American Mineralogist, Volume 71, pages 17-37, 1986

The mineralogy of K-richterite-bearing lamproites

CnnrsutNe WacNrn eNo DeNrrr-r,B Vu-oB

Laboratoire de P4trologie Min4ralogique(U.A. 0736 du CNRS)

Universit€ Pierre et Marie Curie (Paris 6)4, Place Jussieu,75230 Paris Cedex 5. France

Abshact

The mineralogy and chemistry of eleven phlogopite-richterite-bearing lamproites hasbeen studied. It has been found that this mineral assemblage (also found in metasomaticallyaltered ultrabasic xenoliths) is typical of peralkaline lamproites. These lavas are typicallypotassium- and magnesium-rich, with a positive correlation between these two elements,and consequently between peralkalinity and magnesium content. Titanium contents arevariable, but may reach 7o/o TiOr. The peralkaline character was acquired before crystal-lization, all minerals, including the first magmatic phases, having extremely low Al contents.Loss of alkalis, after partial or complete solidification, can be demonstrated in some spec-imens. Typical associations include besides phlogopite and richterite, Cr-rich Al-poorspinels, olivine, diopside, Ti-rich oxides (ilmenite, pseudobrookite, priderite). The peral-kaline character is emphasized by the presence of roedderite-like phases in two specimens.

An electron microprobe study of lamproite minerals shows a general tetrahedral defi-ciency in most Al-bearing silicates, the sum Si + Al being systematically lower than itstheoretical value. Most elements are regularly partitioned between co-crystallizing phases:e.9., Fe, Mg and Ti between richterite and phlogopite; Na and K between feldspar andrichterite; tetrahedral deficiency between phlogopite and richterite.

These observations lead to the conclusion that the peralkaline character of these lam-proites imposes constraints on the mineral compositions. However, the mineral compo-sitions are not affected by the whole-rock silica saturation.

Xenocrystic material has been identified and is abundant in lamproites. Isolated reliccrystals correspond to most major phases, except for richterite, that crystallize from theliquid, i.e., olivine, clinopyroxene, mica, ilmenite, pseudobrookite and apatite.

A comparison can be made between major authigenic phases from lamproites and equiv-alent phases from associations interpreted, in ultrabasic nodules, as metasomatic assem-blages and presumed to have formed in the mantle under high pressures. Most majorelement partitioning trends are not affected by pressure but Ti solubility in silicates isconsiderably reduced by increasing pressure.

The origin of lamproitic liquids cannot be linked to basaltic magmas; basalts are indeedabsent from lamproitic provinces. The observed bulk composition of lamproites couldresult from melting of richterite + phlogopite-bearing ultrabasic associations in the mantle.Calculations indicate that for all specimens considered in the present study the initialproportions could be richterite 30-500/o and phlogopite 56-680/0. Precipitation of olivine(with or without diopside) could then lead to the observed lamproitic lava compositions.

Introduction

The term lamproite was coined by Niggli (1923, p. 105)for rocks whose compositions were extreme with respectto their potassium and magnesium (hrgh) and aluminum(low) contents. The term has been used since, to designaterocks with compositions similar to those of lamprophyres,but whose field relations clearly indicate a volcanic situ-ation (Velde, 1969, 1975).

Recent definitions take into account mineralogical com-positions. The term is thus restricted by Rock (1984) to

0003404x/86/0r024017$02.00 r7

volcanic or subvolcanic rocks with a unique paragenesisthat includes the rare minerals, K-richterite and priderite.According to Scott Smith and Skinner (1984), currentresearch shows that "lamproites are characterized by Ti-rich silicates and oxides, while the absence of plagioclaseand significant amounts of melilite separates them fromother potassium-rich alkaline rocks." Lamproite is usedin the present work in Rock's general definition but, aspointed out by Scott Smith and Skinner (1984), the pres-ence of Tirich silicates and oxides definitely appears tocharacterue this group of lavas.

18 WAGNER AND VELDE: K.RICHTERITE-BEARING I.IIMPROITES

Table l. List ofthe samples studied, geographical localization, age, mineral assemblages and references to previous studies

L o c a l i r i e s' l : :.t i*

Rock rype Asenumbet

uineralogical Assenblag€ References

SPAIN

cancar ix , A lbacete

Calespar ra . Murc ia

Jun i1 la , Murc ia

B a r q u e r o s , M u r c i a

7 4 A l C a n c a l i l e 5 . 7 t o 7 . 6 m . y .

7 2 A i B e I I o n e t a r . ( 1 9 8 1 )B e 1 l o n ( i 9 7 6 ; 1 9 8 1 )

l l A 8 J u m i I I i t eN O D e i e E a f . ( l v 6 l ,

73A8 lo r tun i te MonEenat e t a l .( l 9 7 5 )

01+Cpx+PhI+Richt+Kspar+Cr+I1o

Ac+Ap+r'Roed'r+Ru+Ccx-ol ? x-cr ?

Ap+GIass+X-01 ?

lc+Ac+Ap+CIass

X+Ph1+x-AL-Sp+X-Psb+X-1 lm+x-Ru

L e w i s ( I 8 8 2 )Osann ( 1906)Jerenine and I 'a l lot (1929)hernandez ?acheco ( 1935)San Miguel de Ia Canala et( 1 9 s 2 )I u s t e r a n d c a s t e s i ( 1 9 6 5 )

F u s t e r e t a I . ' ( 1 9 6 7 ) .

B o r l e y ( 1 9 6 7 )v e l d e ( 1 9 6 9 )Ruiz and Badiola (198o)

N i x o n e t a l . ( 1 9 8 2 )

2

3

UNITED STATES

Smoky Butte, MonEana 788

Sbiprock dyke, 586Nev Mexico

Moon Canyon, l j tah MC77

L e p l o i c e 2 7 n . y .h r v i n e t a l . ( 1 9 8 o )

M i n e E t e 2 7 - 3 0 @ . y .N a e s e r ( 1 9 7 1 )A m s t r o n g ( 1 9 6 9 )

Lanproi te 36-40 E.y.

o1 (a1r. ) +cpx+Ph1+Richt+Ksper+Ana1+Ap+GIass+Psb+Prid+cr

01 (a1t) +Cpx+Ph1+Richt-A!fv+Kspar+Ap+Glas s+Ilm+!'lr+Ac

O1 (alE) +Cpx+Ph1+Richl+Kspar+Ap+G1ass+I 1m+Psb+"Roed"+c!+x-Ph1

Matson ( l960)v e r d e ( 1 9 7 5 )

W i l l i a o s ( 1 9 3 6 )N i c h o l l s ( 1 9 6 9 )v e l d e ( 1 9 6 9 )R o d e n ( 1 9 8 1 )

C r i t l e n d e n a n d K i s t l e r ( 1 9 6 6 )

B e s t e t a l . ( 1 9 6 8 )

FRANCE

s i s c o , c o r s i c as i s c o , c o r s i c a

6 1 A 38 A l 2

1 5 . 4 - 1 3 . 5 . n . y . 0 1 ( a l t l c p x + P h 1 + R i c h t -Feraud et aL.(1977) Arfv+(sPar+I1m+Prid+CrC i v e E ! a e t a l . ( 1 9 7 8 ) + R u + A P + S p h + C cB e l 1 o n ( 1 9 8 1 )

v e l d e ( 1 9 6 7 )v e r d e ( 1 9 6 8 )

AUSTRA]-IA

Mount Nor lh ,

t les t K iober ley

s 0 1 3 6 w o l g i d i t e 1 7 - 2 2 n . y .

J a q u e s e t a l . ( 1 9 8 2 )

O1 (al E) +Cpx+Ph1+Richt+Lc+I 1m+Prid+Ap+G1ass

W a d e a n d P r i d e r ( 1 9 3 9 )Carmichael ( 1967)Kaplan et al . (1961)M i t c h e l l ( 1 9 8 1 )J a q u e s e t a l . ( 1 9 8 4 )

ITAI,Yo r c i a t i c o , P i s a s e l a g i t e 4 - l E . y .

b o r s l e t a l . t l v o / ,O1+Cpx+Ph1+Kspar+I Im+Richt+Cr+Ap

Barber i and Innocent i (1967)

s t e f a n i n i ( 1 9 3 4 )

Abbreviations : Ac, amite ; Af-Sp, aiuninous spjne] ,. Anaf, anaTcite ; Arfvt arfveilsonite ; Cc, cafcite ; Cpx, cfinopgroxene (diopside) ;

C t , chron i te ; I tn t i fnen i te ; Kspar , poxass iun fe fdspat , Lc , leuc i te ; Mt , Mgnet i te ; o f , oT iv ine ; Of (a lx ) , a f te rea l o f i v ine ;

ph f , phTogop i te ; psb , pseudobrook ixe ; P t id , p t ider i te ; R ich t , r i ch te r i te ; "Roed" , roedder i te - f i ke phase ; Ru, ru t i fe ;

Sph, sphene. -X jndjcates that tle species whose abbreviated nane folfows is ptesent, but intetpteted as a xenoctgst.

The phlogopite-K-richterite association is also record-ed from nodules found in kimberlites, the uanro suite asdefined by Dawson and Smith (1977). The mineralogicalassociations as well as the composition of the phases pres-ent is similar in the nodules and in the lamproites. Itseemed warranted to examine the compositions of thesephases and their crystallization relationships in lamproitesand consider more closely the similarities and differencesbetween the constituent minerals of lamproites and themetasomatic assemblages from mantle rocks that couldbe the source of lamproites.

Experimental bulk rock analyses were perfbrmed usinga Philips PW 1400 spectrometer. Ferrous iron was deter-mined using a method outlined by Peck (1964) and HrO*by a modified Penfield method.

Electron microprobe analyses were carried out on anMS-46 cAMEcA instrument with natural or synthetic min-erals as standards for olivines, micas, amphiboles andclinopyroxenes. Counting time : 30 s; accelerating volt-age: 15 kV; current : 30 nA (20 nA for K and Na inmicas and amphiboles). Other mineral compositions weredetermined u.ith a cAMEBAx automated electron micro-probe using either oxides or natural minerals as standards.

Counting time : 30 s; accelerating voltage : 15 kV; cur-rent : 30 nA for oxides; 5 nA for feldspars.

Chemical composition and peralkalinecharacter of the lamProites

The eleven specimens studied in this paper come frommost of the classical localities. Their ages vary from 40to 4.1 m.y.; they usually occur as pipes, dikes or necksbut flows are also found. Table I gives the list of all sam-ples studied and Table 2 the corresponding bulk chemicalcompositions.

