CM26_23_LINHAISAI-MINETTE

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CanadianMinoalogistVol.26,pp.2343 1988)ROCK AND MINERAL CHEMISTRY OF THE LINHAISAIMINETTE, ENTRATAUMANTAN.NDONESIA,IID THEORIGINOFBORNEO IAMONDS

STEYEN C. BERGMANExplorationondProductionRxearchDeryrtment,ARCO Oil andGasComryny,PRCD3136' 300PlanoParkwoy'Plano, Tqos 75075,U.S.A,

DENNIS P. DUNNI AND LEENDERT G. KROL2AnocondaMineralsCompany,Denver,Colorado80202'U.S.A'

ABsrRAsrExploration for the primary sourceof diamonds n cen-tral Kalimantan led to the discoveryof 8 Ma, small, shal-low, non-diamondiferous mafic to felsic minette dykes.

Thesedykes ntrude Early Tertiary, non-maritre, interbed-dedmudstonesand sandstones ndLate Cretaceousmarinemudstones n the upstreamKaramu River area, northernBarito Province, Indoneeia.The dykes arevesicular,mas-siveand contact-brecciatedmagnaric rocks that range rommafic 10 furtermediatecompositions. Their mineralogyincludesmoderately zoned phlogopite (core to rim: Mg#S2-73); pargasitichornblendewith two zones,a euhedralFe-rich,green,sieve-texhuedorezone Mg# 70-47 (c-r)and a Mg-rich, brown rim zone [Mg# 65*71 (c-r)];clinopyroxenezoned from augite core (Mg# 80) to diop-side(salitevariety) rim (Mg# 72), sanidine(Abj8Or3?Ant,titaniferous -agFetite, ilmenite, serpentinepseudomorphsafter olivine, apatite,rutile, and zircon. Rock compositionsare$Dical of minettesn terms of major-, minor-, andtrace-elementabundances.The primitive nature of the Linhaisaiminette Oigh Mg#, elevatedNi, Cr, Co and Sc contents)indicatesa mantle derivation. However, the wide range nMgf (5G-73),SiO2 (47-59 wt;90), and atkali (3.G8.5wt.qo) contents and systematicchemicalvariation all indi-cate a significant amount of differentiation (or contami-nation); magmamixing is supprted by the uniquely zonedamphiboles. The elevated rIi+lement contents (Ba, Zr,Rb, REE, efc.) n the more mafic membersof ttresuite sug-gestan enrichedmantle source.Despite somesimilaritieswith kajanite and cocite, the Linhaisai minette is groupedwith typical minettes. In addition, the Linhaisai minettebears no lamproite affinities beyond tlose of typicalminettes.We suggesthat tle alluvial diamondsof centralKalimantan owe their surficial existenceo an unidentifiedlamproite or kimberlite in Borneo or adjacent souttreastAsia.Keywords: amprophyre,minefre,rnajor- and trace+lementgeochemistry, petrology, mafic magmas, mineralchemistry,geocbronology,Katimantan, Indonesia' dia-monds.

lPresent address: 5952 Sklrfarm Drive, Castro Valley,California 94552'U.S.A.2present address: 1m{() E. Grand Ave., Englewood,Colorado80lll, U.S.A.

SoMnaarnsDans le cadred'une recherchede la sourceprimaire dediamantsau Kalimantancontral' enIndcinsie'nou$ avonsd&ouvert de petites dykes non-diamantifOresde minette

mafique i felsique,mis eo placerdcemment(8 Ma) e f3i-bleprofondeur. Cesdyke recoupentdsmudstonesetdesgres intertitds noo-rnarins d'6ge Terti4r-e preco-ceet desLudstones marins d'6ge Cr&tac ardif dans la r6giond'omont de a rivilre Karamu, dans e nord de a provincedeBarito. Lesrochessont vsiculairer,ma$sives t brdchi-fiees,et varient d'une compositionmafique intermddiaire'Elles contiennent: pblogopite i zonation mod6re,allantd'une valeur du tvtg# [rapport lCnMg/(Mg + Fe)] de 82i 73du coeur d la bordure, hornblende pargasitique mon-trant deux zone$,un cqeur idiomorphe vert, riche en fer'e textue en tamis Mg# du coeur 70, de la bordure 47)'et utrebordure brune plus magndsienneMe# de 65 (int6-rieur) I 71 (bordure)], clinopyroxbnezondd coeurd'auglteQr,fg*gO)ei bordure de diopsideau varitd {9 sai.le $vts*iz)isanidne (atrsor3?Art, maentite itanifare,'ilmenit,serpentine enps6riOohorinose deI'otivine), apatite, rutileet zircon.Lescompositionsglohles sont ypiquesdeminet-tes en trmesdesCl6mentsmajeurs, mineurs et en traces'Le caract0reprimitif de a mineue deLinhaisai Mg# 6lev'hautesteneursen Ni, Cr, Co et Sc) estune indication desaprove,lranceu manteau.Toutefois, es ntervallesenMg#(5G?3) et en concentrationsdeSiOz(47-59%)-et desalca-tins (f.O-S.Sqo), ainsi que les variations chimiques syst6-matiques,indiquent une diffrenciation (ou une coatami-natioi) importante. un mlangedemagnas semblendiqupar la zonation particulibre de I'amphibole. Les concen-irations6levesn61fuents ncompatiblc i large ayon (Ba"Zr, Rb, terres rares, elc.) dans lesmembresrelativementmiliques de I'associatiou font pensera un manteauenri-chi cohme source.Malgrdquelquesesse'mblanceslakaja-nite et Ia cocite' on regroupe la minette de Linhaisaiaveclesminetts rypiquc. Deplus,ellene montrepasplusd'af-i-nit6 avec es-iamproitesqu'une minette typique, Les {ia-mants desalluvions du Kalimantan central seraientreli6slun gisement amproitique ou kimberlitique non ideltifi6du Borneo ou des fuions contigusdu Sud-Estde fAsie'

Clraduit par la R6action)Mots-clds: lamprophyre, minette' chimisme (6l6mentsmajeurs, mineurs) Ftrologie, magmasmafiques, chi'miJme des minraux, gochronologie, Kalimatrtan'Indondsie, diamants.23


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24INTRoDUCTIoN

A minette is a biotite-K-feldspar-rich "shoshonit-ic" or "calc-alkaliyre" lamprophyre (Wimmenauer1973,Velde 1969,Rock 1977,lg84). Minettesgener-

THE CANADIAN MINERALOGIST

Loclion MapISabah

ally are regarded as being derived from the mantle(e.g.,Kay & Gast 1973,Jahn193, Bachinski& Scottln9, 1980, ahn et al. 199), although their genesisis the subject of ongoing vigorous debate a9., Velde1971,N6mec1973,lns, Rock 1980,1984,1987).

4is , nR . / ' 'V'J"_-,_\.,,y;.t_

i$"t1 1 4 " 1 1 5 .ffi-1o 5 0 1 @ KMfentary F Sandstones.udstones.' r - - J v o t @ n t 6 r @ K s

lF-l Basalicanoesdeo rhyoritel:31 llows.ulfs.py6clasti6FiiTl plateauSandstonenon.mdne)[ii!:ljl l@allynctudos rins shates

creiac@uem [Xt;Tj:1il.'S,fines.hares)Psmo- E- N4etamrchicnd ntrusive ksCarbonlrercus 4 horntets. chist

- - Majorleltsf rouu".,

a Tertiaryntormediateo elsic lugs

Ftc. l. Geologicaland location maps howing the Linhaisai minette. (a) Regionalgeologicalmap (basedon van Bemme-len 1949' Zeylmansvan Emmichoven 1939,and unpublished Anaconda and C.P. Anekatambang maps). (b) Locdlocation map showing he occurrencesof miuette subcropand outcrop in the Linhaisai and Karamu and River areas.(c) Local geological map showing the Linhaisai minette dyke, tle bestdiscovered exposure n the area. (d) Obliqueaerial photograph of the obscuredLinhaisai River at the LM.

0'@':l


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MINETTE DYKE AND BORNEO DIAMONDS 25This study contributes petrological and geochemi-cal data on the Linhaisai Minette (LM) suite fromCentral Kalimantan, Indonesia, which indicate acomplexpetrogenesisof mantle-derivedmelts. The8-Ma LM is amongthe youngestminettes reportedin Rock (1984),secondonly to thoseof theKarako-rum distrist of Pakistan (Desio 1979).Alluvial diamonds have been recovered inKalimantan Qiterally translated as "River of Goldand Diamonds") for over 1500years (Koolhoven1935).Thesediamond depositsoccur chiefly in threeprovinces: the Landak region of West Kalimantan(Witkamp l9t2), tbe Barito Province of CentralKalimantan (tlovig 1930)andin the Meratus Rangeregion of southwestKalimantan (Koolhoven 1935,and references ited therein).Theprimary source orthesediamondshas been an enigmafor some ime,although most authors have regarded the Pamalibreccia of southeastKalimantan as a kimberlite andthe "Borneo.type" sourcerock for the alluvial dia-monds (e.9.,Bardet 1977 Orlov 1977).Since he re-cent reinterpretation of the Pamali breccia as asedimentary conglomerate with local ophioliteprovenance@ergmanet al. 1987), he Borneo dia-mond sagahas returned to an unresolvedstatus inthe field of diamond genesis.The LM was discoveredby the third author dur-int a searchfor the elusiveprimary sourceof allu-vial diamonds in Central Kalimantan. Minette cob-bles were traced upstream to ttreir parent outcropduring routine stream-sedimentsampling.This dis-covery was significant because,as discussedater,minettes are closelyrelated to lamproites, which arenow recognizedas a well-established,major, primarysource of diamonds n Australia and the U.S.A.(e.9., Jaques et al. 1984, Scott-Smith & Skinner1984). The LM occurs within 150 km of the typelocality of kajanite, an olivine-leucite-nepheline-phlogopite-richterite-magnetite-chromite rock(from the Kajan River) initially reportedby Brouwer(1909) and later discussedby Lacroix (1925) artdWagner(1980. This kajanite possessesomecom-positional and mineralogical similarities with lam-proites @ergnan 1987,Wagner 198O but is not alamproite sensu stricto becauseof the presenceofnepheline and anomalous mineral compositions.Despite some compositional similarities with lam-proites, the LM possesseso more affinity to lam-proitethan doesany otherqpical minette.This paperdiscusses he age, mineralogy, geochemistry andpetrogenesisof the LM and places t in the contextof magmatic activity in Kalimantan, as well as n thecontext of the setting of minettesfrom elsewherenthe world.

