Geochemistry International, Vol. 40, No. 4, 2002, pp. 313-322. Translated from Geokhimiya, No. 4, 2002, pp. 355-364
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- Compositions of Minerals of the Lamprophyllite Group from Alkaline Massifs Worldwide V. A. Zaitsev and L. N. Kogarko
- Table 2.
- 0.46 -0.22 0.39 0.21
- Fig. 1.
- Fig. 3.
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Geochemistry International, Vol. 40, No. 4, 2002, pp. 313-322. Translated from Geokhimiya, No. 4, 2002, pp. 355-364. Original Russian Text Copyright © 2002 by Zaitsev, Kogarko. English Translation Copyright © 2002 by MAIK "Nauka /Interperiodica" (Russia). Compositions of Minerals of the Lamprophyllite Group from Alkaline Massifs Worldwide V. A. Zaitsev and L. N. Kogarko Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991 Russia Received September 10, 2001 Abstract—The analysis of a data base on the compositions of lamprophyllites from alkaline massifs worldwide enabled us to discuss the isomorphic substitutions in structures of the minerals of this group, as well as varia tions of their compositions and typomorphic features in different alkaline massifs. It is shown that the lampro phyllite composition is related to geochemical features of the corresponding massif. However, there is no sim ple relation between the element contents in lamprophyllite and the host massif. Minerals of the lamprophyllite group (Sr, Ba, K, Na) 2
2 T i [ T i 2 0
( S i 2 0 7 ) 2 ] ( 0 , OH, F)
2 are usual accessory phases of igneous com plexes oversaturated with respect to alkalis. They nor mally crystallize at the later stages of m a g m a differen tiation and during the p o s t m a g m a t i c processes up to the latest stages of mineral formation. The wide crystallization range of lamprophyllites makes it reasonable to study their t y p o m o r p h i c (partic ularly chemical) features. A data base was created for this purpose, which comprises the compositions of minerals of the lampro phyllite group from alkaline complexes worldwide. It includes published analyses, a u t h o r s ' data, and several analyses graciously provided by N.V. C h u k a n o v and D.V. Lisitsin. T h e analyses were carried out by wet chemistry or obtained with electron m i c r o p r o b e and by interpreting of the mineral structures. The representative analyses of minerals of the lam prophyllite group are listed in Table 1. The crystal structures of lamprophyllite and the other minerals of its group (baritolamprophyllite and K-baritolamprophyllite) were determined in samples from many alkaline complexes [ 1 2 - 1 7 ] . As a result, the lamprophyllite structure is now well k n o w n . However, some problems of isomorphic substitutions in its struc ture are not yet solved (see below). Several sites c a n be d i s t i n g u i s h e d in t h e lampro phyllite structure, i.e., Si, T i ( l ) , T i ( 2 ) , N a , M ( l ) , M(2), 0 ( 1 ) . . . 0 ( 6 ) , and H. T h e structure is based on the three-sheet layer c o m p o s e d of the central trioctahe- dral sheet with Na, Ti(2), and M ( 2 ) sites and side nets built up of Si 2 0
