1263
Thc Canad,ian M ine ralo g h t Vol. 33, pp. 1263-1284 (1995)
CHROMIANMUSCOVITE, UVAROVITE, AND ZINCIANGHROMITE: PRODUCTSOF REGIONALMETASOMATISM IN NORTHWESTNELSON, NEW ZEALAND
ALVA CHALLIS
Institute of Geolngical and Nuclear Sciences Ltd., P.O. Box 30 368, Lower Hutt, New kaland
RODNEY GRAPES ResearchSclwol of Eanh Sciences,Victoria Universityof Wellingtou P.O. Box 600, Wellingto4 New kaland
KEN PALMER Analytical Facility, Vicnrin Universityof Wellingtotr.P.O. Box 600, Wellingtou New Tzalnnd
ABsrRAsr
Cbromian muscovite ('"fuchsite') with up to 8.5VoCrp3, uvarovite garnet (up to 83%oUv), zincian chromite (up to 13.7Vo7nO), and chromianrutile (up to 3.3VoCrrO3), are variously associatedwith chlorite, biotite, epidote, kyanite, and tourmaline,all Cr-bearing"in Lower Paleozoicquartzite, biotite schist,marble, and carbonatedultramafic rocks in Northwest Nelson,New Z,ealand.Sulfides and carbonatesassociated with the Cr-silicatesand oxides include pyrite, galena,gersdorffite, pentlandite,and calcite, siderite,cerussite, magnesite, dolomite, and ankerite.Chromium mineralization ofthe host rocks takes f1e fe16 ef thin seams,and broadzones tens of meterswide that parallel host-rockschistosity and exhibit varying intensitiesof greencoloration. All the Cr-rich localities occur within 3-4 hn of Early Cretaceousgranitic plutons and are close to, or lie within, major fault zones.Field relationships,mineral textures,rock associations,and compositionsindicate that the mineral paragenesisis metasomaticin origin, and the result of hy&othermal fluids from the granitic plutonsinteracting with ultramafic rocks or detrital chromitederived from ttrem.
Keywords: chromian muscovite,uvarovite, zincian chromite, chromianrutile, Cr-silicates,analyses, metasomatism, Nelson, New Zealand.
SoMNa^rrns
Nous documentonsune associationde muscovite cbromifbre Cifuchsite) contenantjusqu't 8.5Vode Cr2O3,d'uvarovite (usqu'd 837odu p6le Uv), de chromite zincifbre (usqu'i 13.77odeZn0), et de rutile cbromifbre(usqu'd 3.37ode Crpr) aver chlorite, biotite, 6pidote,kyanite et tourmaline chromifbresdans les grbs, schistesh biotite, cipolins, et rochesulhamafiques carbonat6esdu secteurnord-ouest de Nelson, en Nouvelle-Zdlande.Parmi les sulfureset carbonatesassoci6s aux silicateset oxydes chromifdres se trouvent pyrite, galbnq geadorfftte, pentlandite, calcite, siddrile, cerussite,magndsite, dolonite et ankdrite.l,a mindralisationen chromedes roches h6tes se pr6sentesous forme de mincescouches, et de zonesfloues 6tal6es sur des dizainesde mdtres,parallbles I la schistosit6de I'encaissant,et montrantune intensit6variable dbne colorationverig. Tous les exemplesd'emichissement en Cr sont situdsau plus i 3-4 km d'un contact avec un pluton granitique d'tge cr€tac9 pr6coce,et danschaque cas, prbs d'unezone de failles ou bien dansune telle zone. Selonles relations de terrain, les critdres tsxturaux, I'associationdes rocheset les donn6eschimiques, la paragenbsedes min6raux chromiferesaurait une origine par m6tasomatose,et r6sulterait de I'interaction d'une phase fluide issue des plutons granitiques avec le cortbge de roches ultramafiques,ou bien la chromited6tritique d6riv6e de celles-ci. (Iraduit par la R6daction)
Mots-cl6s:muscovite cbromif0re, uvarovite, cbromite zincifdre, rutile cbromifOre,silicates de chrome,composition chimique, m6tasomatose,Nelson, Nouvelle-Z6lande, tzil TI{E CANADIAN MINERALOGIST
za z'l 'ri o a& Ll lt /L ]LJ4 ' E _,/ Nelson\ F pr&\ * ---, J .,.'-- sg o FarewellSpit t/t ad -4:-_JJ, c r'/ / ,-'lcnri*cnurcrr(
7 _ GoldenBay >J-/7/-:._-_ L - -so------;)7- :-- | {*-"/ ----{zf------n-,-_\J_-_-_--9. ',|1)Collingwood **", ^n fil OnelcalraR.
OnahauGranite ,i*.--\\\ N\\\ +i#xl 'i,::iiji il li'li l:All
LEGEND
ffiil Tertiary- Recent E Crelaceous Silurian EastemSedimentary Belt I lN I CentralSedimentary Belt I lmr-l CambrianI WestemSedimentary Belt rI f-----t CretaceousSeparation Point granitoids .\N m Suite Cambrianultramalic bodies 10 15 20 km .A CHROMIAN MUSCOVIIE, NORTIIWESTNEI.SON, N.Z. L265
INTRoDUciloN sedimentsof denital grains of a distinctive chromite with>63Vo Cr2O3that occursin this complex Qlunter Chromianmuscovite (previously termed'trchsite" 1975,Pound 1993). Small lensesof serpentinizedand wherethe Crconient exceedslwt%o Ct2O) is relatively metasomatizedultramafic rockso some possibly rare, alttrough there are eight previously reported representingfault slivers from the main Cobb mass, occurences in New Zealand (Hutton 1942, Cooper occurtlroughout the Cenral SedimentaryBelt (Fig. 1), 1976, Railton & Watters 1990). It was first reported and talcoseultramafic inclusionsoccur in the Onahau from Lower Paleozoicrocks in Northwest Nelson by Granite (Grindley I 971). Bell et al. (1907), in quartzite boulders at Parapara Inlet @ig. l), and in mica-rich layers in quartzite D eformatioa metamotphism,and mineralization (probably the source of the boulders) about 1.5 km soutl of the inlet. Chromian muscovite also was Rocks in all three belts have been subjectedto recordedin the Arthur Marble at CopperstainCreek, severalepisodes of deformationand recrystallization, 8 km south of the inlet (Wodzicki 1972), and in with intense faulting, folding, and nappe formation, quartz-biotiteschist in the OnekakaSchist at Campbell particularly in the Cennal Belt (Grindley 1980,Cooper Creek, 13 km south of the idet (crindley 1971). 1989). The Late Silurian - Early Devonian Tuhua Chromian garnet (uvarovite) has been reported Orogeny was the main pre-Cretaceoustectonic event, previously from only three localities in New Zealatd, resulting in the developmentof a low-grade regional all associated witl ultramafic rocks of the Dun metamorphicfabric with lineations generally parallel Mountain Ophiolite belt @ailton & Watters 1990). to the axesofrecumbent folds. In the Early Cretaceous, Thereare no publisheddata on the chromianmuscovite the Rangitata Orogeny in Northwest Nelson was and associated Cr-Zn-rich minerals in Northwest markedby intrusion of the SeparationPoint Batholith Nelson.In this paper,we describesix new occturences and its satellite plutons, which produced widespread of chromian muscovite, variously associatedwith amphibolite-grademetamorphism in the nortlem part chromian gamet, zincian cbromite, and Cr-bearing of the region, The Cretaceousmetamorphism over- varieties of chlorite, margarite, biotite, kyanite, prints earlier fabrics, resulting in a regional NNE- epidote,tourmaline and rutile, and discusstheir origin trending schistosity(Grindley 1980).The presenceof in terms of regional Cr-Zn metasomatismassociated kyanite, almandine,staurolite and margaritein pelitic with widespreadintrusion of Early Cretaceousgranitic horizonswithin the OnekakaSchist indicates that T-P rocks. conditions of 500-550'C and 6-8 kbar were reached. These minerals are associated with chromian GNnnAL Gsorocy muscovite, which defines tle regional Early Cretaceous S, fabric of the schist and has been Early Cambrian to Early Devonian rocks in crenulatedby a less intense52 fabric. In the southem Northwest Nelson form three main north-south- half of the area remote from plutons of Cretaceous striking belts,terrned the Westem,Central, and Eastem granitic rocks, ttre rocks show only low-grade SedimentaryBelts, which are separatedby ttrrustfaults metamorphism(Grinctley 1980). (Frg. 1). The Westem SedimentaryBelt consists of Molybdenumand Cu-Pb--Znmineralization charac- quartz-richsandstone, mudstone, and graptolitic black terizes the Separation Point Suite (Tulloch & shale. The Central SedimentaryBelt is characterized Brathwaite 1986). Grindley & Wodzicki (1960) by volcanic rocks, volcanogenic sediments,and proposedthat basemetal and Au-Ag mineralizationat carbonate rocks. The Eastem Sedimentary Belt is the junction of the Central and Eastern Sedimentary composed of carbonate and quartz-rich sediments. Befts was concentratedalong low-angle tbrusts and Volcanic rocks of the CentralSedimentary Belt contain was producedby metasomaticfluids active at the front a small layered mafic-ultramaJic body, the Cobb of a deep-seatednappe. However, Brathwaite & IgneousComplex (Grindley 1980),probably emplaced Pirajno (1993)considered that someof this mineraliza- in the Lower or Middle Cambrianand rapidly uplifted tion is associatedwith stratiform sulfide deposi*. and unroofedby the Upper Cambrian,as indicatedby Copper - lead - zinc mineralization in the area of the presence in Upper Cambrian - Ordovician CoppentainCreek in the EastemBelt @ig. 1, locality 4)
Flc. 1. Sketchmap showingmain strlctural features,distribution ofrock types,and localities mentionedin the text I Plumbago Creek, 2 ParaparaInlet, 3 OnekakaRiver, 4 CopperstainCreek, 5 Campbell and Contact 6eeks, 6 Anatoki River - Go-AheadCreek 7 CalphumiaCreelq 8 Cobb Ulhamafic Complex. 1266 THE CANADIAN MINERALOGIST is atfibuted to emplacementof granitic plutons of the TSLE 1. RTSULT' OF XRF ANALYSESOF O-BEARING SCIIISTAND QUARTZTE NORTSWESTN&JONI, NBWZALAND SeparationPoint Suite (V[odzicki 1972), arid in other Plnbago Pal!@ Oaehl.a C()tM ADsld parts of the EasternBelt, Ordovician quartziteca:ries Crcc& Inir sft@ c@L Idw a Pb--Zn-Ag-Au-As mineralizationwhich Bates(1989) *%l 3456789 siq 8624 ug 8664 19:78 6393 44.6 9,6 n.93 78J5 consideredto be hydrothermal in origin. Grindley nO2 0.ll 021 038 0,67 0.76 080 0J4 0m 18 Al2o3 1.81 '.:r3 5.88 13.38 23J6 35.46 3r-e l3S7 1L86 (1980) statedthat the post-Rangitataorogenic phase of F6aCl3x130 325 3 0.u o3t 1.42 5.23 0J1 03r MrO 0J4 o3 0.06 nd 0.0r O02 0.04 o(D 0.01 decliningtemperatures and pressures was accompanied MsO 0.12 0.16 0.43 0.31 061 1.75 556 038 0.g) CsO S-17 0.o3 0.02 0.02 0J9 0.65 0.67 o.(ts by sporadic mineralization of the SeparationPoint N&2O 0.06 0.0E og2 0.55 0.89 0a2 0J4 0.81 0.17 K2O '0.01 0.16 1.60 39 6.4, 9J6 754 354 3:76 contactroclis and alongshear zones. All occurrencesof P2q 0.06 0.09 om 0,@ o0l 0.@ ooa o.92. 0.ll chromian muscovite and associatedCr-rich minerals LOI 221 0.63 0.65 1.81 338 43t 5.90 t:11 199 describedin this paper occur in rocks that lie within T@l 1mr5 99,03 l&71 99n 98.62 98.69 99.35 9952 thermal aureolesof the widespreadearly Cretaceous pp@ granitic plutons,in or nearmajor fault zones,and close &v45M446617 ffi 8 Ba Y 110 1?8 n3 59 1165 1135 191 w to lensesof ultramafic rocks. C€610145542 4 172 * 3029 2m,r2 xn 116 3E4E 8096 8030 gn Co129234454 10 4 C8641018322931 10 17 Age relations k6883334 4 2.fi Nb44614t444, 4 19 M59100422'4 659 Pb 26 2r2 t2 2X X 31 16 15 D Datesobtained from K-Ar (Wodzicki 1972),Rb-Sr Rb a. 5 64 tU 9 254 2,M 142 fa Sc4.38nmn55 11 8 (Aronson 1968) and Ar-Ar (Iakagami & Watanabe, sr !3 5 5 r41 238 188 m $1 104 Th4464,244 13 pers.comm., 1993) give whole-rockages of 51fabric- uE323244 4 v 8 84 72 157 24 162 215 lll forming biotite, muscovite, and hornblende in the 't2928624237E v zA l2S 217 lt3 9 53 (' 104 IE 8 OnekakaSchist ranging from 87 to 106 Ma. A K-Ar 7 217 age for cbromian muscovite from a mica-rich seam a Al Fes F€2O3 at ParaparaInlet yielded an age of 98.7 x, 2.2 Ma LoI tu 16 @ lgnido at lmoPc s (R. Grapes, unpubl. data). The oldest ages of the !d ndd€Ged Ueeortcp@r qu8ldB, Plon$sgo Cl€k OnekakaSchigt overlap the youngestzircon agesfrom Uvrrytts-rlch Lry6 tn I, Plunbgo G6L Me ru$dlE qtreiE, nmbqgo (}€ek the SeparationPoint Suite of rocks, between 105 to Schi@ cht@id |''lls@iE-p@qo6tdE, PEap@ Inf* &omie musieilrh b@d ttrEIatEEd Etlh 4, Pelpara IDIot 116 Ma (Kimborough et al. 1.993),and imply that Chomie ml,siPrbh $hi* Od.Lek! S|l!@ Clmi@ @svttedrh shisr, Oudcle SEae amphibolite-grademetamorphism, mineralizatiori, and ChFmie mrwiE qffiiE, C@@ Gek deformationare related to emplacementa16 seqling of Schi@ ch@i@ ni|s@iF ql@ibi Anabti Riw - Go Ahed Geek the Early Cretaceousgranitic plutons.
