Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology, and Geochemistry

405 Pages·11.399 MB·English

Kimberlites,
Diatremes,
and Diamonds.-
Their Geology,
Petrology,
and
Geochemistry
Henry O. A. Meyer
F. R. Boyd
editors
Proceedingso f the Second
International Kimberlite Conference
Volume 1
AmericanG eophysicaUl nion
WashingtonD, .C. 20009
1979

Preface
Since the first edition was published in 1979, the Third International
Kimberlite Conference was held in Clermont-Ferrand in 1982. Nevertheless,
several of the problems addressed by papers in the first edition of this
publication are still valid and remain unanswered today. For example, we
still do not understand the spatial and temporal relationship between
kimberiite, xenocrysts and xenoliths, nor do we understand why kimberlites
occur where they do or why they often intruded ancient cratonic areas
perioaically throughout geologic time. There is a growi(cid:127)4(cid:127) suspicion that
continental rifting or perhaps doleritic/basaltic volcanism is a precursor
to kimberlitic activity, but the links are tenuous and often conflicting.
The problems of definition and adequate classification of kimberlites,
especially for the southern African rocks, are nearing resolution.
Hopefully, others will embrace this classification, and misnomers concerning
rocks now misleadingly referred to as Kimberlite will be removea.
Diamonds received attention during the intervening years between the two
Kimberñite Conferences, but still there persists the belief that diamonds
an(cid:127) kimberlite are genetically related. And this in spite of the fact that
the richest diamond-bearing rock in the world is a tuffaceous l(cid:127)nproite in
northwest Australia.
Interestingñy, geochemical studies of kimbertite have not been numerous.
This may be because of the brecciated nature of (cid:127)imberlite and the presence
of nu(cid:127)nerous macro- and micro-inclusions of foreign material. The field is
ripe for study if one can separate out the essential minerals of kimberlite.
This comment is pertinent to isotopic studies as well. Curiously, an area
that is lacking is the determination of ages of various xenoliths and
xenocrysts. A(cid:127)mitteGly, this is difficult, but the results would be of
significance with regard to the evolution of the upper mantle, a subject
covered in volume 2 of these Proceedings.
Henry 0. A. Meyer
CONTENTS
I. DIAMONDS
SiLICATE (cid:127)D OXIDE INCLUSIONS IN DIAMONDS FROM THE FINSCH KIMBERLITE PIPE
J. J. Gurney, J. W. Harris, and R. S. Rickard
MINERAL INCLUSIONS IN DIAiv(cid:127)OND: PREMIER, JAGERSFONTgINA ND FINSCH KIMBERLIT'ES,
SOUTHA FRICA, AND WILLIAMSONM INE, TANZANIA H.-M. Tsai, O. A. Meyer,
0. Moreau, and H. Judith Milledge 16
REGIONAL AND LOCAL VARIATIONS IN THE CHARACTERISTICS OF DIAMONDS FROM SC(cid:127)E
SOO2IYERANF RICAN KIMBERLITES J. W. Harris, J. B. Hawthorne,
and M. M. Oosterve!d 27
