S.Afr.J.Geol., 1999, 102(2), 109-121
109
Sovite and alvikite: two chemically distinct calciocarbonatites Cl and C2
M.J. Le Bas*
Geology Department, Leicester University, Leicester, LEI 7RH, UK
E-mail: mjlb@soc.soton.ac.uk
Accepted 10 March 1999
Abstract- This contribution (i) chemically distinguishes the two carbonatites: sovite and alvikite, and (ii) presents new
'average' (median) compositions for them. The best and most used average chemical composition for calciocarbonatite is
that calculated by Woolley and Kempe in 1989, and it is shown here that this composition comprises two distinctively different compositions corresponding to those of sovite and alvikite. Sovite and alvikite are the coarse-grained and the
medium- to fine-grain~d varieties, respectively,. of calcite-carbonatite. It is proposed that the corresponding calciocarbonatites should be termed Cl calciocarbonatites and C2 calciocarbonatites, based on their chemical compositions. The distinction of the two lies, not in the major elements, but in the minor, trace- and rare-earth-element contents. Using a
comprehensive database of post-1970 analytical data, the 'average' compositions for Cl and C2 calciocarbonatites have
been calculated. Instead of the arithmetical average, the arithmetical median has been calculated for each, since this gives
truer estimates of the two compositions. It is believed that the two median compositions will enable Cl and C2 calciocarbonatites to be recognized.
*Present address: ~chool of Ocean and Earth Science,. Southampton Oceanography Centre, Southampton University,
Empress Dock, Southampton, SO 14 3ZH, UK
Introduction
Sovitic carbonatites taken from all' over the world are closely
similar geochemically, apart from the component arising from
a variable content of mafic silicate minerals. Alvikitic carbonatites also have a world-wide similarity to each other. Both
sovite and alvikite are calcite-carbonatites, sovite being coarse
grained and alvikite being medium ·to fine grained (Le Maitre
et al., 1989). Hence, it might have been reasonable to suppose
that both crystallized from magmas of the same composition
and, because alvikite is usually more homogeneous mineralogically than sovite, which commonly has a patchy distribution of silicate minerals, it might be argued that samples of
alvikite provide the better material for determining the chemical composition of sovitic magma. However, isotope, trac~­
and rare-earth-element (REE) analytical data show that sovite
and alvikite differ chemically.
e sovite
x alvikite
magnesioferrocarbonatite carbonatlte
MgO
FeO
Figure 1 Sovites and alvikites used in this study plotted in the
upper portion of CaO~MgO-FeO (wt. per cent) diagram (Le Maitre
et al., 1989). The two calciocarbonatites are virtually indistinguishable using these parameters.
Carbonatites, being derived from a small percentage partial
melts of the mantle, are now being scrutinized by geochemists
for criteria relating to mantle convection and the geochemistry
of carbon. Therefore, it is impo~tant that the different kinds of
carbonatites be distinguished. When carbonatites were .first
noted earlier this century, it was sufficient to establish that the
carbonate rock in question was igneous and not a mobilized
limestone. The detailed studies of Br0gger (1921) and Von
Eckermann (1948) on the carbonatitic complexes of Fen,
southern Norway and Alno, Sweden, respectively, provided
that evidence and laid the foundation for the study of the
petrology and geochemistry of carbonatites.
nation of carbonatite nomenclature, together with the geochemical characterizations of the three principal types:
calciocarbonatite, magnesiocarbonatite, and ferrocarbonatite.
Calciocarbonatite is the chemical approximate equivalent of
calcite-carbonatite.
In 1984, and based on a growing geochemical database of
carbonatites, it was suggested that sovite and alvikite might
not be chemically equivalent and a boundary at 0.4% MnO,
1500 ppm Ba, and 2000 ppm REE separating them was pro-
In 1989, Woolley and Kempe published a careful re-exami-
Table 1 Median compositions of REE contents in ppm for sovite and alvikite,
La
Ce
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
sovite
319
582
58
235
34.1
10.1
28.2
3.71
19.0
2.78
7.80
0.90
5.40
0.70
a1vikite
877 1578
137
445
57
16.2
47
6.59
32.5
5.20
12.2
1.3
7.45
0.87
Pr
Data determined from ICP and INAA analyses of 96 sovites and 25 alvikites (after Le Bas, 1997)
110
S.Afr.J.Geol.,l999,1 02(2)
-1
120
13
6 C/oo pdb
• • •
• • • •• •
• •• • •
-3
~
•
t.
••
-7
•
5
t.
PIC
•
......
.I
• ~• •
•
••
•
•• • •• •
•~·
t.
~
jm
100
calciocarbonatites
80
I
..~~
&~
•
•• •
••
-5
-9
•
~
t.A
, . oovire
&alvikite
t. comb alvikite
60
f
40
I
20
618 07oo smow
0
20
15
10
Figure 2 o 0 <0-o 13 C plot for sovites and alvikites. The 'comb alvikites' are from Kaiserstuhl dyke margins with layers of elongate
skeletal calcite considered to reveal quench crystallization (Katz
and Keller, 1981) but are unlike typical alvikites. The data plotted
are taken from Hubberton et al. (1988), Le Bas and Srivastava
(1989), Suwa et al. (1975), and from the Le Bas database of samples from western Kenya, northern Tanzania, South Africa, and
Cape Verde Islands. PIC -Primary Igneous Carbonatites box after
Taylor et al. (1967). The sovites and alvikites occupy different areas
with some overlap.
posed (Le Bas, 1984). With the advent of improved techniques
of XRF and ICP analysis of carbonatites at Leicester University and the greater availability of ICP and INAA methods for
REE analysis, a database has been built up of 200-300 analyses. An interim report on the trace-element differences
between sovites and alvikites was presented by the author in
0
0
2
3
4
5
Sovites
Alvikites
Sovites
n
n
n
n
n
Si0 2
Sc
31
18
La
110
43
Ti0 2
110
39
v
94
29
Ce
107
43
Al 20 3
110
40
Cr
88
35
Nd
104
43
Fe2 0 3t
117
44
Co
41
17
Hf
21
12
MoO
117
41
Ni
86
33
Ta
22
11
MgO
117
41
Cu
31
10
Th
88
44
CaO
115
41
Zn
82
36
u
41
21
Na2 0
106
37
Ga
22
14
Pb
35
8
K20
109
37
Rb
92
39
Be
8
PzOs
112
41
Sr
116
44
Cs
11
0
41
12
y
107
42
Li
12
0
H2o+
10
0
Zr
104
41
Sn
7
0
so4
12
13
Nb
97
42
Au
2
0
Ba
115
43
Mo
2
0
Sb
2
2
8
4
57
24
to
Alvikites
42
LOI
9
10
1993 (Le Bas, 1993). A more recent .study (Le Bas, il997) of
the REE distribution in carbonatites <;:oncentrated on samples
of sovites and alvikites that had been identified as ,such by
field and petrographic criteria. Then, using a database of 121
samples, all analysed by ICP or INAA, it was shown (Table 1)
that sovitic and alvikitic compositions could be Stjparately
characterized.