Geor,octcAr. CoNrBxrRegional geological and tectonic settingThe LM occursn theupstreamKaramu River area

in the northern Barito Provinceof CentralKaliman-tan at 0o20'N, 114o53'E Fig. l) . The local eleva-tion is about 2fi) m but rises rapidly in the high-gradientstreamsystem o a [email protected] portion of Central Kalimantan forms thesoutheasternmargn of the Sundalandcontinentalcraton, locally formed by Permo-Carboniferous toTriassicmetamorphic and granitic rocks and youn-gerrocks(e.g.,Umbgrove1938,van Bemmelen1949'Hamilton 1978).The region is bound to the northby a Tertiary subduction complex of the Baram,Lupar and Rajang Groups (ophiolite, radiolari?ncherts, greywackesand argillites in a structurallyimbricated complex of southward-dipping thrustblocks). The Lupar chert-ophiolite line, the RajangGroup (m6lange)and Late Cretaceous o Eocene,intermediateto acid, calc-alkalinsvelcanic andplu-tonic rocks form threeparallel beltsthat havegener-ally been regarded as defining an Early Tertiarysouthwestwaxd-dippingocean-continentEarly Ter-tiary convergentmargin in Borneo(Katili 1971' 1973,Haile 1968,Hutchison 1973,Hamilton 1978,Wil-liams & Heryanto 1985)which is continuouswith theEastAsian(China-Indochina)complexof similar age(Iaylor & Hayes1982).The southwarddipping sub-duction zone s also consistentwith the zonation ofCretaceouso Miocene aulg'allkaline gneousrocks;tonalites, diorites and granodiorites aremost abun-dant in the northern SchwanerMountain area andalkalineeranitesandmonzonitesaremost abundantto the south (Sudradjat 1976,Batan 1976,Hamil-ton 1978).The LM occurs ust eastof the Miiller Mountainson the central portion of the Kuching zone of vanBemmelen(1949) and Haile (1974). The Kuchingzone records a complex history of late Paleozoic'Mesozoicand Cenozoicsedimentation,folding andmagmatism. Widespread Tertiary sedimentationocCurred n a shallow marine environment, whichwas ater subjected o the intrusion and extrusionofover 400km3 of magmaticrocks in the mid-Tertiaryand over 800 km3 in the latest Tertiary (Rose &Hartono 1978,Haile 1974).TheseTertiary depositshavebeendeformed by seVeral old-systemswhoseaxial trends range from northerly to east-northeasterly in the area of the LM.Local setting

The local geology s charasterized argely by pre-Cretaceousmetamorphic rocks, Cretaceousmarineshalesand sandstones,and the early to middle Ter-tiary PlateauSandstone e.9., Koolhoven 1935,vanBemmelen1949).The most extensivecountry rockis the Oligocene Plateau Sandstone. Cenozoicandesitic obasaltic volcanicrocks (plugs,necksand -flows) arewidely dispersedmmediatelysouthof theLM area (Fig. l).


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26 THE CANADIAN MINERALOGISTThe LM locally intruded northeasterly striking,gently dipping, uppr Cretaceous, interbeddedmarinemudstonesand sandstonesllorowu Forma-tion?). The Cretaceous strata are exposed onlylocally, wherethe more resistant and thick PlateauSandstone has been eroded. This complex (andunmapped)dutcroppattern is not apparent n Figurela, which shows he area coveredby the more exten-sive Plateau Sandstonehat overlies he Cretaceousstrata. AIso not shown in Figure la are scatteredexposruesof the Late Paleozoicmetamorphicrocksoccurring as windows in the Plateau Sandstone.These ocksare best exposedn lowJying streamval-Ieys where the overlying Cretaceousand Tertiarystrata have been removed by erosion.Wheremassive, le intrusive LM bodiesgenerallyform positive topographic features, although theyare locally extensivelyweatherednear contactsandform topographic depressions.The intrusive rockscompriseseveraldykesthat srop out within a 5 x5 km area; the largestbodiesdiscoveredare cut bythe Karamu River and its tributary, the LirrhaisaiRiver. The macroscopic exturesareextremely vari-able; the rock ranges rom medium-grainedmassiveto fine-grained vesicular or brecciated. Well-developedcolumnar jointing characterizesone sec-tion of the Linhaisai River exposure.Most exposedintrusive sontacts display discordant breccia-richzones,although a few contactsaresill-like andpos-sibly concordant in nature. One well-exposeddykehas hermallyaltered he nearlyunconsolidatedmud-stonewallrock to shale within 0 to 2 metersof tleintrusive contacts.The intrusive rocks are extremely hard wherefresh; some moderately weatheredzonesdisplay apatchytexture reminiscentof theglobular structuresor ocellartexturescharacteristicofall lamprophyres(c/ Rock 1984,Cooper 1979).Extremelyweatheredzonesare representedby a dark green-brownmica-rich soil. The local emplacementof the minettebodieswasstructurallycontrolledby a seriesof smallnorfherly trending faults. Parts ofthe dykesdisplayveining by a more felsic pegmatitic material thatforms both sharpandgradational contactswith theminette. Thesevein contacts are characterizedbyabundant, zoned, coarse-grainedamphibole andfeldspar.

TABLE1. (.AR A6[ DATAONPHLOOOPIIE TPANATES'FROI'I'IIE II{HAISAIMI'IETTEruAr rad roAr radSmple* ( ( r t . t ) (x IO'ml/s) tFto-EaT

Late Cenozoic magmatism in north-centralKalimantanVan Bemmelen (1949) defined a NE-trendingl5O-km-widebelt of Neogene-Quaternaryvolcanicrocks that bisects Borneo. In the upper Barito andKapuas River region, this belt consists of Neogenevolcanicrocksof the (from NE to SW)Nieuwenhuisand Iran Mountains, Upper Kapuas Mountains,Miiller Mountains and Madi uplands. The belt isbounded to the southeast by Quaternary volcaniccentersat Murai, Beluh,and BawangAso. Althoughdetailed geochronologicalwork has not been con-ducted on the upper Barito River Tertiary volcaniccentersand plutonic complexes, he rocks are litho-Iogically and structurally similar to rocks that havebeenstudied o the westand nortl @ergman,unpub-Iisheddata). Williams & Heryanto (1985)describedthe widespreadG3GMa cals-alkalineSintang ntru-sivebodies,200-300km to tle west of the LM (malicto felsichigh-levelstocksofdiorite, granodioriteandgranite,and sillsof basdt, andsite and dacite). Kirk(1968)discussed 16- l9-Vta cdc-alkaline intrusivesuite in Sarawak, locatedmore than 150 km to thenorth of the LM. The widespreadTertiary volcanicrocksto the south of the LM include he followingrecognizedunits: the Habaon andesiteporphyry, theMasuparia Volcanics (andesite o dacite flows andvolcaniclastic rocks), the Kuatan and Lahung Vol-canics basalt lows, tuffs, andvolcaniclastic ocks),

the Sian Andesite, the Kasale Basalt, Tupuh Vol-canics(flow and volcaniclastic rocks) (Metal Min-ing Agency of Japan 1979,Supriatna & Rustandil98l). The Masupariaand Tupuh systems ossessepithermal-type gold mineralization. Williams &Heryanto (1985) attributed the upper Tertiary toQuaternarymagmatismto post-subductionmeltingdue to crustal thickening and increasedheat-flow.Although lamprophyre dykes had not been oundpreviously in the vicinity of the LM in CentralKalimantan, earlier Dutch workers systematicallymapped their widespread distribution in westernKalimantan - .9., the minette, kersantite, spessar-tite, camptonite and vogesitedykesnoted by van Es(1918), Zeylmans van Emmichoven (1939) andZeylnans van Emmichoven & ter Bruggen (1935).

AceConventional 4oK-40Armethods were used todatephlogopite separates rom two unaltered rosksCIable 1). The samplesyielded concordant agesof7 7 andT 8 ( t 0.3 Ma). The ntrusiveageof the LMis limited by field relationships to postOligocene

(


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MINETTE DYKE AND BORNEO DIAMONDS

Frc.2. Photomicrographs and photomacrographs of various Linhaisai minette samples.(a) Photomicrogr,ap_h.of -lshowingvesicllaiitl', glassygroundmass ndqusnchcrystalsof augiteandolivine. (b)Photomicrographof K-5 showingabundint phtogopitJtatls. 1C1notomicrograph of K-2 showing ocellar texture. (d-f) Amphibole p'henocrystsnspecimenK-4. (giOlivine pnenocrystpseudomorph n K-SR. O) Olivine phenocrystpseudomorph n K-5-1. (i) Pho-tograph of slabi of the LM showing he varied textures,Scalebars: (a-c, f, g,h) I mm, (d,e)0.5 mm, (i) 5 cm.


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28 THE CANADIAN MINERALOCISTTABLI 2.. REPRESTITIATIIELECIIOIHTICROPROEE{I'IPOSIITONOF LII{IAISAI iltMTTl PHASTS

!hlogopltel t 12 t 7!r02 38.5 40.1 38.?Tr02 4.05 4.00 4.0741203 2. t 12.5 13.9Cr20! .50 .45 .39Fcor t l .6 8.80 8.43r|no .1.3 .00 .02lg 0 17,4 19.6 19.4C!0 .04 .Ol .04(20 9.54 9.92 8.91rhr0 .t6 .15 .56r .r2 .85 1.1'lcl .01 .m .02B. .08 .0!t .17I 95.4 96.5 95.7n$ 72.5 79.9 80.3

38.9 38.1 38.5d.8? 4.31 4.0614.0 13.7 t3.8.03 .21 .439.t0 9.20 8.1.60.5 .06 .m17.5 18.3 t9. '.28 .03 [email protected] 8.50 8.r8t .@ .66 .621.80 1.60 .19.03 .00 .01.26 . t l .1 695.9 94.8 91.977.3 ?7.9 81.0

38.7 39.2 37.83.68 5.05 5.2413.6 13.3 13.3.41 .18 .q ,7.97 8.87 lo. t.0 3 .15 .1619.9 r9.3 18.0.03 ,01 .1 58.73 8.49 8.64.54 .12 .78.7 5 2.t9 2.16.00 .03 .01.07 .28 .A.9r.{ 97.6 96.5aL6 79.2 75.7

38.6 38.4 38.9 3r.54.?t 4.m 4.10 7.4713.9 14.3 14.5 13.3.42 .38 .43 .008.28 8.70 8.32 t0.3.03 .10 .04 .t6r9.2 tg.l 19.6 16.7.@ .ott .00 .029.92 9.20 9.55 9.07.56 .r0 .59 .r0.5 ' 1.32 .83 1.05.oz .01 .02 .m.14 .t0 .15 .0094.8 96.4 96.9 96.380.5 79.4 80.r 74.3