Mtr{ERALAssslvmt-acEs TABLE 2. MTNERAIJ FRBSENT IN (}-RI(:i ROCKS ANDBULK CoIIPOsmoNs FROM NORTIIII'BST T{EIJON. NEW AALAND t234567891011 Resultsof whole-rock analysesof Cr-rich schistose txxxxxxxxxx PlAlodrc :x quartzites from'Plumbago Creek, ParaparaInlet, K-feldspr xxt MllwitB xxxxxxxx ContactCreek, and Anatoki River - Go-AheadCreek, Chooirie and schist from the Onekaka River, are given in Mib xxxx xxx xx Mrguile x x Table 1. Mineral assemblagesin rocks from all KyeiE x C]ilsirc xx:r x xx localities are given in Table 2. Btodb x x x Epido@ x Uvmle x: PlumbagoCreek T T0lMlim xx ApatiF xxxrxxx At Plumbago Creek, near Q6llingwood (Fig. zrqrr xxxxxxx 1, Rutils xxxxxxxxx x locality l), chromianmuscovite, uvaroviteo and zincian ZMia- cl|@iE xxxxtx chromite occrir in Ordovician biotite schist and Suftbs Py Py Py cs Gs quartzite,mapiped as Bay Schist,faulted againstArthur Pv- Pn Grbom&s an an sid el Mg! Marble to the east @ishop 1971).The outcrop of the Dot marble immediately upstream consists of a fault Abbpiatiw An-caldoi CaFcerus$q DolEdolomitsi Gg =gsrsdcfiEi breccia containing highly deformed and elongate Mgs = Daglssiq PD- pendeditq fy = pyir; Ga - gnlma: Sid - sidsite fragmentsof quartz- muscovite- chlorite - epidote- I Uwvi6-rtc.h quddle, Plmbago Cl6k - a Uwne.par qurdte, Plrml*go Crcek magnetite chpmite schist, quartz - biotite - Ch@iu ffi switg q@?ir, nmbago Clek cbromian - - magnetite- Schistoec.lmDie{tlwiteqlsllziE, Paap@ ]!l€t muscovite chlorite chromite 5 Cr@iu awiF{"Etz wiu ia rchistme qweiE, Irmpm IDIet schist and angular fragmeils of quartzite containing 6 Omim rrmie ei:hist OrekakaRiE 7 ftmim rmir-beriry biotiterchisr, C-'npboll Geek varying {uaountsof K-feldspar, chromian muscovite, 8 Ckonim |Wie-bnniE{bmib-bllmlim wi|l, Csnpbell CrEek muscovite, chromian chlorite, uvarovite, magletite, 9 Cbonim mwiequareiF, ConractGE* 10 Chmim mwite-ricn parh in Anhr Martle" CoppwtBh Cre* rutile, and chromite. The fault breccia is followed to ll Cbmi@ MiE-beqing E€tes@8tiad ulftndc Calphmia G€€k CIIROMIAN MUSCOVrIE. NORTTIWESTNETSON. N.Z. t267
Ftc. 2. Aggregatesofchromian muscoviteenclosing conoded Ftc. 3. Aggregateof uvarovitecrystals fringed by chromian zincian chromite in quartzite, Plumbago Creek. Plane chlorite.lower half of fleld. Smallrosettes of uvarovite light. Width of photo 0.6 mm. surroundingcore of zincian chromite, top centre. Quartzite,Plumbago Creek. Plane light. Width of photo 1.5mm. the west by bands of chromian-muscovite-richand uvaroviteis confinedto aggregatessulreunding scarce chromian-muscovite-poorquartzite, and biotite - grainsof chromite. chromian muscovite schist. The quartzite is schistose Compositionsof chromianmuscovite and uvarovite and foliated, with thin 5-mm bands of micaceous quartzites are comparedwith that of uvarovite-poor quartzite containing tp to LlVo vivid green chromian quartziteinTable1 (anal.l-3). Thereisamuchhigher muscoviteparallel to the foliation. The muscovite is Ca content in the gamet-bearingrocks, and higher slightly pleochroic, wittr s bright aquamarineand Al in the chromian muscovite quartzite. In terrns of y yellowish aquamarine. Many of the chromian trace elements. there is notable enrichment in Cr muscoviteaggregates, in both the fault brecciaand the (at2.6VoCr2O3, Cr is a major elementin the uvarovite quartzite, contain small (<50 pm), highly corroded quartzite).The concentrationof Zn is high in all tbree grains of zincian cbromite (Frg. 2). Calcite is locally rocks, and thereis a positive correlationwith the level abundant interstitially, and as veinlets cutting the of Cr. Lead is enrichedin both the uvarovite-richand quartzite. uvarovite-poor quartzite owing to the presence of Fine-grained quartzite float with thin (20 mm), cerussite.The high loss on ignition (2.27VoLOI) in the bright green, subparallellayers rich in uvarovite and uvarovite-poor quartzite reflects the presenceof zincian chromite occur in the lower reaches of carbonates. Plumbago Creek, where it cuts through Late Pleistocenegravels. Except for quartzite fragmentsin Parapara Inlet the fault breccia described previously, uvarovite- bearing qumtzite was not found in outcrop, and the In a quarryon the southeastemside ofParapara Inlet stream pebbles have probably been derived from (Fig. 1, locality 2), apale green,chromian-muscovite- the gravels,with the original sourceno longerexposed. bearing quartzite member of the Onekaka Schist In the garnet-richbands, finely crystalline aggregates (Bishop 1971), approximately60 m wide, contains a of bright emeraldgreen uriarovite fonn up b SAVoof conspicuous,bright green layer of mica-rich schist the rock. Many of the aggregatesform a coronaafound 0.5 m in width. The layer is exposedfor about 6 m deep reddish brown, almost opaquegrains of ztncian along strike within cream to pale-brown-colored, chromite,and are rimmed by pale brown, rather turgid amphibolite-gradgquartzite. In detail, the mica-rich and distinctly birefringentgarnet, and rarely, chromian layer is mbdeup of alternatingdarker and lighter green chlorite (Frg. 3). Fine-grained,interstitial microcline laminae0.2.4.5 mm thick. The darkerlaminae contain forms up to 5Vo of. the rock, and tiny needles of more cbromianmuscovite, and in the darkestlamin6s, chromian rutile are widespread.In some uvarovite- quartz is virtually absent.The mineral assemblagein poor bands,unsutured quartz grains are sunoundedby the chromian muscovite schist is essentially quartz, a thin fi16 of brown clay, calcite is plentifirl, and chromian muscovite and rutile, with accessory cerussite is a minor constituent as small, scattered chromite, magnetite, zircon and apatite. Chromian crystals associatedwith colorless grossular.In these musdoviteoccurs as single grainsin mica-richlaminae, bands,grossular is the main gamet, and the coexisting with a strongdimensional orientation parallel to the 51 1268 TI{E CANADIAN MINERAI'GIST
Ba, Cr, Ga and Rb betweenthe mica-poor and mica- rich parts of the rock. Pale brownish pink streals tbroughoutthe schistosequxtzite are rich in rutile, as indicated by high TiO2. Analysis of the chromian- muscovite-rich seam shows that it is essentially monomineralicClable 1, anat.6). High bulk Ce and V result from the presenceof theseelements in pseudo- brookite, as qualitatively determined by electron- microprobeanalysis.