Lamproites are magnesium-rich: their CIPW nonnsshow 200/o normative enstatite (or diopside) with or with-out forsterite. They are potassium-rich, and analyses showa positive correlation between potassium and magnesium,a significant difference with usual trends in magmatic se-ries. No correlation is observed between alkalis and ironcontent. In the specimens studied, KrO varies between 7and l2o/o (except the Jumilla specimen where the presentKrO content is only 3.70lo), and is largely superior to NarO.Titanium contents are variable, and can reach 7olo TiOr.This is particularly striking when considered in connec-

I4/AGNER AND VELDE : K-RICHTERITE-BEARING I,,,IMPROITES

Table 2. Chemical composition of the samples studied. All analyses are new but for Nos. 6, 8, lO

t 9

t 2

74At 72A7

3 4

I lA8 73A8

5 6 7

7B8 yrc72 586

8 9 l 0 l r

so l36 6 lA3 8A l2 60A7

s i o 2 5 5 . 4 1 5 6 . 6 I

A 1 2 0 3 8 . 8 3 7 . 9 6

F " 2 0 3 l . l 7 2 . 1 2

F e O 3 . 4 0 3 . 1 3

Mgo I 3 .59 12 .45

c a o 3 . 9 1 2 . 9 7

N a 2 0 l . l 3 0 . 7 5

K 2 O 8 ' 6 3 9 . 2 1

MnO 0 .08 0 .08

T i O 2 1 . 4 1 l . 6 l

P z O s t . 3 5 1 . 2 3

BaO

co2

H 2 0 + 0 , 5 9 1 . 8 6

H 2 O - O . 2 3 0 . 6 5

F 0 . 3 6 0 , 4 1

Clppm 226 321

T o t a l 1 0 0 . I 5 l 0 l . 0 4

0 = F 0 . 1 5 0 . 1 7

T o t a l 1 0 0 . 0 0 1 0 0 . 8 7

4 7 . 3 1 5 8 , 7 7

6 . 5 2 I I . 3 4

3 . 8 3 I . 3 t

2 . 8 8 3 . 4 9

t 7 . t 6 9 . 2 2

8 . 8 2 2 . 7 I

1 . 8 8 I . 0 8

3 . 7 t 8 . 4 6

0 , t 2 0 . 1 0

| . 3 2 I . 3 5

2 . O O O , 1 9

3 . 7 7 0 , 9 6

t . 3 l 0 . 3 1

0 . 3 2 0 . 3 0

t 7 4 8 7

1 0 0 . 9 5 1 0 0 . 1 9

0 . 1 3 0 . 1 3

I 0 0 . 8 2 I 0 0 . 0 6

5 l , 4 1 5 5 . 7 3 5 3 . 7 0

8 . 3 6 1 O , 7 2 I 1 . 0 6

3 . O 2 3 . 7 3 3 . 5 7

2 . 3 1 0 . 9 5 3 . 0 8

8 . 0 5 6 . 9 6 7 . 8 6

4 . 7 t 3 . 8 5 7 . 3 8

1 . 2 5 | . 2 t 2 . 3 1

7 . 8 7 1 0 , 4 9 6 . 6 4

0 . 0 6 0 , 0 8 0 . l 0

5 . 4 6 2 , 8 2 l . 8 l

2 . 2 2 1 . 1 3 0 . 9 1

0 . 3 5

3 , 5 8 l . 1 4 1 . 5 3

t , 7 4 0 . 8 9 0 . 6 2

0 . 4 6 0 . 1 6

78

1 0 0 . 5 0 1 0 0 , 0 5 r 0 0 . 7 3

0 . 1 9 0 , 0 7

| 0 0 . 6 6

4 5 . 8 2 5 7 . 4 6 5 6 . 2 3 5 7 . 8 I

6 . 8 6 1 0 . 8 8 1 2 . 0 6 1 0 . 9 4

6 . 0 7 1 . 4 6 l 9 I 3 . 5 5

1 . 9 8 2 . 5 4 2 . 9 t r . 4 4

1 0 . 9 0 7 . 2 4 6 . 9 0 8 . 2 6

4 . 7 0 2 . 9 6 3 . 4 8 4 . 4 3

0 . 8 4 t . 1 4 1 . 0 3 1 . 0 9

8 . 8 2 1 0 . 7 5 1 0 . 0 0 7 . 9 4

0 . I 0 0 , 0 5 0 . o 7 0 . 0 7

7 . 3 4 2 . 1 9 1 . 1 4 t . 3 7

I . 8 3 0 . 1 4 0 . 7 9 0 . 7 2

t . 2 7

0 . 0 8 0 . 4 1

o . 7 5 1 . 7 0 1 . 5 6 l . t 8

2 . 4 0 0 . 7 2 1 . 5 8 1 . 0 6

0 , 3 8 0 . 3 5 0 . 3 3

4 5 3 1 9 7 4

9 9 . 7 6 1 0 0 . 2 1 t O O , 4 2 1 0 0 , 1 9

0 . 1 6 0 . 1 5 0 . 1 4

1 0 0 . 0 5 1 0 0 . 2 7 1 0 0 . 0 51 0 0 . 3 1

| . 2 6Na+K

A 1l . 4 l 1 . 0 9 0 . 9 6 1 . 2 4 0 . 9 9 1 . 5 9 t . 2 4 1 . 0 4 0 . 9 5

aOrAbAN

AcNeN sKsDA

E nF sFoF aMIHeEIIETnP fRuAPC c

2 . 9 0 2 . 2 7 3 . 1 4 2 . 3 3 4 . 6 14 8 . 1 5 4 3 . 3 7 2 1 . 9 0 5 0 . 0 4 4 5 . 6 5 5 8 , 5 3 3 9 . 2 5 3 7 . 2 5 5 9 . 3 2 5 9 , 1 0 4 6 . 9 8

1 2 . 4 2 9 . t 2 l 7 . 3 4 6 . 3 6 9 . 2 21 . 0 6 0 . 1 4 1 . 4 5

3 . 3 7 5 . 5 7 2 . 6 8o . 2 3

0 . 8 0 3 . 0 88 . 6 5 5 . 2 9 2 4 . O 7

2 1 . 2 0 2 8 . 8 72 . 4 4 2 . 8 56 . 3 0 2 2 , 3 50 . 8 0 0 . 5 3

0 , 2 8 4 . 2 0

8 . 7 3 9 . O 2

0 . 1 6o . 2 6 0 , 9 6

5 . 7 5 4 . 3 42 0 . 7 7 2 0 . 1 3 1 5 . 3 2

3 . 9 2

6 . 4 7 4 . 2 0 2 . 0 8

2 . 6 8 3 . 0 5

3 . 1 9 2 . 9 2 4 . 7 0o . 2 2

1 . 8 8 5 . 2 4 2 . 7 3

1 . 1 9l . l 3

4 . t 6 l l 82 3 , 8 0 7 . 7 6

2 7 . 2 0 1 4 . 6 9o . 9 2

6 . 0 3

5 . 0 I0 . I I 4 . 0 03 . 4 4 4 . 4 t 4 . t 6

1 . 3 76 . 1 20 . 8 8

2 . 1 5 4 . 0 3 1 . 7 50 . 2 0

7 , 9 2 1 2 . 3 3f 0 . 5 5 t 4 . 9 4I . 6 02 . 3 80 . 4 0t . 7 3 0 . 9 0

2 . 9 32 , l 7 2 . 6 0

t , 7 3 l . 7 l0 . 9 3

0 . 6 12 . 5 1 2 . 5 7 5 . 0 0 2 . 1 8

6 . 3 9 3 , 8 50 . 1 8

Ana lye is 6 , Bes t e t a l . , 1968; Ana lys is 8 , Wade and pr ider , 1940; Ana lys is 10 , Ve lde , 1967.

tion with the low iron content of these rocks in general(4.0 to 6.10/oFeO * FerO, and 8go in specimen SOl36).

The specimens examined are either definitely peralka-line or close to peralkalinity. This character is demon-strated by the presence of normative acmite in the CIPWnorrn, accompanied by sodium ald/or potassium meta-silicate, the maximum content ofnormative anorthite being1.45% (Table 2). Fluorine (between 0.2 and 0.470lo) ispositively correlated with potassium content following therelationship discovered by Aoki et al. (1981).

Two lines of evidence indicate the primary origin of theperalkaline character of the lamproitic rnagma. One ar-

gument is the fact that lamproites often occur with glassytextures, frequent among the Spanish lamproites, presentin Smoky Butte and the Leucite Hills, and recently de-scribed in Australia (Prider, 1982). The second line ofevidence is that the spinels found in olivines ofthe Spanishlamproites, Sisco, Moon Canyon, the selagites and theSmoky Butte lamproite are uncommonly chrome-rich (51to 6506 CrrOr) but always alumina-poor (0.23o/o to 4o/oAlrO3) fiable 3). In comparing data on various olivine-bearing lavas, it appears that the AlrO, content of Cr-richspinels is related to the composition of the rocks in whichthey are found. Using, for example, analyses published by

20 WAGN E R AN D VE LD E : K. RI C HTE RI TE - B E AR I NG I.'/IMPRO ITE S

Tabte 3. Representative electron microprobe analyses of chrome spinels found as inclusions in the olivines. Fe3+ calculated assuming3 cations and 4 oxygens

r 2 3 4 5 6 7 8 9 1 0 1 1

7 4A1 7 4Ar 12A7 72A7 1 1A8 11A8 73A8 6818 8Ar2 60A7 60A7

A 1 ^ O ^ O . 2 3 0 . 1 5 3 , O 4 t . 1 2

C r ^ O ^ 5 1 . 4 1 6 2 . 6 4 6 5 . 3 4 6 1 . 4 3

FeO 37.05 26 .40 20 .33 29 .99

M g O 4 . 4 2 8 . O O 1 0 . 4 1 4 , 7 2

MnO 0 .84 O,82 O. 69 O. 90

T i o ^ 4 . 5 2 1 . 1 6 1 . 2 3 t . 6 3

ZnO od nd nd nd

Tota I 98 .47 99 .17 101.04 1OO.39

F e ^ O ^ 9 . 7 7 7 , 7 8 3 . 2 2 4 . 5 4

FeO 28.26 t9 .94 L7 .43 25 .90

A l O . O 1 0 0 . 0 0 6 0 . 1 2 0 0 . 0 7 2F e 3 + 0 . 2 6 7 o . 1 9 o 0 . 0 8 1 O , L 2 lC r 1 , 4 7 6 I . 7 4 2 I . 7 3 6 I . 7 2 OFez+ 0 .858 O.587 0 .49O O.767Mg 0 .239 O.42o 0 ,522 0 .249Un 0 .026 O.O24 O,O2O O.o27T i 0 . 7 2 3 0 . 0 3 1 0 . 0 3 1 0 . 0 4 3Zn

4 . 1 6 3 . 5 6 7 . 8 7

6 3 . O O s s . 6 4 3 6 . 2 2

1 5 . 3 1 3 0 . 1 7 4 7 . 9 5

1 3 . 8 0 5 . 7 7 3 . 3 0

o, 48 0 . 80 0 .86

2 . r 4 7 . L 2 5 , 7 0

O.2O nd nd

9 9 , 0 9 9 7 . 0 6 9 s . 9 0

2 . 9 7 7 . 1 3 1 9 , 2 ' 7

12.64 23 .21 30 .61

0 . 1 6 3 0 . 1 5 1 0 . O 8 20 , 0 7 4 0 , 2 0 9 0 . 5 3 81 . 6 5 6 1 . 5 8 0 7 . 0 6 20 . 3 s 1 0 . 6 9 7 0 . 9 4 9o . 6 8 4 0 . 3 0 9 0 . 1 8 20 . 0 1 4 0 . o 2 4 0 . 0 2 70 . 0 5 3 0 . 0 3 0 0 . 1 5 9o. oo5

2 . O O 1 . 1 6

5 5 . 7 8 5 1 . 4 8

29.34 34 .91

9 . 8 0 7 . 4 3

o . 7 9 0 . 4 7

1 , 0 3 0 . 7 9

nd nd

98.7 4 96 .30

7 3 . 3 2 1 6 . 3 9

1 7 , 3 5 2 0 . 2 3

0 , 0 8 1 0 . 0 4 90 . 3 4 5 0 . 4 4 41 . 5 2 0 r . 4 6 4o.500 0 .6090 . 5 0 4 0 . 3 9 90 . o 2 3 0 , 0 1 4o . o 2 7 0 . 0 2 1

1 . 1 0 0 . 7 1

3 1 . 5 8 4 2 . 7 8

46,72 32 .84

5 . 2 4 9 . 5 4

o , 5 5 0 . 6 1

r 0 . 9 0 9 . 5 0

n d 0 . 3 2

96.O9 96.30

1 5 . 7 9 9 . 5 9

3 2 . 5 1 2 4 , 2 2

o.o48 0 .o30o . 4 3 6 0 . 2 5 7o . 9 1 6 L . 2 0 50.997 0 .12ro . 2 8 6 0 . 5 0 60 . o 1 7 0 . o 1 80 . 3 0 1 0 . 2 5 4

o.oo8

F e O o : T o t a l i r o n a s F e on d : n o L s o u g h t f o r .