DIAMONDS FROM KIFYBERLiTES IN THE COLORADO-WYC(cid:127)ING STATE mINE DISTRICT
M. E. McCal!um, C. D. Mabarak, and H. G. Coopersmith 42
II. KIMBERLITES
FIELD RELATIONS
GEOLOGY OF ThE DOKOLWAYO KIMBERLITE AND ASSOCIATED PALAEO-ALLUVIAL DIAMOND
DEPOSITS J. B. Hawtt(cid:127)orne, A. J. Carrington, C. R. Clement,
an(cid:127) E. W. Skznner 59
STRUCTURAL SETTING OF KIMBEHLITES IN SOUTH-EASteRN AUSTRALIA
K. J. Stracke, J. Ferguson, an(cid:127) L. P. Black 71
KiPzBERLIT(cid:127)S IN BRAZIL: (cid:127)i(cid:127) INITIAL REPORT D. P. Svisero, H. O. A. Meyer,
and H.-M. Tsai 92
PHECAMBRIAN ULTRA(cid:127)]FIC DYKES WITH KIMBER(cid:127).ITE AFFINITIES IN THE KIMBERLEY
AREA C. R. Clement, E. M. Skinner, J. B. Hawthorne, L. Kleinjan,
an(cid:127) H. L. Al!sopp 101
KI(cid:127)3ERLITIC, MELILITITIC, TRACHYTiCA ND CARBONATITEE RUPTIVES AT SALTPETRE
KOP, SU(cid:127)}tERLAND, SOU'iH AFRICA J. R. (cid:127)cIver and J. Ferguson 111
M(cid:127)NERALOGY AND PETROLOGY
MINERALOGICAL CLASSIFICATION OF SOUTHERN AFRICAN KIMBERLITb(cid:127)S
E. M. W. Skinner and C. R. Clement 129
PETROG(cid:127)IESIS OF KI(cid:127)YBERLITIC ROCKS AND ASSOCIATED XENOLITHS OF SOUTHEASTERN
AUSTRALIA J. Ferguson and J. W. Sheraton 140
FLINERALOGOYF THE TUNRAQK IMBERLITE, SOMERSETIS LAND, N .W.T., CANADA
R. H. Mitchell 161
R(cid:127)INERALOGICAL STUDIES ON THE DIAMONDIFEROUS K]hMBERLITE OF THE WAJRAEMARUR
AREA, SOUTHERINN DIA (cid:127). Akelia, P. S. Rao, R. H. McCailister,
F. R. Boyd, and H. O. A. Meyer 172
PETROCHMviISTRAYN D STRUCTUROE F KIIv(cid:127)R(cid:127)ITES IN THE FRONTR ANGEA NDL ARAMIE
RANGEC, OLORADO-WYOMCIN. GB . Smith, M. E. McCallurn, H. G. Coopersmith,
and D. H. Egglet 178
PETRoGEN(cid:127)IS OF KIMBERLITES AND ASSOCIAT-h(cid:127) POTASSIC LAMPROPHYRHSF ROM
C'ENTRALW EST GREENLAND B. H. Scott 190
2(cid:127)E OXIDE AND SILICATE MINERAL CHEMISTRY OF A KIMBERLITE FROM THE PR(cid:127)I(cid:127)IER
MINE: I(cid:127)iPLICATIONS FOR THE EVOLUTION OF KiFmEHLITIC FIAC(cid:127)gS
D. Elthon and W. I. Rialey 206
OXIDE AND SULFIDE MINERALSI N KI[IBERLITE FROMG REENM OUNTAIN, COLORADO
N. Z. Boctor and H. O. A. Meyer 217
ZIHCON-OXIDE REACTIONS IN DIAMfOND-BEARINGK IMJ(cid:127)ERLITES E. Raber and
S. E. Haggerty 229
K, Rb ANDB a IN [v(cid:127)ICASF ROMK INBERLITEA I(cid:127)D PEHIDOTITICX ENOLITHSA, ND
IF(cid:127)PLICATIONS FOR ORIGIN OF BASALTIC ROCKS J. V. Smith, R. L. Hervig,
D. Ackermanma,n d 0. B. Dawson 241
GEOCHF(cid:127)STRY
VARIATIONS IN STABLE ISOTOPE COMPOSITIONS FOR CARBON AND OXYGEN IN SO(cid:127)E
SOUTHA FRICAN AND L'ESOTHANK I(cid:127)R(cid:127)ERLITES B. J. Kobelski, D. P. Gol(cid:127),
and P. Deines 252
ABUNDANCEOSF PALLADIUM, IRIDiUM AND GOLD IN KIMBERLiTES AND ASSOCIATED
NODULES D. K. Paul, J. H. Crocket, and P. H. Nixon 272
SIGNIFICANCE oF URANIUM ABUNDanCE IN UNiTED STATES KiMBERLIT(cid:127)S
D. G. Brookins, R. S. Della Valle, and S. L. Bolivar 2(cid:127)0
GEOPHYSICALA ND Hb-Sr STUDY OF THE PHAI(cid:127)IE CHEEK, AK S. L. Bolivar