OnekalcaRiver
Where the OnekakaRiver passesthrough Arthur Marble Gig. 1, locality 3), and for some distance upstreamfrom the marble, chromianmuscovite schist is commonas float. The sourceof the pebblesis most probably the Bay Schist exposed upstream of the 'ti"l' .s marble. The schist float is essentiallyquartz-free and 3j9 s. .*, consists of the assemblagecbromian muscovite - chlorite - margarite- chromite - rutile - zircon, with *, considerablevariation in the proportions of mica and chlorite. Brownish chromian chlorite has largely *s replacedporphyroblasts of biotile, is intergrown wift,
,::" ,:..,.1
{qr
n*E '{Xl
{!S w
FIG. 4. A. Bact-scatleredelectron image showing Cr-muscovite.richlaminae (denning ,S1) in quarEose schist,Parapara Inlet. Bright grainsare rutile, chromite, magnetite,zircon, and apatite.Bar scale:100 pm. B. Back-scattreredelectron image of areamarked in A showingdistribution and relative grain size and habit of rutile (R0, with ligbtergrey tones richer in Cr, Zn-Mn chromite(Cr), chromian magnetite (Mt), zircon(Zt), nd apalite(Ap). Bar scale: 100 gm.
schistosity(Frg. 4A) and as ooknotso'(100-200 pm in diameter)or, singlg grains within a mosaic of quartz. Tiny (fypically <10 pm) grainsof zinciau cbromiteand chromianrutile arescattered throughout the muscovite- rich lamellae@ig. B). The mica is typically deformed by a 52 crenulation cleavage.Lenses and knots of quartz that occur within the schistosequartzite locally contain segregationsof bright emerald-greenchromian muscovite and tourmaline. Also present is a ca. Fro. 5. Large porphyroblastof chromianchlorite surrounded partly chromian muscovite (darker 3-cm-thick seamof chromianmuscovite within more and intergrown with grey tone) that hasa heterogeneousdisuibution ofCr. The psammitic schist.Blrlk silica contentsof the mica-rich surrounding arca consists of an interlocking mass of and quartz-rich layers (fable 1, anal. 4, 5) indicate chromianmuscovite. Bright crystalsare rutile and zincian proportionsof muscovit€!o quartzof 68:32 alrd38:62, cbromite. Chlorite-cbromian muscovite schist Onekaka respectively.This is paralleledby differencesin Al, K River. Bar scale:100 pm. cItRoMIAN MUSCOVTTE,NORTI{WEST NEISON, N.Z. 1269 and surroundedby, finer-grainedchromian muscovite, CampbellCreek andis setin a mafrix of interlocking chlorite, chromian muscovite,and minor margarite(Fig. 5). Tiny grainsof Chromian-muscovite-richsegtegations up to several zinsian chromite and chromian rutile are scattered om wide occur within biotite schistin CampbellCreek throughoul Although the mineral assemblageis the (Fig. 1, locality 5). The schist is also replacedby fine- samein the two rocks, sample6 containsconsiderably g&ined chromian muscovite associatedwith coarse- and the bulk composition g&ined zoned epidote, biotite, ctrldrite, rutile, and more chromian muscovite, o'fronf' closelyresembles that of muscovite.Higher Fe andMg pynte. A boundaryof the replacement may be in sample7 reflects the higher content of chlorite in partly delineatedby siderite,rutile, andbiotite (Ftg. 6). this rock. High bulk Cr (Table 1, anal. 6, 7) is due to In areaswhere replacementis intense,newly formed the abundanceofchromian muscovite,chlorite, rutile, plagioclase(labradorite) has grown within a chromian and chromite. The chromite contains 2-3Vo ZnO, muscovite mafrix. Other Cr-rich minerals are asso- resultingin a bulk-rock contentof 40 and 104 ppmZn. ciatedwith quartzsegregations that are aligoedparallel High barium contentsof around 1100 ppm are due to to S, and consist of chromian muscovite- kyanite - the abundance of chromian muscovite containing chromite- tourmaline- quartz. Quartz and deepblue A.06-L.4VoBaO. Both the ParaparaInlet and Onekaka kyanite with up to I.4VoCr2O3 (crystals up to 20 mm in River rocls contain considerablymore Ba, Sr and Rb length) are intergrown with chromian muscovite and than rocls from Plumbago Creek; rocks from abundant,euhedral, deep red (in thin section)chromite Plumbago Creek are higher in Pb and 7n (Table L, ranging from 10 to 200 pm in diameter,rutile, and anal.1-3). pyrite. Sfiongly zonedtourmaline ranging from 10 to 300 pm in diameterforms clustersof crystals. CopperstainCreek Contact Creek In the upper reachesof CopperstainCreek, close to the Golden Bay Fault (Fig. 1, locality 4), the Arthur Close to CampbellCreek, in ContactCreek, a few Marble contains pale green films of chromian meters from the Onahau (Separation Point Suite) muscovite along some of the schistosifyplanes. The Granite contact, a layer of chromian muscovite muscovite is associatedwith biotite, chlorite, rutile, quartzite approximately 0.5 m in width associated tourmaline,fluorapatite, and pyrite. along the margins with massive,rusty-colored quartz'
Frc. 6. Replacement'tont" delineatedby siderite, rutile, and biotite in schist from CampbellCreek Planelight. Width of photo 1.5 mm- 1270 TIIE CANADIAN MINERALOGIST
is parallelto the,S,schistosity developed in the biotite ag$egatesof oligoclase.The plagioclasepoikilitically schist host-rock. The quartzite consists of slightly enclosestiny, randomly orientedcrystals of chromian sinuousnmillimeter-thick, closely spacedmica-rich and muscovite. Also present are disseminatedgrains of mica-poor laminae,with the muscoviteflakes parallel rutile and gersdorffite,and pyrite forms thin stringers to the schistosity.On surfacesnormal to the .11 along the 51 schistosity.High levels of As (460 ppm) schistosity, the rock is characterizedby white spots and Ni (659 ppm) (Iable l, anal. 8) are due to the (up to I mm in diameter)and segregationsconsisting of presenceof gendorffite.
_IA!I.E 3. COMPOSITIONOF CHROMIAN MUSCOVnB NORIIIWEST NETSON.NEWAAI_AND
wt,Vo 10 ll t2 13 I4 l5
siq n,90 45,52 46,20 46.46 46.75 47.U 47.25 45.36 45.99 46.61 46.8 47.49 49.t9 u.w 45.88 Tnz 0.66 0.56 0J5 A.47 0.36 0.69 0.51 0.16 0.80 0.62 0.69 0.58 0.31 4.42 0.69 AI2q 34.43 28.67 34.03 35.71 33.53 33.& 34.07 36.9t 33.38 34.65 3t.4 30.68 30.41 35.15 n.6 CtzOs 2J8 8.47 3.61 l.l3 4J4 1.38 t.99 0.06 r.gt t.77 0.r2 1.03 5.19 t.u r.99 FeO* 0.5E 0.63 0.23 0.41 o.32 o.a2 0.46 0J5 0.93 1.04 0.92 l.16 0.86 0.16 0,86 I\,InO nd nd nd nd ud 0.09 nd nd 0.08 0,04 nd 0.10 nd nd 0.04 Mgo 1.94 1J6 0.55 0.48 0.48 0.8? 0.8? 0.8? t.20 0.94 2.62 2.56 2.15 0.40 1.38 Nio nd nd nd nd nd nd nd ad nd O.24 ad nd 0.16 nd 0,16 ZrA nd nd nd nd ad nd nd nd nd 0.14 nd nd O.25 0.13 0.17 CaO 0.06 0.05 nd nd nd nd nd nd nd 0.06 0.16 0.10 0.10 nd 0.14 Na2O 0.41 0.18 0.95 0.99 0.99 0.35 0,41 0.5? O.ulo 0.56 0.31 o.23 0.05 2.t3 0.35 Kzo 11.33 11.40 9.76 9.42 9.62 10.55 10.32 10.26 9.9 10.63 11.51 1t.22 9.39 8.14 t0.2r BO 0.31 0.26 0.28 0.30 0.32 A.M nd O,22 1.50 0.87 nd nd nd nd O,n F 0.69 0.51 0.31 0.29 0.26 0.98 0.35 nd nd 0.ll O.32 0.26 ad 0.62 0.24 nd nd nd nd nd nd nd 0.04 0.04 nd 0.08 0.04 Tosl 97.09 97.n 96.6t 95.6 n37 96.26 96.23 9523 95.46 97JO 94.9 95.35 98.24 95.64 95.48 O=F, Cl o29 0.21 0.13 0.12 0.ll 0.41 0.15 Q.05 0.14 a.D o.28 0.ll
Total 96.80 9736 96.54 95.54 n.26 95.84 95.08 95.23 95.46 n.6s 94.8 9s.239E24 95.36 95.?7
Ionron basis of22(O)
si 6.341 6.t02 6.W5 6254 6.138 6205 6221 6.V28 6.77s 6.13! 62s8 6s6s 6.392 5.962 6Jn IVAI 1.6s9 1.898 t.905 r:745 1.862 t:r95 r:179 r.yt2 1.825 1.867 nm 7.637 1.608 2.038 LE53 X(t€t) 8.000 8.0@ 8.0@ 8.000 8.m E.000 8.000 8.000 8.000 8.000 8.000 8.000 8.000 E.000 E.000 VIAI 3.090 2.623 3.388 3.646 33n 3.4fit 3SO9 3.822 3.458 3.501 32E9 32t9 3.050 3.485 3.368 Cfi o29l 0.898 0.376 o.llE 0.492 o.tM 0207 0.006 0,t77 0.122 0,013 0.109 0.533 0.:161 O27l Fez+ 0.064 0.071 0.025 0.045 0.035 0.002 0.051 0.0s3 0.104 o.ll4 0.104 0.130 0.093 0.018 0.096 lln - 0.010 0.@5 0.020 - 0.005 [,tc 0.383 0.352 0.108 0.094 0.094 0.171 0.77t 0.172 0.240 0.1s4 0525 0.512 0.416 0.0?9 0n6 Ni 0.025 0.017 - 0.017 7^ 0.014 0.014 0.013 0.017 Ti4| 0.066 0.058 o.m4 0.047 0.036 0.068 0.051 0,040 0.081 0.061 0.0?0 0.058 0.030 0.042 0.070 :(oct) 3.894 4.W2 3.971 3.950 3.984 3.862 3.989 4.083 4.60 4.021 4.W 4.t28 4.183 3.968 4.060 Ca 0.009 0.007 - 0.00E 0.023 0.014 0.014 - 0.020 Na 0.105 0.047 0.243 0253 0252 0.090 0.015 0.147 0.104 0.143 0.081 0.060 0.013 0.548 0.091 K 1.914 r950 1.643 1.584 1.611 t:t75 tJ34 t:144 1.643 lJ82 t.976 t.920 1557 t.377 t345 Ba 0.016 0,014 0.014 0.015 0.016 0.023 - 0.028 0.014 >(XID 2.U4 2.0tE 1.900 1.652 1.879 1.888 1.E39 1.898 1.826 LnE 2.080 t.994 1.584 t.925 1.8?0 F 0289 0216 0.129 0.121 0.10E 0./t09 0.146 - - 0.046 0.136 0.110 - 0260 0.102 cl 0.009 0.009 - 0.018 0.009 Xinterldyer) 0289 0.216 9.t29 O.tlt 0.108 0.409 0,146 0.M6 0.145 0.119 - ang 0.111
I Honngeneousgra.in, chromian muscovite quareite, plumbago Cree& 2 Cr-rich prt of a g6a.fu,ckomian nruscoviequaraite, plumbago Creek Main part 1,4'5 of gmin, Cr-por larelhe md Ch-richlanellaer chromian muscoviterbh laya in quartr shist,Paqara Inlef 6 Hornogmeousgrain, quatz*hmmian mwovite vein in quartr schis! Prapon r"bt 7 Ilomogureoosgai4 chromianmuscovite quartzitq Contact Cr€ek 8,9 Cr-poorand Cr-rich partsof grain,cbrunian nusovite-rioh shig pebble,One&aka River 10 Hmogmous grain, chromianrnuscordte-rich replaoennntpct of tdotiteschisq Carpbell &ee& 11,12 Cr-poorandCt-rich palr of gra,in,Arthur Mrble, Coppwtain Creek 13 Hmnogeneousgra.in intqstitial ro cdtonatet rneasomarizedultamafroroc! calphurniacbe* L4 Cr-richpart of gra.iqobromian muscovir-kyaoite*homite-qurtz veia CampbellCreek 15 Chmmianmueovit€,rchirtose chomian musco'itoquraie, Anato&iRiver- Go-Aheadcree.k CHROMIAN MUSCOWIE. NORTHWESTNEI.SON, N.Z. I27l