Eissen (1982) on MORB basalts and Barbot (1983) onspinels from alka[ basalts, it can be seen that for a givenCr content, spinels from tholeitic basalts are richer inAlrO, than spinels found in alkali basalts. Within the fieldof alkaline rocks, spinels are richer in aluminum in alu-mina saturated melilite-bearing compositions than theyare in peralkaline compositions, the two fields showingno overlap (Velde and Yoder, 1983; unpublished data).In the lamproites the Cr-rich spinels can be considered asthe liquidus phase. From their rather unique composition,they definitely belong to the peralkaline field as defined

Table 4. Electron microprobe analyses ofthe gJass (1 : averageof 3 determinations) and olivine (2) included in an apatite crystal

from specimen I lA8

s i o z 5 5 . 0 0 4 o . o o

o 1 2 0 3 1 2 . 0 0

F e o o 6 . 0 0 1 1 . 0 0

u g o 1 . 3 0 5 0 . 0 0

C a O 1 . 6 0 0 . 2 0

N a 2 0 5 . o O

K 2 O 1 2 , O O

M n O O . 2 O

T i o 2 2 . 6 0

T o t a l 9 5 . 5 0 1 o 1 . 4 0

by Yelde and Yoder (pers. com.). The peralkaline char-acter of the lamproites could, in some instances, have beenmore pronounced than presently evidenced by their bulkcomposition. Specimen I lA8, from Jumilla, containsapatite phenocrysts with frequent glass inclusions. One ofthese (0.06 x 0.03 mm) contains besides glass, a euhedralcrystal of olivine and a small mica blade, both phasesappearing as phenocrysts in the rock. This glass (Table 4)is considerably richer in alkalis than the bulk rock andthe (Na + K)/Al of the glass inclusion is 1.72 as opposedto 1.09 for the bulk rock composition. kast squares cal-culations made to estimate whether the glass compositioncould be derived from the bulk composition of the rock,taking into account the presence ofthe olivine and biotitecrystals, show that a reasonable fit is obtained only if itis assumed that the bulk composition has lost alkalis(mostly potassium) after inclusion of the Slass in the apa-tite.

From the above one can consider that the lamproiteliquids that produced phogopite and K-richterite assem-blages had primary peralkaline compositions. This char-acter was acquired before the first liquidus phase (Cr-spinel) crystallized. In at least one specimen (l lA8) it canbe demonstrated that the composition was altered afterthe crystallization ofthe feldspar (see below) and originallyhad a stronger peralkaline characteristic.

Finally, the silica saturation is not a factor critical tothe mineralogical association under consideration sincelamproite compositions can vary from undersaturatedwithrespect to silica (with modal felspathoid) to oversaturated(with modal qtartz).

f e u " = l o E a r l r o n a s r e u

WAGNERAND VELDE: K-RICHTERITE-BEARING LAMPROITES 2I

Table 8. Representative electron microprobe analyses of feldspars from the lamproites studied. Total iron : FerO,

t 2

74A7 72A7

t 4 )

11A8 11A8 7348

6 7 8

7B8 5B6 586

9 1 0 L 7

MC77 6143 61A3

1 2 1 3

60A7 6047

s io2 63 ,90 63 .9r

A l2o3 r7 .46 17 .72

F e 2 O 3 L . I 2 7 . 2 6

l'{go o. 02 O. 03

CaO

N a 2 o o . 4 4 0 . 6 3

K 2 O 1 6 . 1 5 7 5 ' 7 5

B a o O . 2 5 O . 3 9

T i o 2 o . 2 7 O . 2 9

T o t a l 9 9 . 6 1 9 9 . 3 8

s i 2 . 9 4 6 2 . 9 9 3A 1 0 . 9 6 2 0 . 9 4 5Fe3+ o .039 0 .o44Mg O.OO1 o .oo2

Na O,O4O O.O57K 0 . 9 6 3 0 . 9 4 1Ba O.OO5 O.OO7Ti o .oo9 0 .010

5 . o o 5 5 . 0 o 1

6 t . 2 8 6 3 . 1 1 6 3 . 8 1

1 2 . 8 5 t 4 . 4 9 1 8 . 5 9

4 . 9 5 3 . L 7 0 . 3 1

o . 1 0 0 . 2 0

o . 6 6 0 . 3 2 L . 3 9

1 6 . 3 8 1 6 . 2 0 1 4 . 5 0

0 . 1 1 0 . o 8 0 , 6 4

o . 4 2 0 . 2 2 0 , 1 6

9 6 . 7 5 9 1 . 7 9 9 9 . @

3 . o r 2 3 , o 2 8 2 . 9 6 9o , 7 4 5 0 . 8 2 0 1 . 0 2 0o , 1 8 3 0 . 1 1 4 0 . 0 1 1o. oo7 0 . o1 4

o . 0 6 3 0 . o 3 0 0 . 1 2 5L . O 2 1 0 . 9 9 2 0 . 8 6 1o . o o 2 0 . 0 0 2 0 . 0 1 20.016 0 ,oo8 0 .006

5.050 5 .0o8 5 .003

63.61 63 .22 65 .O2

L 5 . 7 6 1 9 . 0 0 1 8 . 4 1

1 . 9 3 0 . 6 2 0 . 6 2

0 . 1 1 0 . 1 0

o . 5 s 3 . 2 5 3 . 5 3

1 5 . 8 3 1 0 . 9 8 r . 5 2

r . 2 1 l . a 1

0 . 3 3 0 . 2 6

99.22 99 . os 99 .46

3 . 0 1 3 2 . 9 4 5 2 . g a 0o . 8 8 0 1 . 0 4 3 0 , 9 9 5o . 0 6 9 0 . o 2 2 0 . 0 2 1

o . o o 5 0 . 0 o 5o . o 5 1 0 . 2 9 4 0 . 3 1 40 . 9 5 7 0 , 6 5 3 0 . 6 7 4o . o 2 3 0 . 0 3 4o.o12 0 .009

s .oo4 4 .996 4 .991

63.23 64 .24 64 .63

1 5 . 8 6 7 7 . 2 9 1 8 . 2 4

2 . 9 7 1 . L 4 0 . 2 0

o . 0 8

o . 3 2 0 . 4 2 0 . 5 6

1 5 . 8 4 7 6 . 2 1 7 5 . 9 7

0 . 5 0 0 . 1 1 0 . 3 4

o . 2 9 0 . I 2 0 . 0 7

99. 03 99 . 53 100. o1

2 . 9 9 4 3 . O o O 2 . 9 9 4o . 8 8 5 0 , 9 5 2 0 . 9 9 60 . 1 0 4 0 . 0 4 0 0 . o 0 7o. 006

o. o29 0 .038 0 . o50o . 9 5 1 0 . 9 6 6 0 . 9 4 4o. oo9 0 . oo2 0 . 006o.010 0 .o04 0 .0o2

4.994 5 .OO2 4 .999

64,99 64 .65

L 4 . 5 7 L 8 . 5 2

o . 5 1 0 . 7 8

2 . 2 5 2 . 2 9

7 3 . 3 4 1 2 . 9 8

o . 0 6 0 . 8 9

o . 1 7 0 . 4 0

9 9 . 8 9 1 0 0 . 5 1

2 . 9 8 2 2 . 9 6 61. OO4 1 . OO20 . 0 1 8 0 . o 2 1

o , 2 0 0 0 . 2 0 40 . 7 8 1 0 . 7 6 0o . o o l 0 . 0 1 6o . 0 0 6 0 . 0 1 4

4.992 4 .988

Mineralogy

A general order of crystallization can be deduced from thetextural relationships of the lamproites studied. In all specimensolivine appears to be the first silicate phase to appear. The Cr-rich spinels are only found as inclusions in olivine. Diopside andphlogopite have probably syncrystallized; amphibole and feld-spar have appeared subsequently and are contemporaneous withan acmitic rim on the clinopyroxenes and in some instances witha deeply red colored edge around the phlogopites. Oxides appearto have formed after the diopside and the phlogopitic centers ofthe micas. The specimen from Moon Canyon shows phlogopitesurrounding olivine crystals, and richterite rimming the diopside,thus supporting the order stated. It should also be mentionedthat, when present, feldspar often shows a skeletal habit. Modalanalyses are given in Table 5.t

Olivine

Olivine is found unaltered only in some Spanish specimens andthe Orciatico selagite. In both types, some crystals (usually an-hedral, and large in size) represent xenocrysts with typical kink-bands. Phenocrysts are generally euhedral in outline, and containnumerous euhedral spinel inclusions. Compositions of the xeno-crysts are similar to that of the cores of the phenocrysts, in majorelements (Foo/o) or trace elements (Ni for example). Compositions, including xenocrysts (Table 6') vary from 92 to 77o/o Fo.Nickel contents are consistently high, vary from 0.10 to 0.700/oNiO, but usually occur between 0.30 and 0.500/0. Such hieh Nicontents are above the values given for olivine in basalts (between0.10 and 0.30 NiO, Simkin and Smith, 1970; Anderson andWright, 1972). They are comparable to values reported by Reidet al. (1975) in olivine from peridotite xenoliths, close to Ni

contents found in olivines from nodules occurring in kimberlites(Nixon and Boyd, 1973; Scott, l98l) and similar also to valuesrecently determined in the Australian lamproites and kimberlites(Jaques et al., 1984).

The NiO content of the olivines is inversely correlated withthe fayalite content. In the selagite, the most ferrous olivine (Forr)contains 0.230lo NiO. Calcium in the olivines is usually low,particularly in the xenocrysts, but always below 0.200lo CaO. Thereis a positive correlation between CaO and fayalite contents ofthe olivine.

The manganese contents are consistently high and positivelycorrelated with the fayalite content; MnO is close to 0.30o/o atForo.

Pyroxene

Clinopyroxene (Table 7r) in the lamproites studied falls mostlyin the endiopside field of the pyroxene quadrilateral. Its abun-dance varies from 6 to 22Yo in volume. It most often occurs asunzoned phenocrysts which contain around 1olo TiOr. The CrrO,content varies between 0.1 and 0.3 but, in the Spanish lamproitesfalls in the 0.44.9o/o range. These values are considerably higherthan those commonly found in lavas and are, for the highestones, consistent with percentages recorded from diopsides fromdunite inclusions (e.g., Berger, 1981).

In all samples, save the specimen from Shiprock (586), thetetrahedral site ofthe pyroxene is incompletely filled by Si andAl; the tetrahedral site occupancy varies from 1.94 to 2.00, usu-ally being between 1.97 and 1.98 atoms. The site can be consid-ered as completed by Fe3* atoms that are present when the stmc-tural formula is calculated on 4 cations and 6 oxygens. Thisdeficiency in Si + Al was noted by Carmichael (1967) for theLeucite Hills diopside and is mentioned by Jaques et d. (1984)for the Australian lamproites. This situation can be related tothe low-alumina content of the liquid from which the pyroxenescrystallized. Acmite is present in many samples, as a thin, laterim around the diopside crystals, or small groundmass grains.

I To receive copies of Tables 5, 6, 7, 14, 15, and 16, orderDocument AM-86-292 frorn the Business Ofrce, Mineralogicalloge1V g{Ameic,a, 1625I Street, N.W., Suite 414, Washington,D.C. 20006. Please remit $5.00 in advance for the microfiihe.

22 WAGNER AND VELDE : K-RICHTERITE-BEARING LAMPROITES

Y+Gz

" . \n

'.:t

C a

o

I

Y

z

F e 3 + f e l d s D a r

Fig. l. The joint distribution of (Na + K) - Al calculatedfrom the bulk rock composition and the Fe3+ content offeldspar(mole%). Solid squares: data from this study (specimen numbersare listed in Table l); solid circle: LH9, Carmichael (1967). Opensquare: Jumilla composition correcled for calculated alkali loss.