and D. G. Brookins 2U9
%(cid:127)E C(cid:127)MICAL COFiPOSITION OF KIM(cid:127)ER(cid:127)!TES COMPARED WITH THE AVERAGE
COMPOSiTiOONF THR(cid:127) BASALTICF IAGMTAY PES K. H. Wedepohl and Y. Muramatsu 300
EXPEHIMENTAL STUDIES
AM OD0E(cid:127) PL HARSE(cid:127) LATIION TNHSSE Y STMEgMO -SiOm-HAmNPODR -CEODpIC TION
OF THE CO(cid:127)POSiTIONS OF LIQUIDS COEXISTING WiTH FORST(cid:127)HIT(cid:127) AND ENSTATITE
D. E. Ellis and P. J. Wyliie 313
KIMBERLIFT(cid:127)GEM ASF RO(cid:127)IT HES YSThP(cid:127) ERIDOTITE-C02-(cid:127)2P0. J. Wyllie
EXPERimeNTAL STUDIES ON THE RELATiONSHiP BETWEEN KIMBEHLITE MAGMAS AND
PARTIAL MELTING OF PERIDOTITE D. H. Eggler and R. F. Wendlandt 330
EXPERIMENTAL STUDY oN TWO PICHITES WITH REFERENC(cid:127) %'0 THE GENESIS OF
KI(cid:127)YBERLITE A. K. Gupta and K. Yagi 339
III. DIATREMES AND CARBONATITES
THE ROLE OF F(cid:127)ACTURE DYNAMICSI N KIMBERLITE PIPE FORMATION O. L. Anderson 344
PHREATO(cid:127)V(cid:127)AGF(cid:127)TIC ORIGIN OF THE OLIVINE MELIL1TITE DIATREMES OF THE SWABIAN
&LB, GERMANY V. Lorenz 354
FI'FJ(cid:127)D GEOLOGYC, HE(cid:127)vlISTRYA, NDP ETROLOGOYF BUELLP ARK(cid:127)IN ETTE DIATREY(cid:127),
APACHEC OUNTY, ARIZONA M. F. Roden and D. Smith
2(cid:127)E OKA CARBONATITE CO(cid:127)PLEX: R(cid:127)GNETI2(cid:127) COF(cid:127)OSITIONS AND 'iHE RELATED ROLE
OF TITBNIUI(cid:127) IN PYROCHLORE B. M. McJ(cid:127)muhona nd S. E. Haggerty 382
RELATIONSHIP OF 2HE œ(cid:127)URFREESBORKOI (cid:127)E(cid:127)LITE AND OTHER IGNEOUS ROCKS OF
ARKANSASU, .S.A. K. F. Steele and G. H. Wagner 393
AUTHORI NDEX 400
Special Publications Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology, and Geochemistry Vol. 15
II. . DDIAIMAOMNDOSN DS
SSILILICIACTEA TEAA NNDD O OXXIDIED EIIN CNLCULSUIOSNISO NIISN N DDIAIMAMOONNDDSS F FRROOMM T THHEE F FINISNCSHC HKK IMIBMEBRELRLITIET EPP IPIEP E
JJ.J.. J.G Guurnrneeyy
GGeeoocchheemmiisstrtyr DDyee ppaarrtmtmeennt,t UU,nn iivveresritsyiy t ooff CCaappee T Toowwnn,, RRoonnddeebboosscchh 77 770000, ,SS .. AAffrirciac a
JJ.W.W. . HHaarrris ris
GGrraannt tII nnsstittuitet uteoof f GGeeoollooggy,y ,UU nniivveresritsyi tooyff EEddiinnbburugrhg, hEE,dd iinnbburugrhg hEE HH99 33JJWW,, U U..KK. .
RR..SS. . RRii cckakrda rd
GGeeoocchheemmiissttrryDDy ee ppaarrttmmeenntt,U U,nn iivveerrsistiy tooyff CCaappee TToowwn,n ,R Roonnddeebboosscchh77 770000,, SS .. AAffrriciac a
AAbbsstrtraactc. t. AA ssyysstetmeamtaict isce arsche aroofcf h 11 44,5,0500 0 ddeerrivievde dff rromom aa pprree-e-xeisxtiinsg tinddgiia ammoonndidfeirfoeusrs o u
ccaarraatst soo ff ddiiaammoonnddss (( aapppprorxoixmiamtealtye l22y332 2,,00000 0ss ttoonnees)s ) eeccllogoigtei tehh oorriziozno nss aammpplleedd bb yy tthhee kkiimmbbeerrllitiet e
ffrromom tthhee FFiinnscschh kkiimmbbeerrliltei tey yieiledledd ed11 00224 4dd iiaammoondnsd s dduurrinign gii tst s aasscceentn ttt hhroruoguhg htth hee mmaannttlel. e.