Anatoki River - Go-AheadCreek substitution(up to L6Voof the octahedralsite occupied by Fe and Mg). Muscovite with greater amounts of Approximately 3 lan south of ContactCreek, three FeO + MgO coexistswith chlorite t biotite. There is pale green, weakly banded chromian-muscovite- limited substitutionof Na for K (0.4-1'.0VoNazO) in bearing layers of quartzoseschist occur close to the most cases,but muscovitein the chromianmuscovite - GoldenBay Fault (Fig. 1, locality 6). The layersrange kyanite - chromite - tourmaline- quarrtzsegregations in width from about 80 m to 100 m and strike parallel in CampbellCreek contztns2.1-2.7 Vo Na2O, indicating to 51,dipping 70oSW.As at ParaparaInlet, veins,pods, a paragonitecontent of between2S-34Vo.Ba is usually and knots of quartzare commonthroughout the schist, present,in amountsrtp to 1.5VoBaO. Muscovitein the and in hand specimen, the chromian-muscovite- Arthur Marble, in the calcite-bearingquartzites from bearing rocks contain nests of brigbt green mica, PlumbagoCreek, and in the CalphurniaCreek sample together with deep red rutile, along fractures and in contains small amounts of Ca (0.05-0.L6Vo CaO) drusy cavities. Notable are the high bulk contentsof consistentwith the bulk composition of these rocks. TiO2,P2O5, Ce, La, andPb (table 1, anal.9), reflecting Small amounts of Zn (up to 033Vo ZnO) and Ni the relative abundanceof rutile and apatite together (up to 0.307oNiO) occur in the chromian muscovite with minor monaziteand galena. from CampbellCreek, CalphurniaCreek, and in more Cr-rich mica from Anatoki River - Go-AheadCreek. Calphumi.aCreek Fluorine, tp to L.3Vo,is presentin all grains of muscovite except those from Onekaka River and A small lens of shearedand metasomatizedultra- CalphurniaCreek. mafic rock in the headwatersof the Anatoki River In muscovite,chromium substitutes for octahedrally (Fig. l, locality 7) is a quartz- magnesite- ankerite- coordinatedAl (up to 22Voofthe octahedralsites), as muscovite rock. The original igneous texture is indicatedby the negativecorrelation between Cr and preservedin partsof the rock, with magnesitereplacing uAl in Figure 7. Exceptfor muscovitein the quartzose olivine, and ankerite and quartz possibly replacing schistfrom ParaparaInlet, this relationshipimplies that pyroxene.Fine-scale layering of alternatingquel.tz-rj'ch increasingCr = uAl substitutionis accompaniedby and carbonate-rich bands may represent original increasingincorporation of Fe, Mg, Ti (and Mn, Ni, mineralogicallayering, commonin the Cobb Tgneous Zn), in the octahedralsites as a phengitesubstitution; Complex (Hunter L977). Tlnn cbromian-muscovite- u(Rt) + usi * vIAl + rvAL and possibleexchanges rich stringers,less than I mm wide, areroughly parallel involving Ti, suchas (Mg,Fe)2++ Tie + 2uAl,Tie + to the quartz-carbonatelayering and are associated IvAl +-IvAl + Nsi or Ti4 + 2ryAl = (Mg,Fe)2+ with widely disseminatedsmall (<50 pm) euhedral + 2NSi. A plot of rvAl + (uAl + Cr + Ti) versus crystals of bismuthian gersdorffite and cobaltian vI112+a NSi in the inset diagramin Figure 7 showsa violarite mantled by an unusually Ni-rich pentlandite good fit to the overall schemeof coupledsubstitution, which, apart from diffrrse patchesof iron hydroxides, taking into account the uncertainty ef thg Ti sub- are the only opaquemineralS in the rock. stitution(s) and the unknown amount of Fe3+present, and shows the extent of muscovite-+eladonitesolid MINSRAL CHHvtrsrRY solution.
Chrominnrnuscovite Uvaroviteand grossulnr
Representativecompositions of Cr-bearing mus- Uvarovite is the rarest of the six commontypes of covite are given in Table 3. In the presentstudy, the anhydrousgarnet.Deer et al. (|982)tecommendedthat highest level of Cr2O3recorded is 8.5Vo,in muscovite the name only be used for gamet compositions in from quartzitein PlumbagoCreek. Variable Cr content which uvarovite is the dominant component, and is found in all muscovitesamples examined, and is the nearly all analyzed garnet grains associatedwith result of bofh intragrain and intergrain inhomogeneity zrncian cbromite from quartzite in Plumbago Creek in any one sample. Most muscovite grains exhibit meet this requirement, with compositions of some zoning, with Cr-rich areasforming irregularly Uv36-sGrs3-r1A&ro-zo.An unusualfeature of the more distributedparcheso rim, core,or more regular lamella- Cr-rich uvarovite at Plumbago Creek (Table 4, like intergrowths of Cr-rich and Cr-poor muscovite. anal. 24) is that the andradite componentis more Maximum compositional variability generally lies importantthan the grossularcomponent. Only in some within a 347o nnge in Cr2O3,but in most grains it rims of zoned grains (Table 4, anal. 5), and in is less than l%o Cr203. TiO2 contents are between birefringen! moreFe-rich garnetmantling somegarnet 0.15 and 7.7Vo,and in the presenceof rutile probably aggregates(Table 4, anal. 1) does the proportion of represent saturation levels at this grade of meta- grossularexceed that of andradite.The garnetin about morphism.FeO + MgO contents(with MgO > FeO) do 80Vo of. rosettes is usually very homogeneousin not exceed 2.6V0, tndrcaing only limited phengite composition (Uv7aAdr16Grs).4 patchy, diffuse 1272 THE CANADIAN MINERALOGIST
4.0
:ro i: Bx_ N+ e r:''[ trD .tr + +! 'l.j'p t - o r,+,'T la D % D a o a tr ,* 'r* o uhr o {a o 3.0 oo' o o o
oo o o o Farapara Inlel o f Parapara Inlot segregations o^qF o PlumbagoCroek o ^ OnekakaRivsr . CampbellCreek-blolite schlst o Mhur Mafblo a GalphumiaCreek * ConlactCreek
x QuartzCrmuscorfte kyanft+chromltesogregalion, Campbdl Creek tr Analoki River-Go-AheadCreek
cf*
Ftc. 7. Compositionof cbromian muscovitein terms of Cfi - uA13+substitution. The inset diagram shows the combined g-oupledsubstitutiory involving tetrahedral and octahedral sites in terms of u(Mg,fe,Mn"Ni + ilSie yersa.r u(A13*,CF*,Tij rvAl3+. 7.^)2+ + Al and Cr concentrationsexpressed in atomsper formula unil
zoning was detectedin a few of the roset0esthat havea which representsthe lowestuvarovite content recorded core of zincian chromite (Frg. 8) and in these, the in gametof the PlumbagoCreek suite. The pronounced garnet nearest the core has the highest uvarovite birefringence (visual estimate) of the rim garnet contentrecorded (Uvs3), whereas the rim is depletedin supports the findings of Mariko & Nagai (1980), Cr, significantly enrichedin Al, and slightly enriched who reported maximum birefringencein the grossu- in Fe, Ti, Mn, and Ca (Table 4, anal. 4, 5). A few lar-andradite series at AdrajGrs66.Disregarding the homogeneousrosettes are mantled by pale, brownish uvarovitecomponent, the PlumbagoCreek gamet has a green, distinctly birefingent garnet and chromian composition of Adra6Grsra.The presence of a chlorite; this garnet is enriched in Fe and A[ and significant uvarovite componentdoes not appear to depleted in Cr, with a composition UvruAdr26Grsrr, affect the birefringence. CHROMIAN MUSCOWIE, NORTHWESTNET,SON, N.Z. 1273
TABLE 4. REPRESENIATTVBCOMPOSITTONS OF contact of the Cu-Ni-Co sulfide deposit of WAROVTIE GARNET,PLUMBAGO CREBK NORIIIWEST NEISON.NEW EAI.AND Outokumpu,Finland (von Knorring et al. 1986).Here, the host rocks are mica schist with bandsof quartzite, wt.Vo 1) 34 and the mineral assemblageis very similar to that Si(}2 36,56 36.18 35.88 35.01 35.08 found in the Plumbago Creek quarteitesand schists. Ti.o2 0.23 0.16 o,m 0.14 0.37 chromite to l4vo ZnO) forms the core of Al2O3 7.74 2.33 2.45 1.50 6.16 Zincian fry GzQ 1t.22 22.56 23.W 24.67 16.81 aggregatesof uvarovite, and chromian muscovite is F%o3 8.71 4.84 3.21 4.37 6.06 developedin parts of the Outokumpuskarn. FeOt 2.4 0.43 1.08 0.93 0.00 MnO 0.48 032 0.36 0J3 0.82 Mgo 0.03 0.00 0.00 0.09 0.1I Zincian chromite CaO 32.25 33.06 32.47 31.91 33.36 Totol 9.49 99.88 99.55 W35 99.37 Representativecompositions of zincian chromite E FeO calcolard asuming sdchiomstry from PlumbagoCreek, Parapara Inlet, ParaparaRiver, Creek are glven in Ioar on basis of24(O) Onekaka River, and Campbell Table 5, together with the composition of chromite st 5.957 5.990 5.959 5.884 5.771 Complex. Chromite with Zn IVAI 0.M3 0.010 0.041 0.116 o.229 from the Cobb Igneous contents of 2.7-L3.7Vo7.nO occurs as tiny corroded VIAI 7.447 0.452 0.439 0.330 1.081 crystals in chromian muscovite grains at Plumbago cr 1.452 2.952 3.t42 3.n8 2.180 Felr 1.O70 0.601 0.400 0.s53 0.753 Creek and ParaparaInlet, and is found as larger and ll 0.031 0.020 0.018 0.018 0.037 less corroded grains at the center of uvarovite MC 0.008 - 0.021 0.030 aggregatesat Plumbago Creek. At Campbell Creek, Fe2r 0.310 0.070 0.153 0.131 chromianmuscovite - kyanite - chromite- tounnaline I4tr 0.062 0.050 0.048 0.104 o.ttz - Ca s.628 5.864 5.781 5.747 5.870 quartz segregations contain abundant zincian chromite,with between2.2 to 4.8EoZnO. Here, all the Aln 5.2 1.1 2.5 0.5 Adr 26,3 16.1 9.6 13,8 ti.o chromite grains are euhedraland have an overgrowth Grs 31.1 7.9 7.9 25.0 PrP o.4 ' 0.4 t.J Scm 0.5 0.4 0.3 0.E sps 1.1 0.8 1.2 1.8 Itr 16.2 74-1 78.7 83.3 sZ.n
1 Fe-rich wrovie overgowth in qureie 2 Avuage (n = 2O) uzmed |JJmviE without cbmmite cues 3 Unzded wrovitg srrotmding cbromiE corc 4 Uvdwi6-rich ganet ln c@tacteith chmie cqe 5 Rimofwarwite-dchg@et
In uvarovite-poor layers of the quartziteowhere there are only scaxce,isolated grains of uvarovile, usually with a core of zincian chromite, the predomi- nant garnet is a colorless grossular,containing over 907ogrossular and no uvarovite.This garnetis locally abundantand is intergrownwith fine-grainedcerussite or calcite (or both). Very similar coexistenceof uvarovite and grossular(grandite) was reported from the Write River arba, Hemlo, Ontario @an & Fleet 1989).The authorsproposed a metasomaticorigin for the gamet and considered that the uvarovite was formed later than the gtossular, in a second,lower- temperatureevent. However, in the PlumbagoCreek quartzite, both garnetsappear to have formed at the sametime, with the compositionaldifference being due to the presenceofscattered grains ofchromite, around which uvaroviteformed in preferenceto grossular. In Figure 9, the compositionsof uvarovitic gamet at Plumbago Creek are plotted on a Uv-Grs-Adr Frc. 8. Back-scatteredelectron image of grain of zincian triangular diagrarn,together with fields of garnetfrom chromite @right) surrounded by uvarovite, showing similar environments.The most closely comparable patchy zonationwith lower Cr and higher Fe (darkerarea samplesof uvarovite are from skarn developedat the at top of grain). Bar scale: 100 Pm. t274 TTIE CANADIAN MINERALOGIST
+ Average homogeneous (n=20)
Grs Adr Ftc. 9. Compositionof uvarovitefrom PlurnbagoCreek quartzit€ in termsof Uv-Grs-Adr content. Fields of garnet compositionsfrom similar environmentsat Outokumpu (von Knorring et al. 7986),White River, Ontario (Pan& Fleet 1989)also are shown.
