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Chromian Muscovite, Uvarovite, and Zincian Ghromite

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Chromian Muscovite, Uvarovite, and Zincian Ghromite 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
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