diorthogroups linked by five-coordi nated Ti(l) polyhedra. T h e a t o m s between the layers occupy the M ( l ) sites. T h e distribution of cations over the sites is shown in Table 2. All of the oxygen atoms in the trioctahedral sheets [except for O ( l ) of hydroxyl groups that is replaced by F and CI] are shared with Ti-Si-O nets. T h e lamprophyllite structure is devoid of vacancies that could be occupied by any additional (foreign) cat ions (R.K. Rastsvetaeva, personal c o m m u n i c a t i o n ) . As a result, the cation total in a correct formula cal culation should not exceed 12. T h e lamprophyllite for mulas are calculated on the basis of four Si atoms. It is suggested in this case that all Al atoms occupy the Ti sites. Another calculation procedure is based on the assumption that Al atoms occupy the sites with tetrahe- dral coordination together with Si. We calculated the mineral formulas by both methods and analyzed the distribution of total cation a m o u n t s (Table 3). T h e statistic data obtained are m o r e consistent with the substitution of Al for Si, rather than for Ti. Based on these data, we used the second calculation procedure and controlled the cation totals. T h e analyses with cation totals deviating by more than 3a from 12 were not considered. T h e analyses with total a m o u n t s of Sr, Ba, and К above two formula units by more than 0.2 were also considered as unsatisfactory. T h e coefficients of correlation between individual cations in the lamprophyllite structure calculated from these data are shown in Table 4. This table demonstrates that the best correlation is observed between Sr and Ba, which is related to the occupation of the M ( l ) site by these two elements. According to structural data [14, 16, 17], potassium also occupies the M ( l ) site and correlates negatively with Sr and positively with Ba. T h e latter is caused by the similarity of К and Ba ionic radii. T h e calculated partial coefficient of correlation 1 between Ba and К is The partial coefficient of correlation is a measure of linear corre lation between any two variables from the X { X 2 ...X n group when the effect of the other variables is eliminated [18]. 313
Table 1. Representative analyses of minerals of the lamprophyllite group Ordi-
nal no. N a
2 0 K 2 0 MgO CaO SrO
BaO MnO
FeO A 1 2 0 3 F e
2 0 3 S i 0 2 T i 0 2 N b
2 0 5 H 2 0 F CI
T h 0 2 L a 2 0 3 C e 2 0 3 Total
- 0 = F 1 11.34 1.61 0.74
1.09 11.71
7.65 0.78
5.06 0.12
n.a. 30.06 27.92 0.11 n.a.
1.87 n.a.
- 0.00
2.70 102.76
101.88 2 9.99 2.41 0.39
1.12 6.94 11.89 1.03 4.14
n.a. 1.32
29.80 29.49 n.a.
0.81 1.65
n.a. n.a.
n.a. n.a.
100.98 100.20
3 12.10
0.62 0.44
4.30 11.50
0.00 5.06
0.00 2.00
2.48 29.98 29.57 0.11 1.58
n.a. n.a.
n.a. n.a.
n.a. 99.74
4 9.60
1.64 0.66
1.27 8.69
9.51 1.40
3.20 0.90
1.44 30.40 29.50 0.27 1.79
n.a. - n.a. n.a. n.a.
100.27 5 9.20 2.30 0.41
1.90 6.54 15.60 0.53 3.19
0.17 n.a.
29.10 28.80 n.a.
n.a. 1.64
n.a. n.a.
n.a. n.a.
99.38 98.61
6 11.99
0.94 1.03
0.26 3.48 20.06 1.60 1.27
0.04 n.a.
29.90 28.68 n.a.
n.a. n.a.
n.a. n.a.
n.a. n.a.
99.25 7 9.67 1.06 0.39
0.56 4.74 26.31 0.84 n.a.
- 1.20
27.96 26.34 n.a.
n.a. n.a.
n.a. - - - 99.07
8 11.14
0.94 0.34
0.36 0.65 24.12 1.10 0.71
0.04 n.a.
28.75 27.80 n.a.
1.83 1.18
n.a. n.a.
n.a. n.a.
98.96 98.40
9 9.20
0.65 0.71
0.29 17.11
5.68 4.95
1.58 0.26
n.a. 30.22 28.42 0.34 n.a.
n.a. - - - - 99.41 10 10.57
1.89 0.53
0.88 11.40
8.67 2.38
1.75 0.60
- 29.00 28.94 0.30 1.56
1.60 n.a.
n.a. n.a.
n.a. 100.07
99.32 11
10.63 1.17
0.67 1.74
14.07 2.31
4.29 1.91
0.44 0.54
30.70 29.14 0.15
n.a. 0.84
0.28 n.a.
n.a. n.a.
98.88 98.48
12 10.04
2.97 1.46
1.44 9.53
4.23 2.16
3.49 0.76
2.68 30.78 28.91 0.24 n.a.
1.63 n.a.
n.a. n.a.
n.a. 100.32
99.55 13
12.45 0.46
0.63 0.91
14.72 0.97
3.86 2.29
0.20 n.a.
31.14 30.16 0.11
n.a. 1.96
n.a. 0.22
0.06 0.45
100.59 99.67
14 12.59
1.15 n.a:
0.34 1.80 19.27 3.60 0.23
0.31 n.a.