wwiitthh mmiiccrroossccooppici iicnn cclulsuisoinosn. s.SS uullpphhiiddeess (( 335588),) ,
ggrraapphhiittee ((113322) )a nda nccdllo ouuddss (( 2233) )cc oonnssttitiuttuet aeall mmoosstt IInn ttror odudcut ci toni on
eexxaacctltyl yhh aallf f ooff tthheesse.e . OOff tthhee rreesst t5 50011
iinncclulsuiosniso nsaar ree mmiinneerarlsa lsoo ff ppeerridiodtiotitc iticco mcpoosmiptioons ition TThhee FFiinnsschc hPP iippee iiss aa mmaajjoor rkk iimmbbeerlritle itmmei innee
wwhhiilslt st1l O0 aarree eecclolgoitgici. tic. wwhhiicch hhh aass pprroodduucecded ddiia ammoonndds sss iinncec e 11996633 a att aa rraatet e
TThhee mmiinneerarla lii nncclulsuiosniso nsaapp ppeeaar rtt oo bbee iinn eeqquui-i ­ wwhhiichc hhh aass bbeeeenn ggrreeaatetr ertt hhaann 22 mmiillliolni oncc aarratast s
llibirbiurmi umww iitht h eeaacch h ootthhere ra anndd ddiiamamonodn. d. aannnnuuaalllyl yiin n rreecceennt tyy eeaarrss. . ThTeh e mmiinnee iiss aabboouutt 3 377
TThhee ppeerriiddootittiict immci inneerraalsl saa rree:: oolliivvinien e(( 6600%%)), , kkmm eeaasst t ooff PPoossttmmaasbsubrugr, gCC,aa ppee PPrroovvinicnec, e,SS oouutthh
oorrtthhooppyyrorxoexneen ((e22 00%%))(cid:127) ,gg aarrnneett (( 2200%%)) a anndd cchhrroommiitte e AAffricra.i ca.
((11%%).) . TThhee eecclolgoitgici ticmm iinneerarlsa lsaa rree ggaarrnnete, t, ThThee ddiiaatrtemree meiis s iinntrtursiuvse iveiin ntot o tthhee bbaannddede d
ccllinionpoyproyxreonex enaaenn dd kkyyaannitie.t e. iirroonnststoonnees s ooff tthhee LLoowweerr GG rriiqquuataotwonw n((PP rreetotroiar) ia)
AA ttootatl alo off 110000 mmiinneerarlsa lsff rromom 8800 ddiiaammonodnsd shh aavve e GGrroouupp,, l lyyinign go ouuttssidied eoo ff tthhee pprreesseennt tdd aayy eexxtteennt t
bbeeeenn aannaallyyssede dii nncclulduiidnngg 1144 ggaarrnneet//toolilviinvei, ne,22 ooff tthhee KKaarroooo s seeddiimmeentnatrya rbbyaa ssini.n . NNeevveerrthtehleeslse, ss,
ggaarrnneett/o/rothrotphyorpoyxernoex,e n11e o,ol ilviinvei/cnher/ocmhirteo, mit1 e, 1 ffrraaggmmenenttss ooff KKaarroooo r roocckkss hh aavvee bbeeeenn s seeeenn iinn tthhee
oorrtthhooppyyrorxoexneen/sei/licsai lippchhaaa ssee,, 1 1 ggaarrnneett/c/licnloi- no­ kkiimmbbeerlritlei taean ndd aa zziircrocno naa ggee ooff 9933 mm..yy.. ((DDaavvisi, s,
ppyyrrooxxeenneea a nndd 11 cclliinnooppyrryooxxeennee//pphhlolgoogpoiptei pptaaeii rrss. . 11997777)) g grroouuppss t thhiis s ooccccuurrrrenecnec wewi itthh t thhee ppoosstt-K-Karaoroo o
TThhee ppeerriiddootittiic timmci inneerraalsl saa rree ddiissttinicntcivteilyv ely kkiimmbbereiirtel itieinn trtursiuvsesi veosof f vviirtrutalulya llyc oncteomnptoeramnp- oran­
ddeepplleettede dii nn ccaallcciiuumm a anndd hhaavvee hhiigghh MMgg//FFee a anndd eeoouuss aaggee ffrroomm BBoottsswwaannaa,t, thh ee KKiimmbbeerrlleey yDD iissttrircit ct
CCrr//AAl1 rraattioiso. s. TThhee eeccllooggitiict icmm iinneerraalsl shh aavvee aanndd NNoorrthterhn ernLL eessotohot. ho.