The study presented here is a further analysis of the minorand trace-element data, mostly XRF, of calcite-carbonatites
that again have been recorded on field and petrographic evidence as either alvikite or sovite. Arithmetical med]ans are
calculated for the two compositions of calcite-carbonatites.
n
F
8
bonatites compiled from data used by Woolley and Kempe ( 1989)
and the Le Bas database for intrusive carbonatites. 89% of the data
have< 5% Si02.
110
C0 2
7
Figure 3 Frequency distribution diagram for Si0 2 contents of car-
Table 2 The elements analysed and the number of analyses available
sovites and alvikites
Sovites Alvikites
6
n - number of analyses available for that particular element; t - total Fe expressed as Fe 20 3
111
S.Afr.J.Geol., 1999, 102(2)
Database
The data used are taken partly from published material and.
partly from the author's carbon:atite database gathered mostly
over the past 15 years. It includes the unpublished data of
Hodgson (1985) and Mian (1987). The analyses are plotted on
Figure 1, which shows that there is little to distinguish sovite
from alvikite using only CaO, MgO, and FeO parameters.
However, a plot of oxygen and carbon isotope analyses for
sovites and alvikites indicates that a difference does exist (Figure 2), as was pointed out by Reid and Cooper (1992) for the
sovites and alvikites of the Dicker Willem carbonatite complex in Namibia.
The database comprises over 200 analyses of calcitecarbonatites, mostly XRF, and was pruned to 164 analyses following the six criteria given below.
(i) Only samples which corresponded to the current definition
of sovite and alvikite (Woolley and Kempe, 1989) were
included.
(ii) Pre-1970 analyses were excluded.
(iii) Only carbonatites with both major ('wet' or XRF-analysed) and trace- or RE-elements (XRF, ICP, or INAA- analysed) data were used.
(iv) Samples with >5 wt.% Si0 2 were excluded.
(v) Samples with >5 wt.% MgO were excluded.
Table 3 XRF/ICP/INAA analyses of continental sovites
2
3
4
5
6
7
8
9
1o:
11
12
13
14
15
16
17
18
19
21
20
0.57
4.86
0.31
1.02
3.33
0.04
0.07
3.04
0.12
4.38
4.01
2.17
0.05
4.89
0.89
0.30
1.61
2.86
na
na
na
Ti02
0.03
0.17
0.16
0.03
0.22
na
na
0.10
0.02
0.14
0.20
0.19
0.02
0.08'
0.07
0.15
0.11
0.32
0.02
0.03
0.06
A1 20 3
0.24
0.30
0.07
0.35
0.54
0.22
2.90
0.19
0.01
0.23
0.80
0.85
0.02
0.09
0.09
0.10
0.17 ··0.20
na
na
na
Fe20 3t 1.22
2.22
0.98
0.23
5.14
na
na
4.51
0.88
5.24
2.39
5.62
0.85
2.62
1.58
5.85
1.78
5.96
1.66
0.40
0.88
MnO
0.19
0.27
0.57
0.18
0.20
0.45
0.17
0.43
0.24
0.83
0.24
0.54
0.25
0.34
0.25
0.55
0.11
0.30
0.24
0.13
0.12
0.49
0.31
0.47
0.18
0.90
0.50
1.00
1.52
2.12
4.92 · 0.70
1.83
0.48
1.07
0.85
3.89
0.32
1.69
0.81
0.01
0.13
na
na
MgO
CaO
53.80 50.45 53.40 52.95 49.70
51.79 51.30 44.24 48.62 48.06 53.56 52.04 50.43 45.39 48.45 49.85 48.17 54.40 49.14
Na20
0.15
1.09
0.61
0.26
0.67
na
na
0.14
0.07
0.26
0.34
0.09
0.01
0.13
0.07
0.06
0.04
0.18
na
na
na
K20
0.12
0.17
0.08
0.09
0.34
0.50
0.50
0.03
0.01
0.08
0.24
0.17
0.01
0.13
0.09
0.01
0.05
0.07
na
na
na
1.00
0.10
0.35
1.72
na
na
4.40
0·.58
2.97
2.82
3.64
0.75
1.26
2.71
1.27
2.16
4.20
2.59
0.01
1.55
na
34.60
na
na
na
na
na
na,
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
42.8 36.07 36.62 36.02 42.05 35.95 39.41 40.03
43.2 34.91
na
na
na
na
0.038
1.31
na
na
mi
na
na
na
3
291
1.1
9.2
P20s
0.76
C02
na
LOI
41.97
Sc
34.84 38.70
0.6
v
na
3.6
189
27
Cr
15
5
22
Co
3
0.66
13
Ni
54
Cu
5
Zn
12
Ga
Sr
28
na
Rb
y
29
na
80
16
1010
4
bd
2
3
6
2
na
1.3
115
180
15
14
5
4
5
5
47
45
15
116
100
113
5
4
9
na
87
5
na
18
3
na
50
na
na
na ·
na
na
na
na
na
38
87
2
49
26
96
79
139
38
3
3
2
2
2
4
5
3
4
3
2
8
5
8
10
5
7
8
8
10
9
5
na
na
9
na
42
3
na
na
na
na
na
37
35
3
.4
6
4.
3
13
5
5
6
6
5
na
na
56
8
26
17
na
na
28
31
4
6
na
54
2
2.7
3
na
na
6
na
11
7
7
9
na
55
13
na
12
. 7
6258 6764 3452 8433 6015 4500 4000 4253 7459 5536 8720 7172 13706 11148 10849 10164 6330 4672 14523 16257 13688
57
43
41
Zr
83
58
50
9
Nb
165 2833
10
6
1971 5320
761
40
189
126
101
15
30
44
17
"770
560
46
630
1883
1377
546
83
90
100
115
77 :
74
26
177
6
211
115
15
882
798
1318
750
742
612
13
18
2i
420
1742
88
68
71
81
459
225
12
16
63
797
464
307
76
99
91
20
4
24
503
1559
1558
885
12
Ba
1673
La
285
322
143
187
176
390
160
336
346
354
525
519
374
404
504
274
441
358
467
448
437
Ce
564
643
261
328
333
350
250
478
633
714
960
999
767
840
985
585
874
758
805
775
790
Nd
222
237 .
80
118
120
na
na
148
224
263
324
427
292
332
361
227
356
296
227
223
244
na
0.79
na
0.05
0.46
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
14.3
na
0.04
0.18
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
na
· Hf
Ta
1.3
Th
15
41
24
5.8
4.4
na
na
u
0.3
104
2.1
0.5
0.48
na
na
Pb
9
na
110
na
9
na
27
5
6
na
23
na
9
33
na
17
10
4
10
8
13
22
20
1.9
2.6
0.1
30
117
46
139
173
43
25
24
50
53
43
14
11
6
8
8
6
3
8
4
2
1-3: Homa Mt, western Kenya, HF84, 509, 500; 4-5: North Ruri Hill, western Kenya N44, 428; 6-7: Legetet, Tinderet, Kenya U 1 (Li 161, Be 18, Mo 196, Ag
13, Cd 397, Bi 8, Sn 28 ppm), U3 (Li 167, Be 24, Mo 178, Ag 13, Cd 380, Bi 9, Sn 26 ppm); 8: Kerimasi, northern Tanzania 24376; 9-12: Si1ai Patti, northwestem Pakistan, SP1, 14, 130, 138; 13-18: Loe Shilman, northwestern Pakistan, SM3, 10, 15, 29, 45, 55; 19-21: Koga, Ambe1a, northern Pakistan, K15, 74, 312.