27.53 25.54 3.09
1.82 1.36
n.a. n.a.
n.a. n.a.
98.63 97.99
15 11.16
0.46 0.44
0.63 15.02
1.10 3.18
3.34 0.27
n.a. 30.64 30.39 0.45 n.a.
1.40 0.00
- 0.07
0.52 99.07
98.41 16
8.40 0.79
0.32 0.46
11.93 8.18
2.43 2.31
0.20 n.a.
31.17 28.03 0.67
n.a. 1.57
0.00 0.02
0.01 0.35
96.84 96.10
17 11.57
0.82 0.18
0.14 7.35 15.01 2.18 1.19
0.32 n.a.
30.04 28.10 0.30
n.a. 1.97
n.a. n.a.
n.a. 0.12
99.29 98.36
18 12.58
0.52 0.52
0.55 14.83
0.65 2.96
3.69 0.14
n.a. 32.27 29.84 0.38 n.a.
2.73 n.a.
n.a. n.a.
0.02 101.68
100.40 19
11.27 0.45
0.42 0.41
14.65 0.87
6.14 2.85
0.13 n.a.
30.51 29.42 0.25
n.a. 0.93
0.01 - 0.16 0.24 98.71
98.27 20
12.59 0.41
0.66 0.42
15.49 0.77
2.08 3.93
0.19 n.a.
30.90 29.45 0.20
n.a. 1.71
n.a. 0.15
0.05 0.45
99.45 98.65
Note: (1) Niva (authors' data), (2) Botogol [1]; (3) Strelka [2]: (4) Turii Mys [3]; (5) Oldoinyo Lengai [4]; (6) Gardiner [5]; (7) Bearpaw [6]; (8) Inagli [7]; (9) Pilanesberg (authors' data); (10) Khibiny [8]; (11) Khibiny [9]; (12) Khibiny [10]: (13) Lovozero, Lephe-Nelm (authors' data); (14) Lovozero, Yubileinaya [11]; (15, 16) Lovozero, differentiated complex (authors' data); (17, 18) Lovozero, eudialyte complex (authors' data), core and rim of a crystal; (19, 20) Lovozero, porphyritic lujavrites (authors' data). Dash means content below detection limit, n.a. is not analyzed. COMPOSITIONS OF MINERALS OF THE LAMPROPHYLLITE GROUP 315 Table 2. Occupation of cation sites in lamprophyllites (data of structure interpretation) Table 3. Mean totals of cations in lamprophyllite formulas Analyses are recalculated on the basis of Si = 4 Si + Al = 4 Mean values for all analyses 12.299 ±0.085 12.073 ±0.088 Mean values for analyses within 3a interval: all analyses 12.320 ±0.059 12.104 ±0.070 microprobe analyses 12.09 ± 0 . 0 5 12.00 ± 0 . 0 5 chemical analyses 12.50 ± 0 . 0 9 12.29 ± 0 . 0 8
Ele
ment Sr
Ba К Na Ca Mg
Fe Mn
Zn Ti
Nb Zr
Al F CI Sr 1.00
Ba -0.91 1.00
К -0.68 0.62 1.00
Na 0.38 -0.39 -0.59 1.00
Ca -0.19 0.01
0.34 -0.14 1.00
Mg -0.03 -0.06 0.02
0.02 0.24 1.00
Fe -0.12 -0.07 0.46 -0.22 0.39 0.21 1.00
Mn 0.43 -0.39 -0.39 0.09 -0.30 -0.30 -0.49 1.00 Zn
-0.08 -0.14 -0.18 -0.01 -0.14 -0.49 -0.22 0.18
1.00 Ti
0.05 -0.01 0.06
0.23 -0.03 -0.22 -0.12 0.11 -0.02 1.00 Nb -0.51 0.50 0.31 0.01 -0.09 -0.23 -0.12 -0.07 0.32 0.05
1.00 Zr
-0.38 0.37
0.11 0.22
0.42 0.09
0.17 -0.17 -0.06 -0.08 0.59 1.00
Al -0.12
0.00 0.11 -0.22 0.33 0.32 0.01
0.02 0.84 -0.19 -0.04 -0.30 1.00
F -0.05
0.02 0.23 -0.09 -0.13 -0.03 0.40 -0.36 -0.06
0.16 0.60 -0.39 1.00 CI
-0.38 0.35
0.32 -0.20 0.33