In two specimens (Shiprock, 586 and Smoky Butte, 7B8) someof the colorless diopside phenocrysts show a gteen center. InShiprock the green cores are richer in Al, Fe and Na than thediopside zone. Barton and Bergen (1981) have reported the pres-ence of green clinopyroxenes with a salitic composition in a ku-cite Hills wyomingite, and this type of clinopynoxene has fre-quenfly been found in alkali-rich, potassic rocks (Barton andBergen, 1981; Lloyd, l98l). These green centers in diopsides arecommonly interpreted as being xenocrysts, coming from the dis-agglegation ofclinopyroxenite nodules, and appear to be a ubiq-uitous feature of potassic volcanics.

Feldspar

Feldspar is abundant (19 to 480/o in volume) and appears latein the crystallization sequence; it is absent from the Mount NorthAustralian lamproite which carries leucite and from some of theglassy specimens. In all but two cases the feldspar compositionis close to that of the potassic end member (Or 95-98). Feldsparsfrom the Shiprock and Barqueros specimens are more sodic (64to 72, and,87 to 890/o Or respectively) (Table 8).

Iron contents are high, usually varying between I and 20lo FerOr,but reaching 2.5o/o at Moon Canyon and 590 in the jumillite.Carmichael (1967) reportsvaluesbetween 3 and 40lo in the LeuciteHills lamproites and Best et al. (1968) 3.830/o in some of theMoon Canyon specimens. According to Smith (1974) the ironcontent offeldspars could be related to a rapid growth rate. Thoughfeldspars in lamproites have crystallized rapidly as exemplifiedby their common skeletal habit, the iron content cannot be ex-clusively linked to the growth rate, but can definitely be correlatedwith the peralkalinity of the liquid (Fig. l). The only exceptionis the Jumilla feldspar whose abnormal position on the diagramis consistent with the alkali loss already addressed above.

Y+Gz

1 . Oo.5

C a

Fig. 2. (a) The distribution of Na + K and Ca in richteritesfrom specimen 7B8. O) The distribution of Na + K and Ca inrichterites from specimen 586.

The feldspars are titanium-rich. Percentages of TiO, in thelamproite feldspars analyzed reach0.45o/o; Best et al. (1968) give0.500/o for a Moon Canyon feldspar, values that are considerablyhigher than the 0.07 to 0.080/o recorded by Smith (1974) in histreatise. Feldspars from the Sisco minette, which coexist in thegroundmass with abundant minute sphene needles, show thelowest values (0.07% TiOr). No simple relationship is apparentbetween the TiO, content of the feldspars and the TiO, contentof the liquid from which they crystallized.

Barium varies betwen 0.1 and 0.390 BaO. but can reach0.620/o(73A8) and l.3ob (7B8). Two specimens show large variations inthe barium contents of the feldspar: in sample 60A7, BaO variesfrom 0 to 0.89%, and in sample 586 from 0.0 to 3.22%BaO.In both cases there is an inverse correlation between BaO andthe sum NarO + KrO.

Amphibole

Amphiboles found in peralkaline lamproites belong to the rich-terite group and are characterized by the presence ofa high pro-portion ofpotassium in the A site. They are among the last phasesto appear and are found, albeit in small amounts, even in somelamproites that do not have a peralkaline composition (e.g., theselagite). In this case, their presence indicates that towards the

WAGNER AND VELDE: K.RICHTERITE-BEARING LAMPROITES z5

o 81 0

:a+o(J os

R i c h t 6 r i t e

t

Arfvedsonite

1 0 0 1 0 5 1 1 0

S i + N a + K

Fig. 3. The distribution of Ca * AlIv and Si + Na + K inrichterites from specimen 61A3.

end of the crystallization sequence at least the residual liquidswere peralkaline. Richterites belong to the calcalkaline amphibolegroup and their general formula can be written(Na,K)NaCaMg,Fe2*)rSi*Orr(OH)r. The richterites analyzed haveat most one Fe2* atom in the C site, except for the amphibolesfound in the Shiprock and Sisco specimens that are richer in iron(varying between MgrFe, and MgrFer).

Their composition is usually close to the theoretical richteritecomposition (e.g., 7B8, Fig.2a), or intermediate (as in Shiprock,Fig. 2b) between richterite and arfuedsonite (Table 9). The struc-tural formulae were computed following the method of Papikeet al. (1974) as advocated by kake (1978). Initially the A site(Na + K) is overfilled and the tetrahedral site is underfilled (Si +At < 8). In Figure 3 the trend shown by the experimental pointsis parallel to the theoretical richterite-arfredsonite line demon-

^ ^ ^o

t A o , ^ oo

oA

15-6 15 8 16 .0

E cat ionsFig. 4. The distribution of Ti and the sum of cations in rich-

terites from 74Al (solid triangles) arrd72A7 (open circles).

strating this tetrahedral deficiency. The tetrahedral site must thencontain another ion which could be Fe3+. When calculated Fe3+is assigned to the tetrahedral site, the structural formula usuallybecomes acceptable, the tetrahedral site is filled and there is noexcess of ions in the A site. In some analyses however (e.g., inCalasparra) the tetrahedral site cannot be filled by Si, Al and Fe3+and the presence of yet another ion should be considered.

The richterites are Ti-rich: the minimal values found are closeto 2o/oT7Or, in Sisco for example, but reach 990 in Moon Canyon.In amphiboles with high Ti contents (Cancarix, Calasparra and

Table 9. Representative electron microprobe analyses of K-richterites from the lamproites studied. Structural formulae calculatedon the basis of23 oxYgens

1 2 3 4

74At 7 4AI 72A7 11A8

1 0 1 1 1 2 1 3 1 4 1 5 1 6

MC77 MC77 61A3 8A12 30136 50136 60A7

5

11A8

6

73A8

7

788

98

)bo

s loz 52 .49

AIzO3 O' 41

F e O o 4 . 5 1

M g o 1 8 . 6 5

C a O 6 . 6 8

N a r O 4 . 2 4

K 2 O 3 . 6 4

MnO

T i o 2 5 . t 4

T o t a l 9 6 . 7 6

s i '1 .632

A l 0 , 0 6 9F e z + o . 5 4 4Mg 4 .017C a 1 . 0 3 3N a 1 . 1 8 5K 0 . 6 6 9ItnT i 0 , 5 5 8

l o t a l 1 5 . 7 O 1

52.92 5L .79 52 .31

o . 5 5 0 . 3 6 1 . O 1

1 3 . 6 4 6 . 6 2 1 . 9 9

t 1 . 1 7 7 7 , 2 4 t 7 . O 9

4 . 4 4 5 . 1 9 3 . 5 1

4 . 6 7 4 . 1 5 6 . 3 3

4 . 1 2 3 . 6 9 2 . a 9

o . 1 0 0 . 1 3

7 . 1 6 5 . 6 6 5 . 4 2

9 8 . 6 1 9 6 . 0 O 9 6 , 6 8

7 , 7 2 5 ' t . 5 7 7

o . 0 9 4 0 . 0 6 21 . 6 6 5 0 , 8 0 92 . 4 3 0 3 , 1 5 9o . 6 9 4 0 . 9 0 8r , 3 2 L 1 . 3 4 7o . 7 6 7 0 . 6 8 8

o . 0 1 2o . 7 8 6 0 . 6 2 2

1 5 . 4 8 5 1 5 , 7 8 4

53.22 54 .40

o . 3 2 0 . 3 3

9 . 5 5 7 . 0 8

1 6 . 7 0 1 8 , 5 8

4 . 0 5 5 , 8 4

6 , 4 3 5 . 0 1

2 . 9 4 2 , 5 1

0 . 1 4 0 . 0 9

4 . 1 9 3 . 8 1

9 1 . 5 4 9 7 . 6 5

5 3 . 2 6 5 1 . t O

0 , 3 8 7 , 7 5

4 . 2 2 1 3 . 2 1

1 8 , 9 3 7 5 . O 2

6 . 1 7 3 , 8 7

4 . 2 7 6 . 9 5

4 , 2 5 1 . 6 2

o , 2 2 0 . 7 7

5 . 1 0 3 . 5 5

9 7 , 0 0 9 7 . 2 5

4 8 . 8 5 5 r . 1 2

r . 6 2 0 . 5 1

1 7 . 8 5 5 . 5 3

12.36 l '7 .06

7 . 9 9 6 . 3 8

8 . 2 6 4 , 3 3

t . 5 2 4 . 2 2

o . 2 t o . 1 2

3 , 2 3 7 . 4 4

9 5 . 8 8 9 6 . 7 r

5 0 . 0 6 5 1 , 5 5

o , 2 5 0 . 3 6

8,29 76 , '78

1 4 , 6 4 7 0 . 1 4

4 . 3 0 r . 2 r

4 , 9 6 6 , 6 6

3 , 9 4 4 , 3 4

o . 1 1 0 . 0 4

a . 4 1 6 . 5 t ,

9 5 . 0 6 9 7 . 6 2

1 . 4 7 0 7 . 7 3 6o . 0 4 4 0 . 0 6 31 . O 3 5 2 . 1 0 63 . 2 6 5 2 , 2 6 70 . 6 8 8 0 . t 9 41 . 4 3 5 1 . 9 3 80 . 7 5 0 0 . 8 3 00 . 0 1 4 0 . 0 o 50 , 9 5 1 0 , 7 3 8

1 5 , 6 5 2 1 5 . 8 7 7

52.O2 52,46

o . 4 0 0 . 3 3

L 2 . 3 5 2 , 9 4

76,25 20 ,55

6 . 4 4 6 . 5 8

3 . 8 5 3 . 2 9

3 . 5 6 5 . 8 1

o . 2 4 0 , o 4

2 . 5 6 5 . 0 4

9 7 . 6 7 9 1 , 7 0

1 , 6 5 1 7 . 5 3 2o . 0 6 9 0 . 0 5 5L . 5 2 0 0 , 3 5 33 . 5 6 5 4 , 3 9 71 . 0 1 6 1 , O r 21 , 0 9 9 0 , 9 L 6o . 6 6 9 r , O 1 60.o30 0 .0050 . 2 8 3 0 . 5 4 4

1 5 . 9 0 8 1 5 . 8 9 0

5 7 . 2 4 5 4 . 5 0

o . 5 3 0 . 9 3

5 . 4 5 8 . 0 5

1 8 . 1 2 1 8 . 1 3

6 . 6 8 8 . 3 4

3 , 6 4 3 . 4

5 . 5 5 1 . 1 2

o . 0 5 0 . 1 1

6 . 3 4 r . 6 4

9 7 . 6 0 9 6 . 4 2

1 , t + 2 2 7 . 8 3 3o . 0 9 0 0 . 1 5 7o . 6 6 1 0 , 9 6 73 , 9 1 1 3 , 8 8 47 , 0 3 7 L . 2 4 5L , O 2 4 0 . 9 4 87 . 0 2 6 0 , 2 4 2o . 0 0 6 0 . o 1 3o . 6 9 0 0 , 1 7 7

1 5 . 8 6 7 1 5 . 5 0 6

7 . 5 8 8 ' t . 7 1 1o . t ' 7 3 0 . o 5 50 . 9 6 9 1 . r 5 73 . 6 9 5 3 . 6 0 6o . 5 4 6 0 . 6 2 91 . 7 8 0 1 . 8 0 6o , 5 3 5 0 , 5 4 3o . 0 1 6 0 . 0 1 70 . 5 9 1 0 , 4 5 1

1 5 . 8 9 2 1 5 . 9 8 0

7 , 7 4 7 7 . 6 3 3o , 0 5 5 0 . 0 6 5o,843 0 , 5063 . 9 4 3 4 . o 4 3o . 8 9 1 0 . 9 7 91 . 3 8 3 1 . 1 8 7o . 4 5 6 0 . 7 7 7o . 0 1 1 0 . o 2 7o.408 0 , 550

1 5 . 7 3 7 L 5 . 1 6 1

1 . 5 2 7 7 , 4 8 8 7 . 4 3 20 . 3 0 3 0 , 2 9 3 0 . 0 8 7r . 6 2 7 2 . 2 A 8 0 , 6 1 23 . 2 9 9 2 . 8 2 4 3 , 6 9 1o . 6 1 1 0 . 3 2 6 0 . 9 9 41 . 9 8 6 2 . 4 s 6 1 . 2 2 1o . 3 0 5 0 . 2 9 7 0 , 7 8 3o . 0 2 1 0 . o 2 7 0 . 0 1 5o . 3 9 4 0 . 3 7 2 0 . 8 1 3

16.o lJ 16 .310 15 .726

t e u ' = I o l a r l r o n a s t e u

o

!