Sources: Kenya, Tanzania- Le Bas database; Pakistan-'- Mian ( 1987)
112
(vi) Samples with >6 wt.% Fe20 3 were excluded.
The first three criteria reduced the database to under 200. To
a large extent, criterion (ii) had the same pruning effect as criterion (iii), both ensuring that only the best of the analytical
data available was used.
Woolley and Kempe (1989) justified an exclusion of carbonatites with >10 wt.% Si0 2 from their compilation of average carbonatite compositions, based on a break at that value in
the frequency distribution. Restricting it to a 5% limit here
requires further justification. The database used in this paper
ha_s been combined with that of Woolley and Kempe (1989),
and the resulting silica frequency distribution (Figure 3) indicates that there are few sovites and alvikites in the range of
6.5- 10 wt. % Si02 • Taking an upper limit at 5 wt.% would
include 89% of the data, but would tend to exclude carbonatites with appreciable contents of silicate minerals. Two questions then arise: (a) is it right to exclude those with appreciable
contents of silicate minerals; and (b) do the silicates seen in
the carbonatites reflect the primary composition of the carbonatite magma, or do they represent, wholly or partly, the product of contamination and assimilation of silicate wallrock
material? The author's observations of many carbonatites
world-wide lead him to believe that while some calcite-carbonatites have appreciable contents of mica, amphibole,
pyroxene, or feldspar, most calcite-carbonatites have few silicate minerals, and those in many instances are locally concentrated. This conclusion finds support in observations recorded
by others. Saether ( 1957) describes the assimilation of wallrock in sovite magma at Fen and notes (p. 74) that the sovite
'has silicatic marginal facies', in particular pyroxene, and that
'the silicate-sovites seem to have been derived from melteigite, ijolite, and fenite by metasomatism' (p. 84). Garson
(1962, Chapter 10) describes and illustrates the incorporation
at Tundulu of fenitic xenoliths into sovite and the dissemination of the silicate minerals, sometimes biotite, sometimes
pyroxene or other silicate, providing 'indisputable evidence of
the origin of the silicate-sovites in the complex'. Likewise, in
discussing the petrography of the carbonatites at Tororo, eastern Uganda, within which pyroxenes and micas occur in
patches and bands, King and Sutherland ( 1966) state 'These
minerals are probably derived from assimilated xenolithic
material.' Pell and Hoy (1989) describe similar relationships
in western Canada. In the calciocarbonatites at Bingo in Zaire,
Woolley et al. (1995) describe aegirine, partly or wholly
replaced by mica and concentrations of mica that appear to be
partly digested xenoliths. This evidence points to the common
occurrence of contamination and assimilation by sovite of
wallrock material, often fenitized, leading to the crystallization of many of the silicate minerals seen in sovites, some surviving as xenocrysts, but more crystallizing from the
contaminated sovitic magma. This process seems to be less
common in alvikites. Thus, putting the exclusion limit at 5
wt.% Si0 2 ensures that the sovites and alvikites used here are
largely free from significant possible contamination. This is
not to say that calciocarbonatite magmas contain no silicate
material. The study of synthetic calciocarbonatite melts at 1
GPa by Lee and Wyllie (in press) demonstrate that liquids with
S.Afr.J.Geol.,!l999, I 02(2)
Table 4 Sources of published analyses of continental
sovites
Locality
Sample nos
Reference
Nooitgedacht, S. Africa
86CN8, 9
Clarke et al., 1994
1
Kruidfontein, S. Africa
86CK30, 70
Clarke et al., 1.994
Bingo, Zaire
8,93
Woolley et al.;, 1995
Lueshe, Zaire
Table 4.1
Maravic and Morteani,
1980
Ngualla, Mbalizi, Nachen- Tables 8.3, 8.5 and
Van Straaten, ·1989
dezwaya and Sangu-Ikola, 8.6
W. Tanzania
Mundwara, Rajasthan,
M1,M2
India
Le Bas and Srivastava,
1989
Aruba Dongar, Gujarat,
AD1228, 1201, 152,
Yiladkar and Wimme-
India
187,227,1271
nauer, 1992
Sung Valley, NW India
88/3,4,5, a5, 15SV91
Yiladkar et al., 1994
Samalpatti, Tamil Nadu,
Table X 4,6
India
Mt. Weld, Australia
Viladkar and Subramanian, 1995
MW2
Nelson eta!., t988
J acupiranga, Brazil
5961,5963
Nelson eta!., 1:988
Jacupiranga, Brazil
JM1, 2, 6a, 15
Morbidelli et CJt., 1986
Jacupiranga, Brazil
HB009.2c
Huang et at., 1995
Catalao 1, Brazil
CTITW
Toyoda et al., 1994
Tapira, Brazil
TP892
Toyoda et at.j994
Anitapolis, Brazil
AP891
Toyoda et al., 1,994
Magnet Cove, Arkansas,
MCl
Nelson et at., ~ 988
Table 9.2.2
Pell and Hoy, 1989
Table 9.2.5,10
Pell and Hoy, 1989
320546, 320460,
Knudsen, 199 ~
U.S.A.
Aley, British Columbia,
Canada
Ice and Perry Rivers, Br.
Columbia, Canada
Qaqarssuk, W. Greenland
249866,320537
Gardiner, E. Greenland
Table 2.9
Nielsen, 1980
Kaiserstuhl, Germany
K3
Nelson et at., 11988
Kaiserstuh1, Germany
425
Hubberten eta!., 1988
Kaiserstuhl, Germany
426, MF-Ca
Schleicher et at., 1991
Kizilcaoren, Turkey
7933, 7944
Hatzl ( 1992)
Sokli, Finland
1973P14(1)
Yartiainen and Woolley,
Sokli, Finland
17.11.10, 17.1V.7
Vartiainen, 1980
Khibina, Kola, Russia
632B/ 1934, 1960
Zaitsev et at., 11998
I
1976
c. 80% CaC0 3 are likely, the remaining liquid being potential
silicate, oxide, phosphate, and other minor phases. The 5 wt.%
Si0 2 also corresponds reasonably well to this limitation.