0.49 0.47 -0.50 -0.52 -0.12 0.11 0.19 1.00 Note: Significant coefficients are shown in bold. 0.02 with consideration of the Sr effect, i.e., К and Ba collectively replace Sr in the lamprophyllite structure. The problem of Na and Ca distribution between M(l) and M ( 2 ) sites was also discussed in the literature [15, 17, 19]. O u r data (Table 5) show no correlation between Na and Ca in lamprophyllite. This fact indi cates that these elements occupy different sites in the mineral structure or they are distributed over several sites with complex isomorphic substitutions. T h e coef ficients of Na and Ca correlation with other elements in the M ( l ) site (structural data) indicate that Na also occupies this site, as it is justified by a large negative coefficient of Na correlation with K, while the coeffi cient of correlation between Ca and К is positive. Sig nificant correlations between Na and Sr, Na and Ba, and Ca and Sr are induced by the effect of K. 2 2 The induced (false) correlation between two variables is the cor relation induced by the effect of the other variables. GEOCHEMISTRY INTERNATIONAL Vol. 40 No. 4 2002
316 ZAITSEV, KOGARKO Table 5. The main isomorphic admixtures in the M(2) site Element
The lowest content The highest content The lowest mean content The highest mean content Element (f.u.) was found in (f.u.) was found in (f.u.) was found in (f.u.) was found in Mn
Khibiny (0.05) Gardiner (0.05) Khibiny (0.90) Oldoinyo Lengai (0.06), s.a. Niva (0.08) Pilanesberg (0.56) Fe Lovozero (0.03) Murun (0.65) Khibiny (0.63) Pilanesberg (0.17) Botogol (0.60), s.a. Murun (0.59) Niva (0.52) Mg Khibiny (0.02) Khibiny (0.38) Lovozero, differentiated Niva (0.16) Lovozero, eudialyte Inagli (0.27) complex (0.07) Gardiner (0.16) complex (0.03) Pilanesberg (0.16) Lovozero, pegmatites (0.03) Ca
Pilanesberg (0.02) Khibiny (0.60) Pilanesberg (0.05) Strelka (0.57), s.a. Lovozero, eudialyte Strelka (0.57) Oldoinyo Lengai (0.28), s.a. complex (0.02) Botogol (0.16), s.a. Turii Mys (0.15) Murun (0.15) Note: s.a. is single analysis. N o t e the high positive coefficients of correlation between К and Fe, as well as between Sr and M n . Con sidering the effect of these dependencies, we obtained a positive partial coefficient of correlation between Mn and K. A positive correlation between the concentration of univalent К replacing bivalent Sr and Ba in the M ( l ) site and the concentrations of M n , Fe, and Ca replacing univalent Na can be illustrated by the following charge- compensation s c h e m e (Sr
2+ , Ba
2+ ) + Na
+ — K
+ + (Mn
2+ , Fe
2+ , Ca
2+ ).