TABLE5. REPRBSENTAUVECOMPOSIIIONSOFZNCIANCHROMFB"NORTITWESTNEIJON.NBWroALAI{D wt,Vo 1 l0 11 t2 L3 t4 t5 siq nd nd nd nd nd nd nd 0.16 0.10 0.06 O.T, !d !d nd Ilq no nd 0,09 rd 0,30 nd nd nd o.n 0.08 0.0? rd ttd ad A12q 1.61 9.63 8.r3 14.63 15.10 0.4r 23.14 20.22 2.82 2A.43 20.83 10.84 6.67 1.69 0.08 Crp3 63.46 54.28 58.35 50.67 49.51 20.86 4050 u.r1 63.W 43.54 43.82 55.14 U.82 58.36 33.38 F%q l.2I 1.90 nd nd rd 4739 nd 0.34 l.l8 0.16 0.u nd 1.@ 9.56 35.51 FeO 2r.76 rg.M 22.69 31.02 17.05 29.93 3r.32 3rs1 26.45 25.79 26.45 26.95 17.05 2L,56 24.15 l*rO 1.65 1.r8 434 0.16 3.51 r52 0.36 nd 2.94 220 2.29 2.69 0.03 2.40 238 Mp 0.17 0.40 r.24 0.48 0.70 !d 0.73 0.80 0.75 l.9l r.67 0.89 10.46 4.05 2.O7 hlO 8.88 l3.5r 9.06 2.35 13.?4 nd 2.E3 2.t0 L2r 4.78 4.U 33r !d r.90 o.92 l.lio nd nd nd rdrdndd nd nd O.l4 0.13 0.09 nd O.m 0.78 Total 98.74 rffi.34 99.90 9931 9.9r 100.11 98.88 9.74 9.46 9930 100.55 tffi,s rfr.O3 9.72 99.27 i Fe2O3assigned assundng stoichiometry nd =not detected Catiomper3 sites 5r 0.006 0.003 0.002 0.@ TI 0.(Xr2 - 0.007 0.007 0.002 0.002 AJ 0.0?l 0.407 a344 0.603 0.625 0.018 0.920 0.E08 0.122 0,E13 0.820 o.449 o.%s 6.ozz 0.004 Cr 1.E95 1J41 r.655 1.399 1.368 0.627 1.080 l.lE4 1.833 r.762 7.156 r.531 1.710 1.668 o.9E2 Fe3+ 0.034 0.051 1.355 0.0@ 0.033 0.004 0.016 0.031 0.260 1.005 Fe2+ 0.688 0.584 0.681 o.n6 4.49 0.951 0.884 0.893 0.813 0.728 0.738 0.7E2 0.62 0.652 4,759 l&r 0.053 0.036 0.010 0.m5 0.lM 0.u9 0.010 - 0.@2 0.053 0.065 0.080 o.c[M 0.073 0.076 MC 0.010 0.021 0.066 0.(D5 0.036 - 0.036 0.M0 0.041 0.096 0.083 0.047 0517 0.218 0.1l6 Zr a.a8 0.359 0.240 0.(K0 0355 - 0.070 0.068 0.06 a.t2 0.114 0.085 - 0.051 0.@6 l.ti o.qx 0.003 0.002 - 0.006 o.oa f Chmmite cue of waovite, waoviro-rich qustzite, plurnbagoCle€k 2 Chromite ore of warovite, qureite. Ptuminso Cre€k 3,4 SmaUdrqnit€ gmins in clinimim miscovite,-quae rchisr, plunbago (}e€k 5 Clnomite from cbrunian prapra 'Ferritcbronrit" rmscovite-rich schisr, Idet 6 frqn chomian mueovite-rich'schisi paaoaa lnlet 7,8 Chromits Aom chrqnian muscovitediloritemuscovitedilorio rchist CinekdtaRiver .lt"mire grain ?^ |{g:gry"* in clromiar nurcovite-kyanie+lromite-oumralinequare segregatioqCarnpbell Ctee,k 19 - ^ Honroge'neoruclnomite lain in segrqgarioaCrnptetf Creef ll,l2 Core 60rim of clnqnitissin ir Cdsaridn C-d;;b€[-Cre* 13 Cbromite frorn cfrqnititclaver 'fenitclrcmif in s€m€trilinite.Cobi hneous Cumlex 14'15 Core aod repiacemenr'rinof ctiromite frain in rn taironatea .ea"nmb, Peapma Riv€r CTTROMIANMUSCOWIE" NORTIIWESTNELSON, N.Z. t275
Fe2*
a Phmbago Creek o PdraparaInlel Onel(akaRlvBr
I C€mpbsnO€d( o Cobb lgneouscomplox
Mg AI Cr
Frc. 10. Compositionof zincian chromitefrom PlumbagoCreek, Parapara lnlet, Onelakg River, and campbell creek' togetherwith that of high-cr chromite from the cobb Ultramafic Complex.
that enclosesabundant quartz, although in most cases, chromite containing appreciableFe3+ (47.39Eo Fe2o3) core and overgrowthhave essentially the sarnecompo- relative to Fe2+(29.93Vo FeO), significant Mn sitron (43.6Vo Cr2O3,26Vo FeO, 20.67o Al2Ot. (1..52VoMnO), low Cr (20.86VoCr2O3), very low Al However, the margin of some grains is richer in Cr (0.417oAzOr), and no Zn or Mg. This composition (557o Cr2O) and poor in Al (10.87oAl2O). Rarer correspondsto that of zone C of "ferritchromit" homogeneous grains of chromite with higher Cr alteration described by Wylie et al. (1987). These (-627o Cr2O), apparentlywithout overglowth, also authorsobserved distinct anisotropyin the "zone-C" occur (Table 5). Notable is fts high Mn content of material, suggestingthat the phasedoes not have the zincian chromitefrom PlumbagoCreek, Parapara Inlet, isometric structure typical of spinel. All chromite and Campbell Cre* (l.lVo-3.57o MnO). Chromite grains analyzed here are highly depleted in Mg compositionsare plotted on Fe2*-Zn-Mg and Fe2+ (Vt.ggo Mgo) relative to cbromite from the Cobb - Al - Cr diagramsin Figure 10.Much of the chromite IgneousComplex (10.5-13.37oMgO; Hunter 1974). occurs as tiny (40 pm) grains, highly corroded, There is an inverserelationship between (Zn+Mn) and with a "spongy" texture that makes analysis by @e+Mg)and between (Zn+Mn+Fe) and Mg (Table5), electronmicroprobe difftcult. The highestZn contents indicating thatZn can substitutefor both Fe and Mg in (>l3.5vo ZnO) are associatedwith small grains of the spinel structure (cf Bevan & Mallinson 1980, highly corrodedchromitp with variableCr2O3 contents. VtarshaU& Dollase 1984,Wylie et al. 1987).Zinc tn Larger, lessaltered grains in uvaroviteare fairly homo- all casesof chromiteanalyzed from the Cobb Complex geneous,with a compositionof uowd 9VoZnO, a/Jld (Ilunter 1974), anddetrital chromitein metasediments Cr2O3contents of 63-64Vo(Table 5, anal. 1). Small distal from outcrops of the SeparationPoint granitic grains of chromite in chromianmuscovite schist from suite(Hunter 1975), was found to be belowthe limit of the OnekakaRiver, andthe mica schistfrom Plumbago detection"-0.08Vo ZnO. Creek, have lower Zn contents(2.3-2.87o ZnO) and considerablyhigher Fe contents,-3l%o FeO.This may Chlorite be due to further alteration of a previously more Zn-ich chromite toward "femitchromit", as Representativecompositions of chlorite are given in documentedby Wylie et al. (7987).In the micaceous Table 6. Values of Xrrr" (Mg/Mg + Fel) range from quartzite at ParaparaInlet, there are ftrre grains of 0.13 to 0.67, and thd chlorite can be classedas 1276 TIIE CANADIAN MINERALOGIST
TABLB6. REPRESENTATIVE COMPOSITTONSOF CHROMIAN CHLORITE BIOTITE AND MARGARITE NORTIIWEST NEISON, NEW ZEALAND
vLalo l0 si02 28.78 2s,75 29.30 26.42 X0.05 25.83 28.qt t7.10 38.9 30.72 Tq !d 0.72 0.09 0.19 0.29 0.16 0.08 r.82 Ln 0.20 Al2Oj n36 21.67 2Xt.44 m.u 6,09 21.88 23.00 18.44 16.81 48.88 cbA 2.76 r.22 0.93 0.05 2.16 r.t4 r,4r rJ6 0.45 0.69 F€08 n10 13.94 17.08 nsl 3t.r6 t52l 12.46 12.86 15.33 0.29 Ivlno 0.70 nd 024 0,lE 127 0.18 ad 0J7 nd nd Iv&O 6.57 20,U 19,16 r4,tt 1.63 2r.42 t8.38 13.65 12,E2 0.19 NiO 0.08 nd nd 0.07 2.49 021 nd nd 0,ll nd 7^O nd nd nd. 0.11 nd 0.13 nd nd 0.ll !d CaO 0,25 nd 0.1I d 0.90 nd nd 0,08 0.10 9,98 NazO nd nd nd Dd O.!7 0.18 nd 03E 0.08 0.84 Kzo nd !d 0.10 0.M nd nd l.4l 9.93 9.47 0.08 BaO nd ad nd nd nd nd Dd 0.63 0,2r 0,46 F nd nd nd nd nd nd nd 0.59 0.65 nd cl 0.25 nd nd ndndndd nd od !d Total 87.45 83.54 87.45 88.68 87.38 84.U 84.y2 97.U 96.& 92.33 .GF 0r5 0.n €=Cl
Tonl 87.39 83.54 87.45 88.68 87.38 U,U U,92 97.59 96.13 92.33 tAllFeasRO nd=rot det€c-ted Ims m basls of 28(O) Ionsm badr of 22(O) SI 6.149 5.373 6J4o 5.893 5.566 6.768 5.318 St 5,398 5.734 4,!9r wAl r.851 2.O7 L107 2.563 2.232 2.6y2 2.22t rvAt 2,6U2 2,166 3,8@ :(re0 8.000 8.@0 8.0fi) 8.000 8.000 8.000 8,000 :(tcD 8.000 8.000 8.000 vIAl 3.273 2.703 L73, 2.414 2.774 2,6n t283 vIAt 0.561 0,648 4.052 (}3+ 0.467 0.200 0.t48 0.m8 0.385 0.218 0.226 Ct3+ 0.202 0.052 0.074 4.948 2.428 2.879 4.U7 6240 2.447 2.tt5 Fe2+ lJ68 1.886 0.033 Tl4+ - 0.018 0.015 0.033 0.054 0.(D8 0.014 n4r 0.199 0.140 0.012 I\dn 0.133 . 0.041 0.032 0242 I\ft 0.070 li4C ?.492 6.48t 5.743 4.417 Os47 6573 5.561 Me Lgff. 2,810 0.039 M 0.010 0.012 0.451 Ni- - 0.013 7^ - 0.017 - 7.\ - 0.012 >(oo0 5.5@ 5.561 4.219 Ca 0,057 - O.mA - A277 Ca 0.012 0.016 1.459 Na Na 0.lm 0.t23 0222 K - - 0.v26 K 1.843 r,n1 0.014 ct 0,090 Ba 0.036 0.012 0.(D5 > 1r.o70 11.6501l.6tp 11.?8010.910 11.895 11.199 t@Erlayer) 1,998 1.828 1.720 xMg 0.30 o.73 O,fl 052 0.08 0.23 0.72 XMg 0.271 0.302 F O.A 0-40
I Gmimc.blorite,wa$vitequnEilc,plmbasocr€e* 2 frmim c;[lorie, ctrrmlm rin'scovite schiq-Orekeke f,iysr 3 Chmtm chlodte,btodrecchlsLOnekaloRivec 4 Glmite, biotire shis{. Cmpbe[ G€€k 5 Gromim chluie(pmini6),namadzdultmafc,CalohmiaCreek 6 cblmitized biotite, cl[omim mrscovite schis" On€kakaRiy€r 7 Cblodtized biodte. cbromim nuscovtte schiqt, On€kakaRhq 8 Cbromian biotite,AflhurMarble.CouDerstailGeek 9 Chromian biorite, biorile schis. Csm;bl cr€ek I 0 Margurie, cbromim muscovite schisc.One}aka River
ripidolite or brunsvigite (Hey 1954). Except for River. The margarite contains 0.46VoBaO, with Ba chlorite in the biotite schist from CampbellCreek, the substituting for Ca. Rare Cr-bearing margarite also chlorite is chromian, containing between 0.9 and occurs with kyanite in more sftongly pelitic schist 2.8VoCrrO3. A penninitechlorite from the Calphumia layers at the ParaparaInlet locality, althoughit is not Creek ultramafic rock contains significant Mn directly associatedwith cbromianmuscovite. (l.27%oN4nO) and Ni (2.49VoNiO), consistentwith the presenceof Ni- and Mn-bearingcarbonate. Biotite