Criterion (v) limited the database to sovites and alvikites
with <5 wt.% MgO. Samples with abundant phlogopitic mica
and sadie amphiboles such as magnesio-arfvedsonite would
already be excluded by the 5 wt.% Si0 2 criterion. Pure dolomite has c. 20 wt.% MgO, and the 5 wt.% MgO limit ']s aimed
at excluding calciocarbonatites that contain appreciable dolomite, whether of primary or secondary origin. Woolley and
Kempe (1989) gave the upper limit of MgO in calciocarbona-
en
~
._~
0
(1l
¥-
~
\0
~
Table 5 XRF/ICP/INAA analyses of oceanic sovites from the Cape Verde Islands
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Si02
na
1.81
0.24
0.82
3.28
1.87
0.89
1.07
0.10
0.63
1.64
1.48
1.09
2.26
1.87
3.36
3.45
0.82
2.53
0.51
0.27
0.48
0.11
0.12
2.86
0.48
0.09
0.32
2.51
Ti02
0.01
0.01
0.09
0.01
0.01
0.02
0.04
0.10
0.01
0.01
0.04
0.06
0.01
0.32
0.01
0.01
0.05
0.01
0.08
0.01
0.01
0.01
0.01
0.02
0.22
0.04
0.03
0.04
0.10
A1 20 3
0.05
0.19
0.24
0.29
0.37
0.27
0.64
0.40
0.18
0.27
0.62
0.29
0.23
0.65
0.20
0.04
0.59
0.17
0.35
0.29
0.07
0.55
0.15
0.25
0.21 · 2.38
0.08
1.14
0.43
Fe20 3t
0.90
0.67
2.28
1.13
0.58
1.81
1.98
3.61
1.11
3.81
1.03
1.47
0.57
3.66
0.76
0.61
1.11
0.32
2.76
0.30
0.24
0.43
0.23
0.18
4.37
0.16
0.73
1.17
MnO
0.12
0.26
0.33
0.40
0.34
0.49
0.12
0.12
0.31
0.77
0.13
0.16
0.22
0.43
0.39
0.52
0.56
0.22
0.28
0.14
0.11
0.15
0.15
0.13
0.18
0:31
0.15
0.28
0.14
MgO
.na
2.20
4.93
2.90
3.56
3.27
0.80
0.76
1.61
2.76
2.28
0.64
0.21
0.34
0.09
0.10
0.27
0.05
0.19
0.22
0.15
0.20
0.09
0.10
0.59
0.53
0.07
0.31
0.79
52.24 49.56 48.29 50.53 48.61 48.36 ·53.58 51.89 52.87 49.54 51.97
~3:33
CaO
Na20
1.51
0.17
0.09
0.15
0.13
0.15
0.06
0.01
0.09
0.12
0.03
0.01
0.21
0.13
0.06
0.10
0.01
0.11
0.27
0.10
0.07
0.09
0.09
0.20
0.40
0.03
0.01
0.01
0.17
K20
na
0.14
0.02
0.12
0.20
0.06
0.13
0.06
0.01
0.06
0.04
0.25
0.01
0.39
0.16
0.01
0.15
0.11
0.09
0.07
0.01
0.09
0.01
0.01
0.04
0.07
0.01
0.04
0.20
P20 5
na
0.19
1.01
1.71
0.80
1.25
3.82
2.76
0.47
1.37
3.46
3.26
1.31
4.87
0.53
2.27
0.60
0.13
0.64
0.46
0.36
1.21
0.17
0.46
2.17
1.98
2.80
0.29
2.15
LOI
na · 42.6 42.38 41.24 41.41 41.33 38.04 38.73 42.65 39.93 38.76 38.74 41.17 35.31 41.41 39.25 40.58 42.65 40.23 42.57 42.72 41.74 43.09 42.64 37.43 40.00 39.600
147
167
118
236
Ill
76
198
16
4
100
66
42
83
71
472
52
28
86
13
256
18
9
17
4
6
191
36
42.2 38.38
45
52
41
Cr
2
3
9
2
2
2
10
5
5
9
15
9
6
10
2
3
3
3
3
2
4
3
6
3
18
Ni
7
7
21
7
5
6
18
7
5
32
13
5
7
12
5
6
5
4
5
3
5
6
4
5
6
16
8
11
8
Zn
6
64
101
60
68
90
17
55
292
146
18
21
15
102
15
28
33
6
39
11
5
12
5
6
56
24
21
27
30
Rb
2
6
5
5
6
3
16
8
5
3
4
25
5
7
15
Sr
10962
5180
3099
3931
4397
5999
4660
3919
2715
2424
2949
y
60
62
149
116
121
90
61
65
68
115
67
Zr
26
12
35
42
24
33
41
48
13
26
74
79
100
35
16
51
16
26
36
522
2658
1486
2572
2484
2503
343
495
6152
Nb
Ba
1848
3
6358 11881
4197
81
68
4
7032
5140
803
79
179
27
. 1
6
5371 17357 18456
68
24
21
2
9943
9696
9565
109
95
104
3
9956 10125
94
98
158
59
221
4
4
133
14
6
35
2
17
3
233
549
662
4004
2795
5029
4913
1724
1171
724
654
661
649
9744
8097 10091
107
147
153
124
119
114
12
13
30
21
81
13
108
1723
722
950
681
22
5
601
9156 10959
545
La
191
374
233
354
378
339
130
139
.129
197
140
200
261
·337
303
404
527
238
209
357
282
293
265
319
312
408
410
334
363
Ce
335
640
429
593
627
584
260
284
121
480
297
340
493
544
474
663
775
351
310
682
513
550
487
612
645
771
880
652
718
Nd
112
247
195
225
245
225
112
122
34
247
139
121
189
201
133
209
168
89
79
262
198
214
186
247
266
318
387
280
296
Th
4.5
18
60
26
3
6
26
14
7
2
199
25
47
33
5
2
6
3
6
4
5
24
9
34
3
14
29
15
B
52.25 50.06 52.84 51.94 50.82 52.?8 50.00 53.77 54.56 53.79 54.36 54.08 50.30 52.81 54.44 53.79 51.98
0.13
v
0t-.J
1: Brava, 82LB35 (Sc 0.09 ppm, Co 1, Ga 1, Hf 1.22, Ta0.02, U 0.1); 2-12: S Vicente, 82LV43, 83HV1, 25, 26, 32, 64, 65, 89, 107, ,191, 201; 13-29: Fogo, 83HF85, 104, 107, 108, 112, 115, 117, 138, 141, 142, 143,_ 144a,b,
83NF52, 54, 55, 57. Sources: LB, LV- Le Bas database; HV, HF, NF- Hodgson, 1985
Vol
114
S.Afr.J.Geol.;1999,102(2)
Table 6 XRF/INAA analyses of sovites from Fuerteventura, Canary Islands
2
3
4
5
6
0.34
2.43
na
4.00
0.92
3.30
Ti02
0.01
0.03
na
0.25
0.02
0.29
Al 20 3
0.16
0.83
na
2.10
0.35
2.90
Fe2 0 3t
0.18
0.23
0.40
2.70
0.36
3.70
MoO
1.55
0.20
na
0.56
0.26
0.69
MgQ
0.38
0.09
na
2.40
0.11
2.00
CaO
50.02
51.00
na
51.20
51.40
49.10
Na20
0.21
0.53
0.65
0.20
0.35
0.01
K 20
0.04
0.08
na
0.03
0.02
0.40
P20s
0.01
0.03
na
0.93
1.36
0.10
C02
44.77
43.33
na
na
Sc
0.03
0.015
0.12
0.31
0.12
v
12
8
Cr
5
4
Co
7
Ni
10
Cu
38
41
na
Zn
36
2
na
13
Ga
38
na
na
13
4
8
4
7
0.7
1.9
2.5
58
8
102
Rb
5
7
Sr
17424
16790
102
132
2
2
y
Zr
48
c:r
~ 10
5
0
0
,_
0
0
0
0
0
0
N
c:,
0
0,....