As a result, we propose the following formula for the K-lamprophyllite end member: K 2 N a ( M n , Fe, C a ) 2 T i [ T i 2 0 2 ( S i 2 0 7 ) 2 ] ( 0 , O H , F) 2 . A l u m i n u m shows significant positive correlations with Ca and Mg and negative, with Na, which can be accounted for by the following substitution scheme: N a + Si — (Ca, M g ) + Al. T h e compositions of minerals of the lamprophyllite group were compared in triangular plots describing the occupation of M( 1) and M ( 2 ) + Na sites (Fig. 1). The Ti site has not been considered, because the N b , the main isomorphic admixture in this site, has not been ana lyzed in many published lamprophyllite compositions. T h e O ( l ) site was also not considered, because most of the analyses do not include CI and H 2 0 contents, while F concentrations are reported only for about 7 0 % of the analyzed lamprophyllites. Fig. 1. Compositions of lamprophyllites from alkaline massifs worldwide in the K-Sr-Ba diagram, (a) Fields: (/) Khibiny, (2) Gar diner, (3) Pilanesberg, (4) Bearpaw, (5) Murun, (6) Niva, (7) Inagli. (b) Lovozero Massif; fields: (/) differentiated complex, (2) eud ialyte complex, (J) porphyritic lujavrites, (4) pegmatites. GEOCHEMISTRY INTERNATIONAL Vol. 40 No. 4 2002 COMPOSITIONS OF MINERALS OF THE LAMPROPHYLLITE GROUP 317
The M(l) site is generally occupied by Sr, Ba, K, and Na. It probably also incorporates rare earth ele ments and Y. The K - S r - B a d i a g r a m shows that the fields of the lamprophyllite compositions from various massifs sig nificantly overlap. However, three groups of lampro phyllites could be distinguished in this diagram, partic ularly for the Ba-rich varieties. Lamprophyllites of the first group are enriched in К ( M u r u n , Turii M y s , Inagli, Niva, and Khibiny massifs). Lamprophyllites of the Murun Massif are richest in К (0.61 f.u., on average) in agreement with the elevated potassium contents in the rocks of this massif. T h e second group comprises lam prophyllites with low К contents (<0.2 f.u.) (Bearpaw, eudialyte and differentiated complexes of the Lovozero Massif, and Pilanesberg). Lamprophyllites from peg matites of the Lovozero Massif c o m p o s e the third group with transitional compositions. The lamprophyllites of s o m e massifs c o m p o s e t w o fields: (1) enriched with Sr and (2) enriched with Ba. However, there is no gap between the Sr- and Ba-rich compositions (Fig. 1), which suggests a continuous solid solution series in the lamprophyllite-baritolam- prophyllite series. T h e occurrence of lamprophyllites of two separate compositional groups within one massif could be caused by the evolution of the mineralizing medium. Pekov etal [20] explained the transition from lamprophyllite to baritolamprophyllite in the Khibiny Massif by the separation of Sr from Ba at the later peg- matitic stages due to Sr partitioning into carbonates (ancylite and strontianite), which are closely associated with baritolamprophyllite. A similar role in s o m e other massifs could be played by the chevkinite-group miner als, as well as R E E phosphates and carbonates (Table 6). Similar evolutionary trends of the lamprophyllite com position in different massifs, including the rocks of the eudialyte complex that have almost no Sr-apatite and contain much smaller a m o u n t s of Sr-bearing minerals as compared to lamprophyllite, suggest that there are some other reasons for the transition from lamprophyl lite to baritolamprophyllite. We believe that this transi tion could be related to the accumulation of compo nents of the lower temperature Ba-lamprophyllite in the melt relative to those of the higher temperature Sr-lam- prophyllite. The triangular N a - S r - B a , N a - K - S r , and K - S r - B a diagrams were found to be less informative. Lamprophyllites can be subdivided by d o m i n a n t cations occupying the M ( l ) site into Sr-rich and Ba- rich minerals (in the general case, this classification is not equivalent to a formal subdivision into lamprophyl lite and baritolamprophyllite). In turn, the Ba-rich lam prophyllites are subdivided into high-, medium-, and low-K varieties. The rare earth elements and Y are usually not ana lyzed in lamprophyllites. T h e available data indicate that the mineral can contain up to 0.02 f.u. La, 0.01 f.u. Nd, and 0.3 f.u. C e ; however, the latter normally does Fig. 2. Mn distribution in lamprophyllites from alkaline complexes worldwide. not exceed 0.05 f.u. Only lamprophyllites from the Niva Massif have exclusively high Ce contents ( 0 . 1 3 - 0.23 f.u.). Yttrium contents are typically below 0.005 f.u., i.e., lamprophyllites are enriched in light rare earth ele ments.
