity (Gresens1967). Calculatedreactions Pegmontdeposit, Ausffalia. Similarly, manganpyros- for ferropyrosmaliteafter ferrosilite at the Thompson malite occurs as mineral inclusions in gamet porphy- mine and after hedenbergiteat the Willroy mine are as roblaststo rlsrn-like calc-silicatesof the Geco mine: follows (in weight units): these most likely crystallized during regional meta- (1) 100ferrosilite + 1.9MnO+ l.9Cl + 4.7H2O= morphismor perhapseven eadier & Fleet 1992). @an 59 ferropyrosmalite+22 gn:lieite + 19.1SiO2+ Ho'ffever, most examplesof pyrosmalite in the l0.5FeO+2.3M9Q, Iiteratureare consideredto have originatedas a meta- somatic replacementof earlier anhydroussilicates or and as aggregatesin cross-cuttingveins (Hutton 1956, (2) 100hedenbergite + 2.3MnO + 9FeO+ 0.5MgO + Stillwell & McAndrew 1957,Watanabe & Kato 1958, l.8Cl + 4.3HrO = 44 ferropyrosmalite+ 49 actinolite Watanabeet al, l96L,Fan et al. 1992),pointing to a + 9SiOr+ l7CaO. late-stagehydrothermal origin (Kayupova 1964, Plimer 1984).This is the most plausible origin for the The first reaction is consistent with not only the ferropyrosmalitein the Geco, Willroy and Thompson presenceof quartz and pyrrhotite (addition of S) but mines(Figs. 7*, d, eof), also the observedvolume ratio (3 to l) of ferrop5nos- Bnoxene is by far the most commonmineral to be malite and grunerite after ferrosilite at the Thompson replacedby pyrosmalite (Hutton 1956, Stillwell & mine (Fig. 2e). Similarly, tlre secondreaction is in McAndrew 1957, Watanabe& Kato 1958, Watanabe agreementwith the presenceof quartz and calcite PYROSMALITEIN CANADIAN STJLFIDEDEPOSNS 705

(addition of CO) in aggegates of ferropyrosmalite in the three hecambrian sulfide mining c:uapsexam- and actinolite after hedenbergiteat the Willroy mine. ined in this study may be estimatedfrom a thermody- It is noteworthy that the metasomaticreplacement of ngmic analysisof the assemblagesof coexisting min- manganpyrosmaliteafter at the Kyurazawa erals. For example,the stability of the'assemblage mine, Japan(Watanabe et al. 196l) also includes the actinolite + chlorite + phlogopite + plagioclase+ K- crystallization of a manganiferousamphibole, quartz feldspar+ epidote associatedwith ferropyrosmalitein and manganoancalcite, similar to the casein the sec- skam-likecalc-silicates of the Gecomine @an& Fleet ond reactionabove. 1992)is constainedby the following modelreactions:

Conditionsof formation of pyrosmalite (3) 2 clinozoisite+ CO, = 3 anorrhite+ calcite + HrO, (4)3 tremolite + 35 phlogopite+ 114 anorthite+ Although thermodynamicdata are not availablefor 88H2O= accurateevaluation of the stability of pyrosmalite,the 24 clinochlore+ 35 K-feldspar+ 60 clinozoisite, extensiveranges of chemical substitutionsof Fe2+for (5) 3 tremolite + 35 phlogopite + 24 anorthite + Mn2+, and of Cl- for OH-, indicate that pyrosmalite 58HrO+ 30CO2= may have a large field of stability in terms of P and T. 30 calcite + 24 clinocblore+ 35 K-feldspar, Consequently,the critical parametersfor its formation and probably are not temperatureor pressurebut compo- (6) 16 clinozoisite + 3 tremolite + 35 phlogopite+ sition. A rather special bulk-rock composition is 50H2O+ 38CO2= requiredfor fonnation of pyrosmalite,and this appears 38 calcite + 24 clinochlore+ 35 K-feldspar. to be supportedby the exclusiveoccuilence of pyros- malite in Fe-Mn deposits and Fe-Mn-rich rocks In the systemK2O - CaO - MgO - FeO - AJzO:- within massivesulfide deposits(Table 1). SiO2- H2O - CO2,the abovefour model reactions The preceding discussionhas demonsffatedthat a define an invariant point It at a temperatureof 440 + close approach to chemical equilibrium between 10'C andX(CO) of 0.005+ 0.001at a total pressrue pyrosmalite and associatedminerals appearsto have [P.,4 = P(H2o) + P(Co2)] of 3 kbar (Ftg. 7). been achievedwithin individual aggregatesof grains. The temperatureof formation of pyrosmaliteat the Thus, the conditions of crystallization of pyrosmalite Mattagami Lake mine can be estimatedfrom the cal-