ooppppoossiittee cchhaarraactcetriesrticiss. tics. TThhee ssuurrfafcae cekk iimmbberelirtel itaeatt FFiinnscshc hhh aass bbeeeenn
TThhee 22 ggaarrnneet/to/rtohrotphyroopxyerneo xeppnaaeiir sr sc coouulldd h haavvee ccoommpplleetteellyya a lltteererde.d . RRuuoottssaallaa (( 11997744)) hh aass ddee­-
ffoorrmmeedd aa tt vviirrtutaullayl lyiid deenntitciacl altt eemmppeerraatutruerse aasnn dd ssccrribiebde dtt hhiis s mmaatteerriail alaa ss ffrriaibaleb leyy eelllolwo wgg rroouunndd
pprreessssuurreess. .T Thheesseec coonnddiittioinosn sww eerree wwiitthhini nt thhee wwhhiicchh p peerrssiisstst stt oo aa ddeepptthh o off aapppprrooxxiimmaatteleyl 1y3 0 130
ddiiaammoonndd s sttaabbiliitlyi tyff iieeldl da att aa tteemmppeerraatutruer cecl loossee ffeeeett. . TThhee yyeelllolwo wgg rroouunnddg grraaddeess i innttoo bblluuee oovveerr
ttoo 11110000ø0CC a anndd aa pprreessssuurer ec locsle otstooe 5500 kkbb.. aapppprrooxximimaatetlye lttyhh ee nneexxtt 110000 ffeeeett. . SSoommee aa ssppeecctts s
ThTeh e ppeerriiddoottitiict iciin ncclluussioinosn asa nndd tthhee aassssoocciiaatetde d ooff tthhee ggeenneerraal lpp eettrrooggrarpahpyh oyof f tthhee FFiinnsscchh kk iimmbbeerr- ­
ddiiaammoonnddssc c rryyssttalalilsledi sefdfrr oomm aa memletl t ffoorrmmeedd bbyy aa lliitet e hhaavvee b beeeenn p prreesseenntteeddbb yy CClleemmeenntt(( 11997755)). .
ssmmaallll d deeggrreeee o off ppaarrttiail almm eellttinign go off aa ggaarnrneett MMoorree tthhaann 9900%% ooff tthhee hheeaavvyy m miinneerrala lcc oonncceenn- ­
llhheerrzzoollitie tem maannttllee i inn tthhee pprreesseenncce eoo ff wwaatteerr a anndd ttrraatet ep prroodduucceedd dd uurriinngg t thhee ddiiaammoonnddr r eeccoovveeryr ypp rroo-­
CCOO2,. CCapatputrueoro eff C Caa+++ + bb yy C C03O-(cid:127)i-is s pprrooppoesods tetood cceessss iinn tthhee mmiinniinngg o oppeerraattioino naa tt FFiinnsscchh i iss ggaarrnnetet..
aacc2ccoouunntt f foorr tthhee ccaallcciuimum d deepplleetetde dnn aattuurree o off tthhee IIllmmeennitiet eaa nndd ddiiooppssidied eaa rree bbootthh vveeryry rraarree. . TThhee
mmiinneerrala lii nncclulsuiosniso nsiin n tthheessee d diiaammoonnddss. .B Baasseedd o onn pprreeddoommininaanncoceofe f ggaarnrente ti iss tthhoouugghhttt t oo bbee o onnllyy i inn
mmiinneerrala la abbuunnddaanncecse -s(cid:127)- -9988%% ooff tthhee ddiiaammoonnddss aa tt ppaarrtt dduuee t too wweeaatthheerriinngigi nn tthhee ssuurrffaacceek k iimmbebrelrilittee..