content not found in the M ( l ) site is >2 f.u. in 8 0 % of all cases). Data on minor admixtures in the M ( 2 ) site are given in Table 5. T h e distribution of Mn has a m i n i m u m at about 0.2 f.u. (Fig. 2). Such a bimodal distribution allows one to subdivide lamprophyllites into high- and low-Mn varieties. H i g h - M n (>0.2 f.u.) lamprophyllites are abundant in the Khibiny, Lovozero, Pilanesberg, Turii M y s , and Strelka massifs, while low-Mn lamprophyllites are typ ical of the Inagli, Bearpaw, Gardiner, M u r u n , Oldoinyo Lengai, Botogol, and Niva massifs. Zinc contents in lamprophyllites normally do not exceed 0.05 f.u. and are usually not analyzed. There is one analysis of lamprophyllite from pegmatite of the Lovozero Massif with 0.4 f.u. Zn. In this case, Zn prob ably occupies the M ( 2 ) site. Lamprophyllites in some massifs have an almost constant Mn/Fe ratio (Fig. 3), which is low in the Niva Massif (0.15), somewhat higher in the Inagli (0.95) and Bearpaw (0.56) massifs, and extremely high in Pilanes berg (3.90). S o m e fields are roughly isometric and characterize significant variations in the mineral com position (low-Mn lamprophyllites of the Khibiny Mas sif, lamprophyllites of pegmatites and the eudialyte complex of the Lovozero Massif and Gardiner com plex). S o m e fields are elongated along the N a - M n side, for example, very similar fields of lamprophyllites from the rocks of the differentiated complex and porphyritic lujavrites of the Lovozero Massif; some other fields gravitate to the N a - F e side (lamprophyllites of the M u r u n Massif). T h e field of high-Mn lamprophyllites of the Khibiny Massif is small and is located at the right-hand sides of the extended field of the Pilanesberg lamprophyllites and the group of fields enclosing 1am- GEOCHEMISTRY INTERNATIONAL Vol. 40 No. 4 2002
Table 6. Occurrences and mineral assemblages of lamprophyllites in alkaline complexes worldwide Massif
Rock Mineral assemblage Lamprophyllite type Genesis
Reference Bearpaw
Pegmatite Nepheline, microcline, phlogopite-annite, magne- tite, rutile, zircon, thorite, betafite, Ce-loparite, crich- tonite, ilmenite, pyrophanite, aegirine, sphene, minerals of the chevkinite group Sr-lamprophyllite with rims of Ba-lamprophyllite Pegmatitic [6, 12] Gardiner Pegmatites and veins
Natrolite, sphene; lorenzenite, melanite, pectolite, magnetite, aegirine-augite Sr- and Ba-lamprophyllites Pegmatitic (?), metasomatic (?) [5]
Gardiner Phonolite dikes (?) Aegirine, lorenzenite, sodalite, albite, natrolite High- and low-Mn Sr-lamprophyl- lite and low-K Ba-lamprophyllite Magmatic (?), metasomatic (?) [5] Inagli
Pegmatite Lorenzenite, neptunite, vinogradovite, albite, nepheline, eudialyte, aegirine, microcline, leu- cosphenite, thompsonite Pegmatitic [7, 17,21] Inagli Metasomatites Albite, microcline, leucosphenite, batisite, innelite High-Mn high-K lamprophyllite Metasomatic [2]
Koksharovka Eudialytic lujavrites Eudialyte, aegirine, potassium feldspar, nepheline Magmatic (?) [22] Lovozero Rock of the diffe- rentiated complex Nepheline, feldspar, aegirine, ilmenite, loparite High-Mn Sr-lamprophyllite Late magmatic (?) [23]
authors' data Lovozero Eudialytic lujavrites Nepheline, feldspar, aegirine, amphibole, murman- ite, mosandrite, steenstrupine, monazite, nenadkevi- chite, vitusite, loparite High-Mn Sr-lamprophyllite and rare low-K Ba-lamprophyllite Late magmatic (?) [23, 24] authors' data Lovozero Porphyritic lujavrites Nepheline, feldspar, aegirine, amphibole High-Mn Sr-lamprophyllite Late magmatic (?) [23] authors' data Lovozero Pegmatites Aegirine, serandite, steenstrupine, narsarsukite, lomonosovite, microcline, sodalite, magnesioarfved- sonite, eudialyte, terskite High-Mn Sr-lamprophyllite and medium-K Ba-lamprophyllite Pegmatitic [11,21,23] Chukanov's and authors' data Murun