o o ro o.2 x

0.o o.oo o.o1 o.o2 o.03 0.04 0.o5 o.06

X"o.-

Ftc. 8. Calcite-dolomite geothermometerof Powell et al. (1984) for coexisting calcite and dolomite of the MattagamiLake mine (datafrom Costa 1980,Costa et al. 1983): Xue,ca= Mg/(Ca + Mg + Fe + Mn) in calcite; X"upos= Fe./(Ca+ Mg + Fe + Mn) in dolomite. 706 TIIE CANADIAN MINERALOGIST

cite-dolomitegeothermometer (cl, Powell et al. 7984, deposit, Sudbury, Ontario (Springer 1989, Li & Anovitz & Essene1987). The high Mn contentsof Naldrett 1993).The timing of the crystallizationof both calcite and dolomite at the MattagamiLake mine pyrosmalite during regional metamorphismand late (Costaet aI. 1983)may havea significant effect on the hydrothermatalteration @imer 1984, Vaughan 1986, applicability of this geothermometer(Powell et al. and above)indicates two possiblesoluces for Cl: a 1984). However, tle compositionsof coexisting cal- pre-existingCl-rich fluid within the Fe-Mn and mas- cite + dolomite pairs in various rocls, including the sive sulfide deposits,and a metasomaticCl-rich fluid pyrosmalite-bearingsamples, of the Mattagami Lake introduced from an extemal source. The exclusive mine yielded temperaturesof less than 400'C (Fig. 8), occunencesof py'osmalite in Fe-Mn and massivesul- which are in fair agreementwith the uncorrected fide deposits seem to favor the former source filling iemperatures(240o-320"C) of fluid inclusions (Vaughan1986, Pan & Fleet 1992). Seyfried et al. in grainsof quartzand sphaleriteof this deposit(Costa (1986) demonstratedexperimentally tlat a chloride et al. 1983, L984). enrichmentoccurs in seafloorhydrothermal altpration The chemical compositionsof pyrosmalite also at elevatedtemperatures (> 400'C). Moreover,high- imply a high activity of Cl but low fugacityof oxygen temperature,highly saline fluids have been docu- in the ambientfluids. Indeed,salt-bearing, hypenaline mentedin presentlyactive seafloorhydrothermal sys- fluid inclusions (up to 38 wt. VoNaCl equivalent) tems @elaneyet al. 1987).Therefore, the initial Cl have been observed in quartz grains from the enrichmentinthepresenthecambriansulfidedeposits MattagamiLake mine (Costaet al. 1984).The average may have occurredduring seafloorhydrothermal alter- 0.2 wt.VoCl content in biotite from the bandediron ation as an integral part of the syngeneticore-forming formationof the Thompsonmine (Table3a) indicates processesfor the associated mineralization (see that the coexistingferropyrosmalite crystallized from a below). Similarly, the oscurrenceof Cl+ich scapolite fluid with log(/crfon) of about -3.56 at 450'C in metamorphosedevaporites and argilliteshas been (cf Munoz 1984).A low fugacity of oxygenfor the attributed to primary concentrationin sedimentary formation of pyrosmalite during regionnl metamor- salts(It4ora & Valley 1989and references therein). phism is readily provided by the reducedsulfide and The Cl-rich calcic amphibolein the skarn-likecalc- oxide assemblages(e.9., the pyrite + pynhotite + mag- silicatesof the Gecomine is almootcertainly a product netite assemblageat the Mattagami Lake mine). of hydrothermalactivify during the waning stageof Similarly, pre-existing metamorphic assemblages tbe regionalmetamorphism (Pan & Fleet 1992) and would also effectively buffer the redox environment therefore does not provide any unique