FFiinnsschc hf foorrmmeedd dduurrinign gt thhiis s pprrooccesess. s. OOlliivvinien ea anndd o orrtthhooppyyrorxoenxneee w woouulldd b bee ccoommpplelteteellyy
TThhee rreemmaaiinninign -g,(cid:127)2 -2%% aarree ccoonnssiiddeererde tdto o bbee rreemmoovveeddbb yy tthhiiss pprroocceessss,, bb uutt wwee h haavvee sseeeenn c chhrroommee
1
Copyright American Geophysical Union
Special Publications Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology, and Geochemistry Vol. 15
diopside and ilmenite persist in yellow ground No attempt was made to allocate olivine,
elsewhere and(cid:127) in addition, current mining orthopyroxene or other essentially colourless
operations are in less altered material with no mineral inclusions to separate categories; they
obvious change in concentrate character. The were all termed colourless inclusions. Subse-
garnets from the concentrate have been studied quent inclusion analyses showed that more than
by Gurney and $witzer (1973). 70% of these are olivine. The rest are ortho-
pyroxene, except for very rare high Si phases,
Objectives believed to be coesite.
Ol ivine is often found in the eye of sulphide
It was the aim of this study to determine inclusions (Harris, 1972) but these are frequent-
which minerals occur as inclusions in diamonds ly masked from view so the sulphide category will
from the Finsch Mine, and to find the range in include a certain number of olivines; sulphide
chemical composition for individual mineral spe- more rarely disguises other inclusions such as
cies. It was also intended to investigate the purple garnet or eclogitic minerals.
conditions under which these minerals might
crystallise and hence to gain an insight into
the natural process of diamond formation. In TABLE ]. (cid:127)ihe Relative Abundance of Inclusions
this respect it was obvious that diamonds con- in Diamondso f Sieve Class -6 +5( a)
taining more than one mineral species as in- from the Finsch pipe
clusions would be particularly important.
Although inclusions in diamonds have been
studied and analysed by various workers in recent
1. Peridotite Paragenes[s No
years, the comprehensive sampling of a single
locality in the manner of this study has not
previously been possible. It was hoped that the Colourless inclusions 381
restriction of the sampling to inclusions from Colourless inclusions + purple garnet 5O
one locality would simplify interpretation of the Purple garnet 63
new data. Purple garnet + sulphide 3
The Finsch locality was of particular interest Ch r om (cid:127) t e 4
because of the presence of low calcium, high
501
magnesium, high chromium garnets in the concen-
trate (Gurney and $witzer, 19 73). The present 2. Eclogite Paragenesis
study was expected to show that the xenocryst
garnets were identical to the diamond inclusions Orange garnet 8
as predicted in the earlier work. Orange garnet plus sulphide
In so far as possible, it was intended to
compare the inclusions in the diamonds with the
same minerals in mantle xenoliths from the same 3. Other Inclusions' Paragenesis not defined
kimberlite. However, the practical difficulty
Suldpi e-----(--b--(cid:127)(cid:127))
experienced in sampling the xenoliths at Finsch 358
has restricted this comparison to only a few Graphite 132
rocks. Clouds (dense particles) 23
513
Diamond Selection
Totals (1 + 2 + 3) 1024
The diamonds were selected from that part of
the general production defined by the -6 to +5
Estimated No. of carats inspected 14,500
diamond sieve class. The diamonds are less than
Estimated No. of stones inspected 232,000
1.83 min. in largest dimension and average
approximately 0.056 carat/stone. This
relatively small size was considered acceptable
as there is no evidence to relate inclusion size (a) Sieve class -6 +5. Diameter of circular
or type to diamond size and it is much easier to aperture = 1,829 m.m. Approximate average
extract inclusions from a small diamond than a weight in carats/stone =0.056 ct.
large crystal.
(b) Sulphides occur with both peridotite para-
The diamonds were first inspected by binocular
genesis and eclogite paragenesis minerals.
microscope and those containing inclusions were
The majority of such silicates are olivine
separated and divided into categories of mineral
(i.e. peridotire paragenesis).
assemblages. The sampling information and a
breakdown of the categories are summarised in (c) In a subsequent search of additional
Table 1. As the ten categories in Table 1 were diamonds eclogitic clinopyroxene, an
compiled on observational evidence only, it was eclogitic garnet/clinopyroxene pair, a
not possible to distinguish between certain kyanite and a phlogopite were found. These
mineral species whilst they were still inside the minerals are included in the discussion but
diamond. not in this abundance table.