Pegmatite Odintsovite, aegirine, sphene, feldspar High-Mn high-K Ba-lamprophyl- lite, Sr-lamprophyllite Pegmatitic [16, 25] Chukanov's data Niva
Agpaitic syenite Feldspar, aegirine-diopside to aegirine, amphib- ole, aenigmatite, natrolite, apatite, shcherbakovite Low-Mn high-K Ba-lamprophyllite Magmatic (?) [26, 27] authors' data
Table 6. (Contd.) Massif
Rock Mineral assemblage Lamprophyllite type Genesis
Reference Oldoinyo Lengai Combeite nephelinite Combeite, sodalite, apatite, nepheline, pyroxene, melanite, delhayelite, C e - N b - S r perovskite, C a - N a - S r - K phosphate, magnetite (rare) Low-Mn high-K Ba-lamprophyllite Late magmatic [4]
Parana Fenites
Sr-chevkinite, Sr-loparite, aegirine, nepheline, sanidine Low-Mn Sr-lamprophyllite Metasomatic [28] Pilanesberg Nepheline syenite
Microcline, nepheline, aegirine, calcite, analcime, pectolite, fluorite High-Mn Sr-lamprophyllite Magmatic (?) [21] authors' data Strelka Metasomatites Eudialyte, lorenzenite, rhyncholite, lomonosovite High-Mn Sr-lamprophyllite Metasomatic [2] Turii Mys Fenites Aegirine, natrolite, quartz, labuntsovite, calcite, sphene, woehlerite, eudialyte High-Mn high-K Ba-lamprophyllite Hydrothermal [ 1 , 3 , 2 9 ] Khibiny
Khibinite Ilmenite, amphibole Late magmatic (?) [10]
Khibiny Melteigite-urtite Nepheline Late magmatic (?) [10]
Khibiny Rischorrite Nepheline, aegirine, amphibole Late magmatic (?) [10] Khibiny
Apatite- nepheline rocks Nepheline, aegirine, amphibole Late magmatic (?) [10] Khibiny
Pegmatites Nepheline, feldspars, aegirine, eudialyte, lomono- sovite, ancylite, strontianite, apatite, cancrinite, villiaumite, analcime, pectolite Sr-lamprophyllite and high-'K Ba- lamprophyllite, usually high-Mn Pegmatitic [1, 8, 10, 19-21] Chukanov's and Lisitsin's data Khibiny Fenites
Ilmenite, sphene, lorenzenite, eudialyte, nepheline, feldspar, pyroxene Metasomatic [30]
Khibiny Apophyllite veins Sodalite, natrolite, cancrinite, microcline, rhyn- cholite, apophyllite, loparite, opal, fluorite, calcite, aegirine, eudialyte, apatite, arfvedsonite High-Mn Sr-lamprophyllite Hydrothermal [9] Yllymakh Metasomatites Sr-lamprophyllite and high-K Ba-lamprophyllite, usually high-Mn High-Mn Sr-lamprophyllite Metasomatic [2]
Fig. 3. Compositions of lamprophyllites from alkaline massifs worldwide in the Fe-Na-Mn diagram. See Fig. 1 for explanation of fields.
prophyllites from the differentiated complex and por- phyritic lujavrites of the Lovozero Massif. T h u s , the occupation of the M ( 2 ) site in lamprophyl lites varies between different massifs and within indi vidual massifs.
the lamprophyllite structure [15, 17]. However, a m o n g these elements, only Mg shows a significant negative correlation with Ti. By analogy with other "titanosilicate micas", we believe that the Ti site can also be occupied by Nb and Zr. This is verified by the significant negative coeffi cient of Nb correlation with Ti. Concentrations of Zr and Nb are low: mean Nb contents are 0.01-0.03 f.u. (up to 0.05 in rare analyses). K h o m y a k o v [11] described lamprophyllite with 0.2 f.u. Nb from the Yubileinaya vein in the L o v o z e r o Massif. Z i r c o n i u m is n o r m a l l y not a n a l y z e d . Its c o n t e n t s in the available m i c r o p r o b e a n d c h e m i c a l a n a l y s e s d o not e x c e e d 0.04 f.u.