38.5 36.9 39.13.05 7.r ) 3.9314.2 14.3 13.4?.08 .00 .0t4.65 10.5 7.16.00 .15 .0721.9 16.3 20.6.01 .03 .039.97 8.36 9.19.35 .66 .55.71 r .07 .86.@ .03 .01.@ .05 .0095.4 95.7 95.589.3 n.2 A2.4

38.1 38.7 39.1 39,27.3: t 3.Ot 3.56 3.r l14.6 14.1 13.7 14.0.0t 2.03 .15 1.739.77 4.80 8.04 4.61.t7 .lIJ .08 .{t015.7 21.5 20.7 21.9.!5 ,lllt .03 .014. 2 9.3t 9. t0 9.61.r7 .42 .59 .381.(F .73 l .5l .9 2.04 .00 .02 .01.@ .00 .00. .0095.9 94.6 96.5 96.573.8 88.9 81.9 89.4

40.3 38.53.21 3.63t3.t 13.7.92 .104.96 t.6l.00 .0922.4 zt.l.02 [email protected] 9,40.44 .66.86 r.76.01 .o2.&) [email protected] 96.688.9 83.40ita ln $.t. rht: to0rf&l(il9*Fel) (.t6tc proport.tons).!9!9!: ,rdlts6 l-12 r@ sdple (-1, 13-22@-(-5, (l) rlo ond 2) coreot 150 550F plcte, (3) @rgln of 7515@ grrrn {ldJ.cent o cpx nlltssfl-2 --T.ble 29)' (a) rls.d (5) @re of 25-r,3@q9 piaie. (6) rl; ind (7) @e of 60 r'40b s ptiti ori ot z0 r 2rlo " itne,'(sj rio ani iioy iori orl?0.r 5@4 Plate' (tl) 116.'td l?) coreor an-rzs on piaiel (r3) rro'aid (la) @reor ioo-r 5ooo pti*, i i5) 'r o i'ra to l aid or 130 '946um late,(17) lo and 18 )ore of lm x 5d )@ plate, (19) lo and z,o)'dre'of 3o r ico'o piaie, it ) ii o aau'izij 'oi.eor t60 3ltl '!n pl.re.

rrBLE2L ntPREsElftArltt ltclR0il-ncaopRoB[o@osrrtors0F ui&AtsAl tlmrrE pHtsrs corr,o)

!6Dhl bol e4 5 6 7 8 9 lO tl t2 ta 14 t5 t5 I t l8sf02 42.4 10.5 10.0 43.1 41.4 41.4 43.0 43.1 44.t 12.8 q2.4 40.8 43.5 42.s 42.3 d!.5 42.g 41.5ll02 2'&3 3.!6 2.63 2. 9 3.40 2,40 2.81 2.88 z..ot z.gt 3.u ?.r3 2.75 z.t6 l.zg r.61 2.81 2,454120311.4 ll.0 13.6 ll.t l l.0 I2.l 10.0 10.5 12.2 10.3 11.0 12.6 9.8/ to.3 ll.z ll.4 ro.5 lt.t!'i9, .(Il .@ .00 .ot .03 .01 .03 .03 .34 .03 .02 .(x) .05 ,(E .03 .(x) .00 .03Fe0'| l r.6 lo-t 16.0 12.4 lt.r 14.1 u.l l l.2 9.90 1t,1 ll.t 15.5 10., t2., 15.9 17.6 ll.O r4.9lino .08 .13 .m .1 4 .1 5 .19 .!o .14 .13 .12 .ll .22 .12 .t0 .25 .28 .10 .2rl{90 14.0 14.9 10.5 12.9 11.2 11.8 14.9 ti.8 15.5 t4.7 14.2 10.8 l4.B 14.0 u.3 l0.z 14.7 rz,Lcao 11.4 r1.l 10.6 10.3 11.5 t1.? tr.z 11.4 to.2 11.{ rt.z l t . t tr.4 lr,2 rr.4 11.4 ll.5 1t.3(: 0 l.l7 l.4z 1.02 1.20 .9 9 r.26 l.l3 1.rg .30 l.l0 l.m r.0z l.16 l.u 1.35 1.36 l.r5 1.50&20 2.16 2.26 2.38 2.46 2.24 1.98 2.2a z.t6 2.07 z.t6 2.23 z.u 2.31 z,z5 l.g9 2.00 z.t6 z.uBao .02 .00 .00 .00 .(n .00 .00 .02 .03 .00 .m .00 .01 .(x) .(X! .0{ .03 .mF .25 .32 .08 .40 ,69 .30 .n .$ .0a .45 .43 ,54 .8t .27 .31 .26 .rt4 .30cl .03 .00 .m .01 .02 ,03 .04 .00 .03 .o2 .o2 .0s ,03 .ol .05 .06 .01 .(}{I 97.5 97.5 9?.1 97.1 9r.3 96.8 96.9 97.8 97.6 97.r 97.0 97.0 97.5 97.4 s7.2 s7.6 97.3 s7.5ts 6a.2 70.9 53.6 64.6 68.1 59,5 ?0.3 69.9 73.4 70.1 6s.2 55.2 70.9 66.4 55.6 50.2 70.3 58,8t' 16.868 16.936 16.8q' r6.e49 17.01i 16.87g 16.89g 16.59, 16.910 16.899 16.98r 16.9g? 16.994 16.930 16.9r, r6.94a 16.919 16.967

0ata ln |t.1.'pr.0!23 (lrcludlng 0n"1) ibt6: rll .n.lys$.4re.f@ s@ple -4. (l) @rgln ond(2) tnterto. prft3 ot bry rtq &ne, (3) @rgtn lnd (4) tntertorpart3 of.g@n core.zoreof stn @ euhedr.l-groln. (5) urgl; or rlo zdm, a6i;a"gi!';id iii "i*'ir-g'iin com :ore of 5tx)@ gr.tn "ggr"gatu;-i8j-lB @rgln-Erd 9) lnterlor core@ne f.euhforal io'@ g;.|n, (lo) ri n orgin ot-4@n oiredralgrain (lt) @rgtn ard (iz)'tnidtor 6i oilm rrozone.or-?00P e{!-e.drr!raln' (13)mrll-n_!rld 14 ) tnterior pi*i 6r o' m it ' io*,-tist 'i.gii "fo-iioi-ri,t"'r6' po*"'i i 'g*in o*-.o*-ii roo o'euhedralgraln, (17) rln rnd (18) core6f ZS0 i Eirtearatorain.

TABLEc. REPREsEtlrlrlvELE0TR0I-I{ICRoPRGEo.postrlons 0F trm$IsAI t{tt{ETnpHAsEscorrD)

Cl Inoplmxem ?st02Tl02Al203Cr,0.Feotin0!lg0Cn0(zoiladil{stIrs0Ent s

50.6 51.2 49.8 51.2 51.01.01 1.02 1.16 .a7 .9 53.62 3.72 4.40 2. * 3.62.50 .sl .00 .07 .016.A' 6.69 8.49 7.39 8.37.1 8 .13 .22 .1 4 .29r4.9 1s.3 13.? 15.0 14.54.9 20.8 zt.t 2t.2 20.0.@ .00 .03 .01 .18.6 0 .59 .4 9 .52 .53ge.r 100.3 100.1 99.3 99.579.O 80.0 73.1 78.0 71.94.019 4.019 4.034 4.019 4.01844.3 43.9 45.7 44.2 42.644.r 44.9 40.1 43.6 43.011.7 t ' .z 14.3 L2.3 14.4

53.6 49.3 52.6.37 1.55 .501.20 3.72 1.51.35 .00 .433.87 6.70 4.11.09 .1 5 .0 918.4 14.9 17.32t.2 22.4 2L,5.01 .03 .02.37 .47 .3999.5 99.4 98.489.3 79.5 88.04.028 4.061 4.02642.5 46.2 44.051.3 42.8 49.36 .2 11.0 6,7

50.4 50.13.37 4.03.09 .047.63 9.25.l? .1614.6 13.621.0 zt.l.02 .01

98.9 100.171.0 72.14.026 4.03144.4 44.542.9 40.0l?.8 15.5

51.4 49.7.89 1.343.19 3.18.08 .017. U 6.t5.11 .1 315.8 15.320.8 n.4.02 .03.49 .3999.9 99.218.7 79.84.02t 4.05743.2 45.6it4.8 43.4t2 . t 11.0Data n |t.1. l{o' En' Fs: ltmlc prcportlonsof Fllastonlte, enstrtlte & feroslllte, no@llzed to100t.'p::0:6 Sgg: erlJ6es.l-8 are f@ smple K-4, 9-12 fm sMple K-5. (l) rto and (Z) core oflr u !o qn{rat.gratn (adJacento phlogoplte@lysts f3 _ Tablo2a), (3 ) ri r ud (4)'c6re of f00 F!euhedrr'r nrn (5) rrn and (6) core'of 30'u uherriar d;h, at) rio ird (gl ore ol iori n durriiiaf 'sraln' (s) frn and (lo) cori 6f rg5 ud euhedrar rarn,-(iry'rio'uJ (iti @L-;i140 ,,i-"ii"iili-iiir".


7/21

29INETTE DYKE AND BORNEO DIAMONDSTSI A. WESmn[ nfcr@n0mmt mrTrm s LrMr$! ilEm 'Ns (c0n'|D]

elhll reldlstr 2 - -3-

Dd. ln 6.t. &r O, &: .t6lc roFdld3 ot .lbt!o, dhla* t edi!!e, m@lld b [email protected] &6r -p &t ror splEl. d &$ tor !l@le (catbn an)M : r o l d r F : , l t I E I - 5 r t f u 3 3 F a l m . ( l ) @ m o f 7 5 r l m @ F t n . ( 2 ) r l D d ( 3 ) @ f r d S r l a d q ! t n , ( l ) r l od (5) cm of lm r l$ @ rrh, (5) core d f r 16 B !.rln.

r&Tl ot l6: t l l rr u i- 5 s@33 s r r l n i . Md@@tl td. (l ) 6E or 12 6 qrd tn , ( 2 ) sn d 6 @ F. tn . (3 ) no.d (1 )cm or 14 @ F. l n r (5 ) il 6 d (6 ) m o l Z q F. rn , (r ) @n or 5 @ rr tnr l l m l t o - (8 ) no d {9 ) on or?4 @ r.in.

sr02 6.1 s,2 d.9 fi.6 a.2 s.$Al2q 19,2 1915 19.3 19.9 19.3 18.8t20t .41 .51 .!9 .45 .18 .49.a .0 .07 ,6 .6 .&ri0o .0t .01 ,01 .01 .01 .0rw .95 l.s ,e l.u .B .41M .m ,07 .m .n .@ .msd .16 .31 .0r ,61 .11 .19&20 4.s 4.14 4,53 4.75 4.lt 3.&x20 l0.l 9.s 10.0 9,6 10.4 u.3t 9.4 S.7 t0.3 S.8 $.5 S.'s 37.6 37.0 S.2 4t.9 S.2 3.2& 5r.8 57.r 5r.0 ?.6 59.3 &,6& {.6 5,3 3.8 5.5 t .3 ?.3I. 5.0tr 5.m !.u6 5.@ 5.OA 5.m

sro, .t0 .26 ,14 .t0 .59 .10 .ll .lr .llTr0, 6.9 8.9 7.r2 8.A 8.S 9,39 9.lt S.3 10.5[r ! .57 1.55 .V .8 l .$ r .S 1.46 .m . l tor0! .03 .05 .6 .u .05 .6 .6 .01 .qt20r .9 .9 $.8 S.? 48.8 .2 49.0 .m 5'3trd 9,6 33.4 il.8 9.5 3.? 35.0 3.4 55.2 S.3m t . l r 1.6 .9 3 l. u I .d r . l l l . l l l .6 l .sao .$ 2.6t .& 1.9 2.& ?.13 2.m .& r.59ilo .01 .@ .@ ,0, .m .05 .o? .0 .&60 .u .22 .49 .t0 .49 .15 .!5 .t4 .SI 97.0 S.9 $.4 97.0 97.9 $.t 91.' 9.8 S.3ln 8.91 a.9E 24.0n 24.A4 8.9S 23.9$ 23.W A.5q 24.0?'