J,
J;,
0
0
0
~
v
(\'")
CD
0
0
co
,.!.
10
10
0
!CI:)
a,
0
0,_
I~
. La ppm
b
2
na
Alvikite ocean
10
2
15
17173
15120
26186
na
274
175
191
435
528
2
249
na
15
::::J
6
na
19080
~
cCl)
0.11
49
na
9 Sovite continent
• Sovite ocean
II AMkite continent
II Alvikite ocean1
na
7
na
a
20
Si02
42.44
25
Nb
4
38
na
119
30
Ba
1150
560
2929
661
908
na
La
319
460
1270
597
606
611
Ce
518
809
1960
1262
1174
1099
Nd
146
287
589
522
441
327
Hf
0.3
0.8
0.4
3.3
0.4
3.8
Ta
0.02
2.9
0.13
1.8
0.3
0.51
Th
0.96
3.7
7
33
12
3.5
u
0.5
0.6
7.2
2.3
0.8
1.5
1, 68SC72; 2-6, LFU75/153, 158, 160, 165 (F 0.19%), 187
tite at just over 8%. Knudsen (1991) quoted 10 wt.% MgO as
his upper limit for sovite (the Qaqarssuk carbonatites have
MgO contents ranging continuously from 0.2 to 18%), but taking a limit at 10% would place a crystallizing carbonatite
8900
300
La ppm
100%
90%
80%
70%
60%
50%
30%
20% 0 % t l i - ·
4
10%
0%
0
0
0
0
-
('f)
~
0
0
~
~
Ll)
I
N
0
0
<nI
"'"
I
00
La ppm
25
d
-+- Sovite continent
20
Figure 4 (Right) Chemical plots of sovites from alvikites. (a) Histogram for La data. Frequency is number of samples within the
range indicated on the abscissa. (b) 3-D representation of frequency
distribution of La data. A distinction of continental and oceanic
sovites from continental alvikites is evident. (c) Percentage frequency distribution diagram for La showing that most oceanic alvikites plot close to the continental alvikites at c. 700 ppm and apart
from the sovites at c. 300 ppm. (d) The normal frequency distribution diagram showing the peaking of La in sovites between 200 and
400 ppm, and with alvikites at higher values.
0
0
---- Sovite ocean
---tr- Alvikite contin~nt
--<>-- Alvikite ocean
5
0~~~~~~~~~~~~~~~
0
400
800
'1200
La ppm
1600
2000
115
S.Afr.J.Geol., 1999,102(2)
magma towards the upper part of the calcite-dolomite solvus,
the product of which would be a dolomite-bearing calciocarbonatite. Limiting the database used here to samples with
<5 wt.% MgO avoids including carbonatites with appreciable
dolomite.
Few sovites and alvikites have high Fe20 3 .contents. Some
come from high contents of magnetite, and some from carbonatites bordering on the compositions of ferrocarbonatites.
Most ferrocarbonatites appear to be the late-stage fractionated
products of calciocarbonatites, usually marked by big
increases in such elements as Ba and the rare earths (Van
Straaten, 1989; Knudsen, 1991; Zaitsev et al., 1998). An
inspection of the literature Cited above indicated that taking an
upper limit of 6 wt.% Fe20 3 would ensure that the database
comprises calciocarbonatites with minimal fractionation.
The data for the 42 elements used are presented in Table 2
where the number of analyses available for each element is
given individually for sovites and alvikites. Of the 164 available for calciocarbonatites (120 for sovites and 44 for alvikites), 81 come fr~m the unpublished Le Bas database (56 for
sovites and 25 for alvikites).
The data are separated not only into sovites and alvikites,
but also into whether they occur within continental land
masses or are oceanic. The undoubted oceanic sovites and
alvikites all come from the Cape Verde Islands (Gerlach et al.,
1988). Sovites from the Canary Islands (all in Fuerteventura)
Table 7 XRF/ICP/INAA analyses of continental alvikites
2
3
4
5
6
7
8
9
10
11
12
Si0 2
1.32
0.40
0.16
2.61
4.36
0.41
na
na
0.91
1.50
3.45
2.82
Ti0 2
0.09
0.13
0.07
0.10
0.24
0.04
na_
na
0.03
0.04
0.12
0.26
AI 20 3
0.11
0.10
0.17
0.69
1.42
0.17
na
na
0.24
0.80
0.11
0.37
Fe20 3t
2.70
5.29
4.04
3.18
5.46
4.18
2.96
0.94
0.87
1.60
5.81
5.62
MoO
0.39
0.58
0.41
0.47
0.74
0.57
na
na
0.29
0.44
0.89
0.27
MgO
Q.03
0.72
0.67
0.89
0.92
0.26
na
na
0.40
0.79
1.71
1.4
CaO
52.01
49.69
51.22
50.58
47.22
50.20
na
na
52.60
49.02
45.69
48.44
Na20
1.73
0.15
0.25
0.72
0.61
Q.42
0.47
0.18
0.09
0.06
0.62
0.13
K 20
0.11
0.02
0.01
0.20
0.27
0.04
na
na
0.07
0.29
0.06
0.05
P205
0.44
0.02
1.52
0.94
1.39
1.93
na
na
0.27
0.79
6.11
5.63
C0 2
38.10
na
39.50
37.92
na
na
na
na
na
na
na
na
LOI
na
na
na
36.38
39.5
na
na
42.31
40.88
32.01
33.33
Sc
0.4
14.9
58
1.4
3.6
1.2
0.69
na
na
na
na
v
73
105
123
60
na
74
na
9
5.1
7
na
10
42
534
na
421
0
na
na
40.43
2
Cr
Co
1.4
5"
Ni
8
19
Zn
48
208
Ga
2
Rb
2.3
na
mi
12
2
17.5
3.5
3.5
5
44
51
2
3
na
na
na
na
na
na
na
na
na
na
8
na
na
7
13
7
10
34
46
11
3
9
54
2
35
2
7
7
5
1033
4340
5690
1596
12032
13313
15390
na
123
na
na
120
127
184
88
na
na
2
15
596
11
15
5059
88
3250
2038
2154
4234
y
53
271
81
136
Zr
16
45
89
Nb
747
1255
703
·574
na
647
na
na
Ba
800
7766
4759
1139
1650
5879
3379
2363
957
3233
1846
1033
La
405
687
770
736
976
862
861
888
755
745
840
401
Ce
814
1450
1577
1578
1654
1779
985
1871
1721
1234
1711
808
- 666
Sr
..