F

WAGNER AND VELDE: K-RICHTERITE-BEARING LAMPROITES

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24

2

ro <N O

o @

r

ooo

x

a)

o

oo

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c)

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WAGNER AND VELDE: K-RICHTERITE-BEARING I-/IMPROITES 25

d

oD

tro

- [t r t r t r

J

t r t r t .I

trB

a

f

tr

r l

a

t . '

a a t ^

^ 6 * - o o o" o o

o*

* *

r*6 *

+ o oo * * '̂*

tr

1*# -"f - - . t

nt

i

o 6

FF

1 5 . 6 1 5 . a 1 6 . 0

E ca t ions

Fig. 5. The distribution ofTi and the sum ofcations in rich-terites from MC77 (open squares) and l1A8 (solid squares).

Moon Canyon) the inclusion of titanium creates a vacancy in thestructure as can be shown on a diagam showing the variationof Ti vs. the sum of ions (Figs. 4 and 5), an analogous situationto that described below in trioctahedral micas. Amphiboles withlower Ti-contents from all other specimens display a negativecorrelation between titanium content and the number of Si + Alions on the tetrahedral site, but no relationship is found betweenTi content and the sum of cations.

Some amphiboles are zoned: richterite from the Cancarix andAustralian specimens show a darker color towards the rims ofthe crystals, and this variation corresponds to an increase intitanium and iron and a decrease in magnesium without anysignificant variation of the other elements, probably indicatingthesubstitutiontr + Ti + Fe2+:3Mg.

The main diference between these amphiboles and richteritesfound in the ulnro suite nodules rests with their TiO, content,higher in the lavas than in the high-pressure xenoliths.

Mica

Trioctahedral micas (representative analyses are listed in Tablel0) represent an important constituent of the lamproite miner-alogy, from 15 to 30% in volume.

Two kinds of micas are present, some are authigenic crystalswhereas others can be interpret€d, with various degrees of cer-tainty, as xenocrysts. In two specimens (7348 and MC77) largeindependent crystals of phlogopite appear to have been desta-bilized, with abundnnt exsolution of needleJike Ti-rich phases.Analyses of these micas show tetrahedral site with 4.00 or closeto 4.00 atoms, low TiO, (2 to 3o/o) and high AlrO3 (12 to l5Vo)contents, unusual values for lamproitic micas. These crystals areconsidered to be xenocrysts. Other large phlogopites may be found

7 . 6 7 8 8 0

E cationsFig. 6. The distribution ofTi and the sum ofcations in phlog-

opites from 3 specimens. Open squares, 586; open circles, SO I 36;solid stars. 8A12.

either as cores of complex micas, or have served as nuclei forlamproitic micas crystallization. They may (7B8, 586) or maynot (7441, 72A7,7B,8,586, 8Al2) appear unstable, with Ti-oxide exsolutions. Surrounding lamproitic micas are higher inTi, Fe and lower in Al than the cores which show TiO, contentsaround 2ol0, and significant Cr2O3 percentages (from 0.30 to 1.0).Such high CrrO, contents have been recorded from peridotites(e.g., Boyd and Nixon, 1978; Delaney et al., 1980; Jones et al.,1982) or from phlogopite centers in some Monument Valleyminettes (Jones and Smith, 1983). Typical lamproite micas plotnear the phlogopite composition, the Fe/(Fe + Mg) ratio alwaysbelow 0.30. They are often zoned concentrically, with an increaseof both Ti and Fe and a concommitant decrease in Al from centerto edge. They show a deficit in the tetrahedral site, Si + Al +Cr < 4 atoms.

Concerning the substitution in the tetrahedral site, several pos-sibilities have been investigated. The presence of Fe3* on thetetrahedral site ofmicas has long been known. Tetraferriphlog-opite is found in nature (Cross, 1897) and has been synthesizedin the laboratory. Silicon and magnesium can proxy for alumi-num on the tetrahedral site (Seifert and Schreyer, 197 l;Tateyarnaet aI., 1974\.

Robert (198 l) showed (using infrared techniques) the presenceof tetrahedral Mg in a Smoky Butte lamproite phlogopite. Hewas also able to demonstrate that this particular mica does notcontain any Fe3+, and that Ti is exclusively located on the oc-tahedral sites.

Ti in micas. Various substitution mechanisms have been pro-posed to accomodate Ti in phlogopite. IfTi is fixed on the oc-

26 WAGNER AND VELDE: K-RICHTERITE-BEARING I-4MPROITES

."^ + 4"^

";

r l ra

t _

#

*

. t....

7 6 E # i o n "

s o

Fig.1 . The distribution ofTi and the sum ofcations in phlog-opites from 5 specimens. Solid triangles, 74Al; solid circles,7247; solid squares, I 1A8; asterisks, 7348; open triangles, 788.

tahedral site, it replaces a divalent ion, and hence all proposedmechanisms are coupled substitutions. These substitutions canbe limited to the octahedral site or involve either one or twoother structural sites. The various mechanisms proposed are asfollows:

o 6

o 5

F 0 4

o 3

o 2

3 s 3 6 " t s i * n t f 3 . 3 e 4 0

Fig.8. ThedistributionofTiandSi + Al + Crinphlogopitesfrom 3 specimens. Solid triangles, 74A I ; solid circles, 72A7; opentriangles, 7B8.

The incorporation oftitanium on the octahedral site allows forthe introduction of a divalent ion, magnesium (Roben, 1981) onthe tetrahedral site (equation 4). In this case, a positive correlationwould exist between Ti and Mg (on the tetrahedral site) and hencea negative correlation between Ti and Si + Al + Cr would ensue.Such a correlation is indeed observed for micas of specimens7441,7247,11A8, 7B8, 8A12, SOl36 (Figs. 8, 9 and 10) withTi contents above 0.26 atoms per structural formula. Amongthose micas that do show a negative correlation three diferentgroups can be distinguished: micas from the first group (7441,7247 and,7B8) and the second group (8,4.12 and I lA8) showsimilar slopes of the line defined by the experimental points onFigures 8 and 9, but for a given Ti value the site occupancy bySi + Al * Cr of micas from the first group is higher than theoccupancy shown for the second group. This difference is mostlydue to a diference in Al content, the micas frorn the first groupbeing richer in Al than micas of the second group. In the thirdtype, which only includes specimen 50136, mica analyses plotalong a slope diferent from that defined by the two other groups.Such a substitution scheme however implies an inverse corre-lation between Si and Ti that is apparent only in specimen 8Al2(Fig. I l) and, to a lesser extent, specimen 7B8.

There is no correlation between the number of Si + Al + Cratoms and the Ti content when the number of Ti atoms is below0.26, indicating a different substitution mechanism. Robert (1976)has proposed substitution mechanism (3) when the Ti content is

o 6

o 5

: - 0 4

o 3

o 2

{ t

* * . * I

3 5 3 0 3 7 3 A 3 9 4 0

Si +A l +C r

Fig. 9. The distribution of Ti and the sum Si + Al * Cr inphlogopites from specimens 1 lA8 (solid squares) and 8A 12 (solidstars).

2Mg: T i + D

3 M g : 1 i + B a + t r

Mg + 2Si: Ti + 2Al

M g + S i : T i + M g

Mg + 2OH: Ti + 20

Forbes and Flower (1974) (1)

Velde (1979) (2)

Robert (1976) (3)

Robert (1976) (4)

Arima and Edgar (1981) (5)

Substitution (l) was proposed after consideration ofthe com-position ofnatural phlogopites, and has been recognized by Velde(1979) for micas found in melilite-bearing rocks where it is prob-ably coupled with a substitution involving the incorporation ofbarium on the interlayer site. When this mechanism is operativea vacancy is created for every 2 Ti atoms entering the structureand the octahedral site occupancy decreases. The existence ofsubstitution (l) is demonstrated in Figures 6 and,7 where Ti isrelated to the total number of ions. It is of course assumed thatboth the tetrahedral and interlayer sites are filled and that noFe3* is present in the structure. It appears that for specimens586, 8A12, 50136 the slope of the line defined by the experi-mental points is close to the expected value, whereas in Figure7 there are more vacancies than would be expected from substi-tution (l) alone.

WAGNER AND VELDE: K-RICHTERITE-BEARING I,,,IMPROITES 27

o 5

'F oo

o 3

o 2

O O

8 ' € o o

orf / o

S i + A l + C r

Fig. 10. The distribution of Ti and the sum Si + Al * Cr inphlogopites from specimen 50136 (open circles) and data fromMitchell (1981), crosses.

below 0.35. This substitution was looked for in analyses corre-sponding to the centers of micas from specimensT2A1. and 586as well as for micas from 73,4,8 which show low titanium conrenrs.The possibility of this substitution is confirmed by positive cor-relations between Ti and Al in all three cases.

In conclusion it seems that the most prominent substitutionmechanisms for Ti in the micas studied are substitutions (l) and(4) for Ti-rich compositions. For Ti contents below 0.26 perstructural formula the likely mechanisms are (1) and (3).

Interlayer ions. Ions in the interlayer site (K + Na + Ba) usuallytotal close to the theoretical value of 1.0 atom per structural

Table 11. Representative electron microprobe analyses oftheroedderiteJike phases, from Moon Canyon (analysis l) andCancarix (analysis 2). For comparison are listed analyses ofroedderite (A, B) and eifelite (C) from Hentschel et al. (1980)

and Abraham et al. (1983) respectively

s i 0 2 7 0 . 2 9

Alzo l

FeOo 12.60

Mgo 1 I .44

l'1n0 O.23

Tto2 o .o2

Na2O O.O4

K2o 4 .44

Tota l 99 .08

s i r 2 . 3 t oAIFez+ 1 ,845ug 2.947Mn 0 .034T i o .oo3N a O . O 1 4K 1 .OO1

69.46 70 .60

o , I 7 0 . 5 0

9 . 8 3 5 . 8 0

1 3 . 9 0 I 5 . 7 0

o . 2 7 0 . 2 1

o . 2 t o . o 7

o . 2 5 1 . 8 0

5 . 1 4 4 . 2 0

9 9 , 5 7 9 8 . 8 8

12.116 12 .Looo . 0 3 5 0 , 1 0 1r . 4 2 6 0 . 8 3 13.594 4 .o I2o ,031 0 .o30o.o27 0.oo9o. 084 0 .5981 , 1 3 7 0 . 9 1 8

7 1 . 3 2 6 9 . 0 6

o . 3 6 0 . 5 7

o . 4 9 0 . 1 9

I 7 , 8 6 1 5 . 4 7

o . 3 1 0 . 5 3

o.o7 0 .o3

5 . 2 9 8 . O 7

4 . 1 6 4 . 1 6

99,79 98 .05

1 1 . 8 1 8 1 1 . 9 20.070 0 .08O.068d O.034 , 4 I 2 3 . 9 8o.044 0 ,08o.0091 . 6 9 9 2 . 1 0o . 8 7 9 0 . 9 2

FeOo: Total i ron as FeO

o : F e 3 +

1, Cancarlx i 2, l loon Canyon

A , B : H e n t s c h e l e t a l . , 1 9 8 0 :

C r A b r a h a m e t a l - . , 1 9 8 3 .

o . 2 0 3 T i 0 4 o . s

Fig. ll. The distribution of Si and Ti in phlogopites fromspecimen 8A12, analyses of crystal edges.

formula, the lowest value found being 0.85. Barium contents arelow, usually below l .006 BaO except for specimens 7B8 and I 1A8where it reaches 30/0. This low barium content of micas in rockswhere barium is abundant (see for example data for the LeuciteHills volcanics in Carmichael (1967), or as exemplified by thepresence of Ba-rich phases in some lamproites such as prideriteor barite) is probably due to the alumina-deficiency ofthe bulkcomposition. Most barium substitutions involve the mechanismBa + Al : K + Si, an unlikely substitution in peralkaline rocks.In the lamproites examined the substitution appears to be of thekind Ba + n : 2K. This vacancy-creating substitution couldplay a role, as does the possible vacancy-creating substitution forTi. It should be pointed out that micas from specimens 7B8 andI lA8 show a correlation between Ti and Ba, with a diferentslope in each specimen.

