Chemistry Reference
In-Depth Information
For natural systems the K
d
(REE) values were determined between kimberlites and
melilite-nepheline basalts, on the one hand, and the perovskites they contain, on the
other hand. The following diagram shows that for the perovskite/kimberlite system
the K
d
values for La, Ce, Pr, Nd, Sm, Gd and Ho
1. A similar trend is ascertained
for K
d
(La, Nd, Sm) in the perovskite/melilite-nepheline basalt system. For both of
these systems the curves of changes in the values of K
d
have a common negative
slope. The curves shown in the same picture reflect the changes in the values of K
d
(perovskite/kimberlite) for the natural system and for some systems studied during
the experiment and also have a common negative slope, but the K
d
values for the
experimental systems were lower than for the natural system. In addition, in some
kimberlites the accessory apatite plays the role of a concentrator of significant LREE
amounts, along with the perovskite, but the modal contents of them are usually
much smaller than those of perovskite.
The study of REE distribution between minerals from jacupirangites, ijolites
and nepheline syenites represented as xenoliths in tuffs of Oldoinyo Lengai volcano
>
Table 7.2
The coefficients of REE distribution between perovskites and
silicate melts (experimental data [Nagasawa et al., 1981]).
Element
Nag-1
Nag-2
Nag-3
Nag-4
Nag-5
La
2,4
2,96
2,15
2,44
3,04
Ce
N.d.
N.d.
N.d.
N.d.
N.d.
Pr
N.d.
N.d.
N.d.
N.d.
N.d.
Nd
N.d.
N.d.
N.d.
N.d.
N.d.
Sm
2,76
3,12
2,16
2,47
3,01
Eu
2,28
2,67
2,07
1,87
2,04
Gd
N.d.
N.d.
N.d.
N.d.
N.d.
Tb
1,45
1,83
1,37
1,49
1,77
Dy
N.d.
N.d.
N.d.
N.d.
N.d.
Ho
N.d.
N.d.
N.d.
N.d.
N.d.
Er
N.d.
N.d.
N.d.
N.d.
N.d.
Tm
N.d.
N.d.
N.d.
N.d.
N.d.
Yb
0,482
0,517
0,445
0,443
0,553
Lu
0,408
0,412
0,389
0,413
0,432
Figure 7.3
The graphs of coefficients of REE distribution between perovskites and siliceous melts
(experimental data [Nagasawa
et al.
, 1981]) (data Table 7.2).
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