na
2530
Nd
340
588
724
556
510
203
705
369
407
584
307
Hf
na
0.6
na
0.59
2.5
0.3
2.1
0.52
na
na
na
na
Ta
2.1
17.7
na
0.35
23
na
na
na
na
Pb
na
109
na
na
Th
50
400
66
u
0.4
8.4
na
1.3
0.73
na
na
80
na
na
62
170
41
23
9.5
42
20
16
9
33
12
8
2.3
0.1
2.3
393
12
1.4
37
45
51
10
1-3: Homa Mt, western Kenya, HF68 (Cu 13 ppm), HF209 (Cu 6 ppm), HC629 (Cu 17 ppm); 4-6: North Ruri Hill, western
Kenya, N340, 614, 318 (Cu 8 ppm); 7-8: Wasaki, Homa Bay, western Kenya, Ul048, 782; 9-12: Silai Patti, northwestern
Pakistan, SPll, 42, Ill, 123. Sources: Kenya- Le Bas database; Pakistan- Mian (1987)
116
S .Afr.J .Geol., 1'999, 102(2)
Table 8 Sources of published analyses of continental
alvikites
Locality
Sample nos
Reference
6336
Nelson et al., 1988
Tororo, E Uganda
. 6330
Nelson eta!., 1988
Chasweta, Zambia
Zl7
Ziegler, 1992
Kruidfontein, S. Africa
85CK49, 50, 58
Clarke eta·!., 1994
Amba Dongar, Gujarat,
AD79, 1272, 1289
Viladkar and Wimme-
1277
Avasia and Viladkar,
Lokupoi, E Uganda
nauer, 1992
India
Panwad, Gujarat, India
1995
Zaitsev eta!., 1998
Khibina, Kola, Russia
633/477.7
Kizilcaoren, Turkey
7022, 7086, 7087, 7096, Hatzl, 1992
lished; Kogarko published several in 1993 of wlhich her
analyses 122, 170, 172, 36P, and 281 fall within the a:bove criteria and are used (Kogarko, 1993).
Similarly, the analyses of 12 continental alvikites, not previously published, are presented in Table 7. The locations and
publication sources of a further 19 continental alvikites utilized are given in Table 8, and the new analyses of 13 oceanic
alvikites from the Cape Verde Islands are given in Table 9.
For each of these groups of sovites and alvikites, the mean
(or average), the standard deviation, the median, the minimum, and the maximum values have been calculated. Table 10
gives the results for the 80 analyses of continental sovites. It is
normal to quote the arithmetical mean when wishing to portray an 'average' composition of a data set. This, however,
7097,7163,7276,7279
a
9
-+- Sovite continent
are listed separately and as possibly oceanic. No alvikites fulfilling the above criteria are known from the Canary Islands.
Table 3 presents the analytical data for 21 continental
sovites not previously published, and in Table 4 are the locations and publication sources of 59 continental sovites also
used in this study. Tables 5 and 6 give the analyses of 29
sovites from the Cape Verde Islands and 6 from the Canary
Islands, respectively, none of which have been previously published. Not all the Cape Verde sovites utilized here are unpub-
Sovite ocean/CV
__._ Sovite Canary Is
-i:r- Alvikite continent
~ Alvikite ocean/CV
7
3
8000
4000
0
10
16000
12000
20000
Sr ppm
a
--+- Sovite continent
8
-
Sovite ocean
b
25
-lr- Alvikite continent
--o- Alvikite ocean
20
>.
u
c
··~
4
0"
~
2
~
Sovite continent
-
Sovite ocean/CV
-+- Sovite, Canary Is
15
-l:r- Alvikite continent
-o- Alvikite ocean/CV
10
5
0+-~~~~~~~~~~~oH~~~~~~~~
0
400
800
1200
Ce ppm
1600
2000
25
20
>.
g 15
2400
4000
6000
8000
10000
Ba ppm
~ Sovite continent
Sovite ocean
-l:r- Alvikite continent
-o- Alvikite ocean
•
14
b
OJ
::I
0"
-+- Sovite continent
12
Sovite ocean/CV
--.- Sovite, Canary Is
-i:r- Alvikite continent
-o- Alvikite ocean/CV
10
c~
8
Q)
~
2000
0
::J
0"
~
10
6
4
5
2
0~~~~~~~~~~~~~
1500'
0
1200
300
600
900
Nd ppm
Figure 5 (a) and (b) Ce and Nd frequency distribution diagrams
showing the separation of so vi tic and alvikitic compositions.
0
10
20
30
40
50
60
70
80
90
100
Th ppm
Figure 6 Frequency distribution for (a) Sr, (b) Ba, and (c) Th. Data
from the Cape Verde Islands is indicated by CV.
117
S.Afr.J.Geol., 1999, 102(2)
Table 9 XRF/INAA analyses of oceanic alvikites from the Cape Verde Islands
2
3
4
5
6
7
8
9
10
11
12
13
Si02
1.62
1.28
0.85
2.37
4.52
3.80
0.13
2.08
4.08
0.28
1.34
1.78
1.98
Ti0 2
0.14
0.01
0.01
0.11
0.05
0.06
0.04
0.65
0.30
0.11
0.23
0.02
0.10
A1 20 3
0.38
0.41
0.26
0.06
0.26
0.44
0.19
0.13
0.95
0.08
0.08
0.38
0.26
Fe 20 3t
4.06
1.55
1.88
5.99
3.40
3.50
1.68
1.90
5.37
2.55
3.26
3.36
2.95
MnO
0.82
1.35
1.26
0.94
0.74
0.72
0.43
0.52
0.82
0.86
0.55
0.93
0.9
MgO
1.79
1.71
2~57
0.95
4.69
4.28
1.98
2.77
3.35
4.59
3.15
0.34
0.71
CaO
49.89
49.23
47.89
50.09
44.84
43.03
52.29
49.50
44.34
47.75
48.51
49.94
49.53
Na20
0.20
0.28
0.20
0.21
0.13
0.51
0.06
0.02
0.05
0.01
0.01
0.18
0.10
K20
0.19
0.01
0.01
0.02
0.11
0.38
0.02
0.03
0.89
0.01
0.01
0.17
0.01
P 20 5
0.71
0.35
0.40
2.19
2.80
1.47
0.62
0.23
1.92
0.18
0.96
0.76
0.66
Sc ·
2.5
0.1
0.1
0.53
na
na
8
na
na
na
na
na
na
v
90
19
30
232
310
373
87
222
473
148
253
201
133
3
8
4
5
3
45
3
Cr
1
Co
5
Ni
4
2
3
Cu
17
15
15
Zn
791
34
40
Ga
4
7
18
186
2
na
16
na
12
11
28
26
na
8
na
27
na
7
na
8
na
na
18
na
na
na
na
226
156
42
130
325
172
152
na
na
na
na
na
11
na
62
na
na
14
na
49
na
Rb
7
3
5
11
2
6
31
5
7
2
Sr
3859
5262
6688
1200
2913
3650
1917
2089
2590
2056
2092
2868
7707
y
188
125
130
104
200
156
90
83
163
67
93
170
376
Zr
43
29
43
38
98
39
37
34
96
20
53
110
3
Nb
21
4
4
166
121
100
206
644
462
221
476
15
1402
Ba
5049
6385
6268
2735
3432
6908
2673
5524
5354
5063
6116
8277
4575
La
890
1066
1054
2S9
591
682
340
472
727
697
459
1160
1216
Ce
1770
2104
2093
545
1084
1032
535
837
1211
1198
801
2306
2380
Nd
658
807
817
218
432
348
263~
343
419
458
311
812
969
Th
5.7
6.1
5.7
12.2
24
61
22
22
70
19
na
79
23
1-3: Brava, 82LB43, 45B, 45W; 4-11: San Vicente, 80LV10 (HfO.l, Ta4.7, U 13.4 ppm), 82LV41, 44,51 (Pb 39,
U 41 ppm), 53 (Pb 45, U 2 ppm), 83HV167, 192, 194; 12-13: Fogo, 83HF111, 121. Sources: LB, LV- Le Bas
database; HV, HF- Hodgson, 1985
gives meaningful values only when the standard deviation is
small compared with the average value calculated. Table 10
also shows that the range from minimum to maximum analytical figures is large for some trace elements, for example, Zr,
Nb, and La, where the high maximum figures grossly influence the average calculated, and this is shown by the big
standard deviations.