Authigenic micas in lamproites differ from phlogopites fromultrabasic xenoliths by their high TiO, contents, but xenocrysticmicas found in lamproites are similar, even in their trace elementcontents, with phlogopites from peridotites.

Roedderit e - like p hase s

Both the Cancarix and the Moon Canyon lamproites containremarkable small prismatic crystals of a pleochroic blue mineral.Electron microprobe analyses ofthese blue minerals in both spec-imens have shown that they have similar compositions to min-erals ofthe roedderite+ifelite series (Hentschel et al., 1980; Abra-ham et al., 1983). Representative analyses from Cancarix, MoonCanyon and ofroedderite and eifelite are reproduced in TableI l. The roedderite-like minerals from the lamproites are distinctfrom those previously described in terrestrial rocks in their com-position and in the fact that, for the lamproites, they are part ofthe mineralogical association, and apparently crystallized fromthe liquid. They are closely associated with feldspars, amphiboleand late crystallizing micas. Their chemical compositions aredifferent from that reported for the Eifel roedderites. The Can-carix mineral (a rare phase in the rock) is a sodium-free and iron-rich relative to the Eifel specimens. The Moon Canyon mineral(quite abundant in the specimen studied) is slightly less iron-rich,more magnesian and sodic than that from Cancarix. The lam-proite minerals show a deficit in alkali metals for an R2+ totalclose to the theorical 5.0 value. Their general formula could bederived from the roedderite formula (Na,K)rMgrSi,rOro througha substitution of the type Fe3+ : Fe2+ + Na. According to thisscheme, the entry of Fe3+ in the structure creates one vacant site(an alkali site), the corresponding end-member being

o 6

2'9

o

2 8

a a

28 WAGNER AND VELDE: K-RICHTERITE-BEARING LAMPROITES

A 4 ^ ^ ^ ,

o , J " ,

2

Fig. 12. The distribution of Na and Fe2+ in roedderite-likephases. Solid triangles, MC77; small solid squares, 74,4'1; solidsquares, eifelites (Abraham et al., I 983); solid circles, roedderites(Hentschel et al., 1980).

KFe3+Fe2+Mg:SirrO3o. This substitution has been proposed byHentschel et al. (1980) and Abraham et al. (1983) for roedderitesfound in the Bellerberg volcanic field of the Eifel in Germany.The Cancarix and Moon Canyon specimens are close to thistheoretical end-member.

These relationships are demonstrated in Figure 12 which rep-resents the variation of the Fe vs. Na. Na is absent, totally re-placed by Fe3+, in the Cancarix specimen. The iron-free eifelites

Table 12. Representative electron microprobe analyses ofpriderites from Australian, Sisco and Smoky Butte lamproites

Table 13. Representative electron microprobe analyses ofpseudobrookites from various lamproites studied. Fe3+ calculated

assuming 3 cations and 5 oxygens

1

7 4L1 t1c77

2 3

73A8 7B8

z

A l 2 O 3 O . O 2

C r 2 O 3 O . 8 2

Feoo 28.97

u g o 8 . 6 5

M n O O . 3 3

T i o 2 6 0 . 3 3

T o t a l 9 9 . L 2

F . 2 O 3 2 6 . 3 8

F e O 5 . 2 4

A 1 0 . o o 1C r O , O 2 3F e 3 + O . 7 I 4F e 2 + O . 1 5 7M g 0 . 4 6 4ltn O.O1OT i 1 . 6 3 1

o . 4 7 0 . 3 0 0 . 0 6

o.43 0 .99 0 .o5

19.66 19 .86 23 .46

9 . 3 9 8 . 9 2 1 . 6 7

O . 1 5 O . I t + 0 . 2 0

69.O2 69.04 66 .32

99.72 99 .25 97 .70

8 . 5 7 7 . 7 t 1 1 . 0 3

L r . 9 4 t 2 . 9 2 1 3 . 5 4

0.020 0 .o13 0 ,oo3o . 0 1 2 0 . 0 2 8 0 . o 0 1o.232 0 .209 0 .307o.359 0 .390 0 .479o.504 0 .480 0 .420o.oo5 0 .oo4 0 .0061 . 8 6 8 1 . 8 7 5 L . a 4 4

1 2

so136 SO136

5 6

788 8At2788

3

7B8

1

8At2

FeOo : Total l ron as FeO

plot along the horizontal axis, as they only show a 2Na : Mgsubstitution.

The deep blue color ofthe roedderiteJike phase appears to berelated to the presence offerric iron in the structure. The Cancarixmineral, richer in iron (total iron) than the Moon Canyon one,has a deeper blue color. Hentschel et al. and Abraham et al.pointed out that their roedderites C and D, with 5.8 and 4.45Vototal FeO show a blue color.

Roedderite appears among the low-pressure breakdown prod-ucts of richterite (Gilbert et al., I 982) and testifies to the stronglyperalkaline character of these two lamproites.

OxidesTitanium-rich oxides are a general feature of lamproites, as

pointed out by Scott Smith and Skinner (1984). In this respect,lamproites differ from peralkaline siliceous rocks that are knownfor the absence of oxides (Carmichael, I 967). Besides chromitesfound as inclusions in olivine (considered below) these rockscontain one type of Fe-Ti oxide: ilmenite (1 lA8), or an associ-ation oftwo oxides: ilmenite + pseudobrookite (MC77 and 7348);ilmenite + titanomagnetite (586); ilmenite + priderite (50136,Sisco); pseudobrookite + priderite (7B8). These minerals andmineral associations are uncommon and will be described insome detail.

Prideritehasbeen found and analyzed (Table I 2) in rocks fromSisco, and Smoky Butte besides the Australian type locality. Theoriginal priderite contained 0.32 atoms of Ba and 0.87 atoms ofpotassium. Carmichael (1967) gave two electron mieroprobeanalyses of priderites from the kucite Hills and Australia. Thepriderites from Smoky Butte (where priderite is present in TypeI lamproite, as noted by Velde (1975) but has also been foundin specimen 7B8) are particularly Ba-rich, and the Ba contentcanreach 0.85 atoms, whereasKis only0.4 per structuralformulacalculated on 16 oxygens. These high Ba-values imply, as hy-pothesizedby Post et al. (1982), the existence of a Ba end-memberofthe priderite series. Another striking variation in the analyzed

F e 2 0 3 o 1 0 . 9 7 9 . 1 9

l , !Co o .92 O.7 4

T i 0 2 7 6 . 1 7 7 2 . 8 9

Cr2o3 0 .O3 4 .36

K 2 0 6 . 4 2 1 . 1 5

B a o 5 . 4 3 6 . 3 0

Tota l 1O0.34 1O0,63

Fe3+ O.98o o .83OM g 0 . 1 6 3 0 . 1 3 2T i 6 , 1 9 8 6 . 5 8 0C r O . o O 3 0 . 4 1 3K 1 . 0 3 2 1 , 0 9 5B a 0 . 2 5 2 0 . 2 9 6

T o t a l 9 . 2 2 7 9 . 3 4 6

9 . 5 3 9 . O 9

1 . 1 5 1 . O 2

7 0 . 4 3 6 8 . 1 8

0 . 8 3 1 . 8 5

2 . 5 6 2 . 7 3

16,22 t6 .73

9 9 . 7 7 9 8 . 6 9

0 . 9 0 1 0 . 8 7 7o . 2 r 5 0 . 1 9 56 . 6 5 3 6 . 5 7 3o . o 8 2 0 . 1 8 7o . 4 1 0 0 . 4 4 6o . 7 9 8 0 . 8 4 0

9 . 0 6 0 9 . 1 1 8

7 . 6 6 1 0 . 7 5

o . 7 6 0 . 1 7

6 6 . 6 0 7 t . 4 6

5 . 1 6

2 . 6 7 2 , 2 7

16.93 76 .39

9 9 . 0 1 9 9 . 9 6

o , 1 4 1 1 . 0 1 30 . 1 4 6 0 . 0 3 26 , 4 4 2 6 . 1 3 2o . 5 2 5o . 4 3 8 0 . 3 6 3o . 8 5 3 0 . 8 0 3

9 , 7 4 4 8 . 9 4 3

9 . 5 9

o.03

7 0 . 8 3

o . 2 6

r . 3 7

1 7 . 0 8

9 9 . 1 6

o . 9 2 20.oo66.804o,026o . 2 2 3o . 8 5 3

8 . 8 3 4

F e 2 O 3 o = T o c a l i r o n a s F e 2 O 3

WAGNER AND VELDE: K-RICHTERITE.BEARING LAMPROITES 29

I o'tI

o6

6.8 7.2 T,* *

8.o 8.4

Fig. 13. ThedistributionofBa + CrandTi + Kinpriderites.Solid circles: 7B8; solid stars: 8Al2; solid triangles: SOl36; solidsquare: LH9, Carmichael (1967).

priderites is their Cr-content: the priderites found in the Austra-lian specimen may contain 4.36oh CrrOr, the minimum foundbeing 0.03. The CrrO, content ofthe Smoky Butte priderite reach-es 5.16%. The general formula of priderite (Norrish, l95l),A2-yB8-,Or6, is not adequately known, but it seems that the vari-ations observed in the three lamproites mentioned are compatiblewith a substitution of the type:

cr3+ + Ba2+ : Ti4+ + K+ (Fig. 13)

This scheme does not however account for the observed variationin the iron content, which could be at least partly in the ferricstate and consequently participate in the above equation.

The presence and abundance of pseudobrookite, atare mineralin terrestrial rocks, is peculiarly common to some of the lam-proites studied. Pseudobrookite usually forms euhedral plates,hexagonal in shape, opaque or barely translucent in transmittedlight. When translucent (as in Smoky Butte) crystals can appeareither green or purple brown a difference that does not appear tobe simply related to compositional variations. In specimen MC77pseudobrookite appears as transparent golden brown crystals,with optical properties very close to those ofrutile. In reflectedlight, these pseudobrookite crystals show reddish internal reflec-tions. The composition of these oxides is 400/o ferropseudo-brookite, 12 to I5o/o pseudobrookite and 42 to 480/o karrooite.Representative analyses are listed in Table 13. Specimen 73,4,8contains pseudobrookite crystals, interpreted as xenocrysts whichare extremely rich in magnesium (up to 52 moleo/o ofthe karrooitecomponent). This particular pseudobrookite is close in compo-sition to armalcolite (Anderson et al., 1970; Haggerty, 1973;ElGoresy and Bernhardt, 1974). Pseudobrookite has been found,as a primary mineral, in few terrestrial rocks: in meteorite im-pactites (El Goresy dnd Chao, 1976), in kimberlites (Haggerty,1975; Raber and Haggerty, 1979), in ultrabasic nodules (Cameronand Cameron, 1973) and lamproites (Velde, 1975). It has alsobeen found in some basalts (Anderson and Wright, 1972; YanKooten, 1980; Von Knorring and Cox, l96l), and in meteorites(Fujimaki et al., 1981). It was described by tuce et al. (1971) asa quenched mineral in a dike rock of basaltic composition. Ac-cording to Haggerty (1976), the presence of primary pseudo-brookite implies a fast cooling rate that prevents a reaction ofthe pseudobrookite with the liquid, a reaction whose end productwould normally be ilmenite. It should be pointed out that in nolamproite was any ilmenite rim found around the early-formedpseudobrookite.