7-10-Ma intrusions in the Sintang ar to the westof the LM (P. Williams, written comm. 1987).PeTRocRAPHY

In hand specimen(Fig. 2), the LM is extremelyvariable in color, ranging from grey-black fine-grainedmafic rock (someglassy),hrcuel daxkgreenmedium-grained varieties, to light brown to greymedium-grained eldspathictypes.All varietiespos-sessan abundanceof phlogopite phenocrysts (> l0- 30 modal 9o). Vesicularif is characteristic of allrocks and ranges rom o l-590 (< I mm veicles) to20-30t/o (24 mm vesicles).In thin sestion (Fig. 2), the LM consists ofphenocrysts f abundantphlogopite aths(commonlyzoned, witl a dark rim), amphibole with two"reverselyzoned" (internally normally zoned)con-centric domains (restrictedto the more felsic vari-ants), serpentinizedolivine, and (restricted to themore mafis variants) augite n a groundmassof thesamemineralogy in addition to a glassymesostasisand sanidine, apatite, Fe-Ti oxides,pyrite and rareplagioclase(andesine)and quartz. Rocks of inter-mediatecomposition display a well-developedocel-lar texture (Fig. 2) consisting of 2-10 mm ovoiddomains definedby a concentric im rich in feldsparand a central portion rich in phlogopite crains.MINERALCHEMISTRY

Wavelength-dispersion electron-microprobeanalyseswereperformed on major phasesrom twocompositional end members from tle Linhaisaiexposure:a primitive mafic sample K-5) anda moreevolved felsic variety (K-4). In all, core, rim andintermediate spots (E n-3N) were analyzed onapproximately l0 grainseachof phlogopite, amphi-bole, clinopyroxene,oxidephases, nd feldspar romeach sample. Representative analytical data are

presentedn Tables2a-d; analytical methodology issummarizedin the APPendix.Phlogopite

In the most primitive rock, trioctahedral micaphenocrysts reTi- andMg-rich andnormally zoned;tle corewith Mg# [atomic 100* Me;/Mg+Fe)] =89, 2.0 wt.tlo Cr2O3,3 wt.9o TiO2, and rim wilhMg# = 73,


8/21

Primttivetn"tt"-47o/o SlO2 |310 pm r ILWholeEvolvedMlnette58% SiOz55 ppm Ni

Whole rock

5-JIr cllnopyroxsnsg

30 THE CANADIAN MINERALOGIST

80Msf

characterized y low K, Fe or high Na, F contentsand intermediate zones with respectivehigher orlower contentsof the elementsand a rim with thereversepatterns (Fig. 4a-iv).Clinopyroscene

Clinopyroxene grains lange from an augite coreto an augite-diopside(var. salite) rim (Fig. 5). In theprimitive variety, augitegrains are normally zonedudth a core of Mg# = 90, l-2 wt.9o Al2Or, 0.4wt.9o Cr2O3,0.5 wt.Vo TiO, and a rim of Mg# =80, 3-4 wt.Vo Al2Or, 0.01 wt.% Cr2O3and 1.6wt.9o TiO2. The more differentiatedrock containsaugite of similarbut more wolved compositionswitha core of Mg# = 80, 0.8 wt.9o Cr2O3,2-3 wt.VoAlrO, and 0.9 wt.9o TiO, and a grain margin withMg# = 72,O.1rvt.9oCr2O3, 4wt,Vo Al2O. and1.2 wt.tlo TiOz (Fig. 6). The margin is generally

't0U

oElL 20

1 001 0020

1 080 90c

80Ms# 90b90aFtc. 3. Plot of LM phlogopile (a)AI2O3 versusMg# and (b) TiO, versusMg#; open symbolsrepresenl he more primi-1t"9 fppJ. K-5; filled symbolsthe more evolvedK-4; where significant, coie (Ci to rim (R) zoning trends withinindividual phenocrystsareschematicallyshown with the arrows. 1c;Histograms oi vtg* oipirtogopije, ctinopyro"-eneand amphibole s6mparing the primitive with evolved phases.Whole-rock Mg# oatue" -.1tio rno*o.

of the nearby kajanite (Wagner 1986). Like theminettephlogopitesdiscussed y Bachinski& SimF-son(1984), he LM micashowsno appreciablecorre-lation betweenAl and Mg#, but it showsa strongerTi-Mg# negativecovariation. In phlogopite of iheevolvedLM sampleK4, Ba and Ti show a positivecorrelation like that displayed by phlogopite inminettefrom Devonshire Jones& Smith t9fi, ari-zona (Jones & Smith 1983) and Czechoslovakia(Schulzeet ql. t986).Compositional profiles arevariableand complex;repre!9ryative profiles are illustrated in Figure 4a.The following distinct profile patternsareobserved:(a)gain interior with uniform Si, Al and gradualydgcreasingCr, K, Mg and Si or increasingFe, Ti,Na and F contents near margin, producing bell-shapedprofiles (Fig. 4a-i, ii, iii); (b) homogeneowprofiles; and (c) more complexprofiles with core


9/21

MINETTE DYKE AND BORNEO DIAMONDS 3 l*.ll \-.2- ^ l"* rJ \-.-

ol ,/\t0 r*, nJ .Z-.-**1 a'r,o"ldl *a J^.^ 41t'",r1 '-

. 4 1Nr' rl \_.-.r'l 5 r t'u lv,310m, 0 3 " ,

U80fr

E ,0,[ '*'

l] *r----- \--';-g -\-/-/-3 Jn - l6J r++rrr+2 1

^ro"""1f943sio,t * ll \\---r 3 aF ua.oL - r J

F I \._G._.--0 JU n O L *

0 J


10/21

32 THE CANADIAN MINERALOCISTI5 '\s z

TiO2 .,wtVo

0

Al203wlo/o

l r l80 900 I90bI800Ms# A Ms#

ef sening in several representative amphibolephenocrysts.Despite he marked optical discontinui-ties observed, the following distinct patterns areapparent: (a)gfain interiors with uniform or gradu-ally decreasingAl, Fe or increasingF, Na, Si, Mg,Ca sontents near grain margins (seeFig. ab-i); O)homogeneous rofiles, e,g., Cr, Na, and (c) morecomplex profiles, with corescharasterizedby uni-formly low Al or high Si contents,ntermediatezoneswith higher Feor lower Mg contents, and rims witllower Feor higher Mg conrents Fig. ab-iii). The LMamphibolecompositionsgreatly contrastwith thoseof richterite from the more primitive kajanite(Wagner 1980.Feldspar

Like tlte extensivelyzoned mafic phases,sanidinegrains are relatively heterogeneousand within thessmpositional limits (molar) of Orrr_6rAb,3_aAa2a

AlcOa*ix" 12

Fro. 6. Plot of clinopyroxene (a) Al2O3 venus Mg# and (b) TiO2 ver,szsMg#; sym-bols and zoning trends are the sameas in Figure 3.

Tl02wto/o

rTu 'o a 50 M g #FIG.7. Plot of amphibole (a)Al2O3uer,nr Mg# and (b) TiO2 versusMg#i all analyses rom K-4; opensymbols representanalysesofthe brownish rim zone, filled symbols the dark greenishcore zone. Where significant, core (C) to rim(R) zoning trends are schematically shown.

b1 , , , , I ' r r r l l60 70

AmphiboleIn the more differentiated rocks, euhedralgrainsof pargasitic hornblende (terminology of Rock &Leake 1984)are reverselyzoned, with a deep-greenc9r9and a brown margin, eachseparatedby a mot-tled black reaction or transition zone (Fig. 2c).Within each zone, .,normal,' (Le., decreasingVtd*toward margin) zoning is observed,but the greencore sgenerallymuchmore ..evolved', than the rim(Fig. b). The core zone displays a compositionalrange (interior - margin) of 68-50 Mg#, 1.5-3.0l'_t.?oTiOz,


11/21

MINETTE DYKE AND BORNEO DIAMONDSTABLE.3.MJoR-AND MCE-ELEMENToMPoSITI0NF THE INHAIIAI-MIXEfiE'ND"*-nriEirnsr.cOMpOiirtOruOFNtnErrr, LAMPRoITENDKAJANITEoRcoMPARISoN

33

ave.*tLl nhalsaln nettaK-5-2 K-5-4 K-sR S-5-l 5-6-2 t6-3 (n"ro)(aJanttr,ll46

ive.l. nvg.fi8 dnette lmproltesr02 46.1 51.8noz r.02 1.55Al203 13.9 12.0Fe203 5.9t 5.51Feo 2. 5 2,2ns 8.38 6.67ttro .14 .05Cro 8.8, 4,2Lllaz0 1.35 l.tlKeO 2.15 6.30Pz0s .94 l.t8H201rH20' 'r.9 4.2@2 .3 .rI . l t .315 .00 .04I 9e.4 98.0ligf 65 62

51.1 46.81.36 1.8015,4 10.83.38 3.8?3 . 1 4 . 13.40 10.2.12 .135.09 9.053.99 1.74x.62 3.tl.58 1.45.7 2, r.6 .l.22 .36.13 .0699.6 95.250 7L

49.5 52. rl . l 2 1.5913.8 LL.l3.30 3.193.6 4 .31.10 7.62. l l .186.88 5.2r{ .18 2 .152.9 5 .15.61 1.005.2 2 .6.3 .6.13 .2 9.o2 .0399.6 98.268 65