constraint on for the formation of pyrosmaliteby late hydrothermal the timing or sourceof the Cl-enrichment.In contrast, activity in the metamorphosedFe-Mn and massive the C1,Al,Na-richcalcic amphibole at the Mattagami sulfide deposits.For example,reduced conditions for Lake mine could not have been produced by low- crystallizationofthepyrosmalite-bearingcalc-silicates grade regional metamorphism (c/. Jolly 1978, of the Geco and Wiilroy mines are indicated by the Robinsonet al. 1982)and may be relict and igneousin compositions of garnet (extremely high origin. Therefore,the occuirenceof such Cl,Al,Na- almandine/andraditeratio), and have beenconstrained rich calcic amphibolemay indicate that the host vol- quantitativelyfromthemineralassemblageofgarnet+ canic rocks of the massive sulfide deposit at the clinopyroxene+ quartz + magnetiteto be at aboutt I Mattagami Lake mine were unusually enrichedin Cl. log unit from the fayalite - magnetite- quartz (FIVIQ) Costa et al. (L984) have attributed tle highly saline buffer at 650'C (Pan & Fleet L992, cf. Zhang & ore-forrningsolutions of the Mattagamilske mins fq Saxena1991). Similarly, the chemicalcompositions of either a contribution by magmaticfluid or seawater- coexisting magnetiteand ilmenite in the bandediron basalt interactions(see also Seyfried et al.1986),IIis formation at the Thompsonmine indicate that the oxi- noteworthy that the Ti-rich biotite from the footwall dation state prevailing there also was close to the rhyolite at the MattagamiLake mine also has been FMQ buffer (Chen 1993; c1f.Andersen & Lindsley interpreted to be a relict igneous phase (Costa ?/ 1988). al. L983), but it only contains a minor amount of Cl (Table3a). Sourceof chlorine Significanceof pyrosmaliteassociated with ore The high Cl contentsof py'osmalite (Tables l, 2) deposits and other members of the friedelite group, such as mcgillite @onnayet al. L980)and caryopilite (above), Costaand coworkers(Costa 1980, Costaet al. are of particularinterest. Pyrosmalite appears to be the 1983)proposed a brine-pool model for the genesisof sink for Cl in the three Precambrianmining camps the MattagamiLake mine 7n-Cu-Ag-Au massivesul- examined in this study. Nore added in proof: fide deposiqbased on whole-rock geochemistry,oxy- Ferropyrosmalite(5.6G6.54 Vo Cl) has recently been gen isotopes,and mineral chemistry.Subsequently, reported in the Deep Copper Zone of the Strathcona Costa et al. (1984) recognizedsalt-bearing, hyper- PYROSMALITEIN CANADIAN SULFIDE DEPOSNS 787 saline fluid inclusions in quartz grains from this lower-temperaturefluids (15G-300'C), with moderate deposit.A brine-pool model has beenproposed for the 6 alkalins pH, high concentrationof H2S,low salinity genesisof sheet-stylevolcanogenic massive sulfide andmoderateflO), Tbe dosumentationof pyrosmalite (VMS) dep300'C) with low pH (<4.5), low concentra- tion of H2S,high salinity and moderateto highflOt, Ar,lovrz,L.M. & Essnw,EJ. (1987):Phase equilibria in the whereasgold transportas Au(HS); is favored in systemCaCO3-MgCO3-FeCO3. ./. Perrol. ?3, 389414. 708 THE CANADIAN MINERALOGIST

BAUER,L.H. & Bmuar, H. (1928):Friedelite, schallerite and schalleritefrom Franklin, New Jersey.Mineral. Mag 48, relatedminerals. Am- Mheral. 13.341-348. 27t-275.

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