which is replaced by F and CI. T h e fluorine contents in lamprophyllite normally range from 0.5 to 1.0 f.u. However, low-F lamprophyllites (0.32 f.u., on average) are typical of the Inagli Massif, while high-F lampro phyllite varieties (up to 2 f.u.) are observed in the Turii M y s and Khibiny massifs. T h e F-rich analogs of lam prophyllite, baritolamprophyllite, and K-baritolampro- phyllite could be described as new mineral species. D a t a on the CI c o n c e n t r a t i o n s in lamprophyllite are scarce. T h e available a n a l y s e s c o n t a i n up to 0.15 f.u. CI. T h e lamprophyllite compositions can be classified by cation amounts in the M ( l ) site and by Mn content. T h e distribution of lamprophyllites of various chemical types are characterized in Table 6. We compared these data with the distribution of К and Mn in alkaline complexes containing lamprophyl lite (Table 7). There is a positive correlation between Mn concentrations in rocks and lamprophyllites for the Khibiny, Lovozero, and Pilanesberg massifs. However,
2 0 and MnO contents in the rocks of some alkaline massifs Massif к 2 о , % MnO, %
Reference Khibiny
6.15 0.20
[31] Lovozero Massif differentiated complex 5.31
0.29 [23]
eudialyte complex 4.60
0.45 [23]
Oldoinyo Lengai, lavas 4.38-5.43 0.34-0.39 [4]
Pilanesberg, foyaites 5.41
0.60 [32]
lujavrites 2.78
0.62 [32]
GEOCHEMISTRY INTERNATIONAL Vol. 40 No. 4 2002 COMPOSITIONS OF MINERALS OF THE LAMPROPHYLLITE GROUP 321
the relatively M n - r i c h r o c k s of O l d o i n y o L e n g a i Vol- cano include l o w - M n l a m p r o p h y l l i t e s . Among the massifs u n d e r c o n s i d e r a t i o n , the K h i b - iny Massif has the h i g h e s t K 2 0 c o n t e n t in its r o c k s . T h e Ba-lamprophyllites from this massif are richest in potassium. T h e h i g h - K B a - l a m p r o p h y l l i t e is also typi- cal of Oldoinyo L e n g a i , w h o s e lavas are c o m p a r a b l e with the rocks of the eudialyte c o m p l e x of the L o v o z e r o Massif in K 2 0 c o n c e n t r a t i o n s . T h e latter, however, includes low-K l a m p r o p h y l l i t e s . The paragenetic analysis s h o w s that l a m p r o p h y l l i t e s are usually confined to the latest differentiates that are enriched in i n c o m p a t i b l e e l e m e n t s a c c u m u l a t e d d u r i n g magma evolution. T h e crystallization of m i n e r a l s of the lamprophyllite g r o u p c o r r e s p o n d s to a certain level of alkaline m a g m a differentiation. T h e variations of the lamprophyllite c o m p o s i t i o n s c o m p l y with the evolution of highly differentiated alkaline m a g m a s . T h e l a m p r o - phyllite c o m p o s i t i o n is related to the initial m a g m a composition a n d p h y s i c o c h e m i c a l c o n d i t i o n s (pres- sure, temperature, and fluid c o m p o n e n t fugacities), which affect the t h e r m o d y n a m i c activities of the lam- prophyllite c o m p o n e n t s . This study w a s s u p p o r t e d by the R u s s i a n F o u n d a - tion for Basic R e s e a r c h , project n o s . 9 9 - 0 5 - 6 4 8 3 5 and 00-15-98497. R E F E R E N C E S 1. Kapustin, Yu.L., Recent Finds of Barytolamprophyllite and the Lamprophyllite Formula, Dokl. Akad. Nauk SSSR, 1973, vol. 210, no. 4, pp. 921-924. 2. Kravchenko, S.M., Kapustin, Yu.L., Kataeva, Z.T., and Bykova, A.P., Agpaitic Mineralization of Mesozoic Alkaline Potassium-Rich Metasomatites of the Central Aldan, Dokl. Akad. Nauk SSSR, 1982, vol. 263, no. 2, pp. 435-439. 3. Evdokimov, M.D., Fenity Tur'inskogo shchelochnogo
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