Two other values are deduced: the mode and the median.
The mode is the peak value and is-meaningful if the data show
normal distribution (i.e. not skewed), but many of the data
here gave positively skew~d plots and therefore the value of
the mode is questionable and is not included in Table 10. The
median overcomes the above problems. It is calculated so that
the number of the values recorded lie equally to each side of a
vertical line, that line being the median. Thus, the median is
scarcely affected by the occasional high value of some trace
elements, and it is concluded that the median gives the best
image of the most common composition.
The medians for the two types of calciocarbonatites, identified in the field as sovite and alvikite, are given in Table 11.
The 'world' figures combine all the sovites and all the alvikites listed.
Histograms or frequency distribution diagrams
Having assembled the data, the question to be addressed is 'do
the data indicate that calciocarbonatites identified as sovites
and alvikites have distinct chemical compositions?' The question is not 'do the data show a bimodal distribution which
might correspond to sovite and alvikite?' If the data show a
continuum, the answer to the latter question would be 'no', but
this would not negate a possible positive answer to the former.
Plotting histograms or frequency distribution diagrams
allows inspection of the spread of the data used in the above
calculations. Such diagrams also make evident whether the
median value is that of a sharp peak or a wide hump (Figure
4a). The latter is more usual. The shape of the distribution is
displayed better in a 3-D representation of a frequency distri-
118
S.Afr.J.Geol., l999, 102(2)
bution diagram (Figure 4b) where the peaking of values for
continental and oceanic sovites can be seen approximately to
coincide, but the peak or hump for continental alvikites is well
a
Table 10 Statistical data for 80 analyses of continental
sovites
n
AVERAGE
ST. DEV.
MEDIAN
MIN.
MAX.
Si02
72
1.95
1.43
1.59
0.05
4.89
Ti0 2
74
0.12
0.19
0.06
0.01
0.96
AI 2 0 3
74
0.29
0.35
0.17
0.01
1.82
Fe20 3t 78
2.50
1.71
2.38
0.08
5.96
MnO
80
0.26
0.17
0.23
0.01
0.83
MgO
80
1.90
1.46
1.70
0.01
4.92
CaO
78
49.84
2.67
49.86
43.86
56.38
Na20
71
0.21
0.25
0.12
0.01
1.09
K 20
72
0.17
0.26
0.08
0.01
1.45
P 20 5
77
2.41
2.39
1.72
0.01
12.1
C02
34
39.92
2.73
39.30
33.32
42.80
HzO+
8
1.07
0.86
0.72
0.27
2.44
12
1.44
1.64
0.87
0.06
6.00
7
0.34
0.56
0.12
0.03
1.60
0.038
Sc
21
7
10
2
v
59
63
63
45
Cr
51
17
23
5
0.3
91
Co
31
11
13
7
0.1
61
Ni
50
20
22
10
80
Cu
24
31
43
17
205
40
Rb Ba Th Pb Nb La Ce Sr Nd' P
Zn
48
77
190
30
1010
20
3
2
3
7
Rb
53
8
8
6
37
Sr
78
8147
4715
7186
1050
23390
y
68
78
43
70
6
310
Zr
70
159
235
50
Nb
67
482
855
82
2
4430
Ba
78
1389
1686
820
35
11600
1028
La
76
369
353
324
25
2385
Ce
73
743
751
641
40
5535
1245
Nd
69
268
221
230
10
Hf
14
3.4
5.8
0.48
0.01
17
Ta
15
10
22
1.5
0.04
86
Th
55
31
42
l3
0.1
202
u
33
36
45
26
0.1
173
Pb
31
21
30
8
Be
4
12
11
10
Cs
6
22
51
65
74
7
ll
Zr
Y
Mn Fe,
V
Cu
291
Ga
Li
Rb K BaTh NbL.aCeSr Nd P Zr Y MnZn;CuPb
110
1.9
24
0.4
125
5
167
Sn
4
14
15
14
Au
2
0.15
0.14
0.15
0.05
0.25
Mo
2
11
10
ll
4
18
Sb
2
0.05
0.01
0.05
0.04
0.06
28
n is number of analyses available for that particular element
Figure 7 (a) 'Spidergrams' for median compositions of continental
and oceanic sovites (Cl calciocarbonatites) and alvikites (C2 calciocarbonatites), given in Table 11, normalized against 'pyrolite' of
McDonough and Sun (1995). Note the tendency for the pairing of
like distributions. See text for explanation of new terminology introduced here. (b) Whole-world C2 calciocarbonatite normalized
against whole-world Cl calciocarbonatite showing the enrichment
factors using the median compositions given in Tablell.
to the right. Neither representation gives a clear picture for the
distribution of the oceanic alvikites because they are so few.
Plotting the data on a percentage basis overcomes this (Figure
4c), and the few oceanic alvikites are seen to lie more within
the spread of continental alvikites than with the sovites. The
frequency diagram, Figure 4d, shows the distribution to the
higher values, which being few and scattered (but individually
interesting petrogenetically), are not considered to be significant except in that their frequency is low.
Figure 5 shows the distribution forCe and Nd, and confirms
the pattern of REE distribution seen for La; that is, thfit continental and oceanic sovites bunch together while the alvikites
have a spread of higher ppm values.
Figure 6 gives the frequency distribution for Sr, Ba, and Th,
and again confirms the distinction of sovites from alviltites, no
matter whether they are continental or oceanic. The antipathy
of Sr with Ba is seen well in Figure 6a and 6b, with Sr high in
sovites and low in alvikites, while Ba is relatively low in
sovites and high in alvikites. Th is also relatively high in alvikites compared with sovites (Figure 6c). Fe, Mn, P, V, Zn, Zr,
and Nb show similar contrasts between sovites and alvikites.