Margarite Red-brown biotite (Xrn in the range 0.34-{.40), with between 0.4 and l.{Vo Cr2O, (Table 6) occurs Margaritewith around0.7Vo Cr2O3 (Table 6) occurs with chromian muscovite in the Arthur Marble at as a rare phaseintergrown with muscoviteand chlorite Copperstain Creek, and biotite schist at Campbel in the chromian-muscoyite-richpebbles from Onekaka Creek. As with coexist'4g muscovite, the biotite CHROMIAN MUSCOWIE. NORTH$TESTNELSON, N.Z. tn7 contains fluorine (0.il.87o). Textural relationships, PlagiocLase suchas intergrowths,suggest contemporaneous growtb of the two minerals. In chromian-muscovite-rich Otgoclase with the composition Anx.z-za pebblesfrom OnekakaRiver, porphyroblastsofbiotite Ab73.9-73Ors.9-1occurs as disseminated clusters of have been chloritized (Iable 6), grving a distinctive gfains in the chromianmuscovite quartzite at Contact brown color to the replacementchlorite. Creek,these clusters give a white spottedappearance to the rock. Labradorite (An63.e-50.1Ab3:.0-+s.1G0.5-{.0) K-feld.spar occurs within the chromian muscovite mafrix that replacesbiotite schistin CampbellCreek. Minor interstitial K-feldsparoccurs in the uvarovite - zincian-chromite-bearingquareite and cbromian Epidote muscovite quartzite in tle fault breccia at Plumbago Creek. The feldspar is very fresh, homogeneous Idiomorphic epidote with Cr2O3varying between microcline of compositionAno.4Ab530re4j. Ba conlent 1.4 and 2.2Vo(tzhle 7) is associatedwith the fine- rangesfrom 0.3Oto 0.434oBao. Crainedchromian muscovite replacement in Campbell
TABLE ?. REPRESEhITATI\/BCOMPOSITIONI OF CAROMIANPIDO'Its AND TOIIRI{ALNB NORTIIWESTNS.SON, TGW 2EAISND
vL% 3 sio2 39.31 38.74 3824 3E.41 36.96 36.59 36.40 85.45 37.12 rq 022 0.08 0.3r 0.n 0.13 0.16 0.49 o57 0.41 AIA 29.t3 28,V) 31.36 30.33 36.& 35.35 35.03 29.51 3155 azQ r.46 2.4 2,U 2.28 tJ3 0.80 1.07 0.06 1.29 F%Q* FeOi :"r 1.ot 2.M 2.16 2.85 7.32 8.16 8.63 1.99 w,# 11.33 11.06 11.05 10,&l 10.90 10.35 10,86 Nho o.zt 0.49 0.08 0.04 Dd nd 0.11 nd nd lr4 0.16 0.n r0.97 10.30 6.89 4.96 457 7.14 10.03 Nio 0.11 0.22 o.l2 0.10 nd nd nd trd nd Z^O o.32 0.15 nd 0.34 0.ll nd nd ClO 2!.74 22.n 2.76 2.16 0.38 0.18 0.70 1.68 r.66 NazO Dd nd t.44 l.E8 7.76 1.70 2.19 156 r.47 Kzo 0.(B 0.10 trd nd nd 0.05 0.07 F {t 0.82 0.42 0.32 0.17 0.14 0.53 0.73 Total 98.4 96,T2 tcz.52 99,E8 9E.s2 98.41 99.83 95J3 97.12 -o::F 0.32 0.18 0.14 0.07 0.06 0.22 0.31 Total tm.m 99.?0 98.38 98.v 99.77 95.31 96.81 $AllRoFe2O3otbo * BzO: calorlstedNming 3 B ot@s in fcmulae nd = not aletscted Iols oDbadr of 12{O) Ionsotr basis of A(O) si 3.024 3.M5 B 3.m0 3.m 3.000 3.000 3.@ 3.000 3.000 Xte0 3.q24 3.u5 sl 5.867 6.OU S.Al 5.869 5.804 5,947 5.939 IvAl 2,ut 2.s96 A(br) 0.133 - 0.179 0.131 0.196 0.053 0.061 Ct3+ 0.089 0.125 ^Z 553E 5.6U 6.000 6.@ 6.0m 5J82 5.889 Fci+ 0.224 0.241 Aly - 0.579 0.553 0.388 Tt4+ 0.013 0.005 G3+ 0.320 0.283 0.215 0,101 0.135 0.008 0.163 EY L967 2.9€t r/+ 0.036 o.M4 0.019 0.059 o,o12 0.049 I\rh 0.014 0.033 Fe2+ 0,262 0284 0,375 0.982 1.088 r.2rr 0266 Ca 1.957 1.8?8 lfo 0.010 0.005 0.015 Mg 0.018 0.032 Ir4C 2508 2.472 1.617 1.186 1.0E6 1.7E52392 M 0.0u 0.014 M 0.015 0.013 >x,W r.996 r.957 7,a 0.036 0.017 - 0.040 0.013 'Y Ps 7.8 E.4 >Y 3.1E7 3.058 2.E01 2.EE7 2.7U 3.065 2.870 Ca 0.454 03& o.au 0.031 0.120 0.3u 0.2E5 Na 0.428 os73 0.537 0.529 0.6n 0.50/ a.4v K 0.018 0.m0 - 0.011 0.014 xx 0.9000.957 0.601 0.56 0.797 0.820 0336 F 0.398 0.m9 0.070 0.0E6 0.071 0.2E1 0.369 1,2 Core@d rin of eDidotefrm biotitesc,hisL CaDDbe[ creek 3,4 Corcmd rin of r;unnalineh fuc.hsite-richreolacemenr of Arthrr Mrble 5,6,7 Cue' imer th andrin of Tonnaline ftm clromte @ auqtz eesresad@"C@obell Cl€e,k 8,9 Coe and-rid of tourmatinein chrmiannuscovir scblsaosequartzite,Anatoli River- Go Ahead Cr€e& 1278 TTIE CANADL{N MINERALOGIST
Creekbiotite schist@g. 6). The epidoteis pale yellow, homogeneous and contain l.4L-I.44Vo Cr2O3, with a dark blue interferencecolor characteristicof 0.214.39Vo Fe',O3,and up to 0.27oZnO. Kyanite clinozoisite, and is weakly zoned betweenthe rather has been reported elsewhere within the Onekaka limited compositionalextremes of Ps7.5and Pss.r.The Schist in associationwith quartz lenses and knots epidotealso contains 0.1 l4.22Vo NiO. (Grindley l97l) that are aligned parallel with 51, and we have collected float samples containing Tourmaline kyanite crystals up to 4 cm long. A bulk X-ray- fluorescenceanalysis of this kyanite indicates that Tourmaline is presentin the chromian-muscovite- it contains only 8 ppm Cr, and it is not usually rich parts of the Arthur Marble in Coppentain Creek, associatedwith cbromian muscovite.Rare kyanite - and hasbeen reported previously in quartzofeldspathic cbromian-muscovite-richlayers also occur at Parapara and pelitic schistsfrom this locality (Y'Iodzickt 1,972). Inlet Q{. Stevenson,pers. comm., 1994),where the The tourmalinein the marble is weally zond with a kyanite forrns porphyroblasts that contain between brown-greenMg-Ca-Cr-rich core, and a pale green 0.5 and l.3VoCr2O3.Associated minerals are chromian Fe-Na-rich rim (Table 7). Cr contentsvary between rutile, rare zincian chromite (2-3VoZnO) and pseudo- 2.3 and.2.7Vo Cr2O3.Significant is the presenceof brookite. -0.Ll7o NiO, 0.15-{.32VoZnO. and 0.4G{.857oF. Abundant tan-colored tourmaline occurs in the Carbonates cbromianmuscovite - lqranite- chromite- tourmaline - quartz segregationsin Campbell Creek. The grains Calcite accompaniesmuscovite and uvarovite are zoned with respectto Fe (2.8-8.27oFeO), Mg in the quartzites from Plumbago Creek. In biotite (6.94.6VoMgO), andCr (1.84.9VoCrrO) (Iable 7). schist at Campbell Creek, yellowish brown siderite The core tendsto have higher levels of Cr and Mg. In with between 2.8 and 3.4Vo MnO occurs with the chromian-muscovitequartzite between Anatoki chromian muscovite along the boundariesof dense River and Go-AheadCreek, tourmaline occurs as tiny areas of fine-grained chromian muscovite (Frg. 6). grains with a greenishbrown Fe-rich core and a pale The ultramaJicrock from CalphurniaCreek contains brown Fe-poorrim. The core containsvirtually no Cr, ferroan mngnesite, ferroan dolornite (ankerite), whereasthe rim has -L.3Vo CrrO3. Fluorine contents and a nickel carbonatewith34.9Vo NiO and 2.97oCoO vary between 0.5 and 0.8Vo (Table 7). Chromian- [possibly zaratite, Ni3CO3(OH)4.4H2O].A small muscovite-bearing quartz segregationsat Parapara amount of cerrusite occurs in the quartzites in Inlet also contain tiny needlesofpale yellow-greento Plumbago Creek and Anatoki River - Go-Ahead olive-greenlqumalins with 0.4-l.4Vo CrrO.. The Creek. crystalsare zonedwith Fe, C4 Cr increasing,and Mg, Na decreasingfrom core to rim. Small amountsof Zn Other minerals (0.1G{.187o ZnO) are present,and the F-content variesbetween 0.30 and 0.62Vo (TableT). Zircon wrd apartte are widespreadaccessories. The apatite contains fluorine, generally in amounts<1.7o. Rutile Gersdoffite occursin the CalphurniaCreek ulffabasic rocko and in quartzite from Contact Creek, near Honey-brown-coloredrutile is ubiquitous as an CampbellCreek. At the former locality, it containsup accessoryin alll samFlesstudied, and is characterized to 2.8V0Bi and is associatedwith cobaltian violarite by Cr contentsranging between0.g and3.3vo CrrO3. In and pentlandite. Pyrite forrns small stringers in the the chromian muscovite - kyanite - chromite - chromian muscovite quartzite at Contact Creek and tourmaline- quartzveins from CampbellCreek, rutile contains betw6en 0.5 and 0.67a NiO. Pyrite also is containstp ta 0.16%oCoO,0.23Vo 7aO,0.087o MgO, present as large anhedral grains in the chromian and between0.16 and 0.23VoF. The presenceof F is muscovite- kyanite - chromite- tourmaline- quartz surprising, and it presumablysubstitutes for OH that segregationsat Campbell Creek, where it contains is known to occur within rutile (Vlassopouloset aL befween 0.23 and 0.72VoNiQ and up to 29Vo CoO. 1993,Rossman & Smyth1990). Although most grains Pyrite is also found with chromian muscovite in the are homogeneous,qualitative electron-microprobe Arthur Marble at CopperstainCreek, and in chromian analyses show that others contain areas that are muscovite quartzite from the Anatoki River - Go- enrichedin }rlb and Ta (up to abolt 4 wt%o). Ahead Creek area. $mall amountsof pseudobrookite occur in the seamof chromianmuscovite at Parapara Kyanite Inlet. Qualitative electron-microprobe analysis indicates the presenceof up to about 8Vo VrO, + Blue kyanite is conspicuousin chromianmuscovite CgO3. The chromium contentvaries between0.3 and - kyanite - chromite - tourmaline - quaru segrega- 0.5VoCr2O3, Zn between0.17 and0.20%oZnO, andthe tions at Campbell Creek. The grains are chemicatly level of MnO is -I.97o. CHROMIAN MUSCOYTIE. NORTTIWEST NELSON, N,Z. r279
DIscussIoN metasomatismby the action of Cr- (and Zn-Mn)- bearingfluids. There is considerablevariation in the scale and The two mechanismsof chromium enrichmentare intensity of developmentof Cr-Zn-bearingminerals in demonstratedin Figure 11, wherebulk-rock Cr content the Lower Paleozoic Onekaka Schist of Northwest is plotted againstK2O (a measureof mica content,or Nelson, from thin seams2-3 cm thick to zonesup to original clay content, in the absenceof K-feldspar). 100 m wide. Field and textural relationships of the Low-grade metamorphiccorrelatives of the Onekaka chromium-bearingsilicates and oxides indicate that Schist, the Hailes Quartziteand metasedimentsof the they can be largely explained by (i) in situ meta- WangapekaFormation (Grindley 1971, 1980) show morphism of Cr-rich sedimentaryhorizonso and (ii) trendsof increasingCr with increasingK, as might be