I lmenite is accompanied by priderite in specimen SO I 36 wherepriderite forms abundant srnall elongated crystals, as well as insome of the Sisco specimens (Velde, 1968) where it is quite rare.Ilmenite forms small crystals (5 to 50 pm maximum) withoutevidence ofexsolution or oxidation, except for specimen 74A1.Ilmenites appear after olivine, diopside and the centers of thephlogopites crystals. They are usually poor in hematite, contain-ing from 64 to 9090 ofthe ilmenite component, I I to 3090 geikeliteand I to 290 pyrophanite. Representative analyses are listed inTable 14.' Specimen 73,{8 conrains probable xenocrysts of amaglesian ilmenite with a rutile core; the composition of theilmenite is similar, though not as Mg-rich, to that of xenocrysticMg-ilmenites described by McMahon and Haggerty (1984), acomposition close to the composition of ilmenites found in kim-berlites (Dawson, 1980).

Chromites (Table 3) found as inclusions in authigenic olivinesare similar by their high Cr,Or, low AlrOr, and high Mg/(Mg +Fe) to chromites found by Danchin and Boyd (1976) in harz-burgites, themselves, as pointed out by these authors, not unlikechromites found as inclusions in diamonds. Their low Al is inkeeping with the peralkaline chemistry of the magma, their highCr could be related to the low Al and Fe3+ contents ofthe liquid.

Ti-rich oxides are commonly abundant in peralkaline lam-proites. This presence and abundance could be ascribed to thehigh TiO, and high FeO contents of these rocks. When projectedin an FeO-FerO3-TiO, diagram the composition of most pseu-dobrookite (+ ilmenite) bearing samples plot close to the fer-ropseudobrookite-pseudobrookite line or do so when the amountof iron (and TiOr) partitioned in the early-crystallized silicatesis taken into account.

Most ofthe oxides do not show any exsolution or oxidationtextures and most compositions can be recalculated into ferrous,rather than ferric, end-members, or minerals with high ferrousiron contents. This observation is taken as an indication of thelow oxygen contents of the melts, compatible with the low Fe3+/Fe2+ ratio ofmost ferromagnesian silicate phases present in theselavas.

Oxides are known to occur with phlogopite and richterite inultrabasic nodules, rutile and ilmenite being common, pseudo-brookite rare.

Conclusion to the mineralogical description

Lamproites described above can be considered aspresenting a magmatic assemblage consisting of Al-poor,Cr-rich spinel, Ni-rich olivine, Ti-phlogopite, Ti-richK-richterite, diopside, Fe-rich feldspar and Ti-rich oxides.Olivine crystals having evident textural (kink-bands) anal-ogies with peridotitic olivines are also found and can beinterpreted as being inherited from the solid layers oftheearth through which the lamproitic magma percolated.

Other such inherited minerals are Cr-rich diopsides, Fe-rich clinopyroxenes, Cr-rich phlogopites, pseudobrook-

ites, Mg-ilmenites and large rutile crystals (accidental insome Spanish lamproites). Jones and Smith (1983) havealso demonstrated the presence, in the Navajo minettes,of apatite and clinopyroxenes xenocrysts. The possiblepresence ofvarious xenocrystic species in the Leucite Hillslavas was also discussed by Kuehner et al. (1981) who,for example, described pleonaste in the Deer Butte wyo-mingite.

Hence care should be exercised before discussing either

o l

!r

1l,l

30 WAGNER AND VELDE: K-RICHTERITE-BEARING 1../IMPROITES

:. ) 2o

Yoz

1

6 4

z 2

l oo

a^^

"."4: ' ''

1N"ri1o amphibo3te 4

Fig. 14. The distribution ofNa/K calculated from the bulkrock composition and the Na,rK content of the A site of therichterite. Solid circles: data from this study; open circles: datafrom the literature: l, LH9, Carmichael (19 67); 2,Type 1, Velde(1975); 3, Velde (1978); 4, S84, Bryan (1970); 5, RHl, Barkerand Hodges (1977); 6, Brooks et al. (l 978); 7, I 2 l, Nicholls andCarmichael (1969); 8, Sheraton and England (1980); 9, S1, Car-michael (1967); 10, Jaques et al. 1984.

the partitioning of elements between phases or the sig-nificance of the trace element geochemistry of these rocks.

Partitioning of elements between phases

Some elements are found in certain phases in propor-tions which can be correlated with the bulk rock com-position. The Fe3+ content of the feldspar is simply cor-related with the peralkalinity index of enclosing rock. Mi-cas are more potassium rich in the most potassium richbulk composition, a relation already described by Edg,arand Arima (1983). Richterites contain variable amountsofpotassium and there is a relationship between the po-tassium content of the richterite and the amount of po-tassium present in the rock expressed in the form ofthe

0 1 0 2 0 3 0 4N"/K retosp..

Fig. 15. Partitioning of Na and K between richterites andfeldspars. Data from this study: solid circles; data from the lit-erature: open circles (a, LH9, Carmichael, 1967; b, Velde, 1978).

FezFe+Mg amphiboleFig. 16. Partitioning of Fe and Mg between phlogopites and

richterites. Data from lamproites: solid circles; data from ultra-mafi c nodules (A okt, 19 7 4, I 97 5 ; and Dawson and Smith, I 9 7 7):solid stars.

Na/K ratio. Figure 14 shows this correlation, as deducedfrom specimens under consideration and examples takenfrom the literature. Richterites also appear to be morepotassic when the rock is more peralkaline, which couldbe another way ofexpressing the previous correlation, theperalkalinity in lamproites being directly related to thepotassium content.

This being established, how are these elements distrib-uted between co-crystallizing phases? Since richterite andphlogopite coexist in some ultrabasic nodules brought tothe surface by kimberlitic magma, these nodules representphysical conditions different from those of lamproiticcrystallization, in particular different pressure conditions.These data have been included in Figures 16 to 18. In

o 6

.E ooE

o'2 ,

o-4 0 '6

Ti amphiboleFig. I 7 . Partitioning of Ti between micas and richterites. Data

from lamproites: solid circles; data from nodules: solid stars (Aoki,1974, 1975; and Dawson and Smith, 1977) and solid squares(data from Jones et al., 1982).

o.9E o "

E')=+o\ o ,olr

F

aa a 63 9

* *?a*? ,

- i 8 o

a 5o 9

a3

o5

o2

o a a6 1 1 0

q *r_*I

WAGNER AND VELDE : K.RICHTERITE. BEARING LAMPROITES 3 l

o 1

F./F+OH amphibole

Fig. I 8. Partitioning offluorine between phlogopites and rich-terites. Data from lamproites: solid circles; data from nodules(Jones et al., 1982): solid squares.

this way the influence of pressure on the composition ofthe minerals under consideration can be evaluated.

Sodium and potassium: there is a direct relationshipbetween the Na/K ratio of richterite and the coexistingfeldspar (Fig. l5).

Iron is equally distributed between amphibole andphlogopite (Fig. 16) in lamproites as well as in ultrabasicnodules found in kimberlites but this is only valid whenconsidering those micas and amphiboles in equilibrium,judged so on the basis of textural arguments (Table l5').

There is a positive correlation (Fig. 17) between Ti inmicas and amphiboles. It should be noted that the local-ization of titanium in the amphibole structure is still am-biguous, and that the problem, for micas, cannot be con-sidered as unambiguously solved even if Ti is probablyincorporated on the octahedral site in lamproite micas.Lower Ti-contents appear to characterize micas and am-phiboles from ultrabasic nodules.

Fluorine: the maximum content of fluorine found in a

8

2 oa

76 7 .7 7A ? .9Si +Al amPhibole

The distribution of Si + Al in phlogopites and rich-

Si+A l m ica

Fig. 20. The distribution of (Na + K) - Al calculated fromthe rock bulk compositions and the Si + Al content of the phlog-opites.

natural mica is 8.50/o (Peterson et al., 1982; Valley et al.,1982) and 4.5o/o in a natural richterite (in a meteorite,Olsen et al., 197 3). Synthetic minerals contain up to 9.2o/oF for phlogopites (Kohn and Hatch, 1955) and 4.7o/o inrichterite (Kohn and Comeforo, 1955). In lamproitephlogopites the fluorine content is, in most cases, belowl0l0, but can reach 40lo (specimen 73,{8). These F contentsare in agreement with what can be calculated from the Fcontent of the rock and the modal amount of phlogopite,with the exception of specimen I lA8, a rock particularlyrich in F-bearing apatite. Representative analyses ofF-richmicas and amphiboles from lamproites are listed in Table16 . '

Figure l8 seems to indicate that F is equally distributed

Si+Al amph ibo le

Fig. 21. The distribution of (Na + K) - Al calculated fromthe rock bulk compositions and the Si + Al content of the rich-terites.

o

I

+z

o.9F o 4

Io+ o 3l!

lro 2

o

z

o 2

6 3 8

E

+a

Fig. 19.terites.

i o iB a

Ia

a1 0

a2

71a1

6a

32 WAGNER AND VELDE: K.RICHTERIT:E-BEARING LAMPROITES

l',*o, ,",01i". 3e6 3ea

Fig.22. The distribution of (Na + K) - Al calculated fromthe rock bulk compositions and the Si + Al content of the co-existing feldspars.

(K" : l) between the two phases phlogopite and richterite(Table l5). It should be pointed out that the diagramincludes values for specimen 73A8 in which the two phas-es are not considered to be in equilibrium (textural evi-dence); their F values follow the same trend as that de-termined for phases thought to be in equilibrium. Thisobservation could be interpreted as indicating that F andOH can equilibrate after crystallization of the two phases.The K" values calculated using the F determinations pub-lished by Jones et al. ( I 982) for mica and amphibole pairsin metasomatized peridotites are widely different fromone another and from those given here. This anomalycannot be explained at present. Note should be made ofthe fact that, in the Spanish lamproites, phlogopites showa distinct correlation between F and Ti. This correlationwas found in richterites only from specimens 74Al,73ABand 7B8.

Si + Al on the tetrahedral sites: most of the phasespresent in the peralkaline lamproites do not contain enoughSi + Al to fill the tetrahedral site to its theoretical numberofions. This point was discussed in the preceding sectionand, in all cases, the nature ofthe other ion (ions) couldnot be decided upon with the data at hand.

In spite of the unknown nature of the supplementaryion (or ions) on the tetrahedral site it is interesting to notethat the amplitude of this Si + Al deficiency is similar inthe coexisting minerals within a given specimen. Figure19 shows the relationship between the value of Si + Alin the micas and in the coexisting amphibole. There is apositive correlation between the tetrahedral Si + Al con-tent ofboth phases. Because tetrahedral deficiency appearsto be linked to the peralkalinity of the liquid, the Si + Alcontent of various phases has been plotted against the(Na + K) - Al value of the corresponding bulk compo-sition (Figs. 20 to 22). The apparent correlation is notvalid for the Jumilla specimen, already commented upon.

Barium is preferentially incorporated in micas (Higuchiand Nagasawa, 1969; Wdrner et al., 1983) but is alsopresent in coexisting feldspars. The distribution of Ba be-

Ba./Ba+Na + K

9a

a

aa l

mtca

Fig. 23. The distribution of Bal(Ba * Na t K) in feldsparand coexisting mica.

tween feldspar and mica in the lamproites is regular asshown on Figure 23. Data from Wiirner et al. (1983) in-dicate that BaO contents in phlogopites are twice the BaOcontents in associated sanidines. Three specimens showKo's for Ba between feldspar and mica that are quite com-parable: 0. 196 (788), 0.192 (7 4Al) and 0. I 75 (7247) butlow when compared to values found in other types ofvolcanic rocks.