Copyright American Geophysical Union
Special Publications Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology, and Geochemistry Vol. 15
It was difficult to distinguish sulphides from diamonds containing peridotitic inclusions were
graphite and at present we have no information on macles. This percentage is three times that of
the sulphide inclusion breakdown nor their com- macles in the same size range from the general
positions. We cannot therefore assess the diamond production at Finsch (see Harris et al.,
extent of misidentification in this category of 19 75; Harris and Gurney, 197 8).
essentially black-looking inclusions.
The purple and the orange garnet categories Analytical Procedure
have been found analytically to correspond to
chrome-rich and chrome-poor compositions The inclusions were released from the diamond
respectively, whilst all the spinels are high by mechanical crushing and fracturing. The
chromium chromites. individual inclusions, usually 0.1 - 0.5 min. in
Clinopyroxenes are so rare in Finsch diamonds size were suitably mounted and polished and
that none were found in the initial sampling. analysed by an electron microprobe analyser,
Subsequently four chrome-poor clinopyroxenes were using standards of similar composition and
found in an inspection of several different size applying the data correction procedure Abfan II
ranges of Finsch production; one co-exists with (Boyd, Finger and Chayes, 1969). Detection
chrome-poor garnet. During this later search an limits for each element are given in Table 4.
extremely magnesian, low calcium garnet with an
unexpected green colour (F87- Table 2), a kyanite Inclusions Studied
(Table 3) and additional chromites (Table 2) were
found and analysed. Although the bright green A total of 100 minerals in 80 diamonds have
colour of chrome diopsides should make them been analysed. These include one garnet/clino-
easily visible in a diamond(cid:127) none were found pyroxene and one clinopyroxene/phlogopite pair
either in the initial sampling of (cid:127)-(cid:127) 232,000 from the eclogitic suite together with 14 garnet/
stones or subsequently. olivine, 2 garnet/orthopyroxene(cid:127) one olivine/
chromite and one orthopyroxene/silica phase of
Mineral Inclusion Selection and Diamond peridotitic origin. The total is made up of 50
Characteris tics garnets, 22 olivines, 6 orthopyroxenes and 8
chromites from the peridotitic suite, 6 garnets,
In accordance with our principal objective, 4 clinopyroxenes, a phlogopite and a kyanite of
inclusions were selected for analysis in such a eclogitic character and 2 silica rich phases
way as to allow investigation of their range in believed to be coesite.
chemistry, both within single diamonds and within The inclusions were wholly enclosed within the
the diamond suite as a whole. Care was taken to diamonds and were not located in cracks, nor
analyse all identified inclusions of relatively along fractures nor annealed fractures. They
rare mineral type (clinopyroxenes, chromite, show little or no signs or alteration. Irres-
kyanite), as well as all inclusions of unusual pective of inclusion type many of the inclusions
colour or lustre. Particular attention was given are clearly xenohedral (Prinz et at., 19 75), and
to the selection of diamonds with more than one commonly exhibit equant or elongate cubo-octa-
inclusion. hedral morphologies, with inclusion faces closely
In addition to the nature of inclusions, parallel to the (1OO) and (111) planes in the
attention was given to the characteristics of the diamonds. Where more than one inclusion of the
host diamonds, in order to investigate relation- same mineral was found in one diamond, the crystal
ships between inclusion types and the diamond morphologies were often different.
habit and colour. Six shape categories of dia- In some instances more than one inclusion of
monds (octahedron, dodecahedron, flattened dode- the same mineral was found in one diamond and
cahedron, macle(cid:127) irregular and aggregate) and two seventeen such cases were investigated. In agree-
principal colour types (colourless and brown) ment with the majority of previous studies of
were determined. In those inclusion groups this aspect; for example by Sobolev (1974) or
(Table 1), where the numbers of diamonds were Prinz et al., (1975); no analytically significant
relatively large (e.g. peridotitic olivines and differences in composition were recorded for
garnets), inclusion-bearing diamonds were chosen grains of the same mineral in one diamond.
in order to represent each of the shape and colour In addition to the above it was also noted
categories. For rarer inclusion groups, all in- that the compositions of different minerals in
clusions were investigated. the same diamond were systematically co-variant.