48.7 51.41.82 r,4210.5 12,41,71 1.445.0 5.49.r9 7.58.09 .t06.33 5.r41.20 2.?o5.62 4.5tt.21 ,t75.0 3.4.2 ,8.38 .24.03 .2298.3 98.393 67

52.0 44,2r.43 2,4512.5 12 .02.43 3.664.5 6.47.65 9.13.1 3 .184.99 8.482.28 2.15{.63 2.85.16 l.t84. 0 3. 9.23 .1 7.13 .0 399.0 98.568 63

1.89 1.2t .8

5i'.1 46.0 43.1 52.61 .7 2 .20 1.84 1.913.2 t2.4 9.27 12.6- 3.t4 6.067.7t 5.58 4.79 t .5 '8.6 12.6 12.4 8. 0. t2 - .18 .13t.? 8.38 8.88 1. 92 .5 1 .62 1.1? e.04.6 4.87 q.tg 6. 0

tl 13.0o l

s.rrL a . L. t05.81.41.21 . 32.f2.83.1 3.55 3.08 2, 20. 4.24.07lo0 100.9 98.6 lO0 1008l3 55

340 580155 420200 1232t tlt7 3t56 52110 84

2 4. '9 3 9

450 280 2q 340 300280 290 320 280 213220 lm lff, 260 m92 0 l t l 7 2 6 m48 52 5l s0 ,xl1501 , 5v. 3I1 . 026

Cr 320 370 64 5m 3@ 310{r lm 470 55 310 260 340Y 2to 240 200 210 160 210Sc 30 It 14 21 18 t8Co 49 36 19 39 55 3lCu 1t0 80 110 150Zn 190 130 140 130sb .2 .2 .l .lA s 3 l l ( lPb 34 38 36 28Br .4 .l .2 .3v 2 < l c 2T! (. 5 .8 1. 5 .8H f 3 3 1 6 2 6 m272

I 'JU51202792095464.9

. 5l lsr0l01345340 3503t 83245.0

1 . 5zN lt o lt o 120 lt o960 970 950 820 ll001200 1lt0 1320 790 150030 20 20 30 zo970 700 120 450 6502 0 2 0 1 0 $ l :5 .4

1 .5 ? .oll 0 160 t01660 1340 13501000 1500 650


12/21

34

caO(ttto/ol

TIIE CANADIAN MINERA,LOGISTt o1412l nI

20

908070Sl02(wt%, 80

J0

Al2O3(wt%)

& Smith 1986)as well as minettes ftom Arizona(Jones& Smith 1983).Baand Srcontenrs fthe LMsanidineare slightly lower than those of sanidine nthe Devonshireminsftg.Fe-Ti oidesTitaniferous magnetite,the principal Fe-Ti oxideobserved, ypically occursas10-25-prngrains n the

80 90b

80 90a

14121 0

Feor I$a%', 0420

4Na2o 3(wt%) 2

10

KzoMo4)

Slo2 e(wr%)FIc.8. Major-element variation diagrams(SiO2and Mg# as the absissa)showingtle compositionsof Linhaisai minetteQarge illed and open circles)comparedwith mineues from the literature (small dots; Rock 1984),and the averageand range(2o) n lamproite compositions@ergman1987).Opencircles represent he two sarnples or which mineralchemical data srist. All analyseshave been r@ast on a volatile-free basis.

oE8l02(r{.t"/4


13/21

MINBTTE DYKE AND BORNEO DIAMONDS 35groundma$s. lmenite rarely occurs. The magnetitegrains are relatively homogeneouswith 7-9 wt'90TiO2, l-3 wt.9o MgO, L-2wt.VoA1203,0.05wt.9oCr263, I wt.Vo MnO and 77-81 wt.9o FeOr.Ilmenitc containrelatively ow Mg ( = I wt.qo MgO)and moderateMn (1-2 wt.9o MnO) contents.

Wnols-Rocr GeocHEl{tstnvMajor and selectedrace-elementdeterminations(26 elements)wereperformed on l0 texturally dis-tinct samples epresenting he entire range of rela-tively fresh and unalteredrock typesobservedn theLinhaisai River exposures.More extensive trace-elementdeterminations(an additional 28 elements)weremade on four samples panning he entirecom-positional range. Results of analytical data arepresented n Table 3; analytical methods are sum-marized in the Appendix.

Major elementsNearly all major elementsdisplay ranges n con-centrations:M-58wt.olo SiO2,10-15wt.9o Al2O'1.0-2,5wt.9o TiO2,7-11 wt.9o MeO, 3-10 wt.9oFeO, 4-9 wt.9o CaO, 14 wt.olaNa2O, 2-6 wt.9oK2O and 0.6-1.3 wt.9o P2O5.Although the LMvaries from mafic to intermediate, the averageLin-haisai composition is nearly identical to that of theaverageminette(fabb 3). The LM ranges rom rela-

tively primitive compositions Kl, K5, 36-3;62-70Mg#,44-47 wt.9o SiO) to extremelyevolvedcom-

positionsGa; 50 Mg#, 58wt.9o SiO2).Compatibleand ncompatible racetlement variations argelyfol-low these major-element features (seebelow).Variation diagrams llustrating the compositionalrelationshipsbetweenmajor elementsn the LM suiteandtypical minettes rom the iterature are llustratdin Figure 8. The variation displayed by the ten LMsamples s similar to that displayed by the entirerange in published minette compositions. In addi-tion, the LM possessesn extremelywide range invarious elemental atios, such as K/Al (0.17-0.58)and K/Na (0.4-3.1,molar), emphasizinghe prob-ability of some subtle alteration.Elements that decreasewith increasingevolutionas indicated by decreasingMg or Mg# and insreas-ing Si include P, Fe, Ti, and Na, whereasAl and Karevariable but generallybehaven an oppositeman-ner. Some elementalratios vary systematicallywiththe degreeof differentiation within the suite. Mostdramatic is the change of AllCa from 1.2 to 3(molar) witl increasingdifferentiation.As observed n Table 3, the averageLM compo-sition is nearly identical to the averageminette, witltthe exception of a slight enrichment in K in theformer. The averageLM showsa marked composi-tional contrast to the "average lamproite" withrespect o Ti, Al, Mg, Ca, Na and K. The kajanitereported by Brouwer (1909)and Waener (1980resembleshe more primitive membersof the LMsuite. The primitive LM samplesdisplay elevatedSiand Al and depressedMg, Fe and P contents, andsimilar K, Na, Ca and Ti contentsrelative to thoseof the kajanite reported by Wagner 0980.

TABLE . CIPI.INORMATIVEOMPOSITIONF THT LINHAISAI 'IINETTE NDCOMPARABLEOCKS

K-4

AverageLinhaisai AverageMinette Minette Kajanite**K-5 K-5-2 K-5-4 K-SR 5-6-1 5-6-2 5-6-3 (r'10) (te50)* i{146q 5.3 3 .9or 13.9 39.8ab 12.4 15.5an 26.2 6.9n e 0 0 1 0 .1 3 . 918.2 16.00 06.1 2 .92 . t 3 .2

d ihyolmti I

8 .921.734.213 . 6

029.O15 . 38 . 101 . 6tz .95.93.603.6I t052.6

0ro . u35 . 4t 2 , 7I . 213 . 6011 . 65 . 1

25.43 .23 . 46 . 1

?3 . 115 . 08 .83 . 54 . 5u.t

4 1 . 1

0?.4d . t

5 .02 .601.41 . 40

2.8 0 1 . r32.0 35.8 28.619.1 10.9 19.77.4 7 .2 11 .10 0 05.4 lL.z 5.720.5 17.6 23.8

2 . t 029.0 I7.920.3 19.610.8 12;80 2.84.4 t6.7

2 .4 2 .7 ! 526.4 34.5 ! 8?0.2 13.6 ! 7.41 1 . 6 5 . 6 r 4 . 60 .4 1 . 7 ! 3 .39 . 1 14 . 9 ! 10 . 5L2 . 8 6 . 5 ! 6 .84 .6 6 .2 r 6 .34 .4 3 . 6 ! 2 .53 . 1 3 . 3 ! 20 . 6 1 .3 I 2 . 52 . 5 2 . 7 L 2 . L

1 . 1 2 . 1 ! 3 . 90 . 4 2 . O6t.2 59.0

04.9 6.2 02.7 2.23 .7 ? .90 0

22.70a 7?.901 0hm 2.4 3.9ap 2.4 3.0cc 0.8 0.2l f o i d 0 0) sa l i c 57 . 9 66 . 3 78 . 5

2 . 3 3 .20 01 .5 2 .50 .7 1 .4r . 2 064.8 61.51 .9 1 . 20 060.7 62.4

3 .20.5054.1

1 0

015.45.75.003.00.72 .853.2Data in t|t.g. Normswere calculated using the reported Feo and Fe203contents.*from Bergman(1987)t*from tlagner (1986)


14/21

36 TI{E CANADIAN MINERALOGIST1000

Ms# sto2lx2o ui l cr

M s # l S i o 2l K 2 o l N t l C l

- r r t t t t t t t t t t t t lLaCe Pr Nd PmSmEuGd Tb Dy Ho Er TmYb Lu57 AToMtc NUMBER t1

Ftc.9. Chondrite-normalized (chondrite from Hanson 199) rare-earth-elementpat-terns cif four Linhaisai minette samplesspanning the full lange in major-elementcomposition. Selectedwhole-rock compositional feature$are listed for easeofcomparison.

100uttE,ozoIo!