Most elements are regularly partitioned between co-existing amphiboles and phlogopites. The bulk compo-sition (either iron, magnesium or titanium contents) exertssome control on the corresponding contents of the min-erals in these elements. The silica saturation is howevernot an important factor in the control of the mineral com-positions, whereas aluminum saturation, on the contrary,is a determinant factor particularly on the content of thetetrahedral site.

Temperature estimations of cooling history

A number of experimental studies have been made oneither phlogopites, richterites or oxides. These data cantentatively be used to estimate temperature of crystalli-zation.

Initially a spinel+livine geothermometer (Sack, 1982)can be used. The authigenic rim around olivine xenocrystsfrom the Calasparra lamproite give 1000'C (7247) where-as the olivines from the rock give 800'C. The selagitespinel-olivine associations give values between 914 and1160.C, whereas a 1000'C phenocryst temperature hasbeen calculated for the jumillite (l lA8). In this specimenan olivine coexisting with glass inside an apatite crystalgave a high crystallization temperature of l22lt with themethod outlined by Watson (1979).

The maximum thermal stability of the lamproite am-phiboles is between 985 and 1030"C (Charles, 197 5,1977)taking into account only the Mg-Fe substitution. Richter-ite is more stable when it is more magnesian and Bartonand Hamilton (1978) have shown that a richterite fromthe Leucite Hills was stable up to 1075"C at HrO pressuresof I kbar. A crystallization temperature, based upon thepartitioning of Na and K between amphibole and liquid,has been calculated for two specimens (Smoky Butte andJumilla) where amphibole and coexisting glass composi-

o 0 2

oq

oo o l

z

o o a

WAGNER AND VELDE: K-RICHTERITE-BEARING I,.IIMPROITES

tions were known, using the relation established by Helz(1979): the values found are 965'C for Smoky Butte and770'C for Jumilla.

Attempts to estimate temperature of crystallization us-ing the oxide phases were obviously hindered by the ab-sence of magnetite and by possible secondary oxidation.However one sample (specimen 5B6) contains coexistingilmenite and titanomagnetite which show neither oxi-dation nor exsolution. These oxides have appeared earlyin the crystallization sequence, judgrng from textural re-lationships, after clinopyroxene. While titanomagnetiteappears homogeneous, there is a variation in the FerO,of the ilmenites which decreases from the center towardsthe rims of the crystals. Using a program published byGhiorso and Carmichael (1981), two sets of temperatureswere obtained: for the centers of the ilmenites and themagnetites the calculated temperature is 827.C for a log.fo, : - 13 .5 whereas considering the edges of the ilmenitesthe calculated crystallization temperature is 755"C for logfor: - 15. These results are similar to those deducedfrom the phase diagrams published by Haggerty (1976).

These temperature estimations for various minerals ormineral pairs allows one to establish the following:

(1) Xenocrysts with included spinels were not found.Olivine xenocryst rims crystallized, at temperatures of1000-1200.c.

(2) Groundmass olivine crystallized at 800-900"C.(3) Amphiboles formed at temperatures between 960

and770"C.(4) When ilmenite and magnetite are present (Shiprock)

temperatures between 800-700rc are indicated.These values pertaining to a range oflavas with differing

compositions are in broad agreement with the liquidusdeterminations of Carmichael (1967) who found 1165"and 1200'C for two different wyomingites. The data pub-lished by Barton and Hamilton (1978) also for wyoming-ites, in water-saturated conditions, are in general agree-ment with the crystallization order found here.

High pressurrlow pressure phases. A comparison shouldnow be made with mineral composition recorded fromultrabasic inclusions. Common characteristics between ri-chterites found in nodules and richterites found in lam-proites are the following: their potassium content is sim-ilar, as is Na/K, their tetrahedral site is incompletely filledby Si and Al atoms, but Fe3+ is present in amounts greatenough to saturate the tetrahedral site. These richteritescan be distinguished from those found in lamproites bya lower TiO, content (less than 0. I Ti atoms per structuralformula). Kushiro and Erlank (1970) have obtained re-crystallization at ll00'C and water pressure of 30 kbarof a potassic richterite close in composition to the Aus-tralian richterite used as starting material, except for TiO,content: the TiO, content of the starting material was 30/0,whereas the artificial richterite contained only 0.50/o TiOr.This result implies that the entry oftitanium in the richter-ite structue is favored by low pressure.

Phlogopite, as well as richterite, is an important con-

stituent of some of the nodules found in kimberlites andboth minerals have been found as inclusions in diamonds(Meyer and McCallum, 1984). Phlogopite-bearing nod-ules are more frequent than nodules carrying both phlog-opite and richterite. These phlogopites (Dawson and Smith,1977; Aoki, 1974,1975) contain less Ti than the phlog-opites found in lamproites (less than 0.I atoms per struc-tural formula), but they also show a tetrahedral site in-completely filled by Si + Al.

The influence of titanium on the stability of micas isnot precisely known. Forbes and Flower (1974) envi-sioned that Ti stabilized the phlogopite; Robert (1981)and Robert and Chapuis (1982) have considered Ti-richmicas as high-pressure phases and this hypothesis is alsoaccepted by Bachinski and Simpson (1984) who considerthe Ti-rich (2.0 to ll.3olo TiOr) cores of minette pheno-crysts to have crystallized at elevated subcrustal pressures.However, Edgar et al. (197 6) established that between I 0and 30 kbar Ti-poor phlogopite is stable relative to Ti-rich phlogopite. Wendlandt and Eggler (1980) have fur-thermore shown that the Ti content of the phlogopitedecreased with pressure for identical compositions, aproposition confirmed by Arima and Edgar (1981). Alllamproite micas considered in the present study, exceptingxenocrysts, have crystallized at low pressures being foundin rocks that have solidified at the surface. Consequently,Ti-rich phlogopites and amphiboles crystallize under pres-sures corresponding to the surface of the earth. The ab-sence of Ti-rich phlogopites in kimberlite nodules, in as-semblages that, for the most part, include Ti-oxides couldbe interpreted as meaning that Ti-phlogopite is not stableat high pressure.

Discussion and conclusions

K-Ti-richterites and Ti-phlogopites are the prominentminerals found in peralkaline lamproites. They common-ly coexist with Tirich Fe-Ti oxides and may be accom-panied by rare alkali-rich phases such as priderite, or roed-deritelike minerals. These associations testifu to theperalkaline composition of the liquids from which theseminerals precipitated. Coexistent with, but genetically un-related to this magmatic association, are found a numberofphases that have been scavenged by the ascending lam-proitic magma. These phases are the same species as thoseprecipitating from the lamproitic magma, i.e., olivine,clinopyroxene, trioctahedral mica, ilmenite, pseudo-brookite, rutile and apatite. The rate of dissolution beinggoverned by the minerals stable on or close to the liquidus(Brearley and Scarfe, 1984). The volumetric importanceof these relics is not considerable (less than 100/o) but,taking into account experirnents performed by Scarfe etal. (1980) on basalts, material might have been dissolvedinto the liquid. Incorporation of Ni-rich olivines at depthcould, for example, account for the precipitation of Ni-rich olivines from the magma at the surface; incorporationof Cr-rich phases for the precipitation of Cr-diopside orCr-rich spinels.

Results of the present study show that peralkalinity of

34 WAGNE R AN D VE LDE : K- RI C HTE RI TE. B E ARI NG LAM PRO ITE S

lamproites is a characteristic of the lamproitic liquid, be-cause of the correlations between some mineral compo-sitions and the alkalinity index, or the precipitation of Al-poor chromite as a liquidus phase. Hence contaminationduring the ascent of the magma cannot account for thehigh alkali (potassium) and low Al contents.

Partitioning of elements between phases, excluding xe-nocrysts, is regular and follows trends in keeping withthose that can be deduced from mantle metasomatic as-semblages of phlogopite and richterite. A conclusion isthat the high K-richterites found in mantle xenoliths areprobably derived from the reactions of highly potassicfluids with ultrabasic rocks. The difference between Ticontents of phlogopite and richterite in lamproites (lowpressure) and metasomatized peridotites (high pressure)reflects the higher solubility ofTi in these phases at lowpressure.

A deep seated origin ofthese liquids is suggested by twoseries of observations:

The presence ofperidotite xenoliths known to occur inthe Leucite Hills (Carmichael, 1967; Barton and Bergen,l98l), in the Australian lamproites (Jaques et al., 1984)and in the Spanish lamproites (Velde, 1969; Nixon et al.,1982).

The discovery of diamonds in a number of Australianlamproite localities (Jaques et al., 1984). This observationalone places the lamproites in a category of rocks akin tokimberlites, at least for the depth at which they originate.Trace element data, and in particular rare earth profiles,when available, indicate for lamproites, as for kimberlites,an extreme enrichment in light rare earth elements (500to 2000 the chondritic values), and a weaker enrichmentin heavy rare earth (Nixon etal., 1982; Mitchell and Haw-kesworth, 1984).

The bulk composition of lamproites is so different fromcommon magmatic rocks that their deviation from, forexample, basaltic magmas is not permitted. As pointedout by Carmichael (1967) when considering the genesisof the Leucite Hills volcanics, the temptation is to imposeon the starting material many of the requirements of theresult that is supposed to be achieved. Since Carmichael'sstudy, however, the concept of mantle metasomatism hasbeen widely commented upon (Bailey, 1982). Ultrabasicrocks have been described with a metasomatic assemblageresulting from the reaction of mantle associations withK-rich fluids (Jones et al., 1982:, Barton and Hamilton,1982) that could be precisely the source ofultrapotassicperalkaline rocks.

It is tempting to pursue this reasoning and calculatewhat percentage of the bulk compositions of lamproitescan be explained with the fusion ofa richterite-phlogo-pite-rutile (or ilmenitepiopside assemblage. kast squarecalculations performed using the compositions of thesephases as listed by Dawson (1980, p. 186) lead to thefollowing conclusions: all the bulk compositions of lam-proites listed in Table 2 can be obtained by the fusion ofthe above kimberlitic nodule assemblage. In all cases,required percentages of phlogopite are between 50 and

700/o (weight), but most cluster between 56 and 680/0. Re-quired percentages ofrichterite vary between 30 and 500/0,

except for Jumilla, whose bulk composition has been al-

tered and will not be considered further, Shiprock and theAustralian lamproite. In these two last samples, diopsidemust be included in the starting material. In all calcula-

tions rutile is added, the proportions being above 10/o(weight) only for the most titaniferous compositions,

Smoky Butte and Australia. Recent experiments (Dick-

inson and Hess, 1984) have indeed shown that the solu-

bility of rutile (K*) increases dramatically with the KrO/

KrO + AlrO, of the liquids, from 9.5 wt.o/o (K* :0.37)

to 41.2 wt.o/o (K* : 0.90).For the calculated values to match the observed lam-

proite compositions, fractionation of olivine, and clino-pyroxene, and a certain alkali loss must be called for.

The fact that lamproite major elements compositions

can be matched in such a fashion cannot be considered

as proofofa particular genetic process. The coincidence

simply permits this scheme to be used as a working hy-pothesis for a more rigourous treatment of the problem

that would include data on trace elements combined with

the precise determination and evaluation of xenocrystic

material that could further constrain the problem.

Acknowledgments

John Hower gave Danielle Velde, in 1968, three samples fromSmoky Butte, Montana; preliminary work on these specimensprornpted a visit to this locality, but large parts of this studyensued from this gift. The first specimen obtained from MoonCanyon was generously given by M. G. Best, Brigham YoungUniversity; the subsequent ones were forwarded to us throughthe courtesy ofProfessor Blanchet, from the University ofBrest.The Australian specimen was obtained through Dr. Esquevin,S.N.E.A.P., Pau. Professor A. Baronnet and J. Fabrids reviewedparts ofthis manuscript at various stages ofits preparation, Pro-fessor W. Schreyer (Jniversity of Bochum) confirmed us in theopinion that our "roedderite" was probable a new mineral, andDr. A. El Goresy (Max Planck Institut, Heidelberg) was mosthelpful in helping to decipher the complex relationships betweenopaque phases.

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