In most groups there were insufficient data to For instance, the most iron-rich olivine co-
make a meaningful assessment of the relationships exists with iron-rich garnet (see Figs. 1 and 3)
between diamond shape, diamond colour, and in- whilst more magnesian olivine and garnet are found
clusion chemistry. Where a number of inclusions together in 12 diamonds. Orthopyroxene is always
were found- that is for the peridotitic olivines more magnesian than olivine as it is in the
and garnets - the restricted range of the in- peridotite xenoliths. In all of these respects
clusions (discussed below) prevented the detect- our results are entirely consistent with other
ion of any correlation. previously published information on diamond
The shape classification of inclusion-bearing inclusions as reviewed by Meyer and Tsai (1976).
diamonds did reveal, however, that over 60% of We consider that this evidence is strongly in
Copyright American Geophysical Union
Special Publications Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology, and Geochemistry Vol. 15
(cid:127)D O uD O(cid:127) O O(cid:127) CD
o o c.,,l ,,.o c,(cid:127) o r'-- o o
c) o (D,-(cid:127) o o c(cid:127) o c',q
(cid:127) C(cid:127)
c(cid:127) ,--(cid:127) o o-., o r"-. o o ch
o", oo o oa0 oo c(cid:127)
(cid:127):u .c(cid:127) . ' c,'.[ '"(cid:127) ' ' '
o a0 zoo o c(cid:127), o o o'(cid:127)
o-(cid:127) ,,(cid:127) -..,T c(cid:127) o ,.no o
cD kO C(cid:127) (cid:127)D CN ,--q kn
00 c--4 o o(cid:127) o o0 o
o-(cid:127) o o o oooo
o 00z oo(cid:127)o(cid:127)7o(cid:127) c(cid:127)
o
zzz(cid:127)4dc(cid:127)zz (cid:127)
o
c-J 0o
c(cid:127) ,-(cid:127)o 00
o o o ,'--(cid:127)
co c(cid:127)j O O
,-(cid:127) Z Z Z u(cid:127) 0 (cid:127)-(cid:127) Z Z c(cid:127)
o-, ,..o -..T c,q (D uP O o',
z (cid:127) c-,4 ,--(cid:127) CDd CDc ',4( D
c-,4 o-, ,--(cid:127) ',.o
o-, ,-'-(cid:127) O o(cid:127)
(cid:127)D OO O ,-q UD o'-, ,--(cid:127) O 0o
ozzz(cid:127)6(cid:127)zz (cid:127)
O C"l (cid:127)D c'q O (cid:127)o O O
.
,-(cid:127)
cid c(cid:127) (cid:127) II
c-.4 4.(cid:127) .u o
(cid:127) o O
(cid:127)½ z
Copyright American Geophysical Union
Special Publications Kimberlites, Diatremes, and Diamonds: Their Geology, Petrology, and Geochemistry Vol. 15
r'". r(cid:127) c',,40'(cid:127) c"q 0 c(cid:127) 0 0 c,,l
u'(cid:127) C',,I .(cid:127)" '(cid:127)D C'(cid:127) 0", O0 C"4 0
4oc(cid:127) o (cid:127)ooo 4
c:h 0 c',q 0 ,---(cid:127) Ln ..(cid:127)' C'q 0
C(cid:127) C) c',l 0 C',l 0 (cid:127)0 ',4D C',l 0
¾o(cid:127)(cid:127)o(cid:127)(cid:127)
,--4
0", 0 0'(cid:127) 0 0 0 "-'(cid:127) r"" 0 0
O',, C) C(cid:127) 0 0 0 ,""(cid:127) o00 0
c(cid:127) ao 0.-, ...,1"u '(cid:127) aO oo c(cid:127) '..,1" 0
,-4o4o4oooo o6
u'-(cid:127) c'-.J, -"(cid:127) u'(cid:127) r'-......(cid:127)' 0 0 o"., '.(cid:127)
I"-- C,,i C(cid:127) 0 O0 0 I'(cid:127)- C"q C(cid:127)I C".I
0'(cid:127) C) C".,I CD, '--(cid:127),- -(cid:127)c (cid:127) 0
C'(cid:127)I C',,l 000 0'40
Copyright American Geophysical Union