30,000
20,000
:. o 1 -- at -{-'3 a a. + + .L ,+ + 'T tr chromian ++ muscovite ,tg 'end memb€r"
Cr ppm
,...---'t .'\ + arl ++ -T:
-r!r-L , I'
K0+
WtToKaO
Frc. 11. l,og-norrnal plot of bulk-rock Cr (ppm) versus K2O (wtVo) for Onekakaschists (crosses).Samples numbered 1-9 (solid circles)refer to compositionsgiven in Table 1. Opensquare represents the compositionof averageshale (Iurekian & Wedepohl1961). An explanationof compositionfields and trendsis given in the inset diagram,and in the text. The trend of normal Cr-K2O enricbmentis given by compositionsof low-grade metamorphicequivalents of the OnekakaSchist (unpublisheddata of Grapes& Palmer). 1280 TTIE CANADIAN MINERALOGIST
expected from sedimentationtrends encounteredin et al. L993). It is significant that the Parapara marine sediments (van de IQmp & Leake 1985), serpentinite occurs close to an area of Pb-Zn{u in which clay minerals absorb Cr from seawater mineralization associated with the Richmond Hill @lderfield 1970). In conrrast, samples of Onekaka granitic pluton @. Wilson pers. comm., 1994). As Schist plot as two separatefields: low-Cr (400 ppml statedpreviously, Cu-Pb-Zn-Mo and Au-Ag mineral- sampleswith KrO rangng between 1. and 6.5Vo,and, ization is typically associatedwith Early Cretaceous high-Cr (>850 ppp) samples,with K2O ranging from granitic rocks in Northwest Nelson. The relationship 0.01to lUVo.Inthe low-Cr field. the increaseof Cr to also suggeststhat the detrital chromite associatedwith values higher than those of the inferred background, chromian muscovite in the OnekakaSchist may also defined on the basis of the low-grade equivalentsof havebeen modified by Zn and Mn substitutionfor Mg OnekakaSchist, reflects Cr-enrichment.Those rocks and Fe2+,respectively, at the same t'me as the that define the high-Cr field contain detrital chromite, mineralizationevent. together with chromian muscovite. The uvarovite Although compositionsof the detrital chromite are quartzites from Plumbago Creek lie on a trend of quite variable(Table 5), variation in Zn andMn can,in increasing modal chromite without any concomitant parf be attributedra in situ reactions.Cbromite with increasein muscovite(clay) content.From considera- someofthe highest7n occursin a reactionrelationship tions of bulk-rock Cr2O3and K2O, the chromite - involving the formation of uvarovite at Plumbago uvaroviteand deepemerald-green chromian muscovite Creek: magnesian chromite + CaCO, + SiO2 + layers in particular are inferred to representoriginal (Zn, Mn) = Zn-Mn-enriched chromite + uvarovite Cr-rich sedimentary layers ("black sand leads") + CO2,and chromianmuscovite at ParaparaInlet and of chromite, or horizons containing Cr-substituted Onekaka River: magnesian chromite + Cr-poor clays derivedfrom weatheringof an uhamafic source- muscovite + Zn-Mn = Zn-Mn-enriched cbromite + rock (Shaw& Bush 1978,Treloar 1987, Gtiven 1988). chromianmuscovite. The almost monomineralic seams of chromian An altemative hypothesis,that the high Zn is the muscovite at Paraparalnlet have the highest Cr and result of an isochemicalreaction involving removal of KrO andrepresent an "end-membe/' composition.The FeCr2Oaand concentrationof Zn in detrital chromite absenceof chromite in these seamscould imply that that alreadycontained a small componentof ZnCr2Oa, it has been completely consumedto form chromian was rejectedin view of the fact that all analyzedgrains muscovite. of chromitefrom outsidethe contactaureoles of Early Cretaceousgranitic plutons contain less than 0.08% Source,compositio4 and reaction ZnO, atd the Zn-enrichedchromite is not depletedin of de*ital chromite Cr or Fe. Some late concentrationof Zn, n already metasomatically Zn-enriched chromite, may have The most obvious source of defiital chromite in occured in the caseof the very small, highly corroded the OnekakaSchist is the Cobb t]ltramafic ComplEx grains in chromianmuscovite, but for relatively large, (Frg. 1). Compositionsof chromitefrom the main iobb less corroded grains at the center of uvarovite ultramaficbody (Hunter 1974),and of detrital chromite aggregates,which typically contain about 9Vo ZnO, that occursin low-gradeCambrian rocls of Northwest someintroduction of Zn seemsrequired, or a possible Nelson (Hunter 1975, Pound 1993) are identicat and precursorsphalerite may havebeen involved. characterizedby high Mg (10.5-l3.3%oMgO), very The inegular distribution of Cr within much of low levels of 7a (<0.08VoZnO) andMn (<0.2VoI{nO). the chromian muscovite suggeststhat Cr was too Suchhigh-Mg and low-Zn-Mn chromite is not found immobile to achieveeven small-scalehomogenization in the Onekaka Schist, which suggeststhat the during metamorphism.It also underscoresthe effect chromitecould either havebeen derived from a source of original sedimentary variations in Cr content, other than the Cobb Ultramafic Complex, for which and the penistence of Cr-rich horizons becauseof there is no evidence,or that Cobb chromite composi- limited ditfrrsion under amphibolite-faciesconditions tions have been modified since they were deposited. of metamorphism.The relatively immobile behavior Regarding the second altemative, the Zn-Mn-rich of Cr during metamorphism contrasts with the compositions of chromite partly replaced by relative mobility of Cr in metal-rich hydrothermal "ferritchromit" and chromianmagnetite in serpentinite fluids asdiscussed below. Similar contrasting behavior at ParaparaRiver (Iable 5, anal. 13) are identical to of Cr has also been noted at Outokumpuby Treloar those fypically associatedwith metasomaticalteration (1987). of ultramafic rocks t}rough interaction with fluids derived from a granitic source,or during serpentiniza- SynmetamorphicCr and Zn mztasomatism tion associatedwith Cu-Zn-Pb mineralization(Thayer et al. L964,MooteL977, Bevan & Mallinson1.980, von Evidence fot a Cr-Zn-(and Mn)-bearing synmeta- Knorring et al. l986,Wylhe et al. 1987,Treloar 1982, morphic fluid responsiblefor the alterationof detrital Pan & Fleet L989, B6nat & Monchoux 1991, Bjerg chromite, precipitating new chromian mica and other CHROMIAN MUSCOWIE. NORTIIWEST NELSON. N.Z. l28L
Cr silicatesand oxides, or resultingin Cr-enrichmentof Sourceof metasomaticfluids Cr-poor muscovite, is provided by: (i) the presence of chromian muscovite,feumaline, and rutile in In addition to the presenceof detital chromite, an metamorphic segregationsof quartz that originally ultramafic sourcefor Cr (togetherwith someNi, Co, lacked them @araparaInlet Anatoki River - Go- Mg, Mn, and Fe) itr a metasomaticfluid is clearly Ahead Creek), (ii) the occurrenceof wide, moderately indicated, and it may not be coincidental that all Cr-rich bands containing disseminatedchromian localities are in close proximity to known outcropsof muscovite and chromian rutile within otherwise Cambrianultarnafic rocks (Frg. 1). The effect of fluids Cr-poor quartzite (ParaparaInlet, Anatoki River - in equilibrium with a granitic source on ultramafic Go-Ahead CreeQ, and (iii) almost monomineralic roctrs is demonstatedby the OnahauGranite, which samplesof chromianmuscovite from OnekakaRiver, containsat leasttwo bodiesof ultramafic rock @g. 1). chromianmuscovite-rich segrcgations in biotite schist These ultramafic bodies are altered to talc and from Campbell Creek, and in the Arthur Marble at antigorite w.ith headewoodite. Chromite is absent, CopperstainCreek, clear texfural evidenceofhost-rock suggesting solution and mobilization of Cr by replacementby chromianmuscovite-rich assemblages. hydrothermalleaching (Kenich & Fryer 1981,Treloar Mineral assemblages from Onekaka River, 1987). Late-stagehydrothermal muscovite in the QamFbell Creek and Copperstain Creek allow an OnahauGranile, near the margins, contains between approximation of some chemical parametersfor the 0.2 and 0.7VoCr2O3, which suggeststhe productionof metasomaticfluid as a function offlO) in the system a late-stagefluid phasecontaining cbromium. Mobility NazO- KrO - CaO - F%O: - AzOg - SiO2- H2O - of chroqium during the alterationof ultramafic rocks 02, where muscovitecoexists with chlorite t biotite * is evidentin the carbonatedrocks at CalphumiaCreek, epidote + margarite * plagioclase t quartz in the and is commonly reported from shear zongs within stability field of kyanite. According to Rosing er a/. ulramafic rocks that havebeen hydrothermally altered (1987),for a(HrO)= I and5 kbarat 550'C,the limiting (locally carbonated) by high-temperature, low-pH parametersare: log cSiO21-1= -1.0, log