15/21

MINETTE DYKE AND BORNEO DIAMONDS 37somparablelithologies are listed in Table 3. Sometrace-elementariations aredisproportionatelyexces-sive comparedto the subtle rangein major-elementcompositions. Most apparent are systematicvaria-tions in several race-elementcontentswiti variousdifferentiation indices(e.9., Mg#, Si, D salic, elc.).For example, in going from the most "primitive"to the most "evolved" compositions in terms ofmajor elementse.g.,K-5, K-SR, K-5-2,K-1' 5-6-1,5-6-2, 3-6-3 primitive toK-2, K-54, K-4 evolved),Cr and Ni decreaseby an order of magnitude, La(and other,LREE) decrease y a factor of 3, andYb(and HREE), Co, Cu, Hf, U and Th decreaseby afactor of 2.Elementssuch asLi, Rb, Sr, Ba, Zr,Y,Ta, andNb show no well-developed systematic variationrelated to Mg, Mg# or Si. Ba and Sr are generallymost enriched n the most evolvedrocls. REE pat-terns (Fig. 9) are subparallel (exceptK-5, which dis-plays a Ce/Yb value twice that of tle other threesample analyzed)andsystematically ecreasen theirdegreeof .LREEenrichment with increasingSi. NonegativeEu anomaly is observed,even or the moreevolvedsamples.This feature s characteristicof allminettes and resultsfrom the restriction of feldsparto the groundmass,ndicating a lack of feldspar rac-tionation.In termsof trace elemenk, the averageLM is verysimilar to tle averageminetteexcept or Cu, Hf, Ni,Cs, Zr and Nb CIable 3). As with major elements,the LM differs greatly from the average amFroite,with the exceptionof similar Sc, Cs, Y and U con-tents. LM Nb contents are unifornly low (1G-20ppm) and similar to the levels observed in calc-alkaline andesiticrocks from subduction zonesandsome lamprophyres (e.9., Caledonian dykes fromScotland: Rock e/ al. 98A. The averageminette,however, is enriched n Nb by a factor of four rela-tive to the LM.Theprimitive LM specimens ossessmuchgtreaterLfuEE (5x) and similar HREE (l-2x) contentscomparedwith the cociteof Wagner & Velde(1980andtle kajanite of Waper 0980. The kaianite andcocite alsopossessmuch lower CelYb ratios (=4Q;than any of the LM rocks analyzed 80-150).Many incompatible elementsare positively cor-relatedwith eachother in the LM. Particularly welldeveloped s a La-Th correlation that follows thekimberlite trend, in contrastto that of minettesandotler lamprophyres, as reviewed by Rogers el a/.(1982). In addition to La-Th, the LM falls outsideof other compositional fields for minettes definedby Rogers et al. (1982).

PBTROGENESISThe major- and trace-elementvariations uotedabovecanbe interpreted in a number of ways. First

and foremost, the Mg#, Mg, Ni and Cr contentsofthe more primitive LM melts, (Mg# 68-73' 8-10wt.9o MgO, Ni 28M70 ppm, Cr 28G-510ppq)demonstiatethat they representprimary melts of amantle peridotite with olivine of Foss-e Frey et at'1978).The generalmantle-derivation of minettes ssupportedby the populations of included xenoliths(e*1.,Ehrenb,lrg1982)aswell asexperimental tudiesie.g., Ruaaocl& Hamilton 1978).The compatibleitement compositions of someLM specimensndi-cate hat olivine hasaccumulated;however,someofthe more "evolved" melts MgO 6-9 wt.Vo, Mg#62-67| contan equally high Ni and Cr contents(=280 ppm Ni, 300ppm Cr). TheseLM 1o9ks-p3v'as an alternative,representmeltsof a slightly differ-entbulk-composition.Relative o theprimitive rocks'the most "evolved" LM are an order of magnitudelower in Ni andCr contentsanda factor of 2-3 lowerin Me MgO 3.4wt.t/0, Mg# 50, Ni 55 ppm' Cr 64ppm). The evolvedmagmaclearlyresults rom crys-tal fractionation.Several elements do not follow well-defineddifferentiation trendson Harker diagrams(e'g', ca,Al: Fig. 8),althoughothers e.g.,Fe, Mg, Si, D dis-play expestedcrystal fractionation-controlled vari-ition tiends. Apatite frastionation is suggestedbythe progressivedecreasen P with increasingSi (anddecieasingMg or Mg#) and the presenceof apatitein all membersof the suite. Other phenocryst ormicrophenocrystphasesncludeolivine, clinopyrox-ene, phlogopite, amphibole and magnetite. Least-squaresmixing routines (Bryan et al. 1969) nvolv-ing various combinationsof olivine, clinopyroxene'phlogopite, amphibole, magnetite, or apatite'1eadlo the best solutions (sum of squaresof residuals


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38whichpreferentiallypartition REtr'(relative o amel!such as apatite ed to theprogressive ecrease REEcontents n the LM as frastionation proceeded.Thisfeature is a general characteristic of minettes andotler lamprophyres. Consideration of other trace-element relationships (e.9., Sr, Rb, efc. ) indicatesa multiplicity of petrogeneticprocesses ecauserac-tionation of the above-noted phasesalone cannotproducethe full spectrumof trace-elementeatures.The least-squaresmixing routines, therefore, areeross simplifications that provide only broad con-straints on the extent to which fractionation souldhaveplayeda role in ssafelling the major-elementvariation.Considering he possiblepartial melting of a lher-zolitic source, in major-element chemistry the LMfalls well below the MoRB-alkali basalt trend onCalTi and N/Ti versus Ti plots (after Sun e/ a/.1979).This indicates hat the LM magmasmay havebeenderived from a source depleted n Ca and Al(or clinopyroxene and garnet) relative toMORB/dkali basaltsourcesfor comparableTi con-tents). The range in Ca./Ti and AllTi values dis-played by the more primitive LM rocks suggestsarange n degreeof partial melting of 5-1090 of aslightly anomalous peridotite composition. Thesecompositional relations suggest hat the LM sourcemust have been considerably enriched in large-ionlithophile (incompatible) elements relative to thesourcs or alkali basaltic melts suggestedby Freyet al. (1978). We interpret the silica-saturated to-oyersaturatedcharacter of the LM to reflect a lowCO2I(H2O+CO) source, in keeping with theexperimental findings of Mysen & Boettcher(1975a,b).The zoning profiles of clinopyroxeneandphlogo-pite largely reflect crystallization from magmas hatwerechangingsignificantly n composition as a resultof differentiation. Thereale, however,sutbleanoma-Iies (e.g., Cr, F and Na in phlogopite) that reflectmore complex histories of crystallization. Widelyvarying Cr contents in phlogopite of comparableMg# hint at a complex evolutiou, the origin of whichwas initially addressedby M6tais et al. (1962).Theamphibole phenocrysts in the most evolved rockexhibit firm evidence or the inhsrilance of crystalsfrom a slightly evolved magma that precipitatedamphiboles with "normal" zoning profiles. Suchamphibole crystals were added to a more primitivebatch of minettemagma, tself evolving in a normalmanner. However, the more primitive LM rocksstudieddo not show evidenceof this contamination(the variable Cr values in phlogopite are possibleexceptions).Theglobularor ocellar exturesobservedin several samples suggest that late-stage liquidimmiscibility may have occurredduring the crystal-lization history of tle LM, basedon the studiessum-marized n Rock (1984).

TIIE CANADIAN MINERALOGISTWhereassome of the major- and trace-elementfeatures ndicate that the LM is similar to minettes,others ndicatedifferences(e.g., the similarity in Nbcontents in the LM relative to arc andesites,yetdifferent relative Rb, Ba, Sr, Y, REE, Hf and Zrcontents).This Nb similarity is anomalous,especiallywhen consideringthe contrast$ n ratios of various

incompatibleelements uchas K/La(0.25x),WCs(0.2x ), K/Rb (0.4x ), C-s/l-a0.2x). Sr,rla (0.25 )and BaJLa (0.5x ) between he LM and arc ande-sites (basedon the compilation of Morris & Hart1983). In contrast, the LM rocks display valuesofthese ratios closer to those of the alkali basalts ofocean slands ascompiled by Morris & Hart (1983).The most primitive LM rocks are highly enrichedin incompatible elements,and require as source ametasomatized mantle peridotite (e.g., Lloyd &. Bailey 1975,Wilshire & Nielson-Pike 1975,Menzies& Murthy 1980, Boettcher& O'Neil 1980, Bailey1982,Dawson1984).Thenatureof this sub-Borneomantle metasomatism, as reflected in the trace-elementgeochemistryof the LM, both contrastswithand is similar to that defined for the asthenosphericwedgeoverlying subduction zones(e.g., Gill 1981,Morris & Hart 1983)and possessesmany affinitieswith thoseof typical source-regionsor alkali basalticmagma.Thevariouspetrogeneticmodels lus far proposedfor minettes have been addressedby Rock (1984).However, modern petrological, geochemical andisotopic data substantiatea broad geneticmodel forminettes nvolving the production of meltsby smallbut variable degrees of partial melting of ametasomatizedmantle peridotite (* zone refining)with subsequent ifferentiation through crystal frac-tionation, liquid immiscibility, and volatile-phasetransfer witl variablebut smallamounts of contami-nation by crustal material. We interpret the petro-Iogical features enumeratedabove in the Linhaisairocks to support this general petrogeneticscenario.The extensivemajor-elementvariation displayedbythe LM intermediate-to-mafic equences interpretedto be largely tle result of crystal fractionation andmagmamixing. DespiteRock's (1984)preferenceorextensive crustal modification of mantle-derivedminettemelts n explaining6ioa11epetrogenesis,wepreferto view minettesas relativelyunmodifiedman-tle melts whosecrustal interaction is the exceptionrather than the rule. The compositional modifisa-tion of primary mantle-derivedmelts is related to"primary" magmaticprocssesuch as crystal frac-tionation andvolatilephaseransfer. We concur withBachinski& Scott (1979,1980) n viewingtheZ.IZ.E-enriched and exotic composition of minettes asreflecting the nature of the mantle source and com-plexity in subsequentpetrological processes e.9.,crystal fractionation, volatile phase ransfer), which,we contend, occurred largely in the upper mantle.