Thus, it is seen that sovites and alvikites are not chemically
equivalent, the difference lying mostly with the tr(!lce ele-
119
S.Afr.J.Geol., 1999, 102(2)
Table 11 Median values for all analyses of sovites and alvikites
ALVIKITES (C2)
SOVITES (Cl)
Canary Is
Cape Verde Is
World
Continents
Cape Verde Is
World
Continents
Si02
1.45
1.59
2.43
1.07
1.57
1.50
1.78
Ti0 2
0.05
0.06
0.03
0.04
0.07
0.07
0.10
A1 20 3
0.22
0.17
0.83
0.27
0.19
0.18
0.26
Fe 20 3t
1.66
2.38
0.38
1.06
2.89
2.70
3.26
MnO
0.24
0.23
0.56
0.23
0.67
0.57
0.82
MgO
1.17
1.70
0.38
0.59
0.81
0.58
2.57
CaO
50.42
49.86
51.00
51.98
49.32
49.40
49.23
Na20
0.11
0.12
0.28
0.10
0.13
0.13
0.13
K20
0.08
0.08
0.04
0.09
0.07
0.08
0.02
P205
1.49
1.72
0.10
1.21
0.67
0.66
0.71
C0 2
39.69
39.30
43.33
42.67
39.85
39.85
40.48
H2o+
0.47
0.72
0.185
so4
0.87
0.87
1.95
1.95
F
0.16
0.12
0.19
4.10 .
4.10
Sc
1.3
2
0.12
10
2
3
0.5
v
47
. 45
12
5Z
107
56
201
Cr
5
5
5
5
2
2
3
15
5
6
5
Co
7
7
5
Ni
9
10
7
7
8
8
11
15
16
152
Cu
20
17
41
22
16
Zn
29
30
2
28
127
112
2
Ga
3
3
Rb
5
6
7
4
5
5
5
Sr
7190
7186
17300
5685
2755
2642
2868
y
80
70
175
101
120
108
130
Zr
30
50
126
23
34
3
39
Nb
36
82
30
16
116
86
166
Ba
851
820
908
950
5354
5366
5354
La
321
324
602
303
763
773
697
Ce
629
641
1137
544
1514
1578
1198
Nd
226
230
384
205
488
550
432
Hf
0.5
0.48
0.6
1.2
0.6
0.6
Ta
1.1
1.5
0.4
0.02
2
1.7
Th
12
13
5
9
41
66
u
14
26
1.2
35
18
20
Pb
10
8
33
23
11
Be
1.5
10
0.5
5
5
Li
9
11
2
Sn
2
14
2
Au
0.15
0.15
Mo
11
11
0.06
0.06
0.24
0.24
22
Cs
Sb
ments. Taking the medians given in Table 11 as the best representative compositions of sovites and alvikites, the contrast
between the two is seen further by plotting the distribution of
the significant elements ag&inst a standard, such as pyrolite
120
S.Afr.J.Geol.,l999,102(2)
0.07
•••
•
•
•
•
••
~
..
..•••
••
-.
• ••
• •
Figure 8 Distribution plots for Ca-Sr and Ca-La of apatites from western Kenyan sovites
and alvikites showing the variation in compositions. Error bars indicated. Partly after Le
Bas and Handley (1979).
(Figure 7a ). It also shows that continental and oceanic (Cape
Verde only) sovites are little different and that continental and
oceanic alvikites also hardly differ from each other, but are
quite distinct from the sovites. In Figure 7b, 'world' alvikite is
normalized against 'world' sovite .and shows the relative
enrichment in alvikite of most trace elements, except Sr, P, and
Cu.
The distinction of sovite from alvikite is also evident mineralogically from the composition of the apatites in them. Apatite is more common in sovite than alvikite, which accords
with the drop in P 20 5 recorded in Table 11, and the change in
apatite composition from sovite to alvikite is shown in Figure
8. The data plotted are based on the compilation of microprobe analyses of apatites from the western Kenyan carbonatite complexes (Le Bas and Handley, 1979, subsequently
updated). The distinct compositions of apatite in sovite and
alvikite indicate a chemical difference between the two rocks.
Terminology
Having demonstrated that sovite and alvikite calcite-carbonatites are chemically different, and maintaining the current
mineralogical definition (Le Maitre et al., 1989) of sovite and
alvikite as the coarse-grained and the medium- to fine-grained
varieties of calcite-carbonatite, new terms are required to
identify the two calciocarbonatite chemical compositions
equivalent to sovite and alvikite. This contribution proposes
C1-calciocarbonatite and C2-calciocarbonatite respectively as
suitable terms, which can be abbreviated to C 1 and C2 types
where appropriate. C 1 and C2 have been used previously as
symbols for sovite and alvikite (Le Bas, 1984). That there are
two systems of classification for carbonatites, mineralogical
and chemical, was established by Le Maitre et al. (1989).
Conclusions
1. Using 164 chemical analyses of carbonatites spanning 42
elements gathered into a database of 120 sovites and 44·alvikites, it is demonstrated that sovites and alvikites are chemically distinct (Tables 2 - 9; Figures 3 and 4 ).
2. Dividing the data further into sovites and alvikites that
occur within continental masses and those emplaced in oce-
anic crust, it is shown that sovites of the continents are little
different from sovites in the oceans (all oceanic data being
taken from the Cape Verde Islands), but sovites fNm the
Canary Islands differ from b~th.
3. Similarly, continental and oceanic alvikites are alike (Figures 3 and 4 ).
4. The chemical difference between sovites and alvikites is
best displayed by the trace elements (Figures 4, 5, ancl6).
5. The principal feature distinguishirng C 1-calciocarbonatite
(sovite in mineralogical terms) from C2-calciocarbonatite
(alvikite in mineralogical terms) on a multi-element ~ariation
diagram is the distribution pattern of Sr and REE. In type C 1,
Sr is seen as a positive feature relative to the REE in th:e distribution pattern, but in C2, Sr is seen as a sharply negative relative feature (Figure 7a).
6. Trace elements Ba, Th, Pb, Nb, ILa, Ce, Nd, andl. V are
enriched in type C 1 relative to type C2 (Figure 7b ).
7. Recalling that sovite usually precedes the emplacement of
alvikite, the pattern of enrichment suggests that alvikite
magma could be derived from sovite magma by fractionation.
8. The arithmetical medians calculated from the database give
more useful compositions for C 1- and C2-calciocarbonatites
than averaged ones (Tables 10 and 11 ).
Acknowledgements
My thanks go to my many carbonatite colleagues, especially
Alan Woolley, for numerous valuable discussions and critical
comments; to Jan Hertogen at Leuven University fm INAA
data; to Nick Marsh and Rob Kelley of Leicester Un:iJversity
for their skill in the creation of high precision XRF analyses of
carbonatites, also to Emma Mansley for her excellent and
invaluable ICP analytical work; to Chris Handley and Rob
Wilson for the many apatite analyses carried out on the Cambridge Mark V microprobe analyser at Leicester, and to Neil
Hodgson and Ihsan Mian, former research students at Leicester, for permission to use the XRF data taken from their theses.
I sincerely thank the two referees who~e criticisms caused me
to rethink and clarify the issues presented.
121
S.Afr.J.Geol., 1999, 102(2)
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