aca2+la2ly fluids (Kerrichet al.1987). - 6, log aKl a?II+n the ranld l.a-+ .9; log aMg2+| a2W Comparedwith the infened leachingof Cr by high- in the range 44.5, and flO) = I0.rt (i.e., between temperatureaqueous fluids, there was only limited that of the HM and QFM buffer curves). Additional removal of Ni from the ultramafic rocks, and only information is providedby the lnesenceof tourmaline, minor amountsof Ni occurin somemuscovite, epidote, which requiresacid fluids OH <6.0), increasedactivity chlorite, biotite, tourmalineand pyrite. Heazlewoodite, of Al (Morgan & London 1989), and the presenceof gersdorffrte,pentlandite, violarite, Ni-carbonate,and boron, whereasthe widespreadpresence of accessory Ni-bearing chlorite remain in the ultramafic rocks fluorapatitepoints to a comparativelyhrgh aIfrlaHrO within the OnahauGranite and at Calphurnia Creek, in suchacid fluids. This is consistentwith the presence although minor gersdorfftte is present in Onekaka of fluorine in chromianmuscovite, biotite, tourmaline, Schistquartzile at ContactCreek. and rutile. Barsukova et al. (1979) showed that If Cr aud lesseramounts of Ni were leachedfrom titanium is mobile under conditionsof high concentra- ultramafic rocks, it is also evident that Zn, together tion of fluoride and low pH of the fluid. It is expected with Si, A1,K Na Sr, Ba"Rb, F,B, Mn, Ti, As, andPb that rutile will precipitatefrom a metasomaticaqueous wgremost probably also derivedfrom a granitic source fluid ifthe activity ofH2O decreasesoe.9., tbrough the (i.e.,theSeparation Point Suite). The Zn andMn could coprecipitationof muscoviteand otherhydrous phases, be scavengedfrom biotite and magretite, the main or dilution of the fluid phaseby CO, at Copperstain repositories of Zn and Mn, respectively (Johnson Creek, where it invaded the Arthur Marble" and 1994). It is significant that newly formed cbromite possibly at CampbellCreek, where rutile is associated containingZn (2.24.8Vo 7nO) aad Mn (2.2-2.9Vo with siderite. Accessory zircon, apatite, and rare MnO) is found in quartz segregationstogether with monazite (this occurring in quartz segregationsat chromian muscovite, kyanite, and tourmaline in Anatoki River - Go-Ahead Creek), are commonly QamFbellCreek, adjacent to the OnahauGranite. This associatedwitl chromian muscovite and rutile supportsthe possibility of Zn-Mn metasomatismof (Fig. 4b), and are possibleprecipitates from a super- detrital chromite elsewhere in the Onekaka Schist. critical aqueousfluid with elevatedF that underwentan Significant also is the Zn andMn containedin cblorite, increasein pH by interaction with the country rock biotite, tourmaline, and some rutile associatedwith (Ayers & Watson1991). At ParaparaInlet andAnatoki chromian muscovite, and in chlorite associated fuver - Go-AheadCreek the associationof chromian with uvarovite. muscovite- chromianrutile t tourmaline,with drusy Chromian rutile is found at nearly all localities of encrustationsof quartz formed along fracture planes chromian muscovite and is inferred to be of metaso- and within cavities in quartz segregations,indicates matic origin, with Ti, Nb, andTa being scavengedfrom that the fluid also was satura0edwith silica" possibly titaniferous magnetite and rutile from the granitic derivedby partial solution of quartzin the host rock. source.Rutile, in particular, is appreciablysoluble in 1282
HrO at high temperature and low pressure, and serpentinitefrom Calphurnia Creek was provided by dissolves by hydrolysis to form T(OII)a (Ayers & CRA Exploration. This paper would not have been Watson 1993).The rare galenaand pyrite in chromian possiblo without the technical assistanceof Neville muscovite quartzite and quartz segregations(Anatoki Orr, who provided excellent polished thin sections. River - Go-Ahead Creek), gersdorffite and pynte Michelle Fraei and Jeff Lyall draughtedthe diagrams, (ContactCreek), and cerussite(Plumbago Creek), are and SueNepe typed the tables.The work was partially inferredto be the productsof the samegranite-derived, funded by the Foundationfor Research,Science and metal-rich fluids that were responsiblefor the minor Technology (A. Challis) and by an tnternal Research Cu-Pb-Zn-Mo and Au-Ag mineralizationassociated Grant from Victoria University of Wellington @. with the SeparationPoint Suite, mentionedpreviously. Grapes). It may also fs imFortant that all occurrencesof the shr'6mirrmminerals described in this paperare closeto RmERENcFS major faults, which may haveacted as channelways for the fluids. The chromian muscovite localities at AnousoN, J.L. (1968): Regional geochronologyof New Plumbago Creek and Onekaka River lie within the Z,ealaad.Geochim. Cosmochim. Acta 32, 669-697. shearzones of the Wakamaramaand Onekakafaults" respectively, which must have been active in Early Avnns, J.C. & WersoN, E.B. (1991):Solubility of apatite, Cretaceoustimes if they did act as channelways. monazite,zircon, and rutile in supercriticalaqueous fluids with imFlicationsfor subductedzone geochemistry.P&l/. Trans.Roy. Soc. London 4335,336-375. CoNCLUsIoNs & - (1993):Rutile solubilityand mobility Chromian muscovite, zincian chromite, uvarovite, in supercriticalaqueous flurds. Contrtb. Mineral. Petrol. and chromian rutile are variously associatedwith L14.321-330. Cr-bearing silicates (chlorite, biotite, epidote, tourmaline, kyanite), carbonates,and sulfides (pyrite, BARsuKovA,M.L., Kuz{E-rsov, V.A., DoRoFEyEvA,V.A. & galenaogersdorffite, pentlandite) in Lower Paleozoic KHoDAKovsKry, LJ. (1979): Measurement of the quartzite,biotite schist,marble and ultrama.ficrocks in solubitty of rutile TiO2 in fluoride solutions at elevated Northwest Nelson. Enhanced levels of Cr in the temperatures.Geokhbniya 7 , l0l7 -1027. sedimentsinvolvpd depositionof detrital chomite and Cr-substitutedclays derived by weathering of ultra- Berrs, T.E. (1989): Paraparasilver/gold/lead-zinc prospect. .fn Mining mafic rocks. Early Cretaceous Mineral Depositsof New Zealard.Austral. Inst. amFhibolite-facies Metall.,Monogr. 13, 117-118. metamorphism and synmetamorphicmetasomatism associatedwith emplacementof granitic plutons BHr, J.M., WEBB,E.J.H. & CLlRxs, E. DEC. (1907):The resulted in leaching of Cr from ultramafic rocks by geology of the ParaparaSubdivision, Karamea,Nelson. metal-scavengingfluids emanatingfrom the granitic N,Z. Geol.Surv,, Bull.3, batholiths. Stabilization of chromian muscovite and uvaroviteoccurred by in situhtgh-tsmperaturereaction BEVAN,J.C. & Mar,mtsor, L.G. (1980):Zinc andmznganese- of the fluid with detrital chromite, and widespread bearing chromites and associated grossular from Cr-Zn-Mn metasomatismresulted in the formation of Timbabwe.Mincral. M ag. 43, 8 I 1-8 14. Cr-silicates and oxides both within original Cr-rich sedimentary horizons, and through replacement of Bftner, D. & MoNcuoux, P. (1991): Les spinelles Cr-poor lithologies. chromozincifdres du district aurifbre de Salsigne (MontagneNoire, France). Eur. J. Mincral.3,957-969. AcK.towLDGENENTS BrsHop, D.G. (1971): Sheet 51, 53 & ft.S4 We thank Drs W.A. Watters and P. Blattner for Farewell-Collingwood.Geological Map of New Zealand constructive,criticism of earlier versions of the l:63 360,Dep, Sci.Indw. Res.,Wellington, New ka.land" manuscriptoand Dr. R.F. Dymek and an anomymous referee for commentsthat considerablyim.Froved the BJB.c,E.A., DEBRoDTKoRB,M.K.'& Srulen, E.F. (19931: Compositional zoning in Zn-chromites final manuscript.We are obliged to Mr. B. Webster, from the of Cordillera Frontal R:rnge,Argentina. Mincral. Mag. 57, Takaka,who brought to our attentionthe uvarovite in t3t-t39. Plumbago Creek, and to Dr. G.W. Grindley, who provided additionalsamples from this locality. Jane4ne Bneruwerrr, R.J. & hnawo, F. (1993):Metallogenic map of McBride, Eric Wilson and Hamish Stevensonof the New Zealand.Inst. Geol. Nuclear Sci.,Morngr3. Geology Department, Victoria University of Wellington, provided samples and information on Coorrn, A.F. (1976): Concentically zoned ultramafic pods Contact Creek, Richmond Hill @araparaRiver), and from the HaastSchist Zone, South Island New Z&alafi. Parapara Tnlsf, lsspsslively, and the sample of N.Z J. Geol.Geoplrys. 19,603-623. CHROMIAN MUSCOVTIE. NORTHWESTNETSON" N.Z, t283
CooPER,R.A. (1989): Early Paleozoicten"anes of New L6prz SANcHsz-VzcalNo, V., FRANZ, G. & G6vrgz- Z,ealatd-J. Roy.Soc. N.Z.19,73-112. PucNArRE,M.T. (1995): The behaviorof Cr during meta- morphism of carbonaterocks from the Nevado-Filabride DEER,W.A., HowE, R.A. & Zussvar, J. (1982): Rock- Complex, Betic Cordilleras, Spain. Can. Mineral. 33, Forming Mirurals. lA Orrhasilicates.Longman, London, 85-104. U.K. MARtr
HEY,M.H. (1954):A new review of chlorites.Mineral. Mag. PaN,Yuammlc & Flrrr, M.E. (1989): Cr-rich calc silicates 30.n7-292. from the Hemlo area,Ontario. Can.Mineral. n,565-577 .
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