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MINETTE DYKE AND BORNEO DIAMONDS 39As far as the tectonic and petrogeneticaffiliationsof the LM are concerned,we considerthat the age,major-, and trace-element ata argueagainstadirectassociation with subduction-related magmatism.Clearly, no known subduction zonewas nteractingwith central and northern Borneo at 8 Ma. The tim-ing of the LM intrusion occurs in a magmatic lullin Borneo, betweentwo major regional magmaticpulses in the Oligocene-Eocene(16-30 Ma) andQuaternary (< I Ma). The only other known mag-matic rocks in the area of this age(7-10 Ma) occurin the Sintang area to the west of the LM (P. Wil-liams, written comm. 1987). Despite a slight"shoshonitic" association e.g., Joplin 1968,Mor-rison 1980) displayed by the LM on the basis ofmajor elements,we prefer to group the LM withintraplate alkaline magmatism resulting frompostorogenicmelting of ttre subcontinental mantlelithosphere,aprocesslat may, in turn, have esultedfrom crustal tlickening associatedwitl the regionalcompressive eformation in Late Cretaceouso mid-Tertiary times.Rock (1984,1987)and Bergoan (1987)summa-rized the petrologic similarities and differencesbetweenminettes and lamproites. Of all mafic tointermediate rock-types, minetts are the closest omafic to intermediateamproites and it ismost prob-able hat these wo groups orm a compositionalcon-tinuum. Nevertheless, ertainfeaturesof tle LM arein marked contrast o those of lamproites,for exam-ple (cf. Bergman 1987):a) The LM are more evolvedOowern Me and Mg#)and possess igher Na and Al and lower K, Ba, Sr,Rb, l.Ib, 1\, LREE, Ta,7-r and Hf sontents thanlamproites.b) The LM mafic phasespossess nomalouslyhighAl contents compared wittr those of lamproites(amphibole: 10-14 wt.Vo versas 0.8 * 1.7 wt.9oAl2O3; clinopyroxene: 1.2-4.4 wt.Vo versus 0.5 t0.7 wt.tlo Al2O3;phlogopite:12.5-14.6wt.Vo versus10 t 3 wt.9o Al2O3,respectively).c) The LM sanidinepossesses high lr[3 content (4wt.Vo versus 0.5 wt.9o NazO) and Ca (l wt.9oversus 0.2 wt.9o CaO) content and lower Fe (0.5wt.$/oversus2.3 wt.aloFqO) and Ba (0.1 wt.9oversus I wt.9o BaO) contents than those of lam-proites.In contrast to the kajanite characterized byWagner(1980, which possessesanyphases harac-teristic of lamproites (olivine + phlogopite + leu-cite + diopside + richterite), the mineralogicalassemblageintheLM (olivine + phlogopite + sani-dine + augite + hornblende + titaniferous magne-tite) is much more allied to typical minettes (e.9.,Velde 9l, Rock 197, 1984). hemajor- andtrace-elementgeochemicalcontrastsbetween he LM ontle one hand, and kajanite or cocite on the other(data of Wagner & Velde 1986,Wagner l98O are

sufficient to justify a fine-scalepetrogeneticdistinc-tion between thesegroups. Furthermore, the LMminslsl compositions are likewise slightly distinctfrom those of kajanite and cocite. So, whereaskajanite is interpreted by Wagner (1980 as a mem-ber of the kamafugitic clan, an interpretation withwhich we agree,the LM is strictly interpreted as amemberof the minette clan. We contendtlat thesetwo clanspossessmany similarities and may be bneand the same. n other words, whereas he LM andnearby kajanite may not bepart of the samecomag-matic suite (in time and space), hey may representa compositionallysimilar rock group n amoreglobalsense.We do not infer a lamproitic parent melt sensustricto for the LM or related kajanite melts becauseof the mineral chemistryandwhole-rockgeochemis-try contrasts.Basedon availabledata, wegloup thekajanite of Brouwer (19@)and Wagner (1980 in avery broad mafic-to-intermediatepotassic(possiblykamafugitic)petrogenetic eries,and nclude he LM.We infer that the LM and petrologically similarmelts, suchaskajanitc, do not form the sourceocksthat hosted he ubiquitous alluvial diamondspresentin Cretaceousandpost-CretaceousdepositsofCen-tral and West Kalimantan (e.9., Koolhoven 1935,Wing Easton 1894, van Bemmelen 1949, Ubaghs1941,Witkamp 1932).Thesediamonds, herefore,probably owe their existenceo an unidentified lam-proite or kimberlite in Borneoor adjacelrtSouthastAsia. The widespreadpost-Cretaceoussedimentarydeposits n the area could easily conceala diamond-iferous lamproite or kimberlite diatreme. Alterna-tively, a local pre-Cretaceouskimberlitic or lam-proitic sourcemay have been largely removed byerosion or amore distant igneoussourcemaybesug-gested.The generaltectonic setting of Kalimantansuggestsa lamproite, ratler than kinberlite, as asource for the local diamonds @ergman 1987), nthat Kalimantanis situatedon themargin of the Suu-daland craton. The closest known lamproites orrocks closelyallied to lamproites occur in the Fitz-roy Basin, northwestern Australia (e.g., Wade &Prider 1940), at Coc Pia, Nortl Vietnam (Lacroix1933,Wagner& Velde1980, and at Chelima, ndia(Berenoan& Baker 1984),but all of theseare overl0m-2000 km from the LM, even in Cretaceous-Tertiary reconstructions of southeast Asia (e.g.,Owen 1983). n keeping with the suggestionsof R.Halligan (pers.comm., 1983),weprqfer o considera yet-undiscovered,more local sourcefor the Cen-tral Kalimantandiarnonds.Howwer, thelack of anyclassickimberlite or lamproite "indicator minerals"in diamondiferoussedimentsand alluvium through-out Kalimantan suggestsa complicated multicyclesedimentarywolution for Indonesiandiamonds.Theidentification of the primary sourceof Kalimantandiamonds clearly requiresmuch more'study'


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40 THE CANADIAN MINERALOCISTACKNowLEDGEt/mNTs

This study was supponed by the AnacondaMinerals Company, a former division of the Atlan-tic Richfield Corporation, as part of its diamondexploration effort in Borneo and ttre U.S.A. Fieldassistancewasprovided by Z. Masalayuk and ottrermembers of the P.T. Aneka Tambang staff ofJakarta and Banjar Baru. Discussious with L.Noddlesand M. Bergmanprovedworthwhile. KenFoland kindly provided the K-Ar age determina-tions. Discussionswitl R. Halligan, W. Turner, andP. Williams improved our understanding of theregionalgeology.Wethank P. Williams for preprintsandunpublished data. We thank Danielle Velde, R.Halligan, W. Laughlin, Nicholas Rock and RobertMartin for very thoughtful reviewsof an early ver-sion of tlis manuscript. We appreciatehe assistanceof J. Toney and D.J. Henry in the electron-microprobe work. We thank ARCO Oil and Gas Co.for assistance nd permissionto publish this paper.

REFERENcESAnar, J. F. & CanMrcnael, .S.E. (1984):Lam-prophyric avas n 1[e Qeliml graben,S.W. Mex-ico. Contr. Mineral. Petrologlt 88, 203-16.Becrnsrc, S.W.& Scorr, R.B. (199): Rare-earth ndother trace elementcontents and the origin ofminettes.Geochim.Cosmochim. cta 43,93-lm.

& - (1980):Replyto "Rare-earthandother trace-elementcontents and the origin ofminettes."A criticalcomment n apaperbyBachin-ski and Ssott (1979)by N.M.S. Rock. Geochim,Cosmochirn.Acta 4, 1389-92.BecnrNsrr, S.W. & Sruesor, E.L. (1984): Ti-phlogopitesof the Shaw'sCoveminette:a compu-i$on with micas of other lamprophyres,potassicrocks, kimberlites and mantle xenoliths. Amer,Mineral. 69,41-56.Banrrv,D.K. (1982):Mantle metasomatism continu-ing chemicalchangewithin the Eafib, Nature 296,525-530.BanoEr, M.C. (1977): Gologie du Diamant.B.R,G.M.,Paris,Mem.83, III.Banar, C.E.A. (1976):Esquissedologique u Born6oOccidental, : 1,000,000unpubl.).Brncuau, S.C. (1987): Lamproites and otherpotassium-rich gueousrocks: a review of theiroccurrence,mineralogyandgeochemistry.0aAlka-line IgneousRocks J.G. Fitton & B.G.J. Upton,eds.).Geol. Soc.Lond. Spec.Publ.30, 103-190.-& Bar


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MINETTE DYKE AND BORNEODIAMONDS 4l-(1914} Borneo.Geol. Soc.London Spec,Publ.4, 333-347.HArvru.roN,W. (1978):Tectonicsof the Indonesianregion. U.S. Geol. Sum.Proi. Pap, IVIE.HANsor*,G.N. (1979): Rare earth elements n

petrogenetic tudiesof igneoussystems. nn. Rev.Earth Planet. Sci. 8' 371-406.Hovro, P. (1930):Diamondsn CentralBorneo. Joar-boekMijnwezen1930'16l-162.HurcrmlsoN,C.S. (1973):Tectonicevolutionof Sun-daland:aPhanerozoic ynthesis.Geol. Soc.MaW-sioBull, 6, 61-86.Jern, B. (1973):A petrogeneticmodel for ttre gneouscomplex in the Spanish Peaks regsor. Contr.Mineral. Petrologlt 41,?Al-258,-, SuN,Sneu-Sutt Nesutrr,R.W. (1979):REEdistributionandgenesis f the SpanishPeaksgne-ous complex,Colorado. Cont. Minerol. Petrologt70,281-298.Jnqurs,A.L., Lswrs, J.D., Surrn, C.B., Gnscow,G.P., Fnncusotrt,., Cueppen, B.W. & McCur-LocH, M.T. (1984): The diamond-bearingultrapotassiclamproitic)rocks of thewestKimber-ley region, westernAustralia. ft Kimberlites andRelatedRocks,Proc. 3rdKimberliteConf. (J.Kom-probst,ed.).Elsevier,Amsterdam.Joxrs, A.P. & SvnH, J.V. (1983):Petrologicalsig-nificanceof mineral chemistryn theAgathla Peakand TheThumb minettes,Navajo volcanic ield. ,LGeol.9t, &3-656.

& - (1985):Phlogopiteand associatedminerals rom PermianMinettes n Devon, SouthEngland.Geol. Soc.FinlondeBull. {1,89-102.Jonml, G.A. (1968):The shoshonite ssociation:review.J. Geol. Soc.Attst. 15,n5-294,Ke^ulr,J.A. (1971):A reviewof the geotectoniche-ories and tectonic mapsof Indonesia. Earth Sci,

Reviews , 143-163.- (1973):Geochronology f W. Indonesiaand tsimplicationsfor plate tectonics.Tectonophys.19,t95-212.Kav, R.W. & Gasr,P.W. (1973):The rare earthcon-tent and origin of alkali-richbasalts. . Geol.8t,653-682.Krnr, H.J.C. (1968):The igneous ocksof Sarawakand Sabah.Bull. Geol. Sum. Malaysia, BomeoRegion 5.Koor.novEN, .C.B. (1935):Het prinaire voorkomenvan den Zuid-Borneo diamant. Geologisch'Mijnbouwkundig Genootschapoor NederlandenKolonien, verh., Geol. Ser. 9t 189-232.

Lacnox, A. (1926):La systdmatique es ocheseuci-tiques: es ypesde a famillesy6nitiqtrc.C.R.Acad.Sci.Paris, Ser.D tt2,59G@l'(1933): Les roches 6ruptives potassiquesleusitiques unon duTonkinoccidettal.C.R.Acad'Sci.Paris,Ser.D 197,625'07.

Lloro, F.E. & BatrY, D.K. (1975):Light elementmeiasomatismof the continentalmantle: the evi-denceand consequences.hys. Chem. Earth 9,389416.Lurn, J.F. & CanMcHesL,.S.E. (1981):TheColimavolcanic complex, Mexico. II. Late-Quaternarycindercones.Contr.Mineral.PetrologtT6,ln-147 .Meuzrns,M.A. & Muntnv, V. RAMA1980):Mantlemetasomatisms aprecursoro thegenesis f alka-line magmas isotopicwidence. mo. J. Sci-?,f,iJ'A,

622-638.Mfrars, D., Ravmn,I. & Duoxc, P. (1962):Natureetcomiosition chiririquededeux amprop-hyres'ul/'Soc.-rang. Mindral. Cntt. 85' 321-3 .Msrar- MnuNc AcBrcv or JapeN 1979):Report onGeologicalSumeyof CentrolKalimantan. tlTlriryof Mines,GeologicalSurvey f Indonesia'Bandung.MonRrs,J.D. & Henr, S.R. (1983):Isotopic andincompatibleelementconstraintson the genesis fisland-arc volcanics from Cold Bay and AmakIsland,Aleutians,and mplicationsor mantlestruc-ture.Geochim,Cosmochim.Acto 47,2015'2030.MoRrusor,G.W. (1980):Characteristicsand tectonicsfiing of the shoshoniteock association. ithos13,97-108.Mvsen,B.O. & BoETrcurn,A.L. (1975a):Meltingofa hydrous mantle. I. Phaserelations of naturalperidotiteat high pressure$nd temperatureswithcontrolledactivities of water, carbondioxide andhydrogen.J. Petrology 16' 52U548,

& -(1975b): Melting of a hydrousman-tle. II. Geochemistry f crystalsand iquidsformedby anatexisof mantleperidotitenf high pressuresandtanperaturesas a functionof controlledactivi-ties of water, hydrogen and carbon dioxide. J.Petrologlt 16, 549-593,NiMsc, D. (1973):Paragenetischenalyse der Gang-gesteineer MinettengruppeChem.Erde 32, 8U97,

(1975): Petrochemieund Geneseder lam-prophyrischenund lamproiden GanggesteinemNordteil der BohemischenMasseCSSR).Z. Geol.Wiss. ,37-52,Oru.ov,Y.L. (1977):TheMineralog! of Diamond. J.Wiley & Sons,New York.


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42 THE CANADIAN MINERALOGISTOwrN, H.G. (1983):Atlas of ContinentolDisplace-ment 240 Million Yearcto Present. CambridgeUniv. Press,Cambridge.Peacocr,M.A. (1931):Classification f ignsousockseries. /. Geol. 39, 5M7.Rocr, N.M.S. (1977):The natureand origin of lam-prophyres:somedefinitions,distinctionsandderi-vations.Earth Sci. Rev.13, 123-169.- (1980):Rare-earth nd other raceelementson-tentsand theorigin of minettes:a critical commentonapaperby Bachinskiand Scott(l%9): Geochim.Cosmochim. cta 44, 1385-1388.- (1984):Natureand origin of calc-alkalineam-prophyres:miqettes, ogesites,ersantites ndspm-sartites.Trons.Royal Soc.Edinburgh,Earth Sci.74, t93-227.- (19@: The natureand origin of lamprophyres:an overview..lnAlkaline gneousRocks J.G.Fit-1oq B.G.J.Upton,eds.).Geol.Soc.Lond.Spec.Publ.30, 9ln6.--------:--:, asrannr, J.W. & Rurqore,C.C. (1986):LateCaledoniandyke-swarmsn southernScotland:aregionalzoneof primitiveK-rich lamprophyres ndassociated ents."L Geol, 94, 505-522.

& Lnaxn, B.E. (1984):The InternationalMineralogicalAssociationamphibolenomenclaturescheme:computerization and its consequences.Mineral. Mag. 48,2n-2n.Rocrns, N.W., Bacnnwn, S..W.,HrNoensoN, . &PaRRy,S.J. (1982):Origin of potash-richbasiclamprophyres:trace elementdata from i\rizonaminettes.Earth Planet, Sci.Lett. Sj,305-312.Rosn,R. & Hanroxo,P. (1978):Geological volutionof the Tertiary Kutai-Melawi basin, KalimantanIndonesia.Proc.Indonqian Petrol. Assoc., venthAnn. Conv.,225-251.Ruooocr,D.I. & HaurrroN,D.L. (1978):Stabilityof

carbonaten a simplepotassium-richock model.Prog,Exp. Petrol.N.E.R,C, Publ. Ser.Dtl,2J.-3t.Scuulzn,D.J., SrrlrrH, .V. & Nirrlnc, D. (1986):Mca chemistry f lamprophyresrom ttreBoheinianMassif, Czechoslovakia.NeuesJahrb. Mineral.Abh. 152,32t-334.ScoT.Sr.rrnr,B.H. & Srnown,M. J.W. (1984): newlook at Frairie Creek,Arkansas.Iz KimberlitesandRelatedRocks,Proc.3rd KimberliteConf. (J.Korn-probst,ed.). Elswier, Amsterdam.Srnecrcnsex, . (1978):Classificationandnomencla-ture of volcanicrocks, lamprophyres,carbonatesand melilitic rocks.Recommendationsndsugges-tions. Naras Jahrb. Mineral. Abh, t34,, l-14.

Suoneoran,S.A. (1976):Geologicalmapof the TewahQuodrangle,CentralKalimantan(scale :250,@).Geol. Surv. Indonesia, Directorate General ofMines, Ministry of Mines, Bandung, Indonesia.SuN, SmN-Sw, NEsBnr, R.W. & Suanasrn, A.Y.(1979):Geochemical haracteristics f mid-ocean

ridgebasalts.Earth Planet.Sci.Lett.44, l19-138.Sueruana,S. & RusrAr.rDr,. (1981):Preliminarygeo-logical map of the Buntok Quadrangle,Kaliman-tar?.SystematicGeologicalMap, Indonesia, scale1:250,0fi)).Geol. Res.Development entre,Ban-dung, Indonesia.Terr.on,B. & Haym, D.E. (1982):Originandhistoryofthe SouthChinaSeaBasin. r The Tectonic ndGeologicEvolution of SouthEastAsian [email protected]. Hayes,d.). Amer. Geophys.UnionMon. tl, part2,23-56.Uoacns, J.G.H. (1941): Diamond in Borneo.Tisityosazyo,Bandung, Indonesia.Uuaonow, J.H.F. (1938):Geological istory of theEastlndics.Amer. Assoc,PetroleumGeol.Bull. t2,t-70.veNBrurrtel,rN,R.W. (1949):Geologlt of Indonesia.Gov. Printing Office, The Hague,Netherlands,3volumes.veu Es, L.J.C. (1918):Es Geologische aart van

Nederlandschndien. Schaal :1,@0,@. Toelicht-ing bij Blad D( (westBorneoen Billiton). Jaarb.Mijnw. Ned, Ind. 2, l-35.Vnnr, D. (1969):Minettw andKersantites:Une Con-tribution d I'dtudedu lamprophyres.Thdse eDoc-torat dsSciences aturelles,FacultddesSciencesesParis, Univ. Paris VI, France.

(1971):Les amprophyres feldspathalcalinetbiotite: minetteset roches oisines.Contr.Mineral.Petrology30,21G239.Waoe,A. & Pmonn,R.T. (1940):The eucite-bearingrocksof the West Kimberleyaxea,WestAustralia.Quort.J. Geol. Soc.London96,39-98.Wacwer, C. (1986):Mineralogyof the type kajanitefrom Kalimantan. Similaritiesand differenceswithtypical lnmproites. Bull. Mindral. 109, 589-598.- & VsLDr, D. (1986): -amproites n North Viet-nam? A re-examinationof cocites.J. Geol. 94,71U716.Wrr.t.taus,P.R. & HERyamo, R. (1985):Geological

Data Recordandprelirninary Geologicmap of theSintang quadrangle, llest Kalimantan (scalel:250,0@). Geol. Res. Development Centre,Indonesia-AustraliaGeologicalMapping project,Bandung, ndonesia,137p.


21/21

MINETTE DYKE AND BORNEO DIAMONDS 43Wusunr, H.G. & Nrcrsou-Prrc,J. (1975):Uppermantlediapirism: evidencerom analogouseaturesin alpine peridotite and ultramafic inclusions inbasalt. Geology3, 467470.Wuraumveunn, . (1973):Lamprophyre,semilampro-phyreandanchibasaltischeanggesteine.orfsc&r.Mineral.53,88-1M. IWmc Eesror, N. (1894):Het diamaut voorkomen nLandak, WesternAfd. van Borneo.JaarbuchMijn-wezen t94,9+130.Wrrranrr, H. (1932): Diamant afzettomgenvanLandak. De Mijningenieur 3, 43-55.ZnvLMANSan EuurcsovrN,C.P.A. (1939):Geologyof the Centraland Eastern art of the WesternDvi-sion of Borneo. DrGeologicalaccountof W. Bor-neo (N.S. Haile, ed.) (Iransl. from Dutch). Bal/.Brtt. BorneoGeol. Sum.2, 1955,159-n2.- & tnn Bnucceu,G. (1935):Provisional eportof the Tertiary westof LakeDistrict in theWesternDivision of Borneo. -& Geologicalaccount of W.Borneo N.S.Haile, ed.)Cfransl. rom Dutch). Bzl/.Brtt, Bomeo Geol. Sumey 2, 1955,ReceivedDecember .23, 1986; revised manusoiptacceptedApril 22, 1987.

APPENDIxAnalytical Methods

Major and trace-element data were determined in thelaboratoriesof X'Ray AssayLaboratories,Ltd. of Toronto,using standardX-rby-fluorescenceechniques or major ele-ments and S, Cl, Cr, Rb, Sr, Y, Zr andh; instrumentalneutron-activationecbnique for REE, Hf, Ta, W, C,s,Mo,Sb, Sc, Th, U, Au, Cr, As, Se,and Be; atomic absorptionfor Li; and direct current plasmaspectroscopy or Pb, Bi,AB, Cd, V, Co, Cu, Zn andNi, and wet methods or H2O,F, CO2 and FeO. Basedon the analysesof standard rockpowders, combined precision and accuracy of elementspresent n quantities > l0 wt.9o is 2-4 relative go;that oftrace elements anges rom < 10 elative 9o or some NAand XRF analyses o < 5090for XRF and INA analysescloseto detection limits.High-precision electron-microprobe nalyseswavelengthdispersion) wereperformed in ttre ARCO Plano ResearchLaboratories using a fully-automated 1983 CamecaMICROBEAM instrument and standard operating tech-niques (15 kV potential, 20 nA beam current, a rasterdbeam at 8,000-20,000 ). A ZAF correctionprocedurewasused 10convert X-ray intensities to concentrations of ele-ments.Estimated errors for major elements lG-70 wt.9ooxide) are < 1-2 relative 90, for minor elements< l0wt.9o oxide) < 5-10 relative 9s and for extremely mino|1elements < I wt.Vo oxide), 10